Coastal Geology-Springer (2022)

Juan A.
Morales
Coastal
Geology
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Juan A. Morales
Coastal Geology
123
Juan A. Morales
Department of Earth Science
University of Huelva
Huelva, Spain
ISSN 2510-1307 ISSN 2510-1315 (electronic)

Springer Textbooks in Earth Sciences, Geography and Environment
ISBN 978-3-030-96120-6 ISBN 978-3-030-96121-3 (eBook)
https://doi.org/10.1007/978-3-030-96121-3
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End of the Earth, unnamed place.
There starts the sea, no limit surface.
Where the foam is born by beating waves
crumbling rocks which the tides take away.
Whistle between clouds, music of the wind,
intense blue water that always is flowing,
red sunset that bathes a wide tidal flat,
sand on the beaches where children splat.
Coast you’re called, poetry place
where land and sea fight every day.
“Eternal change”
E. T. Soro
This book is especially dedicated to my parents:
Alfonso and Mary.
They have lived for their sons.
Acknowledgements
I would like to acknowledge all the knowledge acquired during hours of fieldwork with my
dear colleague, Dr. J. Borrego (Pepe). With him, I learned most of the things that I explain in
this book. I also understood many concepts about coastal geology during my stays and surveys
in research centers of different universities. Doctors Poppe L. De Boer, Richard A. Davis Jr.,
John Loder, José Ojeda, Pedro Proença e Cunha, Pedro Depetris, Paolo Ciavola, José Manuel
Gutiérrez Mas, Mouncef Sedrati, David Menier, Erwan Garel and Cheikh Ibrahima Youm
were my guides during these stays.
The writing of this book would have been impossible without the generosity during dec-
ades of my direct colleagues Berta Carro, Irene Delgado, Germán Flor Blanco, Inmaculada
Jiménez, Nieves López, Claudio Lozano, Jesús Monterde and Antonio Rodriguez-Ramírez.
The true promotor of this book was Dr. Alexis Vizcaíno, who encouraged me to express my
knowledge and helped me through the editorial process. Two people contributed significantly
to this book. Dr. Edward Anthony did a thorough review of the thematic content, while Colette
Folder did an intensive review of the English. Both of them notably helped to improve the
final text and figures.
Finally, the most loving words are to my wife Mar Mateo. Mar (Sea) endured my absences
for endless hours while writing this book during the quarantine confinement of the COVID-19
pandemic.
ix
Introduction
Here is the first complete manual on Coastal Geology. A book that gathers the knowledge of
more than a century of research on different geological aspects of the coast: dynamics of
geological processes, geomorphology, sedimentology and stratigraphy. They are also reflected
from the applications of these sciences to the social problems and challenges of the com-
munities occupying coastal areas. This manual collects many of my research experiences on
different shores of the world, but almost everything written in this book I learned in other
books. That is why I thought this manual would not be the first on Coastal Geology. However,
when I began collecting bibliography, before I began writing, I realized that all the books that
had been written so far collected partial aspects of this science: coastal dynamics, coastal
geomorphology or coastal sedimentary environments. None of them united all geological
aspects into a single vision. They all reach greater thematic depth than this book. I wanted to
write a student book that was complete. A book written in an easy-to-understand language and
including very didactic figures (that worth more than a thousand words). A book that would
cut to the chase and contain only the essentials. The book I would have liked to have had when
I started realizing that my vocation was the coast. The final recipients are not advanced
scientists, but students, well… also coastal researchers who start their careers. For this reason,
the chapters will not be as deep as other books written for expert scientists and professionals.
But then I thought maybe any of those advanced students will need a little more information
on specifics. That is why I created the advanced boxes. A geology student can really
understand the book without them, but advanced boxes are intended for those coastal geol-
ogists who begin their research, those who want to know more.
The structure of this book is a reflection of its objectives. Content is divided into thematic
units (or parts) that include several related topics. Each of its parts is dedicated to completing
information on different aspects of the coast. Some have a purely geological content, and
others focus the applications of coastal geology toward other disciplines of knowledge.
Part I is a purely epistemological section that tells us about the geological vision of the
coast. In this part, this science and its main concepts are defined, a history of science is
outlined, the criteria of classification of the coasts are discussed, the visions that the different
geological disciplines have about the coast are approximated and an inventory of the different
methods and techniques used in research on Coastal Geology is made.
Part II focuses on the study of coastal processes. Some, like waves and tides, act on
dynamics and evolution from a physical point of view. Other processes have a purely chemical
or biological character. Sedimentary and hydrological contributions from the continent and the
sea condition the rhythms and trends of evolution. All processes interact with each other. But
in the end, it all translates into a movement of particles from, to or along the coast.
Part III is the most complex part of the book and the one that requires a broader vision. It
focuses on the study of coastal environments. Some of these environments are erosive, but
most are cumulative. Each of these topics speaks to us first of all of the geomorphological
characteristics, to continue explaining the processes that give rise to that geomorphology and
finally talk about its facies, facies sequences and facies models, in a more sedimentological
vision.
xi
xii Introduction
Part IV analyzes the processes that act on a longer time scale and which in the end result in
the preservation of a geological record. This thematic unit captures aspects such as climate,
sea-level movements, paleoceanography and comparison with some coastal systems that were
preserved in other periods of Earth’s history.
Part V tells us about the problems that arise from the interaction between humans and the
coast. On the one hand, human beings unbalance coastal processes, and on the other hand, the
coast menaces the human being occupying the coastal areas. The end result is that man and
coast have to live together, so we analyze the smartest coexistence strategy: Integral Coastal
Zone Management.
Finally, Part VI consists of a single chapter that gives us a perspective of what Coastal
Geology studies will be in the coming years.
In short, this is a book that aims to provide a firm foundation of knowledge to future coastal
geologists. Then comes specialization and deepening, but for that there are already other
books.
Contents
Part I Geological Approaches to the Coast

1 Coastal Geology as a Science Through Time . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1 What is Coastal Geology? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2 Observation of the Coast in Ancient Times . . . . . . . . . . . . . . . . . . . . . . . 5
1.3 Age of Exploration: The Birth of Marine Geology . . . . . . . . . . . . . . . . . . 7
1.4 Explosion of Human Occupation on the Coast: The Birth of the Real
Coastal Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 8
1.5 Recent Knowledge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 10
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... 11
2 Defining Concepts of Coastal Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1 What is the Coast? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.1 Coast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.2 Coastal Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.3 Littoral Zone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.1.4 Coastal Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1.5 Shore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1.6 Shoreline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2.1.7 Coastline . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.8 Shoreface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.9 Offshore . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.1.10 Shelf . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.2 A Datum Issue . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.3 Coastal Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.1 Coastal Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
2.3.2 Consolidated Versus Unconsolidated Coasts . . . . . . . . . . . . . . . . 18
2.3.3 Erosional Versus Depositional Coasts . . . . . . . . . . . . . . . . . . . . . 18
2.3.4 Open Versus Protected Coasts . . . . . . . . . . . . . . . . . . . . . . . . . . 19
2.3.5 Mechanical Versus Biological Coasts . . . . . . . . . . . . . . . . . . . . . 19
2.3.6 Emergent Versus Submergent Coasts . . . . . . . . . . . . . . . . . . . . . 19
2.4 Coastal Uses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.1 Urban Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.2 Industrial Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.3 Military Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.4 Recreational Use . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.5 Wetland Reclamation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
2.4.6 Waste Disposal on Coastal Environments . . . . . . . . . . . . . . . . . . 20
2.4.7 Exploitation of Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.4.8 Coastal Conservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.5 Coastal Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.5.1 Sea Level Rise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
2.5.2 Shoreline Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
xiii
xiv Contents
2.5.3 Storm and Tsunami Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

2.5.4 Human Destabilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.5.5 Saline Intrusion into Coastal Aquifers . . . . . . . . . . . . . . . . . . . . . 22
2.5.6 Subsidence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.5.7 Changes in Ecological Structure . . . . . . . . . . . . . . . . . . . . . . . . . 22
2.6 Integrated Coastal Zone Management . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
3 Factors Affecting Coastal Evolution: Spatiotemporal Scales . . . . . . . . . . . . . . 25
3.1 The Changing Coast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.2 Factors of Coastal Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
3.2.1 Hydrodynamic Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2.2 Sediment Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2.3 Events on the Coast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
3.2.4 Global and Regional Sea Level Movements
(Tectonics and Eustatism) . . . . . . . . . . . . . . . . . ............. 27
3.2.5 Changes in Position of the Coastline
(Transgressions and Regressions) . . . . . . . . . . . . . . . . . . . . . . . . 27
3.2.6 Geological Influence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3.2.7 Climatic Influence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.2.8 Human Influence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
3.3 The Spatiotemporal Scale of Coastal Processes . . . . . . . . . . . . . . . . . . . . 28
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
4 Coastal Elements: Types of Coasts and Criteria in Coastal Classifications . . . 31
4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2 Coastal Landforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2.1 Erosional Coastal Landforms . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
4.2.2 Depositional Coastal Landforms . . . . . . . . . . . . . . . . . . . . . . . . . 33
4.3 Coastal Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
4.4 Classifications of the Coast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.4.1 Genesis Under Relative Sea Level Movements . . . . . . . . . . . . . . 38
4.4.2 Origin of Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
4.4.3 Tectonic Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
4.4.4 Individual Hydrodynamic Processes . . . . . . . . . . . . . . . . . . . . . . 41
4.4.5 Relative Energy of Hydrodynamic Processes . . . . . . . . . . . . . . . . 42
4.4.6 Sediment Input and Evolving Time . . . . . . . . . . . . . . . . . . . . . . . 42
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
5 Geological Approaches to the Coasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.2 Geomorphological Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.3 Sedimentological Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
5.4 Stratigraphical Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
5.5 Oceanographical Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48
5.6 Environmental Geology Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
5.7 A Multidisciplinary Vision . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
6 Study Methods and Techniques . . . . . . . . . . . . . . . . . . ......... . . . . . . . . 51
6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ......... . . . . . . . . 51
6.2 Methods and Techniques to Study Physical Coastal Processes . . . . . . . . . 51
6.2.1 Instruments for Wave Measurements . . . . . ......... . . . . . . . . 51
6.2.2 Instruments for Tidal Level Measurement . ......... . . . . . . . . 54
Contents xv
6.2.3 Instruments for Measuring Tidal and Ocean Currents . . . . . . .... 56

6.3 Study Methods of Coastal Landforms . . . . . . . . . . . . . . . . . . . . . . . .... 56
6.3.1 Topography: Classification and Measurement of Surficial
Landform Dimensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57
6.3.2 Monobeam Bathymetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.3.3 Multibeam Bathymetry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.3.4 Side-Scan Sonar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
6.3.5 Cartography of Coastal Environments . . . . . . . . . . . . . . . . . . . . . 60
6.4 Study Methods of Short-Term Coastal Evolution . . . . . . . . . . . . . . . . . . . 61
6.4.1 Topo-Bathymetric Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . 62
6.4.2 Comparative Photointerpretation . . . . . . . . . . . . . . . . . . . . . . . . . 62
6.4.3 Numerical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6.5 Study Methods of Coastal Surficial Sediments . . . . . . . . . . . . . . . . . . . . . 64
6.5.1 Sampling of Surficial Sediments . . . . . . . . . . . . . . . . . . . . . . . . . 64
6.5.2 Surficial Coring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
6.5.3 Sediment Traps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
6.6 Methods to Study the Sedimentary Record of Coastal Environments . . . . . 67
6.7 Geophysical Methods for the Study of the Geometry of Coastal
Sedimentary Bodies: Seismic Reflection . . . . . . . . . . . . . . . . . . . . . .... 68
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... 71
Part II Coastal Processes

7 Wave Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
7.2 Genesis of Wind Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
7.3 Morphology and Dimensions of Wind Waves . . . . . . . . . . . . . . . . . . . . . 76
7.4 Wave Energy and Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
7.5 Sea State and Dimensional Scale of Waves . . . . . . . . . . . . . . . . . . . . . . . 80
7.6 Wave Propagation and Shoaling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80
7.6.1 Wave Refraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81
7.6.2 Wave Diffraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
7.6.3 Littoral Drift . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83
7.7 Dissipation of Wave Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
7.7.1 Wave Breaking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84
7.7.2 Wave Reflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86
8 Tide Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
8.2 Genesis of the Tides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
8.2.1 Earth–Moon System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
8.2.2 Earth–Sun System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
8.2.3 Earth–Moon–Sun System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88
8.2.4 Dynamic Theory of Tides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89
8.3 Tidal Cycles and Tidal Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91
8.3.1 Types of Tides Based on Their Periodicity . . . . . . . . . . . . . . . . . 91
8.3.2 Tidal Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92
8.3.3 Critical Tide Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
8.4 The Tide and the Coast . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
8.4.1 Dissipation by Friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94
8.4.2 Amplification by Convergence . . . . . . . . . . . . . . . . . . . . . . . . . . 95
8.4.3 Resonance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95
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8.5 Tidal Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98
9 Continental Processes and Sediments on the Coast . . . . . . . . . . . . . . . . . . . . 99
9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
9.2 River-Induced Processes and Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . 99
9.2.1 Water Mixing Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100
9.2.2 Estuarine Genesis of Particles: Flocculation and Aggregation . . . . 101
9.2.3 Suspended Matter Supply from Rivers . . . . . . . . . . . . . . . . . . . . 102
9.2.4 The Turbidity Maximum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103
9.2.5 Suspended Matter Injection to the Open Coast: The Turbidity
Plumes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
9.2.6 Bed Load Supply from Rivers . . . . . . . . . . . . . . . . . . . . . . . . . . 107
9.3 Wind Supply and Erosional Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108
9.3.1 Sediment Supply from Continental Winds . . . . . . . . . . . . . . . . . . 108
9.3.2 Wind Deflation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111
10 Marine Processes and Sediments on the Coast . . . . . . . . . . . . . . . . . . . . . . . . 113
10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
10.2 Marine Sources of Sediment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113
10.3 Marine Processes on the Coastal Front . . . . . . . . . . . . . . . . . . . . . . . . . . 115
10.3.1 General Oceanic Circulation: Currents in the Coastal Front . . . . . 115
10.3.2 Wind-Driven Currents in the Coastal Front: Geostrophic
Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
10.3.3 Tidal-Induced Currents in the Coastal Front . . . . . . . . . . . . . . . . 120
10.4 Dynamics of Sediment in the Coastal Front . . . . . . . . . . . . . . . . . . . . . . . 120
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121
11 Chemical Processes and Sediments on the Coast . . . . . . . . . . . . . . . . . . . . . . 123
11.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
11.2 Solubility: Control Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123
11.2.1 Ionic Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
11.2.2 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 124
11.2.3 pH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
11.2.4 Redox Potential (Eh) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
11.2.5 Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
11.2.6 Pressure of Dissolved Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . 125
11.2.7 Organic Activity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 126
11.3 Precipitation and Dissolution of Carbonates . . . . . . . . . . . . . . . . . . . . . . . 126
11.3.1 Chemical Equilibrium of Calcium Carbonate . . . . . . . . . . . . . . . . 126
11.3.2 Precipitation of Calcium Carbonate in Coastal Environments . . . . 127
11.3.3 Physical Processes Moving Chemically Created Grains . . . . . . . . 129
11.3.4 Early Cementation and Beachrock Genesis . . . . . . . . . . . . . . . . . 129
11.4 Evaporite Genesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
11.4.1 Subtidal Evaporites: Salinas . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131
11.4.2 Intertidal Evaporites: Coastal Sabkhas . . . . . . . . . . . . . . . . . . . . . 131
11.4.3 Reworked Evaporites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133
12 Biological Processes and Sediments on the Coast . . . . . . . . . . . . . . . . . . . . . . 135
12.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
12.2 Bio-Induced Precipitation and Dissolution . . . . . . . . . . . . . . . . . . . . . . . . 135
12.3 Bioconstructions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 136
Contents xvii
12.4 Bioclastic Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

12.5 Organic Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
12.5.1 Hydrocarbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138
12.5.2 Carbons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 139
12.6 Alteration of the Sediments by Organisms: Bioturbation . . . . . . . . . . . . . . 141
12.7 Bioerosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 142
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143
13 Extreme Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
13.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
13.2 Extreme Storms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
13.2.1 Surges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146
13.2.2 Extreme Storm Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
13.2.3 Combined Surge–Storm Waves . . . . . . . . . . . . . . . . . . . . . . . . . 148
13.2.4 Sedimentary Record of a Storm: Tempestites, Washovers
and Cheniers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 151
13.3 Rogue Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
13.4 Tsunamis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153
13.4.1 Mechanism of Tsunami Genesis . . . . . . . . . . . . . . . . . . . . . . . . . 153
13.4.2 Propagation of Tsunami Waves Across the Open Sea . . . . . . . . . 154
13.4.3 Tsunami Breakers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155
13.4.4 Sedimentary Record of a Tsunami: Tsunamites . . . . . . . . . . . . . . 155
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 158
14 Particle Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
14.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 161
14.2 Processes of Particle Transport by Fluid Flow . . . . . . . . . . . . . . . . . . . . . 161
14.2.1 Grain Entrainment Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
14.2.2 Sediment Transport . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 164
14.2.3 Grain Settling Threshold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
14.2.4 Sedimentation Velocity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166
14.3 Transport of Particles by Tides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
14.4 Transport of Particles by Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
14.5 Transport of Particles by Wind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
14.6 Development and Dynamics of Bedforms . . . . . . . . . . . . . . . . . . . . . . . . 173
14.6.1 Unidirectional Bedforms (Current Bedforms) . . . . . . . . . . . . . . . . 173
14.6.2 Bidirectional Bedforms (Tide-Generated Bedforms) . . . . . . . . . . . 176
14.6.3 Oscillatory Bedforms (Wave Bedforms) . . . . . . . . . . . . . . . . . . . 177
14.6.4 Combined Flow Bedforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
14.6.5 Macro-scale Bedforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182
Part III Coastal Systems: Dynamics, Facies and Sedimentary Models

15 Geologically Controlled Coastal Systems: Rocky Coasts, Bluffs, Cliffs
and Shore Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
15.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 187
15.2 Control Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
15.2.1 Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
15.2.2 Wave Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 190
15.2.3 Tidal Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
15.2.4 Relative Sea Level Movements . . . . . . . . . . . . . . . . . . . . . . . . . . 191
15.2.5 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
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15.3 Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

15.3.1 Wave Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
15.3.2 Mechanical Weathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
15.3.3 Chemical Weathering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
15.3.4 Bioerosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
15.3.5 Slope Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 194
15.4 General Morphology and Morphological Features . . . . . . . . . . . . . . . . . . 196
15.4.1 Rocky Ramps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
15.4.2 Shore Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 197
15.4.3 Cliff Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198
15.5 Dynamics and Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 199
15.6 Associated Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206
16 Wave-Dominated Systems I: Barriers and Barrier Islands . . . . . . . . . . . . . . . 207
16.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
16.2 Control Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 207
16.2.1 Wave Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208
16.2.2 Tides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
16.2.3 Other Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
16.2.4 Sediment Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
16.2.5 Mainland Physiography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209
16.2.6 Sea Level Movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
16.2.7 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 210
16.3 General Morphology and Associated Environments . . . . . . . . . . . . . . . . . 210
16.4 Genesis, Dynamics and Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
16.4.1 Spits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
16.4.2 Welded Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 213
16.4.3 Tombolos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
16.4.4 Barrier Islands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 215
16.5 Facies Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219
16.5.1 Retrograding (Transgressive) Barriers . . . . . . . . . . . . . . . . . . . . . 220
16.5.2 Aggrading Barriers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 223
16.5.3 Prograding (Regressive) Barriers . . . . . . . . . . . . . . . . . . . . . . . . . 224
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224
17 Wave-Dominated Systems II: Beaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
17.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
17.2 Control Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
17.2.1 Wave Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227
17.2.2 Beach Slope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228
17.2.3 Grain Size . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
17.2.4 Tidal Range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
17.2.5 Nearshore Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
17.2.6 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 229
17.3 Zonation and Morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
17.3.1 Fringes of Wave Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
17.3.2 General Zoning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
17.3.3 Beach Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230
17.3.4 Bar Morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
17.4.1 Movement of Sediments by Waves . . . . . . . . . . . . . . . . . . . . . . . 234
17.4.2 Dynamics and Genesis of Transversal Bars . . . . . . . . . . . . . . . . . 235
Contents xix
17.4.3 Dynamics of Longitudinal Bars . . . . . . . . . . . . . . . . . . . . . . . . . 238

17.4.4 Dynamics of Cobble Beaches . . . . . . . . . . . . . . . . . . . . . . . . . . . 240
17.4.5 Equilibrium Profile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 241
17.4.6 Evolution of the Beach Profile . . . . . . . . . . . . . . . . . . . . . . . . . . 242
17.4.7 Longshore Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244
17.4.8 Beach Cells and Sedimentary Balance . . . . . . . . . . . . . . . . . . . . . 244
17.5 Facies and Facies Sequences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
17.5.1 Beach Sediment Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 245
17.5.2 Sandy Beach Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245
17.5.3 Gravel Beach Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248
17.5.4 Cobble Beach Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 249
18 Wind-Dominated Systems: Coastal Dunes . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
18.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
18.2 Control Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
18.2.1 Wind Regime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 251
18.2.2 Sediment Budget . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
18.2.3 Development Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 252
18.2.4 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
18.2.5 Moisture Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
18.2.6 Vegetation Cover . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
18.3 Morphology and Sub-environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 253
18.3.1 Foredunes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
18.3.2 Blowout Dunes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 255
18.3.3 Parabolic Dunes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 257
18.3.4 Transgressive Dune Fields . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
18.3.5 Interdunes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258
18.4.1 Genesis and Evolution of Primary Dunes . . . . . . . . . . . . . . . . . . 259
18.4.2 Effects of the Waves on the Dunes . . . . . . . . . . . . . . . . . . . . . . . 261
18.4.3 Reworking of the Primary Dunes and Evolution Towards
Secondary Dunes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 261
18.4.4 Genesis of Minor Structures on the Dune Surface . . . . . . . . . . . . 263
18.5 Sediments and Internal Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264
18.5.1 Foredunes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
18.5.2 Blowout Lobes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 266
18.5.3 Parabolic Dunes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
18.5.4 Interdune Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
19 Tide-Dominated Systems I: Inlets and Tidal Deltas . . . . . . . . . . . . . . . . . . . . 269
19.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
19.2 Control Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
19.2.1 Tidal Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 269
19.2.2 Wave Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
19.2.3 Combined Action of Waves and Tidal Currents . . . . . . . . . . . . . . 271
19.3.1 Ebb-Tidal Deltas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 271
19.3.2 Flood-Tidal Deltas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275
19.4 Dynamics and Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 276
19.4.1 Origin and Mobility of the Inlets . . . . . . . . . . . . . . . . . . . . . . . . 276
19.4.2 Dynamics and Facies of Ebb-Tidal Deltas . . . . . . . . . . . . . . . . . . 277
xx Contents

19.5 Facies Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
19.5.1 Ebb-Tidal Deltas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
19.5.3 Architectural 3D Facies Model in the Barrier System
Framework . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
20 Tide-Dominated Systems II: Tidal Flats and Wetlands . . . . . . . . . . . . . . . . . 289
20.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
20.2 Control Factors and Global Distribution . . . . . . . . . . . . . . . . . . . . . . . . . 289
20.2.1 Tidal Regime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289
20.2.2 Wave Regime . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
20.2.3 Sediment Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 290
20.2.5 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
20.4 Processes and Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 293
20.4.1 Physical Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 294
20.4.2 Chemical Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 295
20.4.3 Biological Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
20.5 Sediments and Bedforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298
20.5.1 Sandy Tidal Flat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
20.5.2 Mixed Tidal Flat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299
20.6 Facies, Facies Sequences and Facies Models . . . . . . . . . . . . . . . . . . . . . . 300
20.6.1 Subtidal Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
20.6.2 Sandy Tidal Flat Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301
20.6.3 Mixed Tidal Flat Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
20.6.4 Muddy Tidal Flat Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 302
20.6.5 Supratidal Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
20.6.6 Tidal Creek Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 303
20.6.7 Facies Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306
21 Fluvial-Influenced Systems I: Estuaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
21.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 309
21.2 Control Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
21.2.1 River Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
21.2.2 Tidal Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
21.2.3 Wave Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 310
21.3 Classification and Morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
21.3.1 Hydrological Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311
21.3.2 Classification by Tidal Range . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
21.3.3 Classification by Propagation of Tidal Wave into the Estuary . . . . 312
21.3.4 Genetic Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312
21.3.5 Physiographic Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
21.3.6 Dynamic Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 313
21.3.7 Domains and Sub-environments of Estuaries . . . . . . . . . . . . . . . . 314
21.4.1 Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 316
21.4.2 Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 317
Contents xxi
21.5 Depositional Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

21.5.1 Depositional Facies Characteristic of Wave-Dominated
Estuaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320
21.5.2 Depositional Facies Characteristic of Tide-Dominated
Estuaries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 321
21.5.3 Depositional Facies Characteristic of Estuaries in an Advanced
State of Infilling and Bedrock-Controlled Estuaries . . . . . . . . . . . 322
21.6 Facies Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 323
21.6.1 Facies Model for Wave-Dominated Estuaries . . . . . . . . . . . . . . . 324
21.6.2 Facies Model for Tide-Dominated Estuaries . . . . . . . . . . . . . . . . 324
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 326
22 Fluvial–Influenced Systems II: Deltas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
22.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
22.2 Control Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
22.2.1 Fluvial Discharge . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329
22.2.2 Wave Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 330
22.2.3 Tidal Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
22.2.4 Long-Term Factors: Relative Sea Level Movements . . . . . . . . . . 331
22.3 Classification and Morphology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 331
22.3.1 Classification of Fluvial Deltas . . . . . . . . . . . . . . . . . . . . . . . . . . 331
22.3.2 Domains and Sub-environments of Fluvial Deltas . . . . . . . . . . . . 335
22.4.1 Delta Plain Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 337
22.4.2 Delta Front Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 338
22.4.3 Evolution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 342
22.4.4 Post-depositional Processes in the Delta Front . . . . . . . . . . . . . . . 343
22.5 Depositional Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 343
22.5.1 Depositional Facies Characteristic of River-Dominated Deltas . . . 343
22.5.2 Depositional Facies Characteristic of Wave-Dominated Deltas . . . 345
22.5.3 Depositional Facies Characteristic of Tide-Dominated Deltas . . . . 345
22.5.4 Depositional Facies Characteristic of Intermediate Deltas . . . . . . . 345
22.6 Facies Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 345
22.6.1 Facies Model for River-Dominated Deltas . . . . . . . . . . . . . . . . . . 346
22.6.2 Facies Model for Wave-Dominated Deltas . . . . . . . . . . . . . . . . . 346
22.6.3 Facies Model for Tide-Dominated Deltas . . . . . . . . . . . . . . . . . . 347
22.6.4 Facies Model for Intermediate Deltas . . . . . . . . . . . . . . . . . . . . . 347
22.6.5 Facies Model for Coarse-Grained Deltas . . . . . . . . . . . . . . . . . . . 348
22.7 Delta Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 350
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 352
23 Chemically and Biologically Controlled Systems: Carbonate Coasts
and Reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
23.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 355
23.2 Control Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
23.2.2 Physicochemical Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356
23.2.3 Wave Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 357
23.2.4 Tide Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
23.2.5 Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
23.2.6 Relative Sea Level Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 358
xxii Contents
23.3 General Morphology, Associated Environments and Forms . . . . . . . . . . . . 358

23.3.1 Fringing Reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
23.3.2 Barrier Reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
23.3.3 Atolls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 359
23.4.1 Reef Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
23.4.2 Wave-Induced Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 362
23.4.3 Tide-Induced Dynamics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 364
23.4.4 Dynamics of Combined Waves and Tides . . . . . . . . . . . . . . . . . . 365
23.4.5 Long-Term Evolution: Relative Sea Level Movements . . . . . . . . . 365
23.5 Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
23.5.1 Reef Framework Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
23.5.2 Detrital Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
23.6 Facies Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 369
23.6.1 Facies Architecture of Fringing Reefs . . . . . . . . . . . . . . . . . . . . . 369
23.6.2 Facies Architecture of Barrier Reefs . . . . . . . . . . . . . . . . . . . . . . 369
23.6.3 Facies Architecture of Atoll Reefs . . . . . . . . . . . . . . . . . . . . . . . 371
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 371
Part IV Coastal Evolution on a Geological Time Frame

24 Climate: Climate Variability and Climate Change . . . . . . . . . . . . . . . . . . . . . 375
24.1 What is Climate? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
24.2 What is Climate Change? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 375
24.3 Climate Forcing and Climate Mechanisms . . . . . . . . . . . . . . . . . . . . . . . . 375
24.3.1 Explaining the Global Climate Machine . . . . . . . . . . . . . . . . . . . 375
24.3.2 The Role of the Sun as the Main Climate Driver . . . . . . . . . . . . . 377
24.3.3 Internal Modes of Climate Variability: Short-Term Climatic
Cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 377
24.3.4 Earth’s Orbital Influences: Long-Term Climatic Cycles . . . . . . . . 379
24.3.5 The Processes of Absorption and Reflection of Solar Energy . . . . 381
24.3.6 The Modulation of the Atmospheric Composition . . . . . . . . . . . . 382
24.4 A Brief History of Earth’s Climate Changes . . . . . . . . . . . . . . . . . . . . . . 382
24.5 Effects of Climate Changes on the Coast . . . . . . . . . . . . . . . . . . . . . . . . . 384
24.5.1 Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
24.5.2 Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385
24.5.3 Wind Regime and Storms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
24.5.4 Sedimentary Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 386
24.5.5 Sea Level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 387
25 Relative Sea Level: Eustatism and Tectonics . . . . . . . . . . . . . . . . . . . . . . . . . 389
25.1 Why Sea Level Movements Are Relative . . . . . . . . . . . . . . . . . . . . . . . . 389
25.2 Global Movements: Eustatism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 389
25.2.1 Global Changes in the Volume of Ocean Waters . . . . . . . . . . . . . 389
25.2.2 Changes of Shape and Size of Oceanic Basins . . . . . . . . . . . . . . 390
25.2.3 Effects on Coastal Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 390
25.3 Regional Movements: Uplift and Subsidence . . . . . . . . . . . . . . . . . . . . . . 391
25.3.1 Causes of Regional Movements . . . . . . . . . . . . . . . . . . . . . . . . . 392
25.3.2 Effects on Coastal Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
25.4 Combined Tectonics and Eustatism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 392
25.5 Transgressions and Regressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 395
Contents xxiii
25.6 Preservation Potential of Coastal Sequences Under Sea Level

Movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 397
25.6.1 Preservation Potential of Beaches and Barrier Systems . . . . . . . . . 397
25.6.2 Preservation Potential of Tidal Flats and Wetlands . . . . . . . . . . . . 398
25.6.3 Preservation Potential of Estuaries . . . . . . . . . . . . . . . . . . . . . . . 398
25.6.4 Preservation Potential of Deltas . . . . . . . . . . . . . . . . . . . . . . . . . 398
25.6.5 Preservation Potential of Reefs . . . . . . . . . . . . . . . . . . . . . . . . . . 399
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 399
26 Paleoceanography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
26.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
26.2 What is Paleoceanography? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
26.3 A Brief History of the Science . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 401
26.4 Different Paleoceanographical Foci . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
26.4.1 Hydrographic Paleoceanography . . . . . . . . . . . . . . . . . . . . . . . . . 403
26.4.2 Physical Paleoceanography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 403
26.4.3 Ecological Paleoceanography . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
26.4.4 Climatic Paleoceanography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
26.4.5 Oceanic Paleophysiography . . . . . . . . . . . . . . . . . . . . . . . . . . . . 404
26.5 Past Oceans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 405
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 408
27 Older Coasts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
27.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
27.2 Precambrian Tidalites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411
27.3 Late Paleozoic Deltas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412
27.4 Late Jurassic–Early Cretaceous Reefs and Carbonate Coasts . . . . . . . . . . . 414
27.5 Cenozoic Barrier Islands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 416
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 418
Part V The Humans in the Coast: Interaction Problems and Coastal

Management
28 Human Impacts on Coastal Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
28.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 423
28.2 Direct Human Interventions on the Coast (Coastal Engineering) . . . . . . . . 423
28.2.1 Building Rigid Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 424
28.2.2 Beach Replenishment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 429
28.2.3 Destruction of the Foredune Systems . . . . . . . . . . . . . . . . . . . . . 430
28.2.4 Modifications of Tidal Prisms in Restricted Environments . . . . . . 430
28.3 Human Modifications of the Fluvial Sediment Supply
to Coastal Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 430
28.3.1 Building of Dams into Rivers . . . . . . . . . . . . . . . . . . . . . . . . . . . 432
28.3.2 Changes in River Catchment . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
28.4 Human Influence on Global Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 434
29 Coastal Changes and Coastal Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437
29.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 437
29.2 Slow-Rhythm Coastal Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438
29.2.1 Sea Level Rise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438
29.2.2 Coastal Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439
xxiv Contents
29.3 High-Energy Coastal Events . . . . . . . ................... . . . . . . . . 442

29.3.1 Extreme Storms . . . . . . . . . . ................... . . . . . . . . 442
29.3.2 Tsunamis . . . . . . . . . . . . . . ................... . . . . . . . . 443
29.3.3 Other High-Energy Processes Affecting the Coasts . . . . . . . . . . . 444
29.4 A Multi-hazard Perspective . . . . . . . . ................... . . . . . . . . 445
References . . . . . . . . . . . . . . . . . . . . . . . . . ................... . . . . . . . . 445
30 Mitigation, Coastal Policies and Integrated Coastal Zone Management . . . . . 447
30.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
30.2 Mitigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 447
30.3 Coastal Policies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448
30.3.1 USA Policies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 450
30.3.2 European Union Policies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
30.3.3 Australian Policies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 451
30.3.4 Other Countries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
30.4 Integrated Coastal Zone Management . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
30.4.1 The Evolution of ICZM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 452
30.4.2 Future ICZM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 453
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 454
Part VI Final Remarks

31 Future Trends in Coastal Geology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
31.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 459
31.2 Studies on Coastal Dynamics, Geomorphology and Sedimentology . . . . . . 459
31.2.1 Underground Records and Architectural Studies . . . . . . . . . . . . . 459
31.2.2 Study of Coastal Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 460
31.2.3 Extension of Studies to the Submarine Areas of the Coast . . . . . . 460
31.2.4 Upscale and Downscale Studies . . . . . . . . . . . . . . . . . . . . . . . . . 460
31.2.5 Basic Studies on the Coasts of Developing Countries . . . . . . . . . 460
31.3 Studies on Methodological Development and Use of New Techniques . . . 461
31.3.1 Sensors for Process Measurements . . . . . . . . . . . . . . . . . . . . . . . 461
31.3.2 Geophysical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
31.3.3 Remote Sensing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
31.3.4 Bathymetric and Topographic Methods . . . . . . . . . . . . . . . . . . . . 461
31.3.5 Numerical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 461
31.4 Environmental Studies and Integrated Coastal Zone Management . . . . . . . 462
31.4.1 Mapping Vulnerability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
31.4.2 Conceptual Modeling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 462
31.4.3 Interdisciplinary Studies and Debates . . . . . . . . . . . . . . . . . . . . . 462
31.5 Science for Society and Citizen Science . . . . . . . . . . . . . . . . . . . . . . . . . 463
31.6 Concluding Remark . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 463
Part I
Geological Approaches to the Coast
Coast through it all

cause on the other-side i know
there’s a better tomorrow.
“Coast”
Kaiden Patch
Coastal Geology as a Science Through Time
1
the erosional features that appear on the already deposited

1.1 What is Coastal Geology? geological formations (Figs. 1.1 and 1.2).
The fundamental idea of coastal geology is a simple one:
Defining a scientific discipline is not an easy task, because there is no coast without geology. On the one hand, the
each concept has had its own historical evolution and been interface between land and sea is strongly influenced by the
submitted to multiple points of view which have led to geology of the land. On the other hand, how the sea is able to
different definitions or even to distinct concepts. So, the model (by sculpting or building) the coast is a product of
study of geology, and particularly coastal geology, has combined geological processes through time. In conse-
undergone an evolution which has been intimately entwined quence, the term coastal geology extends to the character
with the knowledge and beliefs of every epoch during its and the history of the terrestrial fringe located on the strip of
development. land bordering sea.
Etymologically, geology is the science that studies the Its beginnings go back further, however, since despite
Earth. However, this definition corresponds today with the having been born in the emerged littoral, the development of
concept of geosciences: that is, all of the empirical natural coastal geology arose from the domain of the marine realm,
sciences that study different aspects of the Earth, among thanks to the development of indirect techniques that con-
which geology is only a part. In the past, geology was cat- ducted scientific studies into very different aspects of natural
egorized within natural history, being the most ancient part science. In consequence, the greatest advances in coastal
of the natural world’s history in its examination of the geology occurred at the hands of marine geologists, whose
inanimate entities of the Earth. So, during the eighteenth and work resulted in a new vision of the coast derived directly
nineteenth centuries, geological studies centered on from scientific investigations in shallow marine areas. From
descriptive aspects and collectible samples to be included in this, marine geophysics emerged with force as an essential
museums. Since the second half of the nineteenth century, instrument to understand the structure of the land covered by
however, the geology linked with natural sciences acquired a the sea, especially on the fringes adjacent to the continents.
more scientific focus and began dealing with the study of The techniques included gravity, heat flow and magnetism
matter, its spatial distribution and the processes that operate measurements, using seismic, sonic or electrical waves cre-
on it, to try to explain these properties. Over time, accu- ated artificially and passed through sediments and rocks to
mulation of knowledge caused schisms in numerous bran- understand the basement of submerged coastal areas. Thus,
ches, among them that which is responsible for geological geology and geophysics are closely linked, even though each
aspects that have a close relationship with the coast: coastal has unique aspects that are sometimes very differentiated in
geology. studies of coastal geology.
The coast can be defined as the fringe of terrain where the From a geological perspective, the materials that consti-
continent meets the sea. So, coastal geology is the science tute a coast can be highly resistant to erosional coastal
that aims to study the characteristics, structure and origin of processes or, on the contrary, easily erodible and trans-
the geological materials that constitute this coastal fringe, portable by fluid agents (wind, waves and currents). From
from the emerged waterfront to the sublittoral areas, with this point of view, coastal geological formations may have
special emphasis on the active geological processes that take an erosive character in the case of ancient consolidated
place there. This focus on the active processes (weathering, sediments and rocks, but they can also be sediments. In the
erosion, transport and deposition) tends to explain the nat- first case the littoral is sculpted by the coastal agents, while
ural phenomena that contribute to the genesis of the geo- in the second materials are deposited under favoring con-
logical materials deposited in the coastal environment and to ditions of wind, waves and tides. These sediments may vary
© Springer Nature Switzerland AG 2022 3

J. A. Morales, Coastal Geology, Springer Textbooks in Earth Sciences, Geography and Environment,
https://doi.org/10.1007/978-3-030-96121-3_1
4 1 Coastal Geology as a Science Through Time
Fig. 1.1 Erosional coast: cliffs

sculpted on plutonic formations at
Sines, Portugal
Fig. 1.2 Depositional coast:

Guadiana River Delta at the
southern border between Portugal
and Spain
from fine grains of mud or sand (micrometric or millimetric) sedimentary environments. The final geology in terms of
to bigger elements such as pebbles, cobbles or boulders geomorphology and sedimentology that results in a partic-
(centimetric to metric) and are distributed in coastal ular coastline is the product of combined physical, chemical
1.1 What is Coastal Geology? 5
and biological processes acting on this coastal track over has influenced the historical development of coastal geology
decades, and hundreds or thousands of years. as a relationship between cause and effect.
Therefore, coastal geology may be considered as an Almost certainly, the first observations on marine
extended form of active geology that is specifically devel- dynamics in the Western hemisphere were made by the
oped on the shore and under the sea at the edge of conti- Egyptians, who necessarily had to use knowledge about the
nents. The broad spectrum of disciplines it covers can be oceanic currents and prevailing winds to travel to the coasts
summarized in the study of the more specific and funda- of Syria, Cyprus, Crete and the Middle East. Sometime later,
mental aspects, as follows: structure, tectonics, stratigraphy, the Cretans and the Achaeans also used, without a doubt,
sedimentology, micropaleontology, petrology, geochem- this kind of knowledge, and more broadly, the Phoenicians
istry, mineral deposits, water dynamics and evolution of and Greeks had shown a thorough knowledge of the varia-
oceanic basin margins. tion of these annual currents to circumnavigate the
Mediterranean and so dominate the contemporary economy
with their commercial transactions. At same time, in Western
1.2 Observation of the Coast in Ancient Europe were the Tartessos people from southwestern Iberia,
Times who were able to control marine agents in reaching the
coasts of Brittany and western Africa to get tin and thus
Through history, coastal populations have existed in close manufacture bronze when melting it with copper from their
conjunction with their environment and its problems, own mines.
developing an intuitive and pragmatic knowledge of the In the Asian realm, Persian populations operated a
coastal functioning at the local level and adapting to the commercial trade across the Persian Gulf from the Sumerian
characteristics and peculiarities which the environment period. Indian and Taiwanese sailors extended this trade in
imposed upon them. a network of navigation tracks known as the Maritime Jade
Observation of the coast, and by extension of the sea, was Road. This network connected commercially the main
always related to its use as a resource. Although the use of points of the Indian Ocean, Persian Gulf and Arabian Sea
the coast has its oldest records in the Upper Paleolithic shelly coasts at least since 2000 BC. This same network was used
remains found along many coasts of the world, there were later by Arab peoples, but was known then as the Maritime
probably cultures and peoples that had previously exploited Silk Road. Further east, Chinese people dominated the
it in conditions of lower sea level. Consequently, the record routes of their surroundings, demonstrating an extensive
of their activities would be currently underwater after the rise knowledge of winds and currents since the Song dynasty.
that followed the last Ice Age. A good example of that could In the first century BC, they already used compasses and
be the ancient Briton communities that settled in the had drawn the first coastal charts, which even noted the
now-submerged Doggerland (or Dogger Bank). Throughout position of sandy shoals to make coastal navigation easier
history, there have been people directly linked to the coast (Fig. 1.3).
and that very proximity led them to dare to go into marine In Australia, the Aboriginal communities that had settled
waters. On the other hand, other civilizations avoided the on the coasts also observed and interpreted the movements
coast because they had a negative vision of the sea, seeing it of the sea. The Aboriginals lived for millennia in equilibrium
as a permanent source of danger (from energetic processes with the surrounding nature and this knowledge was trans-
but also from other people’s invasions). The spectacular mitted orally as a part of their cultural traditions and
maritime undertakings of the Phoenicians, the Greeks, the heritage.
Islanders of the Pacific and later the Vikings are well-known, All of these examples demonstrate that ancient peoples
but these adventures would probably have been a response to had knowledge about coastal and marine functioning, but
social stimuli such as population pressure or economic can be that considered coastal geology? Maybe not—but
incentives rather than a direct consequence of the physical their knowledge was the base on which the true coastal
environment. geology was built.
From this point of view, the knowledge of the sea was Nevertheless, there are descriptions of the processes
directly related to the expansion of territorial and economic shaping the coast by Greek philosophers which one would
domains throughout the history of humanity. In Western consider to be real coastal science. These philosophers
culture, this was dominated by Eastern Mediterranean peo- conducted the first observations and reflections about origins
ples (until the Middle Ages) and Western Europeans during and effects on the shoreline. As early as the fifth century BC,
the time of the great geographical discoveries (late 15th and Herodotus anticipated the idea of changes in the sea level,
early sixteenth centuries), and then the countries of North reflected in his observations on the Nile Delta, and described
America together with old Europe and Japan. This control the existence of periodic tides in the Red Sea. It was also
Fig. 1.3 Illustration of an

ancient nautical chart showing
clouds blowing winds to generate
sea waves
Herodotus who first defined the concept of a delta. At the Europe, except for some monks led by the Venerable
same time, Aristotle made wide observations connecting Bede (seventh century) who were able to correctly inter-
physics, meteorology and geology. Among other matters, pret the astronomical control and weather influence of
this philosopher described the origin of hurricanes and the some coastal processes. There was also St. Albert the
interaction between wind and sea giving origin to waves. He Great, who interpreted correctly that wide areas of Europe
observed a continuous flowing of the Mediterranean water, had in the past been under the sea and submitted to
attributing its origin to changes of depth in the marine basin. coastal action, and described transgressions/regressions
He also deduced that coastal changes were caused by the and erosional–depositional processes and their influence
sediment supply from rivers and described the existence of on the coasts.
depositional and erosional coasts. During this time, the Islamic world was the most direct
Two centuries later, Eratosthenes and Antigonus of heir of the classical cultures. During the medieval period
Carystus related tides with reverse currents through the Strait they developed an accurate cartographic science that they
of Messina. Just a century later, the Greek philosopher used to make very precise coastal maps and course books by
Posidonius attributed to the Moon the cause of tides, relating means of oriental or classical discoveries such as the com-
its range with lunar phases on the basis of observations made pass or the astrolabe. Although their purpose was exclu-
in Gadir (Cadiz, Spain). In the same century, the Babylonian sively for navigation, these routes included information
astronomer Seleucus proved that tides were not uniform in about waves, winds and currents that today can be used to
all the coasts nor on all days, offering a meteorological reconstruct not only the geography but also the coastal
interpretation. However, it was not until the second century dynamics of these past times. At the time, the wide expanse
AD when Pliny the Elder correctly attributed the inequality of medieval Islamic dominion extended knowledge to all
of the tides to the joint action of Sun and Moon. coasts of the Mediterranean, the Black Sea and other coasts
Meanwhile, two centuries before had seen the first of Africa and Atlantic Europe. It was indeed an Arab
insights into the relationships between tectonics and geographer, Al Idrisi, who established in 1166 the existence
dynamics of the coastline. Thus, Strabo deduced that col- of a relationship between the evolution of the coastline and
lapses and elevations of land had taken place, proving the the climatic zone where it developed.
role of the related processes of fluvial erosion and trans- At the end of this epoch, the rediscovery of ancient sci-
portation to the coast and the mechanism of formation of entific texts like the volume “Geographia” by Ptolemy and
deltas. This Roman geographer also related earthquakes and its translation into Latin signified a recovery of the classical
volcanic eruptions to vertical movements of the continent knowledge. In this realm, Leonardo da Vinci, following the
and the subsequent invasions of the ocean. texts by Pythagoras and Plato, began to formulate natural
During the centuries that followed the fall of the laws in mathematical terms, and thus was able to formulate
Roman Empire, there were no great scientific advances in other laws, such as the theory of the tides.
1.3 Age of Exploration: The Birth of Marine Geology 7
1.3 Age of Exploration: The Birth of Marine scientists and geographers involved in these expeditions was
Geology presented by Flor [3] in the introduction of his monograph
Marine Geology.
Observation of sediments from the seafloor linked to depth Perhaps the best example was provided by James Cook,
data, especially in the sublittoral fringe, began to become who explored Australia and New Zealand in the name of
common in the sixteenth century in order to facilitate navi- King George III of England, making geometrically reliable
gation in shallow areas. An instrument called a pole, con- charts that included information about bathymetry, sediment
sisting of a lead of 14 pounds (6.35 kg) attached to a rope of nature, currents and geomorphological features (Fig. 1.4).
200 fathoms (365.76 m), was used for this purposed (the Alejandro Malaspina contributed in the same way to the
method of lead and line). A hole was made in the lead to description of the coastal features of South America during a
collect the sediment when touching the seabed. Unfortu- mission for the Spanish King Charles IV.
nately, this instrument only made accurate measures in From a dynamic point of view, these studies correspond
depths of less than 50 fathoms. The information from the to the theories of Laplace from the same epoch (1775) about
coastal bed began to be introduced in nautical charts, the mechanisms that generate the tides, their dynamics
although this information never received a treatment or an expressed in mathematic terms and the role of the Coriolis
interpretation from a geological perspective. force on them.
In the fourteenth century, the contribution of Galileo Throughout these centuries, despite the multiple obser-
initiated a scientific revolution. Since then, the scientific vations on dynamics of marine agents, coastal morphology
method was the base of knowledge in all the sciences. and study of sediments, coastal geology was never defined
Nevertheless, it was not until the end of the seventeenth and as a science, and was not even referred to as a discipline of
eighteenth centuries when society experienced a greater geology. The nineteenth century saw many expeditions that
intellectual understanding of the principles associated with addressed scientific studies from different perspectives.
these examples. Then, the domination of a critical attitude During this period, many contributions focused on the
regarding previous knowledge came to transform the phi- drawing of detailed cartographies, of the emerged coastal
losophy in experimental sciences, with checked proofs strip as well as of the sublittoral fringe, sometimes extending
required to demonstrate truths. This period was initiated in these studies up to several kilometers into deep areas. In the
the eighteenth century and extended to the 19th, and it same way, numerous advances were made in the character-
affected geological knowledge in general, and the coastal ization of coastal agents (waves, tides and currents). One
geological approach in particular. At that stage, there were view of these studies could be that they resulted in the birth
important scientists travelling the world to describe coastal of marine geology and of physical oceanography, both of
natural dynamics along exotic coasts, writing rich texts which were defined as sciences in the middle of that century.
accompanied by accurate maps and excellent drawings. It was in this period when the German Alexander von
A compilation of the discoveries and contributions of the Humboldt characterized surficial ocean currents of the South
Fig. 1.4 Chart of Otaheite, 1769,

by James Cook, from his journal
of the Endeavour’s voyage
Pacific and their influence on the oceanic islands. The warfare. After the war, these techniques were refocused to be
Scottish explorer John Ross explored Baffin Bay, mapping used in science.
the bathymetry and seabed sediments to a depth of almost From the 1970s, the field of marine geology was shaken
2 km. In the Beagle expedition, Charles Darwin, in addition again by enormous knowledge. On the one hand, the
to elaborating his evolution theory, carried out a character- development of plate tectonics theory in 1960 had offered a
ization of the dynamics of coral reefs linked to sea level new vision, not only about the extension of the oceans but
movements. The first studies of the beds located off the coast about a new framework for the coasts. That constituted the
of the Antarctic continent, undertaken by Charles Wilkes basis for the later tectonic classification of coasts stated by
and Clark Ross (nephew of John Ross), were also made Inman and Nordstrom [6]. On the other hand, oil companies
during this period. On the side of the characterization of were contributing a large amount of data about marine basins
coastal processes, Gerstner (1802) and Stokes (1847) offered through the development of seismic stratigraphy techniques
the first theories about wave dynamics expressed in mathe- which, in this case, were developed in greater profusion for
matic terms. use on the continental shelves.
The interest in the new science developing from the However, these expeditions were not primarily focused
knowledge of the sea resulted in the emergence of some on seismic stratigraphy, and studies on the geology of the
important books. The British geographer James Rennell coasts were dealt with in a collateral way or were not even
published in 1832 his Investigation of the Currents of the considered. On the contrary, during this stage the new
Atlantic Ocean. In this work the author placed particular knowledge about coastal geology was linked to the appli-
emphasis on the effect of these streams on some coasts in cation of new techniques of analysis of submarine areas on
terms of sediment transport. Sometime later, in 1855, the the submerged fringe of the coast. For this reason, this stage
American Matthew F. Maury brought a wealth of oceano- meant great development for oceanography, but no break-
graphic information, publishing which is recognized as the throughs for coastal geology.
first textbook of the history of oceanography, entitled The
Physical Geography of the Sea. In the wake of this,
Charles W. Thompson published his investigations of the 1.4 Explosion of Human Occupation
North Atlantic and the Mediterranean seas in his book on the Coast: The Birth of the Real
Depths of the Sea, published in 1873, which included for the Coastal Geology
first time the system of currents due to exchange of water
masses in the Strait of Gibraltar. Coasts were often historically avoided because of their
From the emergence of marine geology as a science, potential danger for human beings and their infrastructures.
knowledge of deeper environments was gaining importance. For this reason, some civilizations never built in coastal
Thus, at the end of the nineteenth century, European gov- areas. On the other hand, other peoples had occupied their
ernments financed expeditions such as the Challenger (Bri- coasts since the beginning of humanity, but typically coastal
tish), Gazelle (German) and Fram (Swedish). The results of sites were used in natural conditions, even in some places
these expeditions are well-known and laid the foundations of where the occupation was high. However, in recent times,
the marine sciences, strengthening marine geology. These the increasing global population, industrialization and the
kinds of expeditions extended into the beginnings of the need for larger harbors meant that human populations had to
twentieth century, when many countries added their efforts modify the coastal environment to adapt it to their require-
to the knowledge of deep areas. During this time, a new ments. Before the present century, the main parts of these
vision of the seabed came to revolutionize the focus of modifications were carried out without causing a great
marine geology. That was the theory of continental drift impact on the coastal dynamics. However, at the beginning
stated by Alfred Wegener in 1912, which signified the pre- of the twentieth century that impact began to be greater,
lude to understanding plate tectonics. although still none of the coastal works, anywhere in the
During World War II, notable advances were made in the world, was accompanied by forecast studies of the possible
understanding of some specific coasts, especially those impacts these could have on coastal dynamics.
where troops planned or made landings or disembarkations The rate of growth in urbanized coastal areas has been too
of supplies. These studies included morphology, sediments high in industrialized countries since the 1940s. One such
and processes (wind, waves, tides and currents). The efforts example is the Spanish coast, where the urbanized coastal
of the main countries involved in the war also contributed to surface quadrupled between the 1960s and 1970s, with the
the development of many techniques that could be applied to development of residential complexes, tourist businesses and
seabed knowledge. So, acoustic (echo sounding, sonar) and infrastructures, and the consequent destruction of coastal
seismic techniques were developed for anti-submarine ecosystems (Fig. 1.5). Something similar had occurred in the
1.4 Explosion of Human Occupation on the Coast: The Birth … 9
Fig. 1.5 Houses built on the

coastline under an urban plan
executed without taking into
account coastal dynamics.
Example shows the southwestern
coast of Spain
United States’ barrier island systems during the two previous England-Acadian Shoreline [8], Johnson starts from mor-
decades and the same model would occur in the European phological features to interpret the evolution of a complex
Mediterranean countries (France, Italy and Greece). Soon depositional coast. Some years later J. Alfred Steers devel-
imbalances caused by human modifications on the littoral oped his studies on British and Australian coasts that cul-
were felt on many coastal fronts as erosional problems minated in his book The Coastline of England and Wales
appeared in unexpected and unwanted ways. Surprisingly, (1946) [10].
the lack of studies about coastal dynamics as a form of urban It was not only American and British scientists who were
planning continued up until the late 1970s. developing research on the coastal fringe in these decades. In
Why did urban planners not predict or consider the Denmark, Axel Schou published in 1945 [9] his monograph
impact of their structures? Perhaps because the knowledge Det Marine Forland, a concise description and interpretation
about coastal dynamics was not well developed in these of the evolution of the Danish coast. A decade later, in 1954,
decades. the contribution of the French [5], Coastal and Submarine
The story of the advances of the early studies of coastal Morphology, approached coastal evolution from a wider
dynamics is excellently described by Carter and Woodroffe oceanographic and geological point of view.
[1]. The geographical studies of coastlines in the late nine- After the war, another notable advance for coastal geol-
teenth century were mainly focused on understanding how ogy occurred in parallel with the development of the study of
and why coastal changes occurred, while the best approaches sedimentology. Curiously, the first approaches to the coastal
to the coastal evolution principles took place in the first environments that were made by authors of the 1930s [4, 11]
decades of the twentieth century. The first approaches to a did not even use the word coast to define the system located
real coastal geology from a geomorphological point of view in the border between land and sea, instead employing the
were made in the first decades of the twentieth century in term “transitional environments.” During the 1950s, sedi-
parallel with the study of Earth’s other landforms (rivers, mentologists continued this trend. Nevertheless, the contri-
glaciers, deserts, mountains…). These first approaches were butions to the knowledge of fluid mechanics, transport of
focused on the classification of the morphological features particles and bedform dynamics were applied to understand
and their explanation in terms of processes. In 1919 the the coast and explain the main sedimentary sequences that
monograph which can be considered the first classic manual were also described in this period.
on coastal geomorphology was published: Shore Processes The decades of the 1950s and 1960s were under the
and Shoreline Development, written by Douglas [7] influence of some very active coastal researchers:
It was also at this time when seminal works by the same Richard J. Russell in Louisiana (USA), Cuchlaine A.M.
Johnson, William M. Davis and Grove K. Gilbert were King in Britain and Charles A. Cotton in New Zealand.
published. These can be considered as the first works of a They, among others, led the interpretations of coastal
real coastal geology. In the monograph The New evolution as a response to the link between long-term
factors (such as tectonic movements and climatic influ- 1.5 Recent Knowledge
ences) and short-term variables (hydrodynamic agents).
A more dynamic vision was that introduced by Davies [2] In the last 30 years coastal geology studies have experienced
as a prelude to the advances of the next decade. So, during a revolution. At present, legions of coastal researchers are
the 1970s, German and French geographers focused their integrated in research teams distributed in almost all the
studies of coastal geomorphology from a climatic point of countries of the civilized world. The cause of this explosion
view under the line of the newly created climatic geo- of knowledge is due to several factors. Firstly, the rate of
morphology. In this sense, the contributions of Jean Tricart urban invasion of the coast that has continued in the last
and André Cailleux demonstrated that the coasts evolve in decades, increasing the problems of stability due to the
different forms according to the climate where they are coastal dynamics but also the problems created by the
developed. building of artificial structures. That created a social need
In parallel, the studies of coastal evolution beyond the that has to be solved by coastal researchers. In addition, the
“iron curtain” were well-represented by the works of the economic development of countries has made available
Russian Vsevolod P. Zenkovich. The importance of his funds for research, especially that which is focused on
contribution can be seen by the fact that his monograph, resolving social problems. In addition, international institu-
Processes of Coastal Development [12], was one of the few tions have created various programs for funds that reinforce
books translated into English. Curiously, this work referred national politics.
to the studies of Gilbert, Davis and Johnson, but not always In this way, UNESCO promoted the International Geo-
to agree with their interpretations of the coastal processes. logical Correlation Program (IGCP), created in 1972. Under
As we can see, when urban development exploded at a this program, the project IGCP274: Quaternary Coastal
global level, the fundamentals of the coastal sciences were Evolution: Case Studies, Models and Regional Patterns
already well-known. Why, then, did the urban planners not (better known as: “Coastal Evolution in the Quaternary”)
apply this knowledge to predict the coastline evolution connected the research developed by several teams by means
before constructing their buildings? The answer to this is not of annual exchange meetings. At the beginning, in 1988,
easy, but would relate to the enormous disconnect between around 400 coastal researchers from more than 50 countries
science and society in these times. In any case, as was were involved. At the end, in 1993, the participants had
previously mentioned, this focus has changed since the late increased to more than 600 from 70 countries.
1970s. The International Union for Quaternary Research
During those years, habitants of the East Coast of the (INQUA) was formed in 1928. The Commission for Coastal
United States and of the most urbanized areas of Australia and Marine processes (formerly the Commission of the
created neighborhood associations with the aim of protecting Quaternary Shoreline) whose aim is “to promote commu-
against the coastal erosion which endangered their houses. nication and international collaboration in basic and applied
These initiatives were funded by working groups on the aspects of Coastal and Marine Quaternary research” was
protection of beaches. On the one hand, this created a dis- created in 1954. During the last 30 years this commission
cipline of coastal engineering that proposed the construction has been the center of the international focus of interest and
of seawalls, breakwaters and groins as beach replenishments also funds projects with concrete objectives.
that set precedents in the resolution of problems. In the The LOICZ project (Land–Ocean Interactions in the
future, these solutions will be extended to coasts all over the Coastal Zone) was established by the International Geo-
world. On the other hand, it created the next generation of sphere–Biosphere Programme (IGBP) in 1993. In its first
coastal researchers, led by Richard A. Davis, Miles O. stages LOICZ focused its investigation on biophysical
Hayes, Orrin H. Pilkey, Donald J.P. Swift and L. Don approaches, but later increased attention to coast–human
Wright, among others, who defended the studies of coastal interactions, including themes such as the influence of
geology as the real base to understand the problems and the coastal dynamics on coastal management.
development of realistic urbanizing plans which take into In Europe, significant advances included the implemen-
account coastal dynamics. The main contribution of this new tation in 1994 of the MAST (Marine Science and Technol-
generation of coastal geologists was to enhance the obvious ogy) program and the ELOISE (European Land–Ocean
critical links between the oceans and the shore, which at that Interaction Studies) thematic network by the Directorate-
moment were practically unstudied. Their works from the General XII of the European Union. The link between these
1980s demonstrated the strong connections between the two entities resulted in the creation of the ICZM (Integrated
coastal systems (dunes, beaches, nearshores, estuaries and Coastal Zone Management) Demonstration Programme in
deltas) with deeper marine environments (shorefaces and 1996. The aim was “to provide technical information about
shelves). sustainable coastal zone management, and to stimulate a
1.5 Recent Knowledge 11
broad debate among the various actors involved in the comparison with accurate images from different dates. Drone
planning, management or use of European coastal zones.” and LiDAR flights have been recently incorporated into
These programs have funded research projects about coastal coastal research, contributing in the same way as remote
research during the last 20 years, with special emphasis on sensing but supplying better image resolution. The posi-
coastal geology. tioning of geological, bathymetrical and geographical
Within this framework, interdisciplinary teams of geolo- records could be acquired in a more accurate way using
gists and archaeologists have created a new discipline named portable global positioning systems (GPS) to treat the
geoarchaeology. The application of the knowledge supplied information in geographic information systems (GIS).
by this science in coastal areas has allowed the interpretation Finally, mathematical models have been employed as a very
of the littoral in terms of coastal evolution. In a retrospective useful tool for the knowledge of the dynamic functioning of
sense, many studies of coastal evolution from geological coastal systems.
data allowed the reconstruction of the ancient geographies Today, the foundations of coastal geology as science are
that had framed the archaeological discoveries. firmly established, with clear links to other related sciences
As a direct consequence of these national and interna- like marine geology, coastal engineering or coastal ecology.
tional developments, research centers have in the last dec- It is interesting to observe how coastal geology has become
ades found good sources of funding to develop research gradually more inclusive and all-embracing, encompassing
projects focused on the knowledge surrounding coastal previous visions like coastal morphodynamics, coastal sed-
geology. Hence, many research groups and laboratories were imentology, even coastal environmental sciences. This is
born during the 1990s and the beginning of the twenty-first especially useful in the present climatic change framework.
century. Today, solid research teams study coastal geology In the future, the world will turn towards an increasingly
in American nations, Western Europe, Asia and Australia. In transversal science, for a more effective transmission of the
parallel, the transmission of the recent knowledge to society latest advances to society. Let’s go!
has substantially improved during these years. Increased
budgets to coastal researchers were accompanied by enor-
mous developments in technology. Thanks to a remarkable References
development of the methodology and the appearance of new
techniques and equipment, measurement processes became 1. Carter RWG, Woodroffe CD (eds) (1994) Coastal evolution.
more and more accurate. With the introduction of new field Cambridge University Press, Cambridge, 517pp
equipment (accompanied by software for processing ever 2. Davies JL (1964) A morphogenic approach to world shorelines.
Ann Geomorphol 8:27–42
more up-to-date information), it could be said these advan- 3. Flor GS (2004) Marine geology. University of Oviedo, 576pp
ces have happened widely across all the sciences, but it is 4. Grabau AW (1913) Principles of stratigraphy. Seiler and Co., New
clear that this model of obtaining and processing digital data York, 185pp
has had a deeper effect on coastal geology studies. 5. Guilcher A (1954) Coastal and submarine morphology. Methuen
& Co. Ltd. London, 314pp
From a sedimentological point of view, the ways to 6. Inman DL, Nordstrom CE (1971) On the tectonic and morpho-
interpret the geological record of coastal systems was logical classification of coasts. J Geol 79:1–21
increased by using different kinds of light corers (hand 7. Johnson DW (1919) Shore processes and shoreline development.
corers, piston corers and vibracorers). Equipment for Wiley and Sons, New York, 584pp
8. Johnson DW (1925) The new England-acadian shoreline. Wiley
acoustic echo sounding, multibeam sounds, side scan sonar and Sons, New York, 608pp
(SSS), reflective seismic and ground penetrating radar 9. Schou A (1945) Det Marine Forland. Folia Geographica Danica, 4,
(GPR) have been incorporated into coastal research and have 236pp
successively very quickly improved. Coastal processes can 10. Steers JA (1946) The coastline of England and wales. Cambridge
University Press, Cambridge, 644pp
be measured in an increasingly precise way by using current 11. Twenhofel WH (1939) Principles of sedimentation. McGraw-Hill,
meters, acoustic Doppler current profilers (ADCP), water 610pp
pressure tide gauges and wave buoys. Remote sensing sig- 12. Zenkovich VP (1967) Processes of coastal development. Oliver
nified a new frontier in coastal geomorphology, since it and Boyd, Edinburgh, 738pp
allowed a more global vision of the coastal areas and a
Defining Concepts of Coastal Geology
2
air interact.” This definition is intentionally broad, since, as

2.1 What is the Coast?
Carter says, water can be salty or sweet and to him it would
include also lacustrine coasts where processes very similar to
As seen in the first chapter of this book, the coast can be
those on seashores occur.
defined as the fringe of terrain where the continent meets the
According to this definition, though, the coast would be a
sea. However, the coast is actually not so easy to define,
really narrow strip of dry terrain, since it would correspond
since there are multiple variables involved. On the one hand,
only to the area of contact between the three elements.
there are land fringes that can be affected by marine pro-
cesses under certain conditions; on the other hand, there are
major submerged areas that are influenced by processes and
sediments coming from land. So, the coast is a complex 2.1.2 Coastal Zone
system which involves many factors that will be explained in
the following chapters. This explains why it is not possible The concept of a coastal zone was defined in a more formal
to supply concrete hypsometric or bathymetric coordinates, way, although its definition preserves the ambiguity of the
width values, lithological or environmental characteristics to concept of coast. Thus, [2] defines it as “the space in which
rigorously delimit the coast. Classification of coasts is also the terrestrial environments influence marine ones and vice
complex since several criteria can be used, so there is not versa,” while [7] defines it as an “area influenced by its
one classification system that is actually accepted from all proximity to the coast.” These definitions deliberately
the different perspectives from which coastal studies can be avoided giving precise limits to the coast, because many of
addressed. However, the purpose of this chapter is to clarify the environments are places of gradual transitions and can be
several concepts that we will encounter throughout this defined by physical, biological or cultural criteria that rarely
book, to give the coastal student a range of criteria enabling coincide.
them to understand the global concept of the coast without The concept of a coastal zone is much broader than the
the need for a precise definition. concept of coast since, as well as the extension of the
As is the case with the proper term coast, there are other above-mentioned strip, it also includes the areas of influ-
terms that are commonly used and sometimes incorrectly ence of mixed land–ocean processes. The landward edge
employed in popular usage. Some of these terms have been clearly depends on the adjacent environments, and can be
previously defined in scientific terms in works and books on very narrow in the case of erosive coasts or extend for
coastal geomorphology (e.g. [7, 2, 14]). The following several kilometers in areas of fluviomarine systems or plains
definitions tend to clarify all of these concepts (Fig. 2.1). of migration of coastal dunes. The seaward limit, mean-
while, is commonly regarded as the contact with the con-
tinental shelf or the last place reached by the base level of
2.1.1 Coast storm waves.
Although the coast is normally defined in two dimensions as

the strip of emerged land meeting the sea, there are really 2.1.3 Littoral Zone
three elements that come together in this coastal fringe,
necessitating consideration of a third dimension—the air. In The littoral zone is defined more precisely. In this case, the
this sense, a more correct definition was provided by Carter definition can be made in biological or sedimentological
[2]: “The coast is the terrestrial place where land, water and terms. For the purposes of this book the most accepted

https://doi.org/10.1007/978-3-030-96121-3_2
14 2 Defining Concepts of Coastal Geology
Fig. 2.1 Graphic definition of

coastal terms, [3] adapted from
the Shore Protection Manual
CERC
definition in coastal geology will be used: “the littoral zone 2.1.5 Shore
is the portion of the coastal zone whose sediment is sus-
ceptible to be transported due to the significant wave action” The shore is formally defined as a “zone that extends from
[7]. The landward limit would be then defined by the action the mean low water line to the effective limit of storm waves
of the significant waves during spring high tides, while the and storm surge” [12, 14]. From the point of view of a tourist
seaward limit would be defined by the base level of signif- it would be defined as “the zone where you can nail an
icant waves. The littoral zone is therefore an area which umbrella,” because there is a great possibility of arriving in
includes the intertidal areas, but is predominantly under an area in an exposed situation, even though it can be sub-
water. merged under different conditions. Obviously, this area can
be divided into two different strips: the lower fringe that is
exposed and submerged every day by tides (the foreshore)
2.1.4 Coastal Plain and the upper one that is submerged only under storm
conditions (the backshore).
A coastal plain is defined as “a low and flat strip of land
adjacent to the coast” [6]. This is a very broad geographical
definition that would include the entire existing flat surface 2.1.6 Shoreline
from the coastline to the first breaking of the relief located in
the interior of the continent, without attending to the origin The shoreline is defined as “the line along which water
or the age of this plain or to the geological formations that meets the land” [8] whereas for the Shore Protection Manual
constitute it. [3] it is the “line that separates the beach from the sea.” One
A definition with a more genetic character is that pro- problem with these definitions is that a line represents only
vided by Cotton [4] which defines a coastal plain as “a flat of an instant in time and that can be a disadvantage, since the
soft decline limited by a continental relief and a simple contact between sea and land is permanently in motion. So,
coast, whose origin is the rise of ancient marine deposits.” defining an instantaneous position can lead to the error of
This definition places the coastal plains in a particular considering this position as a stable situation in time or as an
environment: the coasts of emersion and their deposits are of average position [1]. The first of the definitions would
marine origin but generated during a period prior to the coincide effectively with the shoreline at mean low tide
position of the coastline that borders the plain. level, whereas the second would mean high water level.
From the landforms generated by coastal processes that These references to average tide levels avoid regarding this
act in a given period, the concept of coastal plain could be line as an invariable position.
restricted to that “flat area adjacent to the coast generated by A more accepted concept is raised by authors such as
active coastal processes and occupied by current coastal [15], who considers shoreline to be “not only the line of
environments” [10, 13]. This definition would restrict the contact between sea and land, but throughout the strip in
coastal plain to a zone much more related to the interface which a short-term variation occurs.” Others, like [11],
between land–sea–air which defines coastal zones. considered it most appropriate to acknowledge the
2.1 What is the Coast? 15
variability due to longer term processes. Obviously, this kind until the break of slope that is the edge of the continental
of definition is conceptually more appropriate, but it intro- slope. For marine geologists, however, this environment
duces a degree of uncertainty. What is clear is that today the starts under the base level of the fair weather waves, since
concept of shoreline must be considered in a flexible and the waves only act on this extension of the bed during
dynamic way that undergoes variability, and not as a static specific events.
and unchanging concept.
2.2 A Datum Issue

2.1.7 Coastline
An important aspect in addressing topographical or bathy-
Waterfront is a term less used by coastal geologists, although metric data of the coastal zone, or representing graphically
it is widely used in stratigraphy. It is formally defined by the coastal areas on a map, is the choice of a vertical datum.
Short [17]: “Coastline is the boundary between the coast and The vertical datum is the reference altitude used as level 0 in
the shore.” Having considered the coast as a permanently dry the topographical or bathymetric surveys. All the uprisings
strip and the shore as an area submersible under certain of the relief need a reference level. In addition, as explained
conditions, the coastline is situated at an altitude higher than in the previous section, the sea level is in constant motion
the shoreline. Thus, from a stratigraphic point of view, the responding to different period cycles, thus it is necessary to
position of this line locates all environments that act under consider that any variation of water levels must also relate to
the influence of waves and tides as marine-dominated a fixed reference level. Perhaps the clearest example of these
environments. cyclical variations is the tide, whose levels are subject to
fluctuations with maximum and minimum heights varying in
semidiurnal, biweekly and semiannual cycles, but also spa-
2.1.8 Shoreface tially between coasts with different tidal regimes from
microtidal to megatidal. The averaged and extreme levels
The shoreface is the fringe located under the mean low tide reached by the tide can be determined statistically, with
and extends deeply to just reach the level of action on the some serving as vertical datum for the rest of the levels on
bed of the fair weather waves (wave base level). It is a certain occasions (Fig. 2.2). For example, international laws
coastal fringe that is permanently submerged, except when set the limits of national territories with respect to the level
the water is lower than the mean low tide, when its upper of the mean low water (MLW). However, nautical charts and
part can be exposed. This can also be understood as the some ports often use as vertical datum the lowest tide levels
lower part of the littoral zone [3]. (spring low water or lowest low water), so the rest of the
tidal levels will be considered as positive values. In this way,
the depth values represented in nautical charts are located
2.1.9 Offshore below this value and will be subtidal. Hence, these levels
often receive the name of the hydrographical datum, nautical
The offshore is the fringe located under the level of action on datum or datum of the nautical charts. A summary of the
the bed of the fair weather waves (wave base level) and nautical reference datums used in different countries can be
extends to the level of action on the bed of the storm waves seen in Table 2.1 [3].
(storm base level). It is a fringe permanently submerged and Apart from nautical charts, the most frequent types of
excluded from the action of normal waves, but during storms representation of the relief are topographic maps. In this
significant amounts of sediments can be transported on its case, topographic maps often used as a reference datum the
surface. This fringe is normally understood as the transition mean water level (MWL). This average level can be iden-
between the coast and the inner shelf, but for some authors it is tified with the mean tide level, but usually occupies a dif-
a part of the shelf and cannot be defined as a part of the coast. ferent altitude, since there are level changes other than the
tides.
Regarding the laws governing human activity in coastal
2.1.10 Shelf areas, it is also necessary to establish cartographically those
areas that are floodable by marine processes and thus be able
The continental shelf cannot be considered in any case as to delimit accurately coastal areas. Many of these laws
part of the coast, but “the expansion of the shallow seabed establish the boundary between the public domain and pri-
that runs along the coast to the deep” [14]. For coastal vate property using as vertical datum the mean high water
geologists, the bed of the platform extends from the level (MHW) or the maximum flood level for extreme peri-
boundary of the coastal zone (base level of storm waves) ods of storm high tides (extreme high water level, EHW).
Fig. 2.2 Statistical levels

achieved by tides that are
frequently used by datums
Table 2.1 Hydrographical Hydrographical datum Countries

datums used by different
countries Mean low water US Atlantic Coast, Argentina, Sweden, Norway
Mean lower low water US Pacific Coast
Mean spring low water UK, Germany, Brazil, Italy, Chile
Historical low water Great Lakes (US and Canada)
Lowest spring low water Portugal
Indian spring low water India, Japan
Lowest low water France, Spain, Greece
What happens is that in any country that has a long level variations on different segments of the national coast,
enough coastline, the tide may experience a variation determining statistical values. Secondly, choosing the level
between each of its coastal sections, presenting each of them that suits best the needs for which the datum is intended
with different swings and different mean (and extreme) needs to take into account that its position is as a statistical
values. At a national level it will not be practical to have value, which will need to be reviewed periodically.
different reference levels and thus it is always one of these In this regard, it is better to try to establish a datum that
levels that will be chosen for use in all of the country’s presents a lesser possibility of change in time, if we want this
charts. This reference level is normally indicated in the value to be of lasting use. Either way, the establishment of a
margin of the maps. datum at the national level does not imply that it cannot
One problem that comes from the use of datums that is coexist with other datums used at the local level. In this case,
different for terrestrial and nautical maps is that the coastal a clear vertical relationship between the different datums that
fringes ranging between these different datums are not rep- can be used must be established, both with each other and
resented in any mapping. The use of these different datums with the general datum. On the other hand, it must be borne
can also be a problem when trying to integrate data from in mind that each datum was established for a specific pur-
land (topographic) with data from underwater (bathymetric). pose, but often used later for other purposes without
To solve this problem, the vertical relationship between the understanding well how it can satisfy this secondary use.
different datums should always be clear. A good example is the establishment of the datums of the
Spanish coast, since this country has two coasts with dis-
Advanced box 2.1 tinctly different level variations: the Atlantic and the
Mediterranean coasts. The Atlantic Coast is a coast of
Relationships between different datums: case studies mesotidal and semidiurnal character, with very marked dif-
from Spain and the USA ferences between the spring and neap tides, while the
The use of a datum which takes as its reference the ver- Mediterranean Coast is microtidal, with maximum variations
tical variations of the sea level along the coast of an entire below 0.25 m, which are always related to the conditions of
country is not an easy task. First of all, to set a datum it is wind, waves and atmospheric pressure. Taking into account
necessary to do numerous measures to establish statistical these features, it is obvious that the Spanish Geographic
2.2 A Datum Issue 17
Fig. 2.3 a Location of tidal

stations used as datum references.
b Vertical relationships between
topographic and hydrographic
datums
Institute (IGN) established its geodetic datum on the the coast of the entire country, taking into account the
Mediterranean Coast, using as altitude 0 the “mean water notable differences between the Pacific and the Atlantic
level” in Alicante (MWLA) (Fig. 2.3a). coasts and also other differences between coastal tracks
On the other hand, for nautical charts it is necessary to along each coast. Globally, they have established a national
establish a minimum level, and it is simple to understand that datum called NTDE (National Tidal Datum Epoch) using the
it is not practical for a datum from the coast with minor tidal average data of all the coasts for a period of 19 years.
oscillations, but in which the low tides can reach extreme However, some coasts of the USA have established regional
minimum values, so that need was settled by the Atlantic levels which are based on local measures from different
Coast. To establish these statistical levels, the Navy periods. Good examples of local datums include the Mean
Hydrographic Institute (IHM) used ahigh precision leveling Low Gulf Datum (MLGD), established for the Gulf of
procedure, with an aray of permanent tidal stations (NAP Mexico (microtidal) or the Pacific Coast Datum
network). This procedure allows the linkage of the main (PCD) established for all the Pacific Coast of the United
milestones of the tidal stations with some of the landmarks States (mesotidal). For establishing charts, however, the
of the NAP network (high-precision levelling) of the IGN, so Mean Low Water Level shoreline (MLWL), known as
that the relationships between hydrographic zeros in each Datum EM1110-2-1003, is used as a datum on the Atlantic
local coast, with respect to the mean water level in Alicante Coast, while the Pacific Coast is set by the Mean Lower Low
(MWLA), can be obtained. An example of the result of these Water Level (MLLWL), located 1.60 m below the
relationships can be seen in Fig. 2.3b. EM1110-2-1003. At the same time, for the topographic
In the USA, the National Oceanographic Surey (NOS) set maps the Geodetic Vertical Datum 1929 (NGVD1929) is
up a permanent network of tidal stations. With this network used. The relationship between these datums can be seen in
it can establish the relative variation of the tidal levels along Fig. 2.4 [9].
Fig. 2.4 Vertical relationships

between datums used in the USA
(data from Harris [9])
2.3 Coastal Framework 2.3.2 Consolidated Versus Unconsolidated

Coasts
The morphological characteristics of a coast and the features
that shape it should be known before tackling any more Consolidated coasts are characterized by the presence of
detailed study. Some concepts whose knowledge is essential hard and consistent materials. Coastal areas consist of con-
to understanding the nature of the coast and its relation with solidated rocks typically found in hilly or mountainous ter-
the dynamic and geological environment are therefore rain. In these, erosive processes are usually dominant. The
addressed in this section. degree of consolidation strongly influences the ability of the
coastline to resist the processes of weathering and erosion.
The resistance depends on the susceptibility of the rock to be
2.3.1 Coastal Processes altered by mechanical and chemical processes, as well as the
hardness and solubility of the constituent minerals of their
Intuitively, when we talk about coastal processes, we are grains. The rock type, the disposition of its stratification and
normally referring to processes that act in the short term, also the orientation of the fracturing that affects the rocky for-
called morphological processes. These processes may be mations significantly influence the erosional evolution of the
defined as “a combination of environmental forces subject to coastline.
the dynamics of fluids and sediments and which condition In contrast, unconsolidated coasts are dominated by a
the morphological evolution of the coast” [5]. They could combination of sedimentary and erosive processes, usually
also be defined as “energy sources capable of moving sed- with a depositional balance. In this type of coast, waves and
imentary material, causing erosion or deposit and resulting currents are able to completely alter the features of relict
in a reset of the pre-existing topography” [14]. This second reliefs. Along the unconsolidated coasts, there are usually
definition makes clear the effect of the sediment transport large amounts of sediment available, and therefore the
processes and the consequences of sediment movement on evolutionary changes occur rapidly. These are coasts that
the topography of the coastal environments. This relation- present normally low reliefs and whose coastline has been
ship between topography and fluid and sediment dynamics softened by the erosion of the preexisting headlands, by
acts in a circular manner and each change has a variable deposition of sand barriers or by the infilling of river
effect on the other. The link between processes and mor- mouths.
phological evolution grounds the concept of morphody-
namics. Morphodynamics is understood as “the mechanism
by which morphology affects hydrodynamic processes 2.3.3 Erosional Versus Depositional Coasts
influencing in a circular way the further evolution of the
morphology itself” [19]. Coastal processes are the main suppliers of sediment to the
On the coast, there are also processes acting in the long coast but also of removing it to other places in the form of
term. The term “long-term process” is formally applied to a erosion. Both processes can be simultaneously present on a
century timescale and distances in the order of 10 km, but coastal stretch in different moments and places, but then
informally can also be applied to longer periods of time and there will be a balance between them which will tend
larger spatial scales (e.g., sea level movements, changes in towards one of two senses: erosion or sedimentation.
the climate and tectonic movements). All short- and Erosional coasts are developed in places where there is
long-term processes will be explained in detail in Chap. 3. an abundance of energy from coastal processes or there is a
2.3 Coastal Framework 19
deficit in sediment available to be transported. As a result, 2.3.6 Emergent Versus Submergent Coasts
erosion will be the dominant mechanism of coastal evolu-
tion. Erosional coasts are usually steep and are characterized Global and regional sea level changes, slowly occurring over
by rocky coastlines that are exposed to high energy waves centuries, are also present on the coasts. Some of these
and that contribute a relatively small amount of sediment to changes include intervals of time over thousands or millions
adjacent coastal cells. of years and have been caused by glacioeustatic, climatic or
In contrast, depositional coasts are characterized by an oceanographic factors, affecting the coasts at a global level. In
abundant supply of materials, which results in a net sedi- addition to these, at the regional level changes may occur by
mentation and in the creation of new depositional realms. slow vertical movements of the ground along the continental
They are very common along mature areas with broad margins. Both types of changes, regional and global, are
drainage basins and rivers that are able to supply large responsible for the long-term relative movements of the sea
amounts of sediments which will be redistributed by waves, level and, therefore, for the displacements of the coastline.
tides and currents on the open coast. Along the depositional Most of the movements of the land have a direct tectonic
coasts a wide variety of landforms and sedimentary envi- origin, but this is not their only source. Isostatic adjustments
ronments can be present, which will be described later. are vertical movements by which the Earth’s crust seeks a
If a coastal area does not have a long-term erosional or gravitational balance to suit superimposed forces such as
depositional balance it is a coast in equilibrium. To really crustal thinning or thickening. Significant subsidence
speak of a coast in equilibrium should take into account the movements occur in the vicinity of deltas, where masses of
trends, because that equilibrium will be flexible, regarding a fluvial origin sediment accumulate quickly. On the other
balance through short-term moments of erosion and hand, in the base of deltaic deposits occur phenomena of
recovery. sediment compaction when grains with a low degree of
packing by rapid sedimentation are adapted in a denser
fabric, causing a decrease in volume.
2.3.4 Open Versus Protected Coasts A combination of global and regional effects results in the
possibility that different coastal sections may be in emersion
When we talk about the coast, we always imagine a linear or immersion, and do so at different speeds. An emergent
coastline dominated by wave action. Perhaps it is our rela- coast is a coastal area that has been exposed during a relative
tive ease in the holiday period, looking towards the sea as it fall in sea level. On the contrary, the submergent coasts are
gives a feeling of spaciousness that makes us nominate these those that have been inundated by ocean waters due to a
coasts as open coasts in reference to their opening up to the relative rise in the sea level.
direct influence of marine processes. In the case of immersion and emersion, there may also be
In contrast, there are coastal segments where landforms stationary coasts, where there is a balance of ascending and
and environments are developed landwards from the coastal descending movements and the relative level remains stable
plain. In these instances, the dominant processes tend to be in the long term.
related to the tide, and wave action is absent due to existing
coastal elements that limit or prevent their direct action. We Advanced Box 2.2
refer to these as protected coasts, being those environments
protected from the waves’ action. The Holocene Transgression
The Holocene transgression, also known as the Flandrian
transgression, is a phenomenon of absolute rise in the sea
2.3.5 Mechanical Versus Biological Coasts level related to the global deglaciation that took place in the
past thousands of years (Fig. 2.5). Glacial melting began
The main part of the coast (both erosional and depositional) about 19,000 years ago and accelerated 15,000 years ago.
is dominated by mechanical processes, and these can be The best indication of this thaw was the quickly registered
named mechanical coasts. In addition, other coasts are built sea level rise from 11,700 years ago, which took place due
by the action of organisms. These are called biological to the rapid melting of the remaining ice sheets in Europe
coasts. Perhaps the best example of a biological coast is a and North America. About 6000 years ago the rise began to
reef. Coral and other organisms are able to build enormous slow down, reaching its maximum level at different times
volumes of calcareous solid structures. Note that the Great along the coasts of the world. In general terms it can be
Barrier Reef in Australia is purported to be the largest considered that the current level was reached about
coastal landform on Earth. 4500 years ago.
coastal areas. That is the cause of the presence along the

coasts of military naval ports, airfields and camps. Some of
the military infrastructure, such as harbors, modified the
natural equilibrium of the coast. On the other hand, in some
cases, the presence of military in coastal areas has con-
tributed to their conservation.
2.4.4 Recreational Use

Fig. 2.5 Curve of sea level rise in the last 15,000 years (data from
Waelbroeck et al. [18]) The extensive and often insensitive marketing of the coastal
zone for recreational uses in the last 40 years has not only
led to the unpleasant disfigurement of many shores, which
This rise led to a very rapid invasion of large continental initially had a natural charm, but also to the reorganization of
areas that became continental shelves. Many fluvial valleys many local economies that rely on tourism.
were flooded, turning the course of rivers in estuarine Coasts such as California and Florida in the USA or the
funnel-shaped areas. The arrival of the sea level to its current French and Spanish Mediterranean are very obvious exam-
position can be considered the starting point of the present ples. In these places, many small coastal towns were satu-
coastal dynamics and sedimentation of the regressive rated by new touristic services, which displaced the
sequence that set the layering of the current depositional traditional skills such as fishing, agriculture, livestock or
coastal environments. crafts. Too often, the lack of foresight in the development of
urban and recreational infrastructures has led to the
destruction of fragile ecosystems, both in the emerged coast
2.4 Coastal Uses and along the submerged littoral. This is in fact an irony,
since in many cases the appeal of wilderness that surrounded
2.4.1 Urban Use these localities or the charm of their traditional architecture
were among the factors that initially attracted tourists.
The terrains of coastal areas are attractive and valuable for
urban use, since an outlet to the sea makes them
well-connected zones. Depositional coasts are, among all, 2.4.5 Wetland Reclamation
the busiest, being normally a flat terrain where construction
is easy. This attraction means that coastal areas were to A large area of low-energy coast has been claimed by humans
become the most densely populated areas in the world. In in the last two centuries and this is a process that continues.
developing countries, coastal areas are those that have the The loss of wetlands associated with estuaries, delta plains
highest rates of population growth. and tidal flats (including shallow areas of the inter-, sub- and
supratidal fringes) has had a marked effect on biological
productivity, often for the simple fact that these zones act as
2.4.2 Industrial Use nurseries for adjacent marine water species. In addition to the
ecological impact, loss of tidal land inside the river mouths
Associated with urban use comes the need for the installation has affected the tidal prisms and resulted in a modification of
of industries supplying the products used by humans. the hydraulics and hydrochemistry in the balance between the
Coastal areas are attractive for industries for the same rea- tidal currents and river flows.
sons that drive urban use. In addition, there is the ease that is
represented by the possibility of constructing harbor infras-
tructure for the transport of the freight produced in industry. 2.4.6 Waste Disposal on Coastal Environments
All that means that the most important industrial complexes
in the world are located in coastal areas. Since the Industrial Revolution of the nineteenth century,
littoral and coastal areas have been seen as a perfect dump
for fluids and solid waste materials. Physical and ecological
2.4.3 Military Use disturbance caused by indiscriminate dumping results in
chemical and physical changes in the environment. In
The potential provenance of hostile invasions from the sea extreme cases, such as for example radioactive waste, there
meant that historically many military bases were located in is a direct threat to health, but most often there is only a
2.4 Coastal Uses 21
deterioration of the environment that leads to a decrease of involves the approach from a human point of view. As
biological productivity and in extreme cases to its total rightly stated by Orrin Pilkey, “there is no problem on the
destruction. coast until the presence of a human infrastructure forces one
In the case of solid waste, these can also end up being to measure processes” [16]. This requires understanding that
stacked in piles on reclaimed wetlands, adding a further the presence of processes in themselves do not pose a threat
problem to the land rehabilitation. In most cases, uncon- to a natural system, since the system will adapt to this pro-
trolled drainage from these columns made of waste leaches cess in one form or another. It is the human being who
straight into the natural coastal environment. The imposition understands these processes as a menace by standing in areas
of new environmental laws by international decrees since affected by the same. From this point of view, we should
2010 should lead to improvements in this matter, although consider such issues as the following:
the response to these international standards, as to national
legislation, is always slow and ineffective.
2.5.1 Sea Level Rise
2.4.7 Exploitation of Energy Today it is accepted by the scientific community and also the
common citizen that the global sea level is rising in general
Harnessing the power of waves and tides in coastal areas, terms. Some models predict that the global rise will be closer
such as by the installation of photovoltaic, wind or nuclear to values of 1 m by 2050. The reasons for this increase in the
plants, is cause for concern since, as mentioned, these are sea level are complex, but one of the most influential factors
areas with many other human uses. would be the increase in atmospheric CO2 and other trace
The potential environmental impact of tidal energy tur- gases. The presence of these gases induces an increase in the
bines has been thoroughly investigated in some countries absorption of heat from the Earth’s surface (the greenhouse
such as Canada, France and the United Kingdom, but there effect). Planning for and managing this sea level rise is
are still no major tidal power projects that have materialized. perhaps the biggest current environmental challenge for
Similarly, devices for harnessing the energy of waves have coastal scientists.
been explored on a large scale. In both cases, the potential
impacts are worthy of consideration, even if the projects are
tailored to international laws. 2.5.2 Shoreline Erosion
The use of coastal areas for the settlement of photovoltaic
or wind power plants presents parallel problems, as well as Due to multiple factors, some of them natural and others
the influence that such use of these areas can pose to related to human activity, many coastal fringes present
reclaimed wetlands. erosional trends. Traditionally, coastal engineers have used
The location of nuclear power plants in coastal areas has rigid structures which, in theory, protect the coast from the
additional problems, since these plants may be affected by processes of erosion. These traditional engineering methods
long-term and eventual coastal processes. The case of the are being questioned today, particularly because they are
Fukushima power plant, affected by the tsunami that struck nondefinitive solutions and due to the high economic cost in
Japan in March 2011, is perhaps the clearest example. the long term. Now there are proposals for new, more
flexible strategies for the control of erosion. These strategies
will come about through precise knowledge of the pro-
2.4.8 Coastal Conservation cesses, analysis and intervention on the causes of the
erosion.
Especially in the last decades, many coastal areas are pre-
served as natural reserves, natural parks or marine sanctu-
aries. These protection figures represent a guarantee, not 2.5.3 Storm and Tsunami Hazard
only of conservation of the supported biological ecosystems,
but also of the equilibrium of the dynamic processes. Destructive coastal storms are becoming more common. It is
accepted that global change is causing an increase of storms
and floods along many low and heavily populated coasts.
2.5 Coastal Problems Also, tsunamis represent potentially destructive events. In
recent times, the increase of the population in coastal areas
The intensive use of coastal areas in all the forms that have has brought about an increase in material and personal
been listed above has led to the emergence of certain damage. Perhaps the implementation of better warning sys-
problems. It must be remembered that the word “problem” tems can reduce some risks, although adequate coastal
planning could counteract the potential dangers of these high volume of nutrients can significantly alter any ecosystem,
energy events. and these can be induced simply from a hydraulic or a
geomorphological change in the physical environment. This
idea underpins the concept of ecohydrology managed by
2.5.4 Human Destabilization UNESCO in the past decades.
Some of the problems described above are the product of the

effects of natural processes on the development of human 2.6 Integrated Coastal Zone Management
activity on the coast. However, there are numerous examples
of imbalances in the coastal processes generated by any The interaction of processes and coastal risks, natural envi-
human action that directly affect other human activities or ronments, population growth and uses of the coast (often
infrastructures, or even the natural environment. The most developed without planning), creates a series of problems
obvious disequilibrium may be that caused by port infras- involving the complex challenge of an adequate manage-
tructures on wave dynamics, but there are other actions that ment of coastal areas (Fig. 2.6).
are detailed in further sections. The concept of integrated coastal zone management
(ICZM) is understood as a strategy for the sustainable
development of the coast using as a tool the knowledge of
2.5.5 Saline Intrusion into Coastal Aquifers dynamic and ecological functioning. The need to rely on an
effective administrative structure for management is impor-
The extraction of groundwater from freshwater coastal tant, and for that, today, there are bodies at various levels
aquifers occurs extensively. This water is commonly used and different structures that complement each other. National
for human consumption, irrigation of the coastal plains or for administrations are addressing the general problems of the
use in industrial processes. As a consequence, it often results coastal environments in coordination with inter- and supra-
in a rise of the interface between fresh and salt waters that national organizations. The overall objective of these agen-
moves landwards, causing the salinization of aquifers and cies is to preserve sustainability against the growing use of
the loss of the ability to use these waters for the required resources.
purposes. On the other hand, the challenge to afford the conse-
quences of global change has generated an intense debate
2.5.6 Subsidence
Subsidence is a slow sinking of coastal lands due to multiple

causes. One of the most common is the compaction of old
coastal sediments under the weight of more recent ones.
Other causes may be related to extractive processes as
described in the previous section. In natural environments,
subsidence is normally compensated with an increase in the
sedimentation rate, although in the environments under
human use the collapse results in an increased susceptibility
to coastal flooding (of marine, river or mixed origins).
2.5.7 Changes in Ecological Structure
The uncontrolled exploitation of many coastal ecosystems or

imbalance in the process caused by human activities have
led to changes in the physical environment that supports
ecosystems and thus their ecological structure. These chan-
ges usually involve a decrease in biological diversity and
productivity, as well as other more subtle and hard-to-predict
changes. Many natural coastal systems are under a very
Fig. 2.6 Interactions between natural and anthropogenic processes
sensitive equilibrium regarding the production of nutrients (social and economic) that give rise to the need for an integrated
that support the food chain. Uncontrolled changes of the management of the coastal zone for sustainable development
2.6 Integrated Coastal Zone Management 23
about the concept of “coastal protection.” This is called the 6. Davis WM (1909) The outline of cape cod. Geographical essays.
“debate of the coast,” and it describes the challenge facing Ginn and Co., Boston, pp 690–724
7. Davidson-Arnott R (2010) Introduction to coastal processes and
coastal engineers and geologists on their opposite sides as geomorphology. Cambridge University Press, Cambridge, 442pp
each one defends their strategy of protection [16]. The 8. Dolan R, Hayden BP, May P, May SK (1980) The reliability of
background of this debate was a dissatisfaction among shoreline change measurements from aerial photographs. Shore
geologists with the way engineers tackle coastal issues. and Beach 48(4):22–29
9. Harris DL (1981) Tides and tidal datums in the United States.
Geologists believe that engineers often wrongfully modify Special Report No. 7. Coastal Engineering Research Center, US
the environmental balance of the coast with the construction Army Engineer Waterways
of increasingly large and more expensive structures and 10. Inman DL, Brush BM (1973) The coastal challenge. Science
defend the use of the knowledge of coastal processes and the 181:20–32
11. Komar PD (1976) Beach processes and sedimentation.
ICZM to propose noninvasive solutions to coastal problems, Prentice-Hall, New Jersey, 540pp
enabling the coast to reach its own equilibrium. 12. Mangor K (2004) Shoreline management guidelines. DHI Water
The concept of ICZM and its development will be ana- and Environment. 294pp
lyzed in more detail later in this book. 13. Masselink G, Hughes M, Knight J (2011) Introduction to coastal
processes and geomorphology. Routledge, London, 432pp
14. Morang A (2004) Coastal geology. University Press of the Pacific,
US Army Corps of Engineers, 297pp
References 15. Morton RA (1991) Accurate shoreline mapping: past, present and
future. Coastal Sediments 91(1):997–1010
16. Pilkey OH (1981) Geologists, engineers and a rising sea-level.
1. Boak EH, Turner IL (2005) Shoreline definition and detection: a Northeast Geol 3:150–158
review. J Coastal Res 21(4):688–703 17. Short AD (2012) Coastal processes and beaches. Nat Educ Knowl
2. Carter RWG (1988) Coastal environments: an introduction to the 3(10):15
physical, ecological, and cultural systems of coastlines. Academic 18. Waelbroeck C, Alabeyriea L, Michela E, Duplessya JC,
Press, London, 617pp Mcmanusc JF, Lambeckd K, Balbona E, Labracherie M (2002)
3. Coastal Engineering Research Center (CERC) (1984) Shore Sea-level and deep water temperature changes derived from
Protection Manual (2 volumes). US Army Corps of Engineers, benthic foraminifera isotopic records. Quatern Sci Rev 21:295–
Washington DC, 532pp 305
4. Cotton CA (1955) The theory of secular marine planation. Am J 19. Wright LD (1995) Morphodynamics of inner continental shelves.
Sci 253:580–589 CRC Press, Boca Raton, FL, 241pp
5. Cowell PJ, Thom FG (1994) Morphodynamics of coastal evolu-
tion. In: Carter RWG, Woodroffe CD (eds) Coastal evolution.
Cambridge University Press, Cambridge, pp 33–86
Factors Affecting Coastal Evolution:
Spatiotemporal Scales 3
changes at short time intervals are not reflected in that

3.1 The Changing Coast
record, having been deleted by subsequent changes. In other
words, many of the coastal facies which reflect changes in
Coastal environments are probably the most variable sys-
processes are destroyed if their preservation potential is low,
tems on the Earth’s surface. Many changes that occur on the
and are reflected only in the presence of erosive unconfor-
coast are repetitive in space and in time, while others are
mity surfaces. However, as described in the previous chap-
slowly being produced by way of trends and others take
ter, in recent decades coastal geology has experienced a
place in the form of isolated events. It is also interesting to
revolution in its development, and short-term dynamic pro-
distinguish between the repetitive changes that occur in a
cesses are among those that have received greater attention.
periodic way and the cyclical changes. An example of
Today, the factors affecting the changing coast are better
periodic changes would be the effects of storms with a long
known.
return period, while examples of cyclical changes could
include the effects of the succession of spring and neap tides
on the bedforms of tidal environments or the well-studied
seasonal changes on beaches (with erosion of the sand 3.2 Factors of Coastal Dynamics
caused by winter storms and the spring and summer sedi-
mentation because of the action of fairweather waves). The The previous paragraph makes it clear that coastal sedi-
best example of isolated events would be the action of tsu- mentary environments are natural systems operating under
namis, but this could also be considered as a periodic pro- very intense dynamics that induce morphological changes at
cess with a geological-scale return, whereas a good example different scales which occur under a situation of unstable
of evolutionary trends would be the long-term processes of equilibrium. It should be understood that all of these changes
transgression and regression. are caused by the movement of sedimentary material and,
Considering all this, it is clear that when a study of therefore, from a general point of view, the evolution of
coastal geology is planned, the choice of temporal scale of coastal systems is controlled by the same factors that control
research is important. Indeed, the scale of the observations in the sedimentary dynamics (Fig. 3.1). We must understand
both space and time should be chosen carefully. A further that the coastal fringe is affected by two sets of geological
aspect to take into account is that selected variables should processes, which operate either separately or in conjunction
be chosen according to those whose measurements are [17]: exogenic processes that operate on the surface of the
sensitive to the changes that happen within the chosen Earth and endogenic processes that operate in and below its
scales. The difficulty of this is high, because many of these crust, but can deeply affect the surficial behavior.
variables are closely related to different scales. For geolo- Knowledge of the phenomena of erosion, transport and
gists, habituated to working on very long timescales, deposition of sediment in the littoral environments needs,
understanding changes that occur in such short timescales as therefore, to include the analysis of the movement of sedi-
coastal change is not an easy task. In general terms, geolo- mentary particles by wave action, tidal currents and other
gists are accustomed to interpreting the variables in facies marine currents. This study should place special emphasis on
sequences observed in the sedimentary record, but although the identification of hydrodynamic processes and sedimen-
the sedimentary record is a good information source to study tary products (facies), as well as the longer-term influence of
and interpret the synthesis of long-term processes that have the sediment supply regime and the relative movements of
occurred in coastal systems, it is common that many of the the sea level.

https://doi.org/10.1007/978-3-030-96121-3_3
26 3 Factors Affecting Coastal Evolution: Spatiotemporal Scales
previous paragraph. The sediment supply by rivers repre-

sents the most important connectivity between the continent
and the coast; in fact, the main part of the coastal sediments
enters the coast from rivers. The wind is a secondary source
from the continent, but in some areas can constitute the main
sediment supply. Additionally, the sediment can reach the
coast from deeper marine areas. Sediment from the conti-
nental shelves can approach the coast via wave action. This
sediment usually comes from ancient coastal sediments
inherited from lower sea level stands. Erosion from sub-
marine rocky outcrops can also be a frequent source of
sediment from marine areas. Some coasts are also able to
produce large amounts of sediments that then move along
Fig. 3.1 Factors affecting coastal evolution the coast due to littoral drift. Perhaps the best-known cases
are the erosion and transport from cliffs, but in tropical areas
the chemical and biochemical production of carbonates can
3.2.1 Hydrodynamic Agents be the main source of sediments.
The volume of sediment supply, in relation to the ability
Hydrodynamic agents are most directly responsible for the of coastal agents to rework material, is the determining
functioning of coastal environments. First, waves are factor in obtaining a sedimentary balance of the coast. Thus,
responsible for the erosion of rocky coasts, at the same time if the sediment budget is higher than the transport capacity
carrying out transport (longitudinal and transverse) between of marine agents, then the coast is depositional, while if the
the coastal area and the sea and, finally, being the major transportation capacity is greater than the external contri-
cause of sedimentation of sand on the front of beach and bution, then the coast will be erosive; a balanced coastline is
barrier island environments. On the other hand, the tide is when both factors are in equilibrium.
the main phenomenon that controls deposition in fluvio- It must be borne in mind that an important part of the
marine interaction systems (estuaries and deltas), as well as contribution is seasonal, since the river flows, the force of
in protected coastal systems such as bays and back-barrier the wind and the wave energy are seasonal, and all of them
areas (lagoons and tidal flats). Both of these have been control the capacity of supply sediment to the coast and the
individually considered as the main agent responsible for ability to rework it in coastal systems. Therefore, sedimen-
local coastal morphology [4, 5, 13]. tary balance on the coast can vary in different seasons, and
The wind is responsible for movement of sedimentary this is as important for understanding the functioning of a
material in the emerged coastal fringe, via the control it exerts coastal stretch in establishing an annual balance as are the
over the genesis and migration of coastal dunes. At the same interannual trends.
time, it is also the main agent causing waves and is funda-
mental in the genesis of the meteorological tides (surges).
Finally, river flows are a fundamental component in the con- 3.2.3 Events on the Coast
trol of sedimentation in estuarine and deltaic channels, being
responsible for the processes of mixing of waters and the Events are exceptional geological phenomena that display a
phenomena of dispersion of suspended matter, both within great amount of energy. Events that occur on the coast tend
channels and outside the mouth. The rivers are also the main to be considered geological events of a lower order or are not
agents of transport of material from the mainland to the coast. even regarded as events from a geological point of view.
The relationships of all of these agents in terms of energy That is due to the frequency at which they occur, since they
create the main conditions that confer a determinate coastal cannot be called exceptional, although they may be so on the
morphology and also the distribution of coastal environ- human timescale [9].
ments [6, 11, 12]. On the coast, high energy events can reach from land or
from sea. In coastal areas related to river mouths, floods
represent a rapid supply of large amounts of sediment, which
3.2.2 Sediment Supply must then be distributed throughout the coastal systems by
the processes that act on an ongoing basis.
The contribution of sediments to the coastal system is a key Perhaps the most common high energy events in open
factor in the balance of the coast. This supply can reach from coastal areas are storms. Storms represent a sudden shift in
land through the rivers and winds, as reflected in the the distribution of coastal sediment, generating wide erosive
3.2 Factors of Coastal Dynamics 27
zones in some places and rapid accumulation of sediments in Subsidence can cause the collapse of the coast, resulting
others. Some extreme storms such as those associated with in a deepening. Thereby, in the coastal sequence the deeper
tropical cyclones, typhoons and hurricanes can produce large facies are located on top of the shallower ones. If the sub-
changes in coastal morphology, generating important tem- sidence occurs in a slow way, the facies remain in the order
porary imbalances that lead to the dynamic processes established by Walther’s Law, but in reverse order. How-
achieving a new ordinary equilibrium. ever, if a sudden pulse of subsidence occurs, then interme-
However, the phenomenon that displays the greatest diate terms can be missing. Some coastal environments with
amount of energy on the coasts are tsunamis. In this sense, high accumulation rates such as deltas are particularly sus-
tsunamis, although with a tectonic origin, act on coastal ceptible to subsidence, especially where extractive human
systems in a way very similar to extreme storms. activities (exploitation of water or hydrocarbons) occur.
All of these events are usually reflected in the geological
record of the coastal environments in the form of a high
energy facies sequence. So, the depositional record of a 3.2.5 Changes in Position of the Coastline
tsunami is nearly indistinguishable from the record of a (Transgressions and Regressions)
storm. The record can also occur in the form of an erosional
unconformity, overlapping the sequence of the ordinary The relative sea level movements combined with the sedi-
coastal processes [10]. mentary balance manifest in the coastal fringe as advances or
setbacks of the coastline, which are known as transgressions
and regressions.
3.2.4 Global and Regional Sea Level Movements The term transgression is applied to an invasion from the
(Tectonics and Eustatism) sea on an emerged zone, assuming an advance of the coast
landwards. On the contrary, a regression is defined as a
The relative movements of the sea level result from the withdrawal of the sea, in such a way that a previously
combination of both tectonic and eustatic phenomena. submerged area becomes part of the land, which implies a
Eustatic movements are those related to absolute rises and shift of the coastline to the sea. For coastal environments, a
declines in the sea level. Most are due to variations in the minimum variation of coastline means an amendment of the
volume of water in the oceans, and therefore take place equilibrium and possibly a rough displacement.
globally. Eustatic variations can be associated with different So, the existence of transgressions and regressions
geological phenomena, such as glacial periods (climate depends on the balance between erosional and cumulative
change), post-orogenic volcanism or changes in the mor- processes, rates of erosion or accumulation and the speed of
phological configuration of the seabed. relative sea level motion.
As a result of tectonic activity, coasts can also rise or sink The combination of subsidence and sea level motion can
regionally and locally. The elevation takes place normally as create a space to accumulate significant amounts of sedi-
a result of orogenic compressive processes, while sinking is ments. That links with the concept of coastal accommo-
generated as a response to extensional movements, tilting or dation, which is understood as the space able to accumulate
compaction of the oldest sediments by sedimentary load, a coastal sedimentary sequence which records the history of
constituting the phenomenon known as subsidence. the environmental changes that generated this space. The
The term relative sea level change refers to variations in registered sequence can be transgressive or regressive
the depth of the sea at a point during a specific time interval, depending on the relationships between the accommodation
due to the combined action of eustatism and tectonics and the accumulation rates.
(global and regional factors). In this way, a relative fall in
sea level is an observable effect caused by a eustatic low-
ering, a tectonic uplift, or the combination of both phe- 3.2.6 Geological Influence
nomena. On the contrary, a relative sea level rise may be due
to eustatic rise, subsidence, or the combination of both. An The geology of the coast and adjacent areas plays a sec-
episode of relative stability of the sea level will be an ondary role in coastal evolution. On the one hand, the
absolute stability or also a total counteraction of both lithology of a coastline, as well as of the entire drainage
phenomena. basin of the rivers that drain into that coastal stretch, con-
A relative drop in the sea level will result in a loss of ditions the nature and volume of the sedimentary input.
depth, overlapping shallower environments on deeper ones. From an intuitive point of view, a coast composed mainly of
If the lift is slow and progressive, overlapping facies will soft (unconsolidated) lithologies can supply high amounts of
respect Walther’s Law, which states that the facies will be sedimentary materials, whereas if the coast (or source area)
found in the established order of the coastal sequences. is composed of hard lithologies, then the contributions will
be minor. In both cases, the grain size of the source rocks At the higher level of influence, some eustatic mecha-
may condition the nature of the sediment that reaches the nisms and relative sea level movements and coastline posi-
coast and is finally deposited. Something similar happens tioning are controlled by long-term climatic cycles.
with the coasts whose lithologies are easily alterable by
chemical processes; in this case, the materials will be dis-
solved and enter coastal waters in ionic form to be subse- 3.2.8 Human Influence
quently deposited by chemical precipitation processes. These
criteria would also apply to submerged areas that could The coastal environment has been greatly influenced by
potentially supply sediment to the coast. human action over the past decades. Anthropogenic action
On the other hand, the nature and orientation of geolog- affecting coastal factors has occurred on three levels. In a
ical structures in relation to the coastal relief have a direct way, humans have modified the action of coastal
remarkable influence on the geomorphologic processes that processes on the littoral such as altering the arrival of wave
may occur. From this perspective, alternations of soft and trains to the coastline by means of hard structures (jetties,
hard strata, the presence of fractures and other tectonic groins and breakwaters), decreasing the velocity of the
structures and their geometric relationships (between them currents in the mouth of tidal systems acting on the tidal
and with the coastline) condition the occurrence of gravita- prism by means of dredging or damming tidal surfaces
tional processes such as rock falls, toppling, wedge failures (saltpans and fisheries) and also decreasing the fluvial cur-
or slides, all of which are usually associated with cliffs and rents arriving at estuaries and deltas by means of water
rocky coasts. catchments in drainage basins. This last action has also had
the effect of reducing the input of sediments supplied from
rivers to the coastal systems, modifying directly the sedi-
3.2.7 Climatic Influence mentary balance of the coast.
In some of the world’s coasts, the human influence has
Climate is the main control of coastal evolution because it been present over centuries, even millennia. On the
acts on every variable influencing the coastal system. Cli- Mediterranean coasts, Egyptians controlled the fluvial sup-
mate is subject to cyclical changes that occur in different plies of the Nile River by modifying the delta dynamics. On
timescales. The shorter of these cycles are seasonal varia- the open coasts, Greeks and Carthaginians modified the
tions of the weather due to the tilt of the Earth’s rotational coastal morphology to build harbors.
axis and the relationships with the ecliptic plane during the Human activities on beaches and in tidal channels have
Earth’s orbit around the Sun. This fact, known as obliquity, also directly modified the sediment budget in the coastal
makes the Sun’s rays approach a determined latitude of the systems. Dredging activities, destruction of coastal dunes or
Earth from different angles at different times of the year. artificial beach replenishments are perhaps the best examples
Longer cycles are those related to the total amount of the of that.
heat energy emitted by the Sun’s surface, which vary in But in an indirect way, humans are also responsible for
periods of eight to 12 years. These cycles are responsible for this influence at a higher level, since it is human action that
the well-known phenomena of alternations between El Niño has been proved to be the cause of the current global
and La Niña. warming. Thus, the Earth’s climate is being modified by
Other even longer cycles are related to the radiation mankind with its entire influence on the coastal processes.
received by the Earth and are caused by the combination of Indeed, human action’s influence on the natural environment
the three main orbital cycles: precession, obliquity and has been so great since the second half of the twentieth
eccentricity [1]. These phenomena cause climatic cycles of century that some authors have considered that a new geo-
11,000, 41,000 and 100,000 years, respectively, and were logical period has begun: the Anthropocene.
responsible for the four glaciations and their minor climatic
oscillations that occurred during the Pleistocene.
So, it is clear that climate exerts a strong influence on 3.3 The Spatiotemporal Scale of Coastal
factors controlling coastal dynamics in every level of influ- Processes
ence. On the one hand, winds, waves, meteorological tides
and river discharges are directly controlled by the shorter As can be seen in the previous section, coastal environments
climatic variations. On the other hand, the sediment supply present a wide variability in the scale of their phenomena
is also strongly influenced by climate because weathering and their time of response, since all the analyzed factors (or
processes and potential sediment transport from the source variables) act on different timescales.
areas to the coastal sedimentary environments are controlled Authors in the 1980s (e.g., [2]) and others in the early
by climatic conditions. 1990s (e.g., [15, 16]) divided the action of these processes
3.3 The Spatiotemporal Scale of Coastal Processes 29
into two categories according to their timescale. Thus, on the level would be named historical. The results of the action of
short-term scale (minutes to years) are the actions of the these processes are depositional facies sequences.
hydrodynamic processes (waves, tides and coastal currents), The fourth level corresponds to the longer-term processes
all of them strongly influenced by the regime of sediment that operate from decades to millennia. These are controlled
supply from the mainland, from the platform and along the by global (climatic or tectonic) conditions and for that reason
coast. On a longer time-scale (centuries to millions of years), it is named geological. The record of the processes acting in
tectonics and eustatism condition the relative sea level this level is preserved as major sequences (parasequences
movements and, consequently, have a significant influence and depositional sequences).
on changes in position on the waterfront and in the secular Instantaneous and event scales are considered as
evolution of coastal environments. Controlling these factors short-term factors by the authors of the 1980s, whereas
and exerting a direct influence on coastal dynamics at all engineering and geological scales are defined by them as
timescales are the climate and anthropogenic action. long-term variables. Classical studies have been used as a
However, other authors of the early 1990s (e.g., [3, 18]) method for the separate analysis of the variables involved in
divided the main coastal processes into four spatiotemporal the evolution of media. This analysis facilitates the under-
scales of action (Fig. 3.2). standing of phenomena individually, especially of those
At the lowest level are the instantaneous processes, which act in the short term, however it does not offer an
linking fluid flow processes with forces that cause continu- understanding of the global dynamics of the coast that is
ous sediment transport, generating micro- and mesoforms. presently required.
At this level of action are also rapid fluctuations of energy It is necessary to take into account that, conceptually,
(short-term cyclical oscillations). This scale of processes both processes that occur in the short- and long-term scales
normally generates lithofacies and lithofacies sequences (instantaneous and geological) are regular and continuous
(depositional facies). processes, while those acting in intermediate-term scales
At the second level are the events that act in scales from (event and historical) are unique and unpredictable.
dozens of meters to kilometers and occur from seasons to The representation in a spatiotemporal diagram of
decades (may also be centuries). These phenomena can hydrodynamic and sedimentary coastal processes (Fig. 3a
generate special facies sequences when they are deposi- and b) shows a continuous transition between these pro-
tional, but are normally erosional and are preserved in the cesses rather than separate scales as suggested by Cowell
form of erosive unconformities. and Thom [3], Stive et al. [18]. In this scheme, some
The third level was named engineering because engi- instantaneous hydrodynamic processes like the action of
neers are especially interested in the phenomena of this wave trains, tidal cycles or wind regimes can be linked to
scale. These are scales from decades to centuries and include short-term sedimentological processes such as migration of
cyclical processes and evolutionary trends. For that, this bedforms and sand bars (in beaches, deltas and estuaries).
On the other side of the diagram, long-term processes like
isostasy, eustatic and tectonic cycles or global oceanic cur-
rents would be connected to large-scale sedimentary pro-
cesses such as barrier island formation, accretion of
tidal-delta lobes, deltaic progradation, reef growth or cliff
retreat. However, in the middle area of the diagram there is
not a correspondence of concepts with those suggested by
the original authors. In this sense, eventual hydrodynamic
processes like fluvial floods, storms and tsunamis appear to
be displaced with respect to the area suggested by Cowell
and Thom [3] on the event scale. On the other hand, there are
geomorphological processes such as inlet breaching that
correspond with events, but others located in the spa-
tiotemporal scales correspond with continuous sedimentary
processes (dune migration, seasonal beach cycles and
accretion of estuarine bodies). In any case, the processes of
the engineering (historical) scale are not well distinguished
from the processes of the geological scale.
A multifactor consideration regarding the end result of
Fig. 3.2 Definition of spatial and temporal scales involved in coastal coastal evolution is really a matter of historical accidents [7,
evolution (Adapted from Cowell and Thom [3]) 8], because it is those events that control the geological
References
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frequencies over the Earth’s history for paleoclimate studies. Sci
255:560–566
2. Bird ECF (1985) Coastline changes: a global review. John Wiley
and Sons, Chichester, 219pp
3. Cowell PJ, Thom FG (1994) Morphodynamics of coastal evolu-
tion. In: Carter RWG, Woodroffe CD (eds) Coastal evolution.
Cambridge University Press, Cambridge, pp 33–86
4. Davies JL (1964) A morphogenic approach to world shorelines.
Ann Geomorphol 8:27–42
5. Davies JL (1980) Geographical variation in coastal development
(2nd ed) Longman, New York, NY, 212pp
6. Davis RA, Hayes MO (1984) What is a wave-dominated coast?
Mar Geol 60:313–329
7. De Vriend HJ (1991a) Mathematical modelling and large-scale
coastal behavior: part 1: physical processes. J Hydraul Res Special
issue Maritime Hydraulics, 727–740
8. De Vriend HJ (1991b) Mathematical modelling and large-scale
coastal behavior: part 2: predictive models. J Hydraul Res Special
issue Maritime Hydraulics, 741–753
9. Einsele G, Seilacher A (eds) (1982) Cyclic and event stratification.
Springer Verlag, Heidelberg, 536pp
10. Einsele G, Ricken W, Seilacher A (1991) Cycles and events in
stratigraphy. Springer Verlag, Heidelberg, 955pp
11. Hayes MO (1975) Morphology of sand accumulations in estuaries:
an introduction to the symposium. In: Cronin LE (ed) Estuarine
Research, vol 2. Academic Press, New York, pp 3–22
12. Hayes MO (1979) Barrier Island morphology as a function of tidal
and wave regime. In: Leatherman SP (ed) Barrier Islands.
Academic Press, New York, pp l–27
13. Heward AP (1981) A review of wave-dominated clastic shoreline
deposits. Earth-Sci Rev 17:223–276
14. Morang A (2004) Coastal geology. US Army corps of Engineers,
University Press of the Pacific, 297pp
15. Pilkey OH, Morton RA, Kelley JT, Penland S (1989) Coastal land
loss. Short course in geology. In: 28th international geological
Fig. 3.3 Coastal processes, a Hydrodynamic processes, b Sedimentary congress, vol 2. American Geophysical Union, Washington, DC,
processes (Adapted from Morang [14]) 73pp
16. Pilkey OH, Young RS, Riggs SR, Smith AWS, Wu H, Pilkey WD
(1993) The concept of shoreface profile of equilibrium: a critical
record that is finally preserved. Nevertheless, the possible review. J Coastal Res 9(1):225–278
17. Rust IC (1991) Environmental geology of the coastal zone: a South
combinations of factors acting on these different scales give
African perspective. South African Journal of Marine Sciences
rise to the existence of a variety of long-term dynamic 10:397–405
models that subsequently generate several schemes of rela- 18. Stive MJF, Roelvink DJA, de Vriend HJ (1991) Large-scale
tionships among coastal environments and result in a finite coastal evolution concept. In: Proceedings of the 22nd interna-
number of architectural facies models that build the upper tional conference on coastal engineering, American Society of
Civil Engineers, New York, pp 1975–1983
part of the marine system record. In this sense, the study of
the coastal sequences preserved in the geological record is a
significant help in understanding the global action of pro-
cesses at all spatiotemporal scales.
Coastal Elements: Types of Coasts
and Criteria in Coastal Classifications 4
4.1 Introduction 4.2 Coastal Landforms
Every coast presents a variety of landforms and environ- Coastal forms that have developed along the coast (Fig. 4.1)
ments which have been classically described and classified will be addressed in this section. These are the result of a
by geographers and whose dynamics have been studied by combination of processes that act on sediments and rocks
geologists and coastal engineers. In this way, some of the forming the coastal zone. Some landforms are the result of
elements that make up our coasts can be characterized. Some an erosive combination of these processes and, therefore, do
of these elements can be defined as features or forms at not have associated sediments. Other major landforms are
scales of tens or hundreds of meters, while others are among depositional and develop facies and facies sequences, but
the most common environments that can be found along a can, however, group several environments. In this case,
coast. It is necessary to take into account that many of the sedimentation is carried out under the typical dynamics of
described elements are simply geomorphological features or the respective set of environments and their facies sequences
landforms (mesoforms or megaforms), while others, in are not defining, and so they are regarded as landforms. This
contrast, in addition to being defined as forms possess their is the case for bays and other sandy landforms such as
own depositional realm and are capable of generating a barriers, spits, barrier islands and tombolos.
characteristic sedimentary sequence. In the first case, they
are considered as coastal landforms, while in the second
they are coastal environments. 4.2.1 Erosional Coastal Landforms
The landforms and environments that can be found on a
particular coast, therefore, or the ensemble of environments Cliffs
and landforms that integrate on a coastal stretch, are con-
trolled by the factors analyzed in Chap. 3. These factors act in These are the most significant and recognizable erosional
different scales. So, the climatic, eustatic and tectonic factors coastal landforms. Cliffs are formations of a certain height
exert a global large-scale first-order control, whereas the and high slope which are in contact with the sea and are
hydrodynamic and sediment supply factors exert a more local subject to its dynamic processes. They are reliefs of ero-
small-scale secondary control. The combination of these sional nature and their material constitutes one of the sources
factors allows us to determine what type of coast it is. Nev- of supply to the adjacent depositional coastal segments.
ertheless, throughout history there have been proposed mul- The speed of erosion by marine agents and, therefore, the
tiple classifications of coasts using different criteria, with volume of material that they supply depends on its geolog-
most of the classifications attempting to group the causes that ical nature and the arrangement of the rock formations with
influence the genesis of these landforms and environments. respect to waves and currents. Actually, cliffs constitute a
In this chapter, landforms and coastal sedimentary envi- system (Fig. 4.2) which integrates other erosional forms of
ronments will be defined and the various proposals for smaller dimensions (including abrasion platforms, caves,
classification of the coasts will be analyzed from the per- arches, the headlands) and some depositional environments
spective of the different criteria (local and global) used by (such as beaches and colluvial fans) formed at the foot of the
the respective authors. cliff.

https://doi.org/10.1007/978-3-030-96121-3_4
32 4 Coastal Elements: Types of Coasts and Criteria in Coastal Classifications
Fig. 4.1 Main coastal landforms.

a Erosional landforms.
b Depositional landforms.
c Enclosed bays and different
types of coastal barriers
Abrasion (or wave-cut) platforms highest levels. This action determines the formation of
cavities that can plunge tens of meters below the cliff front.
These are thus named because the dominant process that Sometimes the roof of these cavities can collapse and
generates them is abrasion, but they are also called wave-cut generate holes connecting the interior of the dome with the
platforms since it is the waves performing this abrasion. The surface of the ground. These holes can relieve the pressure of
platform is a flat surface located at the base of the cliffs below the compressed air in the cavities by wave action and
the mean tidal level. It is a surface of a transversal length to function as blowholes, especially in storm wave conditions.
the coastline that can measure from a few meters to hundreds
of meters from where the waves break up to the base of the Arches
adjacent cliff. The duration of the process that generates these
platforms depends on the rheological nature of the rock. This is a very striking erosional landform which is also a
Thus, the existence of extensive abrasion platforms implies result of the differential erosion on lithologies of different
that the sea level has remained stable during their period of resistance. These arches have an opening that extends below
genesis. A rocky coast can present different levels of plat- the water level and is covered by a solid vault that can have
forms, some of which can be located in the continental area, an arched or flat shape and whose height can be up to tens of
while others may be submerged. The presence of these meters above the sea level (Fig. 4.2a, b).
platforms indicates previous stable positions of the sea level.
Stacks and stumps
Caves
As a result of the aforementioned cliff retreat, abrasion
These are formed in the base of the cliffs (Fig. 4.2a, b) as a platforms can develop imperfectly, leaving not completely
result of the existence of different rates of wave erosion on eroded remains protruding from the horizontal surface of the
lithologies of variable resistance, taking also into account platform (Fig. 4.2a, c). These remains are called stacks and
that the waves swash on the cliff base and do not reach its stumps, and present a distinctive type of coastal landform.
4.2 Coastal Landforms 33
Fig. 4.2 a Main coastal forms

linked in a cliff system. b Arches
and caves in the cliff system on
the Algarve Coast (Portugal).
c Abrasion platform, stumps and
stacks on the Asturias Coast
(Spain)
Some of them may have several meters of altitude and 4.2.2 Depositional Coastal Landforms
appear as isolated pinnacles. These are forms that continue
to be subject to erosion and, therefore, they are not perma- Tombolos
nent in time.
These are sandy landforms which connect the mainland with
Capes an ancient emerged rocky island (Figs. 4.1b and 4.3a). The
sand accumulation is generated by the phenomenon of
Capes are prominent on the coastline where a strip of land deformation of the wave trains (refraction and diffraction)
extends towards the sea (Fig. 4.1). A cape is simply a coastal induced by the presence of the rocky element, initially away
morphology, which can have a consolidated and erosional from the coast, which creates a shadow area of deposition.
nature (headlands, Fig. 4.1a) as well as an unconsolidated As a result of this phenomenon a process of sedimentation of
and depositional one (cuspate forelands, Fig. 4.1b) or it may sand begins, just linking the tied island with land.
have mixed features (tombolos). From the point of view of Occasionally, the connecting element is submerged,
coastal dynamics, a cape is a hindrance to the longshore while at other times the union between the tied island and the
transportation of sediments, tending to limit littoral drift mainland is not complete (Figs. 4.1b and 4.3b). In most
cells. cases the tombolo is not symmetrical, though its axis leans
Fig. 4.3 Some depositional

landforms. a Tombolo (example:
Cape Trafalgar, Spain).
b Incomplete tombolo (example:
Pedra do Pontal, Brazil). c Spit
(example: Zinga Coast,
Tanzania). (Images
Landsat/Copernicus from Google
Earth)
towards the coastline. This occurs because the tail shaft Embayments
tends to be parallel to the orientation of the crest of the wave
trains that generate it. Sometimes, instead of generating a This is defined as a coastal track where the sea curves into
sandy landform, two sand barriers develop with a coastal the shoreline towards the continent. They may have different
lagoon between them. In this case we would talk of a double sizes and shapes depending on the physical and geological
tombolo. characteristics of the coast that contains them. In many
4.2 Coastal Landforms 35
instances, the bay is open and their edges are rocky head- Cuspate forelands
lands (Fig. 4.1a), but in others the bays are partially closed
by depositional sandy landforms (Fig. 4.1c). The bays Cuspate forelands, also known as nesses in Britain, are
within can be depositional or erosional and the shoreline can pointed coastal landforms which are also generated by the
be formed by wave-cut platforms or beaches, depending on accretion of sedimentary bars (Figs. 4.1c and 4.4c), trans-
their sedimentary balance. ported by littoral drift in a well-supplied coast. The cumu-
lative process results in progradation and extends the coast
Barriers into the sea in a triangular-shaped form of a sedimentary
nature. Their genesis occurs by a process very similar to the
Coastal barrier is a generic term to define those sedimentary strandplains, but more localized.
landforms formed by sand or gravel that occur away from
the continent and isolate from waves, totally or partially, a
body of water that is subject to the exclusive action of the 4.3 Coastal Environments
tide. This term is used regardless of the shape and the
extension of the barrier (Fig. 4.1c) and it can be grounded at The concept of a sedimentary environment was defined by
both ends (bay barrier) or only at one of them (spit) or be Selley [13]. According to this author, “a sedimentary envi-
unconnected (barrier island). ronment is a part of the Earth’s surface that is physical,
chemical and biologically different from the adjacent areas.”
Bay barriers The surrounding conditions of a sedimentary environment
determine the processes occurring in it and, consequently,
Coastal barriers that are connected with land at both ends, the nature of the sediments that are accumulated. Therefore,
fully closing what was a bay, and subsequently developed in each sedimentary environment will be characterized by
their back area a lagoon, pond, tidal flat, swamp, marsh or sequences of recognizable sediment that are indicative of the
other wetland plain. variability of processes that may have occurred in it. From
this point of view, “a coastal sedimentary environment is a
Spits sector of the coastal zone that differs from the adjacent
others due to its environmental characteristics and present
A spit is an elongated stretch of sandy material in a barrier distinctive facies sequences caused by coastal processes.”
shape that is attached to the mainland only at one end Some environments are grouped within other larger ones,
(Figs. 4.1c and 4.3c). A spit is normally originated by the and therefore these might be termed subenvironments, while
action of the waves in an oblique way to the coastline, others are presented grouped in systems. Some of these
creating longshore transport by littoral drift in the direction systems have particular physiographies which have been
of growth of the landform. previously described as coastal landforms. The most char-
acteristic coastal environments are defined below (Fig. 4.5).
Barrier islands
Beaches
These are coastal barriers that are completely separate from
the mainland (Figs. 4.1c and 4.4a). Barrier islands represent a Beaches are widely distributed depositional coastal envi-
barrier with a wide beach, which commonly provides suffi- ronments. They are primarily subject to wave dynamics
cient protection from the high tide to develop dune systems. although the influence of the tides can also be important.
The back region often supports vegetated and wetland areas. This active dynamic implies an environment where fine
particles are absent, mainly consisting of sands but also of
Strandplains pebbles. Beaches may be present in different geographic
locations, and can be attached to the mainland, in front of a
These are coastal flats generated by accretion to transverse barrier, barrier island or spit, and also form part of pro-
bars of sand or pebbles, transported by the littoral drift along grading landforms such as strandplains or cuspate forelands.
a significant length of the coast (Figs. 4.1c and 4.4b). They
consist only of beaches and dunes although may also have Coastal dunes
marsh areas. From the point of view of processes and facies,
they are similar to the fronts of barrier islands but they are A dune is a hill of sand built up by the wind because of the
not far from the continent and lack the back-barrier elements presence of an obstacle. Coastal dune systems are located in
(the lagoon and, therefore, tidal inlets). They correspond to the supratidal beach area and are aeolian environments
the accretion of many mixed wind–wave systems. where sedimentary materials are deposited on their way from
Fig. 4.4 Some depositional

landforms. a Barrier island
system (example: barrier islands
closing Charlotte Bay, Florida,
USA). b Strandplain (example:
near King Sound, Northwest
coast of Australia). c Cuspate
foreland (example: Darss Cape,
Germany). (Images
Earth)
sea to land. Dunes have a complex internal structure con- developed during storms, when high energy waves erode the
stituted by cross-stratification sets that reflect the stages in frontal sandy bodies (beaches and dunes), depositing this
their evolution. sand on the back area of coastal formations such as barriers.
Washover fans Lagoons
The washovers are sandy fan-shaped formations with con- A lagoon is a body of shallow water with a restricted con-
vexity pointed towards the interior of the continent. They are nection to the sea. The term is generally applied to a subtidal
4.3 Coastal Environments 37
Fig. 4.5 Main clastic coastal

environments. a Environments
involved in a barrier island
system (example: Algarve barrier
islands, Portugal). b Fluvial
estuary (example: Pungwe River
estuary, Mozambique). c Fluvial
delta (example: Coco River Delta,
border between Nicaragua and
Honduras). (Images
Earth)
zone semiconfined by a barrier. Associated with the lagoon from drainage of the land, with its innermost limit consid-
are other environments such as intertidal marshes and tidal ered to be the last point of the tidal influence [6, 12]. This is
flats. one of the two most characteristic types of river mouths, in
which the environment is developed in a coastal concavity
Tidal inlets that is commonly funnel-shaped (Fig. 4.5b). It is an envi-
ronment that usually occurs after a sea level invasion by
These are connecting channels through which the mecha- marine transgression and tends to total infilling due to the
nism of tidal exchange between the open marine environ- active sedimentation that occurs in its interior.
ment and the environments protected by a barrier, barrier
island or spit takes place. They are environments that are Fluvial deltas
subject to tidal currents of relatively high velocities that
reverse in each tidal cycle. The deltas are large, cape-shaped coastal sedimentary bodies
linked to river mouths. The environment consists of a large
Tidal deltas accumulation of terrigenous clastic sediments which expe-
rience a progradation due to scattering phenomena taking
Tidal deltas are one of the elements that constitute a barrier place when flowing fresh water meets the marine water
island system and are located in connection with the tidal mass. Deltas are environments that are characteristic of
inlets in both directions of the tidal current. Thus, ebb-tidal coasts of emersion, but they can also develop as an evolution
deltas are located on the front of the inlet, in contact with the of an estuary, after infilling of the same during a long period
nearshore area, while the flood-tidal deltas are located on the of sea level highstand.
back of it and contact the coastal lagoon.
Tidal flats
Estuaries
Tidal flats are wide depositional areas formed mostly by fine
An estuary is a semi-enclosed coastal water body that has a sediments that are located in the space bounded by tidal
free connection to the open sea and is also connected to a fluctuations. These are present along open coasts with a low
river stream, where salt water is diluted with fresh water relief and are affected by low energy waves, as well as in
coasts under higher wave energy, but are generally located in This section summarizes the classifications that have been
areas protected from wave action, behind barriers or reefs more accepted over time, emphasizing the main descriptive
and linked to back area environments such as lagoons, criteria used for the categorization.
estuaries and deltas.
Swamps and marshes 4.4.1 Genesis Under Relative Sea Level

Movements
Marshes and swamps are vegetated wetland environments
that are characterized by plants saturated in fresh, salt or Early classification schemes were based on genetic aspects
brackish waters. In a marsh, herbaceous plants without any related to the relative movements of the sea level, including
woody stems are the dominant vegetation. Grasses and reeds those caused by static variations as well as by tectonic
are thus the most common plants on marshes, while swamps movements (and also the combinations between both of them).
are dominated by trees and woody plants. It was Johnson [9] who synthesized the ideas of previous
Both types of wetlands are often found along river mar- authors [2, 15, 4, 7] in proposing a classification using this
gins and lake shores (in these cases the water is fresh), but context as the main criterion. Thus, he differentiated between:
both environments can also appear on the coasts, associated
with transitional environments such as deltas, estuaries, – Coasts of submersion,
lagoons or tidal flats. In these cases, the waters can vary – Coasts of emersion,
between salt, brackish and fresh, depending on the degree of – Neutral coasts and
mix between tidal and fluvial hydric volumes. – Compound coasts.
In many cases, the difference between the appearance of a
marsh or a swamp in the supratidal fringe of sedimentary Within this, the shores of submersion were differentiated
environments is marked by the climatic characteristics. between those coasts that appeared after a marine inundation of
an ancient river and those from a glacier valley, and these were
Reefs named respectively ria coasts and fjord coasts. At the same time,
Johnson defined the coasts of emersion as coastal plains.
Reefs are organic constructions built up by the stacking of In addition, this system marked a third type of coast
skeletons of living organisms. These are rigid known as neutral coasts, which corresponded to these coasts
bio-constructed masses, forming a positive relief able to that had no apparent relative movements of the sea level.
resist wave action and exert a sediment control over adjacent Within these shores could be distinguished deltaic coasts,
areas. They can be found in various places, but are often alluvial coasts, flooded coastal plains, volcanic shores and
located on low latitude coasts with low terrigenous contri- coasts of faults.
bution. In their development, they influence coastal physical A fourth type of coast includes compound coasts, which
processes such as chemical and biological factors with an have experienced a transition between two or more types of
important climatic control. those described above.
4.4 Classifications of the Coast 4.4.2 Origin of Processes
The preceding sections have described many landforms and Almost half a century later, [14] delved into the roots of the
coastal sedimentary environments present on coasts all over previous classification, identifying coasts that did not cor-
the world. They also mentioned the importance of different respond to any of the categories proposed by Johnson. To
factors controlling the morphology and the distribution of classify the coasts, this author also used genetic criteria, but
these forms, some with global and others with more local attended to processes different from the sea level movements
action, and all of them with controls over different time- in differentiating between primary and secondary coasts
scales. Since the beginning of research on coastal areas, (Table 4.1). Primary coasts were considered the result of the
there has been a need to classify the coasts with criteria that performance of non-marine processes, while secondary
could explain the presence of the set of landforms and coasts were considered to occur through the direct action of
environments linked in any coastal stretch [10, 11]. Over marine processes or marine organisms. Within each of these
time, different classifications using different criteria have types Shepard made an exhaustive partition according to all
been developed to respond to this need. the possible origins of the coastal morphology.
4.4 Classifications of the Coast 39
Table 4.1 Classification proposed by Shepard [14]

Shepard’s [14] Coastal Classification
1. Primary coasts: configuration due to non-marine processes
1.1. Land erosion coasts. Shaped by subaerial erosion and partly drowned by postglacial rise of sea level (with or without crustal sinking) or
inundated by melting of an ice mass from a coastal valley
1.1.1. Ria coasts (drowned river valleys)
(A) Dendritic pattern; (B) Trellis pattern
1.1.2. Drowned glacial erosion coasts
(A) Fjords; (B) Glacial troughs
1.1.3. Drowned karst topography
1.2. Subaerial deposition coasts. Largely due to deposition, prograding the shoreline since the postglacial sea level highstand
1.2.1. River deposition coasts
(A) Digitate; (B) Lobate; (C) Cuspate; (D) Partially drowned deltas
1.2.2. Glacial deposition coasts
(A) Partially submerged moraines; (B) Partially submerged drumlins; (C) Partially submerged drift features
1.2.3. Wind deposition coasts
(A) Dune prograded coasts; (B) Dune coasts; (C) Fossil dune coasts
1.2.4. Landslide coasts
1.3. Volcanic coasts
1.3.1. Lava-flow coasts
1.3.2. Tephra coasts
1.3.3. Volcanic collapse or explosion coasts
1.4. Shaped by diastrophic movements
1.4.1. Fault coasts
(A) Fault coasts; (B) Fault trough or rift coasts; (C) Overthrust coast
1.4.2. Fold coasts
1.4.3. Sedimentary extrusions
(A) Salt domes; (B) Mud lumps
1.5. Ice coasts. Glaciers form extensive coasts, especially in Antarctica
2. Secondary coasts: shaped primarily by marine agents or by marine organisms. May or may not have been primary coasts before being
shaped by the sea
2.1. Wave erosion coasts
2.1.1. Wave-straightened cliffs
(A) Cut in homogeneous materials; (B) Hogback strike coasts; (C) Fault-line coasts; (D) Elevated wave-cut benches; (D) Depressed
wave-cut benches
2.1.2. Made irregular by wave erosion
2.2. Marine deposition coasts. Coasts prograded by waves, tides and currents
2.2.1. Barrier coasts
(A) Barrier beaches; (B) Barrier islands; (C) Barrier spits; (D) Bay barriers; (E) Overwash fans
2.2.2. Beach plains. Sand plains, differing from barriers by absence of a lagoon
2.2.3. Mud flats or salt marshes
2.3. Coasts built by organisms. Are subclassified according to the dominant building organism
2.3.1. Coral reef coasts
(A) Fringing reefs; (B) Barrier reefs; (C) Atolls; (D) Elevated reef coasts
2.3.2. Serpulid reef coasts
2.3.3. Oyster reef coasts
2.3.4. Mangrove coasts
2.3.5. Marsh grass coasts
Table 4.2 Classification Inman and Nordstrom [8] Coastal Classification

proposed by Inman and
Nordstrom [8] 1. Collision coasts (convergent margins)
1.1. Continental collision coast: the margin of a thick continental plate colliding with a thin oceanic
plate (e.g., west coasts of North and South America)
1.2. Island arc collision coasts: along island arcs where thin oceanic plates collide (e.g., the Aleutian
island arc)
2. Trailing-edge coasts (divergent margins)
2.1. Neo trailing-edge coasts: new trailing-edge coasts formed near beginning spreading centers and
rifts (e.g., the Red Sea and Gulf of California)
2.2. Amero trailing-edge coasts: the trailing edge of a continent having a collision coast on its opposite
side (e.g., east coasts of the Americas)
2.3. Afro trailing-edge coasts: the coast on the opposite side of the continent is also trailing (e.g., the
east and west coasts of Africa)
3. Marginal sea coasts: coasts fronting on marginal seas and protected from the open ocean by island arcs
(e.g., Korea)
Fig. 4.6 Global distribution of

coasts according to tectonic
framework (adapted from and
Nordstrom [8])
4.4.3 Tectonic Location characteristics of those coasts all over the world, which were
well studied in the last quarter of the twentieth century.
A proposal for the classification of coasts developed by Inman and Nordstrom [8] suggested a classification of
Inman and Nordstrom [8] provided a novel conception to coasts into three categories according to their position on the
follow on from the previous classifications. It was a global boundaries of the plates to which they are associated
classification based on the concepts of plate tectonics dis- (Table 4.2, Fig. 4.6).
covered in the 1960s. These authors highlighted that the The types of coasts included in this classification fit
general aspects of the physiography of a coast are in relation broadly with the physiography of the coast. In this way, the
to their position at continental margins regarding the coasts of collision are presented as relatively narrow rocky
boundaries of plates and their relative vertical movements. and steep fringes that usually develop cliffs accompanied by
From this perspective, the strong contrast between the east different elevated flat levels of terraces, joining the front
and west coasts of the United States could be explained, and continental shelves of low amplitude and high slope, crossed
so could the morphological differences between the northern by important submarine canyons.
and southern tracks within the US West Coast. Using the The coasts of expansive plate margins (trailing edge
same criteria, they also explained the physiographic coasts) show a greater variability. The American affinity type

coasts according to wave height
(adapted from Davies [3])
(Amero) develop depositional coastal plains associated with hydrodynamic processes in the development of coastal
extensive drainage networks which bring large amounts of environments emerged. Most of these classifications cate-
sediment to sedimentary environments such as broad gorized coasts using the dimensions of a single hydrody-
strands, barrier islands, tidal flats and deltas, associated with namic process.
wide continental shelves. Thus, Davies [3] identified several types of coasts using
Characteristics of the coasts of expansive margins of only the wave height (Fig. 4.7), taking into account that the
African affinity (Afro) are similar to the American affinity waves are generated by the wind and this is distributed lat-
ones, although the drainage networks tend to be less itudinally reflecting global climatic zones. This method
extensive and, consequently, sedimentary input is minor, differentiated protected areas, coasts dominated by
resulting in narrower coastal plains, deltas and barrier island storms, that would be well localized in areas of higher
systems in most common environments. temperatures in the Arctic (and Antarctic) latitudes and
The coasts of expansive plate margins of recent formation coasts dominated by swell waves, located in middle lati-
(neo trailing-edge) are immature coasts undergoing impor- tudes. In the tropics alternate cycles of fairweather
tant tectonic and gravitational processes. They are developed trade-generated waves dominated, with short periods in
on the edge of shelves that belong to different plates for a which the tropical cyclone waves would be important.
short while. The coast is typically narrow and steep, with The same author subsequently developed another coastal
features similar to the coasts of collision. The cliffs are the classification using only the tidal range as the main criterion
more frequent systems, although they can develop marginal of classification (Fig. 4.8). In this regard, it should be taken
depositional environments. into account that the tidal range increases from the center of
The coasts of marginal seas present a great diversity of the oceans to the coasts, amplifying according to the slope
processes, forms and sedimentary environments, always in a and width of the continental shelves and the coastal phys-
tectonic margin of low activity. The continent may appear iography. Global distribution of tidal ranges on the coasts is,
flat or hilly, although these coasts tend to be associated with consequently, controlled on a large scale by the geometry of
large continental shelves that allow the development of the coastline and distribution of bathymetry. Davies distin-
well-supplied depositional environments such as estuaries guished between macrotidal coasts in those places where
and deltas. the tide range exceeds 4 m, mesotidal coasts which would
have ranges between 2 and 4 m and microtidal coasts in
those places where the range is less than 2 m. The first are
4.4.4 Individual Hydrodynamic Processes mainly located in large funnel-shaped bays, where the tidal
wave experiences a high magnification due to the effect of
In the last decades of the twentieth century some coastal convergence, while the last are generally located in shallow
classifications that emphasized the importance of seas and sheltered bays.

coasts according to tidal range
(adapted from Davies [3])
of the waves. In this way, they proposed a classification

that took into account the relative effect of waves and tides,
more than the absolute values of both parameters sepa-
rately. Their classification distinguishes between:
tide-dominated coasts, wave-dominated coasts and mixed
energy coasts (Fig. 4.9) and suggests that the distribution
of landforms and sedimentary environments on the coasts
would occur according to the relative importance of these
parameters (Fig. 4.10).
4.4.6 Sediment Input and Evolving Time
The morphology of the depositional coasts, especially of

coasts supplied by clastic sediments, responds to the volume
of material contributed from a river source and the ability of
the coast to rework this sediment by waves and tidal cur-
rents. Taking into account this fact, Dalrymple et al. [1]
Fig. 4.9 Classification of coasts according to the relative dimensions proposed a classification that included the relative impor-
of tide and waves (Davis and Hayes [5]) tance of these three agents in their ability to mobilize a
volume of sediments, developing a ternary diagram similar
4.4.5 Relative Energy of Hydrodynamic to the one proposed for the river deltas by Wright [16]. In
Processes this triangular diagram, coastal depositional environments
would be located in accordance with the process that dom-
Davis and Hayes [5] observed that the features (landforms inates their sedimentation. Thus, the deltas would be located
and environments) of many coasts did not correspond to the at the apex dominated by the river, while the coasts pro-
expected physiography in relation to their characteristics of grading due to the performance of marine processes
tidal range. So, for example, long barrier island systems (strandplains and tidal flats) would be located on the oppo-
expected on microtidal coasts also appeared in coasts with site side, to match where sediments were being reworked by
greater tidal ranges but also with higher waves. Conversely, waves and tides, while the estuaries (wave- and
open tidal flats expected on macrotidal coasts also appeared tide-dominated) would occupy an intermediate place
on coasts of smaller tidal range, but with scarce incidence between the three processes.
Fig. 4.10 Frequency of

appearance of coastal
environments in the three types of
coasts distinguished by their
relative dimensions of tide and
waves (Davis and Hayes [5])
Fig. 4.11 Conceptual

distribution of environments
according to the dominant process
and evolution over time
(Dalrymple et al. [1])
The novelty of the classification proposed by these environments displacing the shoreline landwards. Prograda-
authors lies in the inclusion of the time evolution as a fourth tion in river systems means the infilling of estuaries and their
dimension (Fig. 4.11). In this case, time is expressed in transformation into deltas, while in wave-dominated envi-
terms of trends: coastal regression or marine transgression. ronments it implies the development of extensive strand-
Coastal regression occurs usually due to processes of plains and in tide-dominated realms an aggradation of open
sedimentary progradation under a standing sea level and/or a tidal flats occurs. On the other hand, a marine transgression is
large volume of sediment contribution, while marine trans- a movement in the opposite direction, transforming the deltas
gression takes place when the sea level floods coastal into estuaries by inundating the river valleys.
The classification proposed by Dalrymple et al. [1] is a 3. Davies JL (1980) Geographical variation in coastal development
fairly comprehensive classification, because it not only takes (2nd ed). Longman, New York, 212pp
4. Davies WM (1896) The outline of Cape Cod. In: Proceedings of
into account the hydrodynamic processes that are responsi- the American academy of arts and sciences, vol 31, pp 303–332
ble for the morphology of the coast in the short term, but it 5. Davis RA, Hayes MO (1984) What is a wave-dominated coast?
also includes the sediment supply and time and, thus, the Mar Geol 60:313–329
relative movements of the sea level, to give a broader 6. Dyer KR (1997) Estuaries. In: A physical introduction (2nd ed).
Wiley, New York, 195pp
reflection of the processes occurring over a longer time 7. Gulliver FP (1899) Shoreline topography. Proc Am Acad Arts Sci
frame. 34:151–258
In addition, it is interesting to note that there are several 8. Inman DL, Nordstrom CE (1971) On the tectonic and morpho-
sedimentary environments that have their own classifica- logical classification of coasts. J Geol 79:1–21
9. Johnson DW (1919) Shore processes and shoreline development.
tions. So, there are classifications of beaches, barrier islands, Wiley, New York, 584pp
tidal flats, estuaries, deltas or reefs, among others. These 10. Komar PD (1998) Beach processes and sedimentation.
classifications also take into account different factors (mor- Prentice-Hall, Englewood Cliffs, New Jersey, 429pp
phology and dynamics) that affect these environments. 11. Masselink G, Hughes MG, Knight J (2003) Introduction to coastal
processes and geomorphology. Routledge, London, 416pp
12. Pritchard DW (1967) What is an estuary? Physical viewpoint. In:
Lauff GH (ed) Estuaries, vol 83. American Association for the
References Advancement of Science Publications, pp 3–5
13. Selley RC (1970) Ancient sedimentary environments. Chapman &
Hall, 299pp
1. Dalrymple RW, Zaitlin BA, Boyd R (1992) Estuarine facies 14. Shepard FP (1948) Submarine geology. Harper, New York, p 348
models: conceptual basis and stratigraphic implications. J Sediment 15. Suess E (1888) The faces of the Earth, vol II (English translation in
Petrol 62:1130–1146 1906 by HB Sollas). Oxford University Press, London, 556pp
2. Dana JD (1849) Report of the United States exploring expedition 16. Wright LD (1977) Sediment transport and deposition at river
1838–1842 (vol 10, Geology). Putnam American Agency, New mouths: a synthesis. Geol Soc Am Bull 88:857–868
York, 735pp
Geological Approaches to the Coasts
5
ranges and continues with the dismantling of the same, and

5.1 Introduction
among these are especially addressed erosion, transportation
and deposition.
As described in the preceding chapters, coastal areas have
In the coastal area, geomorphology focused on both the
been studied by a broad group of geological disciplines, each
development of mesoforms (erosive and cumulative forms of
of which offers a different focus or approach to these areas
meter scale; Fig. 5.1) and on the genetic mechanisms of the
and the environments developed therein. From this point of
coastal landforms of kilometer scales (Fig. 5.2). In this case,
view, perhaps it is geomorphology that is the science from
studies of both erosive forms (such as cliffs) and cumulative
which there have been classically greater contributions to
forms (such as barrier islands, beaches and dunes) were also
coastal geology, although in recent decades numerous
addressed.
studies have focused on hydrodynamic processes, bringing a
In addressing the genetic phenomena of littoral land-
perspective that is closer to physical oceanography. Simi-
forms, coastal geomorphology had to deal with the charac-
larly, and also recently, many studies have focused on the
terization of the processes responsible for coastal dynamics,
distribution of sediments, facies and sequences of facies in
such as waves, tides and currents, whose combinations are
coastal sedimentary environments using the study of sedi-
what really shape the coast. It is clear that to approach this
mentology. From a wider perspective, other studies have
type of study, coastal geomorphology had to rely on other
addressed the potential for preservation of these sequences in
branches of science such as marine geology and physical
a broader time frame, especially taking into account the
oceanography.
tectonic and eustatic framework, which means a contribution
Chapter 1 describes how the first steps of coastal geology
to the doctrinal body of stratigraphy. Finally, much knowl-
were achieved through the approach of geomorphologies by
edge about the coast supplied by its geology has contributed
almost legendary authors such as Douglas Johnson, Alfred
to an environmental approach, which entails the develop-
Steers, Axel Schou and André Guilcher. The conceptual
ment of the environmental geology of the coasts.
definitions set out in Chap. 2 of this book correspond to the
This chapter details each one of the approaches on coastal
field of coastal geomorphology, as do the descriptions of
research from these disciplines.
coastal landforms and coastal classifications described in
Chap. 4.
5.2 Geomorphological Approach
Geomorphology is a geological (and geographical) disci- 5.3 Sedimentological Approach

pline that aims to study the landforms of the Earth’s surface.
Although this science was initially devoted to the quantita- Sedimentology is the science that studies both the sediments
tive description and classification of landforms from a more and their genesis [8]. In this way, sedimentology takes in the
geographical approach (descriptive geomorphology and study of sediment formation and the processes of transfor-
geomorphometry), it soon led to the study of the processes mation into sedimentary rock, including the physical and
that generate these forms and their dynamic functioning with chemical characteristics of sediments and sedimentary rocks,
a predictive character (dynamic geomorphology), linking which are a result of the processes that originated them [1].
more directly with the geology [2]. These processes are The objective of this geological discipline is to establish
understood as part of a genetic cycle that begins with the present facies sequences and models that allow us to rec-
internal interactions that lead to the uprising of mountain ognize and interpret the sedimentary facies of the past by

https://doi.org/10.1007/978-3-030-96121-3_5
46 5 Geological Approaches to the Coasts
Fig. 5.1 Example of metric-scale

landforms: coastal marmids
(Sancti Petri, Spain)
Fig. 5.2 Example of

kilometer-scale landforms:
Ayeyarwady River Delta
(Myanmar). (Image
Earth.)
applying Charles Lyell’s Principle of Uniformitarianism. relationships between the facies of each of the coastal
Within the objectives of sedimentology, the coast is of environments and the processes that generate them. Today’s
particular interest, as it constitutes an unequivocal marker of coasts have proved to provide an excellent opportunity to
the position of the sea level and the reference to this level is establish such relationships, as they can be observed,
the basis for the establishment of transgressive and regres- quantified and analyzed in detail, both in terms of facies and
sive sequences [7]. processes. Initially, thanks to their easy accessibility, the
Since the application of Lyell’s principles, sedimentolo- surficial sediments of many coastal environments (beaches,
gists have been especially concerned with establishing dunes, lagoons, tidal deltas, tidal plains, estuaries, deltas…)
5.3 Sedimentological Approach 47
Fig. 5.3 Example of a sequence

of facies on a Holocene beach
were the object of study in numerous works regarding the body of stratigraphy, especially for the interpretation of
process causality of the grain size distribution, bedforms and stratified facies by means of application of the Principle of
physical and organic sedimentary structures. These surface Uniformitarianism. This is among the fundamental princi-
studies were approached by taking into account that, ples of stratigraphy. The principle was stated by James
according to Walther’s Law, the facies that were originally Hutton and widely disseminated by Charles Lyell as a
deposited adjacent to each other end up overlapping in a contrast against catastrophism, although the term was
vertical succession in the form of facies sequences (Fig. 5.3). established by William Whewell. According to the principle,
Subsequently, the studies were expanded into deeper geological processes have acted in a uniform way through-
areas, incorporating trench data, manual cores and vibra- out the Earth’s history. Thus, if current processes are the
cores to establish more complex sequences and facies same as those that acted in past geological periods, the
models. The results of these studies showed that it is in interpretation of fossil facies can be made by comparison
coastal environments where the preservation potential of with current environments where both processes and
sedimentary sequences can most easily be determined, thus resulting facies can be observed.
establishing the models of facies to be preserved in the form While sedimentology establishes sequences of lithofacies
of stratigraphic series. (depositional facies) for each of the subenvironments that
constitute a sedimentary environment via models of depo-
sitional facies for each sedimentary environment, stratigra-
5.4 Stratigraphical Approach phy goes further, defining, through the analysis of facies, the
relationships between different sedimentary environments in
Stratigraphy is the geological discipline that deals with the the face of phenomena occurring over a longer period of
study and interpretation of stratified sedimentary rocks, and time (Fig. 5.4). These long-term processes include eustasy,
the identification, description and interpretation of sequences tectonic and other changes in the sedimentary supply regime.
as well as the correlation of stratified rocky units [9]. In the These same coastal sequences also play an important role
past, many sediment sequences were preserved in the geo- during the stages of development of sequence stratigraphy,
logical record and transformed into sedimentary rocks. which studies the relationships between processes that
Ancient coastal records had a significant importance in manifest in the record of sequences of a larger order
establishing classical coastal sequences during the begin- (parasequences and depositional sequences) in which the
nings of the discipline. The results obtained from a sedi- facies deposited in the different sedimentary environments
mentological vision are easily applicable to the doctrinal overlap.
Fig. 5.4 Example of an

architectural facies model of a
prograding barrier island system
[3]
Stratigraphy is also responsible for establishing relation- includes the characterization of physical processes, such as
ships between coastal environments and their surroundings, currents, waves and tides, as well as small-scale geological
both continental and marine, as a part of the same sequence processes, such as erosion and sedimentation, or large-scale
tracking. These relationships are established not only from ones, such as ocean floor expansion, as well as the chemical
the point of view of the sedimentary successions that are and biological phenomena occurring in these waters.
preserved in the geological record, but also from the Oceanographic science considers that the coast, as the
geometry of sedimentary bodies. In underwater environ- boundary of the ocean, is included within it and is affected,
ments, these geometric relationships are easily established albeit with nuances, by the same processes as the rest of the
thanks to the use of geophysical techniques such as reflec- sea [6]. Of all the approaches that oceanography addresses, it
tion seismology, combined with the analysis of facies in is clear that there are two of them that study aspects related
sediment logs. to coastal geology: physical oceanography and marine
The establishment of geometric relationships other than geology.
the simple overlapping of parallel roof and base strata sug- Physical oceanography studies the physical processes that
gests a close relationship between this geometry and the occur at sea, including oceanic currents, tides and waves.
original shape of some of the sedimentary bodies in which These studies are conducted from a dynamic approach by
the facies are contained. This fact gives rise to a link analyzing the movements of ocean water bodies and their
between stratigraphy and geomorphology, so that numerous causes, highlighting a discipline known as meteorological
works use the word “Morphoratigraphy” to describe the oceanography, which is responsible for studying the inter-
studies in which the two disciplines are combined. These actions between cells of atmospheric circulation and the
studies also tend to relate both the facies and their external movements of seawater.
form with the processes that generate both characteristics. Since its birth as a science, oceanography has brought
important knowledge to the thematic development of coastal
geomorphology, since it has applied a robust oceanographic
5.5 Oceanographical Approach methodology such that the global current system has come to
be well understood, as has its genesis in relation to atmo-
Oceanography is defined as the science that studies the seas spheric circulation systems (Fig. 5.5). Similarly, oceano-
and oceans and everything that happens in them [4, 5]. This graphic methods were used to explain the origin and
science addresses research on the structure, composition and dynamics of the waves, both in the open sea, in their area of
dynamics of ocean water bodies [1]. This broad approach approaching the coast and the dissipation of energy in their
5.5 Oceanographical Approach 49
environments have a sedimentary zonation that is related to

the gradation of the physical processes that occur in them,
and this zonation conditions the distribution of benthic
organisms that live in surficial sediments of the environ-
ments near the coast.
Perhaps the clearest example is the interaction between
plants and the action of waves and tidal currents. In this case,
for studies on the meadows of marine phanerogams and
coastal marshes it is important to know the effects, on the
one hand, of the hydrodynamic processes and, on the other,
of the control of the sedimentary substrate. Whereas waves
and currents put stress on plants, the grain size of the sedi-
ment controls the degree of oxygenation of the rhizomes and
roots. On the other hand, the presence of vegetation can alter
the flow conditions near the bed and stabilize the substrate,
and also modifies the chemical conditions of the water that
Fig. 5.5 Thermal Landsat image showing the Gulf Stream affecting surrounds the plants, causing reactions of chemical precipi-
the East Coast of North America tation and flocculation. An additional effect is the important
role of lagoons, estuaries, deltas and marshes as nurseries
during the youth phases of fish development.
breaking. The tides were also described, so their origin and Another classic example of these interactions is that
dynamic functioning in open marine systems and in coastal which occurs on coral reefs. The arrival of waves oxygenates
systems were also established in detail using oceanographic the environment and provides the conditions for optimal
methods. coral development. In addition, the presence of corals con-
Once the fundamental dynamics of each one of the tributes to protect areas so they are safe from the strongest
hydrodynamic processes were known, science was able to wave breakers. Coastal areas protected by the action of the
apply the characterization of these processes on each coast reef body provide an optimal habitat for the youthful
that was studied from a dynamical point of view, in order to development of many of the fish and mollusk species, so that
explain the observed geomorphological features. In this way, many of the species that inhabit the open seawater usually
oceanography and coastal geomorphology have gone hand reproduce in coastal waters.
in hand for decades in the geological characterization of the This environmental vision of the hydrodynamic condi-
coasts. On the other hand, geological oceanography and tions of coastal sedimentary environments is closely related
marine geology focused on the characterization of the to sedimentology, as the action of organisms represents the
structure of the ocean floor and, within its objectives, the genesis of many organic structures that are preserved in the
most coastal-related part is the study of the distribution of sediment and that give rise to a whole science such as
seabed sediments and the large sedimentary prisms gener- ichnology.
ated on the margins of the ocean basins. With these aims, it
is obvious that an immediate relationship was established
with sedimentology and stratigraphy. 5.7 A Multidisciplinary Vision
Although the objectives of these geological disciplines may

5.6 Environmental Geology Approach be somewhat different, they all coincide with a special
interest in discerning in detail the performance of the
Hydrodynamic processes (waves, tides and currents) control physical processes that act on the coast, and so to understand
the physical and chemical variables of the sediment and their dynamics. Most of the time the interest is focused on
condition the biological characteristics of the ecosystems these dynamics in relation to human activities, but also as
that are established on sedimentary environments. These generators of landforms, as well as facies and sequences that
variables can introduce stressors for plants and animals that can be preserved in the geological record. On the one hand,
inhabit the coast and the shallow waters and, conversely, can it is clear that there is an overlap of objectives between
also be important for the dispersion of larvae and adult geomorphology, physical oceanography and sedimentology
organisms in coastal environments. The knowledge of the in the study of coastal processes such as waves and tides, as
dynamics of erosional and depositional processes can be well as erosion and sedimentation. But in addition, in recent
useful in the study of these living organisms. Many coastal years, many of the boundaries between these disciplines
have been blurred, as there is now a tendency towards the timescales, as well as the influence of environmental evo-
transversality of science. When attending any of the inter- lution on the ecosystems that settle in them, and on human
national symposia on the coastal sciences, it can be observed activities.
that the groups of researchers and those behind the major
projects are currently composed of collaborators from dif-
ferent geological disciplines (and some non-geological), References
which translates into a multidisciplinary focus of the works
on coastal areas published in any of the journals in the field 1. Bates RL, Jackson JA (1987) Glossary of Geology (3rd ed).
of geosciences. American Geological Institute, Virginia, p 788
Throughout the chapters of this book, all the points of 2. Davis WM (1899) The geographical cycle. Geogr J 14:481–504
3. Kendall CGSC (2007) SEPM Strata: Barrier Island Morphology.
view included in this one will be discussed. Some of the http:// www. sepmstrata. org/ page. aspx?pageid=306
chapters offer a vision in which a single perspective domi- 4. Krümmel O (1907) Handbuch der Ozeanographie. Band I. Die
nates, as is the case of the chapters dedicated to the char- räumlich, chemise un physikalischen Verhältnisse des Meeres.
acterization of the hydrodynamic processes that act on the Engelhorn, Stuttgart, p 526
5. Krümmel O (1911) Handbuch der Ozeanographie. Band I. Die
coast. However, in most chapters is offered a multidisci- Bewegungsformen Meeres (Wellen, Gezeiten, Strömungen). Engel-
plinary treatment. In particular, in the chapters devoted to horn, Stuttgart, p 766
coastal environments, the aim will be to characterize the 6. Shepard FP (1948) Submarine geology. Harper & Brothers, New
dynamic functioning through the performance of hydrody- York, p 348
7. Twenhofel WH (1926) Treatise on sedimentation. Dover, New
namic processes within them, and then to carry out their York, p 926
geomorphological characterization and description, ending 8. Wadell HA (1932) Volume, shape and roundness of rock particles.
with the facies and facies models that are generated in them. J Geol 40:443–451
In the last chapters, the most stratigraphic vision will be 9. Weller JM (1960) Stratigraphic principles and practice. Harper,
New York, p 725
realized, analyzing the processes that act on the longest
Study Methods and Techniques
6
6.1 Introduction 6.2.1 Instruments for Wave Measurements
In past centuries, wave dimensions were measured at sea

Based on the different perspectives of geological disciplines
from vessels by estimation of the height relative to the deck
on the objectives in the studies of coastal geology, a variety
and from land by recording the dimensions in the breaking
of research methods are used. Taking into account that the
zone, including the directions of approach to the coast. For at
sedimentary dynamics of coastal environments are reflected,
least the last half century, a more precise characterization of
both in coastal processes and landforms of different scales,
the morphological parameters that define the waves has been
as well as in the distribution of sediments generated by these
performed through a complete analysis of each wave train
processes, it is necessary to study the present environments
approaching the coastal area. Currently, there are several
from all these visions, in order to characterize this dynamic
methods for recording swell data: buoys, radars, pressure
in a global way by combining the evolutionary trends of the
sensors and predictive models.
short and long terms (Fig. 6.1). The characterization of
sedimentary dynamics in each of the present coastal sedi-
mentary environments will allow us, by applying the Prin-
6.2.1.1 Wave Buoys
Buoys are measuring stations anchored to the seabed in areas
ciple of Uniformitarianism, to interpret the generating
far from the coast [1] that are used to measure the dimen-
processes from the recognition of sedimentary rocks
sions of the waves before they deform when they touch the
deposited in ancient environments.
bottom (Fig. 6.2 a, b). The simplest buoys are installed with
It is clear that not all studies about coastal geology have
an accelerometer that allows them to obtain the height, the
the same objective; on the contrary, some works have a more
period and the speed of each wave of the train. The most
defined objective that is based on a single one of the per-
modern and advanced buoys also allow the measurement of
spectives that have been listed in the previous chapter.
the direction of origin of the wave trains through the use of
an integral gyroscope.
There are other devices installed in the buoy which also
6.2 Methods and Techniques to Study
allow us to measure atmospheric (such as barometers, ther-
Physical Coastal Processes
mometers and anemometers) and oceanographic (such as
water temperature and conductivity sensors or current pro-
In coastal areas, oceanographic methods for measuring
files by Doppler effect) variables (Fig. 6.2c).
dynamic agents are less complex and costly than those
required for deeper marine areas, given the accessibility of
coastal waters. In recent decades, oceanography has devel-
6.2.1.2 Wave Radars
oped a variety of techniques dedicated to the measurement of Swell radars measure the relief of the water surface by using
these dynamic agents. Most of the measurements are carried electromagnetic waves that are modulated in amplitude or
frequency when recorded in equipment once reflected in the
out by direct methods from records made with the use of
technological instruments. In this sense there are remarkable moving water surface. There are several radar techniques
advances in the measurement of waves, tidal levels and used for measurements of wave dimensions. The different
sensors available on the commercial market, as well as a
currents (tidal and oceanic).

https://doi.org/10.1007/978-3-030-96121-3_6
52 6 Study Methods and Techniques
structure on which the equipment is mounted. This inter-

ference can become important depending on the provenance
of the waves if reliable directional measurements are
required, although they are usually effective in determining
scalar parameters. Due to this fact, the orientation of the
equipment with respect to the tower must be carefully cho-
sen. They present the advantage that having a fixed instal-
lation provides a continuous and prolonged recording over
time.
Coastal radars are installed at fixed stations located on the
coast and act in low grazing-angles using high frequency, so
they can reach up to a distance of 70 km from the coast.
Fig. 6.1 Study objectives of coastal geology
Since the sensors are not in an upright position relative to the
water surface, this method does not use the reflection of the
critical review of them, were summarized, described and waves, but instead dispersion in the roughness of the water
discussed by Grønlie [11]. According to the type of elec- surface (Bragg backscatter). In order to obtain a more reli-
tromagnetic waves used, infrared, microwave and high fre- able record, two radar installations are usually used to record
quency radars can be differentiated. They are distinguished the same sea surface.
depending on their location: platform radars, coastal radars, Marine navigation radars are installed on board moving
mobile navigating radars and remote sensing radars. vessels. Since under large waves the boat will suffer oscil-
Platform radars are installed on fixed shelves and face lations, these usually act in conjunction with accelerometers
vertically towards the water (Fig. 6.3a). Infrared light or and gyroscopes that correct the signal using complex algo-
microwaves may be used. Detection equipment (Fig. 6.3b) is rithms. Either way, the obtained signal is unreliable in
usually cheap, although it may be expensive to install in a determining the dimensions of the waves, although it is
stable structure. These kinds of radars present the disad- useful to obtain data on the direction of propagation of the
vantage of possible interference of the record by the wave.
Fig. 6.2 a and b Different

models of wave buoys.
c Scheme of measuring
instruments installed on and
under water in a standard buoy
6.2 Methods and Techniques to Study Physical Coastal Processes 53
Fig. 6.3 a Example of a radar

installation on a piloted fixed
coastal structure. b Detail of a
coastal wave radar. c Example of
the registration obtained with a
coastal wave radar ( adapted from
Reichert et al. [25]
There are also airborne radar sensors and radars installed proportional to the depth of immersion [20]. The rods must
on satellites (space-borne radars) responsible for character- be installed on the surface of the water in such a way that the
izing the dynamics of the sea surface. These systems usually sine and crest of the wave oscillate at the length of the rod.
use very open radars that synthesize the signal They are very economical devices that work well in labo-
(synthetic-aperture radars or SAR), so they can cover very ratory experiments and channels where the waves are not of
wide surfaces, although this synthetic signal causes the large dimensions.
record to lose resolution. In any case, it is appropriate to Pressure gauges (Fig. 6.4b) are very simple, autonomous
verify, calibrate and validate the measurements obtained by and programmable devices, which are commonly used in
instruments installed on satellites using propagation models short- and medium-term measurement experiments in
through real direct measurements obtained by coastal buoys breaking areas [2]. Measurement instruments are mounted at
or radars. the bottom in shallow water during a low tide. These devices
Whatever frequency and location of the equipment are use algorithms based on the linear theory of the waves to
used, a visual record of the results can be obtained imme- calculate the length of the water column above the sensor
diately (Fig. 6.3c). The dimensional and dynamic charac- using the water pressure measurements as starting data [27].
teristics of each wave train are obtained from the received Normally the data is stored in an internal memory that can be
signal through complex processing and statistical analysis of removed and read in a computer at the end of the
the data [17]. experiment.
Acoustic sensors [18] are also mounted on the shallow
6.2.1.3 Wave Gauges water bed facing the surface (Fig. 6.4c). They are somewhat
Wave gauges or wave sensors are compact and simple bulkier than pressure sensors, but equally versatile for their
instruments that provide a reliable record of the instanta- autonomy and data storage capacity.
neous position of the water surface. This equipment can be
installed on devices easily adaptable to the circumstances of 6.2.1.4 Numerical Models of Wave Generation
the location which are able to measure water level variations and Propagation
caused by waves and also by tides. They are often combined The numerical data modeling comes from mathematical
with data acquisition and processing software that allow the simulations that calculate the wave dimensions from atmo-
calculation of the significant parameters of the wave trains spheric conditions on the sea surface (sea and swell infor-
and individual waves, although not its approaching direc- mation). Databases (hindcast or reanalysis) are calibrated and
tions. Their versatility makes them ideal for measurements in developed from historical weather records. It should be noted
shallow waters such as those in coastal environments. that the data generated by numerical models are not instru-
Depending on the method used for the measurement, there mental data; on the contrary, these databases come from the
are three types of sensors: electrical sensors (wave probes), use of mathematical models but they must be calibrated with
pressure gauges and acoustic resistance sensors (Fig. 6.4). instrumental wave measurements, and can be very useful to
The electric resistance meter (wave probe, Fig. 6.4a) obtain data about the magnitude of the waves. There are
works by measuring the resistance of water to the passage of models applied on a global scale and also models with higher
the electric current between a pair of parallel rods, taking resolutions for regional scales. These models provide infor-
into account that the water resistance between the two rods is mation evenly at regularly selected points in space.
Fig. 6.4 Different types of wave

gauge. a Wave probe (picture
from the webpage of the College
of Engineering of the University
of Wisconsin). b Pressure gauge.
c Acoustic wave sensor
The use of models began in the 1950s, but it was not until analysis of tidal height measurements. This is done using
the 1970s that the first models were obtained on a global tide gauges which record water levels in a continuous way.
scale. The third generation of models is currently being The first wave gauges were deployed in fixed installations on
implemented. The most widely used global model for open the coast, usually in port facilities (Fig. 6.6). This type of
water today is the WAM [16], to which local data can be gauge is still the main data source of the long-term mea-
coupled to establish more accurate regional models. A good surement networks existing in most countries.
example can be the network of WANA points in Spanish Regarding the measurement method, buoy tidal gauges
waters, whose data, with a temporary periodicity of three have been classically used to measure the height of the water
hours, are obtained by applying the WAM model to the level. The mechanism consists of a small buoy that, intro-
atmospheric data provided by the Spanish weather network. duced into a vertical pipe connected to seawater, floats on
In coastal waters, where the waves interact with the bed, the surface, rising and falling with the tidal level oscillations.
it is necessary to apply other models. Another The buoy is hooked to a counterweight by a cable that
third-generation model such as SWAN is currently being passes through a system of pulleys and differentials. The
used [4]. This global model can also be adapted at a regional pulleys transmit the movement to a needle that draws the
level by applying detailed coastal bathymetric and weather curve on a recording paper that is in constant motion as it is
data. In particular, in European waters, the analysis called driven by a reel mechanism. Today, the buoy system has
HIPOCAS—Hindcast of Dynamic Processes of the Ocean been modernized and, although the system of
and Coastal Areas of Europe—has been established [12]. buoy-and-pulley is maintained, a digital record is obtained
The application of the HIPOCAS regional model to the (Fig. 6.7a). Digital data of water levels are stored in an
Mediterranean and Atlantic waters of southern Europe has internal memory or transmitted to control stations by radio
been used to create the database of the SIMAR point net- frequency.
work (Fig. 6.5). All these databases are public and accessi- Currently, there are new techniques that can measure the
ble via the internet. tide through the use of ultrasound. These are the sonar
sensors, which are characterized by a high-resolution record.
The ultrasonic emitting antenna is installed at a coastal sta-
6.2.2 Instruments for Tidal Level Measurement tion at a certain water height, emitting pulses that are
reflected in the water and returned to a receiving antenna.
Tidal characterization is essential work in coastal dynamics The distance to water is calculated through the ultrasonic
studies and is critical in establishing reliable water level pulse velocity. They are usually installed in fixed stations
datums. This characterization is carried out by statistical that emit the data by radio waves to the base where they are
6.2 Methods and Techniques to Study Physical Coastal Processes 55
Fig. 6.5 SIMAR network

database for coastal waves in SW
Europe
Fig. 6.6 Installation of a tide

gauge of the NOAA network in
Virginia Key, Florida, USA
There are also larger instruments that, operating on the same

principles, can be installed at a fixed depth through anchor-
ing. These instruments can record and store data continuously
for months in an internal memory unit. Some of these
instruments have a propeller arrangement with a horizontal
axis, similar to the smaller instruments (Fig. 6.8c), while
others are arranged in a vertical axis position (Fig. 6.8d).
All of these current meters have the disadvantage of
needing a speed threshold to start the movement of the
propeller, so currents below these thresholds are not recor-
ded. However, they do have the advantage of their low cost
and ease of use, when operating from the surface and not
needing complicated installations.
In the 1990s, other current meters were developed which
measure static electricity induced by water friction in an
electrosensitive paddle. These are the so-called electromag-
netic induction flow meters. These sensors can measure the
current speed in the water sheet that is in contact with a flat
sensor (Fig. 6.9a) or in the water volume around the sensor
Fig. 6.7 Different types of tide gauge. a Buoy digital tide gauge.
b Bubble pressure tide gauge. c Membrane pressure tide gauge
(Fig. 6.9b).
Current speed measurement systems using the acoustic
wave Doppler effect are now being used. These acoustic
stored and analyzed. These are expensive systems that are
profilers are called ADP (acoustic Doppler profiler) or
part of long-term data networks in many countries.
ADCP (acoustic Doppler current profiler). These instruments
In recent years, other sensors based on different principles
involve the recording of a speed profile in one direction
of physics have been developed. Some of these instruments
including its three components (Fig. 6.10). There is equip-
are based on the measurement of pressure variations driven
ment on the market covering different measurement ranges
by the rise and fall of water level (pressure sensors). The
and at different resolutions, allowing their application in
sensors of these instruments are usually installed in the
shallow water environments such as coastal environments,
background, anchored to a fixed structure, communicating
but also in deeper systems. The most accurate profilers allow
the sensor with a memory or storage equipment that remains
a continuous time determination of speed profiles in
on the surface. Other sensors calculate the pressure through
20 20 cm cells along columns of water up to 100 m.
volume variations in an air bubble contained in a transparent
These systems can be installed on the surface (on a
tube. These are called bubble sensors (Fig. 6.7b). Other
floating platform), focused to the bed or deployed on the
sensors measure pressure from pneumatic membranes or
bottom focused to the surface, and even on the sides of
strain gauge cells. These are called membrane sensors
channels to measure cross-sectional speed profiles to the
(Fig. 6.7c). None of these instruments requires a fixed
shores (Fig. 6.10a). There is also equipment with sensors
installation, so they are very versatile and are used in short-
oriented at different angles to measure in a two-dimensional
and medium-term characterization projects.
way (Fig. 6.10b). On the bottom they can be installed using
heavy structures that are usually braced and hoisted from a
6.2.3 Instruments for Measuring Tidal boat (Fig. 6.10c). In addition, to perform measurements from
and Ocean Currents the surface the equipment can be installed on catamarans that
remain anchored (Fig. 6.10d). There is also the possibility of
Current meters, flow meters and hydraulic reels have long towing these catamarans or installing them on board to make
been used to measure currents of different origins. The most channel profiles where the two-dimensional distribution of
classical of these instruments work by rotating a propeller currents—in depth and width—can be observed (Fig. 6.10e).
(Fig. 6.8), which allows the calculation of the speed from the
number of spins of the propeller per unit of time. The sim-
plest model allows direct surface measurements to be per- 6.3 Study Methods of Coastal Landforms
formed by manually holding the instrument (Fig. 6.8a). More
advanced models allow speeds to be measured at different The study of coastal landforms was the first topic addressed
depths in shallow channels, by holding the reel on a gradu- on the coast from a geological perspective. These early
ated rod to control the depth of the measurements (Fig. 6.8b). studies were conducted from a purely geomorphological
6.3 Study Methods of Coastal Landforms 57
Fig. 6.8 Different types of

propeller current meter. a Surface
current meter. b Shallow water
current meter. c Horizontal axis
deep current meter. d Vertical
shaft (rotor) current meter
6.3.1 Topography: Classification

and Measurement of Surficial Landform
Dimensions
The geomorphological methodology is applied to the clas-

sification and measurement of landforms of different scales.
On a small scale, direct measurements of quantitative mor-
phological parameters are made. These are taken manually in
the field according to the methodology described by Ham-
mond [13]. The classification and measurement of the
dimensions of current-generated bedforms (ripples, megar-
ripples, sand waves and antidunes) is usually done in this
way. It should be noted that there is a direct relationship
between the presence and dimensions of these forms with
Fig. 6.9 Different models of electromagnetic induction flow meter.
a Flat sensor. b Volumetric sensor
their grain size and the speed of the current that generates
them, so the genesis conditions can be deduced through the
point of view and using the long-contested methods of this use of a simple diagram [14].
geological discipline. In more recent times, the emergence of Another classical technique commonly used in coastal
increasingly sophisticated technologies has methodologi- geomorphology is stereoscopic photointerpretation. The use
cally revolutionized coastal geomorphology studies. Never- of this methodology since the 1940s has allowed the mea-
theless, the way in which the results are analyzed and surement of landforms of meso- and macroscale. In recent
interpreted has not undergone too much evolution. This decades, the resolution of the photographs has increased,
section summarizes all the techniques that are used today, allowing the analysis of even smaller forms.
both the classic ones, which continue to be used, and the In the late 1980s, the emergence of remote sensing and
most modern, results of the advances of the last decades. the use of satellite images allowed measurements of
Fig. 6.10 Acoustic Doppler

current profilers (ADCP).
a Different positions in which the
system can be installed. b Detail
of the measuring instrument.
c Deployment to install on the
bottom and measure upwards
through the water column.
d Catamaran used to measure
towards the bed through the water
column. e Current speed
cross-profile of an inlet
macroscale forms to be made [7]. Similarly, the increased measurements are obtained with a very high resolution due
resolution of the images and the use of multi-band sensors to the narrow spacing between the data [21].
allowed for greater accuracy in the measurements, as well as Drone flights have also been used at intermediate scales.
enabling automation of both classification and measure- This is a cheap technology that, combined with pho-
ments. Remote sensing continues to develop with airborne togrammetry techniques, allows one to perform the accurate
sensor logging. Also, photogrammetry techniques were measurement of landforms using the right software
developed in parallel. Using these techniques to link remote (Fig. 6.11b). It is a much cheaper technology than LiDAR
measurements with the position of previously established and offers very satisfactory results.
checkpoints allows high-resolution topographic surveying. Topographic data obtained through remote sensing tech-
Since the end of the twentieth century, high-resolution niques, whether satellite, airborne and land LiDAR or drone
surveying has been done using flights with LiDAR technol- topography, are usually treated to obtain a digital elevation
ogy (laser imaging, detection and ranging). The LiDAR model (DEM). DEMs allow for very detailed, larger-scale
principle is to determine the distance between the laser emitter studies with a larger number of variables. As numerical data,
and the ground surface using laser pulses [5]. This is usually a the results can be treated with algorithms that allow the
device that launches a beam of pulses that open at a certain automated identification of certain structures on the ground
angle to both sides of the emitter. Being airborne sensors, the surface by statistical analysis of the main components [30] or
trajectory of the flight and its height condition the extent and of fuzzy logic [8].
resolution of the data, but in any case, a high-resolution All of these remote sensing techniques open up an
topographic record is obtained, allowing the identification and enormous potential for work applied to the characterization
measurement of mesoscale landforms (Fig. 6.11a). of coastal zones at different scales and points of view. These
The same principles apply in terrestrial LiDAR technol- applications continue increasing in all domains (e.g., the
ogy, with the difference being the data are taken from the elaboration of digital terrain models, study of changes in the
ground from a point of known position. When the LiDAR shoreline, shallow bathymetrical evolution, water mass
sensor is found in a situation closer to the analyzed surface, movements and wave characterization).
Fig. 6.11 Topographic surveys

with airborne sensors. a Airborne
LiDAR. b Drone flight
6.3.2 Monobeam Bathymetry width of the bottom band being covered, as well as the data
spacing, depends on the thickness of the water column.
Bathymetry consists of the surveying of ocean floor depths The resulting data are numerical datasheets including the
by measuring and expressing them on maps. Initially, the distances to the bed obtained from the pulse speed in the
depths were recorded using ropes knotted with stones water after obtaining the return trip time of each signal.
attached to the lower end, although these evolved to be Normally, latitude and longitude coordinates are obtained
replaced by a graduated metal cable called lead-and-line. when the equipment is connected to a differential GPS
In the 1920s, sonar techniques were developed and the (DGPS) system. The XYZ coordinate files thus obtained are
first detailed profiles of coastal bottoms could be obtained. finally processed to obtain bathymetric maps of contours and
The bathymetric data are obtained from the sonic impulses three-dimensional diagram blocks showing the topography
emitted from an electrical source and, once reflected in the of the bed at very high resolution (Fig. 6.12).
seabed, are collected by receiving hydrophones. The first
probes recorded bathymetric profiles on continuous paper,
but today you get a digital record that can be processed later. 6.3.4 Side-Scan Sonar
The bathymetric echosounders currently work in a fre-
quency ranging from 15 to 200 kHz, with a single transducer Side-scan sonar (SSS) is a geophysical method that uses
responsible for the emission and reception of acoustic pulses. acoustic frequency pulses ranging from 100 to 1000 kHz
Currently, any commercial, fishing and even recreational that are emitted by transducers [3]. The transducers are
vessel is equipped with a single beam bathymetric echo- usually located in a submerged towfish that is connected by a
sounder, although most of these probes are not valid for cable to the data acquisition unit (DAU) installed on board a
bathymetry as they do not have a data storage system. For vessel (Fig. 6.13a).
scientific purposes, bathymetric records must be able to be Acoustic pulses are reflected in the submerged bed and
stored in XYZ files by combining the bathymetric data with returned to the receptors also located in the towfish
the position obtained through a GPS system. The vessel from (Fig. 6.13b). The towfish sends the received information to
which registration is made must travel at low speeds, in order the DAU, which processes the information that will be
to allow the sound to go and return through the water column. transformed into a bed image (Fig. 6.13c). The intensity of
the bed acoustic response depends on the nature (reflectivity
and texture) of the bed material and the orientation of the
6.3.3 Multibeam Bathymetry surface of the material relative to the acoustic pulse.
The use of SSS is commonly applied to coastal geology
In the 1950s, probes that emitted a beam of acoustic pulses for geomorphological mapping of submerged areas. These
were developed, the so-called multibeam echosounders. documents also allow sedimentological interpretations of the
These probes mapped the bed topography along bands configuration of the submerged bed in coastal environments
extended on both sides of a navigating boat. Their data are [23] and [31]. The use of this system is essential in coastal
very useful for the identification and measurement of sub- research because it allows the scanning of large areas
merged landforms. quickly and efficiently, using images or records obtained for
The method consists of the emission of very high fre- the interpretation of landforms.
quency ultrasonic pulses that are emitted in two beams that Correct interpretation of SSS logs requires precise posi-
open several degrees on both sides of the transducer. The tioning of images. To do this, the equipment is normally
Fig. 6.12 Bathymetric surveys

with multibeam echosounder.
a Representation of information
points by color according to their
depth. b 3D shaded relief
representation
connected to a DGPS system, obtaining an accurate geo- 6.3.5 Cartography of Coastal Environments
referenced position of each point of the recorded image.
Systematic navigation allows the scanning of wide under- In coastal geomorphology, as a specific branch of geomor-
water surfaces, and the precise positioning of successive phology, the realization of cartography is vital to represent
records is the basis for building georeferenced photomosaics the distribution of the landforms on the land surface [24].
of the coastal bed. Images obtained by SSS can be as Maps are graphic documents in which the distribution of
accurate as an aerial photograph and efficiently reveal sedi- landforms of any kind is represented. The information on the
mentary features and bedforms. The use of this technique relief that it represents will respond to the specific needs
allows the study of coastal beds from a bathymetric, mor- posed in the objective of its realization. Specifically, in
phological and lithological point of view. It also useful to coastal areas the distribution of morphogenetic systems is
determine the geometry, distribution, dimensions and ori- usually represented, which is for geomorphology a concept
entation of the bedforms, and facilitates the analysis and very similar to that of sedimentary environments in sedi-
interpretation of the flow regime. mentology. Thus, the distribution of beaches, dunes, subtidal
Fig. 6.13 Side-scan sonar.

a Components of the equipment.
b Scheme of the equipment
elements during work. c Example
of SSS registration on a bed with
numerous bedforms
channels, intertidal flats or salt marshes would be repre- processes. In particular, vector processes such as the tra-
sented. It is also common to represent the macro-, meso- and jectories followed by the transport of sediments are
microforms that are present in each one of these coastal interesting.
systems or environments, whether erosive or cumulative. It should be noted that any type of mapping in coastal
From this point of view, dune ridges, coastal berms and areas can be made of both emerged and submerged areas,
bedform crests that acquire mapping dimensions are usually according to available sources of information. It is clear that,
represented. For smaller shapes, whose dimensions do not in most cases, coastal environment mapping overlaps with
allow mapping of individual elements, it is common to map topographic and/or bathymetric information.
shape fields.
In sedimentology, the characters of the geological mate-
rials can also be mapped. In these cases, it is usually rep- 6.4 Study Methods of Short-Term Coastal
resented by the type of facies of the sediment or rock. This Evolution
type of map expresses distributions of grain sizes or content
in certain lithological components. This representation can Since the coast is one of the most dynamic environments in
be easily interpreted in terms of polarity of the movement of existence, it produces changes in very short time spaces that
materials across the coastal environments. can be observed on the human scale. As a result, many of
This method gave rise to a special type of map that is very these changes can be measured by comparing studied situ-
useful in coastal areas: process mapping. This system of ations. Often these comparisons are made between two dif-
mapping not only represents fields with different shapes and ferent dates, revealing evolutionary trends, but most of the
bedform types, but includes symbols that represent specific time they compare situations on many successive dates, with
which cyclical behaviors can be established and that are thus The most modern method is the use of bars connected to
very characteristic of coastal dynamics. The intention of DGPS systems (Fig. 6.14e). This method can be combined
these measurements is to understand the causes of these with the total station and is very useful for large area sur-
changes by relating them to the processes that occurred in veys, especially when the data obtained at reference points
the period between the analyzed dates. Of these behaviors, are also combined with a photogrammetric drone flight. The
reliable short- and medium-term predictions can often be inconvenience is that its accuracy is lower than that obtained
established. This section describes the most frequently used in the above methods.
methods to address the study of these morphological
changes. 6.4.1.2 Comparisons Between DEMs Obtained
from Topographic and Bathymetric Data
DEMs obtained on different dates from topographic and
6.4.1 Topo-Bathymetric Comparisons bathymetric data can be compared if they cover exactly the
same area. For the comparison to be possible, grids of the
6.4.1.1 Beach Profiles same characteristics must be set in the same size. That means
Perhaps one of the first methods addressed in coastal they must have the same spacing and number of nodes, at
dynamics studies was the comparison of beach profiles times with the same start and end points, so that the entire X
carried out on different dates. In this case, in order to com- and Y points must completely match. Typically, the same
pare the profiles it is important that measurements begin software applications that can interpolate curves between
from an easily identifiable point whose position in the three node data can in turn subtract data from both grids. So, in
dimensions remains invariant. The topographic profile will places where the previous date surface is above the later one
thus be measured starting from the top of the backshore and a negative value is obtained, while where the back date
ending at the lower beach. An important aspect is that the surface is above the previous date results in positive data.
measurements are made during low tide to measure as much This then allows the construction of a plot with curves of
of the beach as possible. It is clear that it will also be nec- the same value, interpreting surfaces with negative values as
essary to take the course towards which the profile is mea- areas where erosion has occurred and surfaces with positive
sured, in order to ensure that all profiles are made along the values as depositional areas. Some functions of these soft-
same transect. Classically in the studies of the evolution of ware allow in turn the calculation of erosive and cumulative
beaches, several profiles are usually made, separated at areas, as well as eroded and accumulated volumes.
distances of about 50 m, in order to carry out
three-dimensional surveys and perform volumetry.
The simplest and cheapest method is to use a fixed-length 6.4.2 Comparative Photointerpretation
bar (often one meter or three feet) with a level to keep it
horizontal. At the end of the bar, a graduated stake is placed For decades, comparative photointerpretation has been a
to measure the topographical difference between the start very useful tool to visualize changes in the coastline, as well
and end points along the profile. A more precise method is as changes in the distribution of coastal environments. From
that proposed by Kenneth O. Emery, which is to use an the 1950s to the mid-90 s, the main method was carto-
alidade or a sight whose horizontal position is assured by a graphic work on transparent paper over aerial
bubble level (Fig. 6.14a). The optical horizontal level marks stereo-photographs displayed through a stereoscope. In this
the increments between the starting point and a graduated way, all changes between two aerial photographs of different
stake that is progressively removed meter by meter from the dates were qualitatively compared. However, this method
reference point until reaching the lower beach (Fig. 6.14b). has the disadvantage of not being able to quantify the
This method was improved with the entry into the market of observed changes, since the cartographic product obtained
topographical instruments such as the total station, which was not properly georeferenced.
performs laser measurements of distance and angle between Since the advent of geographic information systems
the station position and a mirror located at the end of a (GIS) in 1962, these systems have become a very useful tool
theodolite of the same height as the station optical instru- in comparative studies of coasts of different dates. Especially
ment (Fig. 6.14c). so, since the generalization of their use at the end of the
These last two methods can even be applied by contin- 1980s meant that virtually all the comparative works are
uing below sea level when moving stakes are placed on a done with GIS software [10]. A GIS can be defined as a set
wheeled buggy that can move under the water surface of tools that can integrate, store, manipulate and organize
(Fig. 6.14d). The University of North Florida has recently layers with appropriately georeferenced geographic data [6].
developed a remote-controlled guided vehicle for measure- These systems allow one to work with layers of information
ments in the break zone, called Surf Rover. in meshes (raster), such as aerial photographs or digital
6.4 Study Methods of Short-Term Coastal Evolution 63
Fig. 6.14 Methods used for

measuring beach profiles.
a Emery method principle.
b Alidade equipment with bubble
level, graduated bars and rope.
c Total station and theodolite.
d Rover for shallow water
measurements, positioned with a
jet ski. e Measurements with
DGPS
elevation models, and with vector information layers (the- system in the short and medium terms. A first step in these
matic mappings), such as sedimentary environment maps or models is the rapid and reliable calculation of the theoretical
systems described in Sect. 6.3.5. In this way, the information capacity of sediment transport by waves and currents.
corresponding to the coast on different dates can be easily A model actually consists of several mathematical anal-
quantitatively compared. ysis modules that can be coupled to get results more adjusted
Today there are numerous applications to work with GIS with reality. Each one of these modules applies the physical
on all operating systems and many of them come as free equations that regulate the analyzed process. In one of these
software. One can even find GIS applications that allow models, for instance, would be the determination of the
work online. A list of the most widely used programs can be propagation and breaking wave patterns, the distribution of
found in the GIS hall of fame [28]. radiation vectors, the calculation of wave-induced currents
and, finally, the transport of sediments induced by combined
waves and currents. This is very useful when studying open
6.4.3 Numerical Models coastal environments, such as beaches, that are completely
dependent on the waves.
The use of numerical models is a very useful procedure for Another of these models is responsible for the modeling
forecasting the future behavior of coastal systems from the of tidal levels and tidal currents, in order to calculate the
analysis of multiple variables, including comparing digital potential transport of sediments induced exclusively by this
models of the successive date DEMs. Mathematical models phenomenon. It is especially useful in the study of tidal
are a very powerful and inexpensive tool that allow analysis systems, such as tidal flats, estuaries or deltas, where an
and forecasting of the dynamic behavior of the coastal additional variable such as the volume of water from the
river system can be introduced. The most complex systems appearing in studies of the top of the sedimentary sequence
are those involving both waves and tides, such as tidal deltas in current environments. This section presents the most
and delta-front bars. In these cases, the models described common methods for sediment sampling and coring.
above should be used together.
The numerical models start from an initial bathymetry
and solve the sediment flow equations within the studied 6.5.1 Sampling of Surficial Sediments
area, as well as changes in bathymetry associated with
spatial variations in sediment transport. The model obtains a Sampling in the inter- and supratidal environments is usually
final bathymetry within the prescribed time frame. The done directly using a manual shovel, taking into account
correct functioning of the model requires the following as that, if the samples are to be analyzed from a geochemical
input data: point of view, plastic material should be used to avoid the
metallic contamination of the sample.
– Initial bathymetry, Different types of bottom dredgers are used for sampling
– Wave data (dimensions and provenance), underwater sediments. There are numerous types of dredgers
– Tidal level data, for this purpose, which are distinguished from each other by
– Tidal current data (speed and direction), and the mechanism used to trigger the closing of the buckets.
– Sediment characterization data (grain size parameters). The most frequently chosen for their ease of use are Van
Veen (Fig. 6.15a), Petersen type (Fig. 6.15b) and Shipeck
The potential transport of sediments can be expressed in type (Fig. 6.15c) grabs. Less commonly used are Orange
terms of the total volume (or weight) of sediment trans- Peel (Fig. 6.15d) and Smith-McIntyre (Fig. 6.15e) grabs.
ported. Bathymetric changes will be the result of such sed- Eckman type (Fig. 6.15f) has the particularity that a box is
iment transport, taking into account the areas with dominant nailed to the sediment to allow the preservation of the
erosion or deposition. However, these models must always internal structure of the sample taken. There are other types
be correctly validated and calibrated for reliable results. of dredgers, such as Lafond-Dietz, that in addition to taking
A common way of model calibration is to apply it to an old sediments are able to sample the rocky substrates.
bathymetry to forecast at a time interval where another more
recent bathymetry already exists. Then, check the degree of
similarity between the actual bathymetry and the bathymetry 6.5.2 Surficial Coring
predicted by the model. The model must be adjusted this
way until you get a satisfactory match percentage. There are Unconsolidated sediments of tidal environments (supratidal,
calibrated models that have reached more than 90% adjust- intertidal and shallow subtidal) can be manually testified
ment between forecast and reality in one-year periods. using plastic pipes (mainly PVC). Any method of coring
Clearly, forecasts done by these models are of great used should seek to not disturb the internal structure of the
uncertainty even if they are properly calibrated. It is neces- sediment since one of the sedimentological aims is the direct
sary to take into account that they are subject to the arbi- observation of the internal order.
trariness of the wave regime which is completely
unpredictable as it is linked to the maritime climate. Even so, 6.5.2.1 Hand Corer
they are a very effective tool for dynamic behavior analysis In those environments where the soil can be directly
and evolutionary trends. Currently, the application to the accessed, the pipe can be inserted directly by hitting with a
transport of sediments on the coast by using numerical hammer. To ensure the correct lifting of the sediment core,
models is recent and these are in the period of improvement. after inserting it, a rubber cap must be used to close the top
The models for estimation of sedimentary dynamics are less end and prevent the entry of air, sucking the sediment into
well-developed. the PVC pipe.
6.5.2.2 Beeker Corer

6.5 Study Methods of Coastal Surficial In environments accessible by walking, where the consis-
Sediments tency is soft and the sediment has high water content, Beeker
type coring can also be used (Fig. 6.16). The Beeker corer is
The study of coastal surface sediments is one of the first characterized by having a flexible rubber at one end that can
objectives addressed on the coast from a purely sedimento- be inflated from the surface once the pipe has been ham-
logical approach. The first works were based on samples of mered into the sediment. When inflated, the rubber cuts the
the most superficial centimeters, but, little by little, tech- sediment at its base and prevents it from remaining in the
niques of sampling and testing to an increasing depth were ground when the pipe is removed. It can also be used
6.5 Study Methods of Coastal Surficial Sediments 65
sediments without compacting. The first models were

designed for the Netherlands Geological Survey by Jan Van
der Staay’s team in the early 1970s [29]. The method is
based on the suction of a piston that ascends inside a tube
thanks to the traction of a cable. This cable is connected to a
winch that acts from the outside of the system through a
pulley that reverses the direction of traction (Fig. 6.17).
The first models were made of metal, but it was very
difficult to extract the sediment cores from the inside without
disturbing the sediment, so in the 1980s design modifica-
tions were made to build it in plastic materials such as PVC
[32].
The corer TESS-1 was designed in the early twenty-first
century by researchers from the University of Vigo, Spain
[22]. It is based on the Van der Staay suction machine, but
Fig. 6.15 Different types of dredger. a Van Veen type. b Petersen allows the encapsulation of sediments in a PVC jacket that is
type. c Shipeck type. d Orange Peel type. d Smith-McIntyre type. inserted through the inside of a steel tube. This facilitates its
f Eckman type subsequent opening and analysis without disturbing the
ordering of the sediment.
6.5.2.4 Piston and Gravity Corers

When sampling in deeper subtidal environments, gravity
corers are often used (Fig. 6.18). This method consists of
dropping a metal pipe with a coupled weight that forces the
tube to be inserted into the soft sediments of the bed. The
metal tube contains an internal PVC coating that will house
the extracted sediment core. The system used in the piston
corers to keep the sediment core inside the pipe is usually an
internal piston that makes the vacuum and prevents the
return of sediments when the sediment column is extracted.
In the case of gravity corers, the anti-return function is
performed by a steel valve with an egg shape.
There are many models of piston corers and gravity
corers, such as Baillie, Hydra, Lundqvist, Meteor, Phleger,
Sjostedt or Strom models. All these types really only differ
in their hydrodynamic design, pipe length and weight
placement.
6.5.2.5 Box Corers

These kinds of samplers are used for the specific study of the
sedimentary structures of the shallowest sediment layer
(Fig. 6.19). This type of coring allows one to obtain samples
Fig. 6.16 Hand corer: Beeker sampler
of large size with minimally disturbed sediment. The
removable characteristic of the system facilitates the study of
through a column of water from a boat. In this case, the top sedimentary structures in two perpendicular planes that
end of the corer must be coupled with the number of steel coincide with the sides of the box.
rods needed to reach the bottom. In this sampler, the PVC The box is fixed by several pins at the lower end of a
jacket containing the sediment core needs to be replaced cylindrical tube that slides through the inside of a guide,
after each extracted core. pushed by a weight of several hundred kilograms. This guide
is welded to a leg-shaped structure that stabilizes the vertical
6.5.2.3 Suction Corer movement of the box. When impacting with the bottom, the
The suction corer is a non-intrusive, economical and manual box goes down vertically until it is nailed to the seabed. This
technique that allows quick and easy extraction of wet impact also acts on a safety display that releases the
Fig. 6.17 Suction corer made in

PVC. a During the thrust
operation. b Detail of the push
bars and the external winch.
c Detail of the inner suction
piston
Once on board, the box can be removed from the rest of

the machine by releasing the pins. Once the box is released,
the water is extracted to minimize sediment disturbance
during the opening process. The boxes are usually remov-
able and the sediment inside is exposed when removing one
or two of the sides.
6.5.3 Sediment Traps
Sediment traps are instruments used to capture particles that

are being transported or are in the process of decanting. In both
cases, the weight of the captured material allows calculations
of the amount of material involved in sedimentary bypassing
in a coastal environment and also estimations of deposition
rates. According to the planned objectives, they can be clas-
sified into suspended matter traps and bed load traps.
Suspended matter traps (Fig. 6.20a) consist of opened-up
section pipes or funnels. These are installed at a given dis-
tance from the surface and held in a capture position for a
predetermined time. After that time the mechanism is
retrieved and the amount of material decanted during that
period is checked. The recovered sediment allows calcula-
tions of sedimentation rates and the amount of suspended
material available in the water column, but, in addition, this
sediment can be analyzed to characterize its nature from
Fig. 6.18 Gravity corer type Phleger, showing a detail of the
egg-shaped valve sedimentological and geochemical perspectives.
Surface traps are also used to measure accumulation rates
extraction instrument. When pulling the winch from the (Fig. 6.20b). They consist of a square plastic surface
instrument to extract the sediment core, a flat shovel swings equipped with a vertical cylinder that is used to fix it at the
under the sample by plugging the mouth of the box to pre- bottom and to visualize its position. They are installed in
vent sediment loss. intertidal beds, matching the plastic surface with the surface
6.5 Study Methods of Coastal Surficial Sediments 67
Fig. 6.19 Box corer. a Just

before submersion. b Installing a
new box before sampling
of the sediment, and are left in place for a certain time. After However, the cores obtained using this technique have the
this time, the sediment thickness that has been deposited on disadvantage that the internal order of sediment is disturbed,
the plastic surface is checked. This sediment can also be so sedimentary structures cannot be observed.
sampled in order to characterize the material accumulated One method that allows obtaining cores of almost 7 m
during that period. without disturbing the internal structure of the sediment is
Traps for bed load-transported material are installed on vibration coring. This is a fairly simple method that is based
the bottom and aim to capture the grains being transported on the application of vibration at the top end of an aluminum
by bearing, drag or saltation (bed load transportation). The pipe that is introduced into the sediment.
objective is to calculate the real transport capacity of coastal There are several methods for obtaining vibration cores.
currents, in relation to sediment availability. This type of Lanesky vibracores are often used from land or in shallow
trap consists of a metal inlet ramp allowing the bed load water from a floating platform [19]. In this technique, the
material to enter across a window where the sediment is held vibration of an eccentric needle connected to a conven-
in an inner reservoir, while the water flow is diverted tional rotation motor is applied to the tube. This type of
outward. equipment is usually sold by construction material com-
There are various trap models that are frequently used in panies to be used in the compaction of concretes. The
coastal sedimentology. The first to be used was the Nesper, vibrating needle is connected to the aluminum tube through
also called basket samplers, widely used before the 1940s. a piece of steel especially built for this purpose. The alu-
They have good efficiency for sand-type sediments and minum pipe with coupling piece and needle must be
currents greater than 30 cm/s [15]. Recently, the most positioned upright before starting vibration. Once vertical,
commonly used are box and basket models or Helley-Smith it is held in this position while it is introduced into the
type (Fig. 6.20c). These traps have greater efficiency and are sediment using tensor straps (Fig. 6.21a). After being
easier to install [9]. Somewhat less used are the tray traps, introduced, the core is removed with a differential pulley
which present the appearance of a solid steel case. Polyakov resting on a tripod, ensuring the sediment’s recovery by
traps belong to this type (Fig. 6.20d), presenting a slightly using a rubber cap.
higher efficiency than those of basket type [26]. Vibration probes can also be performed from the boat,
and in this case they are called vibrocorers. Here, the
vibration mechanism is coupled directly at the end of the
6.6 Methods to Study the Sedimentary pipe, also exerting a weight on it. When operating under-
Record of Coastal Environments water, the verticality of the tube should be adjusted through a
leg structure supported at the bottom (Fig. 6.21b). The
In the more continental area of the coasts, classic rotation removal of the sediment core is performed from the vessel
cores are usually used. This type of sampling has the using a winch. It is necessary to ensure the preservation of
advantage of reaching to considerable depth, allowing one to the sediment inside the tube by using an egg-shaped
analyze the lithological sequence in a fairly complete way. sphincter valve similar to that used in gravity corers.

sediment traps. a Suspended
sediment traps. b Surface trap
installed on an intertidal flat.
c Box and basket trap
(Helley-Smith type). d Tray trap
(Polyakov type)
Advanced Box 6.1: Cutting the Cores

Once sediment cores have been obtained by any of the 6.7 Geophysical Methods for the Study
above-described methods, it is necessary to access the of the Geometry of Coastal Sedimentary
sediment inside the plastic or aluminum coating for the Bodies: Seismic Reflection
study of the facies and the corresponding sampling. It is
very important that the sediment of the core is not altered Geophysical methods are usually used to study the marine
or contaminated during the opening process, so the saw sub-bottom and, in particular, that located in coastal envi-
should cut only the coating without damaging the ronments. These methods are based on measuring the
sediment. physical properties of the materials that constitute the sub-
When cutting on the vessel during the sampling survey, a surface when they are traversed by a sound wave. Methods
manual grinder is usually used (Fig. 6.22a). At first, a lon- such as high-resolution seismics are often used for the study
gitudinal cut must be done to continue with a second one of coastal sedimentary records.
along the diametrically opposed side. The objective of seismic methods is to determine the
If the cutting is made in the laboratory, there is also the structure and geometry of sedimentary bodies through the
possibility of mounting the grinder on a stand with guides on physical properties of subsurface lithologies. Seismic
which the pipe sits. A saw integrated into a cutting table can reflection acquisition systems consist of three elements: an
also be used in the laboratory. In this case, those used for emitting (seismic) acoustic source, a chain of receivers
cutting wood, aluminum or building material (Fig. 6.22b) (streamer hydrophones) and data processing and filtering
may be appropriate. software. Both the emitter and receiver are dragged by the
Once the cylindrical coating has been cut into two valves, ship along pre-set tracks to obtain the seismic profiles.
the sediment is cut by passing a guitar or nylon string In the case of acoustic pulse emitters, marine seismic
through the two opposite slits. So, the cores are opened in studies may use different energy sources that are classified
two halves, already prepared for study (Fig. 6.22c). according to the nature and frequency of the emitted pulses
6.7 Geophysical Methods for the Study of the Geometry of Coastal … 69
Fig. 6.21 Vibration cores.

a Lanesky vibracore. b Vibrocore
VGK from Geomares (Colombia)
operated from a vessel
Fig. 6.22 Cutting the sediment

cores. a With a manual grinder.
b By using a cutting table.
c Example of a sedimentary
sequence observed in a core
Fig. 6.23 Systems for the

emission and reception of
acoustic pulses during the
acquisition of seismic profiles.
a Small compressed air cannon.
b Sparker type plasma transducer.
c Boomer type piezoelectric
system mounted on a floating
catamaran. d Integrated
emitter-receiver system in a
sub-bottom profiler. e Small
hydrophone streamer. f Example
of a seismic record obtained with
a parametric sub-bottom profiler
(Fig. 6.23). From this regard, it should be borne in mind that (Fig. 6.23d) are also common. They allow one to obtain
lower frequencies manage to record thicker subsurface pro- profiles at a very high resolution, but do not reach across
files, but at lower resolution, while sharper frequencies more than a dozen meters. So, their usefulness is limited to
achieve higher resolution but lower penetration into the the geometry of the most superficial units of the record of
subsurface. estuaries, deltas, tidal flats, tidal deltas and beaches.
Compressed air cannons (Fig. 6.23a) and also water Regarding the reception of the acoustic signal, in the
cannons are often used to achieve a record of greater low-frequency systems the hydrophones are arranged in a
thicknesses. These emit frequencies so low that they can long streamer (Fig. 6.23e). This streamer is transported
reach several kilometers thick, so they are often widely used behind the vessel to collect pulses that return with much
in continental shelf studies, but not in coastal environments. delay after crossing a large sediment thickness. In higher
Another source of emission are plasma transducers or frequency systems, such as boomers or sub-bottom profilers,
sparkers (Fig. 6.23b). These work at frequencies between 20 there is not so much delay in the arrival of the signal
and 200 Hz and can reach depths of up to 150 m. They are reflected in the subsurface, so the emitters and receivers are
very useful in large-scale coastal stratigraphy studies. integrated into the same transducer.
In fact, the devices most commonly used in coastal sed- The wave field recorded by hydrophones consists pri-
imentology are piezoelectric transducers or (boomers) and marily of the reflections generated in the geological dis-
acoustic chirps (sub-bottom profilers). Boomers (Fig. 6.23c) continuities characterized by abrupt contrasts of the elastic
emit pulses between 700 and 2000 Hz and can reach parameters between lithologies (Fig. 6.23f). Seismic
thicknesses of about 50 m. They are frequently used in sequence analysis is the methodology consisting of the
sedimentological studies of the complete record of estuaries subdivision of the seismic section into sets of deposits lim-
and deltas. The most commonly used sub-bottom profilers ited by discontinuity surfaces and comprising groups of
are those working at 3.5 kHz, although parametric emitters more or less concordant reflections with similar character-
with adjustable frequency between 2.4 and 5.5 kHz istics. On the other hand, the analysis of seismic facies
6.7 Geophysical Methods for the Study of the Geometry of Coastal … 71
consists of the description and interpretation of lithologies 14. Harms JC, Southard JB, Spearing DR, Walker RG (1975)
based on the seismic characteristics of the reflections that Depositional environments from primary sedimentary structures
and stratification sequences. Dallas, SEPM Short Course No. 2,
constitute the seismic sequence. 161pp
One problem of the method is that the reflected waves do 15. Hubbell DW, 1964. Apparatus and techniques for measuring
not contain direct information of their propagation speed in bedload. US Geological Survey Water-Supply paper 1748, 74pp
the rocky environment. In this way, the vertical axis of the 16. Janssen P (2004) The interaction of ocean waves and wind.
Cambridge University Press. Cambridge, 300pp
seismic sections is usually represented in time (there and 17. Kanevsky MB (2009) Radar imaging of the ocean waves. Elsevier
back) and not in depth. There are techniques, called depth Science, Alexandria, 191pp
migration, that allow the transforming of seismic sections 18. Karaev VY, Kanevsky MB, Meshkov EM (2011) Measuring the
from time to depth. These are complex techniques to apply parameters of sea-surface roughness by underwater acoustic
systems: discussion of the device concept. Radiophys Quantum
and interpretation requires a considerable level of Electron 53:569–579
subjectivity. 19. Lanesky DE, Logan BW, Brown RG, Hine AC (1979) A new
approach to portable vibracoring underwater and on land. J Sed-
iment Petrol 39:655–657
20. Liu HT, Katsaros KB, Weissman MA (1982) Dynamic response of
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Part II
Coastal Processes
Folding waves, in a foamy tide

of salt and brine,
washing in beds of opal shells,
drift over pools, of salt and clay.
“Alcan Road”
Ween
Wave Processes
7
a physical level there are still some questions regarding the

7.1 Introduction
genetic mechanism.
Perhaps the most dynamically interesting wave classifi-
The waves are undulations of the surface between two fluids,
cation refers to the genesis of marine waves according to
water and air, that have a remarkable influence on coastal
their period [9]. This author established a scale that con-
dynamics. This importance is manifested in the dynamic
sidered capillary waves, gravitational waves and tidal waves
functioning and transport of sediments from open coastal
according to their dimensions. He also established a con-
areas. Waves are also the fundamental cause of the genesis
nection between the types of waves with the primary forces
and evolution of environments such as barrier islands and
that generate them, distinguishing between waves generated
beaches, as well as the erosion of rocky coasts. Thus,
by surface tension with the air, induced by the wind, caused
understanding wave behavior becomes fundamental in
by the action of gravity, generated by the Coriolis force,
interpreting the dynamics of these environments, as well as
produced by earthquakes (seiches and tsunamis), meteoro-
in correct decision-making regarding the design and con-
logical surges and astronomical tides (Fig. 7.1). On this
struction of coastal structures such as groins, jetties, break-
scale, the wavelength and period would increase progres-
waters, seawalls or docks.
sively, as would the volume of water displaced by the wave.
Waves as a phenomenon have claimed people’s attention
In this chapter we will refer only to wind waves, which
from antiquity. In classical Greece, Aristotle was the first to
are understood as ordinary gravity waves, and only wind
reflect on the waves in his treatise on physics (335–322 BC)
waves will be analyzed here. Other undulations of different
and he also linked the wind to the genesis of the waves.
origins are studied in other chapters of this book. So, tides
These reflections were expressed in deeper detail by Ben-
are analyzed in Chap. 8, whereas extreme waves (storm
jamin Franklin around 1774, who described how air moving
waves, rogue waves and tsunamis) will be characterized in
when it passes over the surface of the water exerts a friction
Chap. 13.
that deforms this surface into ridges and troughs that move
in the direction of the wind. It was not until the early
nineteenth century, though, that Gerstner [6] articulated the
first wave theory, describing the circular movement of the 7.2 Genesis of Wind Waves
internal liquid particles.
Since the works of Airy [1] and Stokes [10], it has been Although there are different genetic models, it is well known
known that the dimensions and propagation of sea waves that most waves are generated by the transmission of kinetic
respond to basic theoretical equations that function under energy from the moving air to the surface of a water mass
wave motion theory. However, the coincidence of these thanks to the viscous friction between the two fluids. When
equations and reality do not fully fit, because marine waves the wind speed exceeds a minimum of energy, the first
constitute a complex phenomenon. So, the waves do not waves begin to appear [11], especially when in this wind
have a simple mathematical expression as they do not there are fluctuations or vortices of energy. It is these fluc-
exactly match with sinusoidal functions. Since then, efforts tuations that generate the primary waves. These waves
have been made to simplify the phenomenon in a series of usually have an abrupt surface, as well as a very random and
nonlinear differential equations. Thanks to this, today the chaotic arrangement (Fig. 7.2, left). This morphology pre-
swell is a well-studied and well-known phenomenon, where sents high friction to the action of the wind, without pro-
all the principles are very well established. Nevertheless, on ducing a movement of water rather than at the surface level.

https://doi.org/10.1007/978-3-030-96121-3_7
76 7 Wave Processes
Fig. 7.1 Classification of sea waves according to their period. Adapted from Munk [9]
Fig. 7.2 Mechanisms of genesis

and morphology of wind waves
Since these waves are directly related to the wind that is Although the waves grow when regularized, this growth
generating them, they are known as waves in the generation is limited by dimensions, as the heights and wavelengths
zone or by the name of seas. must be in balance—the maximum ratio (steepness ratio) for
Although it is the wind vortices that generate the irreg- the relationship between heights and wavelengths is 1/7. If
ularity in the sea surface, it is the action of the persistent the height exceeds the maximum elevation for its wave-
wind speed in a single direction that pushes and moves the length, a foam-shaped break occurs, which causes a loss of
ridges to give them an orderly shape. In this way, the waves energy and maintains the height magnitude.
begin to move, ordering on wave trains and continuing to Linking these concepts, the surface of the sea on which a
grow. As the waves move, they leave their generation zone set of waves generated by the same wind spreads is known
and migrate to distant areas known as dispersal zones, as the wave field, while the set of waves of similar dimen-
propagation zones or decay zones. At this time, they grow in sions being generated by the same wind is known as the
dimensions while at the same time becoming regular. In this wave train. The dimensions of the waves of the same train
process, the ridges are softened, adapting to a shape close to —i.e., genetically related—can be statistically analyzed
a sinusoidal function, thus decreasing the surface friction through spectral analysis.
(Fig. 7.2, right). Propagation can be carried out through
hundreds of kilometers. These types of waves that appear
outside their generation zone are known as background 7.3 Morphology and Dimensions of Wind
waves or swell waves. The characteristics of the prevailing Waves
wind acting on them may be different from the generating
wind, or there may even be no wind. The dimensions From a morphological point of view, it has already been said
reached by these waves are based on the wind speed and the that the ridges and troughs of seas and swell waves have
water surface on which it acts without changing its direction distinct morphologies. Usually seas have a trochoidal shape
—a parameter known as the fetch. (with pointed ridges and rounded troughs), while swell
7.3 Morphology and Dimensions of Wind Waves 77
In view of the movement of the water mass, the main

difference between the two types of waves is that the sea
wave is a surface wave that does not transfer movement to
the mass of water in depth. However, the swell wave gen-
erates a movement of water particles in circular orbits until it
reaches the WBL. Any coastal area can be affected at dif-
ferent times by the two types of waves, with one of them
being able to dominate over the other during the time of
action on the coast. It is interesting, then, to know the
relationship between the two types of swell in a given
coastal area.
Whatever the type of waves, as mentioned above,
dimensional and dynamic parameters are usually set statis-
tically for the spectrum wave set (Fig. 7.4). For this type of
Fig. 7.3 Morphology of sea and swell waves and the main parameters analysis, data obtained from measurement stations of dif-
characteristic of the waves
ferent types, which have been described in Sect. 6.2.1, are
used. The following parameters are often used to charac-
waves show sinusoidal morphologies (Fig. 7.3). The terize the dimensions of the train:
parameters that characterize both types of waves are the
same as those involved in any undulatory phenomenon. In a • Significant height (Hs or H1/3): This is the average height
characteristic wave, the elements characterized below can be of the highest third of the waves in the spectrum. It is a
distinguished. measure that usually coincides with visual estimations
and has been classically used by geologists to character-
• Wave crest: Higher level reached by the surface of the ize the average energy of coastal environments and by
water at the passage of the wave. coastal engineers to calculate the construction of
• Wave trough: Lower level reached by the surface of the structures.
water at the passage of the wave. • Significant wavelength (Ls or L1/3): This is the wave-
• Wave amplitude or wave height (H): Vertically measured length corresponding to the greatest third of the major
distance between the crest and trough of the same wave. waves of the analyzed train. It is mainly used to calculate
• Wavelength (L): Horizontally measured distance between the depth of the wave base level, and is not a widely used
two successive crests (or two troughs). parameter in coastal engineering.
• Wave period (T): The time elapsed between the passage • Significant wave period (Ts or T1/3): This is the average
of two successive crests (or two troughs) by the same time of passing between different ridges in the greatest
point. third of the major waves of the train. It is a widely used
• Wave speed (C): Distance traveled by the wave in a unit parameter when determining the frequency of the waves
of time. It can be calculated through the ratio between the acting on a given coast, i.e., the number of waves acting
wavelength and the wave period. on a coast per unit of time.
• Wave base level (WBL): This is the depth at which a
volume wave is able to move orbitally the water mass. It In addition to the parameters of the significant waves, the
is set as half of the wavelength. mean wave parameters of the entire train and the parameters
of the maximum wave of the train can be used, as well as
The crest and trough of the wave are morphological other dimensions of interest:
parameters, while the height and wavelength are known as
dimensional parameters. Period, velocity and wave base • Mean height (Hm): Arithmetic average height of all waves
level are dynamic parameters. In this regard, it must be borne in the spectrum.
in mind that swell waves are part of regular wave trains • Mean wavelength (Lm): Average wavelength of all waves
whose propagation responds to a periodic movement, so the in the spectrum.
dimensions of each wave do not depart too far from the • Mean period (Tm or Tz): Average period of all waves in
average dimensions of the train. On the contrary, seas are the spectrum. This parameter is often also referred to as a
irregular waves and their dimensions must be measured zero-crossing wave period.
individually, without there being a relationship between the • Mean quadratic height (Hrms): Obtained by calculating
dimensions of the whole set. the square root at the mean of the heights. It is a
78 7 Wave Processes
Fig. 7.4 Representation of the wave spectrum obtained in a season over a short period of 10 min and, below, curves of percentage of heights
(H) and periods (T). The graphs indicate the statistical indices that are usually characterized on these dimensional parameters
parameter that is directly associated with the significant analysis can be more easily performed by taking into account
height through the ratio Hs/Hrms = 1.41. the propagation directions of wave trains (directional analy-
• Maximum wave height of the spectrum (Hmax): Corre- sis) but it can also be performed in cases where the directions
sponds to the height of the largest recorded wave. have not been recorded (scalar analysis). Actually, the
• Spectral peak period (Tp): The peak period corresponds application of spectral analysis equations is widely used in
to the wave period that reaches the maximum energy engineering, but it escapes the objectives of coastal geology,
level of the full wave spectrum. It is a widely used so they will not be detailed in this chapter. These equations,
parameter in coastal engineering. as well as all the theoretical development of the wave theory,
can be found in the Shore Protection Manual [3].
When performing a statistical analysis, it should also be
taken into account that a wave spectrum can show a distri- Advanced Box 7.1
bution of energy in different frequency bands, especially Studying a Wave Record
when it comes to the spectrum of a field of irregular waves, The characterization of a wave train whose registration
because this type of wave field often includes waves from has been obtained through any of the methods described in
several overlapping trains. This fact makes a wave spectrum Sect.6.2 can be carried out dimensionally and also direc-
more than one energy spike. Using a medium parameter as tionally. For dimensional study the record is usually divided
the only element to characterize the dimensions of a wave into regular periods (of one or several hours). The full
spectrum should be done with appropriate precautions. spectrum of that period can be represented in a time–height
In general terms, to avoid this problem so-called spectral curve. For each time interval, the heights and periods will be
analysis is performed. Keeping in mind that a wave record or represented in the form of frequency curves or histograms.
irregular spectrum is composed of several harmonic wave These graphs represent the dimensional parameter on the x-
trains of different frequency, a separation of these trains can axis, while the y-axis represents the percentage at which
be performed through harmonic or Fourier analysis. This those values have been reached, taking as the reference value
7.3 Morphology and Dimensions of Wind Waves 79
for the calculation the total number of waves, similar to what 7.4 Wave Energy and Power
is shown in Fig. 7.4.
In previous sections it has been mentioned that movement
For each time interval, the dimensional parameters are transmitted by the wind to the waves in its generation zone is
statistically determined, commonly using the significant not transmitted in depth, and therefore the movement of the
height and period as the most representative of the train, water mass is limited to the surface. However, regular waves
although the maximum height reached during that period is displace a larger volume of water in an orbital motion of
also used. particles that extends deep to half their wavelength. Either
The significant height and period values of each time way, this orbital movement, as well as the spread of the
interval can be represented on time in monthly or annual wave in space, causes energy transfer in the shallowest
spectra (Fig. 7.5). These are very representative of the tem- layers of the seawater mass. This energy has two main ori-
porary distribution of wave dimensions in the medium term. gins. On the one hand, the waves have a potential energy
The data thus obtained are also used for statistical frequency associated with the elevation and descent of the water sur-
analyses, in order to characterize the dimensions of the annual face from an initial flat level (i.e., sine/wave crest). On the
average swell. Analysis of the dimensional ratios between other hand, the orbital movement of water particles confers a
heights and periods can also be performed from this data. velocity to the fluid particles that gives the phenomenon a
Once the average and maximum annual data have been kinetic energy. The sum of both energies is proportional to
obtained, year-on-year comparative analyses are also carried the wave height and water density according to Eq. (7.1).
out. This results in drop probability graphs and calculations
of return periods of waves of certain dimensions. E ¼ 1=8 qgH2 ð7:1Þ
For directional characterization, wind rose diagrams are
In this equation, q is the density of water and g is the
used. These diagrams represent the dimensions of the waves
acceleration of gravity.
in the form of columns of different width, oriented according
One of the consequences of this equation is that wave
to their direction of origin (Fig. 7.6a). As measurement
energy depends on the square of height. This means that an
stations are normally located in sectors far from the coast,
increase in height to double will result in a four-fold increase
waves from all directions are usually recorded. From this
in energy. On the other hand, it is necessary to note that this
you can eliminate the ground-facing directions, leaving only
concept actually corresponds to the amount of energy per
the directions of the waves approaching the coast. In this
unit area as it is measured in J/m2, so it is also known as
type of study, a dimensional characterization can also be
energy density. Thus, the total energy associated with a
performed according to the provenance. This characteriza-
long-period wave is greater than that of a short-period wave
tion will follow the steps marked in the previous paragraph
because the long-period wave has a longer wavelength and is
and can end with a distance probability diagram for each of
distributed over a larger surface area.
the directions (Fig. 7.6b).
Fig. 7.5 Example of a wave

spectrum during the year 1990 for
a SW wave measurement buoy
from SW Europe with data
averaged in three-hour intervals
80 7 Wave Processes
Fig. 7.6 Example of directional wave characterization. a Wind rose diagram. b Graph of exceedance probability
Another energy expression that is commonly used is parameters, the state of the sea can be accurately determined
energy flow (P) or wave power. This is expressed according from direct wave measurements or also visually.
to Eq. (7.2). In 1920 British Navy Captain Henry Percy Douglas
created a simple scale for the naming of sea states according
P ¼ CE ð7:2Þ to the rugosity of the sea, as a visual reflection of the height
In this equation C is the propagation velocity and E the of the waves. This scale was quickly accepted by the inter-
total energy. national community, today being called the Douglas sea
In this case it should be noted that C is the propagation scale, also known as the “international sea and swell scale.”
velocity of the entire wave train, which may be different The scale is simple and consists of ten values, listed from 0
from the propagation speed of the individual waves. to 9, accompanied by a description that can be applied in a
very intuitive way (Table 7.1).
7.5 Sea State and Dimensional Scale

of Waves 7.6 Wave Propagation and Shoaling
The general conditions of the sea surface at a given place Previous paragraphs have described the propagation of
and time according to the absence or presence of waves is waves outside their generation zone as a movement of wave
known as the state of the sea. This state is characterized trains, which can travel hundreds of kilometers on open
according to the magnitude of the dimensional parameters ocean surfaces. This propagation involves a wave ordering,
(height, wavelength and period), as well as the state of as well as an orbital movement of water beneath the surface
energy and power. Being characterized by measurable to a depth that equals half the wavelength. According to
Table 7.1 International sea and Degree Average height (m) Description
swell scale suggested by Douglas
in 1920 0 0.00 Calm
1 0.00–0.10 Rippled
2 0.10–0.50 Smooth
3 0.50–1.25 Slight
4 1.25–2.50 Moderate
5 2.50–4.00 Rough
6 4.00–6.00 Very rough
7 6.00–9.00 High
8 9.00–14.00 Very high
9 +14.00 Phenomenal
7.6 Wave Propagation and Shoaling 81
Fig. 7.7 Movement of water particles at the passage of the swell (d = depth; L = wavelength). a In deep water. b In intermediate waters. c In
shallow waters
wave theory [1, 11], in deep waters, where the base level of In intermediate waters, when the interaction with the
the waves is above the bathymetry (d > L/2), the swell does bottom begins, the velocity becomes dependent on the
not interact with the bottom and the orbital movements are relationship between gravity and wavelength with depth,
circular, with orbits that become minor in depth (Fig. 7.7a). through a more complex hyperbolic trigonometric function,
In this case, wave trains move at constant speed and the expressed by Eq. (7.4).
wave maintains its dimensions as it spreads. rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
As wave trains enter coastal areas with depths below the gL 2pd
C¼ tanhð Þ ð7:4Þ
base level (d < L/2) an interaction with the bed begins. This 2p L
process of propagation to shallower waters is known as
where L is the wavelength and d is the depth.
shoaling. Interaction with the bottom results in a deforma-
The fact that in intermediate waters the velocity becomes
tion of orbital movements, which transform into ellipses,
directly dependent on the depth, even though a complex
where height movement tends to decrease faster than hori-
function, implies that a decrease in depth necessarily leads to
zontal swing movements (Fig. 7.7b). The loss of depth
a slowdown of the waves.
makes the ellipses more and more eccentric (flatter and
This dependence is further increased on shallow waters
elongated). The waters where this depth decrease occurs are
where speed becomes a direct function of depth in a simpler
known as intermediate waters. In the depths where the
way, according to Eq. (7.5).
orbital movement speed exceeds the threshold of particle
movement, a portion of the wave energy begins to be pffiffiffiffiffi
C ¼ gd ð7:5Þ
transferred to the bed.
The process of elongation of the ellipses culminates in the Shoaling directly results in a deformation of wave trains
shallow waters, where the ellipses finally disappear. Then, that are subject to depth loss according to two common
the vertical movements are removed and only the horizontal effects of wave propagation: refraction and diffraction.
movements of swing remain (Fig. 7.7c). In general, it is
estimated that shallow waters where this phenomenon occurs
are below one 25th of the wavelength (d < L/25). 7.6.1 Wave Refraction
Interaction with the bed also results in a decrease in the
speed of the waves from a depth less than the WBL. This Since the wave speed is a ratio between wavelength and
decrease in depth follows the rules set out by Knauss [8], so period, the progressive decrease in the speed of approach to
that in each type of water the equation governing the speed the shoreline results in a decrease in wavelength [1]. When
of the wave responds to different functions and variables. the direction of the wave train approaching the coast takes
In deep water, where the depth is greater than half the place in an oblique direction to the shoreline, the ridges
wavelength, the velocity is regulated by Eq. (7.3). So, the begin to experience a greater approach in the shallower area
speed of the waves depends simply on the acceleration of than in the deeper area. You could then differentiate seg-
gravity and the wave period. ments of the same crest of waves traveling to different depths
and therefore at different speeds. In this way, the ridges of
gT
C¼ ð7:3Þ the tails take on a curved shape. This phenomenon is known
2p as wave refraction and as such is regulated by principles
where C is the speed of the wave, g is the acceleration of complying with Snell’s Law, which characterizes the change
gravity and T is the wave period. in speed of a wave when it passes through environments of
82 7 Wave Processes
different nature. In this case, the variation in the orientation elements such as river mouths, inlets, bays, capes and
of the wave ridges can be determined by the angular rela- promontories that prevent perfect linearity. Because of this,
tionship between the wave ridges and the isobaths, according the schemes of waves approaching to the coast tend to be
to Eq. (7.6) (Fig. 7.8). complex. In general, in these schemes the waves approach in
areas where the decrease in depth is more abrupt and sepa-
d1 d2 d3
¼ ¼ ð7:6Þ rate where the isobaths are distant. The result is a concen-
sin a1 sin a2 sin a3 tration of waves on the headlands and a dissipation in the
bays. This explains why capes tend to be erosive zones,
In a segment of rectilinear coastline with parallel iso- while the products of that erosion end up being transported
bathic lines, such as the one shown in Fig. 7.8, the result is and sedimented in the bays (Fig. 7.9).
that the wave ends up reaching the coast in an almost parallel Either way, in a coastal stretch where a bathymetric map
way and, of course, at a much lower angle than the initial is available, a wave refractive scheme can be built from the
approach angle. However, in nature there are coastal stret- initial approach direction and by applying Snell’s Law to
ches that are far from straight and with parallel isobathic each point of the bathymetry. The refractive schemes thus
lines. In fact, it is common that the presence of sandy shoals, obtained are very useful for understanding coastal dynamics
bars and rocky elements distort the linearity of bathymetric in open areas and are widely used by coastal geologists and
curves at the bottom. Similarly, coastlines usually contain engineers in areas where coastal works are projected.
Fig. 7.8 Wave refraction by

shoaling and the application of
Snell’s Law, where d1, d2 and d3
are the depths marked by isobaths
and a1, a 2 and a3 are the values
of the angles between the isobaths
and the wave ridges
Fig. 7.9 Example of a wave

refraction scheme in a zone of
headlands and bays
7.6 Wave Propagation and Shoaling 83
7.6.2 Wave Diffraction This phenomenon allows the wave trains to enter
restricted areas of the coast, either naturally, as restricted
Diffraction is a phenomenon that occurs as a result of bays or lagoons, or artificially, as ports. For its effects on the
interference from a wave with an obstacle that stands in its coast, diffraction is a phenomenon inevitably linked to
way. When this occurs, after this obstacle there is a shadow refraction, and wave propagation schemes in coastal areas
zone to the swell. The obstacle causes a deformation of the are the joint result of both phenomena. An example can be
wave that is incurved to access the shadow sectors behind it, seen in Fig. 7.11.
so that a kind of envelope takes place (Fig. 7.10). The
phenomenon is associated with a lateral transfer of energy at
the end of the crest of the wave after the obstacle, extending 7.6.3 Littoral Drift
to the shadow zone [7]. To understand this in an easy way, it
is often said that by diffraction the waves “bend around The oblique arrival of wave trains to the coast due to
corners.” refraction and diffraction phenomena results in a zigzag
movement in the sediment particles of the bed along the
coastal fringe that is topographically above the WBL (in-
termediate and shallow waters). Each wave arrives with a
direction whose transport vector acts perpendicular to the
crest of the wave. During the swash the sediment particles
are transported at a forward slope, while when the backwash
occurs it does so perpendicular to the shoreline. The two
components of the wave, swash and backwash, result in a
movement of the particles parallel to the coast in the sense
where the angle between the crest of the wave and the
coastline opens. This results in the appearance of a transport
component parallel to the coast known as littoral drift or
longshore transport (Fig. 7.12). So, littoral drift (or long-
shore transport) is the term used to define the transport of
sediment along the frontal area of the coast caused by the
oblique action of breaking waves.
The magnitude of longshore sediment transport becomes
of more or less relative significance depending on the
magnitude of waves and the angle of incidence of wave
Fig. 7.10 Example of a wave diffraction scheme trains. The variability over time of the incident waves causes
Fig. 7.11 Example of

propagation scheme with
refraction and diffraction acting
together. a Original waves.
b Diffracted waves. c Interference
of two diffracted wave systems.
d Diffracted and refracted waves.
(Image Landsat/Copernicus from
Google Earth.)
84 7 Wave Processes
Fig. 7.12 Generation of littoral

drift by the arrival of waves
oblique to the coast
oscillations in the drift transport, both in its magnitude and in of foam spills to the front (Fig. 7.13a). From the moment this
the sense of the same. The net balance of material trans- occurs, the spill moves through a surf area of some length as
ported will depend on the frequency in which the waves of the wave gradually loses height due to energy dissipation.
different directions and dimensions act. When the wave finally reaches the beach, most of the energy
has already dissipated and the wave has decreased its
dimensions until the swash and backwash result in very
7.7 Dissipation of Wave Energy slight movements.
Plunging breaker: This is the type of wave in which the
7.7.1 Wave Breaking forward front of the wave becomes vertical and ends up
curling towards the base, forming an air tube inside the wave
It has been described how, in shallow waters, there is a (Fig. 7.13b). In this case, the surf area is not as long as in the
dissipation of energy due to interaction with the bed. On the
one hand, there is a deformation of the orbits, which become
excessively eccentric causing the waves to lose height. On
the other hand, the ridges approach each other so that the
wavelengths are shortened. The relationship between the
decrease in height and wavelength is of paramount impor-
tance, because if a factor of 1/7 is exceeded the wave breaks.
The breaker is manifested in the appearance of foam on
the crest of the wave that forms when the orbital velocity of
the wave crest exceeds the propagation velocity of the wave.
It is clear that in coastal areas it occurs because the wave is
slowed when interacting with the bottom, while the speed of
the crest is maintained despite the deformation of the motion
orbits. Once the breaker starts, it is maintained during the
wave propagation until the swash reaches the shoreline. This
breaker propagation area is known as the surf zone.
The length of the surf area is variable according to the
dimensions of the waves in relation to the nature of the
bottom and the slope of the coast. How this break occurs can
also vary from one area to another. Most authors describe
three different types of breakers: spilling, plunging and
surging. In addition, other authors (e.g., Galvin [4]) include a
fourth type: collapsing (Fig. 7.13).
Spilling breaker: Characterized by a progressive increase
in wave height as its wavelength decreases until a soft crest Fig. 7.13 Different types of wave breaker Galvin [4]
7.7 Dissipation of Wave Energy 85
previous example and the wave energy dissipates into a use of a breaker index (B), related to the dimensional
much narrower fringe, in which the backwash between parameters of the wave (height and period) and the slope of
waves is the dominant movement. This is the most iconic the beach according to Eq. (7.7).
type of breaker and, of course, is preferred by surfers.
H
Surging breaker: In this type of breaker, the crest of the B¼ ð7:7Þ
wave remains with a relatively mild sinusoidal shape so that gmT2
it reaches the coast without forming true breakers
where B is the breaker index, g is the acceleration of gravity,
(Fig. 7.13c). The dissipation of energy in this type of break H is the wave height, T is the period and m is the beach
is minimal and usually a new wave that moves in the
slope.
opposite direction is formed by reflection.
Thus, for B values higher than 0.068 a spilling breaker
Collapsing breaker: In this case, the wave front also
will form; for values between 0.003 and 0.068 a spilling
becomes vertical because the base of the wave is sharply
breaker occurs; finally, for B values less than 0.003 a surging
slowed. Unlike the enveloping swell, the collapse of the top
or collapsing breaker will be formed. There are other
of the wave occurs in an abrupt and turbulent way, without
equations that have tried to use these same parameters to
forming a curl (Fig. 7.13d). Actually, in his definition Gal-
narrow the genesis conditions of each of these breakers.
vin characterizes it as a transitional type between plunging
A comparative synthesis of these equations was made by
and surging.
Camenen and Larson [2]. This work shows that, while some
The type of breaking wave has direct consequences on
equations work better than others under certain conditions,
the erosional or depositional conditions of the beaches. The
they all use the ratio between slope and height as a defining
spilling breaker is dominated by swash, so produces land-
variable. One of the consequences that can be derived from
ward sediment transport and is therefore a break that tends to
the use of these indices is that an increase in slope has the
deposit sediment. On the other hand, in plunging and col-
same effect as an increase in wave height. On the other hand,
lapsing type breakers, the backwash component and there-
a wave of certain dimensions may present different breakers
fore the erosion predominate. Finally, reflection
on beaches of different slopes. This explains the different
predominates in surging and this is a breaker that also
erosive–cumulative behavior of beaches with different slopes
generates very erosional conditions.
in front of the same waves.
A factor of great importance when studying the interac-
tive relationship between the waves and the coast is the slope
of the coast, since the slope conditions the horizontal
proximity of the first interaction of the wave on the bed. So, 7.7.2 Wave Reflection
it is the main factor for the gradient of energy loss of the
wave in its break, as well as the length of the surf area. The There are coasts whose bed morphology causes the waves to
steeper or slighter slope of the beach directly conditions the reach the coastline without dissipating its energy at the
type of breaker and has direct consequences on the direction bottom, or with a minimal dissipation. In this case, the swell
in which the discharge of energy occurs on the sedimentary is reflected on the coast, forming trains that return to the sea.
material of the beach. In this sense, Galvin [5] proposes the This phenomenon is associated with very high sloped coasts
Fig. 7.14 Wave reflection

pattern on an ideal vertical coast
86 7 Wave Processes
or nearly very vertical areas such as cliff systems or artificial 2. Camenen B, Larson M (2007) Predictive formulas for breaking
walls. In all cases, reflection is also associated with surge depth index and breaker type. J Coastal Res 23:1028–1041
3. CERC (1984) Shore protection manual. Coastal Engineering
breakers. The direction of the reflected waves depends on the Research Center. US Army Corps of Engineers, Washington DC
angle between the incident wave trains and the coast at 4. Galvin CJ (1968) Breaker type classification on three laboratory
which they break (Fig. 7.14). In general, wave reflection beaches. J Geophys Res 73:3651–3659
follows the laws of any kind of undulatory reflection. 5. Galvin CJ (1972) Wave breaking in shallow water. In: Meyer RE
(ed) Waves on beaches. Academic Press, New York, pp 413–456
Actually, the phenomenon of reflection is also present on 6. Gerstner FJ (1802. Theorie der Wellen samt einer daraus
lower sloped shores, although in these cases the reflected abgeleiten Theorie der Deichprofile. Abhand der König. Bömis-
waves have much smaller dimensions than the incident chen Gesel. d. Wiss. Prague
waves, having dissipated most of their energy in the 7. Iribarren R (1964) Obras marítimas. Oleaje y diques. Dossat,
Madrid, 376 pp
breakers. In these cases, although the phenomenon is not 8. Knauss JA (1997) Introduction to physical oceanography. Prentice
visible, it can be measured through the interaction between Hall Inc.
reflected waves and the incident swell. 9. Munk WH (1951) Origin and generation of waves. In: Proceedings
of the conference of coastal engineering, vol 1. ASCE
10. Stokes GG (1847) On the theory of oscillatory waves. Trans
Cambridge Philos Soc 8:441–455
References 11. Tricker RAR (1964) Bores, breakers, waves and wakes: an
introduction to the study of waves on water. Mills and Boon,
Cambridge, 250 pp
1. Airy GB (1845) On tides and waves. Encyclopaedia Metro 5:241–
396
Tide Processes
8
The strength of the tides has surely been known and

8.1 Introduction
exploited since ancient times, however, with the first to
describe practical applications of their use being Islamic
The sea surface, far from remaining static, experiences
authors. At the end of the tenth century, Al Mohaddasi was
periodic oscillations related to the gravitational pull of the
the first to describe how to obtain a mechanical performance
orbiting spheres. These oscillations constitute the phe-
from the tidal force, by applying it to the movement of flour
nomenon called the tide. The tide behaves like an oceanic
mills. Scientific studies about the tides culminate in the
wave; in fact, as mentioned in the introduction to Chap. 7,
statement of dynamic tide theory, which we will discuss
tidal waves are the waves with the longest wavelength. As a
later.
directly observable phenomenon, the tide consists of a cyclic
The action of tides has a remarkable influence on the
ascent and descent of the sea surface. This movement is
coasts and there are coastal environments clearly dominated
divided into two semi-cycles called rising tide and falling
by the action of the tides. However, only 27% of the time
tide (Fig. 8.1). Each semi-cycle is limited by a moment of
are tides able to transport sandy sediment [12], so
maximum level called high tide and a minimum level called
tide-dominated coasts are classically associated with the
low tide. Like other sea waves, tidal waves propagate by
deposit of lutitic materials. Among these environments that
generating currents called flood and ebb.
are heavily influenced by tides are marshes, tidal flats, inlets
Knowledge about and observation of the tides have been
and tidal deltas, lagoons, estuaries and deltas. In order to
rooted in coastal towns since ancient times, although there
understand the dynamic functioning of these environments,
are few records of the phenomenon in the classical texts,
it is necessary to understand in depth the phenomenon, as
since the Greek populations settled on tidal-free coasts.
well as its action on the coast, which differs from the
However, there are several significant citations based on the
dynamics in the open sea.
contacts between Mediterranean civilizations and the peo-
ples of the southwest of the Iberian Peninsula.
Pythagoras was possibly the first to describe the phe-
nomenon and establish its cycles mathematically, although 8.2 Genesis of the Tides
without reaching conclusions about its origin. The first early
reflections on origin were made by Pliny the Elder in the first The genesis of tides is related to the gravitational action of
century of our age. Thus, this Roman sage correctly attrib- the Moon and the Sun on the mass of oceanic water and is a
uted the cycles to the joint action of the Moon and the Sun. well-known and studied phenomenon that is stated in the
Despite these early observations, it was not until the “theory of tides.” The mathematical foundations of this
seventh century that it was concluded that this was a pre- theory were firmly established by Pierre-Simon de Laplace
dictable phenomenon and for the first tidal calendar to be in 1778. Laplace described the equations that govern the
drawn up. It is not surprising that it was a Benedictine monk dynamics of fluids in the mass of ocean water. The French
who carried out these studies, after 19 years of thorough physicist based his equations on the principles of universal
observations—the Venerable Bede knew Latin and Greek gravitation established by Newton almost a century earlier,
and was familiar with the texts of classical authors. His although he modified his formulation by introducing the
researches on the tides are collected in his work De natura strength of the Coriolis effect, and did so 60 years before the
rerum. The Anglo-Saxon friar’s work had direct application formal definition by Coriolis.
in his own country six centuries later, when the first tide The phenomenon of tides can be understood intuitively if
tables were recorded at London Bridge. we look at the relative position with respect to the Earth of the

https://doi.org/10.1007/978-3-030-96121-3_8
88 8 Tide Processes
Fig. 8.1 The elements of a tidal wave
spheres that generate the gravitational forces that give rise to

the variation of the surface of the sea: the Moon and the Sun.
8.2.1 Earth–Moon System Fig. 8.2 System of forces that generates lunar tides
It is intuitive to understand that the attraction of the Moon

draws water towards it, forming a bulge of the sea surface in 8.2.2 Earth–Sun System
that direction. However, the fact that water also accumulates
on the opposite side requires a more detailed explanation. Like the Earth–Moon system, the Earth–Sun system has a
The Earth and Moon form a simple system of action and common center of mass that, in this case, is located near the
reaction with a common center of mass. This center of mass center of the Sun. This also generates a centrifugal force on
is known as the barycenter, and it approaches the center of Earth in the opposite direction to the gravitational action of
the Earth but does not match it. The rotation around the the Sun and a deformation of the surface of the water in the
barycenter causes the Earth to rotate eccentrically, generat- same direction. In this case, the action of this force is
ing a centrifugal force on the face farther from the Moon and understood in a more intuitive way if we imagine the
acting counterclockwise to the sphere’s force of gravity deformation of a balloon full of water turning tied to a rope.
(Fig. 8.2). This is the force that generates the elevation of the These forces generate two daily high tides and two low tides,
sea on the opposite face of the lunar position. which are called solar tides. Although the mass of the Sun is
These two forces (Moon gravity and centrifugal force) are much greater than that of the Moon, its gravitational force on
responsible for two opposite bulges on the sea surface, one Earth is 2.73 times less due to the great distance that sepa-
facing the Moon and one right on its opposite side, and two rates them, thus the solar tides are smaller than the lunar
perpendicular depressions. The diurnal motion of the Earth tides. There is also an angle of variation between the planes
causes each point of the planet to pass each ridge and of Earth’s rotation and the orbit around the Sun. This angle
depression once, generating two high tides and two low tides is known as solar declination.
daily. These theoretical level variations are known as lunar
tides. The different magnitude of the forces of lunar and
centrifugal gravitational pull causes an inequality between 8.2.3 Earth–Moon–Sun System
the two daily lunar tides.
The Moon’s rotation plane around the Earth does not The rise and fall of the sea surface are actually controlled by
match the normal plane of the axis of rotation of our planet, the sum of lunar and solar tides, so that at each point of the
but both planes form an angle of 28º which is named lunar ocean a force resulting from the gravitational and centrifugal
declination. This plane itself undergoes a variation in time, action generated by both celestial bodies is obtained. When
making the lunar declination vary in cycles of 18 years and the three spheres act in conjunction, there are a number of
11 days. This phenomenon causes the maximum and mini- relative positions between them that will cause a sum or
mum levels of lunar tide to vary over a long time on a given subtraction of acting forces on the marine level to generate
coast. resultant tides. In this way, two extreme positions can be
8.2 Genesis of the Tides 89
distinguished: in alignment (syzygy) and at right angles and with the equatorial plane. The angles between these
(quadrature). planes also undergo periodic variations.
When the three bodies are aligned they are in syzygy There is also an influence that has not been mentioned
(Fig. 8.3a). This situation occurs during the days of the new above, and that is the influence of the distance between the
moon and full moon. At these times, there is an addition of spheres. The orbits of the Earth around the Sun and the
forces when the solar high and low tides coincide in space Moon around our planet are elliptical. That causes the dis-
with the lunar high and low waters, giving rise to the spring tances between each pair of spheres to vary over time.
tides. Conversely, when the three bodies form a right angle, In the case of the Moon around the Earth, the maximum
they are in quadrature (Fig. 8.3b). This is the situation that distance is known as the apogee, and the minimum distance
occurs in the first quarter (waxing quarter) and in the third as the perigee. The difference between the apogee and
quarter (waning quarter). In both cases the forces are perigee is 13% of the average distance between the spheres.
countered. The resulting high waters are less high because Keep in mind that there is a turn of the Moon around the
they are only generated by lunar high tide, while the low Earth passing through these two positions every 27.6 days (a
waters are less low because the lunar low tide coincides with lunar month).
the solar high tide. In this case, the neap tides occur. In the same way, the orbit of our planet around the Sun
The conjunction of the different relative positions also passes through two positions of maximum and min-
between the three spheres results in the presence of biweekly imum distance. In this case the maximum distance is
cycles in the temporal distribution of tidal ranges, alternating known as aphelion and is reached in July, while the
two spring tides and two neap tides in a month, with the minimum distance is known as perihelion and is reached
consequent transitions between them, which correspond to in January. As the mean distance is much greater, the
the transit between the different described positions. These differences between aphelion and perihelion are only about
relative positions actually result from an excessive simpli- 4% of it. It takes 365.25 days to travel through the entire
fication, since the planes of rotation of the Moon around the orbit (a year).
Earth, and this in turn around the Sun, differ between them The concordance between the orbital cycles of the three
spheres influences the magnitude of the solar and lunar tides
and, therefore, the concordance between these tides in the
cycles of spring and neap tides. This is reflected in the
existence of six-monthly cycles where differences between
spring and neap tide ranges vary between apogee, perigee
and their intermediate positions. The result is the alternation
over a year between two solstice tides and two equinox
tides. Equinoxes occur during the apogee and perigee
positions (end of March and September). In those months,
there is a very marked difference not only between spring
and neap tides but also between their two springs and their
two neaps. Solstices, on the other hand, appear in interme-
diate orbital positions (end of December and June). So, the
differences between their two spring tides and two neap ones
are very small.
8.2.4 Dynamic Theory of Tides
In the seventeenth century Laplace established the equations

that would theoretically follow the displacements of the
ocean water mass due to the forces described above. Other
hydrodynamic calculation equations concerning the defor-
mations of fluid masses were drawn up almost at the same
time by Bernoulli and Euler. The application of these equa-
tions together culminated almost a century later with the
statement of William Thomson (Lord Kelvin), who modified
Fig. 8.3 Biweekly cycles induced by the relative Earth–Moon–Sun the conceptions of attraction and centrifugal force expressed
positions in the previous sections, taking into account the friction of
90 8 Tide Processes
Fig. 8.4 Functioning of an amphidromic system. Adapted from von Arx [18]
water with the ocean floor and the distribution of continents introduced into his dynamic theory. In the face of this force,
on Earth. the oceanic system responds by generating different rotation
In the simple models explained in the previous sections, systems, known as amphidromic systems. In each of these
the rotating Earth’s mass seems to rotate freely inside a mass systems the tides rotate around a tidal-free central point
of water deformed by astronomical forces, and yet this called an amphidromic point (Fig. 8.4).
assumption departs greatly from reality. On the one hand, Those rotating waves are often called Kelvin waves.
the mass of water is in friction with the ocean floor in its Each system experiences a rotation that completes every
relative displacement. On the other hand, the existence of the 24 h and 50 min. Around this central point the tidal ranges
continents prevents the free passage of the ocean water mass grow concentrically defining co-range lines that join points
in the rotation of the Earth. Actually, if we change the ref- of equal tidal amplitude. Normally, meter-to-meter lines are
erence system and consider that it is the mass of water that represented, where the value 0 corresponds to the amphi-
moves over the oceans, its displacement would reproduce an dromic point, also called the nodal point. According to this
undulatory phenomenon. scheme, the amplitude of the tide on a given coast depends
The dynamic theory of tides is based on the fact that the on its distance to the corresponding nodal point.
tidal wavelength is too large for the depth of the oceans. Similarly, co-tidal lines define radially which tide is in
Considering a wavelength of several tens of kilometers, we phase. In this case, 12 numbered lines from 0 to 11 are
should have an ocean more than 10 km deep so that there is usually represented, the order of which indicates the direc-
no friction with the bottom; however, the average depth of tion of rotation of the tides around the nodal point. The most
the ocean is considerably less. Therefore, the tide has such a significant co-tidal lines are those that join the minimum
large wavelength that, when moving, it necessarily suffers points (furrow) and the maximum points (ridge). The rota-
friction with the bottom. If we use the equation of the tional passage of the ridge and furrow lines of the sea surface
propagation of a wave in shallow water (E. 7.5), it turns out by a point of the coast coincides with the moments of high
that for the maximum depth of the ocean the highest possible and low tides.
speed for the displacement of the tidal wave is 230 m/s. This There are 15 major amphidromic systems in the world’s
speed is much lower than the Earth’s rotational speed, oceans as well as other minor systems in inner seas such as
causing a delay relative to the position of the maximum the North, the Mediterranean and the South China Seas.
lunar gravitational pull point. On the other hand, the pres- Larger systems and their sense of rotation are represented in
ence of continents limits the rotation of the water prism and Fig. 8.5. This figure also depicts the distribution of tidal
prevents the passage from one ocean to another. ranges on the coasts. You can see the relationship between
In short, the speed of rotation of the Earth is too fast for the tidal range on the coast and the distance from the coast to
the inertia of the water mass. That is the foundation for the the amphidromic point that controls the tides on that coast,
existence of the Coriolis force, whose effect Laplace although there are some discrepancies that are based on
8.2 Genesis of the Tides 91
Fig. 8.5 Major amphidromic systems of the Pacific and Atlantic oceans, with indication of the location of the amphidromic point, the direction of
rotation of the tide and the co-tidal lines. The tidal range of the coasts is also indicated
wave amplification due to the geometry of the coasts. tidal wave, making it able to exhibit different behaviors. In
Another observation that can be made in this scheme is that general, there are three types of tides: semidiurnal, diurnal
there are some coasts in the world that are influenced by two and mixed (Fig. 8.6).
different amphidromic systems. These coasts are affected by Coasts with semidiurnal tides are the most common
tides of a mixed nature with characteristics induced by the around the globe. They are the ones that adapt to the theory
phase between the two tidal waves. explained above, so there are two daily high waters and two
daily low waters (Fig. 8.6a). The period of each tidal cycle is
therefore 12 h and 25 min. Although there is always an
8.3 Tidal Cycles and Tidal Levels inequality of amplitude between the two daily tides, in most
cases the two tides result in a similar magnitude. However,
The tidal regime is one of the main factors of control of there are coasts where the two tides are of a very different
coastal sedimentary dynamics and in particular in the evo- magnitude. An example of these tides can be found in San
lution of estuaries, deltas and tidal flats, because the number Francisco Bay, on the US Pacific Coast.
of hours of exposure and submersion of the intertidal fringe Coasts with diurnal tides are much sparser. In these, only
directly controls the bio-sedimentary zones existing in it [16]. one tidal cycle occurs each day, with a high and a low tide in
periods of 24 h and 50 min (Fig. 8.6b). They are typical of
restricted seas and large semi-closed bays, although they can
8.3.1 Types of Tides Based on Their Periodicity also occur on open shores. The best examples can be found
in the Gulf of Tonkin, between China and Vietnam, although
The theoretical approaches described in the preceding points some sections of the Gulf of Mexico and the Alaskan coast,
mean semidiurnal behavior of the tide. In this way, two high north of the Bering Strait, also have such tides. Open coasts
and two low tides would occur throughout the day. How- with diurnal tides can be found in southwestern Australia,
ever, this behavior does not adapt to the reality of many northern New Zealand and the Antarctic continent.
coasts of the world. On some coasts, the geometry of the Coasts with mixed tides have a complex record in which
bottoms and the physiography of the coastline modify the one part of the tidal cycle functions as a diurnal tide and
92 8 Tide Processes
Table 8.1 Types of tide according to the value of the tidal form factor
(F)
F factor Type of tide
0–0.25 Semidiurnal
0.25–1.50 Mixed dominantly semidiurnal
1.50–3.00 Mixed dominantly diurnal
> 3.00 Diurnal
Once the F values for a given monthly record have been

obtained, the curve can be classified according to the ranges
reflected in Table 8.1.
8.3.2 Tidal Cycles
It has been noted in the previous sections that the origin of

the tidal cycles is related to the relative positions between
the Moon and the Sun to Earth. In this way, cycles of
different durations are characterized throughout a tidal
record. On coasts with semidiurnal tides, shorter cycles are
those that are observed in inequality between the two daily
tides, but in the behavior of the tide following astronomical
patterns have become clear major cycles. Of a longer
duration are the cycles of biweekly character [14], con-
Fig. 8.6 Different types of tide according to their periodicity. Adapted sisting of the alternation of spring and neap tides, so that
from Defant [4] each month there are two spring tides and two neap tides
(Fig. 8.7).
another part is in semidiurnal mode (Fig. 8.6c). They usually In a higher temporal order, there are other variations of
occur in open marine areas influenced by more than one a six-monthly character whose consequence is the alterna-
amphidromic point or in transit between open areas and tion over a year between two solstitial and two equinoctial
semi-closed areas. The generic nature of its definition means tides. In solstices the differences between their spring and
that different models of tidal curve can actually exist neap tides are small (Fig. 8.8a), while in the equinoxes
depending on whether diurnal or semidiurnal behavior there is a very marked difference between them (Fig. 8.8b).
cycles dominate. There are very good examples of this type In successive years the tides differ because the angles of
of coastline along the entire Pacific Ocean and also in the lunar and solar declinations vary over time, and these
Caribbean Sea. variations cause the tide values to be repeated in cycles of
The analysis of tidal curves over a 28 day lunar cycle 17.6 years [2].
allows a quantitative way of classifying the tidal record
among the types described above. The tidal form factor
(F) was established by Defant [4] as a relationship between
the sum of the amplitudes of the diurnal cycles and the sum
of the amplitudes of the semidiurnal ones. This factor can be
calculated according to Eq. 8.1.
ad1 þ ad2
F¼ ð8:1Þ
as1 þ as2
Where F is the tidal form factor, ad1 and ad2 are the ampli-
tudes of the diurnal tides and as1 and as2 are the amplitudes
of the semidiurnal tides. Fig. 8.7 Biweekly tidal cycles in a month
8.3 Tidal Cycles and Tidal Levels 93
Mean Neap Low Water (MNLW), Mean Low Water

(MLW), Mean Spring Low Water (MSLW) and Extreme
Equinoctial Low Water (EELW).
The intertidal strip is thus divided into zones by these
critical levels (Fig. 8.9):
• Zone A: Between the Extreme Equinoctial High Water

(EEHW) and the Mean Spring High Water (MSHW). It
is not submerged more than ten times per month and in
total not more than 20 min per month of submersion
(Fig. 4.19).
• Zone B: Between the Mean Spring High Water (MSHW)
and the Mean Neap High Water (MNHW). Its lower level
is exceeded by 95% of the tides, although only just under
17% are those that reach or exceed its upper level; this is
an average of about 600 h per month of exposure, with
the time that remains exposed being slightly less than
triple that of the submerged time.
• Zone C: This is the real daily intertidal zone, since it has
Fig. 8.8 Six-monthly tidal cycles. a Solstice tides. b Equinox tides
two daily immersions and exposures, when both levels
exceed all tides except the below-average neap tides (less
8.3.3 Critical Tide Levels than 10% of the total tides).
• Zone D: This is located between the limits of the Mean
The cyclic variations experienced by the tide induce an area Neap Low Water (MNLW) and the Mean Spring Low
in the intertidal fringe whose zones are separated by what Water (MSLW). Its upper limit is exceeded by 95% of the
have been called critical tidal levels [6], and which are the low waters, while in contrast not even 2% of the number
topographic levels achieved by the high and low waters of low waters reach the lower level. Thus, it experiences
during one year (Fig. 8.9). In Doty’s approach, which has about 550 h per month of average submersion versus
been adopted by other authors [7, 16], they are called critical about 190 h of exposure.
because they delimit areas that differ in both the number of • Zone E: Under the Mean Spring Low Water (MSLW) and
monthly exposures and submersions, and in the time they over the level of the Extreme Equinoctial Low Water
remain exposed or submerged. This time of exposure and (EELW). It is only affected by about five low tides per
submersion is crucial for the tolerance of the species of month that total no more than five minutes of monthly
organisms that inhabit the intertidal band, as well as for the exposure.
transport of sediment in each of these zones.
The critical tidal levels statistically characterized by Doty Advanced Box 8.1. The Harmonic Constants
are: Extreme Equinoctial High Water (EEHW), Mean Spring According to the periodicity of the orbital changes of the
High Water (MSHW), Mean High Water (MHW), Mean three spheres involved in the genesis of the tides, and the
Neap High Water (MNHW), Mean Water Level (MWL), angular changes between the planes of these orbits, the tides
over time may be considered to be composed of an overlap
of different harmonic waves. A harmonic wave is a variation
that is regulated by a trigonometric function of cosine type.
Each one of these harmonics is regulated by one of the
periodic astral variations (Moon orbital changes around
Earth, Earth orbital changes around Sun, changes in lunar
declination, changes in solar declination, changes in the
distance between Earth and Moon, changes in the distance
between Earth and Sun, and relationships between all these
changes).
Therefore, any tidal wave can be calculated through the

decomposition of its harmonic constants. Such calculations
Fig. 8.9 Critical tidal levels and tidal zonation after Doty [6] were already raised by Laplace in his general tide theory, but
94 8 Tide Processes
later development was due to George [3] and the current must take into account other local factors, such as coastal
statement was formulated by Doodson and Warburg [5]. configuration.
Depending on the period of the harmonic wave, the con-
stants described in Table 8.2 [9] can be distinguished in a
composite tidal wave. 8.4 The Tide and the Coast
The main constants are:
The functioning of amphidromic systems and the distance
• The constant M2 corresponds with the given values of the between the nodal points and the coast satisfactorily explain
tide if the effect of the Sun is neglected and considering the tidal regime recorded on most of the world’s coasts.
the Moon orbit as a perfect circle exactly located around However, there are coasts where the tide does not behave as
the plane of the Equator. expected according to its location. The cause of this dis-
• The constant S2 corresponds to the solar tide considering crepancy must be found in the deformations suffered by the
the plane of the orbit of the Earth around the Sun is a tidal wave when interacting with the coast.
perfect circle in a plane that coincides with the Earth’s On the one hand, there are coastlines located in special
equatorial plane. morphological configurations whose gradients of loss depth
• The combined M2 + S2 form the effect of the ideal Sun or width produce deformations in the tidal wave. On the
and the ideal Moon on tides. other hand, there are coastal stretches that are partially
• The constant N2 considers the non-circularity (elliptical) restricted and form small basins, although connected with
of the Moon’s orbit. So, the tides will be higher in the the open ocean. In the interior of these inner seas, and in
perigee and lower in the apogee. their watersheds with the major ocean basins, there are also
• The diurnal constants (K1, O1, P1) consider other small particular phenomena that force the tidal wave propagation.
variations of the ideal conditions given by the described These causes result in three phenomena that need to be
constants. So, aspects of the lunar and solar declinations studied separately: dissipation by friction with the bottom,
are considered. amplification by convergence and resonance.
Applying the periodicity of at least nine of these har-

monics constituents can be used to obtain a fairly accurate 8.4.1 Dissipation by Friction
forecast of the tide at a given time [15]. These calculations
are based on the establishment of tidal coefficient tables. To As mentioned above, the tide behaves like a propagating
obtain a height table from these coefficients in a given wave and therefore responds to the same equations as the
location, a more precise calibration must be performed that waves. In the open ocean, the wave propagates at a rate of
Table 8.2 Main harmonics Harmonic constant Symbol Character Period (solar hours) Amplitude (%)
constituting a complete tidal wave
[9] Principal lunar M2 Semidiurnal 12.42 100
Principal solar S2 Semidiurnal 12 46.6
Larger lunar elliptic N2 Semidiurnal 12.66 19.2
Lunisolar semidiurnal K2 Semidiurnal 11.97 12.7
Larger solar elliptic T2 Semidiurnal 12.01 2.7
Smaller lunar elliptic L2 Semidiurnal 12.19 2.8
Lunisolar diurnal K1 Diurnal 23.93 58.4
Principal lunar diurnal O1 Diurnal 25.82 41.5
Principal solar diurnal P1 Diurnal 24.07 19.4
Larger lunar elliptic Q1 Diurnal 26.87 7.9
Smaller lunar elliptic M1 Diurnal 24.84 3.3
Overtides of principal lunar M4 Quarterdiurnal 57.97 6.2
Shallow water quarter diurnal MS4 Quarterdiurnal 59.02 6.1
Lunisolar fortnightly Mf Bi-weekly 372.86 8.6
Lunar monthly Mm Monthly 661.3 4.6
Solar semi-annual Ssa Semi-annual 2191.43 4
8.4 The Tide and the Coast 95
more than 700 km/h, but entering shallow waters there is a

sharp increase in friction with the bottom and the rate of
propagation towards the coast decreases very quickly.
Generally speaking, tidal wave speeds on continental plat-
forms are reduced to values ranging from 10 to 20 km/h. In
this process there is also a dissipation of the wave energy,
which results in a reduction of its dimensions. In other
words, the tide loses amplitude when it enters into shallow
waters as it approaches the coast. The rate of decline of
speed depends on the variations in the slope in the shallow
water bottom.
8.4.2 Amplification by Convergence
The geometry of coastal areas has a second effect on the tidal

wave, which is amplification by convergence. This effect
occurs in continental areas whose coastline morphology is
funnel-shaped. As it enters these areas, the tidal wave is
forced to pass through increasingly narrow areas and the
only way the water mass can do so is to amplify the tidal
range. Good examples can be found in the Bay of Bengal
and the English Channel (Fig. 8.10).
The case of the Bay of Bengal (Fig. 8.10a) is the most
extreme case, in which the tidal range rises from an
amphidromic point (null range) located at the entrance of the
bay to 9 m in the Ganges–Brahmaputra delta.
In the case of the English Channel (Fig. 8.10b), ampli- Fig. 8.10 Examples of coasts with tidal amplification due to entry into
fication occurs from the entrance to the channel, starting funnel-shaped coasts. a Bay of Bengal. b English Channel
from 4 m. In this case, the configuration of the French coast,
with funnel-shaped bays, further amplifies the wave, reach-
ing 11 m at Mont-Saint-Michel. On the other front, the 8.4.3 Resonance
English coast does not present this form, but there is a
gradual decrease in depth. Consequently, on this coast the When a tidal wave enters a semi-confined basin, the reflec-
friction effect described in the previous section dominates tion of the wave in the margins of the basin causes a wave
and the tidal ranges decrease. The amplification effect is interaction known as resonance. The final oscillations of the
again noticed towards the interior of the channel, reaching water mass are the result of the initial wave propagated into
9 m in the area of Pas-de-Calais. the basin and the wave reflections on its shores. When the
Normally, the effects of friction with the bottom and phenomenon takes place on a small scale, the result is a
convergence work together, especially in coastal inlets such stationary wave that is governed by the equations of the
as bays and estuaries. The decrease or amplification of the principle derived by Merian [13]. According to this princi-
tidal range will depend on what is the dominant effect. Thus, ple, in a small-scale resonance system, there is a central
if the decrease in depth dominates over the narrowing of point called a node on which the stationary wave oscillates
coastal margins, it will dominate frictional energy dissipa- (Fig. 8.11).
tion and the tidal range will decrease. On the contrary, in In wider systems there may be different nodal points, and
coastal inlets where pronounced confinement occurs, while even in wide basins the oscillation of these nodal points can
the depth decreases more progressively, the convergence be subject to the Coriolis force. In this way, resonance can
effect will dominate and the tide will undergo amplification. generate amphidromic points inside a semi-closed basin.
This is what explains the difference between the two coasts A clear example is the North Sea, in which the progressive
of the English Channel. tidal wave enters from the north and through the English
96 8 Tide Processes
tidal wave had no friction with the bottom. However, due to

its large wavelength, for this friction to not take place, an
ocean at least 22 km deep would be required [8]. When
moving, this wave interferes with the seabed and the orbits
followed by the particles become ellipses elongated on their
horizontal axis. These ellipses will be more and more
elongated in a direction parallel to the coast when the tide
propagates towards shallower bottoms. Thus, in coastal
areas, friction is such that vertical movements are negligible
against horizontal movements. These horizontal movements
of the water mass are known as tidal currents.
As stated, it is seen that the magnitude of tidal currents is
directly related to the tidal range; however, this is not always
Fig. 8.11 Resonance effect in a closed ideal system [13] the case, since other factors such as bottom morphology,
horizontal viscous stress on the bed–water interface, water
density and the presence of other non-tidal currents also
intervene. There are known cases where strong tidal currents
are recorded for small tidal ranges and vice versa. This fact
makes it difficult to predict magnitudes of tidal currents,
when some parameters that are difficult to evaluate come
into play (e.g., Shields 17; White 19; Bagnold [1]). How-
ever, general guidelines appear to exist that are normally
satisfied, with some exceptions (Fig. 8.13).
In the open ocean, tidal current velocities maintain a
certain constancy, hovering around 0.28 m/s, and keep to
rotating patterns in terms of their sense [11]. In this case,
they approach a pure undulatory phenomenon, where cur-
rents should experience an inversion when the marine level
is at the midpoint between the high and low water levels;
that is, three hours after the previous high tide or the cor-
responding low tide (Fig. 8.13a).
In open coastal areas there is a turn in the direction of the
currents that usually happens about one to two hours later
than the respective high or low tide (Fig. 8.13b). This
implies that the currents rotate earlier than would be
expected in a pure undulatory phenomenon. This is due to
the friction effect with the bottom. In fact, the reversal of
currents is produced earlier near the bed than on the surface
Fig. 8.12 Example of the North Sea resonance system with three of the water. At peak times, values greater than those
nodal points affected by the Coriolis force, thus generating three obtained in open oceanic areas can be achieved due to an
amphidromic systems
amplification effect [8].
In coastal bays and channeled areas, due to increasing
Channel, and where resonance on the British and European friction with the bottom and the induction of tides from open
coasts has generated a system with three amphidromic points areas, the reversal of currents occurs more or less simulta-
coexisting in a very small space (Fig. 8.12). neously with the high and low waters (Fig. 8.13c). In these
cases, the speed of tidal currents is directly related to the
volume of tidal water that exchanges the open coast with the
8.5 Tidal Currents restricted system [8]. This volume of water is known as the
tidal prism.
The displacement of tidal waves generates movement in the It is very interesting to study the tidal current interaction
mass of water, similar to the circular displacement that models in the contact area between channelized and open
occurs in the phenomenon of wind waves. In this way, the coastal systems. Inlets, deltaic distributaries and estuarine
water particles move in orbits, which would be circular if the mouths present in and out currents which are perpendicular
8.5 Tidal Currents 97
Fig. 8.13 Relationships between tidal currents and tidal levels in different environments
to the coastline, whereas the tidal currents of the adjacent dissipation of frictional energy on the bottom (Fig. 8.14).
open coast are parallel to the shoreline. These interaction The original wave, when entering the shallow bottom,
models, linked with the wave patterns, condition the mor- undergoes a refractive process, sharply shortening its
phology of the coastal sandy bodies existing at the mouths of wavelength while increasing its height. In these circum-
these channels. stances a breaking ridge is formed that penetrates the coastal
inlet, further increasing in height due to the convergence
Advanced Box 8.2. Genesis of Tidal Bores phenomenon. Under normal conditions, this crest is usually
Tidal waves of large amplitudes as they approach confined around 0.5 m in height, but in many cases it can reach
and shallow morphological environments are able to sharply heights greater than 5 m.
increase their height and produce breakers. This phe- This type of wave is typical of estuaries and macrotidal
nomenon is known as a tidal bore in English. The term bays, although they can also occur during spring tides in
corresponds to the words macareo in Spanish, mascaret in systems whose average tides are usually less than 5 m.
French and pororoca in Portuguese. When the phenomenon occurs in an estuary, the waves can
travel up to several kilometers into the river course.
The genetic mechanism of a tidal bore is simple. It Some case studies are very well documented.
requires a tidal wave with an amplitude of more than 5 m, Well-known examples along the American continent are in
propagating towards a coast of high slope, that generates in a Fundy Bay (Canada), Bristol Bay (Alaska), the head of the
small space with a very shallow bottom and that presents a Gulf of California (USA) and Ría de La Plata (Argentina–
narrowing funnel-shaped morphology. In these conditions, Uruguay). In Europe there are examples in the estuary of the
the narrow fringe in which the shoaling occurs prevents the River Seine (France), as well as in the Rivers Severn and
98 8 Tide Processes
References
1. Bagnold RA (1942) Beach and nearshore processes. In: Hill MN

(ed) The sea. Wiley & Sons, New York, pp 507–582
2. Cherniawsky JY, Foreman MGG, Kang SK, Scharroo R, Eert AJ
(2010) 18.6-year lunar nodal tides from altimeter data. Cont Shelf
Res 20:575–587
3. Darwin GH (1914) Las mareas. El correo gallego, El Ferrol
4. Defant A (1958) Ebb and flow. University of Michigan Press, Ann
Harbor
5. Doodson AT, Warburg HD (1941) Admiralty manual of tides. Her
Majesty’s Stationery Office, London
6. Doty MS (1946) Critical tide factors that are correlated with the
vertical distribution of marine algae and other organisms along the
Pacific Coast. Ecology 27:315–328
7. Featherstone RP, Risk MJ (1977) Effect of tube-building Poly-
chaetes on intertidal sediments of the Minas Basin, Bay of Fundy.
J Sediment Petrol 47:446–450
8. Grant M (1987) Oceanography. Prentice Hall, New Jersey, 406 pp
9. Knauss JA (1997) Introduction to physical oceanography. Prentice
Hall Inc.
10. Lynch DK (1982) Tidal bores. Sci Am 247:46–57
11. Marmer HA (1926) The tide. Appleton, New York, 282 pp
12. Masselink G, Hughes MG, Knight J (2003) Introduction to coastal
processes and geomorphology. Routledge, London, 416 pp
13. Merian JR (1928) On the motion of drippable liquids in containers.
Fig. 8.14 Scheme illustrating the genetic mechanism of a tidal bore. Ph.D. thesis. Basilea Switzerland
Based onased on Lynch [10] 14. Pattullo JG (1966) Seasonal changes in sea level. In: Hill MN
(ed) The Sea. Inter-Science, New York, pp 485–496
15. Russel RC and MacMillan DH (1952) Waves and tides. Hutchin-
Trent (England). In Asia, the most well-known cases are the son’s Scientific and Technical Publications
Gulf of Khambhat (India) and the Ganges Delta (Bangla- 16. Swinkbanks DD, Murray JW (1981) Biosedimentological zonation
of boundary bay tidal flat, Fraser river delta, British Columbia.
desh). Finally, in Australia it occurs in the Cambridge Gulf. Sedimentology 28:201–237
A singular case is that of the mouth of the Amazon 17. Shields A (1936) Anwendung der Ähnlichkeits-Mechanil und der
(Brazil), where the wave penetrates more than 500 km into Turbulenz-forschung auf die Geschiebewegung. In: Preussische
the river course. The world’s largest tidal bore is the one that Versuchsanstalt für Wasserbau und Schiffbau, vol 26
18. Von Arx WS (1962) An introduction to physical oceanography.
occurs in the Qiantang River estuary (China), which reaches Addison-Wesley, Reading
5 m in height and exceeds 28 km/h in its penetration 19. White CM (1940) The equilibrium of grains on the bed of a
upriver. stream. Proc Royal Soc (London) 174:322–338
Continental Processes and Sediments
on the Coast 9
To put the importance of these basins in perspective, the

9.1 Introduction
rest of the basins associated with coasts provide less than
300 tons per km2 per year, and most of them even less than
The composition of the materials deposited on the coast
100 tons.
depends on the clarity of the waters, the amount of sus-
When observing the distribution of these basins, we can
pended matter and the distribution of sediments by the
see that all of them are located around the Tropics. The
currents that reach the coast, but, above all, on the sedi-
explanation for this is found in the combination of factors
mentary supply. The amount of sediment that coastal
discussed above. Not only is there more sediment available
hydrodynamic agents (waves and tides) distribute through-
in these areas, but the higher rainfall induces higher flow and
out coastal systems is based not only on the carrying
gives rivers greater transport capacity to the coast.
capacity of these agents, but also on the budget of available
The second of the sources of sediment contribution from
sediment. This sedimentary contribution can reach the coast
the mainland to the coast is the wind. In this case, the wind
from the continental shelf, but the material that arrives from
can also have a secondary effect that acts in the opposite
the mainland is of much greater importance. These materials
direction, removing sediment from the coast to transport it to
can reach the coast carried by rivers and also by the action of
continental areas. In relative terms, the contribution of wind
the wind. Of these, the sediment provided by the rivers is
to the coast has a much smaller influence than the rivers.
much greater. The amount of sediment supplied annually by
However, its influence is not negligible and should also be
the world’s rivers was estimated to be between 10 and 20
analyzed.
billion tons [50], cited in Anthony [4], but more recently the
Either way, the sediment that reaches the open coast from
same author calculated an amount of more than 20 billion
the mainland does not arrive directly [71]. There are tran-
tons [48].
sitional processes that mean some of the materials are trap-
The amount and nature of the terrigenous contribution
ped in the coastal systems of greater continental influence,
from the mainland is influenced by the geology and climate
while some can go ahead and eventually reach the open
of the adjacent continental area. The climate has a direct
coast. This chapter will discuss the processes associated with
influence on all the factors, controlling both the hydrody-
the contribution of sediment from continental areas and all
namic agents and the volume of input from different sources.
the transitional processes involved. These processes are not
In general terms, it can be said that there are greater con-
only linked to continental agents, but to the combination of
tributions in areas where rainfall is higher and where the
these with the coastal processes that will finally distribute the
weathering is more active. Globally, there are four key river
sediment along coastal systems.
basins that make a contribution of sediment to the coastal
areas (Fig. 9.1).
These are: 9.2 River-Induced Processes and Sediments
• Amazon basin: contributes 1438 tons per km2 per year to All of the sediment contribution that arrives from the rivers
the coast; to the sea is transported through the river mouths (estuaries
• China and Indochina basins: 3228 tons per km2 per year; and deltas). The river mouths make up the transition zone
• Indonesia-–New Guinea basins: 3000 tons per km2 per between the mainland and the coastal area. At river mouths
year; there is a conflict between river currents and the movements
• East Asia basins: 1738 tons per km2 per year. of the seawater mass which entails a series of processes and

https://doi.org/10.1007/978-3-030-96121-3_9
100 9 Continental Processes and Sediments on the Coast
Fig. 9.1 Distribution of

continental sediment supply from
the main river basins of the world.
Adapted from Milliman and
Meade [49]
mechanisms that determines sedimentary transit from the although in this chapter they will be studied independently in
mainland to the open coast [17]. This transit occurs in order to facilitate understanding.
relation to numerous changes in the depositional regime. On
the one hand, there is a change in the chemical conditions of
water, from the fresh waters of rivers to normal sea waters. 9.2.1 Water Mixing Processes
In addition, there is a change in confinement conditions,
from a channeled environment to a fully open coast. Finally, Perhaps the most obvious process that occurs when a river
there is a change in the origin of the energy that causes the meets the sea is the mixture of river and sea water. This
movement of water and, with it, the transport of particles [4]. mixture would implicitly mean a certain stratification of
These processes must be understood as a series of interme- water induced by differing salinity. In this way, the less
diate steps that occur between purely continental and purely dense fresh water would move along the top of the water
marine processes. column, while the higher-density salt water would pass
Moreover, on most occasions hydrodynamic processes through the bottom. In the water column there would be a
that occur at river mouths do not only function as transit gradient of salinity from the surface to the bed. The relative
mechanisms between the continent and the ocean, but also importance of river and sea water bodies in river mouth
often involve permanent depositional processes. This implies channels determines whether this gradient occurs more or
that some of the material from the continent will be less sharply. The concentration of the gradient in a particular
embedded in the confined areas, generating a reservoir that is area or its distribution along the mouth gives rise to the
preserved as a sedimentary record of these transitional existence of different water mixing models. Pritchard [65]
environments. In a sense, this sedimentation process inside distinguished three different models in terms of the shape of
fluviomarine systems limits the bypassing of sediment water mixture (Fig. 9.2), with the relationship between the
towards the open coast. volume of river water and the volume of tidal water being
Classically, the processes that happen in the river mouth the variable that determines the transition from one model to
channels have been explained as a result of the mixing of another.
two water bodies with different densities [65]. This mecha-
nism emphasizes the sedimentation of fine particles trans- • Well-stratified mixing model (salt wedge): According to
ported in suspension, as well as other particles that are Simmons [69], this model occurs when the volume of
“born” within these systems as a product of processes such river water is of the same magnitude or greater than the
as flocculation [57], leading to the phenomenon known as volume of tidal water, although for Postma [62] the
the turbidity maximum [56]. However, the water mixing also volume of fresh water must be significantly higher than
means a stop in the currents, which causes the sedimentation the tidal prism, so that the effect of the tide would be
of the material transported as bed load. These mechanisms negligible. In any case, the good stratification of the
occur together, so that each of them influences the rest, waters is reflected in the “double layer” flow, with very
9.2 River-Induced Processes and Sediments 101
Intuitively, it can be thought that each mouth acts

according to one of these models; however, in each river the
circulation model can vary over time, taking into account
seasonal variations in river flow and sea level variations that
respond to long-period tidal cycles. In this way there are
mouths that can vary between a saline wedge model and a
partial stratification model, and others that vary between
partial mixing and total mixing. There are even estuaries that
can present all three models according to the conditions.
It is also clear that the area of water convergence is dis-
placed along certain areas depending on the state of the tide
and the river flow. This becomes important, as the water
mixture carries certain sedimentation processes that are
preserved in the sedimentary record of these areas.
9.2.2 Estuarine Genesis of Particles:

Flocculation and Aggregation
Fig. 9.2 Conceptual scheme representing the three possible types of River waters and also seawater are normally loaded with a
water mixing at a river mouth. Adapted from Postma [62] special type of solution called colloidal solutions. Colloidal
solutions are a particular state of dissolution involving two
phases, a fluid phase and a molecular phase. Large organic
pronounced longitudinal and vertical gradients. These
molecules, such as water-soluble proteins, are able to form
gradients are at their maximum at peak times of tidal flow
these types of solutions. Colloidal solutions undergo a
of spring tides. In this situation the salt water mass cir-
transport that is neither ionic nor physical, with molecules
culates to land at the bottom of the water column, while
forming a kind of agglomerate (looking like mucus) that is a
fresh water can continue to circulate towards the sea
mixture of water with long chains of electrically charged
across the surface. This implies that the contact of fresh
molecules.
and salted water occurs in a fairly horizontal and abrupt
Depending on the relative proportion of molecules and
way and without any mixture of water in a narrow strip
water, colloidal solutions will be able to be in two states: sol
called the halocline. The inclination of this wedge is quite
or gel. In the case of sol, water predominates and the solu-
pronounced and, therefore, it has a good surface exten-
tion is more fluid. In the gel state, the protein predominates
sion, being able to cover longitudinally tens of kilometers
and the solution is more viscous. The change from one state
from its contact with the bottom of the channel to the
to another is reversible depending on physical and chemical
surface [37].
factors that can cause a solution to change without the need
• Partially mixed model: In this mixing model the volume of
to vary the fluid concentration.
water moved by the tides is between 20 and 200 times the
The molecular structures of the sols and gels may be of
volume of fresh water [69], so it is the tide that dominates
different type depending on their morphology, but in all
the mixing process [62]. The flow also occurs in a double
cases, each of these molecular structures has charged atoms
layer, although there is an intermediate strip in which a
located on its surface, with a hydrophilic and a hydrophobic
greater mixture of water takes place (brackish water),
part. The hydrophilic part is usually located on the outside
making the gradients less pronounced. In this case it is the
and causes the particles to be electrostatically suspended in
tide that is responsible for moving upstream and down the
the water (Fig. 9.3a). Chemical changes in water mixing
contact strip between both types of water, achieving a
areas at river mouths can cause hydrophilic face surface
greater mixture and a smoother salinity gradient.
loads to be null and void by joining negatively charged
• Well-mixed model: At the mouths with this type of mix-
molecules with others that are positively charged (Fig. 9.3b).
ture, the volume of salt water is more than 200 times
This process occurs when these molecules get close enough
greater than the volume of river water [69]. In this case
to collide, thus adhesion occurs between them. In these
the tide produces so much movement in the water masses
cases, there is a change in the density of molecules that will
that it is able to eliminate stratification and produce a
no longer be stable and will pass into the solid state. This
homogenization of salinity, which presents a smooth
process is called flocculation [60].
transition to seawater.
The size and density of flocs depend on numerous vari-

ables including: the concentration of suspended matter and
its residence time, current speeds, water chemistry (Eh, pH
and salinity), temperature and influence of biological pro-
cesses (e.g., Dyer and Manning [24]; van Leussen [73]; Hill
et al. [39]; Anthony [4]).
The process of peptization (also called deflocculation) is
just the reverse process, when the particles are chemically
destabilized by again acquiring ionic characteristics on their
surface and entering into balance with water to be electro-
statically lifted once more.
9.2.3 Suspended Matter Supply from Rivers
The finest grains from erosion in river basins are trans-

ported to the coast as suspended matter in the river water
mass. These particles have sizes between 2 and 125
microns in the case of clays, silts and even very fine sands,
so low current speeds are enough to keep them suspended
in the water column [11]. High concentrations of suspended
matter contribute to increased water turbidity. It is well
known that suspended matter influences the primary pro-
Fig. 9.3 Conceptual scheme that represents the flocculation process. duction of organisms, controlling the development of phy-
a The colloids in the river water are in balance with water thanks to the toplankton and bacterioplankton species. Thus, indirectly it
hydrophilic charge of their surface. b River water colloids encounter the also controls the secondary production of the species that
colloids of seawater in the mixing area, canceling their negative charge.
c Transition to the solid state in the flocculation process. d Formation of feed on these microorganisms (zooplankton and fish
large flocs by aggregation, wrapping other solid particles previously in larvae).
suspension Terrigenous suspended matter is generated in river drai-
nage areas by erosion of solid particles during precipitation.
Flocculation results in the “birth” of new particles asso- Normally, the concentration of these particles in river waters
ciated with the water wedge in such a way that the higher the suffers intermittent oscillations, increasing after heavy rains
degree of mixing, the greater the volume of flocculated [14]. The pulses of higher concentration coincide with the
particles generated [22]. The direct flocculation process is high flow rates, especially during flooding events [42].
able to generate particles of than 16 microns (Fig. 9.3c). The During these times, not only the materials from the tribu-
composition of flocculated particles can be diverse. On the taries arrive in the river, but also the fine sediments previ-
one hand, organic molecules can form that give rise to the ously deposited in the intermediate sections of the river are
flocculation of solid organic matter, but on the other hand remobilized.
inorganic molecular structures can form with crystalline There are large differences in concentration, size and
structure. This is the case of the formation of clay minerals nature of the suspended load grains between different rivers.
(hydrated aluminum phyllosilicates), including illite and the It should be borne in mind that the variability of the grain
groups of kaolinites and smectites. size characteristics of the suspended matter and its nature
These particles pass from their creation to be part of the depends not only on the characteristics of the geologic
suspended load, joining with particles that were already being material in its source area, but also on the ability to be
transported in suspension by both the river and the tides. selected for erosion and transport processes [75]. Among the
Flocculated particles also play an important role in the variables that condition the size and composition of the
hydrodynamic behavior of sediment in transition zones suspended matter are [79]:
between the river and sea, as they tend to trap larger sus-
pended particles forming agglomerates called flocs (Fig. 9.3 • Latitude (which controls both the climatic factor of
d). Particles trapped between flocs can be mineral grains, weathering processes and the primary production of
small bioclasts or organic fecal pellets. Each floc can group aquatic organisms),
dozens of individual solid particles reaching millimeter sizes • River flow (fluvial regime),
(e.g., Graham and Manning [35]; Manning and Dyer [46]). • River longitude,
• Percentage of bare rocks in the drainage basin, relative to Matching this accumulation of suspended load with the
forest cover, area where flocculation processes are occurring results in
• The relief of the basin and many of the particles being engaged in floc agglomerates.
• The profile of the river in relation to the equilibrium profile. The sum of both processes—concentration of suspension
and flocculation—results in the formation of a phenomenon
As an example, a comparative study among the tributaries known as turbidity maximum. The dynamics of this cloudy
of the River Exe in the UK showed the enormous spatial water mass will be discussed next.
variability that can occur in a relatively small area due to
differences in the associated variables described above [75].
The suspended matter is of a diverse nature and consists 9.2.4 The Turbidity Maximum
of a mineral phase and an organic phase. Some of the
components of the suspended matter are naturally present in Turbidity is a concept for naming the optical perception of
river water. However, other components (organic and inor- water clarity. The presence of suspended solids as well as the
ganic) come from human activity. It is clear that their dissolved phase reduce the clarity of the water, creating an
quantity and composition, understood as the relative per- opaque, misty or muddy appearance. It has been previously
centage between these components, change seasonally in said that when the river current meets the mass of seawater
parallel with the variation of the flows. (usually displaced by the tide) turbidity levels increase,
As for the mineral phase, grain size has an important resulting in a phenomenon known as the turbidity maximum.
influence on its mineralogy. Thus, for example, the fraction There are three different mechanisms that contribute to the
less than 16 microns is usually composed of phyllosilicates, increase in turbidity in the area where river water converges
while quartz usually dominates the fraction between 16 and with seawater: (1) the concentration of the solid suspended
125 microns. This occurs because minerals from other matter of the river due to the slowdown of the currents;
compositions are easily alterable (chemically and physically) (2) the flocculation processes in the mixing area; and (3) the
and are reduced during transport, so that it is quartz that resuspension of previously deposited bottom sediments.
predominantly gets to reach the coast [28]. The first of these processes is due to the concentration of
The organic phase is composed of fragments of plants and solid material that occurs when the river water, which
some planktonic organisms, both phytoplankton and zoo- transports suspended matter, slowly decelerates when it
plankton. Diatoms dominate (genera Navicula, Pinnularia, meets the seawater mass. Since most of the suspended
Asterionella and Tabellaria), although dinoflagellates (genera material is supplied by the river current, the highest con-
Peridinium and Ceratium), flagellates (genera Euglena, Col- centrations will occur on the surface, where fresh water
ponema and Spiromona), cyanophyceae (genera Oscillatoria circulates over the halocline.
and Rivularia) and chlorophytes (genera Spirogya, Oedogo- The second process involved in the formation of the
nium and Zignema) are also common. Zooplankton is repre- turbidity maximum is flocculation. It is obvious that the birth
sented by species of various phyla—protozoa, ctenophores, of new particles by flocculation in the water mixing area
rotifers, bryozoans—and, above all, by some groups of crus- contributes significantly to the formation of the turbid cloud
taceans such as cladocerans, copepods and ostracods as well [41]. However, it is in the lower part of the halocline where
as insect larvae and eggs and fish larvae. In this case, not all most of the flocculated particles are concentrated. The water
organic components of the suspended matter manage to mass under the halocline also receives the particles that
achieve confluence with seawater in their initial state. Far from come from the top and pass through the halocline due to
this, during transport organic matter undergoes decomposi- decanting. The aggregation processes associated with floc-
tion and fermentation processes, mostly passing to the col- culation trap the falling solid particles, increasing the size of
loidal state. Only the shells of organisms such as diatoms and the agglomerates and favoring settlement [40].
ostracods get to reach the mixing area in their solid state. The third of the processes involved in the turbidity
To reach the open coast, the suspended matter transported maximum is the resuspension of the fine sediments from the
by the river must pass through the mouth area where the bed [57]. This phenomenon is associated with tidal dynamics
water mixing processes occur. For suspended particles, the and occurs independently of saline mixing processes. Either
mixing area means a dissipation of the energy of the river way, the resuspended particles become part of the lower area
currents and a loss of the capacity to transport the of the turbid cloud formed by the other two mechanisms.
mechanical load when the water mass slows. This means an In the formation of a turbidity maximum, both its mag-
increment of the concentration of suspended particles around nitude and the relative importance of each of these three
the contact between river and marine waters, not because of phenomena depend on river variables such as the flow and
their different chemical nature, but because of their differ- concentration of suspended matter of the river waters, but
ential displacement. also on other variables that depend on marine processes such
Fig. 9.4 Conceptual models of

the genesis of a turbidity
maximum. a With a halocline in a
salt wedge (stratified). b With
mixture of water masses in a
volume of brackish water (mixed)
as the tidal regime, the amount of suspended matter intro- intrusion, coinciding with the null point of convergence
duced from the sea and the type of water mixing that occurs between the river and the tidal flood currents. In the mixing
[61]. In general, two models that describe the importance of area, the flocculation processes contribute to the increase in
the water mixing phenomenon can be distinguished turbidity and the aggregation results in the settlement in
(Fig. 9.4). areas where the current speed is lower. The result is a dis-
In the first of the models (Fig. 9.4a), the presence of a persion of the suspended matter to the lower parts of the
halocline located in the same position as a null point of the water column. The turbidity plume migrates landwards as
water current speeds is of great importance. In this case, the the tide penetrates the river system, reaching its peak at the
contact between waters with different nature occurs practi- time of high water [70].
cally on an abrupt surface. The existence of the null point When the tide reaches its maximum height, the water
results in the concentration of particles of river origin on the mass stops its displacement for a few moments and the
halocline as described above. On the other hand, the halo- aggregation and decanting processes increase (Fig. 9.5b). At
cline concentrates the flocculation process, while below it this time, in the innermost parts of the system, where the
occur the settlement processes favored by the aggregation turbidity maximum is closest to the bed, the deposition of
associated with flocculation. the particles of the plume occurs. Because of this, this area is
The second model (Fig. 9.4b) groups any type of saline usually a place of rapid shallowing. During these moments
intrusion where the waters are mixed in a volume of brackish the plume reaches its greater thickness, although, due to the
water. In this case, there is no defined halocline, although the settlement of the particles closest to the bed, the concen-
null point of the current speeds is still present. The con- tration of matter decreases.
centration of river particles also occurs on the null point, The beginning of the ebb current (Fig. 9.5c) implies a
with the difference that in this case the surface with speed 0 disappearance of the null point of the current convergence
is arranged at a less horizontal inclination and covers less zone, since during the cycle the entire water mass moves
extent. On the contrary, as there is a greater mix of water, the seawards. During the ebb cycle, the water mixing area
flocculation process becomes more important and has a moves downstream, while increasing the volume of brackish
wider distribution. mixed water. At this point, the mechanism that concentrates
Evidently, these models conceptually group together the suspended matter from the river loses importance, while
different ways in which a cloud of turbidity can be gener- flocculation increases and the dispersion of matter in the
ated. However, they do not represent the dynamics of the water column gains importance. At moments of maximum
plumes in different tidal situations. Over a tidal cycle, the ebb flow, the bed material is resuspended, causing the cloud
mechanisms of turbidity formation change while moving to gain concentration in the part nearest the bottom. These
along transition zones (Fig. 9.5), and going upstream or are the moments of greatest extent of the turbidity
downstream depending on the displacement of the water maximum.
mass induced by the tidal circulation [1]. The arrival at the low tide slack (Fig. 9.5d) implies a new
We can start the explanation at the moment of maximum halt of currents at the bottom of the water column. This
tidal flood current (Fig. 9.5a). At this time, the suspended provides an opportunity for the aggregation and decanting
matter is concentrated in the terrestrial limit of the salt water flocculation processes to gain importance again, by
Fig. 9.5 Turbidity maximum

dynamics over a full tidal cycle.
Based on Allen et al. [1]
sedimentation of fine particles from the part of the turbidity between a spring and a neap tide, there is a decrease in the
maximum closest to the bed. maximum speed of the currents, as well as a longer duration
When a new tidal flow cycle begins, it returns to the of the slacks. During the week that this semi-cycle lasts, net
initial situation with the emergence of a new current con- sedimentation exceeds the reworking processes. On the
vergence point (Fig. 9.5e). In this case, the upstream circu- contrary, during the semi-cycles of increased tidal range that
lation of the seawater mass is significant, producing a occur between a neap and a spring tide, just the opposite
resuspension of some of the particles deposited during the process occurs, with reworking dominating over accumula-
low water slack. tion. However, the succession of a complete fortnightly
This dynamic model includes only changes in processes cycle results in net sedimentation. It should be noted that the
associated with a turbidity maximum during short tidal fine sediments accumulated during the neap tide are cohe-
cycles. However, the same authors also highlighted the sive. They need to be remobilized at a much higher lifting
dynamics of fortnightly cycles. Thus, due to the alternation threshold and thus withstand spring tide currents without this
between spring and neap tides, the position of the turbidity occurring. This results in an infilling of the confluence zone
maximum and its concentration also evolve. In the transit by net accumulation of fine sediments.
Other dynamic changes of the turbidity maximum are

imposed by river dynamics. Numerous authors (e.g., Nichols
[56]; Allen et al. [1]; Dobereiner and McManus [20];
Gelfenbaum [31]) have described a seaward displacement of
the turbidity maximum of up to tens of kilometers during the
moments of large river floods. During these events, a process
of general resuspension occurs, but in addition the position of
the cloud can be so low that in times of ebb it can even be
injected into the open coast. Conversely, during the summer
river flows the tide can displace the mixing area many kilo-
meters inside the river systems. To this phenomenon it should
be added that, during these times, the low river currents favor
the processes of dispersion by the flood tidal currents to areas
located upstream of the position of the wedge [61]. In some
rivers, marine microfossils have been observed in areas much
beyond the usual position of the salt wedge [9].
These dynamics of the turbidity maximum mean that both
suspended matter and decanted sediment are continuously
recycled in each new tidal cycle. This results in an uni-
formization of grain size and mineralogical composition of
the turbidity maximum. In this dynamic process, the thicker
and denser sediments end up being trapped inside the river
mouths, while the finer and less dense sediments get to pass
through the mixing area and are finally injected into the open
coastal system.
9.2.5 Suspended Matter Injection to the Open

Coast: The Turbidity Plumes
The world’s most important river systems have such a high

flow that fresh water reaches the mouth and the water Fig. 9.6 Examples of turbidity plumes injected into coastal waters
mixture takes place directly in the open sea. This phe- from river systems of different importance (NASA Earth Observatory
nomenon occurs in rivers such as the Amazon, Orinoco, images). a Plume from the mouth of the Yangtse River (China).
b Plumes generated at the mouth of the Guadalquivir (SW Spain) in
Mississippi, Niger and Yangtze (Chang Jiang). In rivers with two successive floods (Images Landsat/Copernicus from Google Earth)
lower flows, this phenomenon can also occur during the
moments of large floods. Even in these smaller rivers, the
finest material from the turbidity maximum generated in the lower water mass and settle in the deeper coastal areas at the
interior of the channels can reach the coast during the front of the channels. This is the case of many fluvial
moments of tidal ebb, as explained in the previous section. prodeltas.
In any of the three cases, the result is the formation of a In the case of large rivers, the presence of the plume is
turbidity plume that is injected to a greater or lesser extent associated with water mixing processes that take place in the
into the open coast (Fig. 9.6). front area of the mouth and not in the channeled areas. The
The dimensions and dynamics of these turbidity plumes case of the Amazon is very significant, where fresh water is
differ depending on which of the three cases described is able to form a tongue that extends about 150 km from the
occurring, but they will also be influenced by the tide and mouth to the sea [33]. Similar cases occur in the Yangtze
wave dynamics of the coastal area where the plume is being River (Fig. 9.6a) [43, 76] and the Huanghe (Yellow River)
injected. These dynamics control the place and the way in [81]. In most cases, the mixing processes that occur in open
which this fine material will finally settle. Thus, the final areas correspond to a good mixing model [13, 32]. An
destination of the lutitic material from the plumes may differ example of this type of mixture is observed at the mouth of
from one system to another. In many cases, the sediment can the Mississippi (USA), where in the absence of tides, the
be redistributed by coastal systems and end up in nearby dynamics of the mixture are controlled by weak river flows
tidal systems. In other cases, the material may move to the and the displacement of the water mass with the wind [2]. In
cases of large rivers with more extreme river currents, situ- the bed load carried by the river (Fig. 9.7, Stage 1). From the
ations of good stratification can be identified in this marine beginning of the tidal ebb semi-cycle, the sediments begin to
plume. An example of this type of plume is that of Song be transported seawards. Through many tidal cycles, the bed
Hong (Red River, Vietnam) described by van Maren [74]. load of fluvial origin is blended with that of marine origin, so
In the cases of plumes associated with good mixing that the sediments of the central part of the confined mouths
conditions, the movement of the water mass generated by the have a mixed composition. This sediment may have a ten-
tide and/or wind, linked with the remobilization by waves, dency to residual seawards movement, or may become
cause a process of diffusion of turbidity in the water column. entrapped within the fluviomarine systems. In this case, open
This results in a greater distribution of suspended sediment estuaries work differently from highly evolved estuaries,
that can be shifted to the prodelta or to the coast, or even to bedrock-confined estuaries and deltas.
both sites. In open estuaries, tidal circulation and current asymmetry
Moreover, good stratification conditions imply greater often create a domain of flood currents. This implies a net
importance of the suspended matter from the river. In these transport that displaces the bed load from sea to land,
cases, the grain size of the suspended matter is usually larger introducing it to the central sector of the estuary where it
and they then decant very quickly in areas near the mouth converges with the bed load of river origin [23]. In these
without even reaching the prodelta area. The latter case has estuarine areas, the sands also coincide with the cohesive
been documented in Po (Italy) and Song Hong (Vietnam) materials that settle from the turbidity maximum during the
[29, 74, 77]. moments of slack. The cohesive material present at the
Despite this, in most river mouths the mixing processes bottom wraps the grains of sand, preventing them from
occur inside the channels and only on occasions of maxi- returning to movement in the following tidal cycles. Both
mum discharge do situations such as those described above mechanisms (residual inland component and cohesive
take place. In these situations, the finest fraction of the entrapping) contribute to the bed load sediment remaining
suspended matter generated in the turbidity maximum can
go out continuously to the outside, while the thickest fraction
is contained in the channels until a river flood can remove it
to the open sea. At this type of river, the fine material from
the turbidity maximum is distributed twice. On the one hand,
the thickest fraction becomes part of the coastal systems,
while the finer fraction associated with flocculation is dis-
persed on the coast and finally settles in the prodelta [17].
These smaller but more common rivers play an important
role in the supply of fine material in coastal and continental
shelf systems. The sediment reaches these systems in par-
ticular during periods that follow the large floods in which
tides and waves have distributed the sediment of the plumes.
Numerous examples of such rivers have been described in
European estuaries, such as the Seine [19], the Guadiana
[51], the Guadalquivir (Fig. 9.6b) [10], the Var [3] and the
Po [77], and also in Australia as is the case of the Daly
Estuary [78].
9.2.6 Bed Load Supply from Rivers
At river mouths, the dynamics of the material transported as

bed load presents some parallels with the suspended matter.
In the innermost areas of the estuary and delta channels, a
current convergence zone usually forms. In this area, a Fig. 9.7 Example of the discharge of bed load material in two phases
low-energy point develops, as the river currents that circulate in the Guadiana Estuary in Spain (bedrock-confined estuary). Stage 1:
towards the coast are slowed when they encounter seawater. During the tidal flood there is a convergence with the river current
which implies a deposit of the bed load. Stage 2: Successive tidal cycles
In tidally influenced systems, this convergence is at its
take the material to the mouth. During the ebb semi-cycles, the output
maximum during flow semi-cycles, so that the current is current collides with wave trains by depositing the load on a front delta
completely stopped allowing the immediate sedimentation of bar (Morales and Borrego [52])
within the estuaries, giving these environments a very high available grain size of the sediment (e.g., Garel et al. [30];
sedimentation rate. This active sedimentation inside the Edmonds and Slingerland [25]).
estuaries causes them to evolve very quickly, contributing to The deltaic front bars may be subjected to strong
greater shoaling and confinement, so that in a few thousand reworking by the waves that generate on the surface bars that
years they can evolve and transform into deltas. This effect is move to the shoreline. These bars can end up joining the
usually much greater in systems where the river is small and delta plain to form barrier islands. This is the case of mixed
provides little material in bed load. In these cases, the central deltas such as the Nile, Senegal and Danube, among many
area of the estuary would be mostly filled by sediments of others [72]. In any case, it is worth noting the role that these
marine origin mixed with the autochthonous sediments of bars play as a source of material in the open coastal systems
the turbidity maximum (e.g., Anthony and Dobroniak [5]). (beaches and barrier islands) adjacent to deltas and confined
In very open estuaries, the action of the waves, at least in the estuaries, because once the sand reaches land, its material
marine sector of the estuary, can also be important. In these can be redistributed by coastal drift currents along the entire
cases, the waves not only introduce sediment into the estuary coast (e.g., Garel et al. [30]; Sabatier et al. [67]).
channels but also contribute to increasing the magnitude of
flood currents, especially during storms [4].
Highly evolved estuaries, as well as confined estuaries 9.3 Wind Supply and Erosional Effect
(bedrock-controlled estuaries) and deltas, have a different
functioning. In these systems, the convergence of river and The action of the wind on the coast is not restricted to the
tidal currents is usually located more towards the sea (e.g., generation of waves, but also acts as an effective transport
Dalrymple et al. [16]). In addition, in these systems it usually agent that moves material from the mainland to the sea and
dominates the ebb tidal current, giving the sediment a net vice versa, giving rise to wind supply processes and wind
movement towards the sea [17]. In the channels of these erosion. Conceptually both processes are involved in the
systems, active sedimentation and bypassing mechanisms are overall sedimentary balance of the coast [63]. The influence
usually distributed laterally in different areas. In this way, on the coast of material movement by the wind is evident on
cohesive sediment traps a significant part of the bed load on some sandy European coasts such as Aquitaine and the
the tidal bars, while the deepest part of the channels continues Pertuis d’Antioche (France), Rosslare (Ireland), Doñana
to allow a bypassing of bed load sediment from the river to (Spain) and the entire coast of the Netherlands [27].
the sea (e.g., Morales et al. [53, 54]). The bars of the estuary Interactions between wind systems and coastal aquatic
are covered by bedforms of different dimensions, so that in systems have been studied in some restricted coastal cells
these we can observe the double sense of bed load transport where the material is continuously recycled from the dunes to
(e.g., Lobo et al. [44]; Morales et al. [54, 55]). In these sys- the beach and vice versa (e.g., O’Connor et al. [59]). How-
tems, the bed load sediment ends up reaching the exit to the ever, most of the knowledge about the exchange of material
sea after numerous tidal cycles (Fig. 9.7, Stage 2). between wind systems and submerged coastal systems
At the front of the mouth channels of these evolved remains conceptual (Fig. 9.9). Although these processes can
systems described above and, especially, in the deltas, the act together, in this chapter they are studied separately.
sediment ends up forming important mouth bars. The case of
deltas is significant, as these bars are almost entirely con-
stituted by bed load of river origin (e.g., Maillet et al. [45]; 9.3.1 Sediment Supply from Continental Winds
Drexler and Nittrouer [21]). These bars have been classically
named deltaic front bars and are located between the delta In most manuals, when talking about the continental con-
plain and the prodelta [7, 80], although they can also be tributions to the coast it is noted that 95% of this is due to the
called estuarine ebb-tidal deltas [18]. The bars are formed rivers. However, the products of weathering in the conti-
when the output river currents, together with the ebb tidal nental rocks can also be transported by the wind. In fact, the
currents, dissipate into the seawater mass depositing the bed remaining 5% of the material that reaches the coast comes
load. The effect is especially significant when the water mass from wind transport. However, the influence of these con-
is moving to land by the action of wave trains running tributions to the coast is not frequently addressed and most
towards the shore (Fig. 9.7, Stage 2). The result is the for- monographs on coastal dynamics do not include a chapter
mation of an important sand body with linguoid morphology dedicated to the influence of wind input on the coast.
(Fig. 9.8). The dimensions, development and subsequent Regarding the wind processes involved in this transport,
evolution of this body will be conditioned by the balance of there are not many details to comment on. It should be
forces between the output jet from the confined systems and pointed out, however, that wind transport is the one that best
the ability of waves to redistribute the sediment on the classifies the grains by their size. On the one hand, the silty
outside. Evidently, the balance of forces is influenced by the sediments removed from land can pass far above the coastline
9.3 Wind Supply and Erosional Effect 109
Fig. 9.8 Linguoid morphology

of the deltaic front bar at the
mouth of the Guadiana Estuary,
indicating the dominant processes
involved in its formation and its
influence on the feeding of the
coast. Based on Garel et al. [30]
Fig. 9.9 Conceptual diagram

showing the influence of the wind
on the coast
when moving through the high layers of the atmosphere [15] regime. Examples include some stretches of the coast of
to end up as sediments in the open sea (Fig. 9.10). On the Libya and Tunisia in the Mediterranean. In the case of the
other hand, the sand grains move closer to the ground and Tunisian coast, the wind supply is sufficient to power some
when they reach the coast they can get trapped in the water barrier island systems and coastal sabkhas [26].
and contribute to the budget of the beaches.
In the case of sand, it must be borne in mind that wind
transport exerts significant particle wear, so that along the 9.3.2 Wind Deflation
journey from the mainland to the coast mineral grains
acquire rounding, while polymineralic fragments are disag- The wind can intercept the sandy particles from the beaches
gregated and less resistant minerals are destroyed. Quartz is and circulate them to the mainland, especially during low tide
not only the most abundant mineral in sedimentary, igneous times. This process is known as wind deflation. This occurs
and metamorphic rocks that outcrop on the continent, but it on most of the world’s shores when the wind blows persis-
is also one of the most chemically stable minerals and is able tently towards the coast. The amount of sediment provided by
to withstand the abrasion processes suffered during transport. foreshore and backshore to wind domain areas depends on
This explains why quartz makes up the vast majority of the several factors, including: the amount of sand on the beach
grains provided by wind to the coasts. and its grain size, the range and tidal regime, the type of
There are some coastal areas in the world where persistent beach, the percentage of sand moisture and, of course, the
winds operate from the mainland to the sea. For example, on direction and strength of the wind (e.g., Pye [64]; Hesp [38]).
the west coast of Mauritania, the trade winds displace the dune In the long term, the balance of sedimentary exchange
systems of the Sahara Desert until they reach the coast [47]. between the coast and the continent is controlled by the
The ergs of Azefal and Akchar continuously feed a strong distribution of erosive and cumulative zones over time. This
coastal drift that redistributes these sediments south along the distribution is determined by the transport mechanisms that
coast. Despite this wind contribution, this coast experiences a take place in the sediment–air interface [8]. Any method that
net erosion by not receiving any type of river input. attempts to quantify the material displaced by these transport
Other coasts of the world have a significant wind con- mechanisms must take into account the measurement of
tribution because they are subjected to a persistent wind variables such as wind speed at the interface, air density,
Fig. 9.10 Satellite image showing the injection of dust from the Sahara Desert into the ocean through the high layers of the atmosphere.
Image NASA Earth Observatory
grain size and grain density (e.g., Bagnold [6]). The sediment evaporation of interstitial water. On the other hand, the water
output from the beaches to the dunes represents a negative table descends from centimeters to decimeters, releasing the
entry in the beach balance. In parallel, a transformation of the particles from this humidity. Therefore, transport becomes
distribution of the grain size into its sediment occurs, since more effective over time from the moment of immersion of
the wind selects only the sizes it can transport, leaving behind the beach, although only the grains above the water table
the largest grains in the deflation zone. will start transport.
Although the wind acts with the same intensity Another variable that influences the wind contribution in
throughout the beach, the amount of material transported these areas is the slope of the beach. The slope, and also the
varies along its sections. The particles begin to be incorpo- morphological changes that occur throughout the year due to
rated progressively into the wind flow: there are very low the beach dynamics, causes changes in wind speed. These
values in the area near water and maximum values towards changes are due to the greater or lesser deceleration that
the backshore. In this way, the wind flow tends to incor- occurs by wind friction when attacking the beach at different
porate grains along the beach profile until particle saturation angles. Higher sloped beaches tend to have a shorter fetch,
is reached in the higher areas. This saturation will be although wind tends to create turbulence that contributes to
achieved if the beach area is wide enough [58]. This incor- exceeding the lifting threshold of particle movement. So, the
poration of particles along the profile is called the fetch sand grains will be incorporated into the flow more quickly.
effect [12] or, more precisely, fetch erosion effect [34]. Conversely, on very shallow beaches, the fetch is much
The moisture content of the sand tends to increase the higher, although it will have less resistance to wind, which
fetch effect, since moisture retains the particles by conferring facilitates sedimentary bypassing to the higher parts [68].
cohesion to the individual grains and increasing their lifting Normally, the arrival of sediment in the upper area of the
threshold of movement [34]. Either way, the first effect of beach contributes to the formation of coastal dunes. The
wind when the tide falls is to contribute to increase the dune that immediately forms over the backshore is called the
9.3 Wind Supply and Erosional Effect 111
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Marine Processes and Sediments on the Coast
10
indicates that papers in this sector have focused on very

10.1 Introduction
specific places in the United States, Northern Europe and
Australia, leaving the rest of the world’s coasts uncovered.
In the previous chapter we analyzed the processes that
Similarly, not all processes have been addressed, focusing
control the sedimentary contribution that reaches the coast
most of the efforts on characterizing the storm relaxation
from the mainland. However, significant amounts of sedi-
currents and the remobilization of fine sediments from the
mentary material can also come from the continental shelf
prodelta areas.
through processes of a purely marine origin. These act in
This chapter analyzes the marine sources of sediment that
combination with the processes associated with tides and
can reach the coast and be part of its sedimentary bodies, as
waves that have already been discussed in previous chapters.
well as the processes of marine origin that, together with the
The arrival of this material in coastal formations is influ-
tide and swell, are responsible for the movement of these
enced by the dynamics of the offshore and shoreface envi-
sediments.
ronments (see definitions in Chap. 2). In this regard, the
functioning of the subtidal zone of the coastal front is a
fundamental factor in the long-term evolution (hundreds and
thousands of years) of emerging coastal systems. This area 10.2 Marine Sources of Sediment
plays a key role in sedimentary exchange between the con-
tinental shelf and the coast, especially on wave-dominated Marine sediments are grains of unconsolidated material, both
coasts. inorganic and organic, that are deposited on the seabed. The
The influence of these processes is not limited to the flow marine sediments that can reach the coast are those that were
of sediments of marine origin towards the coast, but in previously deposited on the continental shelves; thus, sedi-
parallel there is also a flow of sediments of coastal origin ments from the deepest environments such as slope deposits,
towards the sea. Both flows are part of the sedimentary underwater canyons, deep underwater fans and abyssal
balance of the coast and both are linked to the sedimentary plains will be excluded from this section.
exchange with the continent described in the previous The marine sediments deposited near the coast contribute
chapter, as well as to sediment movements between different about 25% of the seabed surface, although, from a volu-
cells along the coast. metric point of view, they are of much greater importance,
Several syntheses on the sedimentary exchange between accounting for approximately 90% of the volume of all
the continental shelf and the coast have been published in sediments deposited in marine environments [29].
recent decades [10, 20, 26, 35]. These have all made an Coastal sediments of marine origin are generally made up
effort to characterize the dynamics of the shoreface as an of a combination of several components. Most of the grains
element of connection between the shelf and the coast. are silicates and come from the weathering and erosion of
Recent papers have highlighted the role of the lower part of the continents (Fig. 10.1a) or from volcanic eruptions
the shoreface as a store of sediments that is fundamental for (Fig. 10.1b) and were previously deposited on the conti-
the connectivity between the continental shelf and the coast nental shelf. Another fraction of the grains of the shelf
[5]. However, all of them also demonstrate that the processes sediments comes from the chemical and biological processes
operating in this area are not sufficiently studied, and that that occur in seawater (Fig. 10.1c, d).
therefore the precise mechanisms that govern the dynamics Normally the marine-derived siliciclastic material that
of the bed load material in this sector are not known in detail. reaches the coast comes from the reworking of relict sedi-
A recent analysis of literature developed by Anthony [4] ments on the platform and is related to sea level movements.

https://doi.org/10.1007/978-3-030-96121-3_10
114 10 Marine Processes and Sediments on the Coast
Fig. 10.1 Microscope images of

coastal sediments with different
compositions. a Sand composed
of quartz grains (Cíes Islands,
Spain). b Sand composed of
silicates of volcanic origin
(Batangas, Philippines). c Mixed
siliciclastic–bioclastic sand (Île
aux Nattes, Madagascar).
d Bioclastic sand (La Cueva de
Las Golondrinas, Dominican
Republic)
Sediments inherited from previous sea level positions can be environments can also be redistributed on the coast during
reworked to build coastal shapes. During lowstand periods these events. Low energy processes can concentrate layers of
there are erodible areas of old continental shelves whose precipitated small crystals around a central detrital nucleus—
materials can enter a new sedimentary cycle when trans- these are called oolites. Elements and processes of chemical
ported by continental agents to the new coast. There can also origin will be specifically addressed in Chap. 11.
be this type of contribution in times of highstand, when Regarding sediments of biological origin, most of these
coastal system tracts are submerged. At these moments the come from the erosion of clastic marine deposits, which in
old shelf sediments can be reworked by waves, tides and turn are the result of the dismantling of organic biocon-
other currents, supplying material available to build the new structions such as coral reefs or sessile mollusk banks.
coast. These sediments are called bioclastic sediments and are
Chemical sediments are generated by precipitation of composed of hard fragments of crystalline material secreted
minerals from seawater. Normally, for these precipitation by organisms. The most abundant composition of these
processes to occur, large changes in the chemical parameters skeletal fragments is calcium carbonate (calcite or aragonite
of the water need to occur. In marine environments near the crystals), although there may also be bioclasts of other
coast these changes are usually associated with increasing compositions (dolomite or silica). Coasts located in areas of
salt concentration, as water evaporates when the saturation high biological productivity usually have sediments com-
threshold is exceeded, especially in arid climates. The most posed almost entirely of bioclasts. This sediment is typical of
common composition of precipitation sediments are calcite subtropical areas, where grains correspond mostly to skeletal
crystals, although dolomite, gypsum and halite also appear. material from the dismantling of reefs or shell fragments. In
This type of component is usually a minority in the sedi- these areas of high productivity, another biological compo-
ments of siliciclastic platforms, although in carbonated nent of sediment may come from the fecal secretions of
platforms it may be the most common. Chemical grains are organisms. This is the case of the carbonated pellets.
also abundant in mixed platforms, where siliceous and car- There are also elements of biological origin from the soft
bonated contributions are balanced. Precipitation processes, parts of organisms, such as the remains of dead plants or
especially those associated with evaporation, can occur animals; these are called biogenic components. On the coasts
directly in coastal environments, especially in restricted of great continental contribution, the organic components are
subtidal and intertidal areas. Sometimes chemical precipita- in the minority; however, in many cases, the components of
tion processes occur in pores, resulting in cementation as biological origin can constitute a substantial fraction of the
part of the digenesis. In any case, chemical sediments coastal sedimentary material, especially where the supply of
deposited on continental platforms can be remobilized and terrigenous material is scarce. The processes governing the
shifted to the coast during high-energy moments in the form origin and distribution of these sediments will be discussed
of intraclasts, while chemical sediments deposited in coastal in detail in Chap. 12.
10.2 Marine Sources of Sediment 115
Fig. 10.2 Map of general oceanic circulation showing the different cells formed by the currents
Biological and chemical processes can act together. This 10.3.1 General Oceanic Circulation: Currents
is the case of the stromatolites, which are built in the in the Coastal Front
intertidal areas by the trapping by cyanobacteria of grains of
previously precipitated sediment. Ocean currents are large-scale waterway movements with
different origins. There are two different circulation systems
in which currents are generated by different causes. In the
10.3 Marine Processes on the Coastal Front deepest water layer, there is a circulation system whose
origin is based on the differences in density of the water
Tides and, above all, waves dominate the dynamics of the bodies due to differing salinity and temperature. This deep
sediment on the coastal front. However, there are a number system has no direct interaction with the coast and will not
of processes that act in conjunction with waves and tides and be addressed in this chapter.
hence have an important influence on the transfer of sedi- On the surface, ocean currents are the result of viscous
ments between marine environments near the mainland and wind friction over the upper tens of meters of the ocean.
the coastal environments. The currents of the cells of general These movements of the ocean water mass result in surficial
oceanic circulation approach some coasts, participating in currents that, although not as visible as waves and tides, act
the mobilization of sedimentary material and interacting with on a larger scale. Thus, the displacement of seawater bodies
the tides. The tides themselves present a system of currents globally follows the same movement patterns as atmospheric
in the open coastal area with a particular dynamic that differs circulation. Generally speaking, this current system is the
from that presented in the interior of the coastal environ- ocean’s response to the flow of energy in the atmosphere
ments. Finally, the winds, in addition to generating waves, from the Tropics to the polar regions and is influenced by the
can induce movements in coastal water bodies that result in Coriolis force and the presence of the continents. These
permanent and ephemeral currents which are able to remo- forces generate a regular system of currents with a perma-
bilize the sediment to and from the continental shelf, as well nent character that affects large areas of the oceans
as along the coast. (Fig. 10.2).
The system of general oceanic currents is now well currents. These currents are known as geostrophic currents
known and responds to well-defined patterns based on the and will be discussed in detail in the section below.
following fundamentals:
• Circulation systems follow very similar patterns in all 10.3.2 Wind-Driven Currents in the Coastal
oceans. Front: Geostrophic Currents
• Trade winds displace the water towards the Equator and
the Coriolis force diverts it westward generating the Apart from the arrival of ocean currents at the coast, the
equatorial currents. wind also acts on coastal waters by transferring energy to the
• Equatorial currents circulate westward until the presence mass of water by friction on the surface of the coast. This
of the continents deflects them and turns them to the north wind thrust can generate currents or modify other currents
and south to balance the level of the water surface. that reach the coast, such as ocean currents themselves or
• Currents flowing to higher latitudes result in a new shift tidal currents. To the same extent as the rest of the currents,
of currents to the east due to the persistence of wind-induced currents can interact with the coast in three
high-latitude winds. In parallel, the water interacts with ways:
the atmosphere and becomes cool.
• In each hemisphere the colder waters of the highest lati- 1. Convergence: Wind-driven surface currents can be
tudes circulate again towards the Equator when encoun- directed against the coast. In this situation there is an
tering the continents. elevation of the water surface towards the shoreline.
• This circulation model generates cells that circulate 2. Divergence: When the wind propels surface currents
clockwise in the Northern Hemisphere and counter- towards the sea it moves water away from the coast,
clockwise in the Southern. producing a descent of the water surface on the coastal
• In some areas, contrary currents are generated that com- front.
pensate for rises or falls of the water surface that take 3. Parallelism: If the wind drives the currents parallel to the
place due to the action of the wind. coast, there is a current that sweeps the coast in the
direction of the wind. This current is known as a coastal
These persistent currents have a clear influence on some jet.
coasts, where they are among the main agents acting on
sediment mobilization. Other currents affect a small area and Each of these configurations in the vicinity of the coast
act for a certain time, especially with seasonal frequencies. results in a sea surface that ceases to be horizontal, inducing
These are temporary phenomena and are the response of the a pressure gradient in the water mass which in turn causes a
sea to local conditions. movement of the deeper water layers to compensate for that
The interaction of these currents with the coasts has been gradient [15]. Secondary currents resulting from this gradi-
studied throughout the 1970s and 80s. During these decades, ent affect the deepest waters and can extend down the con-
some coastal currents induced by the general dynamics on tinental shelf to depths close to 100 m. The in-depth
the East Coast of the USA were characterized (e.g., Bennett transmission of this sea surface deformation through the
and Magnell [7]; Schwing et al. [30]; Scott and Csanady currents results in an offset of the stratification of the water
[31]), although studies on other coasts were scarcer. A clas- column according to its density. The layers of this density
sic example is the research carried out in the Arctic by stratification are regulated by their temperature and salinity,
Wiseman and Rouse [34]. Also in this period, some authors usually there is a contact surface between the warm and less
were able to carry out synthesis work on the dynamics of dense waters of the surface and the deeper dense waters,
these currents at the coastal boundary [3, 14, 15]. called the pycnocline.
The three basic ways in which a current can interact with The three models of interaction of surface currents with the
the coast are: (1) heading towards the coast; (2) moving coast result in three forms of internal displacement of lines of
away from the coast; and (3) circulating parallel to the coast. equal water density (Fig. 10.3). In this way, the surface ele-
In all three forms, the loss of depth that occurs from the sea vation of the convergent model results in descending bottom
to the coast in relation to these currents influences a devia- currents that depress the pycnocline. This phenomenon is
tion of the surface of the water up or down, resulting in the known as downwelling. Conversely, the surficial depression
appearance of secondary currents circulating at depth, in associated with the model of divergence of surface currents
contact with the bottom, to compensate for this gradient of results in ascending deep currents that raise the pycnocline,
the sea surface. These effects are the same as those that arise and this phenomenon is known as upwelling. In the third
when winds act directly on coastal waters, generating local model, the coastal jet parallel to the shoreline is transmitted to
10.3 Marine Processes on the Coastal Front 117
Fig. 10.3 Simplified conceptual

scheme of the three different types
of interaction between
wind-driven currents and the
shallow coast
the deep layer by a drag effect due to the internal viscosity of

seawater through a laminar flow [21].
This laminar flow is not only linked to the coastal jet, but
appears in all surficial currents. The depth transmission of
the currents is affected by the Coriolis effect, so that at depth
the speed of each layer is deviated at an angle. When looking
at the velocity vectors in the water column together, a spiral
turn is observed (Fig. 10.4). This turn is known as the
Ekman spiral [16].
According to this theoretical model [8], for a constant
wind, the angle between the direction of the wind and the
surface current varies between 45º in deep water and 15º in
coastal waters. This turn in the Northern Hemisphere would
occur to the right of the wind, while in the Southern
Hemisphere it would occur on the left. The combined dis-
placement of the entire water mass of the flow sheets that
make up the Ekman spiral results in a net movement per-
pendicular to the wind direction called Ekman transport.
This net water movement occurs 90º to the right of the wind
direction in the Northern Hemisphere and to the left in the
Southern one.
Fig. 10.4 Conceptual model showing the deviation of the wind-driven
If we take into account the data provided by Niedoroda
currents at depth by the Coriolis effect, indicating the direction of the
et al. [26], in shallow areas the water column is not sufficient net water mass movement (Ekman transport)
to develop the Ekman spiral, due to the influence of friction
with the bottom. In this case, the currents of the upper and
lower layers tend to align according to the convergence and the surface layer may circulate differently from the deep
divergence model in Fig. 10.3. Conversely, from a certain layer, as there is a layer of shear between them. In this case,
depth the water column offers enough thickness for the depending on the orientation of the coast with respect to the
Ekman spiral to develop. In this coastal strip the currents of prevailing winds, the theoretical model of convergence and
divergence is slightly more complicated with respect to the own behavior, but is simply an area in which the behaviors of
background currents generated, since these are influenced by the water layers adapt to the circulation of the surrounding
the Ekman transport (Fig. 10.5). areas and thus there is progressive behavior between them. It
These two zones have been defined by Niedoroda et al. is interesting to note that, where the depth allows, vertical
[26] as the friction-dominated zone and the geostrophic currents that cross the shear band appear to compensate for the
zone, respectively, and there may be a transition zone movements of the water mass. These vertical currents may
between them (Fig. 10.6a). The limits and dimensions of this close some convection cells (Fig. 10.6b, c).
zone depend on the speed and persistence of the wind, which The position of these vertical currents depends on where
control friction with the surface layer, as well as the slope of the layer of friction with the atmosphere converges with the
the coast and the nature of the bed, which influence the layer of friction with the bed. Therefore, the thickness of the
friction with the deep layer. Hence, the boundary depth water–bed friction layer is relative to the coastal slope, while
between the friction zone and the geostrophic zone ranges the thickness of the water–air friction strip is directly related
from 20 to 40 m. to the wind speed. So, the width of the coast affected by this
The main difference between the models of geostrophic convective cell varies with the weather conditions. With
zone and friction zone is that, in the first, the winds parallel strong and persistent winds, the topographical anomaly of
to the coast are able to generate currents perpendicular to the the sea surface will tend to be very pronounced, raising the
coast in the deep layer that arise to compensate for the pressure gradient and accelerating the bottom currents. This
pressure gradient caused by the Ekman transport. The result phenomenon contributes to wider turns and goes on to affect
is the development of parallel flows to the coast in the ever deeper areas of the shoreface.
shallowest and nearest fringe. On the contrary, in deeper and One aspect that remains to be analyzed is the effect of
near-bottom areas, the currents tend to be perpendicular, winds that are not strictly perpendicular or parallel to the
either directed towards land or towards the sea depending on coast. In these situations, the shallow and deep currents are
the direction of the wind. intertwined in a loop which circulates parallel to the coast
Another consequence of the existence of this varying zonal (Fig. 10.7). These turns represent the 3D equivalent of the
behavior is that the same wind will have different effects on cells described in the previous paragraph, but they are
the geostrophic zone and the friction-dominated zone. The affected by a longitudinal displacement to the coast parallel
presence of the transition zone between them does not have its to the coastal jet.
Fig. 10.5 Conceptual scheme of

the four different types of
interaction between wind-driven
currents and the shoreface areas
deep enough to develop an
Ekman circulation. The angles
between wind direction, surficial
currents and Ekman transport are
those typical for the Northern
Hemisphere
10.3 Marine Processes on the Coastal Front 119
Fig. 10.6 Scheme of the main

dynamic zones and layers of the
coastal boundary layer and
modeled geostrophic circulation
schemes (adapted from
Niedoroda et al. [26])
Fig. 10.7 Scheme of the gyres of

currents constituting the coastal
jet under winds oblique to the
coast (based on Niedoroda et al.
[26]). The senses of the coastal jet
and the gyres are typical for the
Northern Hemisphere

surficial tidal currents in elliptical
patterns during cycles of spring
and neap tides in the continental
shelf in front of Plymouth (UK)
There is also a longitudinal influence on the dimensions Coriolis turns similar to those shown in wind-induced cur-
of the coastal cells affected by this dynamic and the scale of rents. Work carried out in the 1980s showed that tidal cur-
convective turns. In this way, very long coastal cells con- rents in open marine areas do not simply have a
tribute to an acceleration of the result due to less interference two-dimensional flood and ebb pattern that passes through
of the currents with the features of the bed and the geometry a moment of zero speed before the currents are reversed. On
of the coastline. the contrary, considered in a horizontal plane, the currents
It is important to note that the current patterns explained rotate their direction while accelerating and decelerating,
in Fig. 10.7 represent circulation in a non-stratified water again generating an elliptical pattern (Fig. 10.8). In this case,
mass. If coastal waters have marked stratification in the area the bed slope, linked to the tidal range, make up the variables
affected by the turns, the flow patterns may be distorted by that determine the intensity of these currents [6]. Although
the presence of the pycnocline; however, the overall the patterns are elliptical rather than bidirectional, the pres-
behavior will be essentially the same. ence of the coast is manifested in the orientation of the
A singular situation occurs when winds blowing towards ellipse, since its maximum axis coincides with the averaged
the coast stop, especially if the winds have been strong, such orientation of the coast. In this way, the maximum tidal
as in stormy conditions. When calmed, the abnormal rise of currents run parallel to the coastline, while the currents to
the sea level (surges) that has been maintained during the and from the coast are minimal.
storm tends to be compensated for by strong currents cir- The variation of this elliptical pattern when approaching
culating from the land to the sea. These dense currents will the coast is very diverse, in time as well as in space,
circulate through to the bottom, and are able to deposit depending on the morphology of the shoreface, the nature of
material on the continental shelf. These currents are called the bed and the geometry of the coastline. When the process
storm return currents or also relaxation currents. is underway, the currents can be amplified when approach-
ing the coast if the tide wave enters narrow bays, while in
open areas the opposite effect occurs if the energy dissipates
10.3.3 Tidal-Induced Currents in the Coastal by friction. In any case, in the lower layers of the water mass
Front there is always a decrease in current speeds due to friction
with the bed (e.g., Fjeldstad [19]; Sverdrup [32]). The
Section 8.5 of this book discussed the origin and behavior of thickness of this shear-affected bottom layer depends on the
tidal currents in open marine areas and their relationship to roughness of the bed and the mean speed in the water col-
the tidal level curve. This chapter has described how in umn, which in turn is determined by the tidal range. It is
marine areas near the coast the tide behaves like a propa- precisely in this lower layer, close to the water–bottom
gating wave and the internal behavior of the water mass interface, that the bed load transport of sediment occurs.
closely resembles that of the waves. However, due to the
proximity of the bed and the long wavelength of the tide, the
orbital movements of the water mass are not circular, but 10.4 Dynamics of Sediment in the Coastal
very elongated ellipses [18, 28]. The analysis has only Front
looked at this behavior two-dimensionally in a vertical plane
to be able to compare it with tidal currents in channelized The sedimentary dynamics in the shoreface area have been
systems. In marine areas, however, the amplitude of the synthesized in recent work [13]. This work highlights the
system allows tidal currents to move three-dimensionally in importance of the papers of the end of the last century (e.g.,
any direction. These currents may also be affected by Niedoroda et al. [25]; Wright [35]) and recent efforts to
10.4 Dynamics of Sediment in the Coastal Front 121
determine sediment transport patterns on the coastal front water mass displacement vectors may interact with the
through the use of models (e.g., Aagaard and Hughes [1]). other currents already described in this area, contributing
Despite this, the authors themselves declare that these pat- to increasing or diminishing their potential for the net
terns are simple conceptual models and the complex prin- transport of the bed material. Only on coasts with the right
ciples that govern sedimentary processes in this area remain bathymetry and geometry can tidal currents in themselves
definitively unestablished. be an important agent for the transport of sandy material
Part of the complexity of conducting studies in this area on the open coast. However, these currents can be con-
lies in the difficulty of directly measuring the currents that sidered an effective mechanism for the movement of the
have been described in the previous sections. Any measure suspended material in the water mass, mainly because they
of the speed of the currents can never measure the currents contribute to diverting and redistributing suspended sedi-
individually according to their origin (wind-driven or tidal), ment that has arrived from the mainland rivers via turbid
but the final component of a combination thereof [10, 20]. plumes.
Another part of the complexity can be attributed to the dif- The difficulty that exists in understanding these processes
ficulty of measurement during processes that move a greater through the direct measurement of the currents acting on the
amount of sediment [35]. Intuitively, it will be understood coastal front can be sidestepped by analyzing the processes
that reliable measurements of turbulent processes that occur from a morpho-sedimentary point of view. The analysis of
during a storm are an impossibility [22]. Finally, it should be changes in the topography of the bed and, above all in the
noted that on the few occasions when there have been distribution and dynamics of bedforms appearing on the
attempts to directly measure the processes on coastal fronts, coastal front, can be a useful tool in understanding the
these have always been carried out on a short timescale, and dynamics of sediment transport in this area. This is the type
have not addressed the performance of the long-term pro- of approximation made by Cowell et al. [11, 12]. In this
cesses [23]. regard, although some authors claim that the current reso-
One observation that aroused interest from the beginning lution of the equipment is not enough to characterize these
of the studies of the coastal front was the concave profile, a changes [4], other authors such as [33] highlight the use of
characteristic observed by authors in the late nineteenth and underwater acoustics (side-scan sonar and multibeam echo-
early twentieth centuries [9, 17]. Since then, several attempts sounder) in the two most recent decades for the study of
have been made to explain this phenomenon. It seems that sedimentary dynamics in this area.
the most commonly accepted explanation is based on the The use of these techniques for the characterization of
erosive nature of the contact fringe between the sea and the bedforms and the calculation of transport vectors in bed load
coast (e.g., Aagaard and Sorensen [2]; Ortiz and Ashton deducted from these structures is well known. But, in
[27]). Thus, sediment deposited in this strip during times of a addition, acoustic signals can be used to determine the
different sea level tends to be used by currents and, espe- dynamics of the turbulent flows at the bottom, as they form
cially, by waves to feed coastal and also the deeper marine submerged plumes of highly concentrated suspended matter
environments. that disperses the acoustic signal as it passes through the
From the point of view of magnitude, wind-induced water column. The analysis of the acoustic signal with the
currents have been measured on coasts where the tidal appropriate instruments allows vertical profiles of the con-
influence is minimal. The currents in the water–bed interface centration of the suspended load and particle size to be
range from 5 to 20 cm/s, reaching up to 70 cm/s on the obtained, as well as visualization of three-dimensional
surface [24]. These speeds are enough to move sediments blocks of the turbulent flow. The application of this tech-
with sizes smaller than medium sand. In this case, there are nique is not intrusive and can be carried out with the spa-
works that have measured specific transport rates (e.g., tiotemporal interval deemed most appropriate to finally
Wright [35]), although there are few papers that determine understand the transport of sediments in this complex area.
sediment balances at longer timescales (decades to millen-
nia) from a general point of view. This is significant, because
these net sediment movements are responsible for deter- References
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Regarding the tidal currents, it can generally be said sediment transport approach. Mar Geol 390:321–330
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rise: a process-based approach. Earth Surf Proc Land 37:354–362
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in Fig. 10.8, these currents have a high symmetry, so that shelf. Annu Rev Fluid Mech 12:389–433
net residual transport in a given direction is usually almost 4. Anthony EJ (2009) Shore processes and their palaeoenvironmental
negligible and, if any, would be longshore. However, tidal applications. Elsevier, Amsterdam, 519pp
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beach. Earth Sci Rev 210:10334 Project no. MAS3-CT97-0086, 67pp
6. Battisti DS (1982) Estimation of nearshore tidal currents on 21. Kämpf J, Chapman P (2016) Upwelling systems of the world. In:
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Cont Shelf Res 10:1245–1257 of closure using data from Duck, NC, USA. Mar Geol 148:179–
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Short AD (ed) Handbook of beach and shoreface morphodynam- 25. Niedoroda AW, Swift DJP, Hopkins TS, Ma CM (1984) Shoreface
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JJ, Stede JH (eds) The sea, vol 6. Wiley, New York, pp 107–114 31. Scott JT, Csanady GT (1976) Nearshore currents off Long Island.
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(4):1–88
Chemical Processes and Sediments
on the Coast 11
These processes often go unnoticed, because their precipi-

11.1 Introduction
tation is volumetrically much lower than that produced by
the diffusion of turbidity, but this does not mean that they are
In the previous chapters, the origin of siliciclastic sediments
not important.
has been discussed, including how they reach the coast from
Lagoons, tidal flats and salt marshes are restricted envi-
the continent through the mechanical transport of particles
ronments where significant changes in the conditions regu-
generated by weathering processes. In addition to these solid
lating chemical and biochemical processes are common. As
particles, inland waters transport a dissolved ionic charge
these are quiet environments in terms of energy, they are
that comes from the chemical disintegration of the rocks.
also the most suitable environments for high activity of the
Throughout the Earth’s history, this ionic charge has enri-
organisms that results in the possibility of accumulation of
ched marine waters with salts, which contain much higher
organic sediments. A good example of this is the formation
concentrations of almost all soluble elements than inland
of peat associated with supratidal environments. It is in these
waters. However, this ionic charge does not remain perma-
systems associated with arid climates where evaporation is
nently dissolved in seawater. Through some purely chemical
the factor that regulates the relationship between solvent and
processes, as well as others related to the activity of
solute that causes a strong precipitation of salts, giving rise
organisms, a part of this charge precipitates to form chemical
to the characteristic deposits of chemical sediments called
and biochemical sediments. A typical example of a deposit
evaporites.
produced by chemical processes is the salt deposit resulting
This chapter will study in detail all the processes that
from the evaporation of a volume of seawater.
develop the sediments that will later become the chemical
The basic principles of chemistry state that, for chemical
components of rocks, as well as certain elements that will be
precipitation or dissolution processes to occur, the equilib-
included in terrestrial sediments in a lesser way.
rium conditions of the solution must be altered. Therefore,
the occurrence of these processes in natural environments
requires environmental changes. In the marine environment
these changes rarely occur, because the mass of water con- 11.2 Solubility: Control Factors
taining the ionic charge is enormous. That is why most of the
precipitation and dissolution reactions are related to the The processes of precipitation and dissolution are linked to
activity of organisms. However, coastal environments are the concept of solubility. Solubility is defined as the
especially changeable and theoretically present the ideal capacity of a substance to contain another. The substance
conditions for the chemical changes necessary for precipi- that is found in greater quantity is called the solvent, while
tation–dissolution processes to occur. the one that is mixed in smaller proportion is called the
River mouths are environments that are well known for solute. In natural environments, the most common solvent is
the processes of diffusion of suspended matter from the water, which has a great capacity to dissolve mineral sub-
turbidity maximum, as described in previous chapters. stances. In this chapter, water is always considered as a
However, they are also environments that are particularly solvent and the solid mineral phases as a solute. Thus, dis-
conducive to the processes of precipitation and dissolution. solution is understood as the process of breaking mineral
For example, the increase in salinity of the water from molecules and incorporating their elements into the dis-
mixing induces the precipitation of carbonates, as well as solved phase in an ionic form. In the opposite sense, pre-
iron and manganese (Fe and Mn) oxides, which are also cipitation is understood as the union of different ions
associated with other trace elements such as rare earths. dissolved in water to form mineral compounds that pass

https://doi.org/10.1007/978-3-030-96121-3_11
124 11 Chemical Processes and Sediments on the Coast
directly into the solid state. In this sense, precipitation is a others, the best way to understand the influence of these
form of crystallization that occurs at atmospheric factors on chemical reactions is to analyze them individually.
temperature.
There are several concepts related to solubility that
should be defined in order to understand the functioning of 11.2.1 Ionic Potential
precipitation–dissolution reactions. These are the concepts of
concentration, threshold of solubility, saturation and Ionic potential can be defined as the ability of ions to sur-
oversaturation. round themselves with water molecules. It is, therefore, an
The concentration is the proportion of solute contained intrinsic property of ions that depends on their charge and
in the solvent. It is usually expressed as amounts of solute in their size (ionic radius). Thus, the ionic potential is directly
relation to the amount of solvent. The units used to express proportional to the charge and inversely proportional to the
concentration vary depending on the units used to express ionic radius. The ionic potential is the property that gives the
the amounts of solute and solvent. In aqueous solutions, the elements their soluble or insoluble character.
ratio of weight of solute to volume of solvent is usually used, According to their ionic potential the ions can be classi-
although percentages (%), parts per thousand (%o) and parts fied into:
per million (ppm) are also used if concentrations are very
small. • Soluble cations: their ionic potential is less than 3.
The solubility threshold is linked to the concept of • Insoluble hydrolysable ions: with ionic potential between
solubility itself, since it is the maximum concentration of 3 and 12.
solute that can be dissolved in a given solvent. In other • Soluble anionic complexes: their ionic potential is greater
words, it is the maximum capacity that a solvent can contain than 12.
of a given solute. Mathematically this threshold is expressed
as a solubility constant (also solubility coefficient or solu-
bility product). Solubility threshold is notably affected by the
environmental conditions. 11.2.2 Temperature
Saturation is the relationship between concentration and
the solubility threshold. When a solvent contains all the The temperature of the water controls its solubility constant
solute it can, it will be right at the threshold. It is then said to and therefore its saturation capacity. An increase in tem-
be saturated and therefore in equilibrium. Under these perature implies an increase in the solubility of the sub-
conditions it will neither dissolve nor precipitate. If the stances in water that will favor the dissolution processes.
concentration of a solute is below the threshold it is said to This is because the movement of water molecules decreases
be unsaturated. In these conditions, the solvent can con- their cohesive forces and solute ionization is faster and more
tinue to dissolve solute until it reaches the threshold. If, on effective. A decrease in this will have the opposite effect,
the other hand, the concentration is above the threshold it is favoring oversaturation and, therefore, chemical precipita-
said to be oversaturated. It should be noted that in theory a tion processes (Fig. 11.1).
solvent can never contain a concentration of solute greater
than its capacity. Only if there is a change in environmental
conditions which decreases the threshold of solubility can
oversaturation occur and then precipitation will be induced.
The solubility of two substances and therefore the satu-
ration threshold depend directly on the balance of inter-
molecular forces between these two substances. The factors
that control this equilibrium in coastal environments are the
same as those that regulate reactions in the laboratory from a
chemical point of view [7]. Some are linked to the nature of
the substances to be dissolved (ionic potential), others
depend on the conditions of the environment in which the
reaction takes place (temperature, pH and Eh) and others are
part of the environmental conditions of the natural envi-
ronments (salinity, pressure of dissolved gases and organic
activity). Although in natural environments it is normal for Fig. 11.1 Solubility thresholds of NaCl and KCl as a function of
all these factors to act together, and changes in some affect temperature
11.2 Solubility: Control Factors 125
11.2.3 pH
The pH is the negative log 10 of the hydroxyl ion in a

solution and represents the quantitative measure that deter-
mines whether a solution is alkaline or acidic. Therefore, in
natural environments, as the pH depends on the concentra-
tion of H+ ions dissolved in water, this concentration influ-
ences the dissolution of other substances due to the common
ion effect. The pH also influences the solubility of salts
containing an anion that can undergo hydrolysis, as these
substances have negative ions that can react with the protons
in the water in an acidic environment to produce other
compounds. Thus, the pH can alter the balance in the dis-
solution of mineral substances depending on their compo-
sition, so that the solubility threshold is sometimes raised Fig. 11.2 Geochemical barriers in Eh–pH relationships
and sometimes lowered.
In coastal environments there are frequent changes in pH.
It should be noted that the pH of river water is slightly compounds. In this case, the solubility of one of the sub-
alkaline to slightly acidic, while the pH at the seawater stances influences the other. This is called the common ion
surface tends to be almost constant at 8.3 (slightly basic). It effect in chemistry. In the case of waters from natural
is evident that the processes of water mixing involve a environments, salinity is an important factor of influence,
change in pH for both seawater and river water, altering the since it is a reflection of the concentration of dissolved salts,
chemical balance and meaning a move towards situations of which may have ions in common with other mineral com-
oversaturation or unsaturation depending on the substance in pounds that may dissolve or precipitate. Thus, variations in
question. salinity can alter the balance in the saturation state of other
compounds.
In coastal environments a constant supply of fresh water
11.2.4 Redox Potential (Eh) from the continent, through rivers and rains, necessarily
reduces salinity, while evaporation associated with low
Oxidation–reduction potential (redox potential or Eh) is the water exposure increases it, especially in arid climates.
energy required to lose or gain electrons in a given oxidation These changes in salinity produce a shift in solubility
state. It is, therefore, a relative measure of the oxidation or thresholds that can lead to imbalances which cause precip-
reduction intensity in a solution—i.e., the concentration of itation and dissolution processes. The case of carbonate
electrons in a solution. Eh is directly dependent on the ionic precipitation in fluviomarine systems will be analyzed in
potential and, in natural environments, also on the pH, so detail later on.
that changes in Eh greatly influence the conditions that set
the equilibrium thresholds for solubility.
Both pH and Eh establish what are known as geochem- 11.2.6 Pressure of Dissolved Gases
ical barriers. Each geochemical barrier corresponds to a
value of Eh and pH, or a relationship between the two, and Marine waters contain a wide variety of dissolved gases.
limits the formation of a certain mineral. Thus, barriers Equilibrium processes at the surface of seawater bodies
divide fields of mineralogical stability. In sedimentary normally lead to saturation in dissolved gases and this will
environments, Eh and the Ph are interdependent, so, know- not change unless non-conservative processes occur. In
ing the stability limits of water, it is possible to draw it in a coastal systems, there are several processes that lead to
diagram with Eh as an ordinate and Ph as an abscissa and variation in dissolved gas concentration, mostly associated
show the fields for each of them (Fig. 11.2). with organic activity. Perhaps the most intuitive example is
the variation in O2 and CO2 concentrations due to respiration
of organisms and plant activity. In open coastal systems,
11.2.5 Salinity water movements (waves, tides and other currents) renew
gases at the water–atmosphere interface; however, in more
In solutions where there is more than one dissolved sub- restricted systems, these variations may not be compensated
stance, it is common for there to be some ion (anion or for and may induce chemical processes of precipitation.
cation) that is part of more than one of the dissolved A clear example is the influence of CO2 concentration on
water pH. An increase of this gas in solution can acidify the 1. The dissolution of gaseous CO2 in liquid water leads to
water with an immediate consequence in the dissolution of the formation of carbonic acid:
calcium carbonate. Conversely, the decrease of CO2 due to
processes of photosynthesis can produce the precipitation of CO2 þ H2 O $ H2 CO3
calcite. This phenomenon is often associated with coastal 2. Carbonic acid dissociates. This dissociation generates the
lagoons in tropical climates, such as the lagoon on Andros calcium bicarbonate anion and a hydroxyl cation:
Island in the Bahamas [6].
H2 CO3 $ H þ þ HCO
3
11.2.7 Organic Activity

This is why the dissolution of CO2 leads to the acidification
Physiological processes of organisms, such as photosyn- of the environment.
thesis, respiration or nutrition, directly affect the balance of 3. The bicarbonate dissociates to form the carbonate anion
solubility in coastal waters, as they affect many of the and another hydroxyl cation:
variables that have been characterized in the previous para-
HCO þ 2
3 $ H þ CO3
graphs. Examples that have already been cited are changes in
the concentration of dissolved gases that cause the processes 4. Finally, the carbonate anion can combine with the cal-
of respiration and photosynthesis. These changes in gas cium cation to precipitate calcium carbonate:
concentration directly influence the Eh and pH values of the
sedimentary environment. Other activities carried out by CO2
3 þ Ca
2þ
$ CaCO3
organisms, such as some mechanisms used by plants to
maintain their osmotic balance during tidal immersion pro-
cesses, are capable of directly modifying the pH of the water The combined result of all these reactions is summarized
surrounding plant tissues. In this way, the organisms cause in the following reaction:
imbalances in the environmental conditions that are capable
of inducing processes of precipitation and dissolution. All CO2 þ H2 O þ Ca2 þ $ CaCO3 þ 2H þ
these changes will be analyzed in detail at the end of this
chapter. This reaction shows how the dissolution of carbon
dioxide is responsible for balancing the solubility of calcite
in water, as it controls the pH of the environment in a sec-
11.3 Precipitation and Dissolution ondary way. If the reaction occurs to the right, precipitation
of Carbonates of calcite or aragonite will occur, while the reaction to the
left will produce dissolution.
Among the most common processes of dissolution and It is considered that there are five basic mechanisms
precipitation in nature are those involving calcium carbon- through which calcium carbonate precipitation is achieved:
ate. Many books on geomorphology explain these processes
in relation to karst phenomena occurring in continental • Temperature increase: All gases are less soluble in warm
environments, but these processes are equally important in water. A warming of the water will cause a loss of CO2
marine waters and especially in coastal waters, where sig- pressure and the pH will increase: both effects combined
nificant amounts of calcium carbonate (and also magnesium) will cause precipitation. Conversely, a cooling of the
can be formed in relation to changes in salinity, pH, Eh and water will be responsible for dissolution. For this reason,
dissolved gases. Many of these changes occur in relation to carbonate sediments are formed in warm environments,
organic activity, but many others have a purely chemical with tropical and shallow subtropical areas being the
origin. preferred places for precipitation.
• Increase in pH: The loss of acidity causes an imbalance in
the environment by modifying the pressure of dissolved
11.3.1 Chemical Equilibrium of Calcium CO2. This environmental change can cause the solubility
Carbonate threshold to be exceeded and oversaturation will occur
(Fig. 11.3).
The main control of solubility of calcium carbonate is pH, • Increased salinity: Carbon dioxide is less soluble in saline
which is controlled by the partial pressure of carbon dioxide water than in fresh water; therefore, as salinity increases
dissolved in water according to the following reactions, all through evaporation, the inhibition of calcium carbonate
of which are reversible: precipitation increases (Fig. 11.4).
11.3 Precipitation and Dissolution of Carbonates 127
CO2 produced causes the precipitation of CaCO3. On the

other hand, during the night, photosynthesis ceases but
respiration continues, so that the CO2 content increases,
which favors dissolution.
• Changes in pressure: Under the seawater column, the
partial pressure of carbon dioxide is much higher than the
atmospheric pressure. In general terms, for every 10 m of
water depth there is a pressure increase equivalent to
1 atm. As a result, deep seawater is enriched in CO2
relative to surface water. If deep water rises to the surface
as in upwelling processes, the pressure of the CO2 will
decrease and the gas will be released from the water,
resulting in the precipitation of calcium carbonate
crystals.
Fig. 11.3 Solubility of calcium carbonate as a function of pH in
marine waters (adapted from Langmuir [15]) The dissolution process is also favored by the same fac-
tors, which act in the opposite direction, so a decrease in pH
will raise the solubility threshold and favor the ability to
• Water agitation: When the water is agitated by the wind, dissolve. Similarly, an increase in pressure similar to that
saturation in dissolved gases is favored. The movement of produced in a downwelling process will favor the dissolution
the water favors the dissolution of CO2 and has a sec- of CaCO3. The influence of pressure is notable at high
ondary influence on the ionic imbalance of the calcium depths in the marine environment where there is a carbonate
carbonate. On the other hand, agitation favors the oxy- compensation level of approximately 4500–5000 m in
genation of the water and the development of organisms which the carbonate is completely dissolved; however, this
whose activity also influences this balance. process occurs in areas far from the coast.
• Organic activity: Plants and animals have a metabolism
that influences the concentrations of dissolved CO2 in
water. The activity of both types of organism has an 11.3.2 Precipitation of Calcium Carbonate
influence that shifts the threshold of solubility in opposite in Coastal Environments
directions. During photosynthesis, plants take up CO2 and
release O2 through the reaction: According to the above, the chemical precipitation of car-
6CO2 þ 6H2 O ! C6 H12 O6 þ O2 bonates occurs under very precise conditions. The temper-
ature of the water cannot deviate much from the average
temperature, as water that is too cold or too hot favors dis-
where C6H12O6 is a glucose molecule. solution processes. The same applies to the pH, which
Conversely, both animals and plants emit CO2 and con- cannot deviate more than one degree from neutrality, and to
sume O2 when they breathe. The organic reactions gen- the Eh, to salinity, to depth and water clarity. This means
erate diurnal cycles of precipitation and dissolution. that the environments in which carbonates can precipitate are
During the day, when photosynthesis takes place, the very specific and localized. These environments are found in
Fig. 11.4 Solubility of calcium

carbonate as a function of NaCl
concentration in an open system
[1]
shallow subtidal waters with high clarity. This area has been When the oversaturation process is slow, aragonite
called the carbonate factory by Schlager [18] and, although crystals often try to fix themselves on other pre-existing
in stratigraphic terms it is located on the carbonate platforms, carbonate elements. In this way, they can use carbonate
from a sedimentological point of view it can be considered particles suspended in water [11]. These particles will begin
that most of the conditions refer to coastal environments. to grow in a radial way until they reach a size sufficient to
It is in these areas that the chemical changes necessary to enter into imbalance with the flow that transports them and
achieve oversaturation with the consequent precipitation then they decant. These spherical particles are known as
occur most frequently. This precipitation will normally result radial oolites. Once decanted, the oolith can continue to be
in aragonite crystals, which are the most stable mineral form transported by traction. Its spherical shape will allow it to
at atmospheric temperatures. This type of elements formed roll along the bottom. If the oolith decants on a carbonate
in an abiotic way are called orthochemicals when they mud base, the small crystals can remain adhered to the
appear in sediments and sedimentary rocks. This process can exterior of the oolith, continuing to grow in the form of
take place in two different ways. Normally, these changes concentric sheets similar to a snowball, giving rise to oolites
occur progressively. In that case, there is no high oversatu- with a radial nucleus and a concentric exterior. Other car-
ration, but rather the ions combine to form crystals slowly. bonate elements can also be transported in bearings on this
Under these conditions, crystal growth predominates over micritic bottom. In that case, concentric oolites with a dif-
nucleation, since the latter process requires a lot of chemical ferent core would be formed (Fig. 11.5c).
energy. The result will be the precipitation of large crystals The concept of a carbonate factory is not limited to the
that are known texturally as sparite (Fig. 11.5a). If, on the production of chemical and abiotic precipitates, but Schlager
other hand, there is a sudden change in any of the conditions [18] also considers two forms of precipitation that occur
that control the soluble equilibrium, the state of oversatu- thanks to organic activity: bio-induced precipitation (where
ration is very far from the threshold of solubility. Then, in a the activity of the organism acts as a catalyst for the process)
very short time, there may be a large number of insoluble and bio-controlled precipitation (where the organisms are the
ions available for precipitation. The most effective process ones that cause the precipitation process as one of their
for removing all these ions from solution is nucleation, organic functions). Examples of bio-controlled precipitation
which will dominate crystal growth. Under these conditions would be the formation of bioclasts (Fig. 11.5d) and fecal
the result will be a large amount of crystals and all of them pellets (Fig. 11.5e). From this point of view, carbonate
very small, giving rise to a type of orthochemical known as factories located in shallow subtidal areas would be well
micrite (Fig. 11.5b). suited to support all three types of precipitation.
Fig. 11.5 Textural elements of

carbonate rocks. a Orthochemical
sparite. b Orthochemical micrite.
c Oolites. d Bioclasts. e Pellets.
f Intraclasts
11.3 Precipitation and Dissolution of Carbonates 129
Fig. 11.6 Physical transport of the sediment produced in the carbonate factory to other environments of the sedimentary basin [13]
A study by the same author carried out on a global scale 11.3.3 Physical Processes Moving Chemically
[19], proposes the existence of three types of environments Created Grains
that can be considered carbonate factories:
Precipitated limestone elements of any of the forms descri-
1. Shallow waters of tropical areas: These are dominated bed above in the carbonate factory can be transported by
by abiotic and bio-controlled precipitation (mainly by currents to other deeper or shallower areas of the same
photoautotrophic organisms). sedimentary basin (Fig. 11.6).
2. Cold water subtidal environments: These are dominated Waves are one of the main agents that move the precip-
by bio-controlled precipitates (mainly heterotrophic itates in the form of grains towards the coastline, where they
organisms). can be redistributed by tides. Pellets and ooliths are easily
3. Subtidal mud piles: These are dominated by abiotic and transported and will become part of the facies in many
bio-induced precipitates (mainly microorganisms). coastal environments. The carbonate skeletons and shells of
organisms can also be transported and deposited as bioclasts.
One of the changes related to abiotic precipitation that Micritic and sparitic carbonate muds have different destinies
occurs in cold water coastal environments is related to pH if their crystals remain disaggregated or if, on the contrary,
variations. When seawater enters coastal environments, the they have undergone aggregation processes. If they are
pH decreases and calcium carbonate dissolves. This process disaggregated, the micritic sludge can be incorporated into
is not very effective at higher temperatures. This is one of the the suspended transport of some coastal currents and then be
reasons why the dissolution of aragonite and calcite crystals directed towards the coast or towards the basin. On the coast,
by inorganic processes hardly occurs in warm shallow seas. they usually decant in the less energetic restricted environ-
However, not all of the processes of precipitation and ments such as lagoons or peritidal environments. In the
dissolution of carbonates in the coastal fringe are linked to basin, they will end up as part of the pelagic rain that feeds
the carbonate factory. One of the most characteristic changes the deep oceanic basins.
in the coastal zone is related to the mixing of river and The fragments of carbonate sediments that were depos-
marine waters. Actually, the processes of precipitation–dis- ited on the basin later become part of the carbonate crusts
solution of carbonates in the salt wedge are difficult to that can be fragmented and reworked by energy currents to
quantify. Recent laboratory experiments by Singurindy and give new sedimentary grains [9]. These grains are known as
Berkowitz [23] determined that salinity changes related to intraclasts (Fig. 11.5f). The morphology and composition
water mixing in river mouth channels induced oversaturation of intraclasts can be very varied, since these aggregates can
of carbonate and calcium ions, which then precipitate in the contain any of the carbonate elements described above.
mixing zone according to a salinity-dependent geochemical Intraclasts behave like any grain in water flows and can be
barrier (Fig. 11.4). This precipitation depends on the type of displaced to the coast by tides and waves or to deeper areas
water mixture and the volume of water to be mixed. In by other currents.
well-mixed systems, oversaturation is progressive through-
out the brackish water zone. In this case, a large volume of
precipitated crystals is obtained, which reach a good size 11.3.4 Early Cementation and Beachrock
when precipitation occurs slowly. Conversely, in systems Genesis
with a model of mixture by saline wedge with a well-marked
halocline, a smaller volume of crystals is produced, although Cementing is one of the main processes that produce a
the oversaturation is more abrupt and very small crystals are reduction in porosity (and permeability) in carbonate sedi-
precipitated. mentary rocks. Immediately after the carbonate sediment has
Fig. 11.7 Beachrock developed in a warm climate foreshore
been deposited, seawater begins to circulate through the sparitic, in some cases it can be micritic when situations of
pores. The water that circulates through the pores has a sudden chemical imbalance occur.
chemical composition very similar to the water in the envi- In coastal areas, these processes are often very pro-
ronment; however, different environmental conditions can nounced in intertidal zones. When they occur in open beach
occur in the pores. Therefore, changes can occur within the areas the formation of cements can solidify the beach sedi-
pores that lead to dissolution and precipitation processes, ment. The result is the very fast genesis of a hardened rock.
especially near the water–sediment interface. In the case that This hardened sediment is known by the generic name of
the conditions generate precipitation, carbonate cements are beachrock (Fig. 11.7). The formation of a beachrock stiff-
formed that give cohesion to the sediment. This early ens the beach and prevents the processes that normally
cementing process can build hard crusts or even contribute to remove sand from eroding the beach below its level. There
the transformation of the sediment into a sedimentary rock. are exceptions to this rule, as sometimes extreme events can
The cement in carbonate rocks in coastal environments disintegrate the beachrock, resulting in the formation of
has very varied origins. Invariably, it is a carbonate cement intraclasts that are redistributed on the coast by coastal
whose composition can be of aragonite or calcite rich in agents.
magnesium (Mg). The crystals normally present fibrous or Similar cementing processes can also occur in the topo-
acicular characteristics, radiating from the walls of the pores graphically higher area of tidal flats. In these environments,
on which they crystallize. In these cases, the pores can the interstitial water that fills the pores during periods of tidal
become totally filled due to the continuous precipitation exposure circulates through them, giving rise to superficial
from water circulating through them. Cementation may also capillary precipitation of aragonite and dolomite that act as
occur under conditions where the pores are not completely cement and lead to the formation of calcareous crusts [22].
filled with water, leading to processes similar to those that Accompanying this capillary cementation, evaporite crys-
occur in the vadose zone of inland aquifers. Aggregates of tallization of gypsum, anhydrite and also dolomite may
sparitic calcite of varying grain size, although generally appear [17]. These crusts come to form authentic intertidal
large, are then formed. Although the cement is usually beachrocks [5].
11.4 Evaporite Genesis 131
Fig. 11.8 Scheme of the classic

“barred” model for evaporite
genesis (adapted from Selley
[20])
11.4.1 Subtidal Evaporites: Salinas

11.4 Evaporite Genesis
The subtidal areas located on the coasts of these arid cli-
Coastal environments in arid climates present such extreme
mates concentrate the salts to form brines, especially when
evaporation conditions that the loss of solvent increases the
the renewal of water is scarce, as is the case with environ-
proportion of solute, so that the waters are always close to
ments restricted to the action of the waves. Because of this,
saturation, at least with respect to sodium chloride [4]. The
the genesis of subtidal evaporites is linked to the formation
term evaporite describes sedimentary deposits precipitated
of sandy barriers that favor the appearance of these restricted
from brines supersaturated by evaporation. Evaporites can
environments. Inside the barriers, the water will be trans-
be generated in both marine and inland environments [10],
formed into a brine until it reaches a state of oversaturation.
but coastal environments are capable of generating large
Then, the process of chemical precipitation of the salts will
volumes of evaporite sediments.
begin (Fig. 11.8).
The composition of evaporative precipitates is varied,
Tidal currents are responsible for the distribution of these
with halite, gypsum and anhydrite (chlorides and sulphates)
brines by other coastal environments such as subtidal
being the most common precipitates. Although the evaporite
channels and intertidal flats [12]. Brine can also be released
precipitation of aragonite, calcite and dolomite (carbonates)
to the outside world, being injected into open marine waters
is also very important, the chemical processes that give rise
through inlets during tidal ebb. These outgoing currents
to these minerals have been treated in detail in the previous
move along the bottom towards the shoreface, due to the
section, as they are distinguished compositionally indepen-
high density of these fluids. This process does not normally
dently of the origin of the precipitation.
contribute to the crystallization of evaporites in open coastal
From the point of view of processes, it is necessary to
waters, as the brines are permanently diluted in the large
differentiate between coastal evaporites formed in subaque-
volume of seawater.
ous environments and those formed by capillary evaporation
The aggradation of subtidal environments due to the
in the pores of the sediment [17]. The former would
sedimentary filling evolves towards the domination of the
preferably be formed in subtidal environments such as those
capillary processes; in this way, the evaporite lagoon would
related to lagoons. These environments are usually called
end up becoming a sabkha. In the transition period, it is
Salinas. The second type is restricted to the higher areas of
possible to observe cycles where the domination of direct
the tidal plains and are called coastal sabkhas. The pro-
precipitation and capillary precipitation alternate.
cesses, dynamics and evolution of both environments are
closely related.
Not all intertidal evaporites correspond to sabkhas. The 11.4.2 Intertidal Evaporites: Coastal Sabkhas
intertidal environments of tropical zones and some of the
mid-latitudes can also generate evaporite precipitation [3, The coastal evaporites have been named Gavish Sabkhas
21]. However, in this case they are not called sabkhas, since due to the important studies carried out by Eliezer [8] on the
this type of sedimentation is not dominant throughout the coast of the Sinai Peninsula. Sabkhas are characterized by
environment. salt precipitation associated with capillary circulation of
water through the pores of the sediment. The result is a Deformations such as disharmonic folds of decimeter
mixed sediment rich in salts. Although the origin of the scale and small diapirs may also occur.
water that evaporates is capillary circulation, there are also
surface intakes of brine from the nearby subtidal zone. The presence of anhydrite in these bands is usually sec-
Under storm conditions, the wind may push the brine from ondary, with a polygenic origin. One part is due to dehy-
the lake onto the supratidal flats. In this environment, brine dration of gypsum precipitated by evaporation [16]. Another
sheets of less than 2 cm accumulate and can either evaporate part is due to dolomitization and dissolution of aragonite
directly or infiltrate and then evaporate by capillary action. with formation of intermediate gypsum, which later passes
This process has been called flood recharge by Butler [4]. to anhydrite by dehydration. The anhydrite is usually formed
The evaporative facies of coastal sabkhas are generated in as nodules that vary between the millimeter and decimeter
bands (Fig. 11.9) according to their height with respect to scales.
tide levels [14]. Each of these bands is characterized by All of these processes of capillary precipitation are
different levels of evaporation and recharge, and the result is accompanied by early diagenetic transformations that result
a different mineralogy and texture of the evaporite precipi- in a hard salt crust of varied composition that fills the sabkha
tates, as well as of the sediments that accompany the evap- in a sedimentary sequence. When it rains, part of this saline
orites. The bands from the bottom to the top are: sediment is dissolved and the waters of the lagoon are
recharged with salt. The result of this cyclical process is a
• Upper intertidal: Blue-green algae mats interspersed with dynamic equilibrium in the ionic balance of the lagoon’s
aragonitic mud. It usually has gypsum cement and dolo- brine. This salt recycling is a consequence of the early dia-
mitic cement may also appear. genesis of the evaporites. On the other hand, the evaporation
• Lower supratidal: Soft masses (mush) of plaster and of inland waters after rainfall generates carbonate and gyp-
dolomitic and aragonite mud. Much microbial activity in sum cements. These minerals can also be remobilized
the form of organic salts. towards the lake, saturating its waters and ending up being
• Mid-supratidal: Corresponds to the zone of maximum deposited at the bed when evaporation resumes.
chlorinity and maximum evaporation, occasionally of
mixed waters of marine and continental origin. Halite
precipitates with parallel lamination, altered by the dia- 11.4.3 Reworked Evaporites
genetic formation of gypsum crystals and anhydrite
nodules. Dolomitization is also frequent. The minerals that result from evaporation precipitation can
• Upper supratidal: This area is controlled by inland waters be reworked and transported as grains by physical processes
and is only flooded once every few years, so it has a very in the same way as any of the components of siliciclastic or
low precipitation rate. It is dominated by diagenetic carbonate rocks. A typical example is the wind transport to
processes that totally modify the precipitation by evapo- form dunes (eolianites) that occurs in the intertidal zone of
ration. The gypsum is totally replaced by anhydrite which coastal sabkhas. Mass transport processes (landslides and
can have a nodular or chicken-wire structure. slumps) have also been described, facilitated by the high
Fig. 11.9. 3D-diagram

synthesizing the zones of
capillary evaporate precipitation
in a typical sabkha (based on
Purser [17])
11.4 Evaporite Genesis 133
4. Butler GP (1969) Modern evaporite deposition and geochemistry

of coexisting brines, the Sabkha, Trucial Coast, Arabian Gulf.
J Sediment Petrol 39:70–90
5. Davies GR (1970) Algal laminated sediments, Gladstone Embay-
ment, Shark Bay, Western Australia. In: Davies GR (ed) Carbonate
sedimentation and environments, Shark Bay, vol 13. Western
Australia Memoirs of the AAPG, pp 169–205
6. De Mora SJ (2007) Chemistry of the oceans. In: Harrison R
(ed) Principles of environmental chemistry. Royal Society of
Chemistry Publishing, London, p 263
7. Drever JI (1997) The geochemistry of natural waters: surface and
groundwater environments (3rd ed). Prentice Hall, New Jersey,
436pp
8. Gavish E (1974) Geochemistry and mineralogy of a recent sabkha
along the coast of Sinai Gulf of Suez. Sedimentology 21(3):397–
414
9. Hardie LA (1986) Stratigraphic models for carbonate tidal flat
deposition. Q Colorado Sch Min 81:59–74
10. Hardie LA (1991) On the significance of evaporates. Annu Rev
Earth Planet Sci 19:131–168
11. Heller PL, Komar PD, Pevear DR (1980) Transport processes in
ooid genesis. J Sediment Petrol 50(3):943–952
12. Hsü KJ, Schneider J (1973) Progress report on dolomitization.
Hydrology of Abu Dhabi sabkhas, Arabian Gulf. In: Purser EH
(ed) The Persian Gulf: Holocene carbonate sedimentation and
diagenesis in a shallow epicontinental sea. Springer Verlag,
Heidelberg, pp 409–422
Fig. 11.10 A metric-scale cross-stratification in a Miocene gypsum
13. James NP (1984) Shallowing-upward sequences in carbonates. In:
arenite (Conil, SW Spain)
Walker RG (ed) Facies models. Geological Association of Canada
Reprint Series vol 2, pp 213–229
14. Kinsman DJJ (1969) Modes of formation, sedimentary association
plasticity of these sediments. However, wind and gravity are and diagnostic features of shallow water supratidal evaporites.
not the only ways these grains are transported. Normally, Bull AAPG 53:830–840
aqueous transport is excluded when considering the trans- 15. Langmuir D (1997) Aqueous environmental geochemistry. Pren-
port of evaporite grains due to their high solubility, but they tice Hall, New Jersey, p 600
16. Moiola LM, Glover SI (1965) Recent anhydrite from Clayton
can be transported by fluid flow in saturated brines. Playa, Nevada. Am Mineral 50:2063–2069
For example, in southern Spain, metric-scale sedimentary 17. Purser EH (1985) Coastal evaporite systems. In: Friedman GM,
structures have been described in sandstones whose grains Krumbein WB (eds) Hypersaline ecosystems the Gavish Sabkha.
consist exclusively of gypsum crystals (Fig. 11.10). In this Springer, Berlin, pp 72–102
18. Schlager W (2000) Sedimentation rates and growth potential of
case, the origin of the brine is associated with the Messinian tropical, cool water and mud mound carbonate factories. In:
salinity crisis. Megaripples, ripples and other minor struc- Insalaco E, Skelton PW, Palmer TJ (eds) Carbonate platform
tures formed by the waves and tides may also be made up of systems: components and interactions, vol 178. Geological Society
evaporite mineral grains [2]. of London, Special Publication, pp 217–227
19. Schlager W (2005) Carbonate sedimentology and sequence
stratigraphy. SEPM Concepts in Sedimentology and Paleontology
Series no 8, 200pp
References 20. Selley R, 2000. Applied Sedimentology (2nd ed.). Academic Press,
London. 523pp
21. Shinn EA (1964) Recent dolomite, Sugarloaf Key. Guidebook for
1. Berkowitz B, Singurindy O, Lowell RP (2003) Mixing-driven GSA Field Trip No. 1, South Florida Carbonate Sediments.
diagenesis and mineral deposition: CaCO3 precipitation in salt Geological Society of America, pp 62–67
water–fresh water mixing zones. Geophys Res Lett 30(5):1253 22. Shinn EA (1983) Tidal flat environment. In: Scholle PA,
2. Boggs S (1995) Principles of sedimentology and stratigraphy (2nd Bebout DG, Moore CH (eds) Carbonate depositional environ-
ed). Prentice Hall, New Jersey, 744pp ments, vol 33. Memoirs of the AAPG, pp 171–210
3. Borrego J, Morales JA, Pendón JG (1995) Holocene estuarine 23. Singurindy O, Berkowitz B (2004) Carbonate dissolution and
surface facies along the mesotidal coast of Huelva, SW Spain. In: precipitation in coastal environments: laboratory analysis and
De Boer PA, Davis RA (eds) Tidal signatures in modern and theoretical consideration. Water Resour Res 40(W04401):1–12
ancient sediments, vol 24. IAS Special Publication, pp 151–170
Biological Processes and Sediments
on the Coast 12
plant activities which alter the internal structure of the sed-

12.1 Introduction
iment and others, even more extreme, which can contribute
to the disintegration and erosion of coastal formations. These
Biological processes occur on all coasts to a greater or lesser
are the processes of bioturbation and bioerosion. All these
extent. In many coastal environments these processes are
aspects will be discussed below.
overshadowed by the importance of the energy deployed by
physical processes, and in others by the magnitude of
chemical processes. However, in both cases organisms
always play a role and have a major influence on the effect 12.2 Bio-Induced Precipitation
the dominant processes have on sediments. This influence and Dissolution
has already been described when explaining some of these
processes in earlier chapters. In addition, the presence of The influence of some organic processes, such as respiration
organisms in the sedimentary substrate can influence the and photosynthesis, on the concentrations of dissolved O2
sedimentation and physical reworking processes. A classic and CO2 in the aqueous environment and, secondarily, on
example is the western Wadden Sea, where the activity of chemical precipitation processes has already been described
microorganisms in the pores of sediment generates mucous in previous chapters. In restricted coastal environments,
membranes that give it a cohesive character, making it dif- there are large numbers of microorganisms that make up the
ficult for tidal currents to rework it [2]. zooplankton and phytoplankton, as well as many others that
On the other hand, there are biological processes capable are living on the bottom in benthic communities. These
of generating sediments by themselves: they are the include macrofauna such as fishes, crustaceans, cephalo-
bio-induced chemical processes and the bio-controlled pro- pods, gastropods, bivalves and polychaetes; microfauna such
cesses [13]. Through bio-induced chemical processes, as larvae of these animals, foraminifera and ostracods; and
organisms are able to provoke changes in the surrounding also plants such as upper phanerogams (Fig. 12.1a), green
environment which induce the precipitation or chemical algae, diatoms and cyanobacteria, which populate the waters
dissolution of certain components of coastal waters. and beds of coastal environments [14]. All of these organ-
Organisms are also capable of producing chemical processes isms modify the pressure of dissolved gases in the water
within their forms as part of their biological functions, these with their physiological activity.
are the so-called bio-controlled processes. In this sense, Another example of the influence of these organisms is the
many aquatic animals and plants are able to organically direct modification of the chemical characteristics of their
extract dissolved mineral matter to form their shells and immediate environment to maintain their osmotic balance. In
skeletons. Once dead, these hard parts of the organisms this regard, it should be noted that the concentration of salts in
accumulate in the coastal facies as sediment of biochemical water in coastal environments is much higher than the con-
origin. Organic carbon from the soft bodies of the organisms centration of the same salts in intracellular fluids. In nature
can also accumulate in the sediment and even constitute a there must be a balance in the ionic concentrations of the fluids
type of sediment itself. Through this type of process, the that are located on both sides of an osmotic membrane such as
organisms come to constitute their own environments and the cell wall. In this case, organisms cannot choose to increase
build significant sedimentary bodies. Both processes gener- the salts of their intracellular fluids, because they cannot pass
ate a type of sediment known as biogenic sediments. through the cell wall. On the other hand, to increase the
The activity of organisms is not only expressed in the concentration, the cell must not expel the intracellular water,
genesis of the sediment. Beyond that, there are animal and because this would lead to dehydration that would be lethal

https://doi.org/10.1007/978-3-030-96121-3_12
136 12 Biological Processes and Sediments on the Coast
Fig. 12.1 Examples of

bio-induced precipitation. a The
photosynthesis of marine
phanerogams decreases the
concentration of dissolved CO2.
b Submerged roots of mangroves
alter the pH of the surrounding
water, inducing precipitation of
salts
for the organism. Therefore, since they cannot increase the The action of the underwater plants also plays a role in
internal concentration, the strategy of most aquatic organisms the biomechanical modification of the environment, since
is to modify some of the factors that control the balance of they act as a screen for the currents, reducing their speed by
solubility, in order to reduce the external ionic concentration. friction and contributing to the siltation of the suspended
Usually, the mechanism chosen is the modification of the pH matter.
or the combined Eh–pH equilibrium. In this way, flocculation
processes and chemical precipitation are induced in the waters
surrounding the organisms. This process is very common in 12.3 Bioconstructions
higher halophyte plants (Fig. 12.1b) that are submerged in
inter- or supratidal environments (marshes and mangroves) One of the most typical chemical reactions that acts as a
and generally occurs in both terrestrial [5] and carbonate physiological function inside organisms is the use of
environments [9]. chemical elements dissolved in water to form organic
12.3 Bioconstructions 137
skeletons. Any of the classes of mollusks as well as many which are associated with mean tidal level in intertropical
other microorganisms are able to build external shells to zones [12].
cover their bodies. Sometimes the protection of these shells Another mechanism by which bioconstructions can be
allows the animals to be mobile in the environment; how- formed is by the action of organic activity as a sediment
ever, in many cases the shelly organisms adopt a sessile way trap. The best-known case is the formation of stromatolites
of life and fix themselves to the substrate. This fixation often (Fig. 12.2d), which is a seasonal process. It begins in spring
has a colonial character. Thus, the skeletons of these periods, when blue-green algae (cyanobacteria) cover a stable
organisms are left accumulated after their death and massive solid surface on the bottom of very well-lit coastal waters.
structures are generated that become true buildings due to The adherent character of these algae means that, during
the accumulation of successive generations of organisms at periods of maximum water agitation, the carbonate particles
the same place. These buildings are known generically as that are transported in suspension become stuck to their
bioconstructions or bioherms (Fig. 12.2). surfaces. When many particles adhere, the algae eventually
Perhaps the most typical example of this type of organic die, solidifying a sheet of carbonates on the surface of the
construction are coral reefs (Fig. 12.2a). In this case, corals structure. A new spring will bring a new sheet of algae,
are small colonial polyps that secrete an external shell to fix starting the cycle again. These structures have been present in
themselves and live by capturing the organic particles cir- coastal environments since the Proterozoic. Nowadays, they
culating above them in the water flows with their tentacles. are linked to intertidal environments, although in the past
Actually, the formation of reefs also requires the participa- they have also developed in subtidal coastal environments.
tion of an algae that lives in a symbiotic way with the corals. A similar mechanism is that developed by Rhodophyceae
The algae often provide food for the corals, while the corals algae, which also adhere carbonate particles to their structure
provide the algae with nutrients from their organic waste, as of seasonal sheets. The difference is that in this case the
well as protection. algae are capable of resisting movement and shock, thus
There are other organisms capable of forming simpler colonizing any solid body transported in the well-lit waters.
bio-constructions. Sessile bivalves such as ostreids The algae can thus adhere to carbonate nuclei in traction,
(Fig. 12.2b) are capable of forming massive banks in tidal making them grow concentrically as they roll along the
areas protected from waves, even in estuarine environments bottom. These structures are called rhodolites and are
[11]. This is less common in the case of gastropods, although characteristic of restricted carbonate zones such as subtidal
a typical example includes vermetid banks (Fig. 12.2c) lagoons.
Fig. 12.2 Different

bioconstructions in coastal
environments. a Coral reef
(Dominican Republic). b Ostreid
bank (Atlantic Spanish coast).
c Vermetid bank (Mediterranean
Spanish coast). d Stromatolites
(Shark Bay, Australia)
The same phenomenon of particle adhesion can also be matter is mainly composed of plant tissues, there is a greater
developed by green algae in intertidal environments. This is variety of possibilities, since this matter can be deposited
the case of the so-called eelgrass. In this instance, the after being remobilized or it can also be found in situ. In this
importance of chemical processes is much less, with the second case, the first step of the process is peat and its later
combined mechanism between biological and mechanical transformations give rise to carbonaceous rocks.
processes dominating.
12.5.1 Hydrocarbons
12.4 Bioclastic Sediments
Hydrocarbons are molecular compounds consisting of car-
The rigid shells of the organisms generated through bon bound by covalent bonds to hydrogen and oxygen
bio-controlled precipitation can be transported by currents atoms. Most hydrocarbons have a natural origin and are
when the organism dies. In the case of free-living organisms, derived from sapropelic acids. Petroleum is a viscous liquid
incorporation into the detrital fraction is immediate. Thus, it generated from the decomposition of organic matter of
is usual to find sediment composed of microorganism shells, sapropelic character accumulated in the sediments. Some of
which are part of the bioclastic sand fraction, but the the hydrocarbons are in a gaseous state and are separated
skeletons of macroorganisms or their fragments can also from the oil by migrating vertically through the pores. The
constitute an important part of the sand and gravel sedi- interest of hydrocarbons lies in their use as the main source
ments. Bivalve shells and gastropod or scaphopod shells are of energy in the world today.
the most common examples. The most common sediments which may include animal
In the case of the bioconstructions described in the pre- organic matter include black shales, oil-bearing limestones,
vious section, the incorporation into the bioclastic fraction of oil shales and sapropelites [15]. If organic accumulation
the sediment is not so easy nor so immediate. However, the takes place in highly reducing environments of high bio-
rapid currents and strong waves that develop during storm logical productivity, the percentage of organic matter accu-
periods are able to pull fragments of organisms out from the mulated and preserved can reach significant values, much
banks and reefs and incorporate them into the coarser frac- higher than 3%. Black shales may contain more than 10% of
tion of the sediment by reworking and distributing this organic carbon, oil shales may exceed 25%, oil shales and
bioclastic sediment throughout other coastal environments. oil-limestone may exceed 50% and sapropelites may even
exceed 70%.
The transformation of organic matter into crude oil occurs
12.5 Organic Sedimentation thanks to bacterial activity in anoxic environments. There are
a large number of bacteria that participate in this decom-
The accumulation of soft tissues of animal or plant organ- position process. It is estimated that more than 160 genera
isms can give rise to a type of biogenic facies known as are responsible for the biochemical combination of the C, H
organic sediments. These organic components can be and O atoms in the long molecular chains of hydrocarbons.
mixed with particles of other origins constituting one more Essentially, the organic matter in oil sediments is of four
phase of the sediment. When the organic carbon component types: kerogen, asphalt, crude oil and natural gas. These are
of the facies constitutes a fraction greater than 3%, this forms highly complex organic compounds with a poorly defined
a sediment type called organic-rich sediments that by lithi- nomenclature, since these types cover a continuous spectrum
fication give rise to a group of sedimentary rocks of the same of hydrocarbons. The most abundant compound is kerogen,
name. and it is estimated that more than 80% of the organic matter
The organic matter may appear dispersed in the sediment, in petroleum sediments is found in this form [3]. Kerogen is
giving it a dark gray or blackish color, although it may also a dark and very dense substance, insoluble in water as well
appear as differentiated elements due to differing densities or as in acids, bases and organic solvents. At depth, tempera-
textures. One interesting aspect is the origin of the organic ture and pressure transform kerogen into other hydrocarbons
matter, which can be animal or vegetable, and this will through a process called catagenesis [10]. Asphalt, also
determine the first step of degradation in the transformation called bitumen, is very similar to kerogen, but is soluble in
of the initial organic matter. In general terms, this step can organic solvents, acids and bases. Asphalt can migrate,
generate sapropelic acids or peat. Sapropelic acids originate although with difficulty, and is found filling pores and
in anoxic environments from the organic remains of zoo- fractures in sedimentary rocks. Petroleum is liquid and nat-
plankton, phytoplankton, spores and fragments of higher ural gas is obviously gaseous. Both have a lower density that
plant tissues. These sapropelic acids are subsequently allows them to migrate more easily due to discontinuities in
transformed into hydrocarbons. If the origin of the organic the rocks.
12.5 Organic Sedimentation 139
Although hydrocarbons are generated in sedimentary The rise and fall of sea level mean that these coastal
rock rich in animal organic matter, their volatile nature environments have been developed throughout geological
causes them to migrate from the mother rock and accu- history in different positions on the present continental
mulate in other porous sedimentary rocks that are called shelves. Thus, they form part of the system tracks that
storage rocks. Finally, the presence of an impermeable rock constitute the genetic units that can be found there today.
at the top of the storage rock is necessary to seal the storage That is why numerous studies developed by the world’s oil
and prevent the migration of the oil to the surface, where it companies have been dedicated to the exploration of these
would volatilize into the atmosphere. This rock is known as areas.
the seal rock.
The genesis of hydrocarbons is linked in the collective
mind to the continental shelves, where the conditions of 12.5.2 Carbons
accumulation of organic matter can occur, as well as anoxia
and the high rates of burial necessary for the transformation Organic accumulation of plant tissues can lead to the for-
of this organic matter into petroleum sediments. However, mation of peat, which will later be transformed into carbon
some coastal environments are very conducive not only to through a process known as maceration. These plant
the formation of hydrocarbons, but also to their migration accumulations can be of two types:
and storage in suitable geological traps. Perhaps the deltas
are the best example, since environments rich in organic • Autochthonous accumulations: These are produced in the
matter can occur in the prodelta areas, where they will same place where the plant has lived, including the roots
quickly be buried by the progression of the deltaic front sand or rhizomes as well as the stems and leaves, although
bars producing favorable burial conditions. The sandy sed- only the roots wrapped in their inorganic matrix can be
iment of the deltaic front is also an excellent storage rock, preserved. These accumulations can be formed in conti-
while the clays of the deltaic plain have the right charac- nental and coastal environments. In coastal systems, there
teristics to act as a seal rock. are several ideal environments for the formation of this
Other ideal coastal environments for the accumulation of type of accumulation. Marshes and mangroves are the
organic matter are those located on waterfronts where up- most typical example, since they can accumulate signif-
welling processes occur. Thus, shoreface areas associated icant levels of peat made up of the remains of higher
with this phenomenon develop bodies of organic silty sands halophyte plants (Fig. 12.3a). This is the most common
suitable for transformation into hydrocarbons. case for the formation of coals in coastal environments,
Fig. 12.3 Vegetal

accumulations. a Peat in the
Everglades swamp (USA).
b Seagrass flat (SW Spain).
c Algal mat (SW Spain). d Algal
allochthonous accumulations on a
beach (S Portugal)
since the pores of the clays that surround the organic plant • Oligotrophic environments: Also called ombrogenic or
matter are isolated from environmental water and the ombrotrophic. These are environments with moderately
conditions of anoxia necessary for maceration can occur well-oxygenated water, since it comes directly from
there. Native accumulations of marine phanerogams rainwater or water from the tidal circulation. Large
(seagrass) and algae (algal beds and algal mats) may also communities of vascular plants generally develop in this
develop (Fig. 12.3b, c). However, the decomposition of type of environment. The degree of waterlogging is
such accumulations usually results in humic and sapro- usually so high that the roots do not need to penetrate
pelic acids, which normally oxidize and do not lead to the deeply to obtain the water and they develop horizontally,
formation of carbonaceous rocks. giving rise to a very dense network with hardly any
• Allochthonous accumulations: These occur after plant interstitial inorganic matter and with a practically null
mass transport and accumulation in residual areas. In this edaphic horizon. Therefore, the feeding of the plant is
way, algae accumulate on beaches (Fig. 12.3d) and some produced by capillarity, at the expense of the nutrients
areas of tidal flats, but also exposed fragments of conti- supplied by the plant accumulation itself. This fact con-
nental halophytes that can be uprooted from their place of tributes to a decrease in the plant biodiversity of the
origin by very energetic events and reach estuaries and system, so much so that these populations can even
deltas. Although these accumulations can generate carbon become monospecific. The decomposition of plants pro-
deposits, they rarely do so. Most often they decompose, duces a high quantity of humic acids, which lower the pH
generating volatile sapropelic acids. What happens is that to such an extent that they inhibit bacterial activity and
these allochthonous accumulations are usually not very tend to preserve the internal structure of the plant.
powerful and are dispersed, almost never giving rise to The plant accumulations produced in these environments
economically profitable deposits; however, they can be have the following characteristics: (1) water content over
good paleogeographic markers. 90%; (2) low quantity of mineral impurities; and
(3) cellular structures with a high level of preservation.
As has been observed, not all accumulations of organic Mangroves are an excellent example of this type of
plant matter are transformed into carbon. For an organic environment.
accumulation to result in a carbonaceous sediment, other • Eutrophic environments: Also called tropogenic or
conditions must also be met: minerotrophic. In this case, the water has good circulation
before it is dammed, and it can even involve environ-
1. That the accumulations are thick enough. ments where the water is not completely dammed and has
2. That no oxidation processes of organic matter occur after a relative renewal. In coastal systems, these conditions
burial. In order for this condition to be met, the accu- can occur in environments such as deltas, estuaries and
mulation needs to occur in a sub-aqueous environment, supratidal flats. This circulation makes the water carry
since water, containing less oxygen than air, is usually abundant nutrients and dissolved minerals, which deter-
less effective in the oxidation process. Oxidation occurs mine the high plant biodiversity of the system and the
less when there is less dissolved oxygen in the water and development of a greater humic horizon than in the pre-
it is usually null in anoxic environments. For example, in vious case. After burial, the porewater is isolated from the
water with 10 mg/l of dissolved oxygen, the oxidation overlying water. Then, the great amount of decomposing
time is almost 11 times longer than in the atmosphere. tissue quickly consumes the oxygen dissolved in the
With half that level of oxygen (5 mg/l), the oxidation porewater, supplying favorable conditions for the for-
time is 100 times longer. In supratidal environments, mation of coal.
surface water usually has around 6 mg/l of oxygen, with The coals formed under these conditions present a large
less than 1 mg/l at the bottom. quantity of inorganic impurities and the plant structures
3. The content of nutrients and dissolved salts will deter- are usually less well preserved due to the possibility of
mine the volume of plants, the activity of the roots and reworking the plants by the currents before they are
the volume of inorganic impurities that the coal will definitively accumulated.
contain.
The transformation of plant organic matter into peat is an
Taking these factors into account, there are two types of essentially biochemical process carried out by anaerobic
environments for the formation of native plant accumula- bacteria. These bacteria are capable of decomposing plant
tions that can give rise to the maceration process necessary tissues by draining impurities out of the peat. This peat is the
to generate charcoal: basis for the maceration processes that begin after the
12.5 Organic Sedimentation 141
increase in pressure and temperature that burial entails. The

maceration processes give rise to the rocks of the coal series,
which increase in carbon content at the same time as their
purity and their calorific power increase as they lose H, O
and S. In this process, they also lose the gases associated to
sapropelic acids that accompany the first phases of the for-
mation of coals. The components of the coal series are:
lignite (brown coal), hard coal (bituminous coal) and
anthracite.
12.6 Alteration of the Sediments

by Organisms: Bioturbation
The activities of organisms in the sedimentary substrate of

coastal environments involve an alteration of the primary
structures of the sediment. This physical alteration is known
as bioturbation. Both animals and plants can produce bio-
turbation. Annelids (Fig. 12.4), bivalves (Fig. 12.5) and
crustaceans (Fig. 12.6) that live as infauna in the subtidal
and intertidal flats drill the sediments with their galleries;
gastropods, crustaceans and the organisms that are part of
the infauna develop tracks on the sediment surface and
generate a lower degree of bioturbation, while the roots of
the higher plants intensely bioturbate the sediment of the
supratidal environments such as marshes and coastal dunes.
Within coastal environments, it is the tidal systems that
have the greatest potential for organisms to develop biotur-
bation. Lagoons, tidal flats, channels and channel margins of
estuaries and deltas display a range of tracks and galleries.
Fig. 12.4 Examples of bioturbation by annelids in coastal environ-
Also, shoreface environments, where wave energy and
ments. a Surficial expression of Arenicolides ecaudata in a sandy tidal
sediment remobilization are lower, have many organisms flat. b Profile of annelid bioturbation by Arenicolides ecaudata in a
present at the bottom that alter their original structure. In muddy tidal flat
more energetic and mobile environments such as nearshore
or tidal deltas, bioturbation by bivalves is also important;
however, the high mobility of sediment in these systems animals and plants. In these systems, there is a clear sea-
negatively influences the preservation potential of the gal- sonality of bioturbation [4] due to biomass variations and
leries. In supratidal areas such as tidal flats, it is the roots of changes in the volume of sedimentary input [7]. In general
the upper halophytes that are responsible for most of the terms, bioturbation in the internal zone of estuaries and
bioturbation (Fig. 12.7a). deltas increases towards land.
Physical processes and sediment characteristics have a Organisms capable of generating galleries also show their
great influence on the distribution of benthic organisms. In potential to mix the sediment of different lithologies. It is
intertidal systems, critical tidal levels, which control the common to find in one sediment galleries filled by sediment
degree of exposure and submergence of the tidal band and of another type coming from the upper or lower stratum.
the strength of the tidal currents, mark the degree of toler- There is also a clear influence of sedimentation rates on the
ance of the organisms and their vertical distribution in the filling of galleries by those organisms that live permanently
intertidal zone. In this case, the bioturbation degree has been near the surface to capture the suspended particles as a way
described as one of the most important features in charac- of feeding. The gradual growth of the bed means that they
terizing the tidal facies [14]. In general terms, bioturbation have to re-grow the gallery upwards by filling the bottom. In
increases towards the highest part of tidal environments. this way, an interior lamination of the gallery develops,
In fluviomarine systems such as estuaries and deltas, the whose lines have changes in thickness that show the
chemical parameters of the water (temperature, salinity and long-lasting tidal cycles. These structures have been called
pH, among others) control the inland distribution of both tubular tidalites [8].

bioturbation by bivalves in
coastal environments. a Bivalve
burrow in a mixed tidal flat.
b Muddy sediments completely
bioturbated by burrowing of
Cerastoderma glaucum

bioturbation by crustaceans in
coastal environments. a Surficial
aspect of crustacean burrows in a
sandy tidal flat. b Geometry of a
crustacean burrow (Gyrolites) in a
sandy tidal flat (photograph
courtesy of E. Mayoral)
Bioturbation is also significant in coastal dune systems. systems, there are numerous organisms that cause bioero-
The activity of macroorganisms is marked as footprints that sion. Annelids, sponges, echinoderms, mollusks, crustaceans
deform the internal structure. In some dunes, the passage of and fishes include numerous genera whose activity causes
goats and other animals has been fossilized as a deformation this process. On the coast, there are numerous environments
of the characteristic cross-layering of the dunes. The root where bioerosive organisms carry out their activity. How-
activity is even more significant, as it is able to completely ever, it is the rocky coasts and reefs where this process is
erase the evidence of the internal dune structure (Fig. 12.7b). particularly important.
Bioturbation is shown to be a preserved remnant of the On rocky coasts, abrasion platforms and cliffs, there are
activity of organisms in coastal sedimentary beds. Therefore, good examples of chemical bioerosion. Higher plants, algae,
the potential of ichnofacies as indicators of coastal envi- lichens and some animals living on the rocks produce
ronments is very remarkable [6]. chemical secretions of an acidic nature that degrade the less
resistant minerals and contribute to the disintegration of the
more resistant grains, which are eroded by the waves into
12.7 Bioerosion sand. Also characteristic of these coasts are lithophagous
organisms, which wear down the rocks using a mixed pro-
The physical and chemical activity of organisms in the cess of chemical attack and mechanical wear. There are
coastal substrate can cause disintegration and erosion of the animals such as mollusks (bivalves and gastropods) and
substrate. This process is known as bioerosion. In coastal polychaetes that perform internal drilling activity to the
12.7 Bioerosion 143
degrade coral formations through chemical attack. Also

important is the activity of the fish that feed on the algae that
live on the corals. Parrotfish and surgeonfish grind the car-
bonate material ingested by eating the algae to return it to the
sea in the form of sand-sized bioclasts. Each of these fish is
capable of generating almost half a cubic meter of carbonate
sand per year [1].
References
1. Bellwood DR (1995) Direct estimate of bioerosion by two

parrotfish species, Chlorurus gibbus and C. sordidus, on the Great
Barrier Reef, Australia. Mar Biol 121(3):419–429
2. De Boer PL (1981) Mechanical effects of micro-organisms on
intertidal bedform migration. Sedimentology 28:129–132
3. Boggs S (1995) Principles of sedimentology and stratigraphy (2nd
ed). Prentice Hall, New Jersey, 744pp
4. Dalrymple RW, Makino Y, Zaitlin BA (1991) Temporal and
spatial patterns of rhythmite deposition on mud flats in the
macrotidal Cobequid Bay-Salmon River estuary, Bay of Fundy,
Canada; clastic tidal sedimentology. Can Soc Pet Geol 16:137
5. Frey RW, Basan PB (1985) Coastal salt marshes. In: Davis RA
(ed) Coastal sedimentary environments, 2nd edn. Springer Verlag,
Heidelberg, pp 101–169
6. Gingras MK, MacEachern JA (2012) Tidal ichnology of
shallow-water clastic settings. In: Davis RA, Dalrymple RW
(eds) Principles of tidal sedimentology. Springer, Heidelberg,
pp 57–78
7. Gingras MK, Pemberton SG, Saunders T, Clifton HE (1999) The
ichnology of modern and Pleistocene brackish-water deposits at
Willapa Bay, Washington; variability in estuarine settings. Palaios
14:352–374
8. Gingras MK, Bann KL, MacEachern JA, Waldron W, Pember-
ton SG (2007) A conceptual framework for the application of trace
fossils. In: MacEachern JA, Bann KL, Gingras MK, Pemberton SG
(eds) Applied ichnology, vol 52. SEPM Short Course Notes, pp 1–
25
9. Hardie LA (1986) Stratigraphic models for carbonate tidal flat
deposition. Q Colorado Sch Min 81:59–74
10. Hunt JM (1996) Petroleum geochemistry and geology (2nd ed).
WH Freeman, New York, 340pp
11. Petuch EJ, Myers RF (2014) Molluscan communities of the
Florida Keys and adjacent areas. Their ecology and biodiversity.
Fig. 12.7 Examples of bioturbation by roots in supratidal environ- CRC Press, Boca Raton, 300pp
ments. a Root bioturbation in salt marsh facies. b Root bioturbation in 12. Safriel UN (1974) Vermetid gastropods and intertidal reefs in
dune facies Israel and Bermuda. Science 186:1113–1115
13. Schlager W (2005) Carbonate sedimentology and sequence
stratigraphy. SEPM concepts in sedimentology and paleontology
holes they develop, while others such as urchins or starfish series no 8, 200pp
perform this erosion externally to the rocks, without devel- 14. Swinbanks DD, Murray JW (1981) Biosedimentological zonation
of boundary bay tidal flat, Fraser river delta, British Columbia.
oping cavities. Sedimentology 28:201–237
The activity of these lithophagous organisms is also 15. Yen TF, Chilingarian GV (1976) Introduction to oil shales. In:
present in the reefs, although there it is linked to the behavior Yen TF, Chilingarian GV (eds) Oil shale. Elsevier, Amsterdam,
of others, such as sponges, algae, fungi and bacteria, that pp 1–12
Extreme Events
13
ruled out. The social and political impacts of events depend

13.1 Introduction
on the development of countries and their response capacity.
Typically, more developed countries have been more able to
The action of waves, tides and marine currents, as well as
establish effective strategies to deal with such events. One
their interaction with continental agents, is a continuous
only has to compare the difference in the number of deaths
phenomenon of erosion, transport and deposition of material
between two tsunamis with similar characteristics: that of
in cycles that mark the ordinary sedimentary dynamics of
Indonesia (2006) and Japan (2011). The countries affected
coastal systems. However, these ordinary dynamics are
by the 2006 tsunami were less prepared, with a cost in lives
interrupted at certain times by specific phenomena that dis-
that almost reached 228,000 deaths. In contrast, in Japan,
play enormous energy on the coast. These are the so-called
with a well-educated population, the figure was one order of
extreme events or high-energy events. High-energy events
magnitude lower, at below 16,000 deaths.
are processes that occur in the very short term (minutes,
Knowledge of these events is important in order to
hours, days). These short time intervals could be considered
understand their dynamics and behavior, but also for their
instantaneous from a geological point of view.
impact on society. Perhaps because of this social impact, the
The release of these enormous amounts of energy on the
processes associated with high-energy phenomena have been
coast is manifested in the large volumes of ocean water that
the object of scientific interest in recent decades, especially
move landwards. At the same time, large areas of land are
since media coverage of such events as the aforementioned
covered by seawater. The distribution of this energy on the
tsunamis or Hurricane Katrina in 2005. In spite of this, the
coast involves very radical morphological and dynamic
processes that occur during these phenomena and the
changes. These changes represent great threats of damage to
mechanisms of transport are not very well studied due to the
property and ultimately a high risk to human lives.
practical impossibility of carrying out measurements and
Normally, the high energy of these phenomena is used in
observations during their development.
the transport of sediments. However, the increased transport
capacity is not compensated for by a sedimentary input of
the same magnitude. Therefore, the material displaced by the
flows in these events comes from the reworking of sedi- 13.2 Extreme Storms
mentary material from previous coastal formations.
The time of their arrival and their magnitude are unpre- The term storm is defined in the Beaufort Scale as a situation
dictable, but when a coast is affected by this type of event that occurs above force 8, which is classified as a strong
every certain period, the fact of their arrival should not be gale. Situations of force 9–12 would be defined by the
unpredictable. Coastal inhabitants must necessarily take intensity of the storm. The situations of strong gale, storm,
measures to minimize the effects of these phenomena on violent storm and hurricane are defined respectively. This
infrastructure and their cost in human lives. There are dif- means winds of over 72 km/h and up to 110 km/ in category
ferent types of possible response to extreme events. Some 1 cyclones and up to 250 km/h in category 5 cyclones. In
measures are of an active nature, as is the case with pro- colloquial terms, a storm situation is understood to be one in
tection structures. However, the most effective measures are which the winds and waves reflect conditions that are much
those that come from adequate management and planning, more intense than usual (called good weather conditions). In
which include public education measures and evacuation any case, storm situations always occur in conjunction with
protocols. Even in extreme cases of reoccurrence, definitive low pressure systems. At latitudes above 30°, these low
evacuation and relocation of populations at risk cannot be pressure systems are called storms, while in inter-tropical

https://doi.org/10.1007/978-3-030-96121-3_13
146 13 Extreme Events
areas they take on different names depending on the ocean

they are acting on. Thus, in the central and eastern Pacific
Ocean, they take the generic name of tropical cyclones,
while in the Atlantic they are called hurricanes (from the
word used by Carib Indians) and in Asia they are known as
typhoons (a word taken from Chinese).
All coastlines are occasionally hit by storms or cyclones.
Each storm represents an increase in energy above the
average of the processes that normally act on it. However,
since each coast suffers several seasonal storms per year,
these can be considered as part of the ordinary dynamics of
the coast. There are even coasts whose dynamics are dom-
inated by storms [2]. However, on some occasions, an
exceptional storm develops that involves an increase in
energy that exceeds normal storms by an order of magnitude.
The behavior of these exceptional storms and their sedi-
mentary record are much more complex than those of normal
storms [6].
If a storm is defined by an increase with respect to the
energy that normally acts on the coast, it must be taken into
account that the energy is growing in a quadratic manner
with respect to the height of the waves (Chap. 7, Eq. 7.1).
Thus, a double increase in wave height means a quadrupling
of the energy, while a triple increase in height means that the
Fig. 13.1 Diagram showing the origin of a surge in the center of a
energy is multiplied by nine. Data from Project Stormfury low-pressure system
allowed the calculation that the energy reaching the coast in
one of these extreme events can reach the equivalent of 600
terawatts [22]. This energy is 5000 times higher than the rise in the sea surface (Fig. 13.1). The influence of low
energy generated in an average nuclear power plant. Some pressure is quantifiable [12]. In general terms, for every
authors [15] have estimated that the transport capacity of one millibar that the barometer drops, the sea surface rises
of these events with a return period of tens of years is much 14 mm [17]. This would mean that a 40 millibar drop,
higher than the energy dissipated on the coast by the waves characteristic of a typical Atlantic storm, would be able to
during the period between two successive events. This gives raise the sea level by about 54 cm, whereas a hurricane like
an idea of the extent to which the arrival of high-energy Katrina, with a 109 millibar drop in pressure, would mean a
events on a coast can transform its dynamics and condition sea level increase of 1.47 m due to pressure alone.
its sedimentary record. More storm data can be found on the It is more difficult to quantify the effect of the wind. In the
National Oceanic and Atmospheric Administration open sea there is practically no effect of vertical displace-
(NOAA)’s Atlantic Oceanographic and Meteorological ment of the water surface due to friction with the moving air.
Laboratory website. On the contrary, in coastal areas the presence of the bottom
The action on the surface of the sea of a wind situation and the coastline cause interference with the free displace-
above force 8, together with the low pressures that accom- ment of the water mass due to wind-directed currents
pany the passage of cyclones, make two effects generated by (Fig. 13.2). This raises the sea level when the air blows
a storm. The first, and most obvious, is the increase in the perpendicular to the coast. The magnitude of these vertical
size of the waves generated by wind friction in the water movements is not directly quantifiable, as it is in the case of
mass. The second is a combined effect of low pressure and pressure influence, since the elevation depends on geomet-
wind action, and is the topographic elevation of the sea rical factors of the coast, such as the angle between the wind
surface which is called a meteorological tide or surge [8]. and the coastline or the relationships of slope and width of
the shoreface.
In certain conditions, wind uplifts can even be greater
13.2.1 Surges than those caused by atmospheric pressure. A well-known
case is the elevation caused by the southeast winds over the
The influence of low pressures combined with the action of Argentine coast, especially in the estuary of the Río de la
strong winds characteristic of cyclones is manifested by a Plata, where the funnel shape increases the water level due to
13.2 Extreme Storms 147
Fig. 13.2 Diagram showing the

influence of the wind in
generating a coastal surge. EEHW
Extreme equinox high water
the convergence effect [11]. This phenomenon is known as other hand, the waves exceed the height of the dune system,
the sudestada. The largest wind flood in the history of an overwash phenomenon will occur and the sediment will
Buenos Aires occurred on April 15, 1940, raising the water be displaced landwards.
level by 4.4 m. Chapter 7 explained how the dynamics of a
During a surge, the elevations due to the pressures are wave-dominated coast can be described as a function of the
combined with those induced by the wind. The displacement probability of waves of a certain size acting on it. Normally,
of a low pressure system is usually slow and so this elevation this probability is calculated as an annual exceedance
can be sustained for several days [14]. The duration of this probability (Fig. 13.3). The graph in Fig. 13.3 shows an
phenomenon ensures that at certain points the rise will example for the west coast of Europe: it can be seen that
coincide with high tides. During these times, flood peaks can there is a probability of 1 that a wave will not exceed 9 m,
be particularly significant. which means that waves of these dimensions will not occur
in a normal year. It is clear that ordinary years also produce
storms, although these ordinary storms do not produce
13.2.2 Extreme Storm Waves waves larger than 9 m on the coast analyzed in this graph.
However, as mentioned earlier, there are exceptional
During storms, the action of the wind produces a notable storm situations where this normal situation is overcome.
increase in the size of the waves acting on the coast. It must These situations occur at intervals of many years. In order to
be taken into account that the waves acting on coastal sys- calculate the probability of these storms occurring, and with
tems do not only correspond to the ones being generated by them larger waves, it is necessary to establish the return
the wind in this same place, but they also include those period. The return period is the space of time that excep-
propagated waves that the same cyclone generates offshore tional waves of certain dimensions take to return. Typically,
that now reach the coast. The result is that, during the the return period for exceptional wave sizes is measured in
duration of the storm, the waves discharge an enormous tens or hundreds of years.
amount of energy on the coast. This energy is used to move
sedimentary material from one place to another within the
coastal system, but also to transfer material from the coast to
other neighboring environments, such as the shelf or the
continent.
The larger dimensions of the wave are manifested in the
generation of more energetic breakers. A very frequent
example occurs on a coast of moderate slope, where the
waves normally break in a spilling type way; during storms
these may become plunging type breakers or even more
energetic types such as collapsing or surging. This implies
that the dissipation of energy is lessened when compared
with other phenomena such as the reflection of the waves. At
the same time, the appearance of more energetic breakers
favors erosional processes in the wave-breaking zone.
Under these conditions, it is common for significant
erosive scars to appear in the foreshore and backshore areas.
If the wave height does not reach the maximum height of the
beach, eroded sediment from these zones is displaced to the Fig. 13.3 Graph of annual probability of exceedance for significant
shoreface by the backwash and reflected waves. If, on the wave heights (Hs). Example of a coast from NW Spain
13.2.3 Combined Surge–Storm Waves the first line of human constructions. Therefore, knowing the
dynamics of storms is fundamental for the preservation of
When a storm reaches a coast, the wind acts in such a way both natural systems and human infrastructures.
that it usually surges together with large waves (Fig. 13.4). Although wind surges and waves are usually simultaneous,
The case shown in Fig. 13.4 corresponds to the arrival of sometimes they are not. The internal structure of cyclones
Storm Emma on the southwest coast of Europe in early locates low pressure zones in the center of the system, while
2018. In this event, the dominant winds acted in conjunction the more energetic winds are located around the storm. The
with the low pressures, causing the surge to coincide exactly direction of approach of the cyclones to the continent can be
with the timing of the larger waves. In this situation, the made at different angles to the coastline. This implies a range
height reached by the surge places the height of the wave of possibilities. On the one hand, when a cyclone reaches a
breakers in the areas of greater slope that are located above coast, the center of the cyclone does not always pass over it.
the backshore. The action of the big waves occurs at these On the other hand, the cyclone can arrive from the sea and run
moments at very high levels, but, in addition, the energy of along the coast or enter the continent. According to the route,
the wave is applied to areas with a greater slope. Both and taking into account the direction of rotation of the cyclone
phenomena—larger waves and steeper slopes—favor stron- (counterclockwise in the Northern Hemisphere and clockwise
ger erosion in these areas. The first line of dunes in natural in the Southern Hemisphere), three situations can occur
systems is located there, while in anthropized systems it is (Fig. 13.5; Carter [7] and Woodroffe [28]).
Fig. 13.4 Graphs of wind speed,

significant wave height and surge
that occurred during the arrival of
Storm Emma (February 28 to
March 1, 2018) and a subsequent
storm (March 2–3). The
depression in the curves early on
March 2 corresponds to the
interval between the storms
Fig. 13.5 Graphs of wind speed,

significant wave height and surge
for the three possibilities of storm
pass (Based in Carter [7];
Woodroffe [28])
1. The cyclone runs along the coast in such a way that first exceeds 12 h—this guarantees that at some moment the
the offshore winds blow, then comes the low pressure extreme conditions will coincide with high tidal waters. But
center and finally the onshore winds. In this case, there is taking into account the long tidal cycles, flooding can be
first a drop in sea level. The arrival of the maximum especially severe if it also coincides with spring tides. For
swell occurs before the surge (Fig. 13.5a). example, the conditions of Storm Felix in March 2018 were
2. The cyclone runs along the coast so that first the onshore more energetic than those of Storm Emma, which occurred a
winds blow, then comes the low pressure center and week earlier. However, the effects of Emma on the coast of
finally the offshore winds. In this case, the surge is pro- Europe were much greater, because Emma coincided with
duced first and the largest waves arrive when the surge spring tides while Felix took place during neap tides.
level is already decreasing (Fig. 13.5b). This coincidence depends on chance and does not happen
3. The cyclone enters towards the continent. The winds are very often. In this case, to analyze the frequency of these
blowing obliquely to the coast before the arrival of the phenomena it is necessary to use the return periods as well.
low pressure center. There is first an increase in wave Extreme storm events are marked in the collective memory
height before the arrival of the low pressure center, which by the damage caused on the coasts. Examples of these
coincides with a decrease in winds. Before the final events were hurricanes Andrew (1992) and Katrina (2005)
passage of the cyclone, the oblique winds to the coast on the coasts of the Gulf of Mexico, the “Great Storm of
accelerate again, forming the surge that coincides with March” (1962) on the Meso-Atlantic coast of the USA, The
the arrival of the major waves (Fig. 13.5c). Watersnoodramp (1953) in the Netherlands, storm Daria
(1990) in Northern Europe and tropical cyclones Bhola
The most common trajectories of low pressure centers are (1970) in the Bay of Bengal and Tracy (1974) in Australia.
determined by the general atmospheric circulation. At trop- It is clear that the same event does not have the same
ical latitudes, cyclones always circulate in E–W trajectories, effect on different coasts, so the return period must also be
while at mid-latitudes extratropical storms circulate in the established for each location. The closer the studied coast is
opposite direction, with W–E components (Fig. 13.6). The to the place where the cyclone touches the continent, the
intersection of the cyclone path with the coast and, therefore, more energy will be discharged on the coast and the greater
the model applicable between the three described above the effects of the storm.
depends on the orientation of the coast with respect to these Long-term factors such as global climate change are
general paths. affecting the frequency of occurrence of extreme storms, as
The level reached by the surge, and the effects of the well as the timing of their arrival [3]. Thus, for example, in
wave breakers on these levels, also depend on the tide. We tropical latitudes the number of cyclones per year is
commented in Sect. 13.2.1 that the duration of the surge and increasing. In parallel, the number of storms in the
the time of action of the most energetic waves usually mid-latitudes is also increasing. Another effect that has been
Fig. 13.6 Map showing the

main tracks of the different kinds
of storm and their dominance on
the coasts
observed is that the season for the genesis of storms is name of these storm deposits comes from the word tempest,
changing, so that an increasing number of storms are which is the Latin word used to define a storm. In formal
occurring on abnormal dates. The displacement in time of sedimentological terms, a tempestite represents the preser-
these anomalies has different signs depending on the coast vation in facies form of a storm event within the sedimentary
being studied. record.
The term was introduced into the scientific literature by
13.2.3.1 Relaxation Currents Dott and Bourgeois [10]. The enormous energy developed
When the winds blowing towards the coast during a storm during storms is manifested in a deposit that has a coarse
cease, the sea level rise that has been maintained during the grain size, much larger than the sediments that represent the
storm tends to be compensated for by strong currents flow- average energy of the system and are located below and
ing from the coastline to the sea (Fig. 13.7). The body of above the tempestite strata.
water that moves with these currents is loaded with sedi- The tempestites can be preserved in the sequences of a
ments eroded from the upper areas of the coast. The presence variety of coastal sedimentary environments, including
of the sediment gives the water a high density, so these back-barrier environments, lagoons, estuaries and deltas.
currents will circulate on the bottom through the entire They can also be preserved in inland systems near coastal
foreshore and even shoreface, discharging this material on areas, such as lacustrine environments near the sea. How-
the continental shelf. These are the storm return currents, ever, the sequences where tempestites most frequently
also called relaxation currents. appear are those corresponding to marine waters located
below the base level of fairweather waves and above the
base level of the storm surge [20]. This places them offshore,
13.2.4 Sedimentary Record of a Storm: although relaxation currents can cross this level and carry
Tempestites, Washovers and Cheniers them to continental shelves, as an indication of the sedi-
mentary exchange between the coast and these deeper
In the open coastal areas where the most energetic waves systems.
attack directly, the evidence of the storm is usually an ero- When the surge breaks the foredune line and reaches the
sive surface that clearly cuts the sedimentary formations. areas located at the rear of a sand barrier, a deposit with a fan
However, the sedimentary material produced by this erosion geometry is created; this is known as a washover fan. It is
is transported and deposited in less energetic environments, the most recognizable type of tempestite because it is
where maximum wave energy dissipation occurs. The exposed and accessible in an area that is much used by
deposits left by the direct action of the storm and also those humans.
left by the relaxation currents are called tempestites. The Another place where tempestites are often preserved is on
the inter- and supratidal facies of tidal flats and deltas. In this
case, the preservation of the coarse sediment characteristic of
the tempestite is arranged with an elongated geometry par-
allel to the coast on the fine tidal facies. These formations are
called cheniers, as they were first described in the delta
plains near the Mississippi (Chenier Plain) and interpreted
as the deposits left by successive hurricanes. Washover and
chenier deposits will be described in more detail in the
chapters on the barrier islands and the deltas, respectively.
However, the typical storm described by Dott and Bour-
geois [10] is that developed in shoreface and offshore waters
and is commonly characterized by the presence of
hummocky-type cross-layering. These structures are formed
in a regime of currents in what are known as combined flows.
The origin of these flows is the interaction between strong
unidirectional currents and wave oscillation. The following
base–top order presents an idealized sequence (Fig. 13.8):
(a) erosive base which may also develop molds of transported
clast markings; (b) coarse residual deposit generally com-
posed of disjointed bioclasts (L level) which may present
positive gradation; (c) hummocky cross-layering level repre-
Fig. 13.7 Genesis of relaxation currents at the shoreface sentative of combined flows (H level); (d) parallel rolling
very similar dimensions. However, a much larger wave can

appear between them in an unpredictable way, displaying an
enormous amount of energy (Fig. 13.9). These waves are
known as rogue waves, although they can also be called
episodic waves, extreme waves, monster waves and freak
waves and, much more informally, killer waves. From a
scientific point of view, they are defined as those waves
whose height is greater than twice the significant height of
the train in which they are propagated [24].
Rogue waves have been described by sailors since the
eighteenth century, but there was no evidence of them
beyond those fantasy tales. Nor was their arrival to the coast
known until 1861, when one of them was documented at
Eagle Island Lighthouse (Ireland). This wave broke the
optical elements of the lighthouse, which were 40 m high.
The first rogue wave recorded instrumentally was a 25.6-m
wave that affected the Norwegian oil platform of Draupner,
in the North Sea, in January 1995 [25]. More recently, in
Fig. 13.8 Idealized sequence of a tempestite (based in Dott and
January 2009, a buoy located north of Santander (Spain)
Bourgeois [10]) recorded a 26.13-m wave within a wave train generated
during a storm, with a significant height of 14 m (Fig. 13.9).
Since these waves were documented, some descriptive
level (F level) representative of upper plane bed; (e) spike
advances have been made. Some authors have suggested that
crossbed level (X level) representative of wave action; and
there are actually three types of rogue wave: one corresponds
(f) muddy level (M) corresponding to the post-storm settling
to what has already been described and is an individual wave
of the finest material carried in suspension.
that propagates inside the train in the form of a huge wall of
The three typical deposits described above can be affected
water; a second type is formed by waves that travel in groups
by subsequent bioturbation, when the organisms living in the
of three inside the train [19]; and finally, the third type is
sedimentary beds of these environments recover their
waves that are generated by wave interaction that collapse
activity after the return of the fairweather regime. However,
immediately and do not propagate.
if the bioturbation is too intense it can end up destroying the
On the high seas, rogue waves are very dangerous for
sedimentary structures, mixing the different levels and
navigation due to their large size and unpredictability [4].
finally erasing the evidence of the storm.
However, the structures of today’s large ships are designed
to withstand the stresses generated by this type of wave.
Their arrival on land can have a huge immediate effect on the
13.3 Rogue Waves coast, due to their great energy, although very few cases
have been documented in which these waves seriously
Chapter 7 described how waves travel in trains that were affected human infrastructures.
formed by winds with certain characteristics. As their gen- As this phenomenon was first documented only a few
esis is linked to the same process, most wave trains have decades ago, the studies on the genetic causes that give rise
Fig. 13.9 Record of a wave train

including a rogue wave of
26.13 m
13.3 Rogue Waves 153
to it are not entirely clear and are still under investigation. (a huge number, if we compare it to the Twin Towers dis-
There is probably more than one cause that can generate aster, which did not reach 3000). The tsunami in Japan on
such exceptional waves. There seems to be consensus, March 11, 2011 also had a considerable impact. Although it
however, that more than one factor must come together for did not cause as many deaths as the Indonesian tsunami, it
one of these waves to appear. Currently, the hypothesis that did produce the greatest material damage in history.
gains the most support is the one that attributes its origin to In short, this is a phenomenon that should be considered
the propagation of the wave train over a strong current that as a risk for populations located in coastal areas and is
acts in the opposite direction. In this way, some waves deserving of attention by scientists and authorities.
would slow down until they were captured by the next wave,
adding their mass of water to it. Once formed, this larger
wave would capture other waves, thus increasing its 13.4.1 Mechanism of Tsunami Genesis
dimensions. Although it seems clear that the phased entry
and capture of waves is associated with this phenomenon, The genesis of tsunamis is related to a sudden displacement
the existence of a current does not explain all known cases. of a large volume of water induced in turn by the rapid
This phasing with capture of other waves by a single wave movement of a solid mass. This mass movement can have
can be explained by other phenomena such as diffraction, several possible causes. Small tsunamis are generated during
non-linear instability effects, interaction between two wave the melting of glacial fronts when icebergs break off or in
trains and particular effects of interaction with the wind [1]. steep valleys caused by rock falls. On a much larger scale,
Some of these hypotheses have been successfully repro- mega-tsunamis with waves of tens or hundreds of meters in
duced in the laboratory [16]. height can originate from meteorite impacts or large under-
water landslides. However, the most frequent origin of tsu-
namis is associated with earthquakes, and more than 90% of
13.4 Tsunamis these are concentrated at the plate boundaries. Of all types of
plate boundaries, most are associated with subduction zones,
Tsunamis are tectonically induced ocean waves characterized although they can also be generated in other plate boundaries
by long wavelengths and high speeds. They are usually whenever there is a significant displacement of land mass
associated with earthquakes whose epicenter is under the sea. that is transmitted to the sea.
In the past, they have been called seaquakes and sea surges, In subduction zones, the movement of the subducting
but these names have been discarded from a scientific point oceanic plate generates an accumulation of energy that
of view because they do not adequately describe the phe- results in elastic deformation of the upper plate (Fig. 13.10a,
nomenon. The name seaquake is not appropriate because not b). The release of this energy during an earthquake causes an
all earthquakes with an underwater epicenter are capable of elastic rebound of the upper plate, which moves over the
generating a tsunami. The term sea surge is usually associ- subducting oceanic plate (Fig. 13.10c). This displacement of
ated with meteorological phenomena and not with seismic the ground causes a sudden movement of the water mass,
phenomena, so it is not appropriate either. Finally, the term generating a large wave that will propagate over the ocean
tidal wave that is so often used in the Anglo-Saxon world surface to the nearby coasts (Fig. 13.10d).
should be discarded, because a tsunami does not respond at Although this is the most frequent mechanism, and is the
all to tidal phenomena. The word tsunami comes from the one that took place in the case of Indonesia (2004) and Japan
Japanese language in which it means “harbor wave,” refer- (2011), it is not the only possible one. There are other known
ring to the fact that these are the only waves that are capable cases of large gravitational landslides on steep ocean floors.
of breaking through port defenses. This is the case of the Storegga Slides, which occurred in
From a dynamic point of view, a tsunami represents a Norway 5000 years BC and spread into the North Sea,
high-energy event with a powerful capacity to erode and reaching the coast of Scotland [5]. There are also known
transport marine materials to the continent. It is a rare phe- cases in which large explosions in, or large eruptions of,
nomenon on a human timescale, but it is highly spectacular underwater volcanic structures have generated huge tsuna-
and occasionally causes large numbers of casualties and mis (the case of Krakatoa in 1883). Similarly, tsunamis
material damage. We all remember the Indonesian tsunami associated with earthquakes have occurred on transform
of December 26, 2004, which affected the coasts of the faults when a significant underwater relief is displaced in one
entire Indian Ocean, causing an estimated 230,000 deaths of their blocks.
Fig. 13.10 Scheme showing the

most common mechanism of
tsunami genesis in a subduction
zone
13.4.2 Propagation of Tsunami Waves Across entire mass of water, and generating constant friction with
the Open Sea the bed.
In this way, the speed of the tsunami is predictable and
From the point of view of its displacement in the open calculable, as it depends exclusively on the depth. Remem-
ocean, a tsunami wave responds to the properties of any ber that in Chap. 7, Eq. 7.5 stated that:
progressive wave movement. Theoretically, a wave propa- pffiffiffiffiffi
gated in a fluid would interact with the bottom at a depth that C ¼ gd ð7:5Þ
would be half the distance of the wavelength. As tsunami
where C is the wave propagation speed, g is the acceleration
wavelengths are greater than 50 km, this implies that they
of gravity and d is the depth.
touch the ocean floor at depths of less than 25 km. In this
From the application of this equation, the propagation
regard, it should be borne in mind that the maximum depth
velocity at different depths can be calculated (Table 13.1).
of the ocean is 11 km, thus causing a displacement of the
13.4 Tsunamis 155
Table 13.1 Velocity of Depth (m) Speed (km/h)

propagation of a tsunami wave in
waters of different depths 1000 356.6
2000 504.3
3000 617.6
4000 713.2
It is clear that when the wave reaches the continental shelf outgoing current called a run-down). The outgoing current
and heads towards the coast, the friction with the bottom is maintained until a second wave arrives. The encounter
causes it to deform and be subject to the common effects of between this run-down and the second wave generates a
shallows: refraction, diffraction and reflection. second breaker (Fig. 13.12b). The breaker of the second
As a wave interacts with the bottom along its entire wave carries the remaining water from the first flood that has
length, the orbits follow very eccentric elliptical paths, not yet managed to break through, advancing even faster
unlike smaller waves. Actually, the horizontal axis of the than the first wave. This phenomenon can be repeated up to
ellipses is tens of kilometers, while the vertical axis is of three times. It is common for the second wave to cause more
metric scale. This makes the inflow and outflow currents on casualties than the second, as many people are left unpro-
the coast enormous in relation to the vertical displacement of tected when they see the water from the first wave coming
water. As for the dimensional parameters of the wave, it down, believing that the tsunami is already over.
should be noted that, in the case of a tsunami, the maximum The energy dissipated on the coast by a tsunami is several
height is known as the set-up, while the currents to and from orders of magnitude greater than that of a similar wind–wave
the coast are known as the run-up and run-down. height.
13.4.3 Tsunami Breakers 13.4.4 Sedimentary Record of a Tsunami:

Tsunamites
In shallow water, the wavelengths are shortened and the
wave rises, producing a suction of water from the front of the A tsunami normally generates a complex layer of sediment
first wave. Therefore, the first effect on the coast is usually a that is called a tsunamite by sedimentologists. When this
drop in the water level. Although this phenomenon is layer is found on the coast it can easily be confused with
commonly known, it does not always occur, since it depends storm layers, although in restricted environments and pro-
on the situation of the coast with respect to the movement of tected bays, such as lagoons, deltas, estuaries or tidal flats, it
the land mass that caused the phenomenon. Either after the is easily recognizable as being very different from the muddy
water level drops or directly, the first break occurs when the sediments that are normally deposited in these environments.
first wave reaches the coast. However, due to its large In places close to the coastline, a tsunami can form deposits
dimensions, the break does not occur at the height of the in the same places as extreme storms: washovers and che-
crest as in common waves, but on its front. Thus, when the niers and the run-down currents can also form very thick
wave breaks, the backwash (return current) does not occur layers in the shoreface and offshore.
immediately, but the water continues to enter the coast and Various authors (e.g., Dawson et al. [9]; Fujiwara et al.
rises in a similar way to the bore of a spring tide [13]) have differentiated four types of layers generated by
(Fig. 13.11). tsunamis:
The entrance of the first wave towards the coast
(Fig. 13.12a) generates very strong currents that introduce a 1. Fining upwards sequences of shells and shell fragments
huge mass of water towards the continent. This water with sandy-muddy matrix and ending with layers of
becomes denser as it incorporates coarse sediment, which bioturbated sand (Fig. 13.13a). The common charac-
increases its destructive power. As mentioned, this move- teristic of these sequences is a high number of mol-
ment towards the land is called the run-up. The currents lusks, including open sea species mixed with others
towards land continue until the maximum height is reached typical of environments protected from waves. They
at the passage of the crest of the wave, and then the current is are typical of inland systems such as estuaries, deltas
inverted and begins to go out again towards the sea (the and lagoons.

evolution of the arrival of a
tsunami wave at a coast
2. Massive accumulations of shells and shell fragments 3. Layers of sand that also have an erosive base and nor-
These accumulations present similar faunistic character- mally contain plant fragments and soft pebbles
istics to the base of the previous type (Fig. 13.13b). They (Fig. 13.13c). In these sands, the abundance of organ-
are characteristic of open supratidal systems. They are isms is also present in microfaunal associations, espe-
also observed in the position and geometry of cheniers. cially of diatoms and ostracods. Sometimes, the sands of
13.4 Tsunamis 157
Fig. 13.12 Photographs

showing the breakers of the
Indian Ocean tsunami, 2006.
a First wave breaker entering on a
shoreface drained by the water
retreat. b Second wave breaker
entering on waters moved by the
run-down current. This current
removed various objects from
land which are now projected by
the second breaker. The breaker
height is representative of the
tsunami set-up, because the real
wave crest is coming several
kilometers seaward (Images
captured from TV videos)
these layers have cross-laminations that mark the direc- Cr). Scientists explain this as an accumulation of dense
tion of the outgoing and incoming currents of the tsu- minerals from the erosion of formations adjacent to coastal
nami. They are observed in barrier island areas, usually areas [26].
associated with washover geometries. When the large wave reaches an eroded coast where there
4. Layers of highly disorganized rock edges that often is no loose sediment to form a tsunami layer, it usually
include fragments of marine organisms (Fig. 13.13d). carries large blocks of rock. This can result in dispersions of
They also have an erosive base. They appear in systems large blocks on the seafloor or wave-cut platforms, and also
where bioclastic material is scarce. accumulations of overlapping blocks on coastal rock
escarpments [27].
In all cases, the tsunamigenic deposits present a charac- All these tsunamites bear a remarkable resemblance to
teristic enrichment in heavy metals (Pb, Cu, Ni, Fe and/or those deposits developed by storms. There is an abundance

tsunamites (adapted from Morales
et al. [18])
of literature discussing possible criteria for differentiating 4. Birkholz S, Brée C, Demircan A, Steinmeyer G (2015) Pre-
storms and tsunamis (e.g., Nanayama et al. [21]; Sawai [23]) dictability of rogue events. Phys Rev Lett 114:213901
5. Bondevik S, Svendsen JI, Mangerud J (1997) Tsunami sedimen-
but there are really no clear rules that can be applied in all tary facies deposited by the Storegga tsunami in shallow marine
cases. Normally, to differentiate between these deposits, one basins and coastal lakes, western Norway. Sedimentology
must resort to locally established facies and geometric 44:1115–1131
relationships with the environment. 6. Bourrouilh-Le Jan FG, Beck C, Gorsline DS (2007) Catastrophic
events (hurricanes, tsunamis and others) and their sedimentary
records: introductory notes and new concepts for shallow water
deposits. Sed Geol 199:1–11
References 7. Carter RWG (1988) Coastal environments: an introduction to the
physical, ecological, and cultural systems of coastlines. Academic
Press, London, 617pp
1. Adcock TAA, Taylor PH (2014) The physics of anomalous 8. Chapman S, Lindzen R (1970) Atmospheric tides. Reidel
(rogue) ocean waves. Rep Prog Phys 77(10):105901 Publishing Company, Amsterdam, 179pp
2. Aagaard T (1990) Infragravity waves and nearshore bars in 9. Dawson AG, Foster IDL, Shi S, Smith DE, Long D (1991) The
protected storm-dominated coastal environments. Mar Geol 94 identification of tsunami deposits in coastal sediment sequences.
(3):181–203 Sci Tsunami Haz 9:73–82
3. Bell RG, Goring DG, De Lange WP (2000) Sea-level change and 10. Dott RH Jr, Bourgeois J (1979) Hummocky stratification:
storm surges in the context of climate change. IPENZ Trans 27 significance of its variable bedding sequences. Bull Geol Soc
(1):1–10 Am 93:663–680
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11. Escobar G, Vargas W, Bischoff S (2004) Wind tides in the Rio de 21. Nanayama F, Shigeno K, Satake K, Shimokawa K, Koitabashi S,
la Plata estuary: meteorological conditions. Int J Climatol 24 Miyasaka S, Ishii M (2000) Sedimentary differences between the
(9):1159–1169 1993 Hokkaido-Nansei-Oki tsunami and the 1959 Miyakojima
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Alaska: a comparison of the normal and the catastrophic. Arctic Japan. J Asian Earth Sci 20:903–911
20:83–103 24. Tayfun MA (1980) Narrow-band nonlinear sea waves. J Geophys
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(2011) Sedimentary characteristics of the Holocene tsunamigenic Wijhe R (2003) Shallow marine tsunami deposits in Teluk Banten
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Particle Transport
14
sedimentology manuals (e.g., Middleton [29]; Allen [2];

14.1 Introduction
Dyer [12]).
Some aspects of particle movement are already in our
Weathering residues and pyroclastic particles that reach the
minds almost unconsciously. Everyone can easily under-
coast from the mainland, as well as any carbonate class
stand that, as the speed of a fluid increases, a critical moment
generated in the marine environment, can be reworked,
is reached when the movement of the grains begins. It is also
transported and deposited within the coastal system. Thus,
intuitively understood that the smaller grains begin to move
these particles of sedimentary material end up being part of
first and, conversely, the larger ones do not start moving
the sequence deposited in one of the coastal environments.
until the speed of flow is very high. Similarly, it is easy to
In sub- and intertidal environments, this transport can be
understand that the density of the grains, as well as the
carried out by the flow of water set in motion by currents,
density of the fluid that transports them, are variables that
tides or waves. Meanwhile, in supratidal environments it is
significantly influence the movement of the grains. Perhaps
the wind that plays the main role in the transport of particles.
one of the first things we learned as children about the
The particular processes that occur in environments
movement of grains is that, when a stream slows down,
dominated by waves, tides or other marine currents all
grains are deposited in an orderly fashion, with the coarsest
involve erosion, transport and deposition of particles by
grains being the first to be deposited and the finest grains
fluids. Understanding these processes requires a precise
being the last. All this knowledge that we already have,
understanding of how the physical mechanisms of particle
almost without knowing it, will help us understand the
transport work. These mechanisms involve three different
variables involved in the movement of particles through
aspects: (1) the processes by which a fluid sets particles in
fluids.
motion by pulling them from the bottom; (2) the factors that
Actually, the action of a moving fluid on the grains of
cause particles to continue to be transported within the fluid;
sediment at the bottom can be seen as a conflict between two
and (3) the processes that contribute to particles ceasing to
types of forces acting on each of the grains. On the one hand,
be transported and being deposited on the bed. In this
the kinetic forces (Fm) caused by the movement of the fluid
chapter we will explore the fundamental dynamics of the
applied to the grain try to make the grain move. On the other
initiation and continuation of particle transport by fluids, as
hand, the inertial forces (Fi) try to make the grain remain
well as their sedimentation mechanisms.
motionless. Thus, movement or rest is presented as a balance
between both types of force. Any of the forces acting on a
grain must be broken down into its two components: the
14.2 Processes of Particle Transport
vertical component, upwards or downwards, and the hori-
by Fluid Flow
zontal component, in the particle’s plane of motion.
There are only two inertial forces that act in a general
Between the late 1960s and early 1980s, numerous authors
way: gravity and friction. Gravity acts downwards and is the
made important contributions to the understanding of the
details involved in the processes of putting particles into result of the attraction of particles to our planet; therefore, it
is a function of their mass and acts as a vertical force.
motion by fluids (e.g., Bagnold [7]; Sternberg [44]; Moss
Friction with the bottom is the result of the resistance to the
[33]; Middleton [28]; Moss et al. [34]). This knowledge was
disseminated didactically by the authors Middleton and movement of the grain that is in contact with the other
grains; therefore, it has a horizontal component. To these
Southard [30] and almost immediately included in

https://doi.org/10.1007/978-3-030-96121-3_14
162 14 Particle Transport
two forces, a third one must be added in the case of the finest The buoyancy force appears to be due to Archimedes’
particle grains: the electrostatic attraction between particles. principle. According to this principle, a body immersed in a
The kinetic forces are those that the flow must generate to liquid experiences an upward thrust related to the volume of
try to put the particles in motion. These are: the frictional fluid it displaces. Thus, this force is related to the contrast of
thrust of the flow, buoyancy and the Bernoulli effect. The densities between grain and fluid. It is a force that is directly
thrust of the flow on the particle is the result of the viscous opposed to the action of gravity and it is intuitively under-
friction between the fluid and the grain and acts horizontally. stood that bodies weigh less when they are immersed in
In contrast, buoyancy and the Bernoulli effect have a pre- water.
dominantly vertical component (Fig. 14.1). The Bernoulli effect generates a vertical force that is
Gravity acts on the grain as a function of its size and known as the hydraulic lifting force. This force is a func-
density, so that it exerts the same force on particles that have tion of the speed and shape of the grain. The force is the
the same hydraulic equivalence. In order to calculate the result of the convergence of the flow lines accelerating the
hydraulic equivalence, the product density by volume of the speed over the particle (Fig. 14.2a). As a result of this
grain is used, and those particles that have the same product increase in speed, there is an increase in pressure in the front
are considered hydraulically equivalent (d1V1 = d2V2). In area of the grain and a decrease in the upper area
this way, grains of smaller size and greater density would be (Fig. 14.2b).
equivalent to others with larger size and lower density. As an This drop in pressure on the grain tends to pull the grain
example, in a deposit formed by hydraulically equivalent upwards through a “sucking” effect. This effect depends on
particles, the carbonate grains will be larger than the quartz the shape of the particles. In general terms, it is much greater
grains, as they have a lower density. Conversely, grains of for particles with hydrodynamically efficient shapes. It
heavy minerals (e.g., pyroxenes and amphiboles) would be should be noted that this is the same effect that is responsible
smaller. for airborne support during flight.
Electrostatic forces are usually not important for particles The inertial forces act as vectors which combine into a
larger than 63 l; however, smaller particles, especially single force called the fluid force (Fig. 14.3a). This force is
phyllosilicates, have a charged surface due to the nature of normally broken down into its two components (horizontal
their electrochemical bonds. These particles, when depos- and vertical) called the drag component and the lift com-
ited, are subjected to attraction forces that bestow on the ponent, respectively. These horizontal and vertical compo-
sediment a property known as cohesiveness. nents are those which directly oppose the inertial forces of
Among the kinetic forces, the one that is most easily gravity and friction with the bottom (Fig. 14.3b).
understood is the thrust of the fluid on the grains. Thrust is
the vector that appears due to the friction of the moving fluid
on the particle and is related to the shear stress at the bottom. 14.2.1 Grain Entrainment Threshold
This component is greater in turbulent flows. Although in
principle this vector is parallel to the flow and therefore Let’s consider a situation in which a grain is just about to
horizontal, the pivot angle (a) between the particle and the move by the action of a flow. The force of the fluid must be
bottom (or between different grains) must be taken into great enough to overcome the static inertia of the grain. The
account. Due to this angle, the fluid thrust may also acquire a particle will rise when the sum of the kinetic forces exceeds
vertical component. the inertial forces (Fm > Fi). For each size of particle, there
Fig. 14.1 Balance of forces

acting on a particle under the
action of an aqueous flow
14.2 Processes of Particle Transport by Fluid Flow 163
Fig. 14.2 Bernoulli effect on a spherical sediment particle a Flow lines Fig. 14.3 Scheme of fluid force. a Combination of forces acting on a
(black) and pressure vectors (blue). b Pressure diagram in a flow model particle in the resultant fluid force. b Decomposition of the fluid force
(wind tunnel). Red and yellow colors show high pressures while white into its two components which oppose inertial forces
and blue colors show low pressures
defines the critical speed threshold at which particles are

is a speed at which it is put into motion. This velocity is pulled from the bottom and start to move. The diagram was
called the threshold velocity. The entrainment threshold is made from experiments using quartz grains in water at 25 °C
the curve joining all the points corresponding to the and with a flow depth of 1 m. The results established a range
threshold velocity for each size of particle. of data that can slightly shift the threshold upwards or
The above statement is supported by all the reasoning
expressed in the theoretical approach of the previous para-
graphs. These paragraphs are explained with the aim of
being easy to understand, but they are enormously simpli-
fied. In fact, the movement of particles involves a large
number of variables, among which are the size, shape and
density of the particles, the roughness of the bed, the pres-
ence of cohesive particles, the vertical distribution of den-
sities of the fluid, and the presence and degree of vortices in
the flow. The degree of intervention of all of these variables
does not make it easy to obtain a reliable equation to
determine the thresholds of particle movement. Therefore,
the determination of this threshold had to be done experi-
mentally. The graphic expression of this threshold is the
Hjulström diagram (1935).
The Hjulström diagram (Fig. 14.4) shows the empirical Fig. 14.4 Extraction threshold in the Hjulström diagram (adapted
relationship between grain size and stream velocity, and from Hjulström [21])
downwards, so that the threshold can actually be expressed

as a band.
The mean curve of the entrainment threshold divides the
diagram into two regions of different conditions. The region
above the curve would express flow conditions that could lift
the grains from the bed. The region below the curve, on the
other hand, would maintain the inertial condition of the
grains.
The shape of the threshold curve shows that, as intuitively
assumed, for sand and larger grains (pebbles and cobbles),
the threshold increases with grain size. However, for parti-
cles smaller than 63 l, contrary to intuition, the speed
required for particle removal increases when the grain size
decreases. This is due to the entry into play of electrostatic Fig. 14.5 Graph relating grain size to Shields’ dimensionless viscous
attraction forces. This force increases its degree of influence stress (adapted from Miller et al. [31])
the smaller the particles are.
The problem with the Hjulström diagram is that it only smaller than 63 l due to the electrostatic forces can be
works for quartz grains transported by fresh water. In order observed in the shape of the curve. Later authors have
to know the extraction threshold of particles other than slightly modified the graphic expression of Shields’ thresh-
quartz in a fluid environment other than water, Shields [40] old through empirical experimentation [31]. In this way, a
developed a dynamic parameter that included the influence band of uncertainty can also be established.
of grain and fluid densities. This is the dimensionless vis- The Shields diagram is widely used by sedimentologists
cous stress, which can be calculated through an empirical because, although less intuitive, its application is more
equation (14.1). general than the Hjulström diagram. However, it should be
st used in the transport processes of coastal environments,
ht ¼ ð14:1Þ where changes in salinity and the nature of particles intro-
ðds df ÞgD
duce frequent changes in space and time.
where ht is the non-dimensional viscous stress, st is the
viscous stress of the fluid on the bed, ds is the density of the
grains, df is the density of the fluid, g is the acceleration of 14.2.2 Sediment Transport
gravity and D is the average diameter of the grain. This
equation also shows ht as a function of grain size, but now Once the movement has started after an increase in speed,
includes other variables that can influence the hydraulic the grains acquire different types of transport according to
equivalence. In this case, the viscous stress of the fluid on the dynamic relationship between inertial forces and kinetic
the bed (st) is defined as the force exerted by the fluid per forces (Fig. 14.6).
unit area of the bed [3]. As this is a tangential force per unit For larger grains of sand and also pebbles and cobbles, if
area, it is given in units of pressure. This variable is a the kinetic forces very slightly exceed the inertial ones, the
function of fluid density, bottom slope, water depth (14.2) particles are transported without losing contact with the bed.
and also by flow velocity (14.3). This type of transport is called traction. Transport by trac-
tion implies that the horizontal kinetic forces are able to
st ¼ df ghS ð14:2Þ overcome the friction with the bed; however, the vertical
extraction forces are not able to overcome gravity to lift the
where h is the water depth and S is the bottom slope.
clast from the bed. Traction actually groups three ways in
st ¼ df U2 ð14:3Þ which the grains can move: rolling, sliding or creeping by
impacts. In this case, the cobbles are dragged or rolled along
where U* is the velocity of the fluid at the water–bed the bed according to their morphology in such a way that
interface. only the most spherical ones can roll, while the flattened
An experimental curve is derived from Eq. 14.1 ones are preferably dragged.
(Fig. 14.5). Like the Hjulström diagram, two regions with If, on the other hand, the kinetic forces greatly exceed the
different behaviors can also be seen in this graph. In the inertial forces, transport in suspension occurs. In this case,
same way, the increase of effort required to move the larger the vertical extraction force is able to largely overcome
sand grains and the increase of effort to move the particles gravity. In this situation, the friction forces with the bed
Fig. 14.6 Types of particle

transport by fluids
disappear. The permanence in suspension is favored in very them in motion. This occurs because the forces acting on the
fine particles where the electrostatic forces of the grains help moving particles are not the same as those acting when they
to keep them suspended in the fluid no matter how small the are at the bottom [7]. Perhaps, in fact, it is more obvious in
speed. particles transported in saltation and suspension, since the
Under intermediate conditions, especially in turbulent friction with the bottom has disappeared while the transport
flows, conditions occur in which the kinetic forces are is taking place. On the other hand, the electrostatic forces of
greater than the inertial forces. The presence of vortices the finest particles are not acting to keep them attached to the
generates points or moments in which the inertial forces are bed, but to keep them in equilibrium with the fluid. The last
again greater. In this case, a type of transport called saltation factor implies that the angle and surface of application of the
occurs. In this type of transport, the grains of sand, or even viscous forces of the fluid are full when the particle is away
micro gravels, move by jumping and impacting on the bed. from the bed.
Each impact with the bottom can help other resting particles Due to all these factors, it is obvious that there is a dif-
to obtain the energy needed to overcome the entrainment ferent threshold for the deposition of particles. This thresh-
threshold. These impacts are also responsible for the form of old is called the settling threshold. The Hjulström diagram
transport called impact creeping, named above as a form of also represents this threshold, in this case by dividing into
traction. In this case, the energy of the impacts is what two fields (Fig. 14.6). Above the threshold, the particles are
produces the advance of some clasts without them losing kept in an inertial state, although in this case the inertia is
contact with the bed. that the particles are still transported. Below the threshold,
The transport that takes place in relation to the bed is the particles will be deposited. This threshold does not have
called bed load transport. This transport groups any of the an inflection, as was the case with the extraction threshold,
traction types as well as transport by saltation. but is an ascending line indicating that larger sizes will
always be deposited at higher speeds than finer grains.
One aspect of this curve is that it cuts the horizontal axis
14.2.3 Grain Settling Threshold at the size of 0.016 mm. This means that particles smaller
than 16 l could continue to be transported even at speeds of
Once set in motion, the particles stop moving when the less than 1 mm/s—i.e., almost zero speed. In this case, the
current slows down. It is intuitively understood that, when presence of electrostatic forces acts to keep the particles
the speed decreases, there must come a time when the energy suspended in the fluid. However, it is precisely the presence
of the flow does not have sufficient force to keep the parti- of these electrostatic forces that can cause fine particles to be
cles in motion. One might imagine that the same threshold attracted and form agglomerates that will behave like larger
that had to be crossed to set them in motion would now set particles and eventually decant.
the conditions for sedimentation, but this is not the case. Actually, the Hjulström diagram does not show both
Normally, the clasts continue to be transported when this thresholds separately, as we have seen in Figs. 14.4 and 14.7,
threshold is crossed to lower speed conditions. This implies but groups both thresholds in the same graph (Fig. 14.8).
that the threshold that selects the particles to stop moving This diagram is widely known and reproduced. It clearly
will occur at lower speeds than those that managed to set shows that the settling threshold is below the entrainment
14.2.4 Sedimentation Velocity
Once the threshold is crossed, the particles that were moving

will stop moving. The particles that were transported by
traction, being in contact with the bed, will remain in the
position in which they were when the threshold was crossed.
The particles that were transported by saltation will simply
remain at the bed after a last jump. However, the particles
that were transported in suspension were very far from the
bottom and will begin to settle. The speed at which the
particles fall vertically to the bed is known as the sedimen-
tation velocity, as well as the settling or decanting velocity
(Fig. 14.9).
The sedimentation velocity is a function of the grain size
Fig. 14.7 Settling threshold in the Hjulström diagram
in relation to the viscosity of the fluid. The temperature
changes the settling velocity curves, as it influences the
viscosity of the fluid. In general terms, at higher tempera-
tures the particles will settle more quickly as the viscosity
decreases. Conversely, lower temperatures will decrease the
settling speed. The graph in Fig. 14.9 shows the speed
curves in fresh water at 10 and 30 °C. In parallel, salinity has
an influence, since higher salinities increase viscosity and
vice versa.
This curve shows how the pebbles decant almost imme-
diately, at speeds above 30 cm/s. The sand grains decant at
speeds ranging from 2 mm for very fine sand to 20 cm for
Fig. 14.8 Hjulström diagram showing both entrainment and settling

thresholds
threshold. The area above the extraction threshold is com-

monly indicated as erosion conditions, the area below the
selection threshold is indicated as deposition conditions and
the field between the two thresholds is indicated as transport
conditions. This label in the diagram could confuse anyone
who does not know how thresholds really work, as it could
be thought that particles will be transported in this field
under any conditions, when in fact they would only be
transported under these conditions if the particles have been
put into motion under more energetic conditions before-
hand. The field located between both thresholds is more
correctly a zone of inertial conditions, since the particles
will behave in this zone as they did in the previous ener-
getic state. Those that were at rest will continue to be at rest
when the speed is rising, while, when the speed is falling,
the particles that were being transported will continue to be Fig. 14.9 Diagram showing the curves of sedimentation velocity as a
transported. function of grain size. Curves are for fresh water at 10 and 30 °C
very coarse sand. Again, the problem with the silt particles • Meyer-Peter and Müller [27]
lies in their low sedimentation rate, which will be less than 3=2
1 mm/s. This means that it takes more than a quarter of an 0:047gDðds df Þ
Qb ¼ df U3 8 1 ð14:5Þ
hour for silt particles to pass through 1 m of water. If we add df U2
this information to what was observed in the Hjulström
diagram—i.e., that these particles require almost zero • Bagnold [6]
velocity to decant—we now add the fact that these still water
K1ds U3
conditions must be maintained for long periods of time for Qb ¼ gðd d Þ ð14:6Þ
s f
the suspended particles to reach the bottom. Actually, it may df
be that those grains located in the lower layers of the flow,
• Yalin [46]
near the bottom, manage to cross that distance, but in

channels several meters deep, it is difficult for the conditions 1
to occur for the particles that travel in the fluid to reach Qb ¼ 0:635ds DU S 1 lnð1 þ aSÞ ð14:7Þ
aS
the bed.
• Van Rijn [45]
Advanced Box 14.1: Calculating the Transport Rate
By Currents 0:053ds ðdgÞ1=2 D1:5 T2:1
Qb ¼ 0:3 ð14:8Þ
Among the most frequently addressed problems in the gdf 1=3
D l
studies of coastal system dynamics are those related to
sedimentary balance. This type of problem always requires a
volumetric quantification of the sediment. Thus, it is inter-
esting to be able to calculate the amounts of sediment (in
weight or volume) transported by any of the currents acting In these equations Qb is the potential background charge,
on the coast. g is the acceleration of gravity, D is the mean grain diameter,
Many authors have proposed equations to calculate the ds is the density of the solid and df is the density of the fluid,
amounts of sediment transported. All these equations are and µ is the viscosity of the fluid. U* is the shear rate, or
proposed for different modes of transport. Thus, there are velocity at the water–bed interface. When data for this value
separate equations for the calculation of bed load and sus- are not available, it can be calculated from velocity values
pended load. (Uz) taken at a depth at a distance from the bottom (z), as
long as this distance is less than 1 m, according to Eq. 14.9;
AB14.1.1 Potential Bed Load Transport Rate [9].
Bed load means the material transported in contact with 0:4 Uz
the bottom. Normally, the concept of bed load includes U ¼ ð14:9Þ
ln ln 30z
material transported by traction (in any form) and saltation. ks
What the equations actually calculate is the capacity of the
In this equation Ks corresponds to the bed roughness
fluid to transport material in bed load, so the parameter used
(Nikuradse roughness) and is estimated at three times the
is called the potential bed load rate (Qb). Most formulas
size representing 10% of the largest sample sizes
express the rate of material transported in units of weight per
(Ks = 3D10).
unit length of cross-section to flow and per unit time (e.g., in
In Einstein’s equation (14.3) P is the probability of
grams per centimeter per second).
transport and is calculated through Eq. 14.10.
The most frequently cited formulas in the calculation of
potential bed load are those of Einstein [13], Meyer-Peter 2 3
0:143gD sd f
d d
and Müller [27], Bagnold [6], Yalin [46] and Van Rijn [45]. 6 f
27
6 U2 7
These formulas are represented by Eqs. 14.4–14.8. P¼16 6 pffiffiffi 7 ð14:10Þ
p 7
4 5
• Einstein [13]
( )1=2
P 1 ½ðds df ÞgD3 In Bagnold’s equation (14.6) k1 is a coefficient that is
Qb ¼ ð14:4Þ calculated through Eq. 14.11.
1 P 43:5 df
k1 ¼ 0:10 exp ð0:17=DÞ ð14:11Þ appropriate in channels subject to tidal currents, since both
types of current work on the same principles. It is sufficient
In the Yalin equation (14.7) a is a complex relationship to recalculate by introducing the densities corresponding to
between grain and fluid densities, grain size and critical coastal waters. As can be seen, each of these formulas has
shear rate (14.12) and S is a relationship between bottom been designed for limited conditions and, therefore, when
shear rate and critical shear rate (14.12). making calculations in natural coastal systems it is necessary
0:4 1=2 to choose the equation that should be applied according to
df df U2cr the characteristics of the bed and the usual flows of the
a ¼ 2:45 ð14:12Þ
ds gD ðds df Þ environment to be studied.
The use of any of these formulas in coastal systems
U2
S¼ 1 ð14:13Þ requires action on the bed. In any case, to calculate the
U2cr potential transport through a channel, the following should
In these equations U*cr is the critical threshold speed. It is be measured: (1) the flow section; (2) the flow velocities at
understood that this is the speed at the water–bed interface less than 1 m from the bed; and (3) water and sediment
required to set a particle of a given size in motion (D). samples. Different requirements are demanded for samples
Most of these formulas have in common the variables taken in the field. For water samples, the density must be
used in the flow calculation. All of them consider the determined. In the case of sediment samples, the density of
movement of the grains as the result of the viscous effort of the grains must be measured and a particle size analysis must
the fluid on the bed and, consequently, all of them use as be carried out to determine the mean grain size and 10th
criteria the thresholds of movement of the particles. There- decile (in order to determine the bed roughness).
fore, the contrast of densities between the grains and the
AB14.1.2 Suspended Load Transport Rate
fluid, as well as the size of the particles, the bed roughness
The analysis of suspended transport rates requires three
and the near-bottom flow velocities, are always considered
types of baseline data: (1) the flow section; (2) the distri-
as input parameters in the equations.
bution of flow rates in that section; and (3) the distribution of
The formula proposed by Hans A. Einstein was designed
suspended matter concentrations in the flow section. In
for beds formed by unimodal sands, where all particles have
natural systems, the flow section and velocity profiles can be
the same diameter, geometry and density and are transported
determined through field measurements. Suspended sedi-
in a one-dimensional flow. In contrast, the equation pro-
ment or suspended transport concentrations can be estimated
posed by Meyer-Peter and Müller, although it also assumes a
analytically or numerically.
one-dimensional flow, works for beds with slopes greater
The analytical calculation is complex because there are
than 20% and well-sorted fine gravel grain sizes of up to
too many variables that determine lateral, vertical and tem-
3 cm. The Yalin equation, on the other hand, assumes a
poral changes of the concentrations of suspended matter at a
constant flow of particles transported mostly in saltation.
given moment. The use of equations to calculate the trans-
The Bagnold equation is based on criteria of mechanical
port capacity of the flow (potential transport rate) always
equilibrium between water flow and bottom clasts, taking
assumes stable and uniform conditions. The equations are
into account their size and density, in relation to the
always based on different assumptions that facilitate the
roughness of the bed. This equation is considered to be
calculation [26]. These are:
adapted to non-cohesive beds consisting of multimodal
sediments of different diameters between sand and fine
• That the decanting rate does not vary in time and space,
gravel. All of these equations were designed to be applied to
• That the concentrations of suspended matter are so low
natural flows in river systems; however, the equation sug-
that interactions between grains can be ignored,
gested by Van Rijn is designed for use in experimental pools
• That the viscosity of the vortices depends on the shear
and introduces some parameters that are difficult to measure
rate and a length scale,
in experiments in natural environments, such as the height of
• Other possible changes to the turbulent mixture due to
the jumping particles transported. There are more recent
effects such as saline or thermal stratification by tem-
equations that are valid for sediments with different grain
perature, salinity or suspended sediments to buffer or
sizes between sand and gravel, although they present the
enhance the turbulent mixture are not considered.
problem of the great complexity of dealing with the different
thresholds of movement that exist for each of the grain sizes
One of the most common characterizations of the con-
that make up the sediment.
centration of suspended sediments in a flow is given by the
Although most of these formulas have been designed for
Rouse profile [20]. Rouse’s profile characterizes any differ-
calculations based on river systems, their use may also be
ences in suspended matter concentrations in the water
column, including turbulent mixing of areas with different thresholds, and the particles will be deposited. Then, the
suspended particle concentrations and vertical gradients due same process occurs in the opposite direction.
to particle weight. In accordance with what has been explained in previous
The turbulent mixing starts from the idea of the presence paragraphs, there is different behavior between the grains of
of vortices that produce a net displacement of grains from non-cohesive sediments and those of cohesive sediments,
areas with higher concentrations to areas with lower con- due to the differences between their entrainment and settling
centrations. On the other hand, it assumes that all particles thresholds.
will tend to move downwards due to their weight, and thus In the case of non-cohesive grains, the difference between
there will be a gradient of increasing particle concentration these thresholds is not very high and marks the delay in
downwards in the water column. The Rouse profile assumes depositing the particles once the tide reaches the speed
an equilibrium between the vertical gradient due to required to set them in motion. In this way, the grains will
decantation and the turbulent mixture that will tend to move remain in motion almost until the moment of the tidal
the particles upwards. inversion. This case can be well-illustrated by the behavior
Another problem that arises in the use of empirical of the average sand grains (Fig. 14.10).
equations is the treatment of suspended sediments containing In contrast, for cohesive particles, the difference between
a variety of grain sizes. The reference concentration must these thresholds is very marked. To understand the behavior
take into account the concentration of each grain size and the of cohesive grains we will use the graph of 20-l particles at
shear stress required to keep that grain class moving. the same tide (Fig. 14.11). In this case, the tide must
The calculations required for the use of empirical equa- advance for almost an hour until it reaches the necessary
tions in the potential transport of suspended sediment are speed to set these coarse silt grains in motion. Once these
very inaccurate if they include all those assumptions so far grains are pulled from the bottom, they will remain in
from reality. On the other hand, the inclusion of all these motion until the tide rises.
variables in one equation makes their use too complex. The With regard to these fine particles, it must be taken into
end result is that the easiest and most widely used method account that the time the current is stopped during the upturn
for calculating the rate of suspended material transported by is very short. Due to their slow settling speed, only those that
a flow is the direct measurement of concentrations by taking travel closest to the bed will be deposited there. This means
water samples at the same time as the direct measurement of that most of the suspended charge would continue to be
velocities. transported almost perpetually if the processes of electro-
Equation 14.14 proposed by Bagnold [7] can be applied static agglomeration of the particles did not exist.
directly in this case. The amount of sedimentary material transported in each
Z of the directions depends on the asymmetry of the tidal
h
Qs ¼ cðzÞUðzÞdz ð14:14Þ current curve as a function of the available grain sizes. This
a asymmetry can be manifested in the velocity reached by the
ebb and flow currents, as well as in the action time of both
In this equation the suspended load (Qs) is calculated by
integrating the load values at different depths (z) between the
fluid–bottom interface (a) and the surface (h). In this case, c
(z) marks the concentration at a given depth (determined by
the value of z), while U(z) is the flow velocity at that depth,
with dz being the depth differential.
14.3 Transport of Particles by Tides
The action of tidal currents in the channels of coastal sys-

tems represents a clear example of a continuous increase in
speed from zero to reach a maximum speed that is main-
tained and then decreases again to zero. Throughout this
process, the entrainment threshold of each grain size present
on the bed will be reached to keep it moving as long as the
Fig. 14.10 Curve of velocity over time in a tidal cycle, showing the
transport speed is above that threshold. Finally, the speed entrainment and settling thresholds. The fields highlighted in yellow
will decrease until it progressively reaches the settling correspond to the conditions of transport of medium sand grains
cycles in order to calculate the net balance of sediment that is

transported in a residual way to one of the two directions.
Firstly, the integration in time is considered. Starting with
the data of a time curve of tidal currents taken at a distance
of less than 1 m from the bed, calculations are made by
dividing the curve into set time intervals, calculating the
average speed for each of these intervals. These values are
then entered into the equations along with the rest of the
measurements (grain density, fluid density and grain size).
The final result is a potential load curve with respect to time
(Fig. 14.12).
To obtain the total values of sediment transported by ebb
and flow, it is sufficient to sum the values of Qb for all of the
time intervals in which there was transport, taking into
Fig. 14.11 Curve of velocity over time in a tidal cycle, showing when
the entrainment and settling thresholds of coarse silts are surpassed account the direction of the current. Finally, the total values
(shown in blue) of the flow cycle will be compared with those of the ebb to
obtain the value of the net transport.
Once these values are obtained, the total quantities
currents. The result is always a residual balance acting in one
through the flow section are calculated by multiplying them
of the two senses.
by the length of the bed measured across the channel profile.
It should be noted that the values measured at a single point
Advanced Box 14.2: Calculating the Transport Rate By
may not be extrapolated to the entire channel because there
Tidal Currents
may be lateral variations in the flow. In this case, the channel
The potential sediment load (Qb) carried by tidal currents
should be divided into different sections and measurements
during a tidal cycle can be calculated using the generally
of the flow in each of these sections should be made. The
proposed equations for currents (Advanced Box 14.1). The
calculations obtained from these curves may then be applied
particularity of the application of these equations to tides is
to the length of the section for which these measurements are
that the measurements of Qb are usually given in weight per
considered valid. A clear example could be the presence of a
length of flow section and unit of time, and when tidal
central bar that divides the section of the channel into two
currents are analyzed these measurements are integrated to
well-differentiated sections. In this case, three different speed
cover the whole flow section and all the time of each of the
curves should be obtained, one in each deep zone and one on
tidal cycles.
the bar. Then, the Qb data of each tidal cycle would have to
In other words, in sedimentary balance studies, it is not
be multiplied by the length of the bed of each of these
enough to know how many grams pass through a centimeter
sections to finally add up the three sections and thus obtain
in a second, but rather to seek to know how much sediment
the total for the whole channel.
transits through a channel during complete ebb and flow
14.4 Transport of Particles by Waves
A wave, like a tide, also represents in its movement an

increase in the speed of the current followed by a decrease in
the same, an increase in the opposite direction and a further
decrease. The difference is that the time at which these speed
changes occur is measured in seconds and not in hours, as in
the case of tides. As a result, greater accelerations occur.
The flow behavior of a wave applied to the bed material
differs depending on where the wave acts (Fig. 14.13). In
areas of the shoreface above the base level of the wave, the
water flow at the bed responds to the smaller orbits away
from the surface. In this case, the velocity curve is quite
Fig. 14.12 Curve of velocity over time in a tidal cycle (blue) and
symmetrical, generating a sway where only the movement
curve of potential bed load (Qb) at intervals of 1 min. The entrainment
and settling thresholds are indicated. Observe that between settling and thresholds of very fine and thin sands can be reached
entrainment thresholds of successive cycles the bed load is 0 (Fig. 14.13a).
14.4 Transport of Particles by Waves 171
Fig. 14.13 Curves of velocity over time during the passage of a wave. Fig. 14.14 Curves of velocity over time for breaking waves. a Spilling
a In a shoreface bed. b In a surf zone. The thresholds for very fine, fine, type. b Plunging type. The thresholds for very fine, fine, medium,
medium, coarse and very coarse sands are shown in orange tones coarse and very coarse sands are shown in orange tones
In contrast, in the surfing areas the flow depth is much the longshore vector and its relationship with the entrain-
lower and it is the larger orbits that act directly on the bed. In ment and settling thresholds for the beach grains.
this case (Fig. 14.13b), there is no longer so much symme-
try. The example shows the passage of a wave where the Advanced Box 14.3: Calculating the Longshore
surge develops faster than the undertow, although in both Transport Rate
cases the movement thresholds of all classes of sand (in The calculation of the amount of sediment potentially
progressively darker shades of orange for larger sizes) are transported along the coast can be done through empirical
progressively exceeded. equations similar to those described for currents. In this field,
In the swash areas, the type of breaker has a great the work carried out by different authors in the second half
influence on the development of sediment transport of the twentieth century is essential (e.g., Inman and Bag-
(Fig. 14.14). The most dissipative breakers, such as spilling nold [22]; Komar [25]; Galvin [14]). These works were
types (Fig. 14.14a), show a significant increase in velocity excellently summarized by Carter [10], who also makes
during the swash, where all the thresholds of movement of some personal contributions.
the sand grains are crossed, while the backwash develops In the case of grain transport by waves, it is necessary to
lower velocities that do not manage to cross the thresholds of introduce the concept of longitudinal flow of wave energy by
movement even for very fine sands. This implies that the length of coast (PL). This parameter relates the wave energy
spilling breakers only move the sediment towards the coast, with its propagation speed in relation to the angle of arrival
assuming a sedimentary accumulation. Conversely, more at the coast line (Eq. 14.15) and is given in joules per meter
energetic breakers such as the plunging type develop higher of beach length if we work in SI units of measurement.
velocities during the backwash (Fig. 14.14b). In this case, it
is the speed of the swash that fails to reach the movement PL ¼ 0:0625dfgHs2 C sin 2a ð14:15Þ
thresholds, while the backwash is able to move sand of all
sizes, and even fine gravel. where df is the fluid density, g is the gravity acceleration, Hs
This type of calculation of transport transversal to the is the significant wave height, C is the propagation velocity
coast is useful to know if the sediment has a displacement and a is the angle between the wave crest and the shoreline.
that goes mostly landwards or seawards. It can be comple- Using this parameter, Van der Graaf and Van Overeem
mented with calculations of longitudinal transport if we take [15] proposed the use of a formula for the calculation of the
into account the angles of wave action with respect to the longitudinal background load (Qb) carried by waves
coastline and decompose the velocity vector by extracting (Eq. 14.16).
K PL
Qb ¼ ð14:16Þ
gaðds df Þ
where K is a constant that varies depending on the type of

surf, g is the acceleration of gravity and a is the degree of
packing of the sediment, with ds and df being the densities
of the grains and water, respectively.
In more practical terms, Kamphuis [23] proposed another
equation valid for quartz-grain sand beaches (Eq. 14.17).
tan bHs2
Qb ¼ 1:28 sin 2a ð14:17Þ
D
Fig. 14.16 Wind transport modes as a function of grain size [16]
where b is the slope of the beach, D is the average grain size,
Hs is the significant height in the breaker zone and a is the
also shows the increase in velocity that is necessary to
angle between the crest of the wave and the coastline.
suspend particles smaller than 100 l, although in this case
Subsequent work has proposed certain adjustments to this
this difficulty is not attributed to electrostatic forces but to
equation and optimized it for use in mathematical models
the low roughness of the bed which reduces the air friction
(e.g., Schoonees and Theron [39]; Damgaard and Soulsby
on the particles.
[11]).
Once in motion, the grains will be transported via salta-
tion or suspension according to their density and size. In this
regard, Greeley and Iversen [16] suggested two intermediate
14.5 Transport of Particles by Wind
forms between continuous saltation and long-term suspen-
sion. These are the modes of transport of modified saltation
Air is a low-density fluid and therefore wind can be treated
and short-term suspension (Fig. 14.16). In both intermediate
like any other fluid flow. Under the action of wind, the
cases the particles are partly jumped and partly suspended.
grains also present thresholds of movement that can be
Finally, when the air speed drops, the grains can no
determined using Shields’ dimensionless viscous stress. In
longer be transported and fall when they cross the settling
this case, the thresholds of grain entrainment by air are two
threshold. In this case, the grains fall with less resistance
orders of magnitude higher than those needed to put the
from the fluid because air has a lower density than water.
same particles in motion by water.
This falling speed has also been determined for grains with a
Not many authors have devoted their efforts to experi-
density of 2.6 g/cm3 [5] and is shown in Fig. 14.17.
mentally determining the thresholds of grain movement by
wind. One of these authors [5] has determined the entrain-
ment threshold of grains with a density of 2.6 g/cm3 as a
function of the shear velocity (Fig. 14.15). This density
corresponds to the most abundant minerals in sediments
such as quartz and feldspars. The threshold was determined
experimentally, similar to the Hjulström diagram. This curve
Fig. 14.15 Entrainment threshold of grains under wind action in

Bagnold’s diagram (1941) Fig. 14.17 Fall velocity as a function of grain size [5]
14.6 Development and Dynamics of Bedforms 173
14.6 Development and Dynamics dominates. The internal structure that corresponds to this
of Bedforms surface configuration is the low regime parallel
lamination.
A certain flow velocity higher than the entrainment threshold • Current ripples: These are asymmetrical centimeter-scale
produces a particular morphological configuration of the bottom undulations, which are due to a low flow regime
bed. These configurations are called bedforms. The migra- with saltation transport dominance. The asymmetry is
tion of bedforms over a sedimentary bed also generates a manifested in the angle and length of the two faces of the
particular internal order associated with the surficial shape. ripple. The flow-oriented face (stoss side) has a smaller
Both surface shape and internal structure have been studied angle, while the opposite face (lee side) has a larger angle
in stratigraphy as sedimentary structures of the top and the that coincides with the sediment rest angle according to
interior of the strata, respectively. In this chapter, when its grain size (Fig. 14.19a). According to the crest
referring to bedforms, we do so with respect to their geometry, the ripples can be differentiated into:
dynamics and will associate them with both their external straight-crested ripples, sinuous ripples and linguoid rip-
geometry and their internal structure. ples. Ripples migrate along the bed in the sense of flow,
There are different types of bedforms generated by uni- generating an internal sedimentary structure called
directional flows, bidirectional flows and combined flows. cross-lamination. Each of these ripple geometries cor-
responds to a type of internal lamination (Fig. 14.19b).
Straight-crested ripple migration generates planar
14.6.1 Unidirectional Bedforms (Current cross-lamination (2D). Sinuous-crest ripples generate
Bedforms) curved-base cross-lamination, while linguoid ripples
generate trough cross-lamination. The latter two have a
The most common classification of current-generated 3D geometry.
bedforms is according to the flow regime under which • Dunes: These are also asymmetrical bottom undulations,
they develop. The flow regime is a state of flow related to but on a metric scale. Their size is greater than that of the
the amount of friction of the fluid with the bottom and ripples, which is why many authors call them mega rip-
which controls the amount of energy transferred to the ples or large ripples. They also originate during a low
movement of the sediment [41]. It is clear that this regime flow regime with a dominance of saltation transport, but
is directly dependent on the same conditions that have they are normally made up of coarser grains than ripples.
been established to determine the thresholds of particle They can also be classified according to ridge geometry,
movement, including flow velocity and grain size. In distinguishing between straight ridges, sinuous ridges and
general terms, for the development of bedforms there are linguoid or crescent ridges. Like the ripples, the dunes
two flow regimes determined by the turbulence of the migrate along the bed in the sense of the flow, generating
fluid, the rate of sediment transported and the possible an internal sedimentary structure which is called
relationships between the shape of the bottom and the cross-bedding, of a larger scale but identical geometry to
shape of the fluid surface. These regimes are low flow the cross-lamination. Each dune geometry corresponds to
regime and high flow regime. a type of cross-bedding (Fig. 14.20). Straight-crested
In the low flow regime, there is a laminar flow with a low dunes (also called sand waves and 2D dunes) have
transport rate dominated by the bed load and there is no associated planar cross-bedding. Sinuous-crested dunes
relationship between the shape of the bottom and the shape are associated with curved-base cross-bedding, while the
of the fluid surface. On the contrary, in the high flow migration of linguoid and semi-lunar dunes generates
regime, there is a turbulent flow that generates a high trough cross-bedding. The latter two are also called 3D
transport rate, with the undulations of the bed and the surface dunes.
being in phase.
Thus, the bedforms are developed according to the The nomenclature of ripples and dunes has changed over
regime [18]. Those associated with the low flow regime are time. A magnificent synthesis was made by Ashley et al. [4].
the forms of lower plane bed, current ripples and dunes Similarly, the dimensions used to differentiate the bedforms
(Fig. 14.18). vary from one author to another, although almost all agree
that the transition between ripples and dunes occurs at
• Lower plane bed: This is a bed configuration that wavelengths of 60 cm and heights of 6 cm.
describes a completely flat surface that responds to a very The bedforms associated with the high flow regime are
low transport rate where fine particle traction normally upper plane bed and antidunes.

showing some low regime
bedforms. a Straight-crested
ripples. b Sinuous ripples.
c Linguoid ripples. d Sinuous
small dunes. e Sinuous dunes
with superimposed ripples.
f Dunes totally reworked by
linguoid ripples
• Upper plane bed: This is a configuration of the bottom As with the movement thresholds, the bed configuration
that describes a flat surface without relief, but in this case and the stable shape type is a function of the flow velocity.
it responds to a very high transport rate. Such a high flow Harms and Fahnestock [18] showed that, above the move-
velocity generates a bottom leveling by razing, in which ment threshold, there is a transition of bedforms from low to
the existence of any relief would be unfeasible. The high regime forms with increasing flow velocity (Fig. 14.22).
internal structure that corresponds to this type of bottom Through experiments in laboratory flumes, Harms et al.
is the parallel lamination of the high flow regime [19] proposed the use of a diagram where fields of stability
(Fig. 14.21). of the bedforms are established in relation to the grain size
• Antidunes: These are low-relief undulations with a very and the flow velocity (Fig. 14.23a). This diagram can be
low ratio between height and wavelength, which differ- interpreted in the same terms as the Hjulström diagram, so
entiates them geometrically from ripples. As high regime that, if we know the grain size of the sediment and its
bedforms, the antidunes are in phase with the undulations structure, we can determine the range of flow velocities that
on the water surface. Depending on the dynamics of these were able to generate its deposit. Inversely, we can predict
forms there are two possibilities: (1) they are static (s- the type of morphological configuration that a bed of a given
tanding waves) or (2) they move against the current. The grain size will acquire under a known flow velocity. Years
internal structure of both types of antidunes is different. later, new experiments led Southard and Boguchwal [43] to
The standing antidunes develop wavy parallel lamination, propose a modification of the diagram, establishing new
while the antidunes develop upstream cross-lamination. limits for the fields of stability (Fig. 14.23b).
Fig. 14.21 Geometry and internal structure of the upper plane bed
It follows from these diagrams that several series of

bedforms can be produced by increasing the speed
depending on the size of the available sand. For example, in
fine sand sizes, an increase in speed to high regime would
lead from the development of ripples to the upper plane bed
and antidunes, without lower plane bed and dunes devel-
oping. On the contrary, very coarse sand sizes would pro-
gressively lead to the development of a lower plane bed, 2D
and 3D dunes and antidunes, without the development of
ripples or upper plane bed. Only the sizes of medium sands
or a progressive increase in grain size parallel to the increase
in flow speed would be capable of developing the whole
series proposed by Harms and Fahnestock [18], from the
lower plane bed to the antidunes, passing through ripples,
dunes and the upper plane bed.
It is not only flow speed and grain size that are the control
factors of bedform stability. The flow depth also has a great
influence on bedform development. Flow depths of less than
Fig. 14.19 Current ripples. a Genesis and dimensions. b Different 1 m narrow the space for a good shear band development,
crest morphologies in relation to their internal structure increasing the viscous stress of the fluid on the bed sediment
grains. Rubin and McCulloch [38] established diagrams
showing the relationship between parameters such as grain
size and depth based on experimental data obtained in
flumes by previous authors (e.g., Guy et al. [17]). In these
diagrams (Fig. 14.24), it can be seen that a decrease in depth
lowers the velocity level required to increase the flow
regime, thus reducing the boundaries between shape stability
fields. These same authors illustrated the relationships
between flow velocity, depth and grain size in a
three-dimensional diagram (Fig. 14.25).
Changes of bed configurations when the flow velocity
increases do not occur immediately. Many of them occur
progressively, as it takes time for the bed to transform and
reach a form stable with the flow conditions. This time is
known as the equilibrium time. In the case of ripples,
changes between different crest morphologies have always
been associated with changes in the flow rate. Thus, many
authors identified the presence of straight-crested ripples
Fig. 14.20 Genesis of dunes and different morphologies in relation to with very weak currents and, conversely, linguoid ripples
their internal structure with high flow velocities. However, authors such as Oost
Fig. 14.22 Transition of

bedforms with increasing flow
velocity [18]
and Baas [37] established that, in the case of ripples, the 14.6.2 Bidirectional Bedforms (Tide-Generated
stable form is always the linguoid morphology. What hap- Bedforms)
pens is that the time to reach the stable form varies with the
flow velocity (Fig. 14.26). Thus, when the flow velocity is The migration of bedforms due to tidal currents is governed
low, the equilibrium time is so high that nature does not offer by the same parameters described above. The particularity of
such long actuation times of the current and, consequently, currents in tidal-dominated environments is that their
the stable form is not achieved and straight-crested and direction is reversed in each tidal cycle. The action of
sinuous ripples, which are the intermediate metastable states, opposing currents on the same bed causes the bedforms to
are preserved. move in the opposite sense during the tidal flow and ebb.
Another effect of time is seen in the transition between Under these conditions, the lamination or cross-layering of
large and small forms. In theory, a regime of smaller flow is the interior of the sets of these structures will appear to be
not capable of reworking larger forms into smaller ones. tilted in the opposite direction. This gives the internal
Thus, the larger forms would become fossilized and the structure the appearance of a fish skeleton, which is why
smaller forms would be superimposed on them. However, they are called herringbone structures (Fig. 14.27).
in situations where there is not much sediment availability, Although the most intuitive idea is that in these structures
the sediment of the larger bedforms is used by the smaller the inclination in both directions is equally distributed, this is
ones and, with enough time, the top of the larger bedforms is usually only the case with small shapes such as ripples
incorporated into the flow of the superimposed smaller (Fig. 14.28a). However, the reality is that, in natural envi-
forms. This is the reason why in many cases the surficial ronments, one stream often dominates the other [24]. This is
morphology of these large forms is not preserved but their most clearly evident in the development of the larger forms.
internal structure is. When this occurs, one of the two currents is able to make the
Fig. 14.24 Stability diagram of bedforms in relation to flow velocity

and depth [38] The graph is designed for average sand grains between
0.4 and 0.5 mm and with fresh water at 10 °C
Fig. 14.23 Stability diagrams of bedforms in relation to grain size and

flow rate. a According to Harms et al. [19]. b According to Southard
and Boguchwal [43]
bedforms migrate, while the other only retouches the ridges

creating reactivation surfaces of the form (Fig. 14.28b). Fig. 14.25 Three-dimensional diagram of bedform stability fields as a
Sometimes the residual current is able to generate bedforms function of velocity, sediment size and depth, generalized from natural
that move in the opposite direction, although with smaller system data and flume data (adapted from Rubin and McCulloch [38])
dimensions. In these cases, the dominant current subse-
quently destroys these shapes totally or partially. In this way,
one of the two inclinations is often better preserved in the where the shapes develop in relation to the flow depth. These
record of a tidal formation. forms play an important role in the transfer of sediments on
the waterfront, since their presence increases the viscous
friction generating vortices in the near-bed layer and favor-
14.6.3 Oscillatory Bedforms (Wave Bedforms) ing the transport processes [36].
The forms that first come to mind when we talk about
In wave-dominated coastal fronts, the orbital movement of oscillation forms are the symmetrical or sinuous
the water is able to transfer energy to the bed through vis- straight-crested ripples. These are the forms generated in the
cous effort. This type of flow generates bedforms on a range beds of the shoreface zone, where the action of the waves
of scales depending on the orbital velocity (w), but also on usually manifests itself in a swaying of the water at the
be treated as ripples. The increase in the slope of the ripple

faces has a clear effect on the behavior of the flow at the limit
with the bed. The steep slopes give the ripple a trochoidal
shape that generates a vortex in each direction of the flow of
a wave [42]. This vortex is responsible for the erosion of the
sediment within the ripple and the accumulation of sediment
on the opposite side (Fig. 14.29). The existence of two
vortices, one in each direction, produces an internal structure
in the form of a spike.
There are empirical formulas that attempt to predict the
height and wavelength of shapes as a function of parameters
similar to those that have been analyzed in the currents.
However, there are notable differences in the predictions of
these formulas [35]. The conditions under which these
bedforms appear, as well as their transit to the upper plane
bed, are well established. These thresholds, as well as the
L/H ratios of the shapes, are represented in the Allen [1]
diagram, as a function of orbital velocity (w) in relation to
grain size (Fig. 14.30).
Fig. 14.26 Flow velocity as a function of equilibrium time for ripple It should be noted that not all wave bedforms are sym-
height and wavelength in very fine sand of 0.095 mm [37] metrical. In the areas close to the breakers, one of the two
vortices normally dominates over the other depending on the
bottom. Although these ripples look very similar to those behavior of the wave with respect to the general slope of the
generated by currents, their morphological characteristics beach. In this case, one of the faces will be more developed
and also their internal structure are different, as they are and the shape will be asymmetrical. Normally, the face with
generated by different mechanisms. the greatest slope is the one that marks the sense of the
Larger waves transfer more energy to the bed. This dominant vortex. Inside the shape, the spike will also be
transfer of energy manifests in different ways. On the one asymmetrical, so that the sheets of the face with the greatest
hand, the dimensions of the ripples increase at the same time slope will be thicker.
that the ratio between wavelength and height (L/H) becomes In the breaking zone, the thin water depth influences the
greater, increasing the slope of their faces. On the other transition to more energetic forms such as the upper plane
hand, the waves will be able to move grain sizes greater than bed. Associated with this flat bed are surface marks gener-
the sand, forming small dunes. In any case, these dunes will ated by flow deviations due to the presence of coarser
Fig. 14.27 Centimeter-scale

herringbone structure in the
Phanerozoic Dindefelo formation
(Senegal)
Fig. 14.28 Schemes of

generation of herringbones by
tidal currents. A: With two
equilibrated currents. B: With a
dominant depositional current and
another residuary erosional one
(adapted from Klein [24])
acceleration and deceleration of the unidirectional current,

generating what are known as hummocky structures.
A hummocky structure consists of a surface on a metric
scale similar to an egg box, where depressed areas (swales)
and elevated areas (hummocks) alternate, both with circular
to elliptical shapes in plan. The internal structure consists of
erosive base sets characterized by low angle corrugated
sheets that thicken in the furrows, while becoming thinner or
even truncated in the ridges.
The geometry of the internal structure suggests that the
hummocky structures behave like stream antidunes; the
particularity is that the oscillation of the wave makes it go
Fig. 14.29 Generation of spike cross-bedding by wave vortices cyclically from low angle dunes to static antidunes and
upward dunes and vice versa, preserving these movements in
the internal lamination. This same effect can also be attrib-
elements (i.e., shells), such as crescents (Fig. 14.31a) and uted to the influence of internal waves between the turbulent
rhomboidal structures (Fig. 14.31b). fluid that moves along the bottom and the surface water mass
[32].
Due to their origin, these types of structures are typical of
14.6.4 Combined Flow Bedforms shoreface areas of those coasts where storms have influence
(Fig. 14.32).
The combination of unidirectional flow and oscillatory flow
results in combined flow. In this type of flow, a strong
unidirectional current is usually added to an oscillatory flow. 14.6.5 Macro-scale Bedforms
The combination of this type of flow is typical of storm
action, where high velocity storm relaxation currents are Unidirectional flows acting for a very long time can form
superimposed on the wave oscillation. The result is the macroforms of dimensions of tens or hundreds of meters.
Fig. 14.30 Diagram of stability

fields for wave bedforms [1]. The
red dashed lines represent
different relations of L/H in the
ripples
Belderson et al. [8] classified and described these forms on length. On top of these, smaller bedforms such as dunes
continental shelves, however, they can also be present in and ripples also develop. They can develop crests with
shoreface zones, as well as in the interior of semi-enclosed sinusoidal morphologies and be grouped in trains or be
bays where there is sufficient space to generate forms of isolated with barchanoid crescent-shaped morphologies.
these dimensions, and where persistent streams develop with • Sand ribbons: These are macro-shaped ribbons that
the necessary velocity. These macro-shapes may be subject develop longitudinally in the direction of the current
to different input regimes. This is how they are defined action. They are highly evolved forms that develop when
(Fig. 14.33): they separate from one of the arms in some barchan
shapes, although they can also form due to a dynamic
• Sand patches: Large sand patches deposited on shadow behind an obstacle.
low-mobility bottoms (rocky or cohesive beds) and lim- • Gravel furrows: These are longitudinal forms that are
ited by these same materials. On these sand patches, very similar to the sand furrows but with a coarser sedi-
smaller bedforms develop (ripples and dunes). ment size, which require a high speed to form.
• Sand waves: Large shapes with wavelengths of up to
hundreds of meters that can reach several kilometers in

showing surficial structures
associated with the upper plane
bed. a Crescents caused by action
of the backwash on shells.
b Rhomboidal structures
Fig. 14.32 Scheme showing the surface morphology and the internal
structure of a hummocky bedform
Fig. 14.33 Models of

macro-scale bedforms generated
by tidal currents in sandy facies
on cohesive beds. Each model
corresponds to a different
sediment supply regime. The
average speed of the tidal current
at the surface during a spring tide
appears in parallel to each zone
[8]
References 15. Van der Graaf J, Van Overeem J (1979) Evaluation of sediment
transport formulae in coastal engineering practice. Coast Eng 2
(3):1–32
1. Allen JRL (1984) Sedimentary structures: their character and 16. Greeley R, Iversen JD (1985) Wind as a geological process on
physical basis. Elsevier, Amsterdam, 592pp Earth, Mars, Venus and Titan. Cambridge planetary science series
2. Allen JRL (1985) Principles of physical sedimentology. George 4, Cambridge, 333pp
Allen & Unwin, London, 272pp 17. Guy HP, Simons DB, Richardson EV (1966) Summary of alluvial
3. Allen JRL (1994) Fundamental properties of fluids and their channel data from flume experiments, 1956–1961. US geological
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J Sediment Petrol 60(1):160–172 Depositional environments as interpreted from primary sedimen-
5. Bagnold RA (1941) The physics of blown sand and desert dunes. tary structures and stratification sequences. Short Course 2:161
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6. Bagnold RA (1963) Mechanics of marine sedimentation. The sea: Sediment transport processes in coastal environments. Virginia
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transport. Sedimentology 10:45–56 as illustrated by the River Fyris. Bull Geol Inst Upsala 25:221–
8. Belderson RH, Johnson MA, Kenyon NH (1982) Bedforms. In: 527
Stride AH (ed) Offshore tidal sands process and deposits. 22. Inman DL, Bagnold RA (1963) Beach and nearshore processes
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transport of sediment particles in the shallow marine environment. 23. Kamphuis JW (1991) Alongshores sediment transport rate.
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Part III
Coastal Systems: Dynamics, Facies
and Sedimentary Models
Tread the surface level

wearing answers in layers.
Sediments of sediments unfold
to write new cave scratchings.
“Great News From the South Pole”

Das Oath
Geologically Controlled Coastal Systems:
Rocky Coasts, Bluffs, Cliffs and Shore 15
Platforms
range of ages, from Precambrian to Cenozoic. This type of

15.1 Introduction
lithology offers greater resistance to erosion, which is
manifested in retreat rates measured in millimeters or
Most of the world’s coasts develop in hard or cohesive
centimeters.
materials typical of mountainous continental margins.
Very similar erosive morphologies can be generated in
Indeed, since the work of Emery and Kuhn [3], the literature
lithologies of lower resistance and higher regression rates,
has commonly reported that 80% of the world’s coasts can
although these are normally developed in more recent ages.
be categorized as rocky or cliffs. However, these coasts do
In these cases, the term bluff coasts is used (Fig. 15.1b).
not usually appear in our minds when we imagine a coast.
Normally, these coasts develop in sedimentary rocks of
This happens because humans normally settle their resorts
diverse origin, among marine deposits, tillites, eolianites and
on low coasts associated with depositional systems and
beachrocks. These lithological formations correspond to sea
usually keep them away from steep coasts. The scarcity of
levels and climatic stages different from the current one, but
research work on these rocky coastal systems does not help
they can also develop in non-coherent volcanic lithologies
to favor them as well-known coasts either. In recent decades,
(pyroclastic). The term bluff is much less used, and for many
these environments have attracted less attention than other
authors the term rocky coast also includes bluff coasts.
systems located on coastal plains that are more vulnerable to
The term cliff refers to both rocky and bluff coasts that are
problems associated with global change. However, rocky
steep and sloped at an angle of more than 40° [7]
coasts offer very beautiful panoramas and spectacular views
(Fig. 15.2a). A cliff is never surpassed by the wave breakers,
of processes, especially during storms, and play an important
so it is understood that its height is always greater than the
role as a supplier of sediments to depositional environments.
maximum height of the maximum swell acting during the
The resistance of the materials typical of rocky coasts
moments of maximum surge (maximum flooding level).
(Fig. 15.1a) makes them slow to dismantle. At the same
Cliffs are the most common feature of both rocky and bluff
time, a high wave transport capacity gives this type of coast
coasts, where they take the name of soft cliffs, so the term
a distinctly erosive character. Erosion rates in this type of
cliff coast is also used as a synonym. However, rocky coasts
coastline are highly variable, ranging from a few millimeters
and also bluffs can have slopes less than 40º or levels below
per year to a few meters per year, depending on the con-
the maximum floodable level. In these cases, reliefs are
sistency of the rocks in relation to the wave dynamics.
formed that can be surpassed (overtopped) by the waves
Despite these erosive characteristics, associated deposits can
under certain circumstances. These reliefs of lesser slope and
also appear on rocky coasts. Normally, these deposits either
height are called banks or benches.
correspond to debris that the wave is not able to displace
Regardless of the emergent morphology and the type of
over long distances, or are made up of smaller materials that
materials that control the development of this type of coast, a
the wave deposits in those places where the wave energy is
platform that extends in depth from the coastline and is
dissipated.
subject to the action of the waves usually develops on the
In most discussions, the concepts of rocky coasts and
submerged front. These platforms may have different char-
cliffs are used interchangeably, although there are nuances
acteristics of slope, extension, morphology and location with
between these terms. In general, a rocky coast is understood
respect to wave and tidal action, and are commonly referred
to be a coast formed by rocks of hard and resistant lithology.
to as shore platforms (Fig. 15.2b).
There is a variety of lithologies among igneous (plutonic and
Rocky coasts are widely distributed throughout the world
volcanic), metamorphic and consolidated sedimentary rocks
and can be found in different climatic and tectonic
(sandstones, siltstones, limestones, dolomites), with a wide

https://doi.org/10.1007/978-3-030-96121-3_15
188 15 Geologically Controlled Coastal Systems: Rocky Coasts …
Fig. 15.1 a Rocky coast in

Pliocene basalt lavas (Ngor
Island, Senegal). b Bluff coast in
Cretaceous marls and grainstones
(Praia da Luz, Portugal)
environments, although they have classically been associ- the lithologies means that a large part of the characteristics
ated with tectonically active coasts subject to an uplift pro- of these coasts can be inherited from previous geological
cess. Their high slope and height may mean that sea level times.
movements do not produce large horizontal movements in The possibilities of the combinations of lithology,
the form of transgressions and regressions in the long term. arrangement of lithological bodies and fractures, as well as
The current rocky coasts have been developing since the differing slopes in relation to processes, lead to a wide
arrival of the sea level to its current position after the variety of erosive morphological features. At the same time,
Flandrian transgression. However, although the dynamics coastal erosion systems are important suppliers of material to
over these environments are very energetic, the resistance of other nearby coastal sedimentary environments. In this
15.1 Introduction 189
Fig. 15.2 a Near-vertical cliffs

developed in Cretaceous
limestones (Sagres, Portugal).
b Shore platform in a cliff front of
Pleistocene sands (Larache,
Morocco)
chapter, the variables that control the whole range of pro- the most important control factor is geology, since it is the
cesses and forms will be analyzed, as well as the deposits geological factors that determine the threshold over which
associated with the main erosive features. the rest of the dynamic factors must act [13]. This is why this
type of system is being classified here as geologically
controlled.
15.2 Control Factors
Most of the factors that control the dynamics of rocky coasts 15.2.1 Geology
are those that affect the intensity of the weathering and
erosion processes which contribute to their dismantling. There are several geological characteristics that determine
Thus, we will find among them wave energy, tidal ampli- the degree of a coast’s resistance to erosion. Obviously,
tude, climate and relative sea level movements. However, lithology is a fundamental factor, but so are the structural
characteristics, such as the degree of fracturing and the erode and bays will form, while the less fractured areas will
arrangement of materials with respect to the coastline, in be more resistant and will constitute the coastal overhangs.
determining to what extent dynamic processes will act on Finally, the arrangement of materials is a factor to be
geological formations. taken into account, since different arrangements can generate
Regarding the lithology, this is the factor that determines different coastal morphologies. On the one hand, the litho-
the intrinsic strength of the rock (Fig. 15.3). Igneous rocks, logical disposition plays a determining role in the general
such as granites, or coherent volcanic rocks, such as basalts, morphology of the coast. In this respect, authors such as
present high resistance that can be maintained over wide Johnson [9] distinguished between concordant and discor-
coastal fringes. The presence of plutonic rocks minimizes the dant coasts according to the orientation of the lithological
importance of the structural factor (Fig. 15.3a). On the guidelines in relation to the wave front. Furthermore, it is not
contrary, the presence of metamorphic or sedimentary rocks only the angle between the planes of the lithological units
promotes varying resistance by lithological sections, favor- and the waterfront that must be considered, but also the
ing differential erosion. In this case, there is greater structural angle between the waterfront and the fractures in three
control and the result is a coast with irregular morphology dimensions. This arrangement determines the possibility of
(Fig. 15.3b). Massive limestones tend to give very vertical different slope processes occurring as part of coastal retreat.
cliffs associated with different forms undergoing dissolution It is important to note that it is the disposition of the fractures
processes (Fig. 15.3c). Lithological alterations of unde- with respect to the action of the agents that induces the
formed sedimentary rocks with different strengths result in formation of secondary features such as caves, arches, and
very irregular coasts with numerous collapsed blocks at the stumps and stacks.
base of the cliffs (Fig. 15.3d). Finally, recent sediments and
unconsolidated sedimentary rocks offer little resistance to
dynamic processes, which are accelerated in these litholo- 15.2.2 Wave Energy
gies. The result is the presence of long slopes with many
deposits at the cliff toe (Fig. 15.3e). Wave energy exerts the main control over the physical
In certain lithologies, the degree of fracture plays a fun- processes of erosion, since it conditions the erosive capacity
damental role, since erosion and weathering tend to be of the rocks on the waterfront, as well as the potential for
concentrated in the rock sections with the highest density of transporting the material to other coastal sections.
fractures. On coasts with homogeneous lithology, the areas The energy does not depend only on the dimensions of
with a higher concentration of fractures will be easier to the wave, but also on the type of interaction with the coast
Fig. 15.3 Examples of coast

morphologies of different
lithologies. a Granitic coast.
b Alternating quartzite–schist
coast. c Cliff in massive
limestone. d Cliff in sandstone
with a marly base. e Cliff in silty
sand
15.2 Control Factors 191
that is reflected in the breaker type. In this aspect, the determines the average wave energy throughout the year, but
extension and position of the coastal platform and the gen- also the number of storms and the time they occur. In
eral slope of the shoaling area have a notable influence. If addition, the climate also exercises the main control over
the platform is wide and near the surface, some of the wave physical and chemical weathering processes, selecting the
energy can be dissipated by friction with the bottom of this type of processes and their intensity.
platform. If, on the other hand, the platform does not exist, This influence of the climate causes a latitudinal zoning in
or is located in very deep areas, the waves will reach the the processes that are associated with rocky fronts. At high
coast with all their energy, which will be used entirely in the latitudes, weathering processes related to freezing and the
breaker and will have a greater effect on the physical dis- action of large waves in strong storms predominate. In
integration of the rock. contrast, in tropical latitudes, chemical weathering processes
Wave energy is also a factor in transport capacity. It is dominate and the overall energy of the waves is lower. At
important to measure the transport capacity in relation to its mid-latitudes, global wave energy is higher and there is a
ability to produce material accumulations at the base of the dominance of physical weathering processes.
rock face by other processes associated with the slope. If the
wave is able to rapidly transport the deposits generated at the
foot of the cliff, then the face will remain active and erosion 15.3 Processes
rates will be higher. If the rate of formation of the slope
deposits is very high, and only a part of the deposit is able to Numerous processes act on the rocky coasts, which are
be transported, then the deposits will accumulate at the base, grouped according to their nature into physical, chemical
protecting the waterfront and delaying the retreat. and biological; these combine to result in a recessionary
effect of the coastline. The coastal morphology that we
observe today is the result of several thousand years of
15.2.3 Tidal Range continuous action of these processes acting in a combined
way. The relative importance of each of these processes in
The tide controls the topographic level of wave action and the global erosion of the coast depends on the way they
the time it acts at each level of a rocky coast. The devel- affect the geological nature of the rocks and their struc-
opment of these systems is not related to the tidal range; tural arrangement. The effect of these processes has been
therefore, rocky coasts can develop in any tidal range. When analyzed in detail in the first section of Alan Trenhaile’s
the tidal range is small, the wave action is restricted to a very volume (1987), as well as in the first chapters of Tsuguo
narrow area of the rocky front, while on macro-tidal coasts Sunamura’s work (1992), and is summarized in this
the tide displaces the wave action vertically, dispersing the section.
energy in a wider strip.
15.3.1 Wave Erosion

15.2.4 Relative Sea Level Movements
Direct erosion by waves is the most immediate and impor-
The relative movements of sea level combine eustatic tant process in the retreat of cliffs. Wave action takes place in
movements with the action of tectonics on the ground. The a narrow vertical strip of the rocky front that is located in
relative rises and falls of sea level can place the action of areas close to the average water level and whose position
waves in different positions in the long term, generating varies according to the magnitude of the waves and the tidal
shore platforms at different topographic heights. Higher range [24]. The waves actually act on the cliff via three
positions of sea level will generate emerged coastal terraces, different mechanisms: (1) direct hydraulic strike; (2) abra-
while lower positions will generate submerged platforms at sion using clastic elements; and (3) action of air compressed
different heights and depths. The rhythm of the sea level by the waves.
movements in relation to the erosion rate control the mean
slope of the coast and the development of some particular • Direct hydraulic action: This is the action of direct water
morphologies, such as inclined shore platforms. impact on the surface of exposed rocks on the waterfront
(Fig. 15.4a). In this impact, all of the energy of the wave
is instantly converted into deformation and heat. This
15.2.5 Climate effect is called wave pounding or the “sledge hammer
effect” by some authors [2]. Since the energy depends
The weather controls the wind regime and is therefore a quadratically on the height of the waves, the impacts will
primary factor in wave energy. In this sense, the climate be more energetic the larger the dimensions of the wave.
The effect of these impacts on the rock will depend on but of thousands of waves acting continuously at the
this dissipated energy in relation to the geological nature same topographic level over millennia.
of the rock. In this respect, it should be borne in mind that • Abrasion: In this case it is the erosional effect of clastic
the hammering action is not the result of a single wave, fragments displaced by the waves on the rock face (grains,
Fig. 15.4 a Direct hydraulic

action of waves on a cliff base
(Llanes, Spain) and effect of air
pressure venting through open
fractures (photograph courtesy of
G. Flor-Blanco). b Clastic
elements used by waves as tools
for abrasion in a cliff base
(Larache, Morocco). c Potholes in
a calcareous shore platform
(Menorca, Spain)
15.3 Processes 193
pebbles, cobbles and even blocks). This action is more • Thermal stress: This is the effect of the expansion and
important on surfaces with a low slope, because the drag- contraction of the rock due to thermal changes that occur
ging effect of these lithic elements can also occur on these throughout the day (day–night) or the year (summer–
surfaces, causing wear and tear on the rock. On cliff faces, winter). In general terms, as the crystals that make up the
the effect of projected clast impacts is greater (Fig. 15.4b). rock heat up they expand, putting pressure on the rest of the
In this case, the effectiveness of the abrasion process crystals. The different minerals behave differently, giving
depends not only on the geological nature of the rock and rise to a differential expansion that involves the appearance
the wave energy, but also on the availability of abrasive of internal forces that end up disintegrating the rock
elements (type and quantity). The effect of this action on (thermal fatigue). This is not an exclusive effect of rocks
the rocky outcrop is generally a polishing of the surface. located on the coast, but in coastal environments, espe-
On other occasions, one or more of the clastic elements cially in arid and semi-arid climates, it combines with other
may be trapped in a cavity, turning inside it with the arrival processes. This process normally occurs at a microscopic
of each wave. In these cases, the result will be the genesis level, between grains; however, it can also occur at a metric
of potholes of different dimensions (Fig. 15.4c). scale when rocks of different thermal behavior alternate in
• Action of compressed air: The arrival of the wave crests an outcrop. In this case, fractures with greater separation
to the rocky front usually implies that different volumes may appear and larger blocks may be detached.
of air can be trapped in the rock cavities, increasing their • Expansion by salt crystallization: In coastal environ-
pressure when the breaker occurs. These volumes can be ments, it is common for seawater to enter small rock
of different dimensions depending on the character of the cavities such as pores or fractures. The entry into the
empty space, ranging from the millimetric volume of the seawater cavities is related to tidal oscillations, but also to
pores, the centimeters in the fractures to several meters in the spray effect associated with wave breakers. This
larger cavities of the rock face. The result of the pressure seawater is, after all, a saline solution that can later
increase varies depending on the scale at which it occurs. evaporate and cause the crystallization of salts inside
The greatest effects usually occur at the fracture level, these cavities. Sodium sulfate, calcium chloride, magne-
with the increase in pressure acting as one of the causes sium sulfate and, above all, sodium chloride, are the salts
inducing fracture growth; this can eventually lead to the that most commonly crystallize in these environments.
opening of cavities to relieve pressure towards the surface The appearance of these salts inside the cavities means an
(Fig. 15.4a) and may also contribute to the detachment of increase in volume that generates the forces necessary for
rock fragments. the disintegration of rock fragments.
• Freeze–thaw cycles: This is a process of weathering
In general terms it can be considered that the combined associated with high latitudes. In this case, the internal
effect of these three processes results in the removal of rock forces that break up the rock are generated by the
fragments from the surface [22]. Although waves act con- expansion and contraction of water inside the pores and
tinuously at these topographic levels, it is during major the fractures that develop from changing from liquid to
storms that the effects of their action become more visible. solid state and vice versa. In this case, the expansion of
Different works based on the continuous photography of the the water when it freezes (volume increase of 9%) is a
scars left by the removal of blocks on cliff fronts have shown sufficient force to break up the rocks. In this respect, it
that storm waves are capable of removing blocks of up to should be taken into account that water with a high salt
several tons and displacing them even to the top of cliffs content is more difficult to freeze and, consequently,
more than a dozen meters high (e.g., Trenhaile and Kanyaya generates lesser forces. However, this process can occur
25]; Naylor and Stephenson [17]). with fresh water at higher topographic levels of the rock
profile, contributing to the disintegration of the rock
where the waves cannot act.
15.3.2 Mechanical Weathering
Physical weathering occurs when internal forces act on the

pores or fractures of the rocks towards the outside; these 15.3.3 Chemical Weathering
contribute to the appearance or increase of fracturing at
different scales, ending with the disintegration of the rock. Chemical processes take place in all rocky coastal strips, from
The three processes that are usually associated with rock the underwater areas to the emerged zones, including the
disintegration in the coastal strip are: (1) thermal stress; intertidal fringe. They consist of mineral transformations due
(2) expansion by salt crystallization; and (3) freeze–thaw to the interaction with the water and the ions dissolved in it.
cycles in periglacial climates. They are processes that are concentrated on the surface of the
rock or at shallow depth, sticking to the area where surface 15.3.4 Bioerosion
water exerts its influence. Consequently, their speed of action
is much slower and less visible than physical processes. This Biological degradation of rocks occurs when organisms drill
type of weathering mainly comprises four types of chemical their surface for shelter and/or food. These organisms, both
process: (1) dissolution; (2) hydrolysis; (3) hydration; and animal and plant, perform a double biochemical and
(4) oxidation. These all contribute to the granular disinte- biomechanical action, since they are capable of producing a
gration of the rock, facilitating the erosive processes that act physical breakdown effect on the rock grains as well as
with them. The type and intensity of each of these processes chemical changes that lead to the disintegration of their
has a strong lithological and climatic control. These processes mineral structure.
can act together in an effect called corrosion. The most effective bioerosion is the colonization of the
rock surface by algae in the sub- and intertidal zones. The
• Dissolution: This implies the wear of the rock due to the case of blue-green algae is the best example (Fig. 15.5a).
chemical disintegration of the minerals, passing the ele- These microalgae are capable of rapidly colonizing the
ments that compose the crystals to an ionic state inside surface of carbonate rocks by penetrating more than 1 mm
the water. below the surface. Their activity contributes to the
• Hydrolysis: This is a process that acts preferentially in bio-dissolution of large amounts of carbonate, breaking
feldspars and carbonates, in which the reaction with water down the rock fabric and undissolved grains, thus facilitating
molecules breaks the crystalline structure producing its the subsequent action of the waves. A similar action is
transformation into clay phyllosilicates. It must be taken effected by other types of organisms such as fungi and
into account that feldspars are part of the composition of lichens in the inter- and supratidal zones. The presence of
many rocks of different origins, whether igneous, meta- these microorganisms on the surface of the rock causes the
morphic or sedimentary, and the carbonates are the base appearance of other macroorganisms that feed on them.
of all calcareous rocks. The action of this process implies Among these are some mollusks such as gastropods (snails
a transformation into minerals that pass immediately to and limpets, Fig. 15.5b), bivalves (the most common at
the suspended phase, to be easily removed by the waves. present are those of the genus Pholas) and polyplacophores
• Hydration: This involves the entry of the water molecule (chitons). The same activity can be performed by other
into the crystalline structure of the minerals, meaning a invertebrates such as echinoderms (Fig. 15.5c), polychaetes,
transformation that normally involves an increase in bryozoans, sponges and crustaceans.
volume. The passage from oxides to hydroxides and the The combined activity of bioerosion and chemical
hydration of anhydrite into gypsum are the most common weathering processes gives the rock surface an irregular cell
examples, but these processes are present only in certain texture, made up of holes and partitions known as honey-
lithologies. When this occurs, the chemical process also comb (Fig. 15.5d).
acts in combination with the physical process of expan-
sion that this increase in volume implies.
• Oxidation: This process involves the loss of electrons 15.3.5 Slope Processes
from any mineral compound, but the most common
reaction in geological environments is associated with The processes associated with the direct pounding of the
that between the iron contained in any crystal structure waves can only transform the lower zone of the rocky
and the oxygen dissolved in the water. These reactions shores. For a coastal system with a high retreating slope,
normally result in iron oxides and hydroxides (goethite, other processes occur that affect the part where the waves
hematite and limonite) which are mobilized through the cannot reach. The processes of weathering, although they
pores to concentrate in the form of crusts on the surface of affect the entire profile of the rocky coastline, are slow and,
the rock or in the more porous areas, controlled by in any case, only contribute to the release of particles to
lithology or the presence of joints. facilitate erosion; once these particles are released, they must
be set in motion by other physical processes. In these high
In all of these processes, there is a strong latitudinal areas, high-slope continental processes are responsible for
control from the temperature of the water. In general terms, this task. In these processes, gravity plays a very important
chemical processes run more easily at higher temperatures, role, although surface water runoff is also significant. Both
since, as discussed in Chap. 11, higher temperatures increase contribute to vertically transporting materials from the upper
the ionic capacity. parts of the rock profile to bring them down to a height
15.3 Processes 195
Fig. 15.5 Some examples of

bioerosion. a Blue-green algal
cover of a shore platform
(Larache, Morocco). b Some
fractures in a granite enlarged by
limpet activity (Pointe de
Trévignon, France). c Erosional
action of an urchin in the base of
a cliff (Samaná, Dominican
Republic). d Honeycomb
structure on a shore platform
(Algeciras, Spain)
where the waves can exert their action on them. There are destabilization is usually related to the occurrence of
four fundamental processes: (1) rockfall; (2) landslides; decompression fractures parallel to the cliff surface and to
(3) mass flows; and (4) the action of surface water runoff. the destabilization of the base due to wave action. This
massive drop (Fig. 15.6b) can occur in the form of
• Rockfall: This involves a vertical displacement of rock overturns or collapses (toppling).
masses due to the direct action of gravity on consolidated • Slides: Landslides tend to occur in less consistent
rock faces (Fig. 15.6a). This movement may individually lithologies, especially in bluff coasts. They occur when
affect rock fragments of different sizes released by there is a displacement of masses in favor of a net surface
mechanical weathering processes or, conversely, involve because the resistance of the base is exceeded by the load
large rock masses by large-scale destabilization. This it supports. Depending on the geometry of this surface,
Fig. 15.6 Processes of rockfall

associated with the high slope.
a Small rockfalls, with an
example in southern Portugal.
b Toppling, with an example in
northern Spain
displacing slides may occur when the surface is flat • Surface runoff: The effect of water currents on the rock
(Fig. 15.7a) or rotational slides if the surface is curved surface, especially in lower slope systems, can cause
(Fig. 15.7b). This geometry is structurally controlled. erosion and material transport by fluid flow. This trans-
Another type of landslide occurs due to the presence of port manifests in the upper part of the profile in the form
fracturing in conjugate families arranged at an oblique of large erosive grooves where water flow is concen-
angle to the rock surface, which release large trated, while in the lower part of the profile, small-scale
wedge-shaped masses of rock (Fig. 15.7c). As with the alluvial fans can form with the materials transported from
massive landslides described above, the onset of the the upper part (Fig. 15.8).
landslide is related to the destabilization of the base due to
the action of the waves, although it can also begin when
very intense or very continuous rains cause a decrease in
grain friction by increasing water pressure in the pores. 15.4 General Morphology
• Mass flows: Mudflow, debris flow or grain flow phe- and Morphological Features
nomena may also occur in certain unconsolidated
lithologies. In these phenomena, there is a movement of Taking into account all the factors and processes that
the ground of lower density and more deformation than in influence the development and evolution of a rocky coast as
the case of landslides. Interstitial water also plays a fun- detailed in the previous sections, it can be seen that these
damental role in lubricating the soil and reducing the present a wide variety of morphologies and morphological
density of the material and the friction between grains. features. In general terms, the active morphologies can be
Fig. 15.7 Slide processes

associated with the high slope.
a Planar slides, with an example
in northern Spain. b Rotational
slides, with an example in
Northern Spain. c Wedge slides
by orthogonal fractures
15.4 General Morphology and Morphological Features 197
Fig. 15.8 Grooves and alluvial

fans caused by flow runoff, with
an example in southwestern Spain
grouped into three main features: rocky ramps, shore plat- processes that act in the upper part of the same, resulting in a
forms and cliffs. Each of them can present different features very fast dismantling rate.
and secondary elements and follow different evolutionary
paths according to the combination of the factors and pro-
cesses mentioned above, as well as their relative importance. 15.4.2 Shore Platforms
Shore platforms are low-slope erosive rock surfaces exca-

15.4.1 Rocky Ramps vated from the front of some rocky shores. The origin of the
platforms is mainly erosive and is due to the recession effect
Although this term is not very widespread, it is used to refer of the rocky front. They can be completely horizontal or
to rocky coasts that have a slope of less than 40° (Fig. 15.9). have a gentle slope towards the sea that can reach 10° and
Other terms such as gentle cliffs, benches or uniformly their scale in a transverse direction to the coastline varies
sloping rocky coast are also used to name this concept. Apart from tens to hundreds of meters. Towards the sea, the edge
from the lesser slope, the processes that affect it, its mor- of the platforms presents a sharp increase in slope that results
phological characteristics and its evolution are very similar in a steeper slope that connects the platform with the deeper
to those of cliffs, so many authors include them as a subtype areas. The slope of the platform is closely related to the
of cliffs. Rocky coasts acquire this morphology when the dynamics of the erosion processes that generate it in relation
materials are not very resistant in relation to the continental to the resistance of the rock. Thus, more resistant rocks tend
Fig. 15.9 Ramp-shaped rocky

coast (Algarve, Portugal)
to generate horizontal platforms, while less consolidated The upper part (cliff top) has a low-slope morphology,
rocks generate a greater slope [23]. Within the processes, the usually called tableland. At the marine boundary of this flat
tidal range also exerts an important control, in such a way surface, the cliff face may develop directly, although
that, the wider the tidal range, the greater the slope tends to sometimes there may be a transitional zone of intermediate
be [24]. On the other hand, although there is agreement that slope (cliff crest). This cliff face is the area that is subject to
platforms constitute a relict form of shoreline retreat, there is the most intense erosion and its main tendency is to retreat.
still debate about the process that is actually responsible for The base of the cliff face can link directly to the shore
the development of the shoreline. Classically, they have platform, which is a very low-slope area that means the
been referred to as abrasion platforms or wave-cut platforms, transition to the subtidal zones, where it links to the near-
however, these terms have recently been questioned by some shore slope. Between the cliff face and the coastal shelf, a
authors, as they refer to processes that may not be respon- glacier may develop where debris from continental processes
sible for their development. Specifically, Masselink et al. accumulates on the cliff face before the waves eventually
[13] cite the work of Stephenson and Kirk [21] on the remove it. This debris accumulation area is called a cliff toe.
northeast coast of the South Island of New Zealand, in which Various types of cliffs can be distinguished according to the
they determined that the energy developed by the waves was presence of these elements of the system and the location of
insufficient, even during storms, to cut the rock on the scale the rocky platform [23].
of the platform. Thus, they attributed the fundamental role as The plunging cliffs have a vertical drop to a platform in
breakers of the rock in certain cases to the weathering the underwater area at several meters’ depth (Fig. 15.11).
processes. This is typically the case for the more resistant lithologies
The presence or absence of the platforms, as well as their and the erosion processes are usually very slow, giving the
inclination and position with respect to the tide levels, is an cliff a very low rate of retreat. In these cases, the coastal front
element to be taken into account in the dynamics of rocky is generally quite regular and any irregularities are related to
coasts, since these factors condition the action of the waves the density of fracturing. The waves break directly onto the
on the coastal front. In any case, most of the research cliff face and the direct hydraulic impact is usually accom-
includes these platforms as one of the elements of the cliff panied by phenomena related to the action of compressed
system, incorporating their classification, as well as their air. When material collapses from the upper parts, it tends to
dynamics and evolution, in that wider study. accumulate below sea level, allowing the waves to continue
their action on the cliff face. This continuous action of the
waves at the same level develops a linear erosive feature
15.4.3 Cliff Systems called a notch, which is typical of this type of cliff.
The cliffs with a sloping coastal platform appear in less
The cliffs are very steep coastal forms which hang over 40°. resistant lithologies and form coasts with less general slopes.
The presence of an almost vertical escarpment divides these In these cases, a platform develops at the foot of the cliff
coasts morphologically into several elements (Fig. 15.10). face, although it is not very long and slopes to the sea by
several degrees. In this type of cliff, there is a stronger
recession controlled by the slope processes acting on the cliff
face. These processes contribute to the development of a cliff
toe made up of debris in the intertidal zone (Fig. 15.12).
Wave erosion is based on the destruction and remobi-
lization of these residual deposits. Cliff retreat is controlled
by the balance between the capacity of the slope phenomena
to generate these deposits and the capacity of the waves to
erode them. It is common for erosion to go through a
cyclical phenomenon that starts with the collapse of a seg-
ment of the front and continues with a long period that the
waves need to fragment the blocks and transport them to
other areas of the coast.
Although erosion is a process that dominates horizon-
tally, causing the cliff face to recede, erosion also occurs
vertically on the platform that is being submerged. Together,
Fig. 15.10 General morphology of a cliff system the physical processes related to the action of the waves, and
15.4 General Morphology and Morphological Features 199
Fig. 15.11 Morphology of a

typical plunging cliff, illustrated
with the example of Cape Sâo
Vincente (Portugal)

typical cliff with sloping shore
platform, illustrated with an
example of Chiclana (southern
Spain)
the processes of chemical weathering and bio-erosion, make

the submerged platform deeper, especially in the sectors 15.5 Dynamics and Evolution
closest to the sea. As a result, this platform gains in slope as
the cliff retreats. It is the combination of the processes acting under control
This type of cliff presents a greater heterogeneity and factors such as climate in relation to the resistance of the
morphological variety. Lithological alternation is typical, as rocks that determines the dynamics and short-term evolution
well as differing sections with different degrees of fracture. of the rocky coasts and, in particular, of the cliff systems. In
Thus, all the features described in Sect. 4.2.1 of this book addition, other factors such as relative sea level movements
and illustrated in Fig. 4.2 are associated with these cliffs. control this evolution in the longer term. All attempts by
These features include stacks, stumps, cove beaches, caves, some authors to directly relate the morphology and
arches and blowholes (Fig. 15.13). dynamics of these systems to a single variable have been
Cliffs with a horizontal shore platform develop in even unsuccessful. For example, attempts to correlate higher wave
less resistant lithologies and in situations where the retreat of energy with larger rocky shelf dimensions are not sustained
the cliff face is very rapid in relation to the vertical erosion of since a large platform will dissipate wave energy before
the shore platform. In these cases, the platform may develop breaking at the base of the cliff (e.g., Stephenson and Kirk
widely in the intertidal zone (Fig. 15.14) to end abruptly in a [21]). Consequently, any approach to understanding the
slope break connecting this platform with the shoreface dynamics of these systems must be made from the point of
through a slope. Depending on the wave efficiency and tidal view of considering multiple variables together.
range with respect to the strength of the material, the height In any case, the relationship between the short-term
of this platform may vary from one system to another dynamics of the cliff system and the following four variables
depending on its proximity to high or low tide. The presence is clear: the resistance of the rocks, the rhythm of the
of an increasingly wide platform causes the waves to dissi- weathering processes, the efficiency of the slope processes
pate before they reach the front of the cliff, so this type of and the erosion capacity of the waves, both at the base of the
system usually develops deposits at the base of the cliff. cliff face itself and in the possible deposits generated at the
However, during storms, the action of the waves is intensi- cliff toe (Fig. 15.15).
fied and these materials can be used as abrasive agents at the On the one hand, the strength of the rocks is the result of
base of the cliff. the combination of lithology, arrangement of the materials
Fig. 15.13 Morphological

features of a cliff with sloping
shore platform in a cliff near
Lagos (southern Portugal)

typical cliff with horizontal shore
platform, illustrated with the
example of Aljezur (southwestern
Portugal)
and degree of fracturing. This resistance is what clearly rates were summarized by Sunamura [23] and are shown in
marks the degree of efficiency of the processes, determining Table 15.1.
which of them can contribute most to the dismantling of the On a millimetric scale, the processes of weathering con-
rock at the different possible scales. The result is a different tribute to the weakening and granular disintegration of the
response of each lithology to erosion, resulting in highly rock, both in the subaerial and submerged parts, including
variable erosion rates of several orders of magnitude. These the intertidal strip, which is periodically exposed and
15.5 Dynamics and Evolution 201
acting in the case of unconsolidated lithologies, and rockfall

or planar and rotational landslides in the case of coherent
rocks. In the second phase, the action of the slope processes
produces metric-scale setbacks on the cliff crest and brings
down large volumes of rock from the upper reaches to a
level where the waves can act on them. In the final phase, the
waves are responsible for breaking up and transporting the
accumulations generated by the slope processes at the cliff
base. The definitive dismantling of the deposits at the foot of
the cliff allows the waves to attack the base of the cliff again,
thus starting a new cycle of retreat. The duration of each of
Fig. 15.15 Slope and wave process interactions in cliff systems these cycles depends on the relationships between the nature
of the rock and the capacity to transport the waves; the final
result is the net retreat of the cliff.
submerged. These processes result in micro-erosion that acts In reality, this conceptual model does not always work
on such long time scales that it would be impossible to this way since, on the one hand, not all slope processes are
visualize without the application of precision instruments related to wave destabilization at the base of the cliff and, on
(e.g., Gómez-Pujol et al. [5]; Moses et al. [15]). In the more the other hand, as shown in the flowchart in Fig. 15.15, there
resistant lithologies, these seem to be the dominant pro- are different possibilities of combination between the rate of
cesses. The granular material generated by these processes is action of the slope processes and the rates of wave erosion
easily removed by the waves. In this case the result is on the toe deposits. Taking into account the latter consid-
plunging cliffs. eration, there are three possibilities in terms of the rate of
On a larger scale, in less resistant lithologies, slope pro- erosion of the base deposits by the waves. These rates affect
cesses combine with wave efficiency to take advantage of the both the general dynamics of cliff retreat and its slope and
weakening caused by weathering. Slope processes and morphology [26] (Fig. 15.17).
waves work in different ways. On the one hand, in most Under intense erosion, the model expressed in the pre-
cases the slope processes act instantaneously, displacing vious paragraph would be fulfilled. These conditions mean
large volumes of rock in a few minutes, while the rest of the the deposits in the foot are completely dismantled and the
time they remain latent. In between these processes, return retreat is moved upwards through the slope processes. As a
periods can be established. The action of the waves is much consequence, the retreat generates parallel profiles with a
more continuous, although it is subject to the annual cycles uniform slope (Fig. 15.17a). At moderate erosion rates, the
of fairweather waves and storm surges. The volumes of foot deposits are only partially dismantled, so that the waves
material worked by the slope and wave processes must refer do not cut through and destabilize the base of the cliff. In this
to the same period of time. case, the slope processes that destabilize the upper part of the
This joint action of both types of processes operating at cliff are not related to the action of the waves, but to the
different timescales results in a cyclical model of cliff retreat dynamics of the gravitational processes themselves.
where three different phases follow each other (Fig. 15.16). Although the upper part of the cliff develops a retreat in the
In the first phase, the attack of the waves can destabilize the form of parallel profiles, in the lower part there is always a
base of the cliff, activating the slope processes. Depending debris deposit (Fig. 15.17b). The third case is that in which
on the nature of the rock, its degree of fracturing and the the erosion of the base deposits is minimal. As in the second
slope of the rock profile, the slope processes involved may case, slope phenomena occur unrelated to wave action at the
be different, with avalanches, landslides and mass flows base. In this way, the upper part of the cliff suffers a retreat,
Table 15.1 Erosion rates in Material Erosion rate (m/year)

different lithologies (from
Sunamura [23]) Igneous rocks <0.001
Limestone 0.001–0.01
Flysch and shale 0.01–0.1
Chalk and Cenozoic sedimentary rocks 0.1–1
Pleistocene sedimentary rocks 1–10
Holocene sediments and pyroclastic materials >10
Fig. 15.16 Conceptual model of

a cycle of cliff retreat
Fig. 15.17 Response models of

cliff retreat to toe erosion rate
(adapted from Woodroffe [27]
and based on Vallejo and Degroot
[26])
while at the base the debris accumulates, causing the toe to In parallel with these erosional processes that act hori-
grow rapidly. The profile of the cliff thus undergoes a zontally by causing the cliff face to retreat, others occur that
rotation until a stable slope is reached (Fig. 15.17c). act vertically on the shore platforms [11]. These processes
also include weathering (mechanical and chemical), bio- Roig-Munar et al. [19]). According to this work, the blocks
erosion and physical erosion by waves (hydraulic action and can be distributed along the platforms (Fig. 15.18a), be
abrasion). As on the cliff face, these processes act at different interlocked at the base of the cliff (Fig. 15.18b) or even
scales and their effect is the loss of height of the platforms. climb the cliff face and be deposited on the ridge. The
Obviously, the process of vertical erosion on the platforms movement of blocks due to large storm waves has also been
(lowering) is not uniform, but is subject to the same litho- mentioned in the section on processes. These dynamics have
logical conditioning factors as the cliff face: i.e., the resis- been studied, especially in tropical cyclone contexts (e.g.,
tance of the material and the factors that determine it Morton et al. [14]), but also in high latitudes (e.g., Hall et al.
(lithology, arrangement of the materials and degree of [10]; Etienne and Paris [4]). The location of blocks due to
fracturing). storms is so similar to that of tsunamis that there is currently
Among the most visible processes that work on these a strong controversy in the literature about the origin of these
platforms are the formation and movement of large blocks in some places, often attributed to a mixed origin.
blocks. Most of the time the blocks are delimited by the The movement of these blocks on the platforms is epi-
presence of discontinuity planes, such as the stratification sodic. Work by authors such as Nott [18] have tried to
surface and different families of joints. These blocks can establish through formulas the energy and dimensions of the
be formed both on the upper surface of the platforms as wave (distinguishing between tsunamis and storms) neces-
well as on the submerged front, and can be mobilized sary to move the blocks according to their size. Large blocks
during the action of high-energy events such as tsunamis of several tons can only be displaced in decades or every
and extreme storms. hundred years. However, smaller blocks can be pulled out
The movement of large blocks by tsunamis has been and displaced almost every year. The dragging of these
widely documented over the past 20 years (e.g., Schefers blocks has an abrasive effect on the platforms. On many
and Kelletat [20]; Gracia et al. [8]; Goto et al. [6]; occasions, the displacement followed by these blocks can
Fig. 15.18 Large boulders

generated in a cliff front.
a Boulders displaced over a shore
platform (Laghdira, Morocco).
b Imbricated boulders (Menorca,
Spain)
even be distinguished due to the existence of linear scars 15.6 Associated Deposits
known as bruises [13].
In the long term, the dynamics of the cliff system begins In cliff systems with well-developed shore platforms, there
when the sea is positioned at a certain level, remains in that are usually two types of deposits that can be preserved at the
position for a long time and the system begins to retreat. base of the system [1]: cliff-toe deposits and cliff-beaches.
However, the retreat of the cliff face leads to the growth of These deposits are especially important in cliffs formed in
rocky platforms, and the dissipation of wave energy that unconsolidated rocks (bluffs).
takes place on increasingly long platforms means that the Toe deposits are of a diverse nature. In consolidated rocks
slope processes gain importance against the waves in the they are colluvial deposits resulting from rockfall and
more evolved stages of the cliff. This trend means that the sometimes include large blocks resulting from landslides. In
crest of the cliff begins to retreat more quickly than the base, unconsolidated rocks, the slides may be preserved at the base
where deposits that the waves can no longer erode begin to (Fig. 15.19a) and the colluviums may be constituted by sand
be preserved. The cycle ends when the cliff profile becomes (Fig. 15.19b); in these lithologies, the cliff base deposits
more regular and the base deposits begin to protect the base may also develop alluvial fans of different scale
from extreme wave attack. At this point the cliff becomes (Fig. 15.19c). These deposits, when preserved, usually pre-
inactive. sent important erosive scars from frontal attacks by storm
A continuous movement of sea level rise rejuvenates the surges.
erosion processes at the base of the cliff and gives the waves In the advanced stages of evolution of cliff systems,
more importance. The result is a much greater retreat, but beaches tend to develop on shore platforms due to increased
accompanied by the development of a sloping coastal plat- wave dissipation as these platforms gain width. The volume
form as a consequence of the rising effect of sea level. of material accumulated on these beaches depends directly
Rapid upward or downward movements of sea level on the contribution of sediments from the cliff system and on
interrupted by periods of stability produce a staggered the changes in dynamic conditions generated by factors
coastline where each stable period leads to the development acting in the long term. Initially, the accumulation of sand on
of a different front and platform at a different level. These the platforms influences their evolution by accelerating the
steps are known as coastal terraces and they can be found erosion process, since the beach clasts set in motion by the
both in the emerged area and in the submerged strip of the waves contribute to abrasion. However, when the deposits
system [16]. become thick enough not to move completely during storms,
Fig. 15.19 Examples of toe

deposits in a soft cliff. a Slide.
b Colluvial sand deposits.
c Meter-scale alluvial fan
15.6 Associated Deposits 205

cliff-foot beaches. a Pebble beach
(photograph courtesy of G.
Flor-Blanco). b Sandy beach in a
soft cliff front. c Beach of sand
covering boulders
they end up protecting the platforms, which eventually stop Firstly, it should be borne in mind that the supply of
being eroded. Cliff beaches are governed by the same material to cliff-front beaches is episodic, as these beaches
dynamics that will be studied in Chap. 17 of this book and are normally isolated in circulation cells separated by
their deposits have a great similarity; however, there are headlands from the longitudinal transport of the coast.
certain particularities that are present in this type of beach. Because of this, these beaches are commonly known as
pocket beaches or cove beaches. Due to this isolation, 7. Goudie A (2004) Encyclopedia of geomorphology. Routledge,
material only reaches these beaches after the action of slope London, 1200pp
8. Gracia FJ, Alonso C, Benavente J, Anfuso G, Del Río L (2006)
processes or during the dynamic of storms when sediment The different coastal records of the 1755 tsunami waves along the
can be transferred between cells beyond the headlands. South Atlantic Spanish coast. Zeitschrift für Geomorphologie
Consequently, these beaches suffer from strong variations in Suppl 146:195–220
sediment volume [12]. The behavior of these beaches has an 9. Hall AM, Hansom JD, Williams DM, Jarvis J (2006) Distribution,
geomorphology, and lithofacies of cliff-top storm deposits:
intimate circular relationship with the retreat of the cliff face. examples from the high-energy coasts of Scotland and Ireland.
When the cliff face suffers an erosion process, the beach Mar Geol 232:131–155
volume suddenly increases, increasing the dissipation of 10. Johnson DW (1919) Shore processes and Shoreline development.
wave energy and protecting the cliff face from further Wiley and Sons, New York, 584pp
11. Lange WP, Moon VG (2005) Estimating long-term cliff recession
recessions. The material of this beach can be slowly eroded rates from shore platform widths. Eng Geol 80:292–301
in the subsequent period. 12. Lee EM, Brunsden D (2001) Sediment budget analysis for coastal
With respect to the sedimentary characteristics of these management, West Dorset. In: Griffiths JS (ed) Land surface
deposits, it should be considered that they can be either evaluation for engineering practice, vol 18. Geological Society,
Engineering Group Special Publication, pp 181–187
pebble beaches (Fig. 15.20a) or sandy beaches (Fig. 15.20 13. Masselink G, Hughes MG, Knight J (2003) Introduction to coastal
b). The dynamics differ slightly in both cases, since the processes and geomorphology. Routledge, London, 416pp
energy required to move the pebbles is greater than in the 14. Morton RA, Richmond BM, Jaffe BE, Gelfenbaum G (2006)
case of sand. The slope of the beach and the internal struc- Reconnaissance investigation of Caribbean extreme wave deposits:
preliminary observations, interpretations, and research direction.
ture of the sediment are also different. The pebbles are Open-File Report 1293, USGS, 46pp
usually very rounded and, if they are discoidal, they usually 15. Moses C, Robinson D, Barlow J (2014) Methods for measuring
show overlaps towards the sea without any other type of rock surface weathering and erosion: a critical review. Earth Sci
internal arrangement being observed. On the other hand, the Rev 135:141–161
16. Muhs DR, Rockwell TK, Kennedy GL (1992) Late quaternary
sand usually shows characteristic cross-layering, although uplift rates of marine terraces on the Pacific coast of North
this internal structure is different if the beach is dissipative or America, southern Oregon to Baja California Sur. Quatern Int
reflective. These differences are identical to the beaches of 15:121–133
other locations and will be studied in the chapter dedicated 17. Naylor NA, Stephenson WJ (2010) On the role of discontinuities
in mediating shore platform erosion. Geomorphology 14:89–100
to beaches. A particularity is the presence of blocks inside 18. Nott J (2003) Waves, coastal boulder deposits and the importance
the sediments (Fig. 15.20c). These blocks are the same as of the pretransport setting. Earth Planet Sci Lett 210:269–276
those studied in shore platforms and are encompassed by 19. Roig-Munar FX, Rodríguez-Perea A, Vilaplana JM, Martín-Prieto
beach deposits when they develop there. JA, Gelabert B (2019) Tsunami boulders in Majorca Island
(Balearic Islands, Spain). Geomorphology 334:76–90
20. Schefers A, Kelletat D (2003) Sedimentologic and geomorphic
tsunami imprints worldwide: a review. Earth Sci Rev 63:83–92
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1. Anthony EJ (2009) Shore processes and their palaeoenvironmental 22. Stephenson WJ, Dickson ME, Trenhaile AS (2013) Chapter 10.11,
applications. Elsevier, Amsterdam, 519pp Rock coasts. In: Sherman DJ (ed) Treatise on geomorphology, vol
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Blackwell Publishing, Oxford, 419pp 307
3. Emery KO, Kuhn GG (1982) Sea cliffs: their processes, profiles 23. Sunamura T (1992) Geomorphology of rocky coasts. Wiley, New
and classification. Geol Soc Am Bull 93:644–654 York, 302pp
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on the south coast of the Reykjanes Peninsula (Iceland). Geomor- University Press, Oxford, 384pp
phology 114:55–70 25. Trenhaile AS, Kanyaya JI (2007) The role of wave erosion on
5. Gómez-Pujol L, Fornós JJ, Swantesson JOH (2006) Rock surface sloping and horizontal shore platforms in macro- and mesotidal
millimetre-scale roughness and weathering of supratidal Mallorcan environments. J Coastal Res 23:298–309
carbonate coasts (Balearic Islands). Earth Surf Proc Land 31:1792– 26. Vallejo LE, Degroot R (1988) Bluff response to wave action. Eng
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Islands, Japan. Earth-Sci Rev 102:77–99
Wave-Dominated Systems I: Barriers
and Barrier Islands 16
Examples of such barriers exist along the coasts of all

16.1 Introduction
mainlands (e.g., Dobrovolsky and Zalogin [2, 8, 25, 26]).
Due to the not very pronounced relief, the beaches in the
Barriers in general, and barrier islands in particular, consti-
front zone and the attractive landscape make these systems
tute a significant system between coastal environments.
very busy. Much of the world’s tourist industry is located on
They are sedimentary bodies made up mainly of sand, built
barriers and important port facilities are often located in the
by the action of the waves on the front of the mainland and
rear area, so that the land usually has a high price for owners
separated from it by a body of water called a lagoon (e.g.,
on these barrier islands. On the other hand, those barriers
[16, 29]). The sedimentary building of the barriers can take
that have preserved their natural character constitute
place on the rocky substrate of the mainland or on other
ecosystems of high ecological value. However, the highly
older coastal formations. The name barrier is based on the
dynamic regime imposed by geological processes makes
fact that the presence of these sand bodies protects the
them extremely changeable environments, which can
mainland from the direct action of sea waves (Fig. 16.1).
migrate or be eroded continuously or in moments. In addi-
Barrier systems are distributed along the world’s coasts
tion, the lack of significant relief makes them susceptible to
and are not limited to a particular climatic or tectonic con-
high-energy events such as storms and tsunamis. Therefore,
text. Since Davies [4], most research has stated that these
the occupation of these systems always carries a high risk,
systems constitute about 15% of the coasts at a global level,
especially in a realm of global climate change. In order to
with barrier islands being the most frequent systems among
minimize the impacts of the processes that occur in these
them, occupying 10% of the world’s coasts [27]. They are
systems on the human activities that are based on them, it is
usually associated with wave-dominated coasts where the
important to understand their dynamic functioning.
budget of sediment is abundant, giving the coast a deposi-
From a geological point of view, the sedimentary
tional character. These conditions often appear in passive
sequences of the barriers as preserved in the stratigraphic
tectonic contexts and during periods in which the sea level is
record are of particular interest, because they often constitute
in a stable position for a more or less prolonged time. Thus,
the storage rock of hydrocarbon deposits [11].
barriers usually appear in the form of chains of islands that
develop parallel to the coast, but are also associated with
other well-fed environments such as the front of deltas and
estuaries. 16.2 Control Factors
The dimensions of these systems are highly variable.
There are barriers of hundreds of kilometers in length, while Barriers are open systems in which there is a clear domi-
others do not exceed hundreds of meters. Something similar nance of waves; however, there is also this dominance on the
occurs with the width. We can find islands of only tens of rocky shores. Why, then, this difference? The answer lies in
meters between the coastline and the lagoon, and others with the influence of other factors. In general terms, the main
widths of kilometers. The barrier building may be com- controls on the origin and dynamics of wave-dominated
pletely flat or rise a few meters above the average water level environments are found in the interrelationships of wave
when the action of the wind develops dune systems on the action with the morphology of the seabed, the geometry of
island. The best-known examples of longer and wider bar- the coastline and, above all, sedimentary input [1, 24]. In
riers are located in the 600 km-long sandbanks of the this case, it is a positive sedimentary supply, at least in the
Patos-Mirim system, Brazil [28]. Smaller barriers are com- origin of the sedimentary bodies that constitute the barrier. In
monly found by closing bays located on rocky coasts. the long term, other factors such as tectonic context, relative

https://doi.org/10.1007/978-3-030-96121-3_16
208 16 Wave-Dominated Systems I: Barriers and Barrier Islands
Fig. 16.1 Aerial view of a sandy barrier in New Jersey (USA)
sea level movements and climate also have a significant the wave orbits are asymmetrical. We have seen in Chap. 14
influence. Let’s discuss what these factors are and how they that the thresholds of grain movement are exceeded in dif-
intervene in the sedimentary dynamics. ferent ways in the swash and backwash movements
depending on the type of wave breaker. According to these
data, the less energetic breakers will produce a net transport
16.2.1 Wave Action of the sediment landwards, while the more energetic
breakers will take it in the opposite direction. Clearly, cycles
The arrival of the waves at the coast is characterized by an will occur over time in which one or other direction of net
interaction with the bed from a depth equal to half the transport will dominate, but, in general, for a barrier to
wavelength. This depth was defined in Chap. 7 as the wave originate the landward transport must dominate. Once a
base level. At shallower depths, waves interact with the bed, barrier is formed, if the long-term net transport is seawards,
where they are not only deformed in the process described as it will be eroded and, if this period is long enough, it can be
shoaling, but some of their energy is transferred to the bed completely dismantled.
and used to transport grains of sedimentary material. The The littoral drift transport component acts longitudinally
principles governing the transport of sedimentary material to the coast. This component is fundamental in providing
by waves were described in Chap. 14. On the one hand, the material to the barrier from other stretches of coast con-
transverse component of the wave approach vector describes nected to the cell where the barrier originates. Littoral drift
a movement of particles from and to the shore. On the other works like a current and acts in the long term to generate a
hand, if the wave arrival is oblique there will also be a volume of sediment transport that can be calculated (see
longshore transport component which is also known as lit- Advanced box 14.3). It should be noted that most barriers
toral drift. have been formed by longitudinal growth, which gives an
From a transverse approach to the shoreline, the orbital idea of the importance of longshore transport in the genesis
speed of each wave generates a movement of the particles on and dynamics of barriers. In addition, in the case of barrier
the bed. However, as a wave is an oscillatory movement, the islands, the existence of littoral drift is usually responsible
net transport of particles to and from the shore is minimized, for the lateral migration of the channels, which ultimately
except in certain situations. One such situation occurs when means migration of the islands themselves.
16.2.2 Tides other times, it is the relict coastal sediments that are
reworked in continuous sedimentary cycles. Thus, in situa-
The tidal range determines the amplitude of the oscillation of tions of limited input, it is the destruction of old barriers that
the wave action in the coastal fringe. However, since barriers provides the sediment to build new ones.
separate an inland body of water from the open coast, the Although a positive sedimentary balance underlies the
tidal range, together with the surface of that water body, also origin of the barriers, throughout the life of the barrier this
determines the volume of water that this restricted water balance can be altered and modified by the factors that have
body exchanges with the open coastal waters. This volume is been described in the previous sections. There can be
known as the tidal prism and is responsible for keeping an moments of negative sedimentary balance with the conse-
open communication between the two water bodies. The quent erosion of the barrier or part of it. In these variations of
speed of the currents that develop in the passages between the sedimentary balance during the life of the barrier, it is
islands, and the dimensions of the tidal deltas that form at obvious that variations in the wave energy will play an
both ends of these inlets, depend on the tidal prism. important role; however, modifications in the sedimentary
In the frontal part of the system, the tidal currents have supply that occur at the mesoscale also exert a remarkable
less influence. The currents tend to be parallel to the coast in influence, although this is frequently ignored in many studies
these sectors and have very little capacity to transport sedi- [3].
ments. Although the tides also have an oscillatory character,
the ebb and flow cycles are usually asymmetric, resulting in
a net transport in one of the two directions. The longitudinal 16.2.5 Mainland Physiography
action of these tidal currents usually combines with coastal
drift and other currents to give a resultant transport parallel The physiography of the mainland plays a crucial role in the
to the coast. development of the first moments of the barriers, as well as
in the dynamics that develop during their lifetime. Perhaps
the clearest example visually is the contrast between the
16.2.3 Other Currents presence of an initially straight coast and an intricate
coastline. Both physiographies would generate barriers of
The action of wind-induced currents in shoreface areas has different length, orientation and dynamics. However, coastal
been extensively described in Chap. 10. These currents have physiography also shows its influence at other levels, such as
a weak character and their sediment transport capacity is not the type of interaction that coastal morphology has with the
very high. However, their combined action with tidal cur- arrival of wave trains. From this point of view, a distinction
rents has a significant influence on the transverse and lon- can be made between coasts that are oriented parallel to the
gitudinal components of waves. Under these currents, the wave ridges and coasts where the arrival is oblique. In the
oscillation of the waves can become asymmetric, generating former, the genesis of the barrier would be related to the
a net transport component from or to the barrier front. This action of the waves in a transverse direction to the coast,
component can contribute to the construction of the barrier while in the latter the coastal drift would be the factor that
or, conversely, to its dismantling. plays the most important role in the development of the
barrier. Davies [4] called these cases swash-aligned barri-
ers and drift-aligned barriers. Particular cases of these
16.2.4 Sediment Supply situations can be generated in irregular coasts in relation to
the phenomena of refraction and diffraction.
In the introduction to this chapter, it was noted that a barrier Another effect that can be understood more intuitively is
system corresponds to a depositional coast, and therefore the the variation in depth on the waterfront. Bathymetric dif-
sedimentary balance must be positive, at least in the origin of ferences influence the way wave energy is dissipated. Thus,
the barrier. Most of the barriers that exist today are made up the slope of the nearshore plays a major role in the type of
of sand, although a small but significant number have breaker, along with the dimensions of the wave. There are
developed in gravel. These gravel barriers are concentrated numerous studies that show the relationship between the
in regions of high clast availability, generally in areas that position of the barriers and the existence of banks or steps in
were covered by glaciers during the Pleistocene [21]. Most the waterfront (e.g., Davis and Clifton [5]). This relationship
of this sediment comes from adjacent mainland areas. The comes about because the genesis of the barrier is related to
longest barrier island chains in the world developed along the descent of energy that occurs at this step, since it is there
the coasts of land areas whose geological nature allows a that the wave loses its transport capacity and deposits the
rapid dismantling, generating high rates of supply [6]. At sand, generating the nucleus of the barrier.
16.2.6 Sea Level Movements In the longer term, and at a global level, changes in the
climate will determine the dynamics of the barriers.
The current barriers were established in the period of high- A change in the climate regime will have an influence on the
stand that followed the Flandrian transgression. In general number and intensity of storms, having a direct consequence
terms, stillstand periods favor the formation of coastal sed- on the erosional–depositional character of the system. In the
imentary systems in optimum supply situations, as they give even longer term, it is changes in climate that induce the
the systems the necessary time for the dynamic processes to eustatic movements that control the relative movements of
accumulate the material and build up the sedimentary bod- the sea level described in the previous section.
ies, even in limited input situations. If the budget is suffi-
cient, once the barrier is stabilized there will be a progression
of growth that will lead to a shift of the coastline towards the 16.3 General Morphology and Associated
sea, which means a regression. Environments
In the event of a drop in sea level, the model would also be
regressive, although the trend would be for coastal systems to The barriers can be classified into three types according to
be turned inland. Normally, mainland processes would lead their connection to the mainland (Fig. 16.2). If they are
to the total or partial dismantling of these formations. Only connected to the mainland at two points and completely
early consolidation would contribute to the preservation of isolate the lake, they are called welded barriers or bay
the sedimentary record of these coastal sequences. barriers. If they are connected to the mainland at one end
In any case, many of the current studies of barrier systems only, they are called barrier spits. In this case, there is a
show that many of them were generated before the time of communication between the lagoon and the open sea
sea level stabilization and that they migrated to the mainland through a passage channel. Finally, if they appear totally
in the last centuries of slow sea level rise (e.g., [22, 23]). In isolated from the mainland, they are called barrier islands.
this context, the process of construction of the barrier island Barrier islands usually form continuous chains in which each
depends on the slope of the coastline in relation to the rate of island is separated from the next by a tidal channel. The
sea level rise, the input regime and the capacity of the waves action of the waves is concentrated only at the front, while
to rework sediment. Depending on the combination of these the rear area is dominated by the tide.
factors, either a part of the sediment of the old barrier or the The barrier is a sedimentary body that generates a system
whole of it will be used to build the new barrier, giving rise composed of different sedimentary environments (Fig. 16.3).
to the processes of translation (roll-over) or excess (over- The presence of the barrier divides the system into three
stepping). This fact influences the preservation potential of domains that differ in the presence or absence of wave
the sedimentary sequences of these systems. action: the barrier body, the frontal zone (barrier front) and
the back barrier area.
In each of these areas, there is are associated sedimentary
16.2.7 Climate environments:
The weather exerts control over some processes that act on • The front area is made up of beaches.
the short-term dynamics of the barrier, such as the wave • The body of the barrier is usually constituted by sand
regime and the frequency of storms. In addition, the climatic ridges developed on ancient beaches.
influence is manifested in the amount of contribution that the • Dunes can develop over the body of the barrier. Occa-
rivers are capable of making to the sedimentary systems of sionally dunes are absent.
the coast. At the same time, the climate also influences some • The lagoon is located in the area of back barrier, which is
of the processes that occur in the protected environments a body of shallow water with a restricted connection to
associated with the barrier. In this sense, it is the climate that the sea. The term is applied to a subtidal zone
marks whether salt marshes (temperate climates), mangroves semi-enclosed by the barrier. The intertidal areas of the
(tropical climates) or coastal sabkhas (arid climates) develop lagoon, both attached to the mainland and to the barrier,
in supratidal areas. develop tidal flats and the supratidal areas may be
A less obvious effect of climate is the influence on the occupied by salt marshes, mangroves or coastal sab-
nature of the sedimentary input. For example, in tropical khas, depending on the climate in which the barrier is
climates the content of carbonate clasts generated in the sea framed.
basin itself may be more abundant than the terrestrial clasts • Other very frequent structures in the back barrier area are
contributed from the mainland. Similarly, in high latitude washover fans. These are sandy fan-shaped formations
barriers the presence of clasts from ancient glacial activity is with their convexity pointed towards the interior of the
much higher [6]. lagoon. They are produced during storms which erode the
16.3 General Morphology and Associated Environments 211
Fig. 16.2 Different type of

barriers. a: Welded barrier
(Norton Sound, Alaska). b:
Barrier spit (Mutadua,
Mozambique). c: Barrier island
(Olga Bay, Russia). (Images
Earth.)
front sandy body by opening a channel between the dunes the waves, while the internal zone (flood-tidal delta) is
and depositing the eroded sediment at the back. fundamentally subject to the tides.
• In the case of spits and barrier islands, the system is
completed with an inlet channel. This is a narrow envi- The type of barrier, the relationship between its width and
ronment subjected to very high tidal energy. This means length, and the number of inlets in the case of barrier islands,
there is a continuous remobilization of the sedimentary are regulated by the balance between wave and tidal energy.
material, which is deposited at its end in both directions The classification proposed by Hayes [13], which was
of the tidal current forming delta-shaped sedimentary described in Chap. 4, differentiates three types of coasts:
bodies. The external zone (ebb-tidal delta) has a very wave-dominated, tide-dominated and mixed-energy. Of these
active dynamic due to the interaction of the current with three types, barrier island systems may appear associated
Fig. 16.3 Sedimentary environments constituting a typical barrier system. (adapted from [20])
Fig. 16.4 Different types of barrier island systems. (adapted from mixed energy coast, with the example of Ria Formosa (Portugal).
[13]). a Barrier island system of a wave-dominated coast, with the (Images Landsat/Copernicus from Google Earth.)
example of Machese Island (Mozambique). b Barrier island system of a
16.3 General Morphology and Associated Environments 213
with wave-dominated and mixed-energy, although the bar- is important enough to generate currents that keep the inlet
riers would have different characteristics (Fig. 16.4). generated at the end of the spit open. The action of the tide
when passing through these passages usually develops tidal
• Wave-dominated coastal barriers (Fig. 16.4a): These are deltas, too.
long, narrow barrier islands, part of large island chains The genesis and dynamics of spits are completely con-
with a low number of inlets. The position of the inlets is trolled by coastal drift, but a good sedimentary budget is also
unstable, as they are affected by frequent migrations and necessary to maintain their longitudinal growth rate. Growth
avlusions. Ebb-tidal deltas tend to be small, while is carried out by attaching hook-shaped bars to the curved
flood-tidal deltas are better developed and multilobed. end of the spit. These bars constitute the continuation of the
Washover fans are abundant. Smaller-scale estuaries are bars that the waves make as they migrate along the foreshore
common in the back-barrier lagoon. These morphologies of the open barrier face (Fig. 16.6). In a spit, the attached
are related to high wave energy in the face of a low tidal bars leave growth marks in the form of berms, so that each
range or in systems where the lagoon is highly clogged berm marks old positions at the spit apex.
and the tidal prism is small. In semi-enclosed systems, at the apex of the spit there is
• Mixed-energy coastal barriers (Fig. 16.4b): These are usually an inlet that feeds seawater to the lagoon located
shorter and wider barrier islands separated by a large inside. This inlet is normally associated with a system of
number of inlets. The channels are more stable and tidal tidal deltas whose operation is similar to that located in any
reflux deltas with large frontal lobes develop at the inlet between barrier islands. When the inlet and the tidal
marine end. The flood-tidal deltas are unilobed and have deltas are present, the curved bars make the spit grow over
large ramps. In the back barrier areas, the lagoons usually the facies of this deeper system [18].
have a high rate of clogging, with the tidal flats and
supratidal areas being very well developed. Barrier
islands acquire this morphology when the energy of the 16.4.2 Welded Barriers
waves is compensated for by a greater tidal range, or
where the lagoon is large and a major tidal prism devel- The presence of welded barriers is linked to systems with
ops. They are also usually associated with the frontal area small tidal prisms but a very energetic wave regime,
of estuaries and deltas located on coasts with strong wave although they are also present in systems with a larger
influence. tidal prism. In any case, in this type of system, the energy
of the waves always dominates over the tides. Many of
these barriers were built by the waves closing rocky
coastal bays with the sediment eroded in the coastal
16.4 Genesis, Dynamics and Evolution headlands. Therefore, these barriers are usually short and
their sediment is continuously recycled by being inside
The morpho-sedimentary dynamics of the barriers depends coastal transport cells that have a limited connection with
largely on the dimensions of the system in relation to wave adjacent cells. The sediment that constitutes them is nor-
energy and tidal currents. However, the processes are also mally sandy, although this type of barrier has occasionally
strongly related to the type of barrier, so that, broadly presented with gravel. The small tidal prism is not capable
speaking, each type of barrier has its own genetic and of generating tidal currents strong enough to keep a per-
dynamic characteristics. These characteristics will be manently open inlet. The isolation of the lake at the back
described for each type. of the barrier from marine waters means that it usually has
fresh or brackish water, as it receives water directly from
the mainland.
16.4.1 Spits Being in a closed cell, the welded barrier actually dom-
inates the transverse dynamics of the sediment versus the
On coasts with abundant input and a strong component of longitudinal component. Due to this fact, the genesis of the
transport by coastal drift, coastal spits can develop. When barrier is not usually linked to longshore transport, but to the
the coast is very irregular, some spits are connected to front attachment of wave bars (Fig. 16.7a). In this growth
coastal headlands where wave diffraction occurs (Fig. 16.5 model, under some circumstances there may be a certain
a). On the other hand, any coastal inlet also tends to develop longitudinal transport of the sediment that causes it to move
a spit that partially closes it (Fig. 16.5b). Spits functioning as from one end of the barrier to the other. If the bay occurs on
closure systems are usually associated with large bays, a coast with a strong coastal drift, then a spit may form at
estuaries or estuarine lagoons. In both cases, the tidal prism one end of the bay that may end up closing the bay
Fig. 16.5 Different locations of spits. a Spit formed by diffracting waves in the apex of a headland in Ervadi, (India). b Spit closing the Mayan
estuary (Myanmar). (Images Landsat/Copernicus from Google Earth.)
completely (Fig. 16.7b). In closed cells, if the arrival of the connection is formed between the lagoon and the open coast
waves is frontal, the barrier can be subject to a double drift. (Fig. 16.8). When this happens, the post-storm situation
In that case, two spits will begin to grow at both ends of the tends to rebuild the barrier quickly, since most of the sedi-
bay in opposite directions. Then, the barrier is formed when ment is retained within the cell. In situations where there is
both spits meet in the center (Fig. 16.7c). an ephemeral inlet, before it closes it can migrate in either
Once the barrier is formed, if the lithology is sandy, direction of the barrier if there is a certain longitudinal
sometimes storms can break it completely or create a breach component of the wave.
in some sectors. On other occasions, it is the flow of the river In barriers made of gravel, storms are not usually ero-
system connected to the lagoon that breaks the barrier from sional, but it is during the moments of greatest energy when
the inside out. In both cases, during these moments a bars can be built that can make the barrier progress.
16.4 Genesis, Dynamics and Evolution 215

process of apical growth of a spit
16.4.3 Tombolos the twentieth century, great coastal geologists from Douglas
Johnson to Richard Davis built their science on the studies
The genesis of a tombolo is related to the presence of a hard of the second half of the previous century, making the
element in the coastal front. This element is normally natural genesis and evolution of these systems well known. From
and constituted by a rocky outcrop, but it can also be arti- the middle to the end of the nineteenth century, three
ficial. The interaction of the emerged hard element with the theories for their genesis had been proposed. Each of them
dominant wave trains induces the accumulation of one or tried to explain the origin of all the barrier islands. How-
two sediment bodies which connect the coastline with this ever, all these theories were put forward in a conceptual
element. There can be three different processes in building way and without the support of experimental data. Later,
these sediment bodies (Fig. 16.9). Some of these are similar throughout the twentieth century, some of these hypotheses
to those described in welded barriers. They can occur at were demonstrated by other researchers in individual study
different scales. cases. Today it is accepted that none of the three theories is
valid for all systems; however, there are examples of barrier
– Double drift: The presence of the hard element refracts island systems around the world that were generated in all
the wave trains, inversing the littoral drift. Two con- three ways. These theories are: (1) construction of the
verging longshore transports tend to accumulate sediment island on an offshore bar; (2) breaching of a previous
after the obstacle, creating a prograding band which coastal spit; and (3) separation from the mainland by
finally reaches the hard element (Fig. 16.9a). flooding due to sea level rise. These genesis models will be
– Bar migration: In a well-supplied coast, the deformation described below.
of the wave trains tends to build bars migrating land-
wards. These bars eventually emerge, forming barriers on 16.4.4.1 Building on an Offshore bar
both sides of the obstacle. Usually, this process builds a This theory was initially stated by de Beaumont in 1845
double tombolo (Fig. 16.9b). [7] and was supported by Douglas Johnson’s field data in
– Spit growing: On an irregular coast with a strong littoral 1919 [15]. According to this concept, the shoaling of waves
drift, the apical growth of a spit can link the mainland on an initial coastal slope could generate an underwater bar
with the hard element (Fig. 16.9c) at the place where the waves begin to break. This process
would be favored by the presence of a submerged step or
relief that would facilitate the dissipation of energy. Once the
bar has formed, its presence would make the waves lose
16.4.4 Barrier Islands energy, depositing more sediment and making the bar grow.
Finally, this bar would emerge, preventing the passage of the
More than a century of research has contributed to today’s wave towards the mainland and protecting its rear zone
good understanding of barrier island systems. Throughout (Fig. 16.10).
Fig. 16.7 Scheme showing the different possibilities of welded barrier genesis. a Transversal bar migration. b Littoral drift (spit elongation).
c Double littoral drift (spit and counterspit attachment)
16.4.4.2 Breaching of a Spit valleys parallel to the coast, isolating coastal sandy forma-
As a counterpoint to the theory of offshore bars, in 1885 tions that were previously attached to the mainland
Grove Gilbert [12] suggested that island chains would have (Fig. 16.12). In 1967, John Hoyt [14] developed this theory,
generated through the formation of spits. Originally, longi- extensively basing his arguments on the fact that, in some
tudinal accretion would have occurred through the action of a coastal systems, there was no sedimentary record under the
major littoral drift. In a second stage, a long spit would have lagoon that would demonstrate the existence of an
fragmented during storms, opening inlets that would become open-water situation, such as that expected at a stage prior to
permanent and separate the different islands (Fig. 16.11). In the existence of the barrier island. For Hoyt, the width of the
1968, John Fisher’s sedimentological studies in North Car- lagoon was simply the result of the general slope of the
olina made him a great advocate of this theory [9]. coast, so that on steeper slopes the sand ridge would develop
nearer the mainland, leaving no space for a wide lagoon at
16.4.4.3 Detachment from Mainland the time of the marine invasion. Conversely, a coastline with
by Submergence a low slope would allow a wide marine invasion, with the
This theory was conceived by William McGee in 1890 [17]. consequent development of a wide lagoon.
According to his reasoning, the rise in sea level that occurred Regardless of the way in which the barrier island systems
during the Holocene transgression would invade some have emerged, the dynamics of all of them are very similar,
16.4 Genesis, Dynamics and Evolution 217
Fig. 16.8 Breaching and

rebuilding of a welded barrier
(example of the barrier closing
Lagune Digboué, Ivory Coast in
2017). (Images
Earth.)
as they are constantly modified by the action of waves (in- ends of two barrier islands (Fig. 16.13, years 2006–2015).
cluding littoral drift), and variations in the contribution of The result is a constant renewal of the barrier island sediment
sediments and the relative movements of sea level have a while it undergoes a change in shape and position.
notable influence on their evolution. Sometimes a strong storm is capable of generating a
The influence of littoral drift is manifested in the migration washover important enough to stabilize and create a new
of the inlets. Often the islands grow apically at one end with inlet (Fig. 16.13, year 2017). Often the tidal prism is not
the attachment of curved bars in the shape of a hook, while sufficient to generate currents to keep both inlets (old and
eroding at the other. The combined effect of these processes new) open and the swell closes one of the inlets. Frequently
leads to the migration of inlets that are located between the it is the old one that closes, while the new one gets bigger,
Fig. 16.9 Scheme showing the different possibilities of tombolo growing (example of Puerto Viejo, Costa Rica). (Images
genesis. a Double drift (example of Cap Serrat, Tunisia). b Double Landsat/Copernicus from Google Earth.)
tombolo built by bar migration (example of Orbetello, Italy). c Spit
starting a new migration cycle. The migration of the inlets A common element to all barrier island systems is the
also involves the migration of the ebb- and flood-tidal deltas sedimentary filling of the rear lagoon at a greater or lesser
associated with their ends. The ebb-tidal delta is continu- speed. In the long term, the filling of the lagoon leads to the
ously reworked by the waves and is partially destroyed as it development of tidal flats and the sediment takes up space
moves, yet some of its facies can be preserved among the that previously had to be filled and emptied by tides. This
new sediments at the front of the island. In contrast, the means a progressive loss of tidal prism. As less water enters
flood-tidal deltas are completely preserved. In this way, the and leaves the inlets, the tidal currents that develop there will
successive lobes that develop during migration remain in the also be less. Finally, the currents become so weak that the
lagoon. This can be seen very clearly in the 2013 frame of waves end up closing many of the inlets. In this way, a
Fig. 16.13. These continuous changes in the position of the system of mixed tidal–wave dominance, formed by short
inlets were responsible for many shipwrecks during the islands and a large number of inlets, can end up becoming
seventeenth and eighteenth centuries, when ships tried to wave-dominated, with very long islands separated by few
enter the lagoon through the inlets to protect themselves inlets. If the sedimentary input is abundant, this process is
from storms. Clearly, it was impossible for the nautical accelerated and the final result may be the complete filling of
charts used at that time to reflect these rapid changes. the lagoon and the final closure of all inlets.
16 Wave-Dominated Systems I: Barriers and Barrier Islands 219
Fig. 16.10 Conceptual model to

illustrate the theory of barrier
island genesis by building on an
onshore bar
architecture is the result of the evolutive history of the bar-

16.5 Facies Models rier. This architecture is also variable depending on the
factors acting in the long term, such as sedimentary input
The barriers do not develop their own facies, since these are and relative sea level movements. These are the factors that
not one sedimentary environment, but a system composed of also determine the potential for preservation of the facies of
numerous environments each of which develops its own the different environments that build up the system. The
facies and sequences of facies. The specific facies of all combination of these contributions results in three different
environments associated with the barrier (beaches, dunes, facies architecture models [11]: (1) a retrograding barrier
inlets, tidal deltas, washovers) and the back barrier zone model in a transgressive situation, (2) a prograding barrier
(lagoon, tidal flats, marshes or coastal sabkhas) will be model in a regressive situation; and (3) an aggrading
described in detail in later chapters. What really character- barrier model in a sedimentary equilibrium situation. Each of
izes barrier systems is their facies architecture. The 3D facies these models will be analyzed separately.

island genesis by breaching of a
spit
16.5.1 Retrograding (Transgressive) Barriers rate of lagoons and tidal flats developed in the rear area have
very high rates of filling. This means that they are easily
Retrograding barriers are formed under conditions of rising preserved under the barrier facies in their migration process
sea level, so that the barriers are forced to migrate towards the towards the mainland.
mainland. In these conditions, the rate of sea level rise is When the rise is slow and the contribution is scarce, the
combined with the rate of sedimentary input, and this com- totality of the sediment of the old barriers is reworked to
bination determines the preservation of the facies of the dif- form the new ones. These barriers are transformed by a
ferent environments that make up the barrier during process of continuous landwards movement called roll-over.
transgression [19]. In many cases, the supply of sedimentary In this process, the overwash phenomena that occur during
material is scarce and material from older barriers has to be storms play a fundamental role. These frequently break the
continuously recycled to build new ones. In facies models of dune ridge, moving the sand in the form of fans towards the
transgressive barriers, deposition rates in the associated roll-over. In these conditions of slow rise, the dune systems
environments are also important. Normally, the sedimentation can have enough time to rebuild themselves. In this case, the

island genesis by detachment
from the mainland by
submergence
dune building makes the overwash processes difficult and Thus, the facies architecture model of the retrograding
slows down the landward migration of the barrier. barriers shows a retreat of the barrier facies (Fig. 16.14). In
In situations of rapid sea level rise, the barrier is quickly this sequence, the lagoon facies overlap the tidal flat facies
exceeded, being submerged in a situation of less energy to and the tidal flat facies overlap the marsh facies in a trans-
be below the wave breakers. In this case, only a part of the gressive sequence. Over these rear facies, the barrier facies
material of the old barrier is reworked to build the new one, are superimposed. In the case of minimal sedimentary input,
located in a position closer to the mainland. This process is the barrier facies are thin and rarely exceed 3–4 m [6]. In
known as overstepping. The fast-rising conditions allow the this model, the importance of the washover facies is note-
preservation of the facies of some environments of the bar- worthy, interleaved with the muddy lagoon, tidal flat and
rier body. However, in these conditions, the rapid rise in sea marshes facies, reflecting the process of displacement of the
level prevents the reconstruction of the dunes. It is the barrier towards the mainland. In the position of the inlets, it
material of these dunes that is most easily reworked to build is the characteristic facies of the flood-tidal delta and the
the new barrier. inlets that overlap the facies of the barrier environments.
Fig. 16.13 Process of inlet

migration (2006–2015) and
genesis of a new inlet by
stabilization of a washover
(2017). Example of Faro Island
(South Portugal). (Images
Earth.)
However, the facies of ebb-tidal deltas are usually not pre- washovers, since the scars corresponding to ancient inlets
served, since their sands are easily reworked under trans- constitute areas of weakness that are more easily trans-
gressive situations to build wave bars. The facies model also gressed during storms.
includes all the record of the changes in position of the inlet The first barrier island systems that were studied mostly
under the body of the barrier island, as well as the presence featured this mechanism, as they were built in the early part
in the lagoon of old bodies of flood-tidal deltas related to of the Holocene, during the last stages of the Flandrian
these previous positions of the inlets [24]. There is also a transgression when the rate of sea level rise had slowed
close relationship between ancient flood-tidal deltas and down.
Fig. 16.14 Scheme of facies architecture of a retrograding barrier system (based on Roy et al. [24] and Fitzgerald et al. [10])
16.5.2 Aggrading Barriers In the frontal area of the island, these oscillations are
manifested in stages of erosion or progradation, which
When relative sea level rise is accompanied by a good input accompany the general process of aggradation. On the other
regime, barriers are not transgressed except in specific situ- hand, in the back barrier zone, slight movements towards the
ations. In this case, a vertical growth of the barrier is pro- land can originate washovers, which are reflected in an
duced by piling up the sediment of the environments that interleaving of its sediments with the lagoon facies, tidal flats
make up the system (Fig. 16.15). Small variations in the or marshes. The rise in sea level makes the depth conditions
equilibrium between the rates of rise and the volume of in the center of the lagoon stable within an order. However,
sedimentary input can cause oscillations in the coastline that pulses in the rate of rise can cause the margins to produce
moves towards land or towards the sea in different cycles. rhythmic sequences between sub-, inter- and supratidal
Fig. 16.15 Scheme of facies architecture of an aggrading barrier system (Based on Davis and Fitzgerald [6])
Fig. 16.16 Scheme of facies architecture of a prograding barrier system (Based on Roy et al. [24] and Davis and Fitzgerald [6])
facies. This maintenance of the depth in the lagoon causes very well developed, since in most case the dune building
the tidal prism to be maintained over time, and the inlets prevents the first line of coast from being over-washed by
remain open, although they retain their typical migration storm waves.
processes. The aggradation process does not generate verti-
cal sequences of a higher order, since there is no real overlap
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18. Morales JA, Borrego J, Jiménez I, Monterde JR, Gil N (2001) ics. University Press, Cambridge, pp 121–186
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large spit in the Piedras Estuary mouth (Huelva Coast, South- West RJ, Scanes PR, Hudson JP, Nichol S (2001) Structure and
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19. Moore LJ, List JH, Williams SJ, Stolper D (2010) Complexities in 53:351–384
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change. Geological Association of Canada, pp 179–194
Wave-Dominated Systems II: Beaches
17
this way, there are beaches of very variable lengths, from

17.1 Introduction
tens of meters to hundreds of kms, that depend on the
morphology of the coast. In general, irregular coasts gen-
Beaches are widely represented sedimentary coastal envi-
erate very short beaches limited to small bays, while linear
ronments, occupying about 20% of the world’s coastline
and very regular coasts can generate kilometer-long
[15]. Like the rocky coasts, these are environments domi-
beaches.
nated by the action of waves, although in this case the
In addition to the waves, beaches can be affected by other
genesis of beaches involves their cumulative effect. This
dynamic agents. Above all, tides are important. The tide is
type of sedimentary accumulation can be associated with
responsible for the vertical displacement of the direct action
different environments (Fig. 17.1); thus, they can appear in
zones of breaking waves. The higher the tidal range, the
rocky coastline bays (Fig. 17.1a), along cliff faces
more complex the beaches are and the greater the surface
(Fig. 17.1b) and on barrier fronts.
area of the beach affected by the action of the waves.
Vertically, beaches develop from the base level of storm
Another acting agent is the wind. Its origin can influence
waves, at the bottom of the waterfront, to the height of the
the direction of the waves and, above all, the air exerts an
storm breakers, where they border the wind-dominated
effect of deflation on the sand to form the dunes or, con-
environments. It is a very dynamic environment, since the
versely, introduces sand from the dunes, feeding the beach
action of the waves subjects it to continuous short-term
system.
morphological change (e.g., Komar [38]). Over time, there is
an alternation between moments when the sediment moves
landwards and others when it moves seawards. This alter-
nation subjects beaches to cyclical changes that manifest 17.2 Control Factors
themselves in gains and losses of sediment in the most
visible part of the beach. In a general way, the sediment 17.2.1 Wave Energy
moves transversely between the shallowest and deepest
areas, which leads to changes in the topographic profile of The wave energy is the main dynamic engine of beaches.
the beach. Waves control the mobility of the sedimentary material on
This very active system of wave dynamics generates an the beachfront, both transversely and along the coastline.
environment where fine particles cannot decant. Thus, the Wave energy is used to transport sediment during the
most common sediments on beaches are sand, although fine shoaling process, but also when the wave reaches the shore
gravel, pebble and cobble beaches are also frequent. What- and breakers occur. In the shoaling zone, the waves produce
ever the grain size of the sediment, beaches are characterized a swaying in the transverse direction to the beach that gen-
by the development of bars of different morphology. In fact, erates symmetrical bedforms such as ripples, while the
it is the movement of the bars that causes the change in the breakers can produce asymmetrical forms that result from a
shape of the beaches. net movement of the sediment in one direction or another.
The action of the waves at an oblique angle to the beach The breaker type controls the direction of the movement of
also induces the longitudinal component of transport on the the material from or to the continent and thus exerts a great
beachfront. This littoral drift (or longshore current) is cut by influence on the general slope of the beach. The longitudinal
the presence of elements such as headlands, inlets, river transport capacity on all the fringes of the beach not only
mouths or human infrastructures. These obstacles divide depends on the wave energy, but also on their angle of
transport cells that determine the length of the beaches. In incidence on the shoreline.

https://doi.org/10.1007/978-3-030-96121-3_17
228 17 Wave-Dominated Systems II: Beaches
Fig. 17.1 Photographs showing

beaches associated with different
coastal systems. a: Pocket beach
on a rocky coast (Costa Brava,
NE Spain). b: Beach in front of a
bluff coast (Matalascañas, SW
Spain). c: Beach at the front of a
barrier (Nueva Umbría, SW
Spain)
17.2.2 Beach Slope interaction with the bed closer to the shoreline and will cause
some of the wave energy to be reflected on the coast and
Variations in depth on the beachfront influence the process return to the center of the ocean in the form of a reflected
of wave energy dissipation. On the one hand, the nearshore wave train. In this way, the processes that take place along
slope—along with the dimensions of the wave—plays a the different depths of the beachfront vary with the slope,
major role in the breaker type. On the other hand, the beach giving rise to morphological changes due to the accumula-
slope also plays a role in other phenomena related to the tion or erosion of material. These morphological changes
interaction between the waves and the coast, such as wave are manifested in slope modifications, entering a circular
reflection. Thus, smaller slopes will tend to have the wave model in which the slope, the breaker type and the
dissipating most of its energy in material movement during erosive/accumulative conditions of the beach influence each
the approach to the coast, while larger slopes will cause an other.
17.2.3 Grain Size 17.2.5 Nearshore Currents
The grain size of the beach material is determined by the size The influence on the beachfront of tidal and wind-induced
of the waves and the availability of sediment. These are the currents has been described in detail in Chap. 10. From a
same factors that determine the transport capacity of the general perspective, these currents have a limited sediment
sedimentary material. The grain size greatly influences the transport capacity compared with the waves, especially in
slope of the beach (Fig. 17.2). Smaller grain sizes tend to the breaker zone. It is in the shoreface where the combined
generate beaches with low slopes, while an increase in grain action of these currents is able to modify the transport
size usually implies an increase in slope, such that pebble components of the waves. For example, the landward com-
beaches are usually very steep [36, 54]. ponent of these currents generates an asymmetry in the wave
The grain size also exerts a strong influence on the oscillation. In general terms, this asymmetry displaces
magnitude of the evolutionary changes experienced by material landwards on the shoreface, although in some cases
beaches, both those of a cyclical nature and those that occur the effect may be the opposite.
over a longer period of time. Thus, beaches with finer grains
tend to be very dynamic places that are affected by small
changes in wave dynamics, while pebble and cobble beaches 17.2.6 Climate
tend to be more stable.
Climate exerts an important control over all the variables
described above. On the one hand, it is the weather that
17.2.4 Tidal Range controls the wind regime and, therefore, the wave energy. In
this sense, the climate will determine the average energy of
The tide controls the topographical level of wave action and the waves that affect the beach and also their distribution
the time it acts on each level of the beach profile. On throughout the year. Ultimately, it is the climate regime that
microtidal coasts, the action of the waves always occurs at imposes the number of storms that affect the beach each
the same height of the profile, while on coasts with a wide year, their magnitude, their length of time and the moment at
tidal range the tide widely displaces the level of action of the which they occur.
waves, which will disperse the energy by transporting sed- In the short term, the annual climatic cycles mark those
iments in a broader strip. The tide is responsible for the rhythmic pulses of accretion and erosion that are so typical
existence of a specific area delimited by the high and low of all beaches. Over periods of several years, solar cycles are
tidal levels (the foreshore), but it also displaces the limits of responsible for the El Niño–Southern Oscillation (ENSO)
the rest of the areas that are located in deeper waters of the and North Atlantic Oscillation (NAO). These climatic
subtidal zone. This displacement can mean a significant oscillations are manifested in other interannual cycles of
change in the way energy is transferred from the waves to erosion and reconstruction.
the sediment, since the high and low areas of the beach A perhaps less evident effect of the climate is the influence
usually have different slopes. on the volume and nature of the sedimentary input. Since
Moreover, the tide also influences the number of bars that most of the sediment on the beaches comes from the conti-
the waves can develop on the nearshore. On macrotidal nent and reaches the coast through the rivers, and since the
beaches, the number of bars that simultaneously migrate flow of the rivers depends directly on the rainfall regime, the
landwards can be numerous. connection with the climate becomes immediately obvious.
Fig. 17.2 Example of

relationships between beach slope
and grain size (based on the data
of Shepard [54] and Jennings and
Shulmeister [36]
17.3 Zonation and Morphology presence of fringes with different dynamics and divided by
wave levels related to the linked action of waves and tides
The zoning of the beach system is determined by the (Fig. 17.4).
dynamic factors established by the different action of the The most dynamic area is the one where the wave energy
waves. Using this dynamic criterion, the zones will always dissipation bands described in the previous paragraphs are
occupy strips longitudinally to the coast, succeeding each most frequently found. This zone is called the nearshore. Its
other transversally. lower limit corresponds to the place where the significant
waves begin to interact with the bed—i.e., the wave base
level—while its upper limit is the middle level of the high
17.3.1 Fringes of Wave Action tides. This nearshore zone is divided into two zones with
different behavior. In the subtidal zone, the strip where the
Dynamic zoning is therefore established by the action of the shoaling process takes place is called the shoreface. Here,
waves on the bed. This action combines, on the one hand, there is also a greater influence of the tidal currents and the
the different effects that the waves produce on the bed and, wind-induced currents. The shoreface also includes the
on the other hand, the deformation that the bed produces on breaker and surfing zones during low tide. Above it, the
the wave in terms of energy dissipation. The main division is intertidal fringe includes the beach between high and low
determined by the breaker (Fig. 17.3). The interaction with tides. This area, called the foreshore, is where the breaker,
the bed that has been described in Chap. 7 as the shoaling surfing and swash areas are located during high tide,
process [34] begins in areas shallower than the wave base emerging during low tide.
level. Hence, the zone where it takes place is called the The subtidal zoning is completed with another deeper
shoaling zone. In this zone, the action of the wave on the band called the offshore, which is only affected by storm
bed is manifested in an oscillatory movement. surges and is delimited by the base level of the extreme
The place where the breaker starts is called the breaker storm waves. Above the foreshore there is another supratidal
zone and it is a zone that usually coincides with a change of strip dominated by the wind and which precedes the first
slope, and most often with the presence of a bar. The breaker ridge of foredunes. This area is called the dry beach or
zone is the fringe in which the transition from oscillation backshore and its upper limit is the maximum level of
waves to translational waves takes place. Here, there is a swash of extreme storm waves.
whole strip in which translation waves are produced, called
the surf zone, which is characterized by a more or less
uniform transport of sediments to the shore. The arrival of 17.3.3 Beach Types
the wave to the shoreline is a last stroke and is called the
swash zone. There, a laminar dynamic will be established, The general typology of beaches is established according to
represented by swash and backwash processes. the balance between the processes of dissipation or reflection
The surf area may be absent on steep beaches where the of the energy of the waves, which is in turn established
wave practically breaks on the beach. These beaches go according to the slope of the beach. In the previous sections
directly from the breaker zone to the swash zone. discussing the influence of the slope, we saw that this bal-
ance defines two different situations [60]:
17.3.2 General Zoning (1) Steep beaches. These are characterized by the absence
of the surfing area and the breaking and swash areas
On tidal beaches, the zones of wave action move up and being located right on the shoreline. Because of this, the
down the slope of the beach. This displacement generates the swell suffers an important reflection process. They are
Fig. 17.3 Zoning of the beach

strip with respect to the wave
breaker [34]
17.3 Zonation and Morphology 231
Fig. 17.4 Complete zoning of beaches with tides. (adapted from CERC [12])
dominated by the backwash and have an erosive presence of certain beach morphologies related to the phe-
behavior. These are called reflective beaches. nomena of dissipation or reflection. The mobilization
(2) Gently sloping beaches. In these, the wave energy capacity was also determined through a dimensionless
dissipates in a gradual way along the surf zone. These parameter previously established by Gourlay [25], calculated
are beaches where the landwards component of the through an equation (17.2).
wave dominates and they usually have a cumulative
H0
character. These are called dissipative beaches. X¼ ð17:2Þ
ws T
However, these two situations evidently describe the In this equation, X is the non-dimensional fall velocity,
extremes of a wide spectrum of possibilities, with an infinite H0 is the original wave height, ws is the settling velocity of
number of cases in between. In fact, the same authors the average grain size of the beach and T is the wave period.
described an intermediate type. In this type, the slope is not With fall velocity, the authors refer to the particle sedi-
very gentle, but neither is it very steep. So, the wave suffers mentation velocity when the flow loses the capacity to
some dissipation, but there is also reflection, since not all the transport it, and it is calculated for grains of volumetric
energy of the wave is dissipated. In this type of beach, there equivalence to a sphere through the equation 17.3.
is a complex model of circulation. Wright and Short named rffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
this type intermediate beaches. 4gDds
Ws ¼ 1 ð17:3Þ
This spectrum of combinations between energy dissipa- 3Cddl
tion and reflection depends on the dimensions and frequency
of the waves in relation to the beach slope. All this is very In this equation, Ws is the rate of fall, g is the acceleration
much linked to the width of the surf band and the breaker of gravity, D is the diameter of the mean grain, ds is the
type. These relationships were expressed by Guza and Inman density of the solid grains, dl is the density of seawater and
[26] in equation 17.1. Cd is a hydrodynamic coefficient that depends on the Rey-
nolds number. For quartz grains, the rate of fall velocity in
2p2 Hb relation to grain size is represented in the graph in Fig. 17.5.
e¼ ð17:1Þ
gT 2 so2 b The name used by the authors could lead to confusion,
since it does not have dimensions and the word speed could
In this equation, e is a dimensionless parameter known as give an idea that it is a vector, when in fact it is a matter of
surf scaling, Hb is the height of the wave in the break, g is observing the space–time relationship of the breaking wave
the acceleration of gravity, T is the period of the wave and b in relation to the movement of the particles. Davidson-
is the slope angle of the beach. Arnott [15] proposes the use of the term surf similarity to
The surf scaling parameter was actually intended to pre- designate this parameter.
dict the width of the surf zone, but was later used by Wright In any case, according to this parameter Wright and Short
and Short to differentiate the type of beach as a function of the defined six types of beach. In addition to the dissipative and
dissipation/reflection processes. Thus, dissipative conditions reflective extremes, they divided the intermediate beaches
would remain above values of 20, while reflective conditions into five types. This classification is shown in Table 17.1.
would occur below values of 2.5. Then, intermediate condi- A decade later, Masselink and Short [40] proposed a new
tions would occur for values between 2.5 and 20. classification, this time taking into account not only the
The same authors found a relationship between the parameter, but the relationship between the tidal range and
capacity of mobilization of the sediment by the wave and the the wave dimensions. They quantified the relationship
Fig. 17.5 Graph showing the

relationship between grain size
and orbital velocity
Table 17.1 Beach types X value Beach type

according to non-dimensional fall
velocity (surf similarity) < 1.5 Reflective
1.5–2.5 Low tide terrace
2.5–3.5 Transverse bars and rips
3.5–4.5 Rhythmic bars and troughs
4.5–5.5 Longshore bars and troughs
> 5.5 Dissipative
between tide and waves using the parameter RTR (relative The transversal bars characteristic of reflective beaches
tidal range). RTR actually quantifies the importance of the are commonly known as rip-and-cusp systems. The rips and
maximum tidal range (STR: spring tidal range) versus the cusps form a system of repetitive forms with regular spacing
height of the waves in the breaker (RTR = STR/Hb). ranging from a few meters to over a hundred. Actually, these
According to the authors, for RTR values lower than 3, the forms constitute the most visible element of the system,
influence of the tide would be negligible. Conversely, values since they develop in the emerged zone; however, the
higher than 15 would be typical of tidal plains where the tide transversal bars that are associated with the submerged part
totally dominates the processes. In the case of intermediate develop more widely. The morphology of these systems
values between 3 and 15, tide and waves combine to control gives the beach a saw blade appearance (Fig. 17.7).
the transport processes. The values of X and RTR can be The longitudinal bar systems characteristic of dissipative
combined to obtain six types of beach (Fig. 17.6). Among beaches are known as ridge-and-runnel or bar-and-trough
these types, the three corresponding to RTR values lower systems. Bars or ridges are sandy crests parallel to the beach
than 3 would be the three initially differentiated by Wright with a clear tendency to migrate landwards. Behind them,
and Short [60], distinguishing three new types of RTR val- furrows (runnels or troughs) develop, which are elongated
ues higher than 3: low tide terrace beaches, low tide bar and depressions in the same direction (Fig. 17.8).
rip beaches and ultradissipative beaches. The most common systems have only one bar in the
foreshore zone, although there may be a few more in the
nearshore zone. However, in macrotidal zones more than
17.3.4 Bar Morphology one bar can be emerged during low tide (Fig. 17.9a). Under
favorable conditions, multiple small bar systems can develop
A large fraction of the beaches described in the previous even in microtidal systems (Fig. 17.9b).
section is characterized by the presence of bars. Classic works There is much debate about the causes that condition the
differentiate between two distinct types of bars: the transversal appearance of multiple bars on the beaches under different
bars and the longitudinal bars (e.g., [22, 27, 47, 53]). tidal regimes. Early on, authors who worked on bars (e.g.,
17.3 Zonation and Morphology 233
Fig. 17.6 Classification of beach morphology according to the values of X and RTR. (adapted from Masselink and Short [40])
[22]) stated that one of the main factors involved in the Xs

B ¼ ð17:4Þ
genesis of a high number of bars, along with wave dimen- gT 2 tan b
sions and grain size, is the shoreface slope. Thus, the slope
conditions the distance to the coast of the first breaks and In this equation, Xs is the width of the surf zone, g is the
thus determines the width of the surf zone. In a general way, acceleration of gravity, T is the wave period and b is the
very wide surf areas subjected to small waves moving fine nearshore slope. In this case, the grain size is absent from the
sediment allow the development of a greater number of bars. equation, but the authors understand that it is the grain size
The same studies also established that the dimensions of that conditions the beach slope.
the bars tend to become larger as they move landward, while For values of B* that are lower than 20, no longitudinal
their spacing becomes smaller. This is evident from the bars will be generated; for values higher than 20, an increase
change in water column above the bars and the deformation in value will allow a greater number of bars to be developed.
that this decrease in depth generates in the wave orbits Although two types of bar (transversal and longitudinal)
during the shoaling process. In this regard, it should be noted were described from the beginning, in fact these two types
that the deeper bars do not migrate during the arrival of are once again the extremes of a broad spectrum
smaller waves. (Fig. 17.10). The spectrum includes the crescentic bars as
In order to try to quantify these factors, Short and Aagard intermediate morphology and a good number of transition
[55] established the parameter B* (17.4). This parameter morphologies that take into account the orientation of the
relates the width of the surf zone to the wave period and the bars, whether they are attached to the beach or whether they
nearshore slope. have grooves that separate them [42].
Fig. 17.7 Aerial view of a rip-and-cusp system at Mazagon Beach, SW Spain
the lower level to which the sand can descend during storms
17.4 Dynamics and Evolution without losing its ability to return to the upper zone of the
beach. In morphological terms, it is the shallowest depth that
17.4.1 Movement of Sediments by Waves delimits the most marine zone in which there are no sig-
nificant changes in the bathymetry. Consequently, under this
The sediment present on beaches, whether sand or pebbles, level there is no significant net exchange of sediments, in
is easily transported by the forces that the waves exert on the contrast with the beach zone, which is dynamically active
bed. However, these forces go through cycles, alternating and morphologically changing.
fairweather waves with those developed in periods of storm. To calculate this parameter, the most energetic conditions
When faced with the forces of the waves, the clasts can be of the wave must be taken into account. This depth is
transported in two different ways, depending on the rela- established through the relationship between the entrainment
tionship between their size and the force of the wave: sus- threshold of the grains present on the beach and the force of
pension and bed load. From a morphological point of view, the dominant wave. This strip can be determined from
this transport manifests in the development of an upper plane bathymetric profiles and the grain size of the sediment, and
bed or in the migration of bars. represents the area where the processes of remobilization
A dynamic concept directly linked to sedimentary envi- and circulation of sediments take place.
ronments is the closure depth. The closure depth is the Hallermeier [28] established an equation for the calcula-
bathymetric level at which the waves can start their transport tion of the closure depth (17.5), which he later modified in
to land. In terms of sedimentary balance, it can be defined as 1983 (17.6).
Fig. 17.8 Panoramic view of a ridge-and-runnel system at Agate Beach, Oregon, USA
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Dc ¼ HsTs g=5000D ð17:5Þ With waves oblique to the coast, undertow currents are
generated at the entrance of each new wave. Then, the
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Dc ¼ 0:018HsTs g=DðS 1Þ ð17:6Þ transversal vectors are compensated for, but longitudinal
vectors appear and a drift current is generated. This com-
Where Dc is the closure depth, Hs and Ts are the sig- ponent is responsible for the longitudinal transport of sedi-
nificant wave height and period that are exceeded 12 h per ments along the beach.
year (storm surges), g is the acceleration of gravity and S is
the relationship between densities of sand grains and
seawater. 17.4.2 Dynamics and Genesis of Transversal
In 1985 this equation was simplified so that the granu- Bars
lometric parameters did not have to be used, and was thus
established solely as a function of the wave dimensions In order to understand the dynamics of a reflective beach
(17.7). with a system of transversal bars, it is necessary to know
2 how the energy discharge occurs on the surfaces of high
Hs
Da ¼ 1:75Hs 57:9 ð17:7Þ slopes during the wave-swash process. According to studies
gT 2 by Hughes and Turner [33], the arrival of a wave on a highly
Above the active depth, the breaker is the key for sepa- sloped surface occurs in several phases (Fig. 17.11).
rating areas with different transport models. At the moment a The first phase involves the concentration of a landward
wave breaks, a sudden discharge of energy is produced, current in a diminishing section. This current increases sig-
which puts the finest particles in suspension and displaces nificantly from the presence of the beach step, which is
the coarser clasts in the form of bed load. Depending on the located at the front of the rip-and-cusp system. In the second
type of breaker, the moving particles can be transported phase, the swash is produced when the step is overcome.
landwards or seawards through the surf zone. On dissipative This means the entry landwards of a sheet of water of a few
beaches, the spilling type breakers dominate and the main centimeters, which acts by transporting particles over the
transport is landwards, while on the characteristic breakers beaten surface. In the third phase, the sheet of water moves
of reflective beaches (plunging, collapsing or surging) it is in favor of the slope as a high-regime flow. This flow is of
the undertow currents that cause a dominant transport much greater energy than the previous one and it displaces a
towards the sea and erosion in the higher parts of the beach. great quantity of particles towards the sea. These particles
Fig. 17.9 Panoramic view of multiple bar systems. a: Macrotidal beach at Formby, UK. b: Microtidal beach of Mississippi Sound, USA
are deposited at the front of the step, when the increase of the allows us to delimit a zone of divergence of the swash
flow section decreases the velocities. With the arrival of a towards two successive bays during the arrival of the wave
new wave, the undertow flow is abruptly slowed down by crest at the front of the cusps (Fig. 17.12a).
forming a hydraulic jump at the front of the step. There, the At same time, a convergence of the crests occurs at the
encounter with the new wave takes place. The presence of center of the bays. This convergence results in an undertow
this jump implies a settling of the particles that the undertow being channeled into the center of the bays, generating a
transported down the slope. Finally, at the front of the step, a current stronger than the simple undertow. This rip current is
vortex is produced between the undertow current of the capable of reaching and maintaining the supercritical flow
previous wave and the pounding of the new wave. This (Fig. 17.12b). Each rip current deforms the crest of the next
vortex can remove the particles deposited under the step and wave, causing the arriving wave advancing to the cusp zone
transport them uphill when the next wave is produced. to give rise to a new zone of divergence (Fig. 17.12c). The
This model takes only a two-dimensional view of the encounter between the rip current and the crest of the new
swash. However, the morphology of a reflective beach wave is what produces both the convergent upturn and the
includes the development of rips and cusps, so the process undertow vortex, which in this case are located in the front
must be observed three-dimensionally [48]. This perspective of the bay areas.
Fig. 17.10 Different beach bar morphologies. (adapted from Masselink et al. [42])
Taking into account the fluid dynamics and the move- and depositing the bedload. The sedimentation of
ment of sediments in a rip-and-cusp system, two zones can transversal bars takes place in these deposit zones.
be differentiated in terms of sediment movement:
One of the questions that has interested researchers since
(1) Feeding zone: Located above the step. This is the zone the last quarter of the twentieth century has been the cause of
where the swash and undertow of the waves act. It is the regular spacing of the cusps. A possible origin was
where the undertow currents dominate and the energy is proposed by Guza and Inman [26], based on the interaction
concentrated. The flow of particles is produced towards of the dominant waves with a stationary wave train that
the sea, cutting the breaker. usually forms on reflective beaches running parallel to the
(2) Deposit zone: In this zone, the undertow current faces coast. These waves are called edge waves. If the period of
the pounding of the next wave, cancelling out its forces the edge waves is double that of the incident waves, the
Fig. 17.11 Flow patterns during

the different phases of a swash–
backwash process. (adapted from
Hughes and Turner [33]
interaction of these wave trains generates a system of nodes More recently, the results of the GLOBEX project
and antinodes, which was the basis of these authors’ pro- showed the importance of infragravity waves in non-linear
posal. In this way, bays would be formed in the nodes where wave transport patterns in high slope beaches. These could
the amplitudes of the two waves combine, increasing the be responsible for linear patterns in systems where the
erosive power of the waves. Conversely, the cusps would be presence of edge waves has not been observed [43]. The
formed in the antinodes, where the amplitudes are counter- presence of these infragravity waves would influence the
acted, resulting in less erosional power. The spacing of the formation of groups of waves of different wavelength and
cusps depends directly on the period of the waves in relation height. These wave groups would cause higher and lower
to the beach slope. energy density bands to be produced every certain number of
Decades later, other authors proposed a different theory waves. The distance of these energy density bands would
for the origin of the cusps [14, 58]. This is the theory known coincide with the spacing of the cusps.
as self-organization. In this case, the proposal is based on the
feedback that exists between the presence of irregularities in
the coastline and the arrival of the wave trains. If we start 17.4.3 Dynamics of Longitudinal Bars
from an irregular coastline, the coastal inlets would generate
undertow currents that would deform the waves. This There are two mechanisms proposed for the genesis of bars:
deformation of the waves would cause disturbances that the mechanism of the breaking point and the mechanism of
would have a direct effect on increasing the erosion of these standing waves. The breaking point mechanism was pro-
coastal inlets. The end result is the regular arrangement of posed by Aagaard et al. [1] and attributes the deposition of
the cusps and bays, whose spacing in this case would depend the bar to the convergence between the land transport in the
on the length of the sheet of water in the breaker (swash shallow zone and the sea transport in the surf zone
excursion). These two theories are not contradictory. If there (Fig. 17.13a). These differences in transport are due to the
are irregularities originated by a wave interaction, these orbital asymmetry of the waves in both zones, especially
could initiate a later self-organization that would adapt the during periods of high wave energy. The standing wave
resulting forms to the characteristics of the dominant wave. mechanism is based on the presence of standing waves in
Fig. 17.12 Flow patterns in a rip-and-cusp system. (adapted from the ideas of Pethick [48])
the waterfront area acting parallel to the coast [11, 32]. greater than 1 m per day, but have in some cases exceeded
Similar to what has already been observed in the formation 30 m per day [21]. In this way, a bar can take less than a
of rips and cusps, the presence of these waves results in the week to climb up the foreshore and be fully attached to the
formation of nodes and antinodes. This mechanism would upper zone of the beach [52].
give rise to a system of multiple bars generated in the The mechanism of migration is simple in the passage of
antinodes, where the currents of different rotation orbits each wave. The swash generates a millimetric sheet inclined
converge (Fig. 17.13b). towards the land. To do this, it uses sand that is eroded by
Once formed, the bars tend to migrate due to the dissi- the swash on the face inclined towards the sea.
pation of wave energy that is produced over them. Under There may also be migration of bars towards the sea. This
significant wave conditions, there is usually a migration type of migration usually occurs during very energetic wave
towards land through the surf zone, especially under the conditions, in which the breaker is either plunging, surging
action of spilling type breaks [3]. This implies that the bars or collapsing. These types of breaker are characterized by a
cross the shoreface to the foreshore and end up on the beach dominance of the undertow, in which erosion concentrates in
(Fig. 17.14). The migration rates of these bars are usually the highest areas of the beach and sands are transported
Fig. 17.13 Mechanisms of bar

genesis. a Breaking point
mechanism by Aagaard et al. [1].
b Standing wave mechanism by
Carter et al. [11]. Figure adapted
from Masselink et al. [42]
Fig. 17.14 Example of bar

migration on the foreshore to be
attached to the beach in only four
days [52]
towards the sea. These conditions usually occur during these conditions, the influence of the edge waves is minimal.
storms. Instead, all the dynamic load falls on the energy flows
Another characteristic of these systems is the existence of associated with the breakers, which are usually of plunging,
longitudinal currents channeled into the runnels above the surging or even collapsing type. In these processes, and with
bars. These currents increase in magnitude when the bar such a coarse grain size, the characteristic mode of transport
reaches higher levels and enters the foreshore. When the is traction, although in some vortices and for finer sizes,
swash exceeds the bar, entering the runnel, the water cannot saltation may also occur. Thus, most of the particle transport
return downstream and is forced through the trough. The is concentrated in the vortices that are generated around the
water thus channeled into the runnel seeks exit to the sea break point, where the undertow currents of one wave are
through undertow channels that cross the bar. In these confronted with the pounding of the next wave. The most
channels, true rip currents can form with an almost contin- influential studies on these processes have been summarized
uous character. by Buscombe and Masselink [9].
One of the big differences with sandy beaches is that the
porosity reduces the speed of the undertow currents when a
17.4.4 Dynamics of Cobble Beaches part of the water filters through the clasts. This effect also
produces a decrease in the wave reflection process, so that
The profile corresponding to the size of these clasts is always the beaches with edges produce less reflection than sandy
reflective, so longitudinal bars never appear, but instead beaches with the same slope [49]. In this case, sorting plays
there are almost always cusps (Fig. 17.15). This type of an important role in permeability, since the presence of
high-slope profile is characterized by a coincidence between different clast sizes reduces pore volume. Another effect of
the breaker and the swash zones, so that the dynamics are the large grain size is created by the bed roughness, which
dominated by the swash and undertow processes [61]. In has a significant influence on the shear stress of the fluid on
Fig. 17.15 Examples of cobble

beaches in Asturias, N Spain,
showing reflective profiles and
rip-and-cusp systems. a:
Panoramic view of Arreas beach.
b: Shorefront view of Portizuelo
beach. (Photographs courtesy of
G. Flor-Blanco.)
the clasts by increasing friction. This roughness also affects shoreface, including the berm and the intertidal beach
the dissipation of the fluid energy in the formation of small (foreshore). It is usually studied during extreme low tides,
vortices near the bed [41]. which expose the entire intertidal zone and a part of the
One of the characteristics of the ridge beaches is that the subtidal front. Theoretical studies by engineers compare the
dynamics during storms introduce most of the changes in the beach profile with an equilibrium profile to predict the ero-
profile, while the fairweather swell hardly causes any sive or cumulative behavior of the beach. The equilibrium
movement of the clasts. In this regard, it should be noted that profile is the theoretical topographic outline that a beach
many gravel beaches correspond to relict situations and the with a certain granulometry adopts when it is subjected to
clasts are in clear imbalance with current dynamic conditions constant wave characteristics for a long time.
[46]. It is already established in the definition that it is a the-
oretical profile that is rarely reached, since the wave con-
ditions are not constant, but highly variable. However, the
17.4.5 Equilibrium Profile use of this profile allows the prediction of behavioral trends
between different wave situations. Other profile models take
The beach profile is a topographic profile made from the into account only the characteristics of the sediment, con-
highest areas (usually the dune ridge) to the front of the sidering that the wave regime only introduces profile
Table 17.2 Application equations for the calculation of parameter A This equation is applied to obtain the equilibrium profile
as a function of the average grain size (D50), according to the proposal in the upper section of the beach, between the level reached
of Dean and Maurmeyer [20]
by the surfacing up to a depth equal to the value of 0.75 Hs.
D50 A For the lower stretch of beach, between 0.75 Hs and the
D50 < 0.4 A = 0.41 D500.94 closure depth is considered a stretch of constant slope
0.4 < D50 < 10 A = 0.23 D500.32 (y = 1.25 x).
10 < D50 < 40 A = 0.23 D500.38 Using this equation, it is possible to predict, for example,
D50 40 A = 0.46 D500.11 the erosion profile that a beach will have in the face of a
storm with a determined wave size, or the response that it
would have in the face of a variation in the grain size of the
sand that feeds the beach.
oscillations, with the equilibrium profile being a central
position of these oscillations.
The theoretical profile is established through models of 17.4.6 Evolution of the Beach Profile
wave transport calculation. The most widely used method is
that proposed by Bruun [8] and modified by Dean [19], The beach profile responds to variations in the wave regime
which takes into account only the characteristics of the as a result of the different transverse transport trajectories
sediment, because of the latter consideration mentioned. The that occur under waves of different dimensions. Through the
expression for calculating the point-to-point height of the observation of the beach profiles, it is possible to monitor the
profile is given by equation 17.8. evolution of beaches. Knowing and understanding the evo-
lutionary tendencies of beaches is of notable social interest,
y ¼ Ax2=3 ð17:8Þ since they are locations of important economic activity.
However, it is also of interest from a purely sedimentary
where y is the beach elevation at a given point, x is its perspective, since this evolution influences the sedimentary
distance from the coastline and A is a grain size parameter sequences that are preserved in the geological record.
related to the sedimentation rate and established from the There are variations of the beach profile at different time
mean grain size (D50). The calculation of the parameter A intervals. Short-term variations are daily modifications,
depends on the range of grain sizes and is reflected in which respond to sediment transport trends under the action
Table 17.2 [20]. of wave trains with similar characteristics. Seasonal varia-
The choice of the 2/3 value for the coefficient is based on tions respond to annual cyclical changes that alternate
the Gaussian distribution of energy dissipation in the profile; between clearly constructive and clearly erosive periods. The
however, other authors [7] noted that, on lower energy variations of decades mark the trends of the beach in periods
beaches like the Caribbean ones, the profiles fit better to a higher than interannual climatic cycles, such as ENSO or
1/2 coefficient. NOA, and respond to variations in the intensity and number
The balance profile takes a concave shape and fits quite of storms over the years.
well to beaches without bars, but it departs from the typical The best-established changes are the seasonal ones
profile of dissipative beaches with bars. (Fig. 17.16). This type of process was established by
One of the drawbacks of an equilibrium profile as con- Shepard [53] and later verified by numerous authors through
ceived by Brunn and Dean is that it is unable to predict records in successive profiles. All authors who have
changes in response to different wave dimensions. Vellinga addressed the subject agree on a seasonal alternation of the
[56] proposes the calculation of the equilibrium profile for two characteristic processes of erosion and sedimentation.
different waves through a more complex equation (17.9), but The variations can be summarized in two different moments
with easily determinable input parameters, such as signifi- that follow each other in a cyclical way. The morphology of
cant wave height and mean grain size (through their fall the profile after calm periods is different from the mor-
velocity). phology after the storms.
82 sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi3 9
Hs 4< 7:6 1:28
Ws 1:28 =
y¼ 0:47 x 52 ð17:9Þ (1) Calm conditions: During these periods, a transport of
7:6 : Hs 0:0268 ; sediment towards the highest areas of the beach takes
place over days, weeks and months. In profiles with
In this equation, y is the beach elevation at a given point longitudinal bars, at the beginning of the process these
less than the value 0.75Hs, x is its distance from the shoreline, are located in the lower part of the profile and pro-
Hs is the significant wave height and Ws is the value of the gressively migrate towards the higher part. In the
average grain size fall velocity of the beach (in m/s). reflective and intermediate profiles, the calm period is
Fig. 17.16 Typical cycle of

seasonal variations of a beach
profile
the moment of greatest approach to land of cross bars. interrupted and they migrate towards the sea. On the
At the end of the period, the process of attaching the other hand, in the reflective profiles, the transversal bars
bars to the front of the berm achieves a convex profile at experience a greater development in the submerged
the top and concave at the base. part. The characteristic profile after a period of storms is
(2) Storm conditions: During these periods, large waves act concave in the highest part, where the erosive phe-
with a peak of energy on the beach. These storm waves nomena are concentrated, and convex in the lowest part,
generate erosion processes in the high areas of the where the undertow accumulates the eroded material.
beach, accompanied by the transport of sediment to the
submerged areas. It is precisely during these processes It is common that, on occasions, small storms interrupt
that the genesis of bars in the lower part of the shoreface the process of accretion of calm waves; however, the calm
begins, due to the mechanism of the point of rupture period is usually prolonged and fairweather waves quickly
when the storm surge faces the waves in the process of rebuild the action of a small storm. It is during large storms,
shoaling. This type of event takes place during short or periods where successive storms occur, that the change in
time intervals that, once they stop, are replaced by trend restarts the cycle.
successive moments of calm. On dissipative beaches, These two periods give rise to the characteristic summer
the process of migration of bars towards land is and winter profiles described by Shepard as the end result of
both periods of different wave conditions. The same concept 17.4.8 Beach Cells and Sedimentary Balance
had been described earlier by Johnson Johnson (1919) using
the terms normal and storm profiles. Taking into account the existence on the beach of a trans-
verse dynamic and longitudinal transport, the beaches would
be divided into semi-closed transport cells. Each cell would
17.4.7 Longshore Dynamics be limited by obstacles that interrupt the coastal drift totally
or partially. Examples of obstacles that serve as boundaries
The existence of a longitudinal component to the beach when between cells may be capes, river mouths, shoreface ele-
the waves approach the coast in an oblique way, as well as the ments that divert the arrival of the waves to the coast by
calculation of the potential transport of sediments, are topics inverting the drift, or even artificial elements such as groins
that have already been covered in previous chapters. This or jetties. Some of these cells can be tens or hundreds of
littoral drift is manifested not only in a continuous transport kilometers long, while others barely reach a hundred meters.
of sediments along the surf zone, but also in the morphology In each of these cells, or even in a certain stretch of beach,
and dynamics of the bars. On the one hand, the orientation of there are inputs and outputs of sedimentary material from
the transversal bars associated to the rip-and-cusp systems, as and to the systems or bordering the cells (Fig. 17.17). The
well as the direction of the undertow currents, may have an following sediment inputs can be counted in any coastal
asymmetry imposed by the littoral drift. In this case, the segment:
sediment may bypass from one bar to another through the
rip-and-cusp channels. On the other hand, in the case of the • Material introduced from the land (by the rivers and the
longitudinal bars, the longshore component marks the ori- wind).
entation of the currents that run through the runnels in the • Material introduced by the waves from the continent
foreshore area. The longitudinal dynamics is also reflected in through the erosion of dune areas or rocky shores located
the trajectory of the bar’s sediment particles during their behind the backshore.
migration towards the land, since the bar has a longitudinal • Material introduced by the waves from the front of the
component that adds to the transversal movement. In this shoreface. This material can be brought in by relict
way, when a bar moves towards the sea during the storms, it formations.
does so in a totally transverse trajectory, parallel to the line of • Material introduced by coastal drift from the updrift
maximum slope of the beach; however, when it returns to the segment or cell.
beach line, it does so at an oblique angle, reaching a different
stretch of beach located under the flow of the place where it And the following sediment outflows are also accounted
was eroded. for:
Fig. 17.17 Inputs and outputs in

a beach sediment budget. Inputs:
C + = from the continent.
O+ = transversal transport
onshore. L+ = longshore
transport from updrift cells.
Outputs: C− = to the continent.
O− = transversal transport
offshore. L− = longshore
transport to downdrift cells
• Material extracted by the waves towards deeper areas. observed both on sandy beaches [23] and on gravel and
• Material extracted by drifting towards the segment or cell pebble beaches [39].
located downdrift. The differences in grain size are even more apparent
• Material extracted by the wind towards the dunes. between the different layers that make up the beach sedi-
ment. These variations between layers reflect temporary
The sediment budget will result from the algebraic sum of variations in energy over longer periods of time. Thus, there
the sediment volume inputs and outputs, counting the inputs is a clear relationship between the average grain size in a
with a positive sign and the outputs with a negative sign. layer and the wave energy that generated it. This means the
It is important to precisely determine the time intervals to alternation between layers of different grain size reflects the
compare the amounts of sediment from each of these inputs variations in time of the wave dimensions and the changes in
and outputs, since the beach undergoes continuous changes the way the wave energy is dissipated. It is very frequent to
and there are situations that are not comparable. One type of find intercalations of gravel (siliciclastic or bioclastic) and
balance that is often established is the annual balance. This heavy minerals that correspond to the action of more ener-
balance would reflect the synoptic situation throughout a getic waves at certain moments. This alternation of layers of
complete year, taking into account that this would be the different grain size can even become rhythmic, responding to
probable result of a period with positive balance in the calm seasonal changes between periods of fairweather and storms
period and another with negative balance during the period (Bascom 1951). Gravel beaches present patterns very similar
of storms. Another type of balance is made with longer to sand beaches; in fact, many gravel beaches also present
intervals to evaluate erosive/accumulative tendencies. Given interspersed sand levels that correspond to moments of lower
that there are multi-year cycles, such as those associated with wave energy.
climatic oscillations, it is important that the initial and final Despite the clear influence of wave energy on grain size
situations of the balance be located at similar times in the in relation to transport capacity, there is a primary control
cycle. exercised by the availability of sediment. Thus, although in
some beaches there is a capacity to transport coarser grains,
these will not exist if these grain sizes are not available at the
17.5 Facies and Facies Sequences source feeding the system.
Edge beaches usually have less variation in grain size,
17.5.1 Beach Sediment Characteristics precisely because of the availability of sediment. Some
pebble beaches show no temporal variation in size, despite
The sediment on the beaches is the product of the interaction the existence of clear alternations between waves of different
between the beach slope and the dimensions of waves. These dimensions (e.g., Carr [10]). This lack of variation is due to
interactions determine the process of energy dissipation that the absence of clasts of other sizes and in many cases only
is transferred to the transport of sediments. In general terms, the largest waves reach the movement threshold of these
the grain size of the sediment is a function of the intensity of clasts.
the breaker, which depends on both factors. However, there
are variations in the grain size across the transverse beach
profile, so that the larger clasts are located right in the break 17.5.2 Sandy Beach Facies
zone, with a gradient of size loss towards the higher areas of
the beach and also towards the deeper areas [45]. There is The facies on sandy beaches are distributed according to the
also a zone of larger grain size in the zone of the first depth, since this factor, together with the dimensions of the
breakers, where the dissipation of energy begins to be waves, conditions the type of interaction of the wave with
transferred to the movement of particles. This transfer of the bed. Thus, each of the distinct areas has its own facies.
energy to the movement of particles can be understood in Moreover, in beaches with longitudinal bars, the bars and
terms of sediment dynamics subjected to the orbital velocity troughs have different facies, giving rise to characteristic
of waves until they cross their entrainment and selection sequences of the ridge-and-runnel systems (Fig. 17.18).
thresholds, as seen in Sect. 14.4. On tidal beaches, these The characteristic facies of each of these areas have been
larger grain size zones move vertically, causing a size established in successive works by Edward Clifton, and
variation over time in a particular area of the beach profile, summarized in a synthesis paper [13]. In the case of
which results in an increase in grain size dispersion that reflective beaches, the facies are less studied, since the upper
coincides with a loss of sorting [5, 6]. In this way, the part of this type of beaches is erosive and does not usually
highest grain size and the lowest sorting coincide precisely generate preservable facies. However, facies associated with
where the highest values of energy dissipation are reached. the transversal bars can be generated. This type of facies has
Such variations in sediment size and classification have been been described by Isla et al. [35].
Fig. 17.18 Facies distribution scheme of a ridge-and-runnel system (Based on Davidson-Arnott and Greenwood [16])
The following describes the characteristic facies of each On reflective beaches there is usually a coarser grain size
of the distinct areas in the beach systems. of the sand. From the point of view of the structures, this
zone is characterized by the monotonous development of
– Offshore: Alternating silts, very fine and fine sand with parallel lamination inclined towards the sea, which passes at
oscillation ripples that can be asymmetrical. These deeper levels to parallel sub-horizontal bedding [35] or
alternations may contain coarser grain size intercalations cross-stratification inclined towards the sea, typical of the
and hummocky stratification corresponding to storm transversal or crescentic bars.
levels. In all cases, the bioturbation usually alters the
original structure. – Foreshore: The facies developed in the foreshore area also
– Shoreface in the shoaling zone: In this zone, fine sand is depend on the type of beach. In beaches with bars, the
usually sedimented with asymmetrical ripples of lunar distribution of facies is very similar to the one described in
morphology (Fig. 17.19a and b). Sometimes, bars with the shoreface zone; however, the inclination of the lami-
vergent cross-bedding are formed towards the sea, product nation is usually greater, both in the parallel laminations
of the erosion of the storms in the highest zones of the inclined towards the sea, and in the cross-stratification
beach. Although these bars are subsequently reworked inclined towards the land. This occurs because the fore-
during fairweather periods, parts can be preserved. shore bars usually have a greater relief than the submerged
– Shoreface in the breaker and surf zones: They are bars. In profiles parallel to the beach line, the migration
usually composed of medium-sized sand grains. The and filling structures of the exit channels of the undertow
facies developed in zones of smaller depth to the currents are also usually observed. In the troughs, the
breaker depend on the type of beach. In beaches with asymmetric ripples are usually well developed and even
bars, there is also a difference in the position of the acquire linguoid morphologies (Fig. 17.19d). Their
facies with respect to the bar. In the outer zone of the migration is always oriented in the direction of the drift.
bars, a parallel lamination inclined towards the sea is On beaches with multiple bars, these facies repeat as much
developed, as a result of the asymmetric swash of the as the number of bars.
waves and the transport of the material towards land. At On reflective beaches, this zone is usually erosive
the crest of the bars, there is cross-bedding inclined (Fig. 17.19e), although parallel laminations may develop
towards land, as a result of the migration of the bar in in an ephemeral way, strongly inclined towards the sea.
this direction (Fig. 17.19c). In the troughs, asymmetric The three-dimensional geometry of these laminations
ripples are usually formed, which migrate in the direc- shows the typical concavity of rip-and-cusp systems.
tion of the littoral drift. Although 3D megaripples may In both types of beaches, the development of coarser
also be present, migrating landwards like the bars. grain layers formed by siliciclastic or bioclastic material
17.5 Facies and Facies Sequences 247
Fig. 17.19 Different facies in

beach systems. a Wave ripples
with erosive curved base.
b Asymmetric wave ripples.
c Landward-inclined
cross-bedding and
seaward-inclined parallel bedding
corresponding with the record of
a migrating bar. d Linguoid
ripples in a foreshore trough.
e Erosive surface cutting a
parallel lamination in a reflective
beach. f Structure of clogging of a
backshore trough by a welding
bar
and also of heavy mineral sheets is typical of the fore- limited instead to establishing a sequence of facies that
shore. These layers have a residual character and corre- follows the guidelines of Walther’s Law under coastal
spond to the deposit of storm waves. progradation [13, 44]. The different sequences proposed
– Backshore: This is usually characterized morphologically [24, 50, 57] do not present many conceptual or descrip-
by the berm. This morphology responds to the final tive differences, although the consideration of the thickness
attachment of bars, so its characteristic facies show the of the series and the grain size range are different
development of sands with sets of cross-stratification (Fig. 17.20). Both characteristics are the reflection of the
inclined towards the land, which culminate in concave dimensions of the wave, which translates not only into a
beds that mean the final filling of the runnels difference in the energy put into play, but also in the
(Fig. 17.19f). On these, parallel lamination can be bathymetry in which it can exercise its action and deposit
developed that corresponds to the remobilization of the sediments.
finest fractions by the wind. In this way, all the proposed sequences mark a
coarsening-upwards character, while, at the same time, the
The facies models for this type of environment do not sedimentary structures also manifest an increase of the
really reflect a three-dimensional distribution of the facies, energy towards the top of the sequence as we approach the
but, given the tabular character of the beaches, they are facies originated in the swash area (Fig. 17.20).
Fig. 17.20 Facies sequences

suggested by different authors,
based on ancient beach
sequences. a: Walker and Plint
Walker and Plint (1992). b:
Reading [50]. c: High and low
energy sequences suggested by
Galloway and Hobday [24]
17.5.3 Gravel Beach Facies base of the sequence, corresponding to the deposits of the
lower shoreface, there is usually a finer grain size with
Gravel beaches are much less documented than sandy bea- development of wave ripples, often asymmetrical and ori-
ches. Excellent synthesis papers are included in Hart and ented towards the sea.
Plint’s monograph [30] and the same authors have also In the high part, most of the gravel beaches have reflec-
published a review article on facies sequences [31]. Gravel tive profiles, with development of transverse bars. However,
beaches are known to be those with grain sizes ranging from in swell conditions, intermediate beaches can develop cres-
2 to 64 mm, including clasts of granules (2–4 mm) and centic bars. One of the characteristics of gravel beach facies
pebbles (4–64 mm). In general terms, it can be stated that is the presence of fining-upward sequences inside the bars.
gravel beaches present a dynamic and morphology similar to In the long term, the periods in which they move sea-
reflective-type sandy beaches, with concave profiles of high wards alternate with others in which they move landward. In
slope. However, their larger grain size requires higher wave the sequence of sediments, this is manifested in a different
energy to transport the larger-sized clasts (2 mm). At the orientation in the slope of the cross-bedding (Fig. 17.21). In
17.5 Facies and Facies Sequences 249
Fig. 17.21 Facies sequence

typical of a gravel beach
these sequences, the seaward-inclined stratification typical of References

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Wind-Dominated Systems: Coastal Dunes
18
sand store whose presence is vital in the preservation of the

18.1 Introduction
beaches, constituting a supply of sand that feeds the beaches
during storms. Similarly, dune systems can be the source of
The action of wind as a transport agent on the coast was
sedimentary contribution to other coastal environments such
analyzed in Sect. 9.3. Its role can be summarized by three
as washovers.
different effects: (1) contribution of sand from the continent
From an ecological point of view, the dunes constitute
to coastal systems; (2) erosion by deflation on the surface of
one of the most notable environments of the coastal
beaches; and (3) accumulation in coastal areas protected
ecosystem, where a wide variety of animal and plant species
from waves. In this last sense, deposits of sand from wind
are developed [17]. Perhaps a geologically more outstanding
deflation can reach the back-barrier systems in various
aspect of the dunes is their capacity to recharge fresh water.
forms. On the one hand, the material transported by wind
Indeed, dune aquifers are sometimes the only source of fresh
can feed the coastal lagoons and the tidal flats, contributing
water in barrier systems.
to their aggradation. On the other hand, overblow processes
This chapter will analyze all the dynamic processes that
can build sand fans very similar to washovers but with a
contribute to the genesis and evolution of coastal dunes, as
purely wind-based origin. Eolian sandy plains can also
well as their relationships with the adjacent coastal envi-
develop in the supratidal areas of the strandplains. However,
ronments and their most characteristic facies.
the most common forms of deposit associated with wind
transport are coastal dunes.
A dune can be defined as a mound made up of sand
accumulated by the action of the wind. Coastal dunes are 18.2 Control Factors
those that develop in coastal environments. The origin of the
sand that constitutes them is normally linked to the wind Three conditions are needed for dunes to be created: a suf-
deflation on the beaches that are situated at their front [20]. ficient supply of sand, a wind with enough energy to
In one way or another, dunes are part of almost all deposi- transport that sand, and a large surface area on which it can
tional coasts, especially if they are wave-dominated, so they accumulate. There are also other conditions that can influ-
are widely distributed across the world. Many coastlines ence the development of coastal dunes, such as the climate,
develop small chains of dunes associated with the upper part the degree of humidity of the land and the vegetation cover
of the beaches,however, where sand input is abundant, large [1].
areas may be covered by extended dune fields that can even
migrate inland [21]. In sand barriers, the dunes occupy the
highest topographic level and are what really prevent the 18.2.1 Wind Regime
action of the waves at the back of the system. There is
actually a wide typology of dune forms in relation to the Section 14.5 discussed how wind transport is a function of
combination of factors involved in their genesis and evolu- the viscous stress of the wind on the sand grains. The vis-
tion (Fig. 18.1). cous stress is a direct function of wind velocity. The for-
Due to their location and origin, the dunes and the beach mation of dunes requires the existence of winds of
are intimately linked and their dynamics act together. For intermediate speed between the entrainment and selection
instance, while the deflation on the beach is the main con- thresholds. Velocities below the entrainment threshold will
tribution in building the dunes, the dunes themselves form a not produce grain movement, while velocities much higher

https://doi.org/10.1007/978-3-030-96121-3_18
252 18 Wind-Dominated Systems: Coastal Dunes
Fig. 18.1 Coastal dune developed in the backshore area of a sandy beach
than this value will tend to transport so much that they will the first ridge of dunes depend directly on the volume of
prevent the genesis of dune forms or even end up eroding the input. In conditions of insufficient supply, the dunes do not
pre-existing dunes [7]. form. This need is further evidence of the important con-
In addition to velocity, a very important issue is the nection between the beaches and the dunes, which form a
directional regime of the wind. The genesis of dune systems circular feedback system of coastal dynamics [19, 22].
usually requires the presence of persistent winds with a The relationships between the volume of sand input, the
dominant transport component. The persistence of the wind is wind transport capacity and the coastal dynamics are shown
an even more important factor than its velocity in the for- in the development of successive chains of coastal dunes. On
mation of dune chains. In coastal systems, the differential prograding coasts, the lines of coastal progradation are often
heating between the continent and the seawater mass is marked by the presence of successive ridges of foredunes.
responsible for the presence of breezes that blow coastwards a However, on stable coasts with sufficient input, those that are
large part of the time, ensuring a wind circulation pattern that generated as foredunes can begin to migrate inland, while
favors the formation of coastal dunes. It is evident that the new foredunes are built in the original position.
orientation of the coast with respect to these trends influences
the wind efficiency in both the process of wind deflation on
the beaches and the piling up of sand in the dunes. 18.2.3 Development Surface
The existence of winds with different vectors from the
dominant direction influences the growth and possible By now it has become clear that coastal dunes develop in
migration of the dunes in these directions. This process then connection with the beaches that supply the sediment to
influences the geometry of the dunes, as well as the presence build them. But the beaches can appear in different coastal
of complex sets of internal stratification. systems: at the front of sand barriers, on the coastal platform
of cliff systems or on the strandplains. Thus, the dune chains
can reach greater or lesser dimensions depending on where
18.2.2 Sediment Budget these beaches are located, and whether dune migration
landwards will be possible or not.
The development of coastal dunes requires a constant supply On sandy barriers, the width of the dune field is limited to
of sand from the beaches. The dimensions and geometry of the dimensions of the barrier. On spits or drumstick-type
barrier islands, the foredune ridges mark the growth lines of In the interdune areas, the water table can be exposed by
the barriers. Where some of these ridges are formed by dune migration. In this case, these zones act as a deflation
mobile dunes, the migration landwards is limited by the surface, whereby the wet zone is preserved and the zones
lagoon presence. In some cases, the dune may migrate into where the pores are full of air are removed and eroded. The
the lagoon, where its sediments may be reworked by the surfaces thus formed can be covered by the migration of a
tides and re-sedimented as tidal facies. In other cases, the new dune; in these cases, the positions of the phreatic levels
dunes may migrate over supratidal systems such as tidal flats can be preserved as ravinement surfaces.
or coastal sabkhas.
In dunes that develop in the backshore of frontal beaches
linked to cliff systems, the wind turbulence caused by the 18.2.6 Vegetation Cover
presence of the rocky front favors the development of eolian
accumulation at their base. However, the cliff prevents the A unique feature of coastal dunes is that they arise from the
migration of these dunes towards land. If the cliff face is not interaction of physical processes generated by the wind with
completely vertical, some dunes can pile up and climb over biological processes influenced by the presence of vegeta-
it, reaching considerable heights. The dunes may even tion. The first studies considered that plants only colonized
manage to exceed the height of the cliff and migrate over its the dune surface by adapting to it; however, today the
crest. relationships between vegetation and dune dynamics are
On beaches developed in coastal plains, the dunes have considered to be a system of mutual interaction [12]. Thus, it
enough space to migrate to land. In these cases, extensive is now known that biological factors play a role as important
mobile dune fields can develop over the continental as sand transport conditions in the geometry and dynamics
systems. of many coastal dune chains.
To start with, plants can play an important role in the
genesis of the incipient dunes. Once the dunes are formed,
18.2.4 Climate the plant roots contribute to their stabilization. Dune systems
well fixed by vegetation can achieve a notable increase in
Coastal dunes can develop in any climate. There are dune height without the dune changing its position. These dunes
systems distributed latitudinally from the poles to the are characterized by a complex internal structure, where sets
Equator, in different degrees of humidity, ranging from dry of different inclination angles alternate [5, 8]. Hence, the
deserts to tropical systems [9, 16, 26–27, 15]. With this vegetation cover can be a primary factor in determining the
widespread distribution, climate cannot be used as a diag- dimensions of the dunes [6].
nostic criterion for coastal wind systems. However, climate One consequence of this fact is that the vegetation begins
determines the type of vegetation and the degree of vege- to exert a direct influence on the volume of sand stored in the
tation cover, as well as the sand moisture level and wind coastal system to be used during high wave energy condi-
regime. Thus, it can be considered that, although climate is tions. The presence of this sand storage is a controlling
not a determining factor in dune formation, it does exert a factor on the beach profile during storms. In this way, the
significant influence on the development and dynamics of existence of the vegetated dune not only ensures the survival
dune systems. of the beach, but is a guarantee of self-protection.
18.2.5 Moisture Content 18.3 Morphology and Sub-environments
The degree of humidity of the sand is a factor in the mobility The morphology and dimensions of dunes depend on a
of the grains, since the presence of water in the pores exerts a complex relationship of all the factors analyzed in the pre-
viscous friction that acts as an inertial force. On a beach vious section. There is a wide morphological variety of
surface that is used as a wind deflation platform, there is dunes, although the most-used classification is based on
usually a high degree of humidity, so it is necessary for the genetic criteria, since it is the genesis that imposes the
air flow to dry the ground before the particles can be moved morphology. Firstly, one needs to differentiate between
from it. primary and secondary dunes [4, 25]. Primary dunes are
The dune system itself may also contain a significant generated directly on the upper part of the beaches using the
degree of porewater during and after rain, as dunes often act sediment from the deflation processes that occur on the
as a recharging element for coastal aquifers. The presence of foreshore surface. Secondary dunes come from the
this moisture in the dunes makes the particles remain longer reworking of the sandy material of the primary dunes or
in the formation and contributes to their preservation. from the migration of the same towards the land.
Fig. 18.2 Morphogenetic classification of dunes (based on Davies [4, Short and Hesp 10, Hesp 24], and Tsoar [25])
The primary dunes are known as frontal dunes or fore- When there are several chains of coastal dunes, depressed
dunes, while the secondary dunes can be divided by their areas known as interdune zones may be established between
morphology and are linked to their degree of evolution into them. These zones can function as wind deflation surfaces,
blowout dunes, parabolic dunes and transgressive dune although, depending on the climate and the position of the
fields (Fig. 18.2). water table in them, inter-dune lakes may also be present.
18.3 Morphology and Sub-environments 255
18.3.1 Foredunes Relict dunes are characteristic of prograding coasts. They

were once established dunes, but the progradation of the
These are primary dunes and thus formed with the con- beach has allowed the birth of a new established dune chain
tribution of sand directly from the beach. The name in front of them, resulting in these dunes taking up a rear
derives from their location at the front of the coast—that position (Fig. 18.3). They present the same morphology as
is, from their position close to the beach, as they are established dunes, although their growth is less, as they do
located in the area immediately behind the backshore. not receive the direct contribution of sand from the beach
From a physiographic point of view, they are transverse due to the presence of a new foredune.
dunes that generally form a continuous ridge parallel to the
beach line. Morphologically, they have a convex profile
that can be symmetrical or asymmetrical and the 18.3.2 Blowout Dunes
height/width ratio depends on their degree of evolution,
with those that are more evolved having greater height. These are dunes that have developed from deflation holes
According to their evolutionary development [10, 24], the that arise in the foredunes. As they are associated with an
foredunes can be classified as incipient, established or erosional phenomenon, they have two different zones: a
relict (Fig. 18.3). deflation area and an accumulation lobe. Depending on the
The incipient dunes, also called embryonic dunes, are geometry of both zones, they can be distinguished as saucer
small discontinuous or continuous mounds formed in the blowouts, bowl blowouts or trough blowouts.
shade of objects or vegetation (Fig. 18.3). They usually have Saucer blowouts have a semicircular deflation surface
more width than height and their dimensions do not go without a depositional lobe (Fig. 18.4a) or with a low relief
beyond the metric scale. lobe. The bowl blowouts present a similar shape to the
The established dunes present a greater degree of evo- saucers, but with a greater degree of incision and also a
lution and are formed by vertical growth of the incipient greater development of the depositional lobe (Fig. 18.4b).
dunes. They are already continuous chains of convex shapes The trough blowouts present an elongated geometry with a
that correspond to the initial morphological description corridor-shaped deflation surface with steep lateral margins
(Fig. 18.3). They are normally stabilized by vegetation, so and a parabolic-shaped depositional lobe with much vertical
the effect of vertical accretion dominates. development (Fig. 18.4c).
Fig. 18.3 Panoramic view showing the different types of foredunes at Punta de San Jacinto, Doñana National Park (SW Spain)

blowout dunes. a Saucer blowout
in Cruden Bay dunes (Scotland).
b Bowl blowout in Haasvelder
dunes (the Netherlands). c Trough
blowout in Heemskerker dunes
(the Netherlands)
18.3.3 Parabolic Dunes shape, it can be considered that a deflation basin is estab-
lished in its center, whose orientation is usually parallel to
These are more evolved dunes that have undergone a process the direction of the dominant wind.
of migration towards land from an original frontal position. Morphologically, two types of parabolic dunes can be
The name refers to a morphological criterion, since the dune distinguished: the elliptical dunes and the long-walled dunes.
crest is in the form of a parabola due to the migration of the The elliptical dunes are not elongated, presenting more
central part of the dune exceeding that of the extremes, semicircular shapes (Fig. 18.5a). They acquire dimensions
acquiring the shape of a linguoid ripple but of decametric of hundreds of meters and usually appear in fields where
dimensions (Fig. 18.5). Since they are mobile dunes, one of dunes overlap. They are characteristic of areas with a large
their faces is erosive (stoss side), while the other face is sandy input but without strong winds, so their migration
accumulative (lee side). As the erosive face has a parabolic speed is low.
Fig. 18.5 Different types of parabolic dune. a Elliptical dunes in Castilla Beach (SW Spain). b Long-walled parabolic dunes in Lagoinha (NE
Brazil)
The long-walled parabolic dunes have large central areas develop. These are known as interdune depressions or
deflation basins and very elongated arms (Fig. 18.5a). They simply interdunes. In addition to their depressed morphol-
tend to develop greater dimensions and can reach the kilo- ogy, the interdune depressions present other characteristics
meter scale. They are characterized by large areas of flat that can be different depending on the nature of these
terrain, large sedimentary inputs and strong and persistent depressions. In areas where dune piling occurs, the char-
winds. They acquire very high migration speeds. acter of the interdune is depositional and in these we can
find evidence of the dunes that developed in the lower level.
On other occasions, dune migration gives these depressions
18.3.4 Transgressive Dune Fields an erosive nature and deflation processes dominate them.
A special case of interdune depression that is dominated by
These are sand deposits that cover large areas and are formed deflation occurs when the dunes migrate on a cohesive
by the landward movement of sediments of wind origin substrate. In this case, the deflation exposes the surface of
(Fig. 18.6). If the sand is displaced in a laminar fashion due the lower formations in the interdune. In many cases, this
to strong winds, an eolian mantle can develop, where the surface is covered by clasts with a clear residual character
dunes take on the form of low domes. They can also develop (Fig. 18.7a). On other occasions, the deflation process digs
due to an extensive migration of dune fields towards land. down to reach the water table. There, it meets a layer of
These sandy formations can reach scales of tens of square sand in which the pores are filled with water and the
kilometers. Within them, dune forms can be as complex as in moisture prevents the threshold of particle movement being
desert areas, including transverse dunes, parabolic dunes, reached [14]. The interdune is then characterized by a
barchans and barchanoids. completely flat erosion surface. In situations of aquifer
recharge, the water table can rise, flooding the interdune
depressions. In that case, interdune lakes are formed
18.3.5 Interdunes (Fig. 18.7b). If the flooding period of these lakes is pro-
longed, they may have a depositional character, generating
When there are several chains of dunes, or between indi- characteristic deposits that will depend on the climate where
vidual dunes in a field of transgressive dunes, depressed they have developed.
Fig. 18.6 Transgressive dune field in NE Fraser Island (Australia)

Fig. 18.7 Different types of interdune depression. a Coarse deflation lag in St Fergus (Scotland). b Lagoonal interdunes in the Lençóis
Maranhenses National Park (Brazil)
leading to the formation of coastal dunes. In this section we

18.4 Dynamics and Evolution will analyze the mesoscale processes that give rise to the
genesis, dynamics and evolution of all the types of dunes
In Sect. 14.5, the mechanisms of entrainment and selection that can be present in coastal areas.
of the particles by the wind were described in detail. The
mechanism of entrainment acts preferably in the backshore,
as well as in the foreshore during low tide. It is on that 18.4.1 Genesis and Evolution of Primary Dunes
surface where this mechanism generates a deflation process,
which obtains all the sand particles that are transported The sea winds loaded with sand grains on the surface of the
towards the coastal supratidal fringe. In this strip, other beach can lose speed when entering the supratidal fringe.
mechanisms that favor the decrease in wind speed occur, The main effect of the loss of speed is that the threshold of
Fig. 18.8 Genesis of incipient dunes. a Sand sheets formed on the backshore by wind deceleration. b Sand mounds formed in the dynamic
shadows of plants
particle selection can be crossed, and the particles will then the wind. Normally, after this turbulence, a shaded area
stop being transported and settle on the surface of the coastal where particles tend to deposit is generated. These irregu-
land. This deceleration mechanism may simply be due to larities in the terrain can be rocks, driftwood, accumulations
friction with the ground when the wind enters an area with a of algae or dead animals, even garbage, but very often it is
slope greater than the slope of the deflation surface. In this the dune vegetation that causes this effect. Thus, it is very
case, the continuous accumulation of sand on this slope can common for sand piles to form in the shade of plants
give rise to incipient or embryonic dunes (Fig. 18.8a). (Fig. 18.8b). These mounds tend to grow, and in them the
Via this mechanism, the presence of any element intro- influence of saline water decreases as the spray effect
ducing roughness in the terrain can generate turbulence in diminishes and fresh water is recharged during rainfall. At
the same time that the dimensions of the incipient dune sand is redistributed back to the beach and contributes to its
increase, the levels of nutrients also increase, giving rise to preservation during erosional moments. The return of fair-
an ideal place that can be colonized by new plants, which in weather conditions allows the beach to function again as a
turn will tend to increase the accumulation of sand. The final deflation surface and thus the sand will be transported back
result is the generation of a dune that is more and more to rebuild the dune [19].
stable. The first stage of reconstruction of the dune front begins
As the size of the dune increases, the sand tends to be with the development of small incipient dunes that form with
deposited more and more on the marine face rather than in the reflection of the wind on the erosive escarpment of the
the shaded area. The presence of vegetation covering the established dune. Due to this wind flow inversion effect,
whole dune also causes a large fraction of the sand to be these dunes are known as echo dunes (Fig. 18.9c). The small
deposited on the crest of the dune, increasing its height. In echo dunes represent an obstacle to the wind flow and they
the absence of erosional processes, the growth of these grow until they deviate from the established dune front. At
mounds can in a short time give rise to a continuous ridge of this point, the inversion of the wind flow concludes and the
sand that will acquire the characteristics of an established echo dunes begin to function as incipient dunes that end up
foredune. The dimensions that the foredune can reach adhering to the established dune front (Fig. 18.9d). Thus, the
depend on factors such as the rate of transport, the extension dune profile is reconstructed and the foredune can continue
of the deflation surface and the time that the dune continues its growth. The old erosive escarpment is preserved inside
to receive sand from the beach front without suffering ero- the dune structure as a reactivation surface.
sional processes. Due to these factors, it is understandable This process can be repeated with the arrival of succes-
that dissipative beaches develop the largest dunes. There are sive storms, alternating periods of erosion with periods of
cases of foredunes that reach heights of over 20 m [12]. reconstruction. The internal structure of the dune will pre-
The genesis of a new chain of dunes in front of the old serve the erosive–accumulative history as numerous sets of
foredune makes it a rear form. The roughness of the new cross-stratification separated by reactivation surfaces.
foredune generates greater wind turbulence, making it less
effective in transporting sand to the old foredune, which has
thus become detached from the deflation surface. In this 18.4.3 Reworking of the Primary Dunes
way, the dune is fixed in its growth. At this point we can and Evolution Towards Secondary Dunes
speak of a relict foredune [11]. Successive chains of relict
dunes are characteristic of prograding beaches, since on Erosional processes in an established foredune can be caused
these beaches the advance of the coastline towards the sea not only by waves, but also by the wind. One of the most
generates space and guarantees the supply of sand for the common processes that causes wind erosion of foredunes
development of new foredunes. A prograding coast can (established or relict) is the “out-blow” process. This pro-
show dozens of chains of relict foredunes. These lines mark cess usually starts when there is some cause that triggers a
the position of old shorelines. loss of vegetation cover in a part of the dune. The local
absence of vegetation facilitates the movement of sand
grains during times of high wind speed [3]. Among the
18.4.2 Effects of the Waves on the Dunes natural causes that can initiate the loss of vegetation are
erosion by waves and gravitational processes by destabi-
Both the incipient dunes and the established foredunes can lization of the dune front. In recent times, the causes of the
be subject to the action of waves during storms. The overlift initiation of these processes have usually been related to
caused by surges and the swash of large storm waves usually human activities on the dune system [18]. An out-blow
attacks the front dunes once or several times throughout the process causes an erosive structure known as a blowout,
year. These conditions subject the dunes to a process of which is recognized as a form of secondary dune.
erosion, which is especially intense when they coincide with The geometry and dimensions of a blowout depend on
spring high tides. the initial size of the surface that has lost vegetation, but
The incipient dunes are the most sensitive to these con- also on the speed and persistence of the wind at the local
ditions and can suffer total destruction during the most level and the wind flow conditions over the erosive zone.
severe storms. Often, the incipient dunes are ephemeral The type and density of the vegetation in the surrounding
forms and never become established foredunes [12]. area also often has an important influence on the develop-
The wave attacks frequently occur at the front of estab- ment of the blowout. A blowout does not only consist of an
lished dunes. In these cases, the front of the dunes suffers an erosive zone, but under favorable conditions the eroded
erosion process that generates a vertical escarpment and the sand can accumulate on the margin giving rise to a dune
dune loses a significant volume of sand (Fig. 18.9b). This lobe.
Fig. 18.9 Cycle of wave erosion

and wind rebuilding of a foredune
The three types of blowout that have been differentiated develop the dune lobe by accumulation of sand on the lee-
morphologically can form an evolutionary sequence. A lack ward side [13]. The interaction of wind with a blowout is
of vegetation of small dimensions can form a saucer blowout complex, since the presence of this lobe produces turbulence
(Fig. 18.10a). In this form, the out-blow process usually in the flow that tends to increase erosion. The morphological
extracts the sand beyond the dune system without the for- response is an increase in the size of the blowout. If the
mation of a cumulative lobe. However, in a more advanced process continues, the erosive depression can deepen by
stage of evolution, this initial blowout can enlarge and developing near-vertical walls. The exit of the wind in the
leeward side of the blowout normally implies a decrease in causes that can induce the disappearance of the vegetation
the speed and a tendency to accumulate sand, developing a cover are usually associated with changes in the climate,
dune lobe of greater dimensions. In this case, the complete although there can also be other causes of an anthropic nature.
transformation will have taken place to form a bowl blowout. In very well-fed coastal areas, significant migration of
The most advanced process continues with a deepening of the dunes towards land can occur. Then, successive lines of
depression and a migration of the lobe, which is fed by the parabolic or even barchanoid dunes develop, spreading and
deflation that occurs in the depression. In this case, the lobe overlapping in an increasingly extensive field. These are
migration is usually accompanied by an elongation of the known as transgressive dune fields. The source of sand can
erosive depression. This lengthening usually continues until be limited and the migration of the dunes can lead them to
the depression takes the form of a groove or corridor leave the area where they originally developed. The only
(Fig. 18.10b). The geometry of this corridor tends to increase remainder of them in this area will then be a low-relief eolian
the wind speed when crossing it. The process culminates mantle. Eolian mantles and transgressive dune fields are part
when this corridor completely crosses the profile of the of the same erosive process and are usually related laterally.
foredune and the dune lobe moves to the rear zone, where the
wind acquires a radial disposition when it leaves the corridor.
The dune lobe of a trough blowout can continue to move 18.4.4 Genesis of Minor Structures on the Dune
until it is disconnected from the primary dune. In this case, it Surface
acquires a curved shape and can start to be called a parabolic
dune (Fig. 18.10c). At first, the dune shape is elliptical and The action of the wind on the dune surface generates
continues to be linked to the deflation corridor located in the small-scale structures. In most cases these structures are
primary dune, without the existence of a core in the elliptical ephemeral and are destroyed by the very evolution of the
dune shape that functions as a deflation basin. If the process of dune, but sometimes they can be preserved inside. The
advancement of this dune continues, it will acquire a shape minor structures that often form at the front are usually trains
closer and closer to a parabola, developing in its center a of small ripples that migrate towards the ridge (Fig. 18.11a).
deflation basin that is flanked by the two elongated arms of the During low-speed winds they tend to concentrate in the most
parabola. This is the type called a long-walled parabolic dune. depressed areas, while during moments of high wind
It must be taken into account that both types of parabolic intensity they form in the shaded areas, under the protection
dune can also develop during the total dismantling of the of plants or the dune crest.
primary dune, when different sections of the primary dune The back side is usually dominated by avalanche pro-
begin to migrate landwards at different rates. The final result is cesses that form sheets tilted towards the land that tend to
the development of parabolic dunes not linked to an existing achieve an angle of repose. These avalanches originate on
primary dune. This process is usually associated with episodes the dune crest by destabilization and generally first generate
of massive destruction of the vegetation cover. The natural an erosive groove through which the sand slides. The friction
Fig. 18.10 Evolution from a saucer blowout in a primary dune to a secondary parabolic dune (Based on [2])
Fig. 18.11 Minor structures on the dune surface. a Wind ripple trains on the crest of a foredune. b Avalanches on the back of a parabolic dune
and detail of the internal structure
of the sand in this groove causes the deposit of parallel origin of the sand is usually linked to wave processes that
sheets that finally fill the groove (Fig. 18.11b). subject the grains to multiple sedimentation cycles which
wear away their surface. It must be taken into account that,
once the grains pass into the dune system, they can still be
18.5 Sediments and Internal Structure reworked by the waves again or several times more during
the processes of storm erosion and fairweather reconstruc-
The dune sediments present a characteristic textural maturity. tion. This explains why the sands are composed of very
They are normally very well-sorted sands, because the wind rounded grains. This process of reworking in multiple cycles
is the agent that best classifies grains. In coastal dunes, the also means that, from a compositional point of view, the
18.5 Sediments and Internal Structure 265
dunes are normally composed of the most stable minerals As for the internal structure, in general terms it could be
such as quartz, although heavy minerals are also generally said that the entire internal structure is composed of med-
concentrated in the dunes. In coastal carbonate systems, some ium- to large-scale cross-bedded sets that tilt in the direction
dunes are mainly composed of allochemical elements such as of wind transport. However, this simple description hides a
bioclasts, oolites or intraclasts. In these cases, the grain size is much more complex reality. Coastal dunes usually present a
usually somewhat larger, since the specific weight of calcite greater diversity and complexity than desert dunes. The
is lower than the more stable silicates. In evaporative coasts, simple fact that the internal structure of coastal dunes is
there are also dunes composed mainly of gypsum grains. influenced by vegetation already makes a significant differ-
The dunes developed in lithologies susceptible to chem- ence. This description also does not include such
ical processes can produce cementation phenomena that singularities.
contribute to the consolidation and lithification of the dune A first distinction could be made between the internal
deposits. Lithified dunes are known as eolianites. The term structures of primary and secondary dunes, since the fore-
eolianite was proposed by Sayles [23] to refer to the lime- dunes are characterized by the process of accretion, while the
stone dunes of the Bermuda Islands, which have a carbonate secondary dunes are characterized by migration; these pro-
nature. For this reason, some authors tend to identify the cesses are marked in the geometry of their respective sets of
term eolianite with the calcareous composition of the dunes. cross-bedding.
Fig. 18.12 Internal structure of an established foredune. The upper part of the figure shows a GPR record and its interpretation. The lower
photographs show the internal structure discovered during the formation of washover channels
18.5.1 Foredunes disturb the cross-stratification, especially in the central area

of the dune.
The internal structure of the foredunes is characterized by In detail, there are two minor structures that can be
the presence of sets of trough cross-bedding, separated by observed in the sheets that make up the sets of cross-layers:
reactivation surfaces (Fig. 18.12). The internal stratification the cross-lamination corresponding to the migration of small
presents a greater continuity in the core of the dune, with a ripples and the filled grooves that correspond to the ava-
wedge shape towards both front and rear areas. Some sets lanches which occur on the leeward side.
appear truncated by others, showing that among the delim-
iting surfaces are erosive disconformities. The complete
structure corresponds to a stack of sets. In humid climates, 18.5.2 Blowout Lobes
the presence of vegetation influences the internal structure of
the dune. In addition to contributing to the growth of the The dune lobes of the blowouts have an even more complex
dune, the vegetation is encompassed by the sandy sediment structure than the foredunes. The core of these dunes may
in such a way that not only the roots but also the entire plants present a relict structure made up of remains from the rear of
Fig. 18.13 Internal structure of a blowout lobe. The upper part of the figure shows a GPR record and the lower part shows its interpretation. The
numerous parabolas correspond to the presence of vegetation
18.5 Sediments and Internal Structure 267
the foredune. Above this, sets of curved cross-stratification grooves corresponding to the leeward face avalanches. The
are developed as a result of vertical growth, on which sets of sets on the windward side are clearly cut by the topographic
plates inclined towards the ground are arranged. The internal surface as a result of the migration.
structure becomes more complex towards the top, since, as
the dune lobe grows, it can include existing vegetation at the
back of the dune. Meanwhile, pioneer plants may try to 18.5.4 Interdune Sediments
colonize the blowout lobe during periods of slower growth.
All these plants are encompassed by the growth of the dune The deflective interdunes do not present sediment except for
lobe and incorporated into the internal structure, increasing the residual lags and some laminar sand deposits where
its complexity (Fig. 18.13). ripples develop. These interdunes are preserved as uncon-
formity surfaces. However, depositional interdunes may
present characteristic sediments whose nature will depend on
18.5.3 Parabolic Dunes the relationships of the interdune with the water level. The
characteristic common to all interdune deposits is the sedi-
The internal structure of the parabolic dunes is composed of mentation in sub-horizontal layers since its genesis is not
sets of planar cross-beds or cross-beds with a slightly curved linked to dune migration.
base, separated by reactivation surfaces between sets of The most characteristic interdune deposits are those that
different slope (Fig. 18.14). The inclination of the cross-beds occur in relation to the existence of a sheet of water that
ranges from 20º to 40º. Some internal levels present minor covers all or part of the interdune. Under these conditions,
cross-laminations correlated to the migration of wind ripple swampy or lacustrine sediments can be deposited. These
trains. In section, parallel to the crest, there are filling sediments are obviously very much influenced by the sandy
Fig. 18.14 Internal structure of a parabolic dune. The upper part of the figure shows a GPR record and its interpretation. The lower photograph
shows the internal structure of an Eolianite
material introduced by the wind, although they are pre- 8. Goldsmith V (1973) Internal geometry and origin of vegetated
dominantly composed of fine material (clay or silt). Inter- coastal sand dunes. J Sediment Petrol 43:1128–1143
9. Goldsmith V (1985) Coastal dunes. In: Davis RA (ed) Coastal
dune lake sediments may have abundant freshwater sedimentary environments. Springer, New York, pp 171–236
microfauna such as foraminifers, ostracods and diatoms, as 10. Hesp PA (1988) Foredune morphology, dynamics and structures.
well as macrofauna of bivalves, gastropods and worms. All J Sediment Geol Special Issue: Aeolian Sediments 55:17–41
these organisms are responsible for a high degree of bio- 11. Hesp PA (1999) The beach backshore and beyond. In: Short AD
(ed) Handbook of beach and shoreface morphodynamics. Wiley,
turbation. Swamp sediments are strongly influenced by Brisbane, pp 392
plants, and peat formation is frequent in these environments. 12. Hesp PA (2002) Foredunes and blowouts: initiation, geomorphol-
Often, the water level undergoes oscillations that give the ogy and dynamics. Geomorphology 48:245–268
flooded interdune environments a short-lived character. In 13. Hesp PA, Hyde R (1996) Flow dynamics and geomorphology of a
trough blowout. Sedimentology 43:505–525
humid climates, periods of drying out can be accompanied 14. Hotta S, Kubota S, Katori S, Horikawa K (1984) Sand transport by
by wind deflation of these sediments and during these wind on a wet sand surface. Coast Eng 19:1265–1281
moments surfaces of unconformity can be generated. In arid 15. Kelletat D (1995) Atlas of coastal geomorphology and zonality.
climates, the drying of the interdune lagoons is accompanied J Coastal Res Special Issue 13:286
16. Klijn JA (1990) Dune forming factors in a geographical context.
by evaporation, so it is common to find evaporites associated In: Bakker TWM, Jungerius PD, Klijn JA (eds) Dunes of the
with these interdune spaces. European coasts, Catena, Supplement vol 18. pp 1–14
17. Martínez ML, Psuty N (eds) (2004) Coastal dunes: ecology and
conservation. Springer, Heidelberg
18. Nordstrom KF, Arens SM (1998) The role of human actions in
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Geological Survey Professional Paper 1052, pp 137–140
Tide-Dominated Systems I:
Inlets and Tidal Deltas 19
the position of their channels with jetties and maintaining

19.1 Introduction
their depths by dredging.
Keeping these inlet channels open is not only important
Tidal inlets are channels that separate different barrier
for the development of ports that are located in lagoonal
islands or are located between a barrier and the mainland. It
waters, but also to preserve the ecology of the natural
is through these channels that the mechanism of tidal cir-
environments that are associated with these systems, since
culation between the open marine environment and the
these places are used as breeding grounds for many species
environments protected by the barrier takes place. Tidal
of marine fauna.
deltas are sandy bodies located at the ends of the tidal inlets
There are several systems in the world that are very well
in both directions of the tidal currents. Ebb-tidal deltas are
studied, such as those on the East Coast of the United States
those located on the sea front, in contact with the nearshore
and the Wadden Sea [3], but there are also well-documented
area, while flood-tidal deltas are developed at the back
cases on the coasts of Iceland, Portugal and Spain, as well as
barrier area, in contact with the semi-restricted body of water
other less-studied coasts such as Brazil, Senegal, Ivory Coast
represented by the lagoon.
and Mozambique.
Conceptually, tidal inlets and tidal deltas are defined as
part of the barrier island systems (Fig. 19.1a), where the
barrier island constitutes the confining element and the tidal
inlet is the channel that separates two different islands.
However, later tidal deltas have come to be defined as
Although factors such as sediment input and the initial coast
possible elements of other coastal systems [19], such as
slope significantly determine the dimensions of deltas, other
estuaries confined by barriers (Fig. 19.1b) or barrier reef
factors such as tectonic and eustatic conditions may even
systems (Fig. 19.1c). In all cases, the absence of confining
inhibit their development. The main factors that control the
conditions, both seaward and landward, allows the building
genesis of tidal deltas and their short-term dynamics, how-
of extensive sandy bodies that are essentially very similar
ever, are tidal currents and wave energy [3].
morphologically and genetically to the underwater portion of
river deltas. Tidal deltas can theoretically arise on any
depositional coast where the sandy input is adequate and
19.2.1 Tidal Currents
where the substrate physiography and relative sea level
fluctuations allow bodies with this geometry to develop [6].
The action of the tidal currents is the main physical process
Because they are subjected to the action of tidal currents
acting on the deltas. The speed of the currents depends
and waves, these environments have a high dynamic
directly on the volume of water that circulates through the
mobility and their position and morphology is in constant
tidal inlet draining the protected part of the barrier system.
evolution. As they correspond to passage environments
This volume of water drained by the tide is known as the
between open and restricted waters, navigation through these
tidal prism and it depends on the tidal range in relation to
systems has always historically been a factor to be taken into
the dimensions and morphology of this restricted area.
account. In the sixteenth to eighteenth centuries, many
The dimensions, shape, dynamics, distribution and
shipwrecks took place in these passages when vessels tried
abundance of tidal deltas were originally associated with the
to take refuge in the restricted systems using charts that did
magnitude of the tidal range [16]. For this author, the
not reflect these changes. This is why, today, many of these
abundance of tidal deltas would be at a maximum on coasts
environments have been artificially modified by stabilizing

https://doi.org/10.1007/978-3-030-96121-3_19
270 19 Tide-Dominated Systems I: Inlets and Tidal Deltas
Fig. 19.1 Tidal deltas in different coastal systems. a Associated to a barrier island system (Fuseta, Portugal). b Associated to barrier estuaries
(Foz, N Spain). c Associated to reef keys (Nassau, Bahamas). (Images by Landsat, Google Earth.)
with tidal ranges between 2 and 2.5 m, then decreasing energy balance between the tidal currents and the dominant
sharply towards greater amplitudes so that they would no waves [16]. With this new criterion, tidal deltas would be
longer form on coasts with tidal ranges greater than 5 m. typical of mixed-energy coasts, decreasing their frequency
This probability would also decrease towards smaller ranges, when one agent dominates the other (Fig. 19.2). This
although not so abruptly, so that tidal deltas would appear, decrease in frequency when the tide becomes more impor-
though less frequently, even on microtidal coasts with tant is related to the absence of barriers on the coasts where
almost no tidal influence. Thus, according to this criterion, tides dominate. The number and size of inlets also decrease
the distribution of tidal deltas along the coasts of the world when the waves become dominant, as the wave bars gen-
would be determined by the tidal range. erally tend to close them.
While flood-tidal deltas are subject only to tidal currents The energy balance between tides and waves influences
in and out of the lagoon, ebb-tidal deltas are further influ- not only the abundance of tidal deltas on the coasts, but also
enced by tidal currents that run parallel to the shoreline. the morphology of tidal inlets and associated tidal deltas. [9]
These currents are usually of lesser magnitude than the distinguished four types of inlet morphology depending on
currents that circulate through the tidal inlets. Nevertheless, the dominance of one or another agent (Fig. 19.3). The
they have an important effect on the deviation of these presence of two different typologies corresponding to mixed
ebb-tidal deltas, generating an asymmetry factor on the energy conditions highlights the significance of these
orientation of the inlets and on their morphology. systems.
19.2.2 Wave Energy 19.3 Morphology and Sub-environments
The genesis of the barriers is related to the action of the There are differences in the distribution of processes and
waves, so this factor must also be taken into account as a facies within flood- and ebb-tidal deltas, as well as their
dynamic agent in the inlets that separate them. The waves morphological variations, so they will be considered sepa-
developed during storms can even be a determining factor in rately here.
the creation of new inlets from overwash processes, facili-
tating the exit of the tide through them. In addition, the swell
is the main agent that takes charge of closing some inlets by 19.3.1 Ebb-Tidal Deltas
means of the attachment of parallel bars to the coast when
these lose functionality. For this reason, the waves represent The morphological model of an ebb-tidal delta (Fig. 19.4)
a crucial factor, both in the number of inlets in barrier island consists of several sub-environments:
systems, and in their immediate evolution.
Ebb-tidal deltas are permanently subjected to the action • The body starts from a wide and deep channel dominated
of waves. At the front of these deltas there is a conflict by ebb currents. This is known as the main ebb channel.
between the capacity of sediment transport by tidal currents • This channel is flanked by elongated channel margin
and the capacity of sand remobilization by waves. While ebb linear bars in a perpendicular or oblique direction to the
currents tend to generate sand bodies perpendicular to the coast.
coastline, waves rework the sand to try to place it in parallel. • These bars separate the main ebb channel from two
In this way, the influence of waves is unequivocally mani- marginal flood channels.
fested in the existence of wave bars in the frontal zone of the • Towards the sea, the ebb channel connects with a ter-
ebb deltas. minal lobe, which is the most distal part of the delta and
the most important sedimentary body. The terminal lobe
originates due to the loss of speed of the tidal ebb when it
19.2.3 Combined Action of Waves and Tidal meets the waves and deposits its sedimentary load,
Currents mainly sand.
• On the sides of the terminal lobe and on the channel
The conflict between the sediment mobilization capacity of margin linear bars, the waves cause swash bars to
tides and waves would suggest that the final morphology of migrate, which can be attached to the barrier island or fall
the tidal inlets and, above all, of the ebb-tidal deltas, depends into the marginal flood channel to be reworked by the tide
on a balance of forces. Although Hayes [16] had associated [14].
the morphology and distribution of tidal deltas with the tidal
range, some years later the same author studied some par- The different relative energy between tidal currents and
ticular cases in more detail, and linked these factors to the waves that has been previously mentioned gives rise to
Fig. 19.2 Frequency of barrier

islands, inlets and tidal deltas
according to the dominance of
tide and wave energy, adapted
from Hayes [16]

different types of tidal inlets
according to the balance of
energy between tides and waves
[9]
Fig. 19.4 a General

morphological model for an
ebb-tidal delta as suggested by
Hayes [16]. b Example showing
the elements of the general model
important morphological variations in the ebb deltas. This (2) Wave-dominated ebb deltas, on the other hand, are
variability can be summarized by distinguishing the three usually smaller in length as well as wider, with a form
types of ebb-tidal delta (Fig. 19.5). dominantly parallel to the coast (Fig. 19.5b). In this
case, the inlet is usually shallow and highly unstable
(1) Tide-dominated ebb deltas, which are characterized by with constant changes in position and morphology.
a perpendicular arrangement to the coast (Fig. 19.5a). The marginal flood channels are generally absent. The
In this type of delta, the tidal inlet is erosive and very terminal lobe of the delta takes the form of a crescent
deep, sometimes even reaching the substrate. This depth and is often found in the intertidal fringe. This pro-
reduces its mobility, so that it does not usually present duces a number of swash bars that attempt to com-
migration. Its sandy sedimentary body develops with pletely close the inlet because tidal currents are lower.
greater length than width, reaching deeper and further They tend to have a marked asymmetry and a high
areas from the coast. rate of migration.

ebb-tidal deltas.
a Tide-dominated (Nabule inlet,
Myanmar). b Wave-dominated
(Machesse inlet, Mozambique).
c Mixed energy (Saharabedi inlet,
India). (Images: Landsat from
Google Earth.)
(3) The third type of ebb-tidal delta is the mixed type. It has wide and deep inlet appears, connecting directly to a
a smooth and rounded morphology, in response to the main ebb channel that becomes progressively shallower
combined action of tides and waves. Of the three types, towards the terminal lobe. The marginal flood channels
this is the one with the most complex dynamics and may be absent or present only at one of the margins.
sedimentology, presenting an intermediate character Marginal bars tend to be triangular rather than linear in
between the other two types (Fig. 19.5c). Here, again, a shape and develop abundant swash bars and other
bedforms due to tidal action. A similarity to far from the inlet (Fig. 19.6d). These two situations will tend
tide-dominated deltas is that the terminal lobe is subti- to present a greater symmetry. When the currents of the open
dal. However, this is usually very shallow. zone are asymmetrical and one of the currents is greater than
the other, it induces an asymmetry in the orientation of the
The presence of wave bars is very significant in deltas (Fig. 19.6b, c).
wave-dominated and mixed-energy deltas, where these Later, [32] added to these tidal current interactions the
migrate over wide marginal bars. Then, these behave like incidence of wave trains on the shoreline (Fig. 19.7). For
swash platforms. However, this is a minor process in this author, the relative importance between waves and
tide-dominated deltas, where the marginal bars take on a outgoing ebb currents is the factor that really controls the
more linear character and are arranged perpendicular to the geometry and dimensions of ebb deltas. In this case, the tidal
coast. Another important difference is that in tide-dominated prism controls the speed of the outgoing currents. The
deltas the terminal lobe is further away from the coast and presence of a frontal wave brings the terminal lobe closer to
the wave action on it is less intense [3]. In general terms, land (Fig. 19.7a), while oblique waves add or subtract tidal
deltas tend to be smaller when the wave influence increases. currents from the open zone to generate a coastal drift
A common characteristic of all ebb deltas is the presence of component that deflects the outflow backwash (Fig. 19.7b–
bedforms in all environments, although these bedforms are d). A well-defined littoral drift increases the asymmetry. This
mostly oriented according to the dominant current. asymmetry of the ebb deltas also induces an inlet instability
Both wave-dominated and mixed-energy deltas are usu- that manifests in the migration of the entire system associ-
ally asymmetrical. Oertel [28] researched studies of the ated with the tidal channel.
deltas of the East Coast of the United States and attributed
the causes of this asymmetry to the direction of the ebb
currents that circulate in the open coastal zone and divert the 19.3.2 Flood-Tidal Deltas
ebb that comes out of the inlet. According to the relative
importance of these currents, he differentiated four different The shape and dimensions of the flood deltas are not related
types of morphology (Fig. 19.6). When the outgoing ebb to the balance between tides and waves, as the waves do not
current has little importance with respect to the external act on this environment. There is, however, a variation in
currents, the terminal lobe will have a longitudinal devel- their shape depending on the tidal amplitude. Broadly
opment to the coastline and a position closer to land speaking, it can be said that, on microtidal coasts, the flood
(Fig. 19.6a). Conversely, when the outgoing currents are deltas tend to be multilobate, since the reworking by the ebb
much greater than the currents in the open zone, the terminal is minimal. These are the narrowest deltas, rarely reaching
lobe will have a greater development being located in areas 3 m in thickness. In contrast, in areas where the tidal range is
Fig. 19.6 Different

combinations of in/out tidal
currents with outer tidal currents
to obtain different ebb-tidal delta
morphologies, adapted from
Oertel [28]
Fig. 19.7 Different

combinations of in/out tidal
currents with outer tidal currents
and oblique wave trains to obtain
different ebb-tidal delta
morphologies, adapted from Sha
[32]
greater than 1.5 m, the velocity of the flood currents is high the associated tidal deltas develop when the barrier stabi-
enough to transport a large amount of material. Then, the lizes. The second possibility is that the inlets originate from
flood currents rework the sediment, creating their own a process of breaching of the barrier. Normally, this process
morphology, and the delta usually acquires a horseshoe of rupture is associated with the dynamics of storms and the
shape. incidence of overwash processes. These processes originate
The general model reflects this second situation new inlets in previously stabilized barriers, being able to
(Fig. 19.8). It consists of a flood ramp connected to the tidal generate islands from spits or to divide previously existing
inlet. This flood ramp loses depth and thus allows bedforms islands.
to migrate in the flood direction. The flow ramp can develop Once formed, an inlet can tend to migrate when the
a tidal flat in its shallowest area. This tidal flat is shaped like incidence of the waves is oblique and is accompanied by
a horseshoe and is surrounded by very shallow flood chan- littoral drift phenomena. Normally, the migration of inlets is
nels connected to the ramp. The boundary of the semicir- associated with their asymmetry and the dominating agent,
cular tidal flat is its highest topographical part which being much greater in the cases of wave-dominated and
partially protects it from the action of ebb, hence its name mixed-energy deltas.
ebb shield. The ebb current circulates around the front of the The appearance of a new inlet by a breaching process
delta and can sometimes overcome this screen by generating implies a division of the tidal prism between the previous
overflow deposit named spillover lobes. It is also the ebb and the new inlet. This always induces a decrease of the tidal
current that ends up circling the delta to connect to the inlet currents across the two inlets. The decrease of the tidal
through marginal flood channels, which are flanked by currents implies an increase of the relative influence of the
longitudinal ebb spits. waves, which tries to close the inlet by attaching frontal bars
reworked from the ebb-tidal deltas. Generally, one of the
inlets ends up closing and the system chooses to maintain the
19.4 Dynamics and Facies new inlet while closing the old one. This means that barrier
systems can have ephemeral inlets, but also that the opening
19.4.1 Origin and Mobility of the Inlets of new inlets usually starts migration and barrier renewal
cycles. An example of this type of cycle generated by the
There are different origins of inlets and tidal deltas. The first opening and migration of an inlet was analyzed in Chap. 16
of the possibilities is intimately associated with the birth of (Fig. 16.12).
the barriers. If the barrier originates separated from the The progressive loss of tidal prism due to the infilling of
continent and from other barrier islands, the separation the lagoon into tidal flats and marsh environments usually
channels are already born with the barrier itself. In addition, means the increase of wave dominance in the ebb deltas
19.4 Dynamics and Facies 277
Fig. 19.8 a General

morphological model for a
flood-tidal delta, adapted from
Hayes [16]. b Example showing
the elements of the general model
associated with the inlet. The final stage of the cycle cor- This diagram shows how the inversion of the currents to a
responds to the total filling of the back barrier system and the flood situation occurs earlier in the marginal flood channels
final closure of all the inlets. than in the main ebb channel (situation marked in Fig. 19.9
with an ellipse). Thus, in the last moments of the cycle, the
flood begins to penetrate the lagoon through the marginal
19.4.2 Dynamics and Facies of Ebb-Tidal Deltas channels, while the ebb conditions in the main channel are
still maintained. This time interval results in the current
Ebb-tidal deltas develop large differences between the main circulation model (Fig. 19.10) presenting a transitional sit-
ebb channel and the marginal flood channels in terms of the uation between the general ebb and flood conditions
asymmetry of velocities and duration of tidal currents (Fig. 19.10b).
(Fig. 19.9). The main channel develops a time/velocity Regarding the sediment transport and the generation of
curve in which a clear asymmetry is observed in the direc- bedforms, in the main ebb channel the velocity conditions
tion of the ebb, in both the developed velocities and duration necessary for the migration of ripples are reached only half
of these currents. On the other hand, in the marginal flood an hour after the beginning of the ebb current. About another
channels the asymmetry is opposite, with greater flood half an hour later, the velocity necessary for the migration of
velocities and longer duration being observed. dunes is reached. Under these conditions, the dunes remain
under migration for more than three and a half hours.

Conversely, during the flood semicycles, the speed required
for the dune movement is maintained for only a little more
than 75 min (Fig. 19.11a). Thus, in the main ebb channel,
cross-laminations and cross-bedding are usually preserved,
corresponding to the migration of ripples and dunes in the
ebb sense. These calculations are made for medium sand
sizes, which are the ones that preferentially circulate along
these channels. Nevertheless, larger sand levels and gravel-
size shell fragments with 2D cross-bedding may also be
present. In the marginal channels, the opposite occurs.
During the flood, the velocity conditions necessary for the
migration of dunes are only maintained for about 40 min
(Fig. 19.11b), while during the ebb, these conditions barely
Fig. 19.9 Time/velocity curves in a main ebb channel and a marginal
flood channel for a tidal range of 2.5 m (data from Morales et al. [25]). exceed two hours. Due to this fact, small-scale cross-
The ellipse highlights a situation when the marginal flood channel laminations corresponding to the migration of ripples and
already has flood conditions, whereas the main ebb channel maintains cross-bedding generated by dune migration, both in the
the ebb current
Fig. 19.10 Conceptual model

showing the general tidal
circulation in an ebb-tidal delta.
a During ebb conditions.
b Interval of flood inversion in the
marginal channels. c During flood
conditions, adapted from
Hubbard and Barwis [21]
direction of the flood, are mainly preserved [25]. This

dynamic is consistent with that described by other authors
(e.g., [3, 21]).
In channel margin linear bars, the current pattern is much
more complicated, as they do not stick to a channel and have
rotational rather than bidirectional patterns. In addition, it
should be noted that these bars are emerged during the last
moments of the ebb and first moments of the flood. In
general, ebb currents dominate. However, flood currents
from the marginal channel to the main one can also play a
role [21].
Due to this distribution of currents, there is a wide vari-
ability of bedforms with different dimensions and orienta-
tions. Thus, in the areas that flank the main ebb channel, 3D
dunes of metric dimensions usually develop. Sometimes,
these shapes have superimposed linguoid ripples
(Fig. 19.12a) and sinuous ripples with perpendicular direc-
tions may be installed in the troughs between ridges of the
larger forms (Fig. 19.12b). At the seaward edge of the swash
platform, swash bars are developed and start to migrate
inward (Fig. 19.12c). Extensions between different bars
develop sinuous wave ripple fields with a general direction
more or less parallel to these bars (Fig. 19.12d).
In the frontal lobe, there is a pattern of currents similar to
the main ebb channel, although with lower speeds, since the
section is larger. Therefore, ebb bedforms and structures
Fig. 19.11 Time/velocity curves of Fig. 19.9, where the thresholds for dominate, although the grain size is finer.
development of ripples (yellow) and dunes (orange) are marked. The The action of waves also affects the frontal lobes, since
curves correspond with the main ebb channel a and a marginal flood
they are pounded for quite some time due to their shallower
channel b (data from Morales et al. [25])
Fig. 19.12 Different bedforms

developed in the marginal linear
bars (swash platforms). a Medium
3D dunes with superimposed
linguoid ripples located in the
border of the main ebb channel.
b Medium 3D dunes with sinuous
crests and perpendicular ripples
developed on the troughs.
c Intertidal swash bars developed
on the front of the platform.
d Sinuous crested wave ripples
located on the troughs between
intertidal swash bars
Fig. 19.13 Bedform distribution

and sand transport patterns in a
mixed-energy ebb-tidal delta
system (Piedras inlet, Spain). This
scheme is based on the type and
direction of the main bedform lee
facies [24]
depth. This swash that takes place in the frontal lobe has a margin bars and the marginal flood channels), there are also
special character. On the one hand, the waves are refracted usually interleaved sheets of mud that correspond to the
by changing direction, losing energy and depositing the settling of the material transported in suspension that takes
material they transport. On the other hand, these are waves place during the moments of slacks, when the currents stop
without a runoff, so that the process also produces an inward completely.
migration of bedforms, especially during the moments of All the characteristics described in each sub-environment
flood. These bedforms are usually swash bars and 2D dunes, of the ebb-tidal deltas are summarized in Table 19.1.
as well as 3D dunes and linguoid ripples.
The forms are not generally preserved in the frontal lobes,
although they are preserved in the channel margin bars [20]. 19.4.3 Flood-Tidal Deltas
A good scheme of the distribution of bedforms and their
preferential directions of migration in the environments From a dynamic point of view, there are great differences
associated to a mixed energy ebb-tidal delta system was between the different elements of the delta. As with the
proposed in the work of Morales et al. [24] based on the ebb-tidal deltas, the velocities and durations of the tidal
Piedras inlet in SW Spain (Fig. 19.13). currents are clearly asymmetric. There are, however, differ-
In the shallower areas of the delta and, above all, in those ent types of asymmetries in the different sub-environments
places protected from the action of waves (such as the less of the delta (Fig. 19.14). In order to better understand the
energetic areas of the main channel, adjacent to the channel dynamic functioning of the flood-tidal delta, it is necessary
Table 19.1 Summary of the Sub-environment Processes Bedforms Sedimentary structures Grain size
main characteristics of the
different sedimentary Main ebb Tidal ebb and Ripples and Metric and decimeter scale Fine and
sub-environments within an channel flood dunes in the cross-layers inclined towards medium
ebb-tidal delta reworking ebb direction the sea sand. Shell
lag
deposits
Marginal flood Tidal flood Ripples in the Decimeter scale curved base Fine and
channel and ebb flood direction cross-lamination towards the medium
reworking land. Flaser beds sand. Silt
Channel margin Tidal currents Ripples with Decimeter scale Medium
bars with rotational directional cross-lamination sand. Shell
patterns. dispersion. fragments
Wave swash Swash bars
Frontal lobe Tidal ebb. Ripples in the Metric scale cross-bedding Very fine
Wave direction of the inclined towards the land. sand. Silt
oscillation ebb reworked Cross-lamination of decimeter
by waves scale. Flaser beds
Fig. 19.14 Morphology and flow patterns in a flood-tidal delta. curves, the thresholds for migrating bedforms are indicated: ripples
a Current velocity/time in the flood ramp. b Current velocity/time in the (yellow) and dunes (orange)
marginal ebb channels. c Current velocity/time in the ebb shield. In all
to consider the velocity/time curves in three different zones: dominate (Fig. 19.14b). Most of time they are self-currents,
(1) the flood ramp; (2) the marginal ebb channels flanking able to make ripples migrate. Nevertheless, dune migration
the ramp; and (3) the tidal flat front (ebb shield). conditions can be reached during the ebb cycle for about an
Similar patterns of tidal currents and bedform migration hour (Fig. 19.15b). The typical structures of these environ-
are present in the flood ramp. The curve shows a clear ments will then be complex small-scale cross-laminations
asymmetry in the flood direction (Fig. 19.14b), so that once sloping in the direction of the ebb. However, the same
the flood current starts, the minimum velocity required for structures sloping in the opposite direction are also less
the start of ripple migration is reached almost immediately. abundantly present, and together they form the typical her-
About one hour later, the 2D and 3D dunes begin to migrate, ringbone structures (Fig. 19.15d). In all the sectors, more or
and these conditions remain for at least three hours. Con- less thick layers of fine material usually appear interspersed
versely, during the ebb, only the velocity required for the with the sands. These layers correspond to the settling of
start of the ripple migration is reached. These conditions are material transported in suspension during the moments of the
maintained for about three and a half hours. Consequently, current lapses. These constitute flaser and wavy bedding
the dominant bedforms are dunes and ripples oriented in the structures, depending on the average energy of the place
flood direction (Fig. 19.15a). The migration of these forms where they appear (Fig. 19.15e).
generates cross-stratification and cross-laminations with One situation that differs from those previously descri-
mostly landward-sloping sheets (Fig. 19.15c). bed is that which occurs on the ebb shield, which is a
A situation contrary to that described occurs in the mar- shallower area where higher speeds are reached
ginal ebb channels which flank the delta as well as in the (Fig. 19.14c). In this case, there is a near symmetry of tidal
spillover lobes. In these environments, ebb currents currents. Consequently, the conditions for the migration of
Fig. 19.15 Different bedforms

developed in the
sub-environments of a flood tidal
delta. a 3D dunes with
superimposed ripples on a flood
ramp. b 3D dunes and ripples on
an ebb spit. c Cross-bedding of a
flood dune with superimposed
ripples. d Herringbone structure
of a reversing form developed on
an ebb spit. e Interbedded mud
and cross-bedded sands.
f Structures on an ebb shield
3D dunes are reached during both ebb and flood

(Fig. 19.15f). The particularity is that the ebb and flood 19.5 Facies Models
circulate in perpendicular directions. In this area, 2D and
3D dunes are dominantly developed, both oriented in flood The depositional models proposed for these environments
and ebb directions. are built on ideal sequences. Thus, their theoretical spatial
Frequently, the tidal flats of the central zone of the delta variations have been obtained mostly in existing tidal deltas.
quickly aggrade until they are colonized by halophytic This means that they are comparable with the geological
vegetation and transformed into marshes. At this point, the record under conditions of maximum preservation potential.
flood stops going beyond this zone and sticks to the flood It is evident that the general models suffer variations in
channels that surround it. In this situation, this environment thickness and geometry of the sedimentary bodies, depend-
increases its depth because the currents increase. From then ing on the type of delta as stated in the introduction.
on, all the water exchange between the lagoon and the sea
takes place through these channels and the flood delta stops
working as such. The evolution continues when new flow 19.5.1 Ebb-Tidal Deltas
deltas are built at the end of these channels. All of the
characteristics described in each sub-environment of the In general terms, it can be said that the facies of the ebb-tidal
flood deltas are summarized in Table 19.2. deltas are arranged over other external facies of the barrier
19.5 Facies Models 283
Table 19.2 Summary of Sub-environment Processes Bedforms Sedimentary structures Grain size
dynamic and sedimentary
characteristics of the different Main channel Tidal Ripples and dunes in Cross-bedding of decimeter Fine and
sub-environments linked to the and flood ramp flood and the flood direction and metric scale inclined medium
flood-tidal deltas ebb towards the land sand. Shell
reworking lag
deposits
Tidal flat Tidal Ripples in the flood Decimeter scale curved-base Fine and
flood and direction cross-bedding inclined medium
ebb towards the land. Flaser, sand. Silt
reworking wavy and lenticular bedding
Marginal ebb Tidal ebb Ripples in the ebb Decimeter scale curved base Medium
channels and flood direction cross bedding inclined and fine
reworking towards the sea. Herringbone sand. Silt
and flaser beds
Ebb shield Tidal ebb Ripples and dunes in Decimeter scale Fine sand
and flood the flood direction cross-bedding. Herringbone
reworked at the beds
sides by the ebb
island system, such as the nearshore facies. Assuming a sequence proposed by Imperato et al. [23] for the US East
stable sea level, the internal disposition of the facies gen- Coast.
erated in the different components of the tidal delta corre- In the proximal sector (Fig. 19.16a), the sequence from
sponds to a regressive model of progradation. In this base to top would consist of:
scenario, both ebb and flow channels fill up when they are
abandoned (by breaching), when they migrate or when they (a) Erosive contact with nearshore facies.
lose an effective section due to the decrease of the tidal (b) Lag deposit of shells and shell fragments at the base of
prism. An ideal sequence was proposed by Sha and De Boer the marginal flood channel, on which are arranged sets
[34] for Frisian Island ebb deltas. This is consistent with the of medium to coarse sands with flood-oriented trough
Fig. 19.16 Ideal sequences for

an ebb-tidal delta, adapted from
Sha and De Boer [34]
cross-bedding of decimeter scale. These facies are not facies are arranged over the shoreface facies or even over the
very thick (less than 1 m) due to the fact that they are offshore facies if the delta is large enough.
generated during the operation of the channel, when the
dominant process is the sedimentary bypassing of sands
towards the tidal inlet. 19.5.2 Flood-Tidal Deltas
(c) Deposit of more than 2 m of fine and very fine sands
with ripple-type cross-lamination. Dominant bedforms The sequence that results from the process of a flood-tidal
are oriented in the flood sense and less abundantly in delta advancing into the interior of the lagoon is a regressive
the ebb sense. These facies are interlaminated with sequence of shallowing. This sequence presents at the base
muds in variable proportion forming flaser and wavy the sediments corresponding to the deepest environments,
bedding structures. It is a very bioturbed body that which will be progressively transformed until reaching the
corresponds to the infilling stage of the marginal flood supratidal zone. In general terms, the facies of the flood
channel when losing functionality. deltas are arranged over the facies of the lagoon, and they are
(d) These facies, oriented laterally towards the sea, are interleaved both longitudinally and laterally. Like ebb deltas,
interleaved with parallel laminated fine sands with flood deltas can undergo variations in thickness and geom-
abundant lenses of shell fragments and inland-oriented etry. The theoretical sequence is composed of five litholog-
planar cross-bedding. This level corresponds to the ical units [3]:
marginal linear bars and to the swash bars that migrate
over them. The lamination is planar due to the action on (a) Sedimentary continuity with the fine lagoon sediments.
these of spilling-type breakers, without undertow that (b) On the lateral faces of the delta there are 2–3 m of fine
could redistribute the sediment on the surface. sand at the base of the series. These present sets of
(e) The sequence is completed with sets of planar small-scale trough cross-bedding and cross-lamination.
cross-bedded fine sands, corresponding to wave- These structures correspond to the migration of 3D
generated 2D bars that migrate towards the land. dunes and ripples. Normally, (more abundantly) dunes
are oriented in the ebb direction. These facies corre-
In the middle sector (Fig. 19.16b) are the facies of the spond to the typical sediments of the marginal ebb
main ebb channel, which are embedded through erosive channels and ebb spits.
contact with the shoreface facies. These channel facies are (c) Over these facies, the most important sedimentary body
the thicker of the system, being able to exceed 15 m, and of the delta by its size and thickness is arranged. This is
consist of: the one corresponding to the flood ramp and the shallow
flood channels. These consist of metric sets of
(a) Body of more than 5 m composed by sets of medium to flood-oriented planar cross-bedded fine and medium
thick sands with intercalations of shells and shell frag- sands. The sets are separated by laminations of coarser
ments with ebb-oriented trough cross-bedding. These sediments or by sets of ripple-type cross-laminated
correspond to the migration of 3D dunes through the sands. This sedimentary body can exceed 6 m in
bed of a main ebb channel that migrates laterally and thickness depending on the tidal range.
allows the preservation of these forms in the less (d) Limiting the facies of the flood ramp towards the
energetic areas. lagoon, a horseshoe-shaped body of fine sand is located.
(b) Above this level there is about 1 m of fine and very fine This presents ripple-type lamination oriented in a very
sand with flaser bedding structures and abundant bio- dispersed way, although those directions that coincide
turbation. These are interpreted as the less active sectors with the orientation of the limit of the sedimentary body
of the ebb channel. tend to dominate. These are the facies corresponding to
(c) Finally, the top culminates the sequence with about 5 m the ebb shield.
of fine sand with parallel lamination, corresponding to (e) On the top of these facies are the sediments of the tidal
the already described swash bar facies. flat. These are very fine sands with mud intercalations
forming flaser and wavy bedding structures. In any case,
In the distal sector (Fig. 19.16c), fine and very fine sand these are affected by abundant bioturbation. The sands
bodies are developed in which sets of cross-bedding origi- usually present flood-oriented ripple-type lamination.
nate from both the tidal ebb and the wave action. These
correspond to the frontal lobe facies, which laterally trans- This sequence could be covered by saltmarsh mud bio-
form into parallel lamination associated with tidal bundles, turbed by roots when the delta has ceased to be functional.
where spring and neap tidal cycles are recognizable. These On the other hand, the sequence can also be covered by a
body of land-oriented cross-bedded fine sands corresponding and other sandy bodies corresponding to the rest of elements
to the installation of a washover fan. This situation occurs of the barrier island system, respond to different architectural
when the tidal inlet is totally closed, but its traces remain as a schemes.
depressed area of the dune system. This depression can be These relationships have been studied by Hubbard et al.
over-washed by waves during storms. This has been [22], who reduced the geometry of barrier island systems to
observed in the geological record by Murakoshi and Masuda a three-case model according to whether they were domi-
[27] in the Pleistocene infilling of the Paleo-Tokyo Bay nated by tidal currents or wave energy or a combination of
(Fig. 19.17) and also by Boersma [2] in a Miocene the two (Fig. 19.18). These models have been proposed
flood-tidal delta of Rhine Bay (Germany). In the geological assuming a 100% preservation potential and moderate
record, some terms of the sequence can be repeated when upward movement of sea level.
there are pulses of relative sea level rise. Thus, in the tide-dominated model the main sandy bodies
are located outside the island, so that in this case the
ebb-tidal delta is the environment with the greatest thickness
19.5.3 Architectural 3D Facies Model and surface extension. Here, the flood-tidal delta is usually
in the Barrier System Framework absent. This is the model that presents the greatest stability
of the tidal inlet.
The morphological variability of the sandy bodies of tidal Conversely, the wave-dominated model shows a signifi-
inlets and tidal deltas associated with barrier island systems cant development of multilobate flood-tidal deltas. At the
has been explained as a response to the action of tides and same time, the ebb-tidal deltas are usually smaller and
waves. Nevertheless, other factors such as the tidal prism, crescent-shaped in the direction of the coastline. In this case,
freshwater input, the nature of the substrate, the initial slope, the swash platforms are poorly developed. More than one
the sedimentary input and relative sea level movements also tidal inlet and a high migration rate may occur, contributing
exert influence. All these controls make the relationship to the presence of more than one flood delta in the geological
between the sandy bodies of the ebb- and flood-tidal deltas, record, as described by Boersma [2] in the German Miocene.
Fig. 19.17 Stratigraphic

sequence of the Pleistocene
infilling of the Paleo-Tokyo Bay,
adapted from Murakoshi and
Masuda [27]
Fig. 19.18 Conceptual block

diagrams showing the geometry
and 3D relationships of
sedimentary bodies generated by
the three types of tidal inlets,
adapted from Hubbard et al. [22]
The mixed or transitional model presents intermediate 7. Davis RA, Clifton HE (1987) Sea-level change and the preserva-
characteristics. Here, the extension of the ebb- and tion potential of wave-dominated and tide-dominated coastal
sequences. J Sedim Petrol 41:167–178
flood-tidal deltas is usually more equilibrated. However, it is 8. Davis RA, Fox WT (1981) Interaction between wave- and
the model that can present more variations in one or other tide-generated processes at the mouth of a microtidal estuary:
direction, depending on the relative importance of the energy Matanzas River, Florida. Mar Geol 40:49–68
of tidal currents and waves. Usually, there is only one main 9. Davis RA, Gibeaut JC (1990) Historical morphodynamics of inlets
in Florida: models for coastal zone planning. Technical paper 55,
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Estuary mouth (Huelva Coast, S.W. Spain). Mar Geol 172:225– Special Publication. Blackwell Science, Oxford, pp 101–120
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Tide-Dominated Systems II:
Tidal Flats and Wetlands 20
Bahamas or the Trucial Coast in the Persian Gulf. Much of

20.1 Introduction
what we know about the tidal flats preserved in the geo-
logical record comes from research carried out in the exist-
Tidal flats are depositional surfaces where sedimentation of
ing ones through the application of the principle of
mud and sand occurs and that are located in the space limited
uniformitarianism.
by sea level between high and low waters. Because of their
The scientific interest in tidal flats as a sedimentary envi-
location, they are completely covered by water during high
ronment is reflected in the many monographs devoted to their
tide and are exposed to air at low tide (Fig. 20.1). Obviously,
study [12, 20, 37, 25, 26, 42, 43, 45]. In addition to appearing
these are tide-dominated environments and therefore have
as a chapter in a large fraction of the works dedicated to the
minimal wave influence. Thus, they develop along open
general study of sedimentary environments [27, 41, 50, 56,
coasts with low relief and affected by low energy waves
31], among others), there are also numerous articles that are
(open-coast tidal flats) or on coasts with higher wave energy
constantly published in scientific journals focused on the
but in areas protected from direct wave action, behind bar-
dissemination of this topic. In addition to the purely scientific
riers, spits or reefs (back-barrier tidal flats).
engagement with tidal flats, they have also been found to be of
In the first case, when they have developed on low wave
great economic interest due to the deposits of uranium, oil and
energy coasts or macrotidal coasts, tidal flats are born as
natural gas that can be found in these systems.
independent environments and are usually located inside
bays that amplify the effect of tidal currents [15]. The
development of massive deposits of fine sediments results in
this type of coastline being generally known as muddy
20.2 Control Factors and Global Distribution
coasts. The best-studied examples at a global level are found
in Mont Saint-Michel in France, Inchon in Korea, the Wash
20.2.1 Tidal Regime
in England, the Bay of Fundy in Canada, the Bay of San
The distribution of tidal flats on the world’s coasts has been
Sebastian in Tierra del Fuego, Argentina and the Gulf of
classically associated with tidal range. Thus, this type of
California in Mexico. When they appear in protected areas
system was at first described as part of the macrotidal coasts
of high wave energy coasts, tidal flats can also appear
(for tidal oscillations greater than 4 m). Later, tidal flats were
associated with other sedimentary environments (Fig. 20.2).
also described on mesotidal and even microtidal coasts.
In this context, they can develop as sub-environments of
However, tidal flats associated with tidal ranges below 4 m
estuaries, deltas or barrier island systems [17].
were described as exceptional cases, since their abundance is
At present, the widest tidal flat is the Yellow Sea in
considered much lower than on macrotidal coasts.
Korea, which reaches a width of 25 km [6]. Despite its large
In any case, tidal dynamics are responsible for the sedi-
extent, the distribution of its sedimentary texture is similar to
ment dynamics in these environments. It is the tidal current
those described for the smaller tidal flats, such as those of the
that controls the transport, deposition and distribution of
North Sea [57].
sedimentary material in the extension of the plain. In turn,
Most of the current tidal flats are places where mainly
the temporal variation of the currents is regulated by the
siliciclastic sedimentation takes place. This is the case for the
periodic oscillations of the tidal range. These variations
best-known examples. Nevertheless, there are also signifi-
result in modifications to the grain size that can be trans-
cant examples of tidal flats consisting of carbonate and
ported and the bedforms that can be generated. The tidal
evaporite sediments, such as the flats associated with Laguna
range is also responsible for the presence of a marked
Madre in Texas, the northern zone of Andros Island in the

https://doi.org/10.1007/978-3-030-96121-3_20
290 20 Tide-Dominated Systems II: Tidal Flats and Wetlands
Fig. 20.1 Panoramic view of a

tidal flat comparing the moments
of high and low waters (Wadden
Sea, the Netherlands)
vertical zoning, both by the levels of exposure and sub- 20.2.3 Sediment Supply
mergence, as well as by the velocities that the current
develops at each level of the flat. The development of a tidal flat requires a significant supply
All these features are recorded in the sedimentary of sedimentary material. In general terms, it can be asserted
sequence in the form of variations in the internal lamination that the high sedimentation rate of these environments is
of the sediment that is generated in each of these zones. responsible for their characteristic low slope, influencing the
loss of wave energy by dissipation while favoring the
acceleration of tidal currents. In most cases, it is fine-grained
20.2.2 Wave Regime material, although in some areas coarser material can also be
transported. The origin of this material is generally linked to
Following the ideas introduced by Hayes [22], it is not the the presence of river mouths when the tide is associated with
tidal range, but the balance between the tidal range and the estuaries or deltas, although it can also be of marine or
wave dimensions, which determines the possibility of a tidal coastal origin when the sediments come from other nearby
flat developing on a given coast. For this author, the distri- coastal environments.
bution of tidal flats is at its maximum on tide-dominated There are situations in which the absence of a continuous
coasts and decreases on mixed-energy coasts, being mini- terrigenous contribution determines a domain of reworking
mum or absent on wave-dominated coasts. It is understood, processes of precipitated materials in the subtidal areas of
then, that the influence of the waves for the development of this same environment. Then, material generated by bio-
tidal flats must be minimal or null. However, as already logical activity can also be deposited dominantly. In these
mentioned, tidal flats can appear on wave-dominated coasts cases, the nature of the most abundant sediments is car-
as long as the existence of a morphological element gener- bonate or evaporite.
ated by the waves itself inhibits the action of the waves—so,
for instance, the creation of an area of dynamic shade for the
waves in which only the tides act. This explains the presence 20.2.4 Organic Activity
of tidal flats on microtidal coasts and wave-dominated
coasts, as is the case of the Bahamas Islands or the mud flats The activity of the organisms on the tidal flats is of vital
of the East Coast of Florida. importance. As they are tranquil environments, they are
20.2 Control Factors and Global Distribution 291
Fig. 20.2 Development of tidal flats linked to other major environ- Madagascar). c Barrier island systems (example of the Wadden Sea,
ments. a Estuaries (example of a tide-dominated estuary in Amborovy, Germany). (Images: Landsat/Copernicus from Google Earth.)
Madagascar). b Deltas (example of a mixed-energy delta in Ankatrafay,
home to ecosystems with a wide profusion of life, both • Secondly, the organisms (specially plants) can act as a
animal and plant. This influence of the organisms on the screen for the currents by slowing them down and caus-
sedimentary environment, which has already been described ing decantation. Many plants can also trap sediment
in Chap. 12, has a special influence in the case of tidal flats, particles by means of cohesive mucous membranes
where four types of processes related to organic activity (biomechanical sedimentation).
usually occur: • In addition, some organisms are able to modify the
chemical conditions of their surrounding environment by
• Firstly, the accumulation of soft parts, shells or pellets can inducing precipitation or flocculation processes (bio-
lead to the formation of biogenic sediment. chemical sedimentation).
• Finally, the activity of the organisms on the sedimentary coastal flats of the Wadden Sea in Germany and the
substrate causes a significant alteration of the internal Netherlands [47, 48, 49, 35, 36] and also in the Bay of San
structure of the sediment (bioturbation). Sebastian in Tierra del Fuego, Argentina [51, 52, 53].
However, there are cases where there is more complex
zoning, such as the Wash on the east coast of England,
where up to five intertidal zones can be distinguished [13].
20.2.5 Climate Each of these zones has a different distribution of dominant
processes and preserved sediment. Most of the large tidal
In addition to dynamic and biological factors, climate flats described coincide with the existence of a decrease in
introduces notable variations in processes, reflected in the grain size from the subtidal to the supratidal areas.
nature of the sediment. In principle, tidal flats can develop in However, in small tidal flats where the aggradation is so
any climate, although there are particularities in the flats rapid that no areas are distinguished, the decrease in grain
depending on the climate in which they develop. size takes place over time. This is the case of some tidal flats
that have developed on mesotidal coasts and are associated
• In regions of temperate climate, tidal flats composed of with back-barrier areas [29].
siliciclastic sediment are predominant. The tidal flats Following the most general model, in a typical tidal flat
usually cover the highest parts of the flat, while in the the areas that can be distinguished are (Fig. 20.3):
central part a mixture of mud and sand accumulates, and
finally in the lower areas and the channels mostly sand (a) The subtidal area: The subtidal zone of the tidal flats is
accumulates. located below the mean spring low waters. So, its upper
• In sub-arctic areas, they are characterized by a huge zone will only occasionally be exposed during extreme
fraction of edges dragged by the ice blocks that in turn tides. This area may have different characteristics
leave small grooves on the surface of the plain. depending on its location (open-coast or back-barrier)
• In the Tropics, the composition of the sediment depends or be associated with another type of tidal system. Its
on the sediment supply. If the terrigenous contribution is identification is important, since this is the area with the
abundant, the differences between the flats of temperate greatest preservation potential. Thus, the subtidal zone
climate are minimal. In this case, the marshes of the of tidal flats can be constituted by a typical nearshore,
supratidal zones are replaced by mangroves. If, on the by a bay, a lagoon or by different types of channels in
other hand, the siliciclastic contribution is minimal, clear cases where they are associated with deltas or estuaries.
waters and high temperatures will allow the development (b) The intertidal flat: This is found between the mean
of flats where carbonate sedimentation predominates. spring low waters and the mean high waters in such a
• In the conditions of arid climates, areas of occasional way that it is subject to continuous alternation between
flooding and extreme evaporation known as coastal periods of exposure and submersion. However, the
Sabkhas occur in the high part of the tidal flats. These number and duration of these exposures and submer-
areas are frequently affected by drying processes, so it is gences do not affect the whole flat equally. So, the
common to find desiccation cracks and also growth in the topographically lower part of it presents higher rates of
pores of the anhydrite, gypsum and halite crystal mud. submergence and, conversely, its higher part presents
higher rates of exposure. Obviously, this transition is
gradual, although it results in the existence of three
20.3 Morphology and Sub-environments different zones within the intertidal flat: low or sandy
intertidal flat, mid or mixed intertidal flat and high or
The processes of transport and deposition of sediments, as muddy intertidal flat. The names of these zones are
well as the colonization of organisms, lead to the existence related to the most frequent sediment in them.
of several sub-environments or elongated zones parallel to (c) The supratidal area: This appears above the mean high
the coast. These zones have a variable width that depends on waters so that it is only flooded during the high tides
the slope of the tidal flat in relation to the tidal range. In and also during periods of storm. In warm and tem-
general terms, there are three perfectly distinct zones: the perate climates, it is abundantly colonized by vegeta-
supratidal zone, the intertidal zone and the subtidal zone. In tion; for that reason, these are known as coastal
turn, the intertidal fringe is compartmentalized into several wetlands. The kind of vegetation varies according to
different zones. the type of climate, so marshes or mangroves can
In most cases, three intertidal units can be distinguished, develop. Within the supratidal zone itself there may be
which are named according to their height or dominant another topographic zone marked by a succession of
sediment [2]. This is the type of zoning described in the
Fig. 20.3 Vertical zoning in the

tidal flats with an example from
Tierra del Fuego (Chile)
plants and animals that colonize it, although this is not The distribution of the tidal drainage system of tidal flats
always present. represents, in a way, the early pattern of the tidal network
later consolidated on the marsh or mangrove areas that,
In arid climates, the vegetation of this area does not consequently, may be inherited from the older intertidal flats
develop and the sediment that reaches it during extreme tides [32]. Some depressions not yet filled, such as ponds or salt
is subjected most of the time to the action of the wind. This pans, may even be relict forms of the initial stages of the
is how the wind tidal flats develop. drainage network [13, 34].
Both the intertidal and supratidal zones are crossed by a
complex network of meandering channels, which constitute
the tidal drainage system. This drainage system presents a 20.4 Processes and Dynamics
hierarchy in terms of its functionality and topographic
location [23, 59]. Thus, there are feeder and distributor Sedimentary dynamics in tidal flats are controlled by a series
channels (subtidal) and terminal channels (intertidal). of processes related to: (a) tidal dynamics (water levels and
In the open-coast tidal flats developed inside a bay, the currents); (b) the contribution of land sediments; (c) the
subtidal zone does not present overly strong currents. This action of waves on the flat; (d) the processes of chemical
allows the development of wide muddy deltas in the area precipitation and flocculation; and (e) the organic activity.
where the intertidal channels flow into the subtidal area. This All these processes are in turn influenced by the climate,
is a different type of ebb delta from those described in barrier which controls: the occurrence of surges, the wind regime,
island systems that have been identified in the tidal flats of the sedimentation rates, the physicochemical conditions of
the Bay of Cadiz, for example. the environment and the type of colonizing organisms. For a
better understanding, we will differentiate between physical, predominates, while in the upper levels of the flat,
chemical and biological processes. decantation of suspension grains becomes relatively more
important. On the intertidal flat, a mixed process takes place
between bed load and decanting of suspended matter. Most
20.4.1 Physical Processes of the bed load is transported during the moments of greatest
energy, while decantation occurs during the slack of the
The most important physical (mechanical) processes on the upstream currents [26, 27]. The relative importance between
tidal flats are obviously related to tidal activity. However, the the two processes is gradual, so that, as we move to higher
small waves that agitate the waters flooding the plain also topographic areas, decantation processes become increas-
play an important role, as do the storms that eventually act ingly important. On the other hand, as a consequence, the
on the flat. existence of tidal cycles of different period has a cyclical
Tidal energy is distributed unevenly in the areas charac- capacity of transport of the currents that is reflected in the
terized in the previous section. Stronger tidal currents characteristics of the sediment deposited in each cycle. In the
develop in the subtidal areas and the low intertidal flat. supratidal flat, decantation processes clearly predominate,
These tidal currents can exceed 1.5 m/s in the channels, due to the lower energy of the currents when the water
while on the surface of the flat, the velocity ranges rarely reaches this level. The high exposure rate can generate
exceed 0.5 m/s [38]. However, these velocities are sufficient drying cracks in this high zone.
in both areas to transport sand and generate bedforms. Tidal The channels draining the tidal flat usually reach maxi-
currents introduce sandy sediment into the tidal flat through mum energy during ebb times. The meandering morphology
subtidal channels and transport it to higher topographic causes currents to concentrate in certain areas. This results
areas. There, it is trapped, taking into account that as we in a migration similar to that produced in meandering river
move in height not only the currents are increasingly smal- channels, with erosion on the concave margin and sedi-
ler, but they are also of shorter duration. On the other hand, mentation on the convex one (Fig. 20.5). This erosion can
it often happens that the tidal currents are asymmetrical. This exceed millimeters per day and, if it takes place on cohesive
situation is synthesized in the diagram proposed by Postma sediments, generates abundant soft pebbles in the tidal flats
[33] (Fig. 20.4). [36]. The action of this process in carbonate tidal flats is
This diagram shows how the flood currents raise the responsible for the genesis of intraclasts. In both cases,
grains to levels where the ebb currents remove them for a these lithological elements become part of the material
shorter time but are not able to return them to the initial transported through the bed of the channel and are finally
point. From this point, a new flood current would transport deposited in the point bars that are generated in its convex
them to a higher point and, in turn, a new ebb current would margins [21].
not be able to return them to the initial point. In this way, The innermost part of the channels, especially if they
successive currents would make the particles go back to drain supratidal areas (salt marshes and mangroves), usually
places where the currents would no longer be able to set presents a cumulative character. These channels are filled
them in motion. with cohesive sediments and the filling process results in a
This demonstrates that the distribution of the energy of narrowing with an increase in the slope of the margins
the currents in the different zones of the tidal flat determines (Fig. 20.6). This narrowing is often accompanied by a
the sedimentary processes and the facies that are deposited in deepening that is achieved by erosion of the bed, so it can
them. Thus, in the subtidal zones, bed load transport accumulate sediments in a residual way [23].
Fig. 20.4 Diagram of the

transport of solid grains
ascending the tidal flat with
decreasing tidal current velocity,
adapted from Postma [33]
20.4 Processes and Dynamics 295
Fig. 20.5 Scheme and view of a

meandering tidal creek, with
erosion in the concave margin and
development of a tidal point bar
by deposition in the convex
margin
In the highest areas of the intertidal zone, the importance deposition takes place. Since these are clean water envi-
of tidal currents in the transport of sandy material is lessened ronments during fairweather conditions, it is during the
when faced with the action of small waves [7]. These waves periods following storms that the water has the greatest
can be incoming from open coastal areas or be generated amount of suspended matter from the subtidal areas [46].
within the tidal flat itself during high tide if there is sufficient
fetch. This process has a significant influence on the distri-
bution of the sedimentary facies in the flat. 20.4.2 Chemical Processes
The action of eventual storms can also affect tidal flats in
two different ways. On the one hand, in the lower areas there Chemical processes play an important role in tidal flats as
is strong erosion and reworking of previously deposited suppliers of autogenous sediment. On those tidal flats where
sediments. On the other hand, it is during storms when large terrigenous sedimentation is predominant, the flocculation
amounts of coarse sediment can be introduced into the processes which take place during times of lower tidal cur-
higher areas of the flat that accumulates in the form of rents result in a significant amount of organic sediment being
cheniers [53]. This sediment has a high preservation poten- added to the sediment from silting.
tial, because the range of energy normally put into play in However, it is in the carbonate flats where chemical
these areas is much lower and cannot rework this coarse processes play a more important role. In these environments
material. In the intertidal zones of carbonate tidal flats, it is the siliciclastic contribution from land is minimal and almost
precisely in the moments after the storms that most of the all of the sediment comes from the action of chemical
Fig. 20.6 Scheme and view of a

depositional tidal creek, with
narrowing in the margins and
deepening at the bottom, and
development of a lag deposit
processes. In Chap. 11, the shallow subtidal zones were 20.4.3 Biological Processes
characterized as the place where most of the primary pre-
cipitation of calcite (carbonate factory) occurs. This pre- Perhaps the most typical example of biomechanical sedi-
cipitated calcite is subsequently reworked by physical mentation is the screen action that plants exert when they are
processes until it is distributed throughout the intertidal immersed in an aqueous flow. The presence of plant for-
zone. Organisms have, in addition, a remarkable influence in mations contributes to generate turbulence, slowing down
the primary precipitation of calcite, catalyzing the process by the flow speed due to friction and contributing to siltation.
providing the main part of the elements composing these Plants also exercise chemical control of the environment
facies, i.e., the pellets [5]. when they are submerged, contributing to biochemical sed-
Other types of chemical processes that take place on the imentation. By remaining submerged, the tissues of some
tidal flats occur in their topographically highest area. There, plants are capable of secreting substances that modify their
interstitial water that fills the pores during exposure periods chemical environment to maintain their osmotic balance.
circulates through them, resulting in capillary precipitation These substances cause changes in the factors that determine
of aragonite and dolomite that act as cement leading to crust the ionic stability of certain elements, inducing chemical
formation [41]. These crusts go on to form intertidal bea- precipitation and flocculation processes. These biophysical
chrocks [9]. However, the action of energetic physical pro- and biochemical sedimentation processes are present in both
cesses can fragment them into intraclasts [14, 21]. Evaporite clastic [18] and carbonate environments [21].
crystallization of gypsum, anhydrite and also dolomite can Another type of organic activity that induces sedimenta-
accompany this cementation by capillarity [5]. tion is exercised by some types of algae that act as a sediment
In the supratidal areas, the capillary circulation of fresh trap. The most characteristic case is that of algae that achieve
water can produce the first diagenetic transformations, the growth of geological structures through the adhesion of
extracting the Ca and replacing it with Mg through a detrital particles. Thus, blue-green algae (cyanophyceae) give
dolomitization process. However, the result can easily be rise to the formation of stromatolites (Fig. 20.7a) and onco-
confused with the typical cementation of a beachrock [21]. lites, while some red algae (rhodophyceae) by the same
20.4 Processes and Dynamics 297
Fig. 20.7 Biologically induced

structures. a Stromatolites.
b Rhodolites
process generate spherical structures called rhodolites bonding element that keeps the sediment grains together,
(Fig. 20.7b). A similar phenomenon occurs in siliciclastic allowing the currents to put it back in motion.
environments, where the activity of microorganisms such as The arrangement of all of these biological processes
diatoms in the pores of the sediment generates mucous along the tidal flats is clearly zonal, as the organisms are
membranes that agglutinate the particles and give them a distributed vertically according to their degree of tolerance to
cohesive character, preventing the currents from remobilizing exposure and submersion levels (Fig. 20.8). Thus, animals
them [11]. such as crustaceans, gastropods, bivalves, annelids, for-
While the processes described above contribute to the aminifera, ostracods, or plants such as higher halophytes,
accumulation of sediment on the tidal flats, bioturbation green algae, cyanobacteria, and diatoms are located in
processes have just the opposite effect. Bioturbation involves specific fringes within the intertidal zone [55, 56]. In general
the alteration of a large part of the sediment due to the terms, the degree of bioturbation increases towards the
activity of macroorganisms, which totally or partially higher areas, since the downwards migration of bedforms
destroy the previous internal order. On the other hand, some can be inhibitory to benthic activity. However, the presence
organisms digest the organic matter that represents the of certain organisms such as algal mats or eelgrass can
Fig. 20.8 Vertical distribution of

benthic organisms in a
mid-latitude tidal flat, adapted
from Weimer et al. [56]
contribute to the fixation of the sediment, increasing the covered by the tide at times when the speed is decreasing.
content of shaly material and inhibiting the migration of The most direct consequence of this is the presence of a
bedforms. In short, organic activity can alter the normal vertical and horizontal gradation of sediment grain size.
sedimentary zoning of tidal flats [44]. Thus, the coarser-grained material is found towards the
subtidal area, while the finer material increases towards the
supratidal zone. This fact means that the lower zone of the
20.5 Sediments and Bedforms flat is generally known as the sand flat and the upper zone as
the mudflat, while the intermediate zone is called the
The distribution of sediment in the tidal flats is clearly mixed flat.
determined by the vertical distribution of sedimentary pro- On the other hand, the different associated bedforms are
cesses. It should be noted that tidal currents only act on the also graduated vertically and horizontally. Figure 20.9
surface of the tidal flat when the tidal water reaches the level shows the thresholds for the development of different bed-
at which that surface is located (Fig. 20.9). The subtidal area forms. In the subtidal areas and low intertidal flats, where
is always submerged, so the currents in that zone experience higher current velocities are reached and the sediment is
the full range of ebb and flood velocities, from zero to thicker, dunes and ripples develop. Towards the mid flat, the
maximum speed. In contrast, the higher elevations are most frequent forms are the ripples, while in the upper flat
Fig. 20.9 Vertical distribution of

tidal currents and development of
bedforms in each vertical zone of
the tidal flat
20.5 Sediments and Bedforms 299
the current is only able to develop a low regime plane bed facies and muddy facies. These alternations can be classified
and then parallel lamination dominates. into three groups according to the relative proportion of
muddy and sandy sediments they contain. Each group, in
turn, can be subdivided according to the morphology of the
20.5.1 Sandy Tidal Flat mud and sand lenses (Fig. 20.12).
Conceptually, the structures can be classified into flaser
The most frequent bedforms in this area are 2D and 3D bedding, wavy bedding and lenticular bedding.
dunes (sand waves and megaripples), often with superim-
posed ripples (Fig. 20.10a). The internal structure corre- (a) Flaser bedding: Corresponds to those sets of layers in
sponding to these dunes are sets of planar or trough which the proportion of sandy sediments dominates
cross-lamination (Fig. 20.10b). The dimensions and orien- over the muds (Fig. 20.13a).
tation of the bedforms and their corresponding cross- (b) Wavy bedding: These are structures in which the sandy
layering are controlled by the velocity and the asymmetry and muddy sediments are in the same proportion
of the tidal currents. The alternating cycles of spring and (Fig. 20.13b).
neap tides can generate differences in the dimensions of the (c) Lenticular bedding: These are the deposits in which the
bedforms as well as in the thickness of the cross-laminations proportion of muddy sediments is greater than the
generated in each cycle [35, 24, 4, 54]. sandy lenses. The sand sheets can reflect a symmetrical
If the velocities in both directions of the current are of the cross-lamination if they have been generated by wave
same intensity, and the input is sufficient, the structures can ripples, since, as mentioned, small waves can act on the
show bipolarity (Fig. 20.10c). In section, it appears as a area where these structures originate (Fig. 20.13c).
herringbone cross-layering or cross-bedding [35]. If, on the
contrary, the contribution is insufficient, each tidal semicycle These mixed structures of sand and mud are distributed
reworks the sediments and bedforms generated during the vertically in the tidal flat, so that in the lower areas the flaser
previous semicycle. Then, the preservation of bedforms is structures dominate, while towards the higher areas lentic-
minimal [10]. When asymmetry is the dominant feature, the ular ones take over.
internal structure will present abundant reactivation surfaces. In carbonate tidal flats, the sandy fraction is usually
In this case, the most frequent sets of cross-bedding will composed mainly of pellets; however, depending on the
be those oriented in the direction of the dominant current average energy involved in the subtidal zone, and the type of
[8, 24]. organisms that inhabit the environment, intraclasts, oolites
The waves can also leave their mark in this low intertidal and bioclasts may also be present. Meanwhile, the fine
zone, so that in open-coast tidal flats they can make bars fraction is usually formed by micrite. The origin of this
migrate in a very similar way to the beach ridges [28]. The micrite can be directly from the processes of chemical pre-
rate of migration of these bars is determined by the com- cipitation, although the micritic grains can also be remobi-
bined factors of the tidal range and the wave energy. lized from the subtidal zones and deposited by settling in the
intertidal areas.
Settling is the most important process in the high intertidal
20.5.2 Mixed Tidal Flat zone and in the supratidal area. Only muddy material is
deposited there. In these areas, the presence of tidal cycles is
The most frequent bedforms in the mid intertidal zone are recorded in the lamination that characterizes the tidal flat
ripples (Fig. 20.11a) whose typical internal arrangement is facies. These structures are generally known as rhythmites
cross-lamination in sets of centimeter scale (Fig. 20.11b). (Fig. 20.13d). In this way, the cycles of spring and neap tides
These structures also present double vergence (herringbone- are reflected in the grain size of the different laminae (tidal
type), developed when the migration of the bedforms under bedding), while the cycles of long period (six-monthly) are
ebb and flood currents is reversed. reflected in the changes of thickness of the plates (tidal
However, throughout the tidal cycle, there is an alterna- bundles).
tion between moments of high current and moments of zero In open-coast tidal flats, wave action can develop a type of
speed that occur during tidal slacks. Thus, there are intervals macroform called cheniers (Fig. 20.14a, b). These sediment
where mechanical sedimentation and moments of floccula- bodies have the geometry of chains consisting of coarse
tion and settling dominate. The migration of small-scale material (very coarse sand and gravels). These are normally
bedforms is fossilized by covering them with muds from generated during periods of storm [40, 51]. However, they can
settling during high tide surges. This dynamic alternation also develop due to the action of fairweather waves under
results in an interleaving between cross-laminated sandy high supply conditions [30]. The material that constitutes the
Fig. 20.10 Bedforms typical of

low tidal flats. a 3D dunes with
superimposed ripples. b Internal
cross-bedding of a 3D dune.
c Herringbone cross-bedding
cheniers can be contributed by coastal drift or be coarse

material from the residual fraction of the reworking of muddy 20.6 Facies, Facies Sequences and Facies
sediment [1]. Its internal structure is usually composed of Models
metric sets of bioclastic sands or gravels with planar
cross-bedding inclined landwards (Fig. 20.14c). In the interior The typical depositional facies of tidal flats are defined by
of the set, the plates can have different grain-size, forming three fundamental factors: lithology, internal ordering, and
positive sequences. These sequences are arranged on the type and degree of bioturbation [19]. Obviously, all these
muddy facies of the high tidal flat. characteristics are determined by the topographic position
20.6 Facies, Facies Sequences and Facies Models 301
Fig. 20.11 Sinuous ripple field

in a mid-tidal flat a, showing the
internal structure b
which, in turn, influences the sedimentary processes gener- whose crests form open angles with the channel margin.
ated by the facies. Thus, in most tidal flats we can distin- The sheets are inclined in both directions (herringbones), but
guish: (a) subtidal facies, (b) sandy flat facies; (c) mixed flat usually only one of the two is dominant in response to the
facies; (d) muddy flat facies; (e) supratidal facies; and asymmetry of the currents. The orientation of the bedforms
(f) intertidal channel facies. These depositional facies coin- presents a fanning that responds to the meandering character
cide with the zoning described for this type of sedimentary of the channels [56]. Subtidal flasers may also appear in the
environment. convex margin of the channels when cohesive mud is
deposited during slacks [39].
In open-coast tidal flats, the subtidal facies are usually
20.6.1 Subtidal Facies muds or muddy sands with the most representative structure
being the parallel lamination slightly seawards inclined. In
In back-barrier tidal flats, these are usually represented by addition, the bioturbation of these fine sediments is usually
the infilling sequences of subtidal channels. Although in significant. These facies may also include some of the coarse
current tidal flats these represent less than 50% of the surface elements available as soft clasts or bioclasts [52].
of the plain, their migration makes their facies appear below
those of the intertidal zone. They tend to be the thickest
facies, and their thickness is equal to the depth of the channel 20.6.2 Sandy Tidal Flat Facies
that is filled, thus being able to exceed a dozen of meters.
The sediment is usually composed of sandy material forming This remains submerged for most of the tidal cycle. It is
positive sequences. The bedforms present vary in scale from almost completely constituted of sands of different grain
sand waves to megaripples and current ripples. All these sizes which are moved as bed load. This sand forms various
bedforms generate cross-laminations and cross-bedding types of bedforms such as sand waves and megaripples, on
Fig. 20.12 Internal structures

characteristic of tidal
environments [16, 39, 17]
which current ripples with variable orientations are super- and current ripples. These are covered and fossilized by
imposed. In carbonate tidal flats, most of this sand is made cohesive sediments. Internally, this facies presents flaser,
up of pellets, although bioclasts and intraclasts can also be wavy or lenticular bedding, depending on the volumes of
frequent. The internal structure presents cross-bedding with sand or mud contributions and the topographic position.
frequent reactivation surfaces, including the presence of
herringbone-type structures. Bioturbation is scarce, due to
the high degree of instability of the sandy substrate: some 20.6.4 Muddy Tidal Flat Facies
organisms such as Lanice conchilega or Arenicola marina
build fixed galleries. This is dominated by fine-grained sediments, silts and clays,
deposited during the brief periods of submergence by the
high water, when current velocities are minimal, thus
20.6.3 Mixed Tidal Flat Facies forming a characteristic tidal lamination. Burrowing biotur-
bation by the local infauna is abundant, causing partial
This occupies the mid part of the intertidal flats and receives destruction of the internal structure of the sediments.
both suspended sediments and bed load. Thus, it is charac- Superficially, they can also show root bioturbation, which
terized by a mixed lithology composed of alternating layers represents the advance of the colonization by pioneer-type
of sand and mud. This alternation is due to two types of vegetation from the supratidal area.
sediment transport. On the one hand, bed load takes place, In cool climate intertidal flats, the internal structure of the
both immediately after submersion as well as before emer- sediments can also disappear due to the effect of ice and
sion. On the other hand, the settling of suspended matter thaw in those sectors of greater air exposure. The channels
occurs when water covers the flat. This generates plane bed that constitute the drainage network are poorly developed
Fig. 20.13 Structures of

interbedded sands and muds.
a Flaser bedding. b Wavy
bedding. c Lenticular bedding.
d Tidal rhythmite
and are frequently abandoned, giving rise to areas of per- Abundant mud cracks and evaporite crusts (gypsum, dolo-
manent waterlogging until they are completely filled. In mite or aragonite) also occur in areas under an arid climate
carbonate tidal flats, the fine sediment is mostly composed of [56]. Both the burrowing and the holes left by the roots, as
pellets. Crusting and mud cracks are frequent in arid climate well as the mud cracks, are usually filled with sand or iron
areas. Sediments composed only of a bioclastic sand fraction oxides. This chemical environment gives rise to the neo-
of microorganism shells are also typical in carbonate flats. formation of pyrite [3].
20.6.5 Supratidal Facies 20.6.6 Tidal Creek Facies
The swamp facies (marshes or mangroves) are composed of Mainly fine sediment from suspension is deposited in the
the finest sediment on the flat and have a rhythmic parallel intertidal part of the drainage channels. In the higher areas of
lamination similar to that observed in the muddy flat. In this tidal flat, and also across the swamps, these channels
case, the lamination is usually intensely altered by root undergo the processes of lateral migration with erosion in the
bioturbation of the only plants capable of colonizing such an concave margin and deposition in the convex one, in the
extreme environment (usually of the Espartina or Mangal form of a characteristic point bar. Rhythmic sheets of fine
genera, depending on the climate). The galleries of a few sediment inclined towards the channel are deposited in the
crustaceans that prefer to live on the lower zone of the marsh accretion bars. At the base of the channel, there is normally a
may also be present (e.g., fiddler crabs of the genus Uca). lag deposit composed of the shells that cannot be transported
The long periods of air exposure cause the organic matter to by the tidal currents. When the channel is totally filled with
oxidize, giving rise to a characteristic reddish color. this coarse material, it is covered by finer sediments [50].
Fig. 20.14 Cheniers developed

on a tidal flat. a Aerial view.
b Panoramic view. c Chenier
facies
20.6.7 Facies Models mean slope of the flat, its extension and its location with
respect to other sedimentary environments.
The continuous progression of the different depositional The most general typical sequence for siliciclastic tidal
facies, according to Walther’s Law, generates a vertical flats was proposed by Reineck and Singh [38], based on data
shallowing sequence [38]. In this way, the sandy flat facies provided by the Wadden Sea mudflats (Fig. 20.15a). Actu-
are superimposed on the subtidal facies, and on these appear ally, this sequence is representative of all the clastic tidal
the alternation of sands and muds of the mixed flat and on flats, simply by varying the vertical scale according to the
this the muddy flat, finishing the sequence with the swamp tidal range. In the case of carbonate tidal flats, a standard
facies (Fig. 20.15). sequence was proposed by Wright [58], using the microtidal
There are numerous examples of this type of sequence of example of the tropical climate and transgressive framework
depositional facies in the literature. All of them roughly of Andros Island in the Bahamas (Fig. 20.15b).
agree, although there is a wide range of differences in the These ideal sequences would correspond to the final
small details of the facies constituents. This diversity is filling of the fully extended tidal flat. The sequence would
introduced by the variability of environmental control fac- only be cut off by the presence of intertidal creeks, which
tors such as tidal range, climate, relative sea level move- would have their own filling sequence. This infill sequence
ments, the volume and nature of sedimentary inputs, the is developed over the erosive surface created by the channel
Fig. 20.15 Sequences generated in tidal flats in different conditions. a Classical tidal flat [38]. b Carbonate tidal flat [58]
Fig. 20.16 Block diagram

showing the facies relationships
of the different sub-environments
of the tidal flats (based on Boggs
[5])
incision and consists of a basal lag that fills the channel bed, these infill sequences is quite simple and is summarized in
and a sequence decreasing in energy that is very similar to the block diagram presented by Boggs [5] (Fig. 20.16).
that of the adjacent tidal flat, but of lesser thickness [23]. The The facies models of carbonate tidal flats, also called
bodies where the sequence of the intertidal channel develops peritidal flats, have an equivalent three-dimensional
may have different geometry, depending on whether the arrangement. However, there may be differences in the
channel tends to migrate or simply fills by lateral narrowing. detail of the composition of facies from both the lithological
The upper part of the tidal flat may have chenier coarse point of view and the sedimentary structures, in accordance
facies superimposed. The three-dimensional development of with the previous paragraphs.
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28:151–170 31. Perillo GME (ed) (1995) Geomorphology and sedimentology of
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Fluvial-Influenced Systems I: Estuaries
21
estuaries to a relative sea level rise, emphasizing their role in

21.1 Introduction
highstand system tracts. Thus, the starting point of today’s
estuaries would be the Holocene post-glacial transgression
River mouths can be considered as transitional environments
(Flandrian transgression). From the marine invasion of the
affected by river dynamics and marine processes (tides and
pre-existing valleys, the estuaries are characterized as sys-
waves). In general terms, there are two main types of river
tems that tend towards sedimentary infilling, which causes a
mouth: estuaries and deltas. The first of these are established
regressive aggradation in their interior.
as those systems where the main sedimentation occurs in a
Thanks to this characteristic infilling, estuaries often
coastal valley, while in the second ones the sedimentary
develop complex facies models that can be preserved in the
body develops as a coastal prominence that grows towards
sedimentary record. Normally, estuaries are identified by
the open coast.
three fundamental characteristics: (1) the presence of tidal
There are numerous definitions of the concept of estuary;
facies; (2) the relationship of these facies with bodies of
however, practically all of them refer to a semi-enclosed
fluvial origin; and (3) the elongated geometry of the bodies
basin where fresh river waters meet saline marine waters.
developed along a valley.
There is an excellent summary of the evolution of estuary
At the end of the twentieth century, after several decades
definitions over time by Perillo [25]. Etymologically, the
of advances based on the knowledge of current estuaries,
word estuary comes from the Latin aestus, meaning tide,
Dalrymple et al. [5] approached these environments from a
which gives an idea of the importance of tidal processes in
more geological bias, emphasizing the role of the tidal facies
these systems. Perhaps the most frequently cited definition in
as a signature of the estuary sediments. For Dalrymple and
books on estuaries is that given by Pritchard [27]: “An
his team, the estuarine facies are those in which tidal activity
estuary is a semi-enclosed body of coastal water that has a
can be established. One problem addressed by these authors
free connection to the open sea and where the sea water is
was the identification in the geological record of the last
measurably diluted with fresh water coming from a
point of tidal influence, defined until then as the boundary
land-based drainage” (Fig. 21.1).
between river and estuary. It must be taken into account that,
It was also Perillo [25] who highlighted the main short-
in the innermost areas of the fluvial–marine systems, there is
coming of this definition—that is, it does not include the
a transition between the estuary and the river in terms of
influence of the tides, when it is the tide that provides most
processes and facies. In river-dominated estuarine areas, the
of the energy that controls the process of mixing waters in
erosional action of the river can mask the sedimentary result
every estuary. This is curious, since the same Pritchard who
of tidal activity. With this in mind, these authors proposed
proposed this definition also used the tide as the main cri-
that the most internal point where tidal facies are preserved
terion for classifying estuaries.
must be considered to be the geological limit of the estuary.
One long ongoing discussion regarding estuarine systems
In the same way, a transition with the wave-dominated facies
concerns the location of their innermost boundary. In this
is produced towards the sea. Taking into account these
regard, Dyer [11] proposed the most internal point of
considerations, these authors proposed a definition that
influence of the tide as the limit with the river. From this
contemplates these aspects from a geological point of view:
perspective, the action of the tide substantially modifies the
“An estuary is the portion towards the sea of a flooded valley
river water mechanisms in terms of sediment transport and
system that receives sediments from both fluvial and marine
also in terms of ecology.
sources, and contains facies influenced by fluvial, tidal and
In the context of the development of the principles of
wave processes. The estuary is considered to extend from the
sequential stratigraphy, Russell [30] related the genesis of

https://doi.org/10.1007/978-3-030-96121-3_21
310 21 Fluvial-Influenced Systems I: Estuaries
Fig. 21.1 Example of an

estuarine system: a semi-enclosed
mass of coastal water connected
with the sea and where the fresh
fluvial water undergoes dilution
inner edge of the tidal facies at its headwaters to the outer relation to time is also fundamental in the establishment of
edge of the coastal facies at its mouth.” the water mixing processes that characterize the interior of
these environments. These aspects have been explained in
Chap. 9 of this book.
21.2.2 Tidal Action
Given all the considerations set out in the previous section, it
is clear that three main factors control the dynamics of estu-
As mentioned in the introduction to this chapter, the tide is, by
aries: river, tides and waves. However, there are secondary
definition, one of the factors that control the dynamics of the
factors that also influence the geological development of the
estuary and allow its facies to be recognized in the geological
facies: the climate and the local geology [9] (Fig. 21.2).
record. The influence of the tidal regime on water mixing
On the one hand, the climate exerts a control on the
processes has already been demonstrated; however, this is not
precipitation regime that in turn controls the fluvial contri-
its only influence. In the central areas of the estuaries, the tidal
butions, but in the highest latitudes it also has influence over
currents are responsible for the redistribution of sediments
the ice fraction. One only has to consider that one type of
brought by the river as bed load, generating bedforms and
estuary, the fjords, has developed on glacial valleys and is
structures that characterize the tidal facies in these sectors of
strongly influenced by ice dynamics. In addition, it is the
the estuary. On the other hand, the rise and fall of the tidal
climate that controls the wind regime and thus the energy of
level is responsible for a vertical zoning of the margins,
waves that influence, in a fundamental way, the processes of
similar to that described in the tidal flats, due to the rates of
the marine environment of the estuary.
exposure and submergence. However, the tidal regime is also
The geology exerts an important influence on the mor-
responsible for the temporal variations in river discharges,
phology of the valleys. Weak lithologies allow the rivers to
which are slowed down during the moments when the tide is
dig wide valleys that, when flooded by the sea, form open
entering the estuary. In this way, the tidal wave can propagate
estuaries with a typical funnel shape. Conversely, the pres-
to the river above the mixing zone without the salt water being
ence of resistant lithologies forces rivers to run through
able to enter these exclusive freshwater zones.
narrow valleys, developing very confined estuaries when the
In short, according to the criteria of Perillo [25], it can be
sea level rises.
stated that the integral evolution of the estuary is controlled
by the tidal dynamics even in the innermost areas of the
estuary. This influence is not only fundamental in the dis-
21.2.1 River Discharge
tribution of the estuarine facies, but also in the ecology of the
estuary, considered as an ecosystem.
It is evident that river discharge exerts one of the main
controls over the development of estuarine processes. The
aqueous flow of the river determines the speed of the fluvial 21.2.3 Wave Energy
currents, thus controlling the capacity of sedimentary con-
tribution, both in the form of bed load and of the material Wave action is not fundamental for the development of
transported in suspension. The volume of river water in estuaries; however, the waves are present in the marine area
Fig. 21.2 Factors influencing the

development of estuaries, adapted
from Dionne [9]
of many estuaries and influence the development of facies 1. Horizontal or salt wedge estuaries: In these estuaries, the
and coastal sedimentary bodies that tend to develop in these river flow is much greater than the tidal flow. A layer of
environments. In this way, in some types of estuaries the fresh water is formed and circulates at the top of the
waves are capable of generating barriers that partially con- water column, while the salt water introduced by the tide
strict the inland water body, conditioning the passage of circulates at the bottom. The contact between the two
the tide towards these areas. In any case, the wave energy, waters of different chemical characteristics is net and
when it is present, usually limits the outermost zone of the very abrupt. This limit is normally named the halocline.
system. 2. Vertically homogeneous or totally mixed estuaries: In
Regardless of the river’s capacity to provide water, there this kind of estuary, the tidal flow is greater than the river
is no doubt that the dynamics of estuaries, like other coastal flow, and the water becomes totally mixed. The transition
systems, are controlled by the balance of tidal and wave between salt and fresh waters occurs progressively, with
energy to redistribute this sediment. As will be seen later, the waters becoming more saline seawards and fresher
this balance is used as a fundamental criterion when char- landwards. When the estuary is wide enough, the Cori-
acterizing estuaries. olis effect is important, making the entering salt water
concentrate in one margin during floods, while the exit-
ing fresh water during ebbs takes place in the opposite
21.3 Classification and Morphology margin. As usual, there is a different direction of circu-
lation in each of the Earth’s hemispheres.
Over a century of estuary studies, a large number of clas- 3. Partially stratified estuaries: In these systems, the river
sifications have been proposed and numerous criteria have and tidal flows have the same order of magnitude. This
been used to characterize estuaries. Many of these classifi- type represents a sequence of infinite possibilities
cations use geographical criteria, while others use purely between one and the other extremes. Normally, there is a
biological or ecological arguments. In this section, only certain vertical distribution of water, but also a horizontal
those with a more direct geological application will be gradient, with different waters on the surface and at the
considered. bottom, and an intermediate mixed brackish layer.
This classification has been subsequently adopted by

21.3.1 Hydrological Classification several authors, who have themselves modified the specific
thresholds of the relationships between river and tidal flows
Since an estuary is the meeting point between a river system in order to distinguish the different types of mixtures [10, 16,
and a tidal one, a process of water mixing takes place in the 19, 31, 32]. However, all of these authors maintain the
estuary channels whose characteristics allow a classification qualitative relationships expressed in the previous section.
of estuaries. In this regard, one of the most accepted clas- The dynamics of these types of mixtures, as well as the
sifications is that proposed by Pritchard [26]. This classifi- cloud of turbidity associated with these processes, have
cation distinguishes three types of estuaries: already been extensively studied in Chap. 9 of this book.
21.3.2 Classification by Tidal Range the opposite effect of attenuating the tidal range. This clas-
sification differentiates three types of estuaries:
Hayes [17] used the tidal range criteria proposed by Davies
[6] for the classification of the generality of coastal systems • Hyposynchronous estuaries: These are those in which the
and applied these to estuarine systems. Thus, he distin- tidal wave progressively decreases in amplitude as it
guished between: propagates towards the head of the estuary. The effect of
friction with the bed dominates.
• Microtidal estuaries: For ranges under 2 m. • Hypersynchronous estuaries: In these, the tidal wave
• Mesotidal estuaries: For ranges between 2 and 4 m. increases its range when propagating to the interior, to
• Macrotidal estuaries: For ranges over 4 m. decrease abruptly when entering the fluvial sector. The
effect of convergence of the margins dominates.
Later, Kirby [18] introduced the concept of the hypertidal • Synchronous estuaries: These are where the tidal wave
estuary for those estuaries with ranges of more than 6 m. maintains its range by propagating towards the headwa-
ters of the estuary to also decrease sharply when entering
the river area. There is a balance between the effects of
21.3.3 Classification by Propagation of Tidal friction and convergence.
Wave into the Estuary
Another type of criterion used for the classification of 21.3.4 Genetic Classification
estuaries is that proposed by Le Floch [13], who studied the
model of tidal wave propagation when entering estuaries. Several years after proposing the hydrological classification,
Each of these models is produced according to the greater or Pritchard [27] proposed a new classification of estuaries
lesser relative importance of the processes of convergence using morphology as the main criterion, but associating each
and friction with the bed. Convergence is produced by the morphology with genetic conditions. This classification was
narrowing of the margins of the estuary, which would cause actually the modification of a previous one made in 1952. It
an amplification of the tidal range. Friction with the bed has distinguishes four basic types of estuary (Fig. 21.3):
Fig. 21.3 Different types of estuary according to Pritchard [28]. (Bontalakoduru estuary, India). d Tectonic estuary (Maitland Bay, NW
a Drowned fluvial valley (Gironde estuary, France). b Drowned glacial Australia). (Images Landsat/Copernicus from Google Earth.)
valley (Erik Harbour fjord, Baffin Island, Canada). c Barrier estuary
21.3 Classification and Morphology 313
• Flooded river valley: These normally develop in coastal 21.3.6 Dynamic Classification
plains and present fusiform bar systems that have their
axis parallel to the axis of the valley. These estuaries are The most recent classification was made by Dalrymple et al.
generated under conditions of intense tidal current speeds. [5] who used the dynamic criterion as a definition, distin-
• Flooded glacial valley or fjord: These are estuaries linked guishing two types of estuary according to the dominant
to the loss of ice from an ancient glacial valley. They are agent. The classification of estuaries is part of a broader
described as more or less straight and deep valleys, with a consideration that includes all coastal environments as part
high rocky threshold. of a system in which the three fundamental agents (river, tide
• Barrier estuaries: This type of estuary is distinguished by and waves) intervene in the short term, whereas in the long
the presence of a characteristic barrier mouth generated term there is a control by the relationships between sea level
by wave activity. The system is developed in coasts of and sedimentary input. In this classification, the estuaries
very low relief. According to the author, it is the most would be systems that are born after a transgression, but tend
common type of estuary. The state of sedimentary over time to be transformed into deltas through a process of
infilling is important in these. sedimentary filling. According to this classification, there
• Tectonic estuaries: These are flooded tectonic depres- would be two extreme types of estuary:
sions. They are usually deep and have a complex phys-
iography. Given their great depth, they are not usually 1. Wave-dominated estuaries: Waves are the dominant
much filled by sediments. agent in the marine zone of the estuary, capable of
developing a sand barrier that partially closes the estuary
(Fig. 21.5a). In this marine zone, tidal energy is used to
keep the inlet open, at whose ends ebb and flood tidal
21.3.5 Physiographic Classification deltas develop. Most of the tidal energy is dissipated
across the systems associated with the inlet and is quickly
Two decades after Pritchard’s last proposal, Fairbridge [12] lost to the interior. The central zone of the estuary
elaborated a new classification, this time using the physio- behaves like a large confined body of water, with a
graphic criteria as the main guideline. This classification dynamic very similar to that of a lagoon. It is in this
includes eight types of estuary (Fig. 21.4): central zone where the process of water mixing takes
place. The internal zone is dominated by fluvial pro-
• U-shaped high-relief valley profile estuary (fjord). cesses and is characterized by the development of a flu-
• V-shaped moderately high relief valley profile estuary vial delta over the body of water in the intermediate zone.
(fjard or firth). This delta is called the bayhead delta. This type of
• V-shaped moderate relief valley profile (ria or aber) and estuary corresponds morphologically with Pritchard’s
karst-incised estuaries (cala). [28] barrier estuary or the so-called bar-built estuary
• Funnel plan-shaped low relief estuary (coastal plain described by Fairbridge [12].
estuary). 2. Tide-dominated estuaries: This type of estuary is char-
• L-plan shaped low relief estuary (bar-built estuary). acterized by low wave energy. Consequently, the waves
• D-plan shaped low relief seasonally blocked estuary are not able to build a confining barrier. For this reason,
(blind estuary). the tide is the dominant agent, both in the marine part
• Estuaries located in deltaic distributaries (delta front and in the central part of the estuary. The tidal power
estuary). has the capacity to develop tidal bars longitudinal to the
• Compound estuary (tectonic estuary). estuary’s axis, separating different channels in which the
ebb and flood currents are concentrated (Fig. 21.5b).
The shape of each one of these estuaries is determined by The system thus maintains its funnel shape. In the most
the relationships between the factors described above, with a continental part, the river is not able to develop a true
remarkable association to the balance between the relative bayhead delta, because the tide is capable of reworking
movements of sea level (combination between eustatism and all the river sediments. This fluvial area is usually
tectonics) and the volume of sedimentary contribution; other limited to a single channel that passes through sections
factors such as the relief of the coast are also significant. with straight and meandering morphology as an indi-
This last factor is conditioned by the geology of the rocky cator of the dominance of the river or tide in each
outcrops. section.
Fig. 21.4 Physiographic

classification, adapted from
Fairbridge [12]
This classification is not limited to the simple morpho- different agents that control sedimentation: river, tide and
logical description, but extends to the description of the waves (Fig. 21.6). Thus, an estuary is divided into three
distribution of processes in each sector of the estuary and is domains: marine, central and fluvial.
completed by the facies models that result from the total
filling of each type of estuary. It is, therefore, the classifi- • Marine estuary: This is dominated by marine processes
cation with the widest geological application of all those (tides and waves). The environments present different
described. morphologies and distribution according to whether waves
or tides dominate. In a wave-dominated estuary, the mouth
complex develops the barriers that confine the estuary.
21.3.7 Domains and Sub-environments This barrier delimits an inlet channel that allows the pas-
of Estuaries sage of the tide and at its ends develops flood and ebb tidal
deltas. In tide-dominated estuaries, longitudinal tidal
Whatever the type of estuary, there is a longitudinal zoning bars are deposited, which in this sector show an incipient
that takes into account the distribution of energy among the development and are generally found in the subtidal area.
Fig. 21.5 Dynamic classification

of estuaries. a Wave-dominated
estuary. b Tide-dominated
estuary, adapted from Dalrymple
et al. [5]
Fig. 21.6 Longitudinal domains

of estuaries according to their
distribution of energy.
a Wave-dominated estuary.
b Tide-dominated estuary,
adapted from Dalrymple et al. [5]
• Middle or central estuary: This is an area with a net dom- estuary basin. Associated with this basin, intertidal envi-
inance of tides and where the mixture of fresh and salt water ronments such as tidal flats and salt marshes are widely
occurs. In wave-dominated estuaries with a low degree of developed. In estuaries with a high degree of clogging, this
sedimentary filling, it corresponds to a wide low-energy central basin is replaced by an estuarine channel or several
area dominated by the processes of flocculation and settling tidal drainage channels with anastomosing morphology,
processes—and thus the sedimentation of fine material. In which separate inter- or supratidal islands. In the case of
this case, due to its amplitude, it is usually called the central tide-dominated estuaries, there is always a dense network

morphology of a
bedrock-controlled estuary
of braided channels that separate longitudinal intertidal of longitudinal bars separating several tidal channels as in
bars in the shape of a spindle. tide-dominated estuaries (Fig. 21.7). The sedimentation in
• Fluvial estuary: This represents the innermost sector of this estuarine channel is distributed longitudinally into three
the estuary, with a net dominance of the river’s energy. It areas, the fluvial, tidal and wave domains, respectively; in all
usually has only one main channel flanked by tidal flats. of them, the energy is very high. The narrowness of the
These flats have a mixed character between river flood- channel means that river currents can be maintained up to
plains and tidal flats. In the case of wave-dominated the central areas of the estuary, and may even reach the
estuaries, this area has a deltaic progradation over the marine areas during times of flooding. The same narrowness
central basin, which is called the estuary bayhead delta. means that the tide can move many kilometers inland. This
In tide-dominated estuaries, large marshes develop, which characteristic of strong tidal and river currents makes these
are crossed by a single very sinuous estuarine channel estuaries normally behave as well-stratified estuaries (salt
that connects the river to the network of braided channels. wedge). The only variations that may occur laterally are due
to the sinuosity that may be present in the incised valley. In
In addition to this longitudinal zoning, there is a vertical this way, the current is distributed laterally in the channel,
bio-sedimentary zoning controlled by the tidal levels of making it possible for lateral tidal bars to develop on the
exposure and submergence. This is the same vertical distri- margins in place of the typical longitudinal bars. In these
bution of processes and sediments that was described for the bars, an active sedimentation is produced, mainly composed
tidal flats. This zoning is very evident in the central basin of of intercalations of cohesive sediments with sandy material.
wave-dominated estuaries, as well as throughout the whole At the same time, the deeper areas of the channel act as
system of tide-dominated estuaries. bypassing zones for bed load-transported clasts.
The asymmetrical action of tidal currents makes the river
Advanced Box 21.1. Narrow Bedrock-controlled sediment continue to bypass until it reaches the open coast,
Estuaries where a delta can begin to form even from the early stages of
Estuaries that are installed in very incised and narrow valleys evolution. In this case, the deltaic progradation in the open
present a distribution of processes and facies that differs coast is compatible with the presence of the estuary in the
from the general models described by Dalrymple et al. [5]. In confined part of the system. This type of dynamic distribu-
this case, the morphology of the substrate exerts an impor- tion has been described in the Guadiana estuary in the SW
tant control over the dynamics and processes of transport Iberian Peninsula [15, 23].
and deposition. This fact led Chaumillon et al. [3] to
describe these as a different type, called incised
bedrock-controlled estuaries, based on examples studied in 21.4 Dynamics and Evolution
the NE coast of France.
The main feature of these estuaries is the presence of a 21.4.1 Dynamics
single estuarine channel, since the narrowness of the valley
does not allow the lateral development of the broad central The sedimentary dynamics of estuaries are controlled by the
basins typical of wave-dominated estuaries, nor the presence distribution of energies of the agents that control the
transport of sediments, as well as by the processes of water In the marine zone of the wave-dominated estuaries, the
mixing. The water mixing processes are responsible for the action of the waves controls the accumulation of sandy
generation of new solid particles in the central zone of the material. The development of barriers restricts the action of
estuary through flocculation processes. These flocculated the tides in the inner zone of the estuary. However, the sand
grains have a very fine size (less than 16 microns) and a of marine origin manages to circulate inside the estuary
strongly cohesive character. The new flocculated particles during the action of the flood tidal currents, developing wide
become part of the turbidity maximum and are subsequently flood-tidal deltas that also grow towards the central basin.
redistributed to the other zones of the estuary before being
deposited in the less energetic zones. The dynamics of the
processes of water mixing and the settling of particles from 21.4.2 Evolution
the cloud of turbidity have been extensively described in
Sect. 9.2. The tendency of estuaries to accumulate sediments in their
In general terms, the fine particles that settle from the interior has as a consequence of loss of depth in the short
maximum turbidity are usually retained and deposited inside term (decades), and on the longer temporal scale (centuries
the estuary. Due to their cohesive nature, these grains, once to millennia) the total filling of the estuary. The speed of
deposited, are not usually resuspended, resulting in very filling of each estuary depends on the relationships between
active sedimentation in the internal areas of the estuary. In the volumetric capacity of the estuary and the rate of sedi-
this way, the estuary tends to fill up with sediment through a ment retention within it. In general terms, it can be said that
process of aggradation that also contributes to the narrowing. the evolution of an estuary starts from the moment when a
When the tidal wave enters the estuaries, it suffers a valley is flooded and ends when it completes its filling and
deformation. The origin of this deformation is due to the evolves into a delta [5]. Each type of estuary presents dif-
higher speed of movement of the wave during high tides, ferent evolutionary patterns, however, they all have in
because the water column is larger and there is less friction common the fact that the evolution tends towards the
with the bed. This causes an asymmetry of the wave, which occupation of its entire surface by supratidal environments,
translates into a longer duration of the ebb semicircle while the surfaces drained by the tide diminish and the tidal
(Fig. 21.8). Similarly, the ebb currents will not only act for a prism decreases. One consequence of these phenomena is
longer time, but will develop stronger currents. Because of that there is an increase in the degree of canalization of the
this, river sediments transported as bed load tend to circulate system while the model of tidal wave propagation towards
downstream until they are deposited in the innermost position the interior areas of the estuary is modified. The sedimen-
of the mixing zone. It is in this zone where the river sedi- tation rate in different estuaries of the world gives values
mentary discharge takes place, as the river current meets the ranging from 1 to 12 mm per year [21]. However, data based
flood tidal current at its highest speed. In wave-dominated on the comparison of sedimentary environment mapping,
deltas, it is where the estuary’s bayhead delta begins to form. bathymetric maps and hydrodynamic data showed that the
This delta tends to evolve through a progradation of the interior volume of an estuary changes at a rate of less than
sedimentary bodies of the delta over the fine sediments of the 0.1% per year without resulting in dynamic changes in the
central basin. In tide-dominated deltas, the bayhead delta period studied [20]. This means that, despite the reduction in
does not develop, since sand is recirculated to the marine volume, the hydrodynamic conditions in an estuary can be
sectors through the deeper areas of the channels during the maintained over periods of time greater than a century.
tidal ebb. The shallower areas are characterized by the
appearance of sandy shoals. It must be taken into account that • Wave-dominated estuary: The evolution of
the course of the fastest currents of ebb and flood do not wave-dominated estuaries was described by Roy et al.
usually coincide, in the same way that the course of a For- [29]. The filling of the estuary takes place through three
mula 1 racing circuit would not coincide if it were to run in different processes: (1) the aggradation of estuarine
the opposite direction. Shoals tend to develop where the accretion bodies in the central basin, (2) the seaward
lower speed of both currents coincide (Fig. 21.9). progression of the estuary’s bayhead delta onto the cen-
The longitudinal tidal bars begin to develop over these tral basin sediments; and (3) the landward progradation of
lower areas. In this case, the lower energy sectors are located the seaward-domain flood-tidal deltas also onto the cen-
in the dynamic shadow zones generated by these bars during tral basin sediments (Fig. 21.10). Thus, the resulting
the moments of maximum speed of the tidal currents. In effect of this triple action is the retraction of the central
these areas, there is a sedimentation of cohesive materials basin. The entrance of the sedimentary bodies of the inner
that contributes to the vertical growth of the bars, which end parts of the estuary into the intertidal zone leads to the
up reaching the intertidal zone and further into the supratidal development of tidal flats over them. These tidal flats are
area. distributed in the form of islands separated by tidal
Fig. 21.8 Deformation of the

tidal wave when propagating into
an estuary
Fig. 21.9 Scheme showing a

pattern of tidal circulation of flood
(blue) and ebb (red) currents.
Shoals (dashed lines) are formed
in the areas of less energy,
adapted from Dalrymple et al. [4]
channels. These islands tend to transform into salt mar- • Tidal-dominated estuary: Perhaps the best description of
shes as a result of sedimentary aggradation (Fig. 21.10b). tidal-dominated estuaries is provided by Dalrymple et al.
As the islands grow vertically, the channels that separate [4]. When the tide is the dominant energy, tidal currents
them begin to deepen. The filling culminates when the are responsible for all sediment transport within the
flood delta channels migrating towards the interior man- estuary. The development of longitudinal tidal bars is the
age to connect with the channels of the bayhead delta, process that controls the evolution of the entire estuary
constituting what from that moment on will be estuarine (Fig. 21.11). The bars develop from sandy shoals that
channels, with a morphology very similar to that of an sediment in the lower energy areas of the currents
anastomosing river (Fig. 21.10c). (Fig. 21.11a). As the innermost bars aggrade until they
reach the intertidal zone and further toward the supratidal
The loss of tidal prism also implies dynamic changes in
zone, new subtidal bars appear on their front, closest to
the environments outside the estuary, as tidal currents will be
the sea domain (Fig. 21.11b). The channels trace braided
less and the ebb delta will begin to be dominated by waves.
trajectories between the emerged bars. In more advanced
At the same time, the front of the barriers will begin to be
stages of evolution, some channels are more efficient than
reworked by the waves, resulting in an erosional phe-
others from a hydrodynamic point of view. The rest of the
nomenon (Fig. 21.10b). The total filling of the estuary
channels lose their functionality and are thus abandoned
implies that the sands of the ebb-tidal delta can be used by
until they are filled with sediments. In a parallel way,
waves to build bars that reattach to the barrier front beaches,
several bars can be merged, thus expanding the marsh
causing them to prograde (Fig. 21.10c). At this point, the
areas. The innermost zone is reduced to a single mean-
tidal energy in the final infill can be so low that the estuary
dering estuarine channel (Fig. 21.11c). This channel
can behave like a blind estuary.
Fig. 21.10 Typical evolution of

a wave-dominated estuary,
adapted from Roy et al. [29].
a Initial stage with a low rate of
infilling. b Intermediate stage
with a partial infilling. c Stage of
total infilling
Fig. 21.11 Typical evolution of

a tide-dominated estuary, adapted
from Dalrymple et al. [4]. a Initial
stage with a low rate of infilling.
b Intermediate stage with a partial
infilling. c Stage of total infilling
progressively changes in response to the filling of the estuaries can be classified as blind estuaries (Fig. 21.12c).
estuary. It usually tends to deepen as it narrows, since all Finally, the intermediate stages of tidal-dominated estuaries
tidal drainage must take place through it. would be classified physiographically as funnel-shaped
estuaries (Fig. 21.12d).
Today, estuaries appear on coasts all over the world in As the sedimentation process fills the estuaries, the
any of the filling stages, since each estuary evolves at a boundaries between the different areas change position in a
different speed depending on the volume of sediment progressive migration towards the sea. This has a clear
available. For that reason, some of the intermediate evolu- influence on the distribution of the facies. Another effect of
tionary stages of estuaries dominated by waves and tides the filling of the estuaries is the increase in the deformation
appeared in some of the first morphological classifications as of the tidal wave. The relationships between the effect of
characteristic types. Thus, the initial unfilled stage could be channel narrowing and depth loss can be modified over time,
classified as a drowned fluvial valley or ria-type estuary with an effect on the model of wave propagation into the
(Fig. 21.12a). Wave-dominated estuaries in intermediate estuary. However, it is common for the tidal wave to become
stages are clearly barrier estuaries from a morphological more asymmetrical in the sense of the ebb. This means an
point of view (Fig. 21.12b), while in their final stage these increase in the circulation rate of the bed load to the sea in
Fig. 21.12 Examples of estuaries in different states of infilling. Kijiweni estuary (Tanzania). d Tide-dominated partially filled estuary,
a Empty estuary, with the example of Ría de Muros (NW Spain). with the example of Dawei estuary (Myanmar). (Images
b Wave-dominated partially filled estuary, with the example of Kosi Landsat/Copernicus from Google Earth.)
estuary (NE South Africa). c Totally filled estuary, with the example of
advanced stages of estuarine infilling. These same phe- sequence of lithofacies that depends on the variability of
nomena appear in the early stages of tide-dominated estuary processes that can occur in it. These sequences of lithofacies
channels, but are also common in estuaries with advanced (depositional facies) characterize each sedimentary envi-
filling. Once the estuary is completely filled and becomes a ronment and allow us to recognize them when they appear in
single channel, there are no dynamic differences between the the geological record. In this regard, it should be noted that
two types of estuary. This dynamic is similar to that of rocky part of the sediments is trapped in estuaries, while another
substrate-controlled estuaries. The evolution of the last part travels until it reaches the open coast. In some
stages is also the same in all three cases. With total canal- sub-environments, active sedimentation dominates, while
ization, the estuary becomes almost completely a sedimen- others are bypassing environments [24]. Thus, the preserved
tary bypassing zone towards the coast and the bed load facies simply reflect the nature of the sediment that manages
sediment of fluvial origin can reach the marine zone after to remain in the estuary. As early as 1957, Moore and
several cycles of tidal transport. From this moment on, the Scruton made a magnificent summary of the facies and
river mouth system will have finished its stage as an estuary bedforms present in the various environments associated
and will begin a new stage as a delta by starting a process of with the estuaries. This information has been supplemented
progradation towards the sea. by numerous papers over the last few decades. The fol-
lowing paragraphs summarize the details.
21.5 Depositional Facies

21.5.1 Depositional Facies Characteristic
As can be seen in the previous sections, an estuary is a of Wave-Dominated Estuaries
complex environment, whose distribution of sedimentary
sub-environments is different depending on the morphology, Wave-dominated estuaries are the systems with the most
the stage of evolution and the type of dominant agent. pronounced bipolarity, because the sub-environments asso-
Obviously, there is a wide variability of facies depending on ciated with the central basin produce the typical black
the factors that control sedimentation; however, there are a muddy facies. These are associated with the turbidity max-
number of common characteristics that can be synthesized. imum and the lowest energy of the whole estuary. The sandy
Each of the environments that build the estuary has a facies are arranged both towards the river area and towards
21.5 Depositional Facies 321
Fig. 21.13 Depositional facies

generated on the different
sub-environments linked to the
early stage of a wave-dominated
estuary
the marine domain. The characteristic lithofacies sequences bivalves and annelids always evident. Only in the vicinity
(depositional facies) of this type of estuary are the following of the marine area and the front of the bayhead delta does
(Fig. 21.13). the percentage of sandy fraction increase and intercala-
tions of sand and mud appear.
• Bayhead delta front: The front of the bayhead delta • Barrier environments: The wave-dominated environ-
develops prograding bars of a sandy and gravelly nature. ments are considered as a part of the confining barrier.
These are sands with planar cross-bedding on a metric Those located at the front as beaches, dunes and ebb-tidal
scale. When there is a wide central basin, these bars deltas are not strictly inside the estuary. The only back
develop lobe geometries; however, in more advanced barrier environments developed inland are flood-tidal
stages, the geometry becomes longer until it is reduced to deltas. In this case, their facies have been described in
the interior of the channels. Chap. 19 and correspond to horseshoe-shaped sandy
• Fluviomarine floodplain: These are fine-grained deposits bodies whose internal structure are sets of cross-bedding
with alternating centimeter-scale layers of silts of fluvial with a dominant landward vergence.
origin, black muds with parallel lamination of tidal origin,
siliciclastic sands with ripples and immature gravels
without internal organization. These alternations respond
to energy fluctuations corresponding to the regime of 21.5.2 Depositional Facies Characteristic
fluvial contributions and extreme tides when they flood of Tide-Dominated Estuaries
this part of the estuary. All the facies are finely inter-
spersed in the form of fining-upwards sequences. The This type of estuary is characterized by a high tidal energy in
sequences are often bioturbated by the activity of plants. the central part of the estuary. So, it does not develop a
• Estuarine accretion bodies: These are subtidal bodies that textural bipolarity as pronounced as in the type described
fill the central basin of the estuaries. They are constituted above. The depositional facies that characterize these estu-
fundamentally by massive or laminated organic muds, aries are the following (Fig. 21.14).
strongly bioturbated, with some fine intercalations of
sands that correspond to the distal contributions from the • Subtidal bars: These represent the embryonic develop-
bayhead delta or from the marine system. ment of the bars. Their characteristic facies are sands that
• Tidal flats: These develop on the intertidal margins of the develop ripple and dune fields. These sandy facies are
central basin and could be called the lower flow regime usually intercalated with mud levels, developing flaser
(LFR) tidal flats. The LFR have mainly muddy facies or and wavy bedding. The lower contact of each sandy level
gray sandy muds, with strong bioturbation by burrows of usually presents erosive characteristics. In relation to

sub-environments linked to the
early stage of a tide-dominated
estuary
these moments of erosion, the facies also tend to present and 3D dunes) oriented in both senses of the tidal current.
abundant soft clasts. Consequently, their characteristic facies present sets of
• Intertidal bar margins: When aggrading to the intertidal trough cross-bedding forming metric-scale herringbone
zone, the longitudinal bars facies become more diverse. structures. The mixing of waters also occurs in these
There are differences between the areas closer to very channels, reflected in the existence of black mud levels on
active channels and those located in areas of dynamic the bed. These levels can be partially reworked to produce
shadow. All of them present characteristics of sand–mud soft clasts that are preserved inside the sandy facies.
interlayering. The intertidal margins of more active
channels develop into upper flow regime (UFR) tidal In addition to these, fluviomarine floodplain environ-
flats, with characteristic flaser structures. Conversely, the ments very similar to those already described are also pre-
channels that are abandoned develop lower energy sent in the fluvial zone of the wave-dominated estuaries.
structures such as wavy and lenticular bedding. Towards Also found are LFR lateral tidal flats similar to those
the supratidal areas, the muddy facies start to dominate described and salt marshes, typical of all estuaries in an
the environment, with characteristic laminated muds that advanced state of filling.
present very visible tidal bundles. Bioturbation by bur-
rowing of organisms such as bivalves, annelids and
crustaceans can be intense. This activity can even destroy 21.5.3 Depositional Facies Characteristic
the primary laminate structure. There are channels that are of Estuaries in an Advanced State
definitely abandoned and filled with muddy sediments of Infilling and Bedrock-Controlled
until they reach the level of the marshes and are then Estuaries
colonized by vegetation. This process involves the fusion
of previous longitudinal bars to form increasingly When the estuaries are completely filled, the distribution of
extensive supratidal islands. facies is very similar to that developed in estuaries controlled
• Interbar channels: The channels between bars concentrate from the beginning by the rocky substrate. This system is
the maximum tidal energy of the system. They usually reduced to an estuarine channel that can be single or forked
develop sandy beds with significant mesoform fields (2D and that connects the river directly to the open sea. In both

generated in the different
sub-environments linked to a
rock-bounded estuary (the
sequences are also valid for the
late stages of infilling of
wave-dominated and
tide-dominated estuaries)
types of system, the intertidal areas are reduced to narrow usually preserved as thin lenticular layers. The sand–mud
fringes located on the estuary channel margins. In all of association becomes predominantly muddy towards shal-
them, marshes occupy the highest areas in the marine and lower areas of the channel, where monotonous bodies of
central zone of the estuary, while the same topographic areas black muddy sands bioturbated by annelids usually appear.
are occupied by the fluviomarine floodplain in the fluvial • Intertidal channel margins: These facies are very similar
domain. The difference between the different types of estu- to those of the UFR tidal flats of more incipient estuaries;
ary lies in the surface area occupied by the marshes, being however, they present a greater slope, reflected in the
much narrower on rock-controlled estuaries. The deposi- inclination of the tidal parallel lamination. The dominant
tional facies developed in the characteristic environments of facies are muddy sands that pass upwards to bioturbated
these estuaries are as follows (Fig. 21.15). muds. Some centimetric intercalations of shells of resid-
ual origin can be found. Sometimes, millimeter- to
• Bypassing estuarine channels: In the fluvial domain, centimeter-scale intercalations of muddy sands and muds
macro-forms composed of gravel are present. These (wavy bedding) can also appear. These are due to changes
gravels can alternate with very coarse-to-medium sands in in the energy of the environment, produced by the alter-
the deeper areas of the channel or even with sandy silt in nation of spring and neap tidal cycles.
the shallower areas of the system. This lithofacies alter- • Salt marshes: The sequence produced in the marshes
nation is mainly due to seasonal and interannual flow consists almost exclusively of plant accumulations (peat)
changes, which infer variations in both the type of fluvial and root-bioturbated muds. The mud usually presents tidal
contribution and in the relative domain between the river lamination if it is not totally destroyed by the action of the
and the tide. In the central domain of the estuary, the roots. In the zones near the marine sandy contribution, the
deeper zones of the channel mainly present alternating facies can be constituted by muddy sands or even present
muddy sands and black muds. In the marine estuary, the intercalations of clean sand reflecting energetic alterna-
sequence is made up of monotonous deposits of clean, tions of the environment. The top of the sequence consists
coarse-grained, non-bioturbated sand with frequent lenses of a decimetric level of saline mud with mud cracks.
of bioclastic gravels. Towards shallow areas, the grain
becomes finer, and can then also present muddy matrix
and burrowing bioturbation.
• Shallow estuarine channels (lateral tidal bars): These 21.6 Facies Models
facies have transitional characteristics with the deeper
channel to which they are linked. They are usually com- The three-dimensional facies models also show very marked
posed of meso- and micro-formed sands. Sometimes the differences between wave- and tide-dominated estuaries in
bedform fields are covered by black tidal muds, which are terms of the geometry of the sedimentary bodies. The
geometric differences are the result of the different evolution Thus, the base of the sequence presents an estuarine accre-
of these estuaries. The architectural facies models shown tion body of a muddy nature that corresponds to the filling of
correspond to the final stage of filling of both types of sys- the estuary in the incipient stage. This body is linked land-
tems after a long period of sea level stability and with suf- wards with the sand and gravel facies of the initial bayhead
ficient sedimentary availability. These models represent the delta (Fig. 21.17). Volumetrically, these sediments represent
disposition of sedimentary bodies formed by the deposi- the greater fraction of the estuary’s filling.
tional facies (lithofacies sequences) described in the previous The upper part of the infilling along the entire estuary is
section. Both models coincide in presenting a basal body of composed of the elongated bodies of the longitudinal bars,
fluvial nature, developed in the bed of the valley during the interspersed with the interbar channels composed of sandy
lowstand period prior to the marine invasion. facies. Upwards, when reaching the intertidal zone, the bars
develop UFR tidal flats, which are finally transformed into
salt marshes. The abandoned channels are transformed into
21.6.1 Facies Model for Wave-Dominated tidal creeks that become blind when they are filled with
Estuaries organic mud and ultimately they are also transformed into
marshes. In the fluvial part of the system, the aggradation of
The sequence that has been classically described as charac- the old bayhead delta gives rise to the development of a wide
teristic of these estuaries is that developed in the central fluviomarine floodplain drained by a channel that passes
basin. In this sector, the characteristic process is the aggra- from fluvial to tidal domain with a reflection in the change
dation of estuarine accretion bodies composed of organic from straight to meandering morphology.
black muds coming from the water mixing process. This The described architectural model presents some varia-
aggradation leads the sediments to reach the intertidal zone, tions in different estuaries [33], especially in the lower part
where they will begin to sediment the tidal flat bodies and of the model. These variations correspond to the history of
finally marshes (Fig. 21.16). the infill, since the depth of this type of estuary allows that
The river zone is characterized in depth by a large body some bodies developed during the transgressive stages prior
of sand and gravel with a prograding disposition towards the to the stabilization of the sea level can also be recorded.
central basin. In this way, the river bodies that constitute the
estuarine bayhead delta overlap the estuary accretion bodies Advanced Box 21.2. Mixed Models of Dynamic
until they reach high levels where the fine facies of the Changes
fluviomarine floodplain develop in a tabular body. The The sedimentary infilling of the estuaries necessarily implies
marine zone shows a facies model similar to the one a decrease in the tidal prism. This decrease in water volume
observed in barrier island lagoon systems. Towards the of tidal drainage results in a loss of tidal current velocity.
interior of the estuary, the sandy bodies of the flood-tidal The lower tidal energy increases the relative capacity of
deltas stand out, which present a progradation towards the waves to build a barrier in the marine area of the estuary.
central basin, migrating over the black muds of the estuary Thus, an estuary that begins its filling with longitudinal tidal
accretion bodies. These sandy bodies are the basis for the bars due to tidal dominance can end its evolution as a
development of tidal flats and marshes when the level wave-dominated estuary if the waves build a barrier closing
reaches the intertidal zone. The estuarine channel facies are the estuary mouth.
installed in the last stages of infill and develop longitudinally This change in the dynamic conditions brings with it a
by cutting into the facies of the estuarine accretion bodies. change in the facies architectural model. Thus, the internal
sector and the base of the estuary sequences can be filled
according to the tide-dominated estuary model, while the
21.6.2 Facies Model for Tide-Dominated surficial part of the marine zone can be filled according to
Estuaries the wave-dominated model (Fig. 21.18). In this way, the
innermost sector will show the typical architecture of lon-
The facies model developed by the infilling of a gitudinal bars and UFR tidal flat, separated by tidal channels.
tide-dominated estuary presents a much simpler architectural It is common to find in this sector marsh islands that result
facies model. Early papers on this type of estuary asserted from the fusion of several bars by filling of the channels that
that the river area does not develop a true bayhead delta, due separated them. At the same time, the marine sector will be
to the absence of a large central basin and the fact that river composed of the sedimentary bodies of the barrier and the
sediments are reworked upon reaching the tidal channels. ebb- and flood-tidal deltas. The intermediate sector, in this
However, according to Tessier [33], in the first stage of case, may correspond to the filling of a central basin located
filling, this type of estuary presents an estuary-type mor- between the longitudinal bars and the bodies closing the
phology that allows the development of this type of delta. estuary.
Fig. 21.16 Facies model for a

wave-dominated estuary (based
on Roy et al. [29] and Dalrymple
et al. [5])

tide-dominated estuary (based on
Tessier [33])
Fig. 21.18 Mixed facies model

for an estuary under a change
from tide-to-wave domination
(based on Aguilar et al. [1])
Fig. 21.19 Aerial photograph of

the Odiel Estuary (SW Spain),
displaying a morphology that
reflects a dynamic change from
tide- to wave-domination
Within this architectural scheme, the estuaries have four 12. Fairbridge RW (1980) The estuary: its definition and geodynamic
distinct morphological zones. The mesotidal estuary of the cycle. In: Olausson E, Cato I (eds) Chemistry and biogeochemistry
of estuaries. Wiley, New York, pp 1–36
Odiel River in SW Spain (Fig. 21.19) fits this model of 13. Le Floch P (1961) ropagation de la Marée dans l’Estuaire de la
filling [1]. Seine et en Seine Maritime. Université de Paris, Thèse Doctorat
d’État, p 507
14. Gallivan LB, Davis RA (1981) Sediment transport in a microtidal
estuary: Matanzas River, Florida. Mar Geol 40:69–84
References 15. Garel E, Pinto L, Santos A, Ferreira O (2009) Tidal and river
discharge forcing upon water and sediment circulation at a
1. Aguilar ME, Morales JA, Morales-Mateo R, Feria MC, González rock-bound estuary (Guadiana estuary, Portugal). Estuar Coast
MA, González-Batanero D (2019) Geometry of the upper units of Shelf Sci 84:269–281
the Holocene infilling of the estuarine channel of Odiel River del 16. Hansen DV, Rattray M Jr (1964) Gravitational circulation in straits
Odiel (Huelva, SW Spain) (in Spanish). J Geol Soc Spain 32 and estuaries. J Mar Res 23:104–122
(1):127–142 17. Hayes MO (1975) Morphology of sand accumulation in estuaries:
2. De Boer PL, Nio S (eds) (1988) Tide influenced sedimentary an introduction to the symposium. In: Cronin LE (ed) Estuarine
environments and facies. Reidel Publishing Co, Boston, p 530 research, vol 2. Academic Press, New York, pp 3–22
3. Chaumillon E, Proust JN, Menier D, Weber N (2008) 18. Kirby R (1989) Sediment problems arising from barrage construc-
Incised-valley morphologies and sedimentary-fills within the inner tion in high energy regions: an example of the Severn Estuary. In:
shelf of the Bay of Biscay (France): a synthesis. J Mar Syst Telford T (ed) Third conference on tidal power. Institution of Civil
72:383–396 Engineers, London, pp 189–200
4. Dalrymple RW, Mackay DA, Ichaso AA, Choi KS (2012) 19. Knauss JA (1997) Introduction to physical oceanography. Prentice
Processes, morphodynamics, and facies of tide-dominated estuar- Hall, New Jersey, p 309
ies. In: Davis RA, Dalrymple RW (eds) Principles of tidal 20. Lane A (2004) Bathymetric evolution of the Mersey Estuary, UK,
sedimentology. Springer, Heidelberg, pp 79–107 1906–1997: causes and effects. Estuar Coast Shelf Sci 59(2):249–
5. Dalrymple RW, Zaitlin BA, Boyd R (1992) Estuarine facies 263
models: conceptual basis and stratigraphic implications. J Sedim 21. McManus J (1998) Temporal and spatial variations in estuarine
Petrol 62:1130–1146 sedimentation. Estuaries 21(4A):622–634
6. Davies JL (1964) A morphogenic approach to world shorelines. 22. Moore DG, Scruton PC (1957) Minor internal structures of some
Geomorphology 8:27–42 recent unconsolidated sediments. Bull Am Assoc Pet Geol
7. Davis RA, Clifton HE (1987) Sea-level change and the preserva- 41:2723–2751
tion potential of wave-dominated and tide-dominated coastal 23. Morales JA, Ruiz F, Jiménez I (1997) The role of the estuarine
sequences. J Sedim Petrol 41:167–178 deposition in the sedimentary exchange between the continent and
8. Davis RA, Fox WT (1981) Interaction between wave- and the littoral. The Guadiana Estuary (SW Spain–Portugal) (in
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Matanzas River, Florida. Mar Geol 40:49–68 24. Nichols MM, Biggs RB (1985) Estuaries. In: Davis RA
9. Dionne JC (1963) Towards a more adequate definition of the St. (ed) Coastal sedimentary environments, 2nd edn. Springer,
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Fluvial–Influenced Systems II: Deltas
22
common site for important cultural settlements. One only

22.1 Introduction
needs to recall that early civilizations such as Egypt and
Mesopotamia settled on delta plains. The proper name of this
Like estuaries, deltas represent another kind of river mouth.
environment was coined by these civilizations, enduring to
In this case, the river has been able to accumulate such a
our times from the first definition of a delta as made by the
significant amount of sediment that it has been able to build
geographer Herodotus of Halicarnassus in the fifth century
a large sedimentary structure, thus forming a coastal
BC. Nowadays, large cities and important industrial and port
ledge (Fig. 22.1). Therefore, a delta is defined as a pro-
facilities are often developed in deltas. Due to the nature of
grading body built with the sediments contributed by a river
their sediments, they also present great economic interest,
at its mouth and which protrudes from the coast into the sea
since these sedimentary formations are likely environments
[1]. According to [2], a delta usually evolves from a simple
for the accumulation of substantial amounts of energy
sedimentary lobe located at a river mouth to a complex
resources, such as coal, oil, natural gas and other elements of
three-dimensional entity that could be defined as a sedi-
value including uranium [2].
mentary system. Authors such as [3] understand that,
although the primary source of materials is the river, tides
and waves can also act on these sediments. In this case,
marine processes are responsible for the total or partial 22.2 Control Factors
redistribution of sediments of fluvial origin, although waves
can also act as a supplier of sediments to the delta front by The dynamics of deltas and, by extension, their morphology
contributing sands from adjacent marine areas [4]. are related to a variety of factors (Fig. 22.2). On the one
According to this definition, deltas can also develop at the hand, the characteristics of the drainage area of the river
mouths of rivers that flow into lake waters—in this case. system that feeds it determines the volume and nature of the
Their sediments will not be redistributed by tides, although water and sediment inputs, as well as their distribution over
in large lakes they can be reworked by waves. On the other time. On the other hand, several factors intervene in the
hand, small deltas can be built in the inland water bodies of basin where the deposition occurs, such as the marine pro-
estuaries in their early stages of evolution. These are the cesses that redistribute the sediment and the relative sea level
estuarine bayhead deltas studied in Chap. 21. movements. These movements are in turn related to the
The distribution of deltas on present-day coasts has been tectonic regime of the basin and global eustasism. In this
analyzed by Inman and Nordstrom [5], who estimate that regard, it should be noted that the presence of the delta
most deltaic systems are located on passive margin coasts, sedimentary prism usually induces strong subsidence in the
although there are also a significant number of deltas coastal areas where it develops. Finally, it must be consid-
developed in protected areas of active margins, such as the ered that climate is the overall driver, exerting a notable
back zone of island arcs. In addition to the deltas currently influence on the rest of the factors [6].
developed on the coasts of the world, there are numerous
examples of deltas in the geological record that have been
very well studied. 22.2.1 Fluvial Discharge
From an ecological point of view, deltas are diverse and
prolific ecosystems. They are highly sensitive to changes in The water inputs that reach the deltaic system from the river
sea level and river basins, and are greatly impacted by are important in terms of the dynamics of water mixing that
human activities. Throughout history, they have been a occurs in the distributary channels or at the marine front. This

https://doi.org/10.1007/978-3-030-96121-3_22
330 22 Fluvial–Influenced Systems II: Deltas
Fig. 22.1 Example of a deltaic system (Po River Delta, NE Italy): a prograding sedimentary body built by the river at its mouth. (Image
Landsat/Copernicus from Google Earth.)

development of deltas (Based on
[6])
mixing involves important flocculation and diffusion pro- 22.2.2 Wave Action
cesses that have already been discussed in Chap. 9 of this
book. However, the fluvial inputs that most influence deltaic Waves are present in most deltaic systems and are absent
development are sedimentary inputs. The fluvial systems that only in deltas developed in confined seas, on coasts with an
feed deltas usually contribute a significant volume of sedi- orientation contrary to the prevailing winds or in deltas
ment, both in the form of suspended matter and bed load. associated with small lakes. The action of the waves is
These materials are the ones that mostly become part of the usually manifested in a significant reworking of the sediment
deltaic bodies. However, the materials contributed by the river that acts in the opposite direction to the prograding trend
can be redistributed by marine agents such as waves or tides. imposed by the river. When waves are present, the sediments
that the river throws onto the open coast are used by the place in a coastal valley invaded by the sea. This valley is
waves to build bars parallel to the delta front. The waves subsequently filled in and begins to progress towards the
migrate these bars landward to attach them to the areas outer part of the coast. Thus, deltas developed after or during
between the distributaries, building beaches attached to the a sea level rise evolve from a previous estuary once it has
delta front or barrier island systems. In any case, waves been infilled.
impose their dynamics on the sediment and, being respon- The study of ancient deltaic formations shows that their
sible for its final deposition, their action is reflected in the sequences have a clear cyclical character [9]. Large deltas
sedimentary sequences. fed from extensive river basins are maintained over very
long timescales spanning different cycles of sea level
movements. These systems alternate between prograding
22.2.3 Tidal Action and retrograding phases of growth. Prograding phases occur
when sea level falls or when the rate of sedimentary input
The tide is usually present in deltas that develop on the exceeds the rates of sea rise. Conversely, retrograding phases
coasts of oceanic areas; however, it is absent in deltas of are erosional in nature and are associated with times when
restricted seas such as the Mediterranean or the Gulf of the rate of sea level rise exceeds the rate of input. The typical
Mexico and, of course, also in lacustrine deltas. The pres- example of a large delta where such cycles are observed is
ence of tides provokes the entry of seawater into the interior the Niger Delta on the west coast of Africa. Such sequences
of the distributary channels, making them function as small have been studied frequently in deltaic systems preserved in
estuarine channels. Thus, the mixing of water and the pro- the geologic record.
cesses associated with the turbidity maximum take place
inside them. These have been classified as delta front estu-
aries by Fairbridge [7]. The tide is also responsible for the 22.3 Classification and Morphology
development of tidal flats in the sheltered fringes of the
delta. When the tide is so significant that it becomes the Although dictionary definitions of a delta emphasize a tri-
dominant force, materials are reworked into longitudinal angular plan shape, there is actually a wide morphological
bars similar to those observed in tide-dominated estuaries. variety. In addition to the triangular shape that gives it its
However, in deltaic systems, these bars develop outward name, there are deltas with cuspated (rhomboidal), lobated
from the coastline and not in the interior of the valleys as (arched), elongated (fingered), intricate and other mixed
occurs in the case of estuaries. shapes (Fig. 22.3). From the point of view of grain size,
there is also great variability, from muddy deltas to gravel
deltas, including sandy deltas and deltas of mixed lithology.
22.2.4 Long-Term Factors: Relative Sea Level
Movements
22.3.1 Classification of Fluvial Deltas
Relative sea level movements act over long periods of time,
but largely determine the genesis of deltas and their subse- The morphological variability of deltas is a consequence of
quent development. Some authors have associated the their sedimentary dynamics. Ultimately, this is the dominant
development of deltaic systems to moments of relative sea agent in deltaic processes that imposes the morphology.
level lowstand, since after a relative fall there is no marine Gallowayw et al. [3] proposed a classification adopting this
invasion of the river mouths and, therefore, there is no criterion that continues to be used today. The practical
possibility of estuarine formation. Thus, they would form character of this classification consists of the association of
part of the lowstand system tracts [8]. However, deltas can morphology with the hydrodynamic agents that control it.
also be generated during times of stand following a sea level The classification consists of a triangle at whose vertices are
rise or even during the rise itself. Under these conditions, it placed the three potential agents of sediment transport and
is the relationship between the space generated by the sea reworking: river, waves, and tides (Fig. 22.4).
level rise and the volume of sediment brought by the river River-dominated deltas show elongated and fingered
that sets the pattern of its development. Thus, a delta will morphologies that are commonly referred to as “bird’s-foot”
develop if the volume of sediment contributed by the river shaped, especially when associated with fine sediments. The
exceeds the volume of space generated by the rise. To fingering is due to the presence of numerous distributary
understand delta dynamics, both parameters must be con- channels separated by levees, leaving in the frontal zone
sidered with respect to time, so the rate of input and rate of concave spaces known as intradistributary bays. The
rise must be compared. In the case of systems developed in progradation of the system occurs from the sedimentation of
the context of a sea level rise, sedimentation initially takes lobate bars whose reworking by marine processes (waves
Fig. 22.3 Different morphologies of deltas. a Triangular shape (Volga shape (Mahakam River Delta, Indonesia). e Bird’s-foot shape (Yellow
River Delta, Russia). b Cuspate shape (Jequitinhonha River Delta, River Delta, China). f Mixed cuspate/lobate shape (Ebro River Delta,
Brazil). c Lobate shape (Yukon River Delta, Alaska, USA). d Braided Spain) (Images Landsat/Copernicus from Google Earth)
and tides) is minimal or null. For this reason, the sediments of the São Francisco River in Brazil, but similar deltas
maintain the morphology imposed by the fluvial discharge. appear along the Brazilian coast in a number of river mouths.
They usually occur in rivers that flow into closed, microtidal In mixed river–wave deltas, the waves are not able to
basins with reduced fetch. The typical example, and also the rework all the sediments brought by the river and a mixed
most studied case, is the Mississippi River Delta. morphology is presented. There are a high number of dis-
Wave-dominated deltas present a very different aspect, tributaries, as in river-dominated deltas, but the waves are
developing cuspated morphologies. All fluvial sediments able to build barrier islands between them, closing the
tend to be reworked by the waves to build parallel bars that interdistributary bays, which are then converted into
end up adjoining the shore to make the shore prograde into lagoons. The delta front is not as cuspate, since the waves
the sides of a reduced number of distributaries or a single displace the sediments, giving the delta a lobated or arched
channel. The waves can also act as a supplier of marine morphology. These are usually deltas that present varied
sediments that add to the volume of fluvial input. Thus, the lithologies, including muds and sands distributed in different
deltaic physiography is similar to that of a strandplain, with sub-environments. The most typical example is the Nile,
no interdistributary environments. They are usually associ- although other deltas located on the Mediterranean microti-
ated with sandy lithologies. The classic example is the delta dal coasts also belong to this type.
Fig. 22.4 Triangular

classification of fluvial deltas after
[3], indicating the position of
some major deltas (data from
Briggs et al. [10])
Tide-dominated deltas present an intricate shape and tide-dominated deltas, there are the characteristic tidal bars
physiography very similar to the tide-dominated estuaries and braided channels, but the overall morphology of the
described in Chap. 21. For this reason, their physiography delta is much more elongated, and wider interdistributary
has been referred to by some authors as estuarine mor- bays are also present. Sediments tend to be somewhat
phology. Morphologically, they consist of a large number of coarser than in tide-dominated deltas. The classic example is
braided or anastomosing channels separated by longitudinal the Mahakam River Delta in Indonesia.
tidal bars. The difference in the case of deltas lies in the The mixed wave–tide marine-dominated deltas present
location of the bars outside the fluvial bay. With these, it is complex morphologies, with an inner part characterized by
the tidal energy that is responsible for reworking the sedi- the presence of typical tidal bars, but with an outer part that
ments of fluvial origin, although much autochthonous sedi- presents barrier islands rather than interdistributary bays.
ment can also be generated due to water mixing processes. They usually occur on macrotidal coasts that also present
These are deltas that develop on macrotidal coasts but with high wave energies. The most studied example is the Copper
reduced fetch or dominant winds acting from land, both River in Alaska, although it is not really a delta, but an
circumstances inhibiting wave action. Lithologically, they estuary.
are deltas made up of fine sediments (muds and fine sands). Intermediate river–wave–tide deltas are the most
The best-known example is the delta of the Ganges and complex of all. They are usually large deltaic systems whose
Brahmaputra Rivers in India. overall morphology depends on the agent exerting the
In mixed river–tidal deltas, the tide is not able to rework greatest influence on sediment distribution. The most char-
all the sediments contributed by the river, with faster rates of acteristic example is the Niger River Delta on the west coast
progradation than in tide-dominated deltas. As in of Africa.
In addition to Galloway’s typology for deltas associated formed by coarse sediments, mainly gravels, but also
with river mouths [11] described a type of delta that sands.
appears when an alluvial fan develops directly on the The arrival of high-gradient braided rivers at the coast
coast (Fig. 22.5a). These are called fan-deltas. These gives rise to a special type of delta closely linked to
systems are characterized by high-slope systems. fan-deltas. These are the Gilbert-type deltas (Fig. 22.5b)
Fan-deltas are powerful sedimentary bodies with a com- and were first described by Grove Gilbert [12]. They are
pletely alluvial terrestrial section that continues into the deltas consisting mainly of gravels that develop at the mouth
submerged region through a zone where the interface of braided rivers and have minimal reworking by other
between the two systems occurs. They are usually deltas agents, so they usually occur in lacustrine waters.
Fig. 22.5 Coarse-grained deltas. a Fan-delta, with the example of Agua del Pueblo Creek, Chile. b Gilbert-type delta, with the example of
Avellano River Delta, Chile. (Images Landsat/Copernicus from Google Earth.)
22.3.2 Domains and Sub-environments distributaries is usually very small, while in

of Fluvial Deltas tide-dominated deltas there is usually a high number of
channels, which may be even higher than in the case of
Being constituted by a powerful sedimentary body, deltas river-dominated deltas.
have a visible subaerial part and a significant submerged • Levees: These are established as raised areas on the
part. Classically, the structure of deltas has been divided into margins of distributary channels. Their behavior is iden-
three different components (Fig. 22.6). The emerged part is tical to that of the natural levees of the fluvial systems,
usually flat or of very low slope, constituting the section marking the overflow level of the channels during floods.
known as the delta plain. In front of this plain there is a They occur as terrains colonized by subaerial vegetation.
zone of greater slope that is constituted by the main They are usually better developed in river-dominated
bed-loaded sediments that manage to leave the mouths of the deltas, although they can also be present in other types of
distributaries. This region is called the delta front. Beyond deltas.
the front, there is a very low-slope zone consisting of sedi- • Interdistributary swamps: These are large vegetated areas
ments decanted from the suspended matter plumes. This is that extend between the channels in the rear area of the
the section called the prodelta. levees, having a somewhat more depressed relief than
Different sub-environments are distributed in the delta their surroundings. This topography makes these areas
plain. The inclusion and distribution of sub-environments susceptible to flooding during river floods, and also
vary among the different types of deltas, since they are the during spring high waters in those deltas affected by tides
result of the action of certain processes that work in different and by surges in deltas affected by waves. Evidently, they
ways (Fig. 22.7). In general terms, the environments that would also be areas flooded by mixed surge and spring
may occur in this plain are as follows: high tide processes during extreme meteorological events.
The vegetation that occupies these environments depends
• Distributary channels: These are the channels responsible on the climate of the region where the delta develops. In
for distributing freshwater flow and sediment load, con- deltas of tropical areas, mangroves and tree swamps are
necting the river source with the open sea. Their mor- common, while in mid-latitudes the most common
phology can be varied, ranging from straight to swamps are marshes and in deltas of periglacial areas
meandering channels and constituting networks of sim- permafrost may even develop.
ple, bifurcated or rejoining channels, depending on the • Delta plain lakes: These are the depressed areas between
dominant processes. In river-dominated deltas, their different slight distributaries that may not reach the
behavior and dynamics are no more than extensions of topographic level to become emerged. In this case, these
typical river channels; however, in tide-dominated deltas, areas are occupied by interdistributary lakes. Oxbow
they behave like estuaries, with water mixing and all lakes may also form in abandoned distributaries. The
processes related to the turbidity maximum taking place dynamics of these environments is similar to that of any
within them. In wave-dominated deltas, the number of lacustrine environment, with endorheic characteristics
Fig. 22.6 Typical components of a delta in the emerged and submerged areas
Fig. 22.7 Sub-environments

linked to the delta plain of
different types of delta.
a Fluvial-dominated delta, with
the example of the Mississippi
River Delta, USA. b Intermediate
river–wave delta, with the
example of the Nile River Delta,
Egypt. c Tide-dominated delta,
with the example of the
Irrawaddy River Delta, Myanmar.
(Images Landsat/Copernicus from
Google Earth.)
and stagnant waters. However, during floods, the waters limiting the extension of the distributary channels towards
and sediment distributed by the deltaic system can access the marine zone. However, in this case, and due to their
these lakes. topographic position, they are not colonized by
In addition to these, other different environments may vegetation.
develop in the frontal zone of the delta plain in response • Interdistributary bays: These develop in deltas where
to the marine processes that act at the delta front. These waves are not an important factor, being located between
environments can include: different levees in the open area of the delta. Their
• Submerged levees: These represent the continuation of dynamics are not directly affected by the currents circu-
the levees of the delta plain towards the submerged zone, lating through the distributary channels, but are more
closely related to the movements of the open water 22.4.1 Delta Plain Dynamics
masses.
• Barrier island/lagoon systems: In deltaic systems where In summary, it could be said that the dominant process in the
waves are important, a large fraction of the sediments of delta plains is aggradation. All the environments linked to
the delta front is reworked towards the coast in the form this deltaic domain tend to fill in until they reach the level of
of bars. In these cases, the bars can build barrier islands, the maximum level of the fluviomarine floods.
thus closing the interdistributary bays, whose position As mentioned above, the sedimentary dynamics of all
will then be occupied by lagoons. deltas is strongly conditioned by fluvial dynamics, since the
• Strandplains: In wave-dominated deltas, the entire river plays the role of main sediment supplier. It must be
deposit of fluvial sediment is reworked by waves to build taken into account that this supply is subject to seasonal and
prograding beaches. In this type of delta, the whole delta interannual oscillations in river flow. We can, then, consider
plain is made up of old beach strands and successive that deltaic construction goes through three different phases:
primary dune systems. periods of regular flow, periods of low flow and flood
At the front of the distributaries, just at the apical zone of events. The relative duration of each of these phases is
the submerged levees, the material transported along the regulated by the climatic regime.
channels is deposited in the form of bed load. In that During normal regime periods, two types of process
position, the environment that makes the delta front occur in distributary channels, depending on the presence or
prograde is located: absence of tides. In non-tidal deltas, distributaries function in
• Delta front bars: These are bars made of the coarsest a similar way to river channels. Through them, sediment is
material of the delta. Their shape depends entirely on the transported from the river system to the open coastal waters.
dominant agent that acts on them. In river-dominated In these deltas, the main deltaic accretion processes occur at
deltas, their shape is usually elongated, with an the delta front. In the case of tide-influenced deltas, the
ellipse-shaped plan, since no marine agent reworks the distributary channels behave as estuarine channels, and
morphology of these bars and they are preserved just as processes associated with water mixing occur within them.
the river deposits them. When the tide is the marine agent Processes such as flocculation and the concentration of
that reworks the sediments, the elongation is accentuated, suspended matter at the meeting of freshwater and saltwater
acquiring a spindle shape. Meanwhile, in deltas domi- masses cause the appearance of a turbidity maximum inside
nated by waves, they acquire crescentic shapes. these channels. The dynamics of these processes have
already been described in Chap. 9. Different tidal cycles
In deltas located in areas affected by severe storms, part cause the transit of sediments to the delta front, although a
of the coarse material deposited on the delta front can be large part of the fine sediments may be trapped in the mar-
remobilized by storm waves to build sandy ridges that cause ginal areas of the delta plain.
them to migrate over the delta plain. These ridges are pre- Despite the drama they represent for humans occupying
served in the upper part of the plain, since no other agent the deltas, floods are very beneficial for delta dynamics,
reaches this area during the normal functioning of the delta. since the highest rates of sediment delivery and the periods
These ridges are called cheniers and have already been of greatest delta accretion occur during these times. During
described as forms that can occur in association with tidal river floods, when the channels overflow their limits, a large
flats. part of the sediment load is immediately deposited on the
banks. This is caused by the rapid loss of velocity and
transport capacity that occurs during overtopping. This
22.4 Dynamics and Evolution causes the sediments to pile up and form levees. The
breaching of the levees cuts transversely through these
Deltas are sites of intense interaction between river and sub-environments, producing the transport towards fans of
marine processes. In this dynamic, the river represents the coarse sediment that are deposited on the swamps or lakes
main supply of sediment, while waves and tidal currents tend located in their rear zone. The scale of these breaks deter-
to rework all or part of the sediments coming from the river. mines the dimensions of the crevasse splays, which can
For a delta to develop, it is necessary that the river sediment range from several tens of meters to kilometer scale. The
supply exceeds the capacity of waves and tides to redis- erosive zone in the levee remains depressed after the flood,
tribute this sediment to other coastal environments. When so that the fan can be reactivated through this same break in
this occurs, the result is a net accumulation of sediment in successive floods, acquiring larger and larger dimensions. In
the form of a large sediment prism. The dynamics of deltas interdistributary swamps, currents only act during river
are regulated by this interplay of processes. floods. In these environments, there is a characteristic sheet
flow that is also slowed down by the presence of plants. The within the distributaries and the effluent water has a homo-
consequence is a loss of velocity, resulting in the deposition geneous vertical distribution of suspended matter. Hyper-
of finer sediments. pycnal flows occur when the denser waters are extruded
from the lower part of the water column (Fig. 22.8b). These
flows also occur in deltas with tidal influence and mixing
22.4.2 Delta Front Dynamics processes in the interior of the channels in which there has
also been previous settling, although they can also be
Sediments that reach the mouth of the distributaries do so in associated with deltas with a thicker load concentrated in the
the form of suspended matter and bed load. Once in open lower part of the water column. On the contrary, in hy-
water, the path followed by both types of material is dif- popycnal flows most of the suspended matter is located at
ferent. In both cases, the mouth of the distributary behaves the surface (Fig. 22.8c). This type of flow occurs when
as an effluent. From this effluent outlet, the suspended matter freshwater injected above the seawater flows directly out of
undergoes diffusion processes. These processes depend to a the mouth of the channels. The outflow of turbidity above or
large extent on the vertical distribution of densities of the below the water column influences a factor known as
aqueous flow. Bates [13] described three forms of density buoyancy.
distribution in outflows from deltaic effluents: homopycnal, In reality, sediment diffusion processes and the vertical
hypopycnal, and hyperpycnal flows (Fig. 22.8). density distribution model depend on the balance between
In homopycnal flows, the densities are homogeneously outflow velocity, turbulent friction with the bed and buoy-
distributed in the water column (Fig. 22.8a), whereas in the ancy of the outflow with respect to the coastal water mass
other two types of flow there is a vertically heterogeneous [14]. Different combinations of these three factors result in
distribution. This type of flow is associated with the presence of three different dispersion phenomena
tide-dominated deltas, where mixing of water has occurred (Fig. 22.9): inertia-dominated dispersions (axial jets),

different vertical distributions of
water density. a Homopycnal
pattern. b Hyperpycnal pattern.
c Hypopycnal pattern. The
isopycnal units are expressed in
g/cm3 (Adapted from Bates [13])

three models of dispersion
described by Wright [14] and by
Orton and Reading [15]. a Axial
jet. b Plane jet. c Surficial plume
friction-dominated dispersions (plane jets) and convection, moving outward in a spiral shape. This differ-
buoyant-dominated dispersions (plumes) [15]. ence in velocities between the two waters induces turbulence
Inertia-dominated dispersions occur when water exits in the seawater that is in contact with the plume, favoring
the mouth of the distributary with a high-velocity homopy- dispersion towards areas further from the distributary. The
cnal flow and enters a deep, high-gradient delta front. Under sediment from these plumes is dispersed seaward and
these conditions, the buoyancy factor is absent and there is deposited in areas away from the delta front, usually in the
little or no friction with the bed. The axial jet consists of a prodelta.
turbulent flow that disperses under homogeneous conditions. Negatively buoyant dispersions can also form when the
In the core of the turbulent flow, eddies develop that favor water leaving the mouth of the distributary has so much
the exchange between the flow and coastal waters. However, suspended matter that it has a higher density than the coastal
towards the sides and bottom of the flow, the velocity vec- water. In this case, the hyperpycnal flow will result in the
tors decrease due to friction with the coastal water mass. formation of a bottom-transiting plume. The behavior of
This decrease in velocity at the margins of the flow causes a these bottom plumes is similar to the surficial plumes;
lateral extension from the outlet at a reduced angle of about however, as they are influenced by friction with the bed,
12º. The mean flow velocity decreases with distance from their deceleration occurs more abruptly, depositing their load
the effluent until it gradually disappears completely in areas closer to the delta front.
(Fig. 22.9a). The result of this progressive decrease in flow The behavior of plumes mainly affects the dispersion of
velocity is a loss of transport capacity. Thus, the sediments suspended matter, while that of jets also influences bed load,
end up being deposited in the form of a bar elongated especially in the case of plane jets. Obviously, the deposition
towards the sea. Inertial flows are also characteristic of of bed load material is more closely linked to the flow
newly created distributaries before the sediment deposited velocities in the near-bottom shear zone than with the dis-
on the outflow bar causes its front to lose depth. These persion occurring in the water column. The velocity loss that
conditions do not usually persist for long periods of time. occurs at the outlet of the distributaries, especially in the
Friction-dominated dispersions also occur when a near-bottom zone, is responsible in all cases for the depo-
high-velocity homopycnal flow arrives onshore. However, in sition of delta front bars. The progressive or abrupt loss of
this case, the friction process dominates as it enters shallow velocity influences the dimensions and morphology of the
water, usually due to the presence of sediments deposited bars. Thus, the bars generated by axial jets are elongated
previously at the same mouth front. Plane jets are charac- towards the sea, acquiring a lunate morphology, while the
terized by minimal vertical expansion that is restricted by the bars generated by plane jets have lobate morphologies. The
shallow depth of these coastal waters. Under these condi- bars associated with plume-shaped flows develop in areas
tions, there is a more rapid slowing of the overall flow due to even closer to the mouth of the distributary and acquire a
the dominance of friction with the bed. This causes lateral less elongated and more laterally extended morphology.
expansion to occur at a greater angle of about 16°. Friction These bars are commonly referred to as bar-finger sands
with the bed also manifests in the presence of a strong shear (Fig. 22.10).
that drastically reduces the flow velocity towards the bottom In the previous sections, the behavior of dispersion at the
(Fig. 22.9b). At the surface, energy dissipation also occurs mouth of the effluent has been explained, taking into account
towards the sides, but in a more progressive manner. The only the energy of the river and considering the sea as a
result is that plane jets do not extend as far seaward as axial static body of water. However, in most instances, tides and
jets. The drastic loss of velocity has an immediate effect on waves also exert their influence, both in the dispersion pat-
sedimentation, so this type of dispersion generates bars very tern of suspended matter and in the development of delta
close to the effluent that contribute to a loss of depth and a front bars.
further increase in friction. The main effect of the tide is the entry of seawater
Buoyancy-dominated dispersions occur when freshwa- through the distributaries, contributing to mixing within
ter reaches seawater directly through the distributary with them. This effect favors the action of homopycnal flows in
moderate or low velocity, forming a hypopycnal flow. Under the delta front during ebb times, which are accompanied by
these conditions, the salt wedge occurs in the frontal zone of dispersions dominated by inertia and the development of
the channel and not in its interior. Thus, turbidity plumes lunate bars. However, the presence of opposing tidal currents
originate in the upper part of the water column and are reworks these bars during flow cycles, when seawater enters
dispersed at the surface (Fig. 22.9c). The lack of contact of the distributaries. The action of these currents reworks the
these flows with the bed inhibits the action of friction, so that marine end of the bars and gives them a spindle-shaped
the loss of velocity of the currents to the sides and bottom of morphology (Fig. 22.11). The movement of the sandy sed-
the flow occurs abruptly due to shear with the seawater. Due iment in these bars is reversed during a tidal cycle, although
to this effect, the waters of the plume enter into a double the currents may preferentially use certain sides of the bar.
Fig. 22.10 Morphology of

different types of delta front bars
without wave and tide action
Fig. 22.11 Morphology of delta

front bars under tidal and wave
action
Thus, it is common for one side of the bar to be used mostly The action of high-energy waves on distributary front
by ebb currents and the other by flood currents, although the effluents has an effect similar to friction with the bed [16].
net transport is always seaward, consummating the process On the one hand, waves hinder buoyancy by dispersing
of progradation. suspended matter throughout the water column. On the other
hand, they shorten the dispersion distance by acting against the waves transports the sediment along the coast, away
the outflow current and causing a drastic decrease in its from the mouth of the distributaries, and forms a continuous
velocity. The result is that the dispersion in the presence of delta front. Thus, the progradation of the delta front takes
waves behaves like a plane jet. In this way, the bars tend to place in a manner identical to that of the strandplains. In
be deposited in an area closer to the distributary mouth. The tide-dominated deltas, it is the superposition of tidal bars that
presence of the distributary front bars represents for the swell generates a progradation mechanism. Finally, in deltas
an element where the shoaling process takes place. The where there is a joint action of waves and tides, successive
action of the waves on the sediment of these bars results in a systems of barrier lagoon islands usually develop, and their
reworking of the material of the bars towards the land, attachment in the frontal zone generates a progradation–
especially at the ends of the bars, where the action of the aggradation mechanism.
outflow jet is minor. Thus, surge bars will develop parallel to It may seem that a continuous flow of sediment from the
the coast, which migrate towards the delta plain until they river, coupled with a constant reworking of the sediment by
end up against its front. Via this process, the outflow bars marine agents, would generate an uninterrupted progradation
acquire a crescentic morphology (Fig. 22.11). Being the of the delta. However, the progradation process is modified
result of similar processes, these bars are completely iden- by the delta dynamics and the preferential action of different
tical to ebb-tidal deltas, with the only conceptual difference sectors of the distributary network may shift progradation
being that they are not developed at the outlet of an inlet, but from some segments of the delta front to others. This is the
at the mouth of a distributary channel. process described by Coleman Prior [18] as delta switching.
In reality, delta switching is an effect that can be the con-
sequence of three different causes: channel extension,
22.4.3 Evolution channel switching and lobe switching.
Channel extension occurs as a consequence of progra-
By definition, deltas evolve towards the formation of a large dation and seaward advance of the delta plain. When
sedimentary prism at the mouth of a river. The main effect of extension occurs, the orientation of the channels as they
this evolution is deltaic progradation, which is what finally reach the delta front may change, causing the delta to change
forms this sedimentary prism. Progradation, in addition to the direction of its progradation. When there is more than
representing a seaward advance of the coastline, involves the one distributary channel, the relative proportion of load
generation of a characteristic internal structure consisting of between the two channels may be different. The conse-
the frontal attachment of sedimentary bodies with sigmoidal quence is that the deltaic sector at the front of that channel
or oblique morphology (Fig. 22.12). This process causes will prograde faster. This load ratio between different
delta front environments to advance over the prodelta at the channels may also vary over time with the extension process.
same time as the delta plain environments are superimposed Thus, areas of preferential progradation may migrate from
on the delta front. one part of the delta to another.
This progradation pattern manifests itself differently in Channel switching is another mechanism that is linked
different types of delta, depending on the dominance of one to the presence of several distributaries. However, in this
or other process. In river-dominated deltas, progradation is case, there is no change of relative load between the chan-
best observed in the growth of bars created by diffusion at nels, but rather the loss of functionality of one of them. This
the front of the distributaries. The internal structure of these phenomenon shifts the preferential transport to another
bars is composed of prograding foresets that extend over the channel, causing the progradation to migrate to the area in
prodelta. In wave-influenced deltas, this process results in a front of it. Normally, channel switching occurs due to
redistribution of sediment from the frontal bars that con- internal processes of the channels in the delta plain linked to
tributes to a homogeneous growth of the delta front envi- fluvial dynamics, such as plugging or capture.
ronments in a typical beach dynamic. The oblique arrival of
Fig. 22.12 Conceptual model of the progradational structure of a delta (Adapted from Gani and Bhattacharya [17])
Lobe switching involves the loss of functionality of processes do not move the material very far from the source,
complete branches of distributive channels. This process while lower density processes can move the material long
deactivates the progradation in complete areas of the delta distances. This material, especially in the case of turbidites,
front, activating other different areas and making the deltaic may be deposited as lobes in the prodelta.
progradation occur by complete lobes. Another post-depositional process that is linked to deltaic
The areas abandoned by channel switching and lobe sedimentation is subsidence. Subsidence of the delta base
switching processes are usually reworked and eroded by due to the weight of the significant sedimentary prism gen-
marine processes. This erosion is preserved in the record as a erated in these systems is a common process. Sometimes
ravinement surface. The presence of successive processes of subsidence is due to increased packing of the lower materials
progradation and abandonment of deltaic lobes gives rise to due to compaction. At other times, however, the weight may
the cyclicity observed in many deltas preserved in the geo- affect the bedrock, which yields and sinks under the weight.
logical record. Subsidence manifests mainly in the upper part of the
sequence, where different subsidence pulses can cause a
transgressive effect. On the other hand, differential subsi-
22.4.4 Post-depositional Processes in the Delta dence in some parts of the delta can cause the appearance of
Front adaptive faults, which cut the most recent sedimentary
formations.
The delta front reaches high slopes in some deltas, especially A phenomenon related to subsidence is diapirism. In this
in the case of coarse sediment deltas such as fan-deltas and case, the weight of the upper materials on the fluidized muds
Gilbert deltas. In these environments, the possibility of of the prodelta can cause them to rise and intrude diapirically
gravitational processes is high. These re-sedimentation into the sands of the delta front. These diapirs may even
processes require three conditions: (a) a high slope; (b) low reach the surface and extrude in the form of mud volcanoes.
cohesion between sediment grains; and (c) a trigger for the
initiation of movement. The low cohesion of the sediment
can be found in a low degree of packing that may be related 22.5 Depositional Facies
to a high rate of sedimentation. Movement is initiated by
destabilization of sediments previously deposited at the delta The depositional facies developed in each of the
front. The causes of destabilization can be diverse. They are sub-environments present in the deltas depend to a great
usually associated with the action of high regime flows extent on the variability of the processes occurring in them.
induced by fluvial activity, but can also be caused by the It is evident that these facies will depend on the type of delta,
action of storms or seismic movements. The processes since in each of them the sub-environments present are
involved may be of different nature, depending on the den- different and so the combinations of processes in them will
sity of the material that is set in motion downslope. These also be different [19].
vary in a wide range between landslides, slumps and debris
flow, which involve higher density, and other flows of lower
density, such as turbidity currents. 22.5.1 Depositional Facies Characteristic
Turbidity currents deserve special attention, as they may of River-Dominated Deltas
be responsible for the deposition of significant volumes of
sandy sediment in the prodelta. A turbidity current is a In deltas dominated by river action, many of the features
dense, highly concentrated flow with negative buoyancy. observed in the sub-environments are similar to those
This causes it to move downslope in a near-bottom fringe described in purely fluvial environments (Fig. 22.13).
reaching a high velocity and high shear rate. The flow may The distributary channels are dominated by sandy
be initiated directly at the mouth of an effluent during a facies that are organized in sets of seaward-sloping
negative buoyancy plume, or it may be initiated by trans- cross-stratifications. There are also sets of ripple-type
formation of other types of gravitational movements from cross-laminations, as well as scour-and-fill structures,
sediments already existing at the delta front. In the latter gravel intercalations and silt lenses.
case, it is common for the flow to start from the erosion of The lithofacies sequences of delta plain swamps are
incised channels that feed the sediment supplying the flow. similar to those of meandering river floodplains. They con-
The upper part of the delta front acts as a feeder for these sist of the superposition of fining-upwards sequences gen-
processes, while the base of the delta front and the prodelta erated by the weak currents that flow across this plain during
receive the materials eroded there. In the feeder zone, the flood periods. The base of each sequence may consist of a
occurrence of these processes is preserved as depressions, level of medium to fine sands with parallel lamination, fol-
erosional scars and incised channels. Higher density lowed by finely laminated silts and ending with clays

sub-environments linked to a
river-dominated delta

generated in the different
sub-environments linked to an
ideal intermediate delta
marked with drying cracks. The whole sequence is usually and silts, where parallel lamination dominates, although
intensely bioturbated by plant activity. Also typical is the sometimes the sands may show ripple development. These
accumulation of plant tissues that can lead to the formation sequences are also usually highly bioturbated by roots. The
of peat layers, which will be transformed into coal. crevasse splays are organized as fining-upwards sequences
At the margins of distributary channels, environments that begin with a cross-bedded, fan-geometric body of sands
such as levees and crevasse splays are also very similar to intruded from the river. Each sequence ends with the devel-
those present in meandering rivers. Their facies are similar as opment of a silt body that may have sand lenses in the form of
they are developed by the same processes. The facies of the flaser structures. These sand lenses disappear towards the top
levees are characterized by fine alternations between sands of the sequence, where parallel-laminated silts dominate.
At the mouth of the distributaries, delta front bars type of delta as an “estuarine delta” and their morphology as
develop. These bars are the result of the deposition of sed- “estuarine form” [10]. Similarly, there is no difference
imentary material due to diffusion processes. In between the depositional facies of these environments. Thus,
river-dominated deltas, the bars are composed of the facies sequences of the tidally dominated deltas are the
cross-stratified sand bodies that progress towards the sea. At same as those shown in Fig. 21.14.
the base of the sequence, represented by the most distal part
of the bars, there are intercalations of sand and mud.
In the area located in the delta front between the dis- 22.5.4 Depositional Facies Characteristic
tributaries are the interdistributary bays. The facies of Intermediate Deltas
developed in these bays are characteristically fine, although
some levels may be interspersed with ripples developed There is a wide variety of typology of intermediate deltas,
when these environments are crossed by flows during floods. depending on the relative transport capacity among the main
These muddy sediments usually have a high organic matter agents. The deltas in which there is a greater variety of
content and are greatly bioturbated by invertebrate activity. sub-environments and a greater richness of facies are those
The sediments of the prodelta are very similar to those of found in the central part of [3] triangle. In the intermediate
these bays. They are finely laminated silts and clays, often deltas, there are areas dominated by each of the agents that
interrupted by sheets of sand that may enter during times control delta dynamics. Thus, in the innermost zone of the
when the floods extend the jets or by the action of turbidity delta plain there are river-dominated environments. In this
currents. It is also common that their internal structure is zone, distributary channels and interdistributary swamps also
disturbed by the bioturbation of marine organisms. develop, and levees, crevasses and oxbows may exist in the
abandoned channels. These facies do not differ in any way
from those already described in river-dominated deltas.
22.5.2 Depositional Facies Characteristic In the frontal zone, there are environments dominated by
of Wave-Dominated Deltas waves, with a succession of beach sequences that, in this
case, constitute barrier island systems together with dune
The deltas dominated by waves are the ones with the least ridges. There are also no differences in the depositional
variety of environments, since only distributary channels, facies with the barrier islands that appear in non-deltaic
beach ridges and eolian dune ridges exist in them. None of contexts. Behind these islands are located systems domi-
these environments is exclusive to deltas. The depositional nated by the tide. In this case, lagoons are installed and tend
facies generated in distributary channels are indistinguish- to fill in until they become tidal flats. The depositional facies
able from those generated in river-dominated deltaic chan- characteristic of these sub-environments are also the typical
nels. Likewise, the facies of the sandy strands that constitute lithofacies sequences that have already been described.
these deltas are identical to the facies characteristic of any Here, the differences between the different types of
beach environment such as those that were studied in intermediate deltas are not so much in the nature of the
Chap. 17 of this book (see Fig. 17.18). For these reasons, facies, but in their distribution and amplitude, which are
some authors consider that they are not true deltas, since reflected in the geometric scale and thickness of the sedi-
they do not present diagnostic facies and their geologic mentary bodies that contain them.
record cannot be differentiated from the record of a strand-
plain. On the other hand, not even all the sediment accu-
mulated in this type of delta comes from the river, since it is 22.6 Facies Models
common for part of it to reach the delta transported by lit-
toral drift [20]. As can be seen in the previous section, there are no depo-
sitional facies exclusive to deltas. The innermost facies may
be mistaken for fluvial facies, while other outermost facies
22.5.3 Depositional Facies Characteristic may be associated with a variety of coastal systems such as
of Tide-Dominated Deltas barrier islands, estuaries, bays or strandplains. Therefore,
none of these facies can be used individually as diagnostic
If a tide-dominated delta is compared with a tide-dominated criteria in the identification of fossil deltas. However, deltas
estuary, it can be seen that the environments present are are complex systems and their three-dimensional architec-
identical: interbar channels, spindle-shaped subtidal bars and ture of depositional facies, studied integrally, can be used to
intertidal marginal bars. The only difference is conceptual, recognize them in the sedimentary record. However, the
and lies in the development of sedimentary bodies inside or dynamic complexity of deltaic systems means that there is
outside the funnel bay. In fact, some authors refer to this no single type of facies architecture characteristic of all
deltas. Far from it, in fact, as each particular delta seems to interrupted by sandy bodies that laterally connect with the
present a different geometrical arrangement in its facies. distributary channels. These are the crevasse splay facies.
Nevertheless, clear facies models have been established for Over all these facies are superimposed the marsh or mudflat
each of the deltas constituting the vertices of Galloway’s facies characteristic of the delta plains.
triangle, as well as for some intermediate types. These
models present a quite different architecture among them and
only coincide in the occurrence of prograding mechanisms. 22.6.2 Facies Model for Wave-Dominated Deltas
For this reason, the geometry of prograding mechanisms has
been widely used in the geological literature. Wave refraction phenomena lead to the reworking of the
delta front sands landward, to form prograding beaches on
the marine side of the delta. This process gives the delta a
22.6.1 Facies Model for River-Dominated Deltas characteristic cuspate geometry and a very simple facies
architecture consisting of the coalescence of beach ridge
The absence of waves and tides that rework the sandy sed- bodies. It is this amalgamation of sandy bodies that shows
iment at the delta front, the large number of distributaries the prograding mechanism in this type of delta (Fig. 22.16).
and the ease of occurrence of switching phenomena give the Each of these beach ridges may be overlain by foredune
facies architecture of river-dominated deltas an elongated ridge facies. The presence of numerous foredunes instead of
geometry and a characteristic bird’s-foot shape (Fig. 22.15). parabolic dune fields is the superficial diagnosis of the
In this model, distributary channel facies appear elon- progradation. On the other hand, in these deltas the number
gated in divergent directions, flanked on both sides by levee of distributaries is small, often presenting a single channel
facies. These levee facies extend underwater in the frontal that connects the river with the open coast crossing the entire
zone of the channels, guiding the currents outward, where bar system. In this type of delta, the channel switch phe-
dispersion phenomena occur. It is there that the delta front nomenon is frequent, which is reflected in the presence of
bars are formed. abandoned channel facies that also cross the system. These
The facies model shows numerous bar-finger sands. The old channels are observed on the surface as scars that cut the
arrangement of the sandy bodies within these bars clearly dune system. At the mouth of the distributaries, crescentic
shows the prograding mechanism characteristic of these bars develop as a result of wave-modified spreading phe-
deltas. These bars overlie the thin facies of the prodelta and nomena. However, these bars are not usually preserved and
are laterally bounded also by thin facies, in this case of the are completely destroyed by waves when a channel is
interdistributary bays. The fine facies of the bays may be abandoned.
Fig. 22.15 Facies model for a river-dominated delta (based on Reineck [21])

wave-dominated delta (Adapted
from Weise [22])
It should be noted that in this model the prodelta facies 22.6.4 Facies Model for Intermediate Deltas
are absent, with the delta front bars migrating directly over
the shoreface facies. The cause lies in the action of the waves The intermediate deltas in which the three main processes
on the dispersion phenomena, since the finer particles are (rivers, tides and waves) act together present very complex
washed by the waves and transported to other marine facies architecture (Fig. 22.18). This scheme shows the
environments. frontal advance of the delta based on the attachment of sandy
facies bodies of beach ridges that form barrier islands sepa-
rated by distributary channels. Unlike the wave-dominated
22.6.3 Facies Model for Tide-Dominated Deltas delta model, each of these ridges is separated from the pre-
vious one by tidally dominated depositional facies sequences.
Where tidal currents dominate the deltaic system, the dis- Each of the wave-dominated bodies shows internal evi-
tributaries form a network of rejoining channels separated by dence of progradation through the attachment of new bars.
spindle-shaped bars oriented in the tidal direction. The However, the rear of these bodies show landward fingerings
characteristic sandy facies of these channels are interbedded as evidence of sandy body migration in this direction. The
between the bar facies (Fig. 22.17). Progradation causes upper part of these sandy fingerings corresponds to the
these bars to grow above the muddy prodelta sediments. In development of washover fans. Coastal dune facies are
the innermost part of the delta, tidal flat facies overlying the developed over the entire body.
bar facies are characteristic. These tidal flats may be filling in Between different barrier islands, distributary front bars
some of the channels, which are then abandoned and closed, develop due to dispersion phenomena, which are of the
causing the more evolved bars to coalesce. Swamp or salt plane jet type due to wave action. The bars acquire a cres-
marsh facies cover the tidal flats when their topographic centic morphology that is very similar to that of ebb-tidal
level reaches the high tide level. Filled channels are usually deltas. As in wave-dominated deltas, these bodies are not
observed on the surface as geomorphological scars in the usually preserved, being reworked by the waves to build the
marshes. The abandonment of channels in the inner parts of beach ridges that accrete the barrier islands.
the system gives rise to lobe switching phenomena, which A tidally dominated regressive sequence is present in the
are very common in this type of delta. These phenomena are back zone of each of these sandy bodies. In this sequence,
also reflected in the progradation cycles of the different parts the vertical succession of depositional facies shows how the
of the system. system progressively somerizes as a result of sediment
The facies model also shows the connection of the deltaic aggradation. At the base of the sequence are the subtidal
system with the former estuarine system located in the inner lagoon facies, which progressively change to tidal channel as
part of the river valley. The base of the sedimentary fill in the system narrows. Over these facies, wide tidal plains
this part of the system is composed of fluvial sediments develop and are covered by marsh or mudflat facies. This
corresponding to the lowstand period and estuarine accre- entire tidal system is crossed by a dense network of tidal
tionary bodies (estuarine type) developed during the estu- creeks that flow into the main distributary channels of the
arine period preceding the development of the delta. delta.
Fig. 22.17 Facies model for a tide-dominated delta (Based on Maguregui Tyler [23])
Fig. 22.18 Facies model for a river–wave–tide intermediate delta (Based on [24]). The pattern shown in this facies model is repetitive in time,
which results in a progradational setup of the system
River-dominated facies develop only in the innermost 22.6.5 Facies Model for Coarse-Grained Deltas
parts of the system, where fluvial sediment fills a smaller
number of distributaries, and lateral bars, levees, crevasses Gilbert-type fan-deltas and other coarse-grained deltas do
and fluvio-marine floodplains similar to those described in not present a delta plain in the strict sense, since their
elongated deltas may develop. emerged part is a high-slope zone that connects an alluvial
Fig. 22.19 Facies model for

Gilbert-type deltas (Adapted from
Nemec [25])
fan or a braided river with the coastline (Fig. 22.19). In this delta type was proposed by Coleman and Wright [26] and
emerged part, the typical facies pattern of a braid plain is consists of the study of the thickness arrangement of the
developed, with interlocking channels separated by bars. sedimentary bodies. These thicknesses are reflected in their
These channels have a high capacity for avulsion and are isopach maps (Fig. 22.20).
filled with mixed gravel facies during the action of chan- In river-dominated deltas, the isopachs are arranged in a
nelized or sheet flows. These delta sectors may also be digitate shape, although in this case the design resembles the
affected by destabilization processes such as landslides and leg of a gecko more than that of a bird (Fig. 22.20a). A to-
slumps. Fan-deltas and Gilbert deltas differ in the relative tally opposite form is show by the wave-dominated deltas,
extent of the emerged zone, as well as in the slope. Gilbert where the thicker strips are arranged parallel to the coast
deltas have a lower slope and a greater extension in relation (Fig. 22.20b). At the third vertex of Galloway’s triangle,
to the submerged part. tidally dominated deltas present a distribution of isopachs
The delta front usually develops the prograding mechanism perpendicular to the coastline, with a shape reminiscent of a
characteristic of deltas. In this case, the prograding bodies are baseball bat (Fig. 22.20c).
made up of alternations of gravels, sands and silts from the jets In addition to the three delta types that occupy the
coming from the emerged part during confined and unconfined extremes of the triangle, Coleman and Wright distinguished
flows. This prograding structure is usually interrupted by three more intermediate types. In this sense, when there is a
erosional scars formed by the onset of mass movements such mixture between fluvial transport and wave reworking, two
as submarine landslides, slumps and debris flows, as well as by types are distinguished according to the greater or lesser
incised channels formed by turbidity currents. relative importance of the wave compared with the volume
The prodelta usually consists of fine sediments inter- of sediment contributed by the river. When the volume of
rupted by lenses of coarser facies generated by turbidity fluvial sediments cannot be completely reworked by the
currents. Turbiditic deposits have the characteristic Bouma waves, the innermost part of the system maintains the ori-
Sequence within them. This type of deposit occurs less entation of maximum thickness parallel to the river, while at
frequently in fan-deltas, whose facies are dominated by the delta front the isopachs become curved with a prefer-
debris flow deposits. ential elongation parallel to the coastline (Fig. 22.20d).
Advanced box. 22.1 Isopach distribution When the wave reworking capacity equals the fluvial input,
In present-day environments, the different types of delta the thicknesses are distributed in a more regular way, and
are easily recognized by their elongate, cuspate, lobed or then the isopachs acquire a more lobulate morphology
intricate morphology. However, in the sedimentary record (Fig. 22..22.20e). In the center of the triangle is the mixed
the recognition of delta types is not so simple. The facies model controlled equally by river, tide and waves. In this
architecture can be a clear indication, but in the intermediate case, the isopach pattern is distributed by zones, being fin-
types there is such a variety that it is can also be very dif- gered in the innermost sector and intermediate between types
ficult to identify them. One of the criteria for recognition of B and C in the central and frontal zones (Fig. 22.20f).
Fig. 22.20 Isopach distributions

of different types of delta
(Adapted from Bhattacharya [27])
Coleman and Wright’s study of the distribution of iso- accommodation and erosion at the delta front (Fig. 22.21a).
pachs actually shows a continuous spectrum, depending on Conversely, during the retrograding (transgressive) phase,
the relative work capacity among the three main agents, in the eroded volume exceeds the sedimentary input and the
which the six types described are merely identifiable delta front retreats, causing the delta plain to lose extension
patterns. (Fig. 22.21b). The result is that the regressive phase devel-
ops the prograding mechanism described in the previous
sections, while the transgressive phase develops discordant
22.7 Delta Cycles surfaces that separate different prograding units (Fig. 22.21
c). Thus, each unit developed during one of these cycles is
All deltas go through successive cycles. From a physio- composed of a set of obliquely arranged strata, where
graphic point of view, each of these cycles involves the progradation dominates over aggradation. This type of cycle
succession of a phase of extension of the delta plain, fol- was described by Frazier [28] in present-day deltas, and
lowed by another phase of reduction of its surface. From a identified in numerous fossil deltas.
sedimentary point of view, however, they can have different It should be noted that these cycles can occur on a
origins. In general terms the cycles can be classified into delta-wide scale when variations in input volume are due to
autocycles and allocycles. Autocycles are controlled by a general cause that affects the entire delta. The scale of these
changes in the dynamic conditions that determine sedimen- cycles is in the order of thousands of years. Lower order
tation in the delta, while allocycles are imposed by external autocycles may occur in specific delta lobes due to the
conditions such as relative sea level movements caused by switching mechanism. When this second case occurs, the
the combination of eustatic variations and subsidence. prograding phase of one lobe coincides with the retrograding
In the autocycles, the most important factor is the sedi- phase of another. The timescale of these cycles is in the
mentary contribution in relation to two variables: the order of hundreds of years.
accommodation space and the wave reworking capacity. Allocycles are more complex, since they are due to
Each cycle is composed of a prograding phase and a retro- phenomena unrelated to the input and processual dynamics
grading phase. The prograding (regressive) phase occurs of the delta (Fig. 22.22). Thus, allocycles are imposed by
when the volume of input exceeds the levels of subsidence variations or by sea level movements (or a
22.7 Delta Cycles 351
Fig. 22.21 Stages of autocycles

in a delta lobe
Fig. 22.22 Possible stages of

allocycles in a delta lobe
Fig. 22.23 Seismic profile across the Brazos River Delta (Texas, USA) showing the different units resulting from the combination of autocycles
and allocycles (Adapted from Bhattacharya Walker [27])
combination of both phenomena). They are cycles that 8. LeBlanc RJ (1975) Significant studies of modern and ancient
exceed the timescale of tens of thousands of years. Super- deltaic sediments. In: Broussard ML (ed) Deltas: models for
exploration. Houston Geological Society, pp 13–85
ficially, this type of cycle also involves an extension or 9. Scruton PC (1960) Delta building and the deltaic sequence. In:
reduction of the extent of the delta plain, and is composed of Shepard FP, Phleger FB, Andel TH (eds) Recent sediments
a regressive and a transgressive phase. However, the causes Northwest Gulf of Mexico. American Association of Petroleum
of the transgressive phase are not due to erosion or Geologists, Tulsa, Oklahoma, pp 82–102
10. Briggs D, Smithson P, Addison K, Atkinson K (1977) Funda-
reworking phenomena, but to marine invasions due to a rise mentals of the physical environment. Routledge, London
in the relative sea level. Thus, cycles dominated by input 11. Holmes A (1965) Principles of physical geology. Ronald, New
during a rise in relative sea level develop sigmoidal units York, p 1288
with progradation and aggradation mechanisms (Fig. 22.22 12. Gilbert GK (1885) The topographic features of lake shores. US
Government Printing Office, Washington, p 123
b). Conversely, cycles generated during a relative sea level 13. Bates CD (1953) Rational theory of delta formation. Am Asso
decline develop oblique units where there is only progra- Petrol Geol Bull 37:2119–2162
dation and the upper boundary of the sedimentary bodies 14. Wright LD (1977) Sediment transport and deposition at river
composing the unit is increasingly lowered (Fig. 22.22d). mouths: a synthesis. Geol Soc Am Bull 88:857–868
15. Orton GJ, Reading HG (1993) Variability of deltaic processes in
Contrary to what is observed in the autocycles, the units terms of sediment supply, with particular emphasis on grain size.
generated by different allocycles are separated by angular Sedimentology 40:475–512
unconformities and corresponding paraconformities. The 16. Wright LD, Thom BG, Higgins R (1980) Sediment transport and
end result of the combination of autocycles and allocycles is deposition at wave dominated river mouths: examples from
Australia and Papua New Guinea. Estuar Coast Mar Sci 11:263–
a complex pattern of progradation and progradation that 277
may be further modified by subsidence and affected by 17. Gani MR, Bhattacharya JP (2005) Bedding correlation versus
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Giosan L Bhattacharya JP (eds) River deltas: concepts, models and
examples. SEPM, Special Publication, vol 83, pp 31–47
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ments. American Association of Petroleum Geologists, pp 139–
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systems in the exploration for oil and gas: a research colloquium: 20. Reading HD, Collinson JD (1996) Clastic coasts. In: Reading HG
Univ. Texas, Bur. Econ. Geology (ed) Sedimentary environments. Processes, facies and stratigraphy.
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6. Elliott T (1986) Deltas. In: Reading HG (ed) Sedimentary tide-dominated deltaic sandstones, Lagunillas Field, Maracaibo
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25. Nemec W (1990) Aspects of the sediment movement on step delta James NP (eds) Facies models: response to sea-level change.
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Chemically and Biologically Controlled
Systems: Carbonate Coasts and Reefs 23
symbiotic relationship with a special type of algae. In this

23.1 Introduction
relationship, the algae supply photosynthetic material to the
coral, and in turn the coral provides shelter to the algae and
The previous chapters have described how chemical and
feeds them with nutrients contained in their metabolic
biological processes are active on all coasts, although it is
wastes.
the physical processes that determine the patterns of
In addition to coral reefs, there are other biogenic struc-
morpho-sedimentary evolution. However, on many coasts,
tures that are not related to corals. A particular type of reef is
chemical and biological processes exert the main control of
generated by colonies of tubeworms. Serpulids and sabel-
sedimentation and, therefore, are directly responsible for
larids are two types of worms that build important reef
coastal morphology. Carbonate coasts and reefs, as part of
structures by attaching themselves to the rigid tubes in which
these systems, are the best example of coasts controlled by
they live. Serpulids build their calcareous tubes directly from
chemical and biological processes [31].
secretions, while sabellarids use their secretions to build
Carbonate shores are located in the warm, clear waters
tubes by agglomerating sand grains and shell fragments.
typical of tropical seas. These are coasts that are associated
These organisms begin the construction of their structures on
with platforms where there is elevated carbonate production.
a coherent bed (rocky or cohesive) that provides a substrate
Chemical processes are rarely solely responsible for this
for anchoring. As in the case of corals, the attachment of the
high carbonate production, so, in most cases, organisms are
tubes of the new organisms to the abandoned structure of
responsible for inducing these chemical processes as part of
dead worms builds the reef. Worm reefs are also more
their biological activity. In particular, reefs often appear as
characteristic of tropical climates.
the main element of carbonate coasts and are the clearest
A third type of reef common today is the oyster reef. These
example of shorelines built by biological activity (e.g., [3,
reefs are completely different from the previous two. While
21, 33]). This type of coast is not only associated with the
oysters prefer turbid and brackish water conditions, they can
shallow areas of continental shelves, but also constitutes the
also form their reefs in temperate waters. These conditions
typical shoreline of many oceanic islands in areas located
mean that oyster reefs can be associated with siliciclastic
below 30° at both latitudes (Fig. 23.1).
environments such as bays, lagoons and estuaries.
In the past, there were many types of organism capable of
In the context of shallow carbonate environments, reefs
building reefs, but today corals are the most common species
can occur in different locations. While in many cases reefs
that make up these formations. Coral reefs are large struc-
are found on the coast itself, in other cases they are found in
tures of limestone secreted by these marine invertebrates to
offshore positions and extend into deeper areas. Thus, we
build their skeleton. In fact, each of these organisms is not
can find reefs on the coastal fringe, but also in the form of
capable of producing more than a few grams of limestone;
offshore barriers (on the outer edge of rimmed platforms), in
however, as they are colonial organisms, together they
shallow patches of carbonate platforms, or in oceanic atolls.
produce large quantities of rock. The coral colony lives in a
In this chapter we will deal with reefs in general, including
thin layer on the surface of the structure, settling their
those found in areas that are not strictly coastal.
skeletons on layers of older dead corals. In this way, the
Although reefs are the primary environments on car-
coral structure extends to the surface, out to sea and into
bonate shores, there is a suite of environments associated
deeper water to form large, complex systems. Although it is
with reefs or that constitute non-reef carbonate shores.
the corals that form the solid structure of the reef, they would
Among these environments are lagoons, tidal deltas, tidal
not be able to perform this task without the presence of
flats, mangroves and coastal sabkhas.
algae. The tissues of reef-building corals maintain a

https://doi.org/10.1007/978-3-030-96121-3_23
356 23 Chemically and Biologically Controlled Systems …
Fig. 23.1 Global location of the main carbonate and reef coasts, showing the biological provinces (Adapted from Davies [4]). Many oceanic
islands in both provinces also present carbonate and reef coasts
then become part of the sandy fraction to be redistributed to

23.2 Control Factors other environments. Other non-reef-forming carbonate shell
macrofauna, such as echinoids, mollusks, barnacles and
The environments present in carbonate environments are bryozoans, can also be a source of bioclastic sediment when
controlled by the distribution of organisms capable of gen- their remains are fragmented and redistributed by waves.
erating carbonates; however, this distribution is in turn Similarly, the shells of planktonic and benthic microorgan-
controlled by the interaction of several physicochemical isms, such as foraminifera, ostracods and coccolithophorids,
(temperature, salinity, nutrient concentration and water can become carbonate grains. In restricted environments,
clarity) and sedimentary (substrate type and volume of ter- diatoms and radiolarians are a source of siliceous grains.
rigenous inputs) factors and is strongly influenced by wave In the aforementioned cases, organisms contribute to the
and tidal activity (Fig. 23.2). generation of sedimentary bodies that give the environment a
prograding nature, extending the coasts towards the sea.
Although some organisms exert an erosional effect by
23.2.1 Organic Activity excavating the sediment or perforating the rocks, their action
is of minor importance. In this sense, some types of fish also
On carbonate coasts, the existence of reef-producing extensively corrode the reef structure; however, this action
organisms controls the distribution of other physical pro- contributes to the generation of large volumes of carbonated
cesses such as tides and waves. Corals and calcareous algae sandy sediment [10].
are responsible for building the reef structure. The presence
of this structure provides a hard substrate for anchoring other
organisms, but also divides the coastal zones, as the reef 23.2.2 Physicochemical Controls
structure protects the back areas from direct wave action.
The skeletons of these organisms are also an important There are several physicochemical parameters that control
source of sediment for the rest of the carbonate coastal areas. both the primary production of carbonates and the distribu-
Wave action removes fragments of the coral structure that tion of organisms in carbonate coastal areas. Among them

development of carbonate coasts
and reefs
are: temperature, salinity, oxygenation, water clarity and • The limit of light penetration also depends on water
nutrient concentration. clarity and determines the depth to which the coral bodies
can develop [18]. Most corals can form carbonate
• Water temperature is a major parameter in the control skeletons effectively up to 30 m deep. Although some of
of living organisms [32]. Most organisms capable of them can grow in deeper zones, corals are rarely able to
forming reefs do not tolerate cold water. One of the main form reefs below a depth of 50 m.
reasons is that corals can only reproduce if the water • Reefs are usually associated with good water oxygenation
temperature exceeds 20 °C. This is the factor that main- [18], but this is not a limiting factor, since zooxanthellae
tains the reefs. This factor also keeps coral reefs and produce oxygen during photosynthesis. However, the
mangroves restricted to tropical latitudes. The high concentration of dissolved CO2 in the water can be a
evaporation rates associated with warm waters are also limiting factor. A high concentration of this gas contributes
capable of generating carbonate environments uncon- to an acidification of the water that can be lethal to corals.
trolled by the activity of organisms. In these high tem- • The concentration of nutrients in the water also greatly
perature environments, reefs cannot form because the influences reef development [11, 19]. Nutrients are the
algae associated with corals cannot develop above 35 °C. nitrogen and phosphorus compounds used by photosyn-
• The distribution of many organisms is also limited by thetic organisms to make organic matter. It is evident that
salinity. In particular, in the case of corals, the formation a low concentration of nutrients will prevent zooxan-
of carbonate skeletons does not occur when salinity is less thellae from adequately performing photosynthesis.
than 27%°. Because of this conditioning, reefs do not However, excessive nutrient content can lead to the
develop in areas near river mouths where important dif- development of other types of algae that will eventually
fusion phenomena occur [18]. smother the coral [9]. Another harmful effect that can
• Corals need clear water in order to form reefs. On the occur is the proliferation of zooplankton to such an extent
one hand, the zooxanthellae algae that nourish the coral that it ends up consuming all the oxygen and causing
need light in order to photosynthesize and synthesize the eutrophication of the environment.
organic matter on which the coral feeds. On the other
hand, both corals and algae need to be free of sediment on
their surface to effectively perform their vital functions
[25]. Although corals can remove a certain amount of 23.2.3 Wave Action
sediment from their surface by secreting mucus, a high
sedimentation rate will prevent them from performing The energy range of waves in these environments is several
their functions and kill them [2]. orders of magnitude higher than the energy of the other
physical agents acting on them [23]. The way in which dynamics and distribution of carbonate shores and reefs. For
waves dissipate their energy on a carbonate coast in general, this reason, this type of environment is found specifically in
and on a reef front in particular, defines its erosional or the intertropical band discussed in the first section of this
depositional character, but also exerts a significant influence chapter.
on water clarity and dissolved oxygen concentration. Factors
that are directly controlled by wave action in turn control the
distribution of sediment grains and nutrients. The strategies 23.2.6 Relative Sea Level Changes
of living organisms to adapt to wave energy have a signifi-
cant influence on their physical design and also on the way Combinations of subsidence, tectonic uplift and eustatic
they carry out their vital functions. movements directly influence changes in the location of
For corals, moderate wave energy is needed to keep the topographic levels of wave and tidal action, as well as reef
water transparent and to disperse larvae. This wave energy growth fringes. Although these changes occur on very slow
will also help to limit competition and predation and to timescales, most of the present-day reef bodies show evi-
select the most effective coral geometric shapes to resist the dence of organic growth at times when the sea level was in
wave swash. These shapes are distributed according to the different positions. Thus, the resulting facies architecture
energy range that exists in each zone of the reef, depending often reflects evolutionary trends controlled by these posi-
on the depth and their location in the front or rear areas. tional changes.
The waves are also responsible for the genesis of car-
bonate beaches in some frontal reef areas. These beaches
function under wave dynamics in the same way as any other 23.3 General Morphology, Associated
beach. Environments and Forms
Carbonate shores are zoned according to the distribution of

23.2.4 Tide Action reef growth, the physical processes affecting the reef and the
development of sedimentary bodies resulting from the action
In coral reefs, the tide level controls the upper limit of of these processes. In general terms, geologists differentiate
growth of the reef body; since corals cannot withstand three zones in carbonate shores: the reef front, the reef body
prolonged periods of aerial exposure, they cannot grow and the back-reef zone.
vertically above the mean low spring tide. On other reefs, the The reef front is the area located in the open part of the
levels of exposure and submergence imposed by the tide reef, exposed to wave action. The reef body is the carbonate
exert another type of control. For example, oyster reefs are structure generated by the accumulation of coral skeletons.
concentrated in the central part of the intertidal zone The back-reef zone is the innermost domain of the reef,
according to the minimum time of inundation and the time protected from wave action by the reef body, but subject to
when the tide carries the highest concentration of suspended tidal action. It is usually a zone dominated by sedimentation
matter filtered by the oysters. based on carbonate grains produced by chemical precipita-
In other coastal carbonate environments, the tide is the tion (carbonate factory), secreted by planktonic and benthic
main factor controlling the dynamics. In this sense, the tide microorganisms or introduced from the outside by tidal
is responsible for the transport and deposition of carbonate currents.
sands in the tidal deltas located between reefs or other sand The area of the reef front usually has high slopes, pre-
bodies, as well as for introducing the carbonate muds that are senting gradients between 30° and 40°. This slope is usually
deposited in the lagoons and tidal flats behind them [30]. not constant and is often interrupted by steps and horizontal
zones that developed during lower sea levels. In the upper
zones, it is common for algal ridges to develop above the
23.2.5 Climate low tide level, which corals cannot overcome. These ridges
can rise more than 1 m above the body of the reef, which is
Climate exerts control over the physicochemical parameters protected behind them. At the front of the algal ridge, car-
that influence organic activity [27]. In this sense, water bonate beaches may also develop, which the waves accu-
temperature, salinity and nutrient distribution are mainly mulate from the fragments torn off the corals or from the
controlled by climate. On the other hand, climate controls debris produced by herbivorous and corallivorous fishes. In
the precipitation regime and insolation, exerting a notable the deepest areas of the reef front, there is a wide diversity of
influence on water salinity. Finally, climate regulates the coral forms that are distributed vertically depending on the
wind regime, and with it the wave regime. In general terms, light and their tolerance to hydrodynamic stress, subaerial
it can be said that it is the climate that really controls the exposure and the amount of suspended matter. In these areas
23.3 General Morphology, Associated Environments and Forms 359
it is also common to find a system of structures called spurs land, with no true back-reef zone. The contact with land is
and grooves, where longitudinal ridges of coral growth often occupied by a carbonate beach (Fig. 3f), constructed of
alternate with erosive grooves filled with bioclastic gravels. bioclastic sand composed mainly of coral fragments.
These structures usually occur in reefs where wave energy is
moderate, since grooves are generated by undertow currents.
23.3.2 Barrier Reefs
The contact of the spur and groove systems with the open
sea can be smooth or abrupt.
Barrier reefs are elongated islands separated from the
Most of the reef body develops behind the algal crest. The
mainland by a wide shallow-water lagoon (Fig. 4a). As with
upper part of this body is usually flat, as it is vertically
fringing reefs, the coral bodies of the reef body may be
limited by exposure to the air, and is therefore often referred
relatively continuous or separated by channels that act as
to as the reef flat. The extent of this reef plain can vary from
inlets, allowing the passage of open marine waters into the
tens of meters to several kilometers, depending on the fac-
lagoon due to tidal action. At both ends of these inlets, flood-
tors discussed in the previous section. Most of the reef body
(Fig. 4b) and ebb-tidal deltas develop, although the ebb
is constructed from the skeletons of dead corals, while the
deltas are usually less developed because the frontal areas
reef flat is where the main biological activity of the reef is
have a very high gradient.
concentrated. In this area, the wave action is not intense, as it
The characteristics of the reef front and reef flat can be
is protected by the algal crest; however, the high exposure of
very similar to those observed in fringing reefs. The reef
organisms to ultraviolet rays is a significant environmental
front is where most of the coral growth occurs (Fig. 4c),
stress factor.
while the reef flat may have different environments that vary
In the back-reef zone, waves are totally absent, although
between the development of live coral fields, dead coral
tidal action is present. The most common environments are
skeletons, or sedimentary sand or carbonate mud flats. The
lagoons, tidal flats and mangroves, where there is a tendency
presence of an algal crest just in front of the main body of
for sedimentary aggradation. There are usually inlets
the reef, as well as spurs and grooves to the fore of the
between the different reef bodies that allow seawater to enter
frontal zone, are common in this type of reef (Fig. 4d).
the lagoon, which can be associated with the development of
Sometimes, waves are able to form carbonate beaches that
ebb and flood tidal deltas at both ends of the channel.
partially cover the algal crest or the body of the reef front.
Not all reefs have the same three-dimensional distribution
What really distinguishes this type of reef from those
of these three zones and their associated environments.
described above is the existence of a large-scale lagoon that
Classically, several types of reefs have been differentiated
separates it from the land. This lagoon usually has a very
according to the geometric arrangement of these three zones
active sedimentation of carbonate muds, although, in
[28], distinguishing between: fringing reefs, barrier reefs and
large-scale systems, the sector of the lagoon closest to the
atolls. In addition to these three main types, there may also
mainland may also have terrigenous material (extraclasts)
be smaller reef bodies in the form of patches and tabular
from land. In the vicinity of the flood-tidal deltas, there is an
flats.
increase in sediment grain size, due to the greater influence
of tidal currents and material from the exterior in these
sectors. Patch reefs may appear along the lagoon. These reef
23.3.1 Fringing Reefs
patches can be coralline, although they can also be formed
by other organisms such as ostreids.
This type of reef develops attached to the mainland or sep-
arated from it by a very narrow and shallow back-reef zone
(Fig. 3a). Its width depends on the overall slope of the coast. 23.3.3 Atolls
The frontal zone usually has a high slope with a good ver-
tical distribution of coral forms that show a high growth rate Atolls are reefs that form a ring-shaped barrier around a
(Fig. 3b). This frontal zone also usually has pinnacles sep- central lagoon (Fig. 5a). They sit on the cusp of submerged
arated from the coral front (Fig. 3c). volcanic edifices, which may sometimes outcrop in the
The reef crest may have continuity in the reef body, central zone of the lagoon (Fig. 5b). These structures
although it most often has discontinuities in the form of develop mostly in the Indian and Pacific oceans, with very
channels that allow the tide to pass into the reef flat. These few examples in the Atlantic [28]. Their shape can vary
channels can reach tens of meters in width, and may even between circular, elliptical, parabolic or irregular, and their
extend some hundreds of meters [8]. Coral growth is scarce scale varies from hundreds of meters to several tens of
in the reef flat, being frequently covered by fragments of kilometers. Geometrically, they are usually asymmetrical,
dead corals (Fig. 3d) or fine sediments, or sometimes colo- due to the greater persistence of the swell on one of their
nized by seagrass (Fig. 3e). The reef flat is often attached to faces.
Fig. 23.3 Different elements linked to a fringing reef in Puerto Plata of a pinnacle in the reef front, d Dead corals in a reef flat, e Border
(Dominican Republic), a Aerial view showing the general aspect of a between the reef front and a seagrass prairie developed on the reef flat,
fringing reef, b Branching coral forms in the reef front, c Vertical wall f Carbonate beach in the inner part of a reef flat
The coral building zone shows few differences from a with coral patches scattered among calcareous mud surfaces,
barrier reef and the beaches that usually form in the higher although in this case the facies show a total absence of
areas of the reef flat. There is also a great similarity in the terrigenous material. Despite this facies similarity, the major
distribution of environments associated with the lagoon, difference between atolls and barrier reefs is the architectural
23.3 General Morphology, Associated Environments and Forms 361
Fig. 23.4 Features of barrier

reefs, a Aerial view showing the
general aspect of a barrier reef in
Belize (Landsat image from
Google Earth), b Aerial view of a
flood tidal delta developed
between different reef bodies in
the Bahamas (Landsat image
from Google Earth), c Coral
forms in a reef front (Belize),
d Spurs and grooves in a frontal
reef area (Florida Keys)
Fig. 23.5 Features of atoll reefs,

a Asymmetric ring-shaped atoll
(Hiti Atoll in the Tuamotu
Archipelago, French Polynesia),
b Atoll around a central volcanic
structure (Maupiti Atoll in the
Society Islands, French
Polynesia) (Images
Earth.)
arrangement of these facies, as will be discussed in rate is the rate of metabolic production of calcium carbonate
Sect. 23.5. by living organisms. This rate ranges from 1 to 10 kg per
year per square meter of coral surface. Obviously, this cal-
cification will result in different longitudinal growth rates
23.4 Dynamics and Evolution depending on the density of the resulting calcium carbonate
crystalline structure, but it will also result in a different value
The dynamics and evolution of carbonate shores is closely of reef volume depending on the density of the reef structure.
related to the interrelationship of the factors listed in In general terms, different authors have shown that, in recent
Sect. 23.2 of this book. In the short term, three factors decades, there has been a decrease in the rate of calcification
determine the dynamic functioning of the systems associated in all reefs worldwide (e.g., De’ath et al. [5]). This decrease
with the reef bodies: reef growth, wave action and tidal has been attributed to the effects of ocean water warming and
dynamics. On a longer timescale, climate variations and acidification, due to increased concentrations of dissolved
relative sea level movements influence the vertical and CO2.
horizontal displacements of the environments associated Once the reef body reaches the water surface it acts as a
with these coasts and are determinant in the facies archi- physical barrier to the waves. Thus, the action of the breaker
tecture. In the following section, these effects on the takes place only at the reef front, restricting the environments
dynamics will be discussed individually. associated with the lagoon, which are dominated by the
action of tides.
23.4.1 Reef Growth

23.4.2 Wave-Induced Dynamics
In coastal reefs, biological rhythms determine the growth
rate of the reef body and control the distribution of the other It has been described how wave action directly influences
dynamic agents, thus setting the general dynamic patterns of the shape and growth of corals and subsidiarily the growth
the sedimentary environment. In the reef body, there is an rate of the reef body. A different orientation of the reefs with
ecological zonation controlled by the vital factors of the respect to the dominant wave trains and the arrival of storm
corals (water agitation, luminosity, ultraviolet radiation and waves will determine ecological differences. On the one
nutrients) and these factors vary with depth and reef zone hand, the average energy dissipated by the waves controls
(front, top or back). In each of these ecological zones there the type of coral forms that can proliferate on the crest and
are corals with different shapes, ranging from encrusting, the reef front. This will determine the morphological dif-
globous, plate, branching, fragile branching and fan-shaped ferences in these environments according to the different
(Fig. 23.6). growth rates of each of the coral species capable of resisting
The growth rate is different for each species, where the this energy [13]. In this sense, it should also be taken into
coralline form is a determining factor [26]. Environmental account that waves and wave-induced currents are mainly
factors also significantly influence these growth rates [20]. responsible for the distribution of both larvae and nutrients
Depending on these determinants, longitudinal growth rates that feed corals [29]. Due to this fact, seasonal differences in
range from 1 to 16 mm per month. Despite these coral the wave regime induce the presence of ecological cycles
growth rates, the volume of the reef body itself develops at a [15].
much slower rate. This difference is due to the fact that coral Conversely, the morphology of the reef front conditions
growth leaves numerous gaps in the overall structure. These the wave energy dissipation gradients and the way in which
gaps are filled more slowly with a matrix consisting of waves can reflect part of their energy back to the open ocean
secretions from other organisms (mainly calcareous algae, or, under certain conditions, cross the reef plain and pene-
sponges and bryozoans) as well as fragments of corals and trate the back-reef areas. In many reefs, the presence of a reef
other organisms with fragile structures, broken and reworked ridge acts as a bar separating two zones with different
by the waves. This implies that much of the constructive behavior. The behavior of these two zones depends on the
activity performed by corals is, on the one hand, compen- topographic height of the ridge. At the front of the crest,
sated for by the destructive activity of other organisms phenomena associated with wave reflection and backwash
(bioerosion) and wave energy, but, on the other hand, the are responsible for the appearance of bottom currents that
material generated by this destructive activity contributes to control sediment transport. If the arrival of waves is oblique
complete the massive structure of the reef. to the reef front, these currents can circulate longitudinally in
However, longitudinal growth is not the only parameter the form of littoral drift. However, the morphology of the
for determining coral growth, as it results from the bio- reef front tends to channel these currents to deeper areas with
chemical process known as calcification. The calcification a strong coarse material transport component (Fig. 7a).
Fig. 23.6 Different coral forms, a Encrusting coral, b Globous coral, c Plate coral, d Branching coral, e Fragile branching coral, f Fan-shaped
coral
These currents are responsible for the genesis of spurs and When the waves exceed the topographic height of the reef
grooves and the filling of the grooves with bioclastic sands crest, the water circulates over the reef flat, transporting
and gravels from the dismantling of corals and other significant amounts of sandy bioclastic fragments to the back
organisms on the reef crest. reef zones (Fig. 23.7). Most of the wave energy in these
Fig. 23.7 Genesis of

wave-induced currents in a reef.
a In the reef front, b Through the
reef crest entering the reef flat
shallow areas is dissipated by friction. On fringing reefs, the small, the overwash processes become the main mechanism
sandy material transported by the waves is usually trapped on responsible for the environmental renewal of the lagoon
the reef flat, although under favorable conditions it may reach water and the introduction of sandy material into the lagoon.
the mainland to form a back beach. In barrier reefs and atolls, In some atolls, it has been observed that the surge that
these sandy bodies are preserved in the form of washovers at accompanies storms generally raises the sea level, causing
the contact between the reef body and the lagoon. The water sediment-laden seawater to enter the lagoon from one side
that overtops the frontal ridge to enter the flat or lagoon while the lagoon water exits from the opposite side [1]. This
usually returns to the open ocean in the form of rip currents type of process increases the rate of sedimentation in lagoon
entering channels that pass through the reef body. These environments.
currents also transport sediment into the deep areas.
The channels also allow waves to pass into the lagoon,
especially in the case of long wavelength waves. Another 23.4.3 Tide-Induced Dynamics
way in which waves can penetrate the back areas of the reef
is by passing through depressed areas of the reef crest when Most of the reefs are found in mesotidal and microtidal
it is irregular. In these cases, the surges associated with the coasts. Tidal influence is felt in two different aspects: water
action of persistent winds provide an additional rise in the levels and tidal currents. The main tidal currents occur in the
water level that facilitates this process. When this occurs in inlet channels between reef bodies, especially in barrier reefs
barrier reefs, complex refraction and diffraction processes with extensive lagoon systems. These internal tidal systems
determine the distribution of erosional and depositional allow drainage and renewal of lagoon waters. The more
zones on the continental shores of the lagoon [14]. Even so, extensive lagoons of mesotidal systems may have large tidal
the overwash through the reef crest always exerts an atten- prisms allowing the development of strong currents in the
uation effect on the waves that act in the rear zone. This channels that cross the reef body. These channels, unlike
attenuation increases with the width and height of the reef inlets in barrier island systems, are morphologically com-
body. In many instances, wave attenuation can also build plex. Their bed may be erosional or sedimentary, the latter
sand or carbonate gravel forms on the reef crest, which grow being filled with very coarse material.
vertically until they completely close off the wave passage to Towards the reef front zone, the channels usually flow
the reef flat along segments of the barrier. These forms can into slopes or areas of high gradient, in most cases inhibiting
exceed the height of the spring high tides and begin to the development of ebb-tidal deltas. However, in the case of
behave like islands with frontal beaches. lower slopes, ebb deltas tend to be complex and develop
In atolls, where the reefs restrict the direct connection between irregular reef bodies. In the area of the reef flat, in
with the ocean and where the tidal prism is usually very contact with the lagoon, flood-tidal deltas usually
develop. This type of delta is very frequent and presents a 4500 years. However, these reef systems are heirs of the
remarkable development, having dynamic and sedimentary systems that followed the Flandrian transgression that began
characteristics that are identical to the flood-tidal deltas of about 12,000 years ago. In fact, many of them developed on
the barrier island systems. the remains of reefs developed during the Eemian inter-
The filling of lagoons on barrier reefs and atolls can bring glacial period, when the sea level was at a position very
sediment to the low tide level. When this occurs, tidal flats close to the present one. Studies of ancient reef systems
develop, although many authors refer to them as peritidal show that reefs can adapt to sea level changes when they
environments. The nature of the sediment in these flats is occur at a slow rate, since the system can respond by
carbonate and has been studied in detail in Chap. 20. In accommodating its growth rate to compensate for these
some of these flats, stromatolites may develop, built by the changes. In this context, sea level changes imply modifica-
action of cyanobacteria. tions in the energy of the environment, as well as in the
Tide levels are essential to the functioning of carbonate ecological patterns that control the amount of nutrients.
tidal flats, but they are also important in the area of the reef These variations entail changes in the configuration of
front since they determine the height that the coral body and coastal systems to which organisms must adapt. Whether or
the algal crest can reach, in addition to controlling the swell not they succeed will depend on the direction of these
action band. The joint action of tides and waves will be changes, as well as on the rate at which the changes occur.
analyzed in the following section. When changes occur at a slow pace, the communities of
reef-building organisms manage to adapt by migrating the
reef body landward or seaward by constructing new struc-
23.4.4 Dynamics of Combined Waves and Tides tures on the substrate of those that are being abandoned.
In the event of a fall in sea level, the reef flats are the most
The combination of wave action and tidal levels controls the vulnerable environments, as they would be easily exposed to
sediment transport from the outer zones to the interior of the continental processes, constituting the morphology known as
lagoon across the tidal flat. The magnitude of the waves reef terraces. In this case, these are the parts of the reef that
combined with the tidal levels, marked by alternating high are first degraded when their materials are reworked by
and low waters and spring and neap tidal cycles, controls the surface waters, even becoming karstified. One particular
depth of water in the reef flat. In this regard, it should be example occurs in carbonate beaches that are exposed to
noted that wave propagation over the flat requires a mini- fresh waters, producing a cementation process that turns the
mum depth. carbonate sands into a solid beachrock. The core of some of
Wave inflow across the reef flat at times of high waters the barriers that constitute the current reefs is made up of
drives the transport of nutrients and larvae to the back areas older reefs that have been left hanging after a small fall in
of the bar, which contributes to the ecological renewal of the sea level. The presence of these cores is an elevated area that
lagoon water. In parallel, this process also determines the prevents waves from passing over it to the back areas. They
volume of sediment transferred from the reef front areas to are often areas where current carbonate beaches can develop
the inner areas. It has already been mentioned that the due to their action as a dissipator of wave energy.
drainage of lagoon waters due to simple tidal action is very Conversely, a rise in sea level creates an accommodation
important; however, it is necessary to take into account that space that stimulates vertical growth of the main body of the
many reef systems (especially atolls) develop very small reef. The relationship between the rate of rise and the rate of
tidal prisms. In these cases, and also on microtidal shores, reef growth can give rise to three situations [24]. These
waves may be the main agent responsible for the renewal of situations are known as sustained vertical growth (keep-up),
lagoon waters. In each stretch of the reef, the relative forced vertical growth (catch-up) and drowning (give-up).
importance between the volume of water introduced by These three cases can be recognized in the evolution of some
waves and that introduced by tidal currents is different. In reefs in response to upwelling during the Holocene trans-
this respect, important differences will be established gression, but are also reflected in the evolution of many
depending on the spacing and depth of the connections atolls where relative upwelling occurs by subsidence. In the
between the lagoon and the open sea. case of sustained vertical growth, the rate of sea level rise
can easily be matched by the rate of reef growth and, con-
sequently, there is continued aggradation of the reef body. In
23.4.5 Long-Term Evolution: Relative Sea Level many cases, vertical growth does not occur in all areas of the
Movements reef and involves a shift of reef environments towards the
mainland. In the case of forced vertical growth, the rate of
The current coral structures are the result of a relative marine upwelling begins at a higher rate than the rate of growth;
stabilization that has been maintained for at least the past however, the reef responds by increasing its rate of growth
until it finally matches the rate of upwelling and the reef entire volcanic structure would leave on the surface only the
survives. When this occurs, it is even more common for the atoll barriers around a central lagoon.
reef to migrate landward. In the latter case, the rate of In many cases, the rate of sea level rise is not constant,
upwelling is so high that the reef is unable to compensate for but takes place in pulses. Sometimes a rising pulse drowns a
the upwelling by increasing the rate of growth. In this situ- reef that is abandoned at depth while the spread of larvae in
ation, the depth of the reef body increases until a threshold is the new submerged zones consolidates new reef bodies. The
reached at which the organisms fail to survive and reef former reef plains are preserved underwater in the form of
drowning occurs. Even so, it is possible that the larvae submerged terraces. Successive horizontal terraces may be
manage to colonize shallower environments and new reef separated by more or less vertical slopes several meters high
bodies are formed in the newly flooded areas. as steps. These steps are visible in the bathymetry of many
The vertical growth model was used by Charles Darwin to Caribbean reefs.
construct his theory of atoll formation (Fig. 23.8). Darwin
deduced that the reefs of the Pacific archipelagos began by
forming fringing reef bodies on the shores of a volcanic island. 23.5 Facies
Subsequently, the subsidence of the volcanic structure would
cause a vertical growth of the reef body, which would move In principle, the complete study of a carbonate coast makes it
away from the emerged part of it until it formed a circular easy to distinguish between the reef formation and the sed-
chain of barrier reefs around it with a doughnut-shaped lagoon imentary environments built with transported carbonate
separating the two elements. Finally, the subsidence of the material. From this point of view, a first distinction could be
made between reciprocal framework facies and detrital
facies.
23.5.1 Reef Framework Facies
A quick glance may lead one to think that a reef framework

is built as a more or less homogeneous body constituting a
single facies. This facies was named boundstone by Dunham
[6]. Taking as a criterion the function of the corals in
building the carbonate body, [7] were somewhat more pre-
cise and distinguished three facies: bafflestone, bindstone
and framestone. However, from a sedimentological point of
view, there is a much wider variety of facies. To begin with,
there is a major structural difference between dome-growing
organisms (coralline algae and encrusting and globose cor-
als) and interlacing corals (plate-shaped, branching, fragile
branching and fan-shaped corals). The main difference is that
the first organisms build a solid structure with very few
voids, while the latter build a cavernous structure full of
voids that will later be filled with sands or gravels made up
of bioclastic fragments or coralline algal growths.
Recent studies [22] have distinguished seven different
reef framework facies. The main criterion used is the type of
coral growth, as each type is indicative of the environment in
which the corals develop. Each of these forms is designed to
adapt to environments with higher or lower wave energy,
luminosity, dissolved oxygen and nutrient availability, and
are therefore indicative of specific locations within the reef
structure. The identification of these facies in boreholes has
allowed us to interpret the evolution of numerous reefs in
response to Holocene sea level variations (e.g., [12, 16]).
The facies that have been distinguished are as follows
Fig. 23.8 Conceptual model showing Darwin’s theory of atoll genesis (Fig. 23.9):
23.5 Facies 367
Fig. 23.9 The seven reef

framework facies of [22],
indicating their common location
in a reef-building profile
• Coralline algal facies: These are laminated crusts of the reef front or in the back zone of the reef, as these
centimeter or decimeter thickness. They may include corals are fragile and do not support the continuous
in situ corals or fragments of reworked corals. They are movement imposed by wave oscillation.
located on the flat and the reef crest because their com- • Foliaceous coral facies: These are sediments formed by
pact growth allows them to resist the indirect action of the flat corals and often enveloped by muddy sediment or fine
breaking waves. sands. They develop in sheltered areas in the transition
• Domal coral facies: Coral bodies intermixed with between the reef flat and the lagoon, as these corals
encrusting coralline algae or scattered colonies separated support higher turbidity environments.
by bioclastic sands and silts. They are located on the flat
and the reef crest, and also on the frontal slope, since
these corals are capable of resisting the action of the
highest energy waves. 23.5.2 Detrital Facies
• Facies of encrusting corals: Masses developed in situ,
sometimes related to coralline algal facies and sometimes Montaggioni [22] studies include three detrital facies asso-
with a matrix of detrital material of different sizes. They ciated with the reefs, in addition to the seven framework
develop in the reef crests of high wave energy. facies already described. These facies are:
• Robustly branching coral facies: Bodies formed by a cav-
ernous structure of branching corals, with the cavities filled • Skeletal debris facies: These are formed by fragments of
with a matrix of bioclastic gravels and sands. They develop corals and coralline algae pulled from the reef in a matrix
in the upper part of the reef front, as they resist some wave of carbonate sand. The origin of these facies is direct
energy, although not the direct action of the breakers. wave action.
• Tabular coral facies: Masses with a rigid structure con- • Carbonate sand facies: These are sands of different sizes
sisting of in situ or reworked tabular corals with a matrix consisting of fragments of carbonate organisms (corals,
of carbonate sands or silts. These facies are typical of the coralline algae, mollusks, green algae and foraminifera).
reef flat and reef front, excluding the ridge, as they are The origin of the grains may be physical fragmentation
sensitive to wave spray. due to wave action and currents or biological fragmen-
• Arborescent coral facies: Structures formed by finely tation by fish and other vegetarian and corallivorous
branched corals with latticework filled with fragments of organisms.
the branches or simply accumulated from fragments of • Carbonate mud facies: These are made up of fine particles
reworked branches. They develop in the lower parts of from direct inorganic precipitation or from the
accumulation of defecation or skeletons of microorgan- • Pisolite gravels: Pisolites are subspherical grains formed
isms. They form the beds of lower energy zones, such as by regular concentric sheets of micrite around a core.
lagoons and seagrass meadows developed in the reef flat. Their size exceeds 2 mm. Spheres of smaller sizes are
called oolites. Their formation requires rolling transport
These facies describe well the sediments that are directly on a micritic background. They are typical of inner
linked to the reef body; however, they do not describe the margins of lagoons with moments of high energy.
totality of sediments that can be found associated with other • Oolite sands: Oolites are laminated subspherical grains
carbonate coastal environments linked to the lagoon and tidal that are similar to pisolites but smaller in size. Their most
action. Kendall [17] distinguishes a much greater number of frequent size is between 0.2 and 0.5 mm, although they
detrital facies, considering that the type of carbonate particles can reach 2 mm. They characterize the sandy shallows of
which constitute gravels, sands and muds, as well as other high tidal energy lagoon margins and almost entirely
biologically controlled facies, provide information on the constitute the sands of carbonate tidal deltas.
particular depositional environment within carbonate coasts. • Intraclast sands: Intraclasts are irregular grains formed by
Kendall identified the following facies (Fig. 23.10): previously cemented carbonate fragments. Intraclast
sands are composed of fragments of carbonate crusts
• Gravels and sands of skeletal grains: These correspond to removed from supratidal zones by energetic events. They
the carbonate sand facies described by Montaggioni [22] for are usually found accumulated in the form of cheniers in
reefs. These are sands composed offragments of skeletons of tidal flats or in aprons developed in deeper areas of the
reef-building organisms. They are typical of beaches, reefs.
grooves between reef bodies and reef slope aprons. • Pelletal sands: Pellets are grains composed of micrite,
• Gravels of grapestones: These are coarse sediments with a massive internal structure. Sizes are between 0.1
consisting of complex grains that appear as aggregates of and 0.5 mm in diameter. Their origin is a product of the
sand grains cemented by aragonite. They are revealed in fecal activity of organisms. They are typical facies of
margins of lagoons with moderate wave energy. lagoons.
Fig. 23.10 Detrital and

biologically controlled facies
defined by Kendall [17]
23.5 Facies 369
• Micritic muds: These are non-organic chemical precipi- spaces there are detrital facies of gravel and sand, dominated
tates. Their deposition requires calm subtidal waters, so by skeletal elements. In the transition to deep zones, a vertical
they are usually formed in lagoons. slope of several meters in height may extend, whose front is
• Stromatolites: These are built by the action of blue-green built of robust branching corals. This slope is interrupted by
algae on a fixed substrate. They alternate sheets formed furrows where metric-scale aprons composed of skeletal and
by algal filaments and others by carbonate particles intraclastic sands and gravels develop. At the base of the
trapped by the algae. The lamellae have an irregular slope, within the photic zone, there is usually a lower slope
shape. They are characteristic of the intertidal zones of section. This zone of the reef is dominated by arborescent
the carbonate tidal flats developed in the continental part coral facies, although their fragility causes them to frequently
of the lagoon. fracture, forming fields of skeletal sands whose grains are
• Oncolites: These are rounded but irregular clasts with mainly composed of reworked fragments of this type of coral.
concentric micritic lamination around a core. Like the In the reef flat zone, there are large areas dominated by
stromatolites, the precipitation of the lamellae is the result detrital sedimentation (facies of carbonate sands and muds).
of the activity of blue-green algae, but in this case on a The composition of the sands is dominated by skeletal
mobile substrate. They usually develop in very shallow fragments and oolites, although grapestones can also be
lagoons and very clear waters. found. These facies may be accompanied by others gener-
• Rhodolites: Very similar in appearance and origin to ated by organisms, such as oncolites, rhodolites and stro-
oncolites, but developed by rhodophycean algae. They matolites. The muds are of micritic origin and have a high
also develop in lagoons. organic matter content. On top of these muds, seagrass
plains usually develop. In the continental zone, there is
Obviously, the components of the detrital facies may appear usually a beach attached to the mainland. This beach is made
mixed, resulting in a much larger number of mixed facies. up of sands and microgravels with clasts of different origins,
although skeletal fragments usually dominate. Between these
detrital facies, there are usually patches of reefs composed of
23.6 Facies Models arborescent, tabular and foliaceous coral facies.
The way in which these facies intertwine

three-dimensionally depends on the type of coastline. This 23.6.2 Facies Architecture of Barrier Reefs
results in a facies model for each reef type: fringing reefs,
barrier reefs and atolls. Barrier reefs present a much more complex facies architec-
tural model (Fig. 23.12). As in the fringing reef model, the
reef ridge separates the reef front and reef flat environments,
23.6.1 Facies Architecture of Fringing Reefs although in this model there is an extensive shallow-water
lagoon that separates the reef structure from the mainland.
The architectural facies model for a fringing reef is the In the distribution of structural facies of the barrier reef,
simplest of all. The reef structure rests directly on a conti- there are practically no differences with the fringing reefs,
nental substrate. This substrate can be any type of rock, nor in the distribution of detrital facies of the reef front—
although it is often older reef systems. For example, in many although in this sector there may be systems of spurs and
Caribbean reefs, the present development is supported by an grooves, in whose depressions skeletal gravels and sands
Upper Pleistocene structure that developed in the last inter- accumulate. There are, however, differences in the reef crest:
glacial period (Eemian), more than 100,000 years ago, when in some sectors the waves manage to accumulate significant
the actual sea level was about 2 m above the present level. bodies of skeletal gravels on the crest, developing skeletal
The reef structure consists of the classic distribution of sand beaches on its front. Conversely, in other sectors the
environments described in Sect. 23.3.1, with a reciprocal waves frequently cross the reef crest, developing bodies of
ridge separating the environments of the reef front and the oolitic sands on it, and extending towards the reef flat in the
reef flat (Fig. 23.11). The entire framework is built by form of washovers. There are also numerous passage chan-
boundstone facies, although the types of structural facies nels between the reef crests. These channels are tidally
described by Montaggioni [22] can be differentiated in the dominated and have the same function as the inlets of barrier
different sectors. The reef ridge is made up of massive cor- islands. The bed of these channels can be erosional or
alline algal facies, dome corals and encrusting corals. On the depositional. In the latter case, skeletal and oolitic sands with
reef front, pinnacles built by robust arborescent corals are herringbone structures may accumulate on the bed. At the
often found; between them there may be spaces where the lagoon-facing end of these channels, flood-tidal deltas are
facies of tabular branching corals dominate. In some of these frequent, built mainly by oolitic sands arranged in
Fig. 23.11 Scheme of facies architecture of a fringing reef
Fig. 23.12 Scheme of facies architecture of a barrier reef
herringbone cross-stratified sets, although sets showing Towards the mainland, the influence of land input is
landward migration of carbonate sandy bodies dominate. apparent, and the muds may be of a marly type, incorpo-
In addition to branching, planar and foliaceous coralline rating the terrigenous fraction.
facies, other fixed algal constructions such as stromatolites The intertidal zones adjoining the mainland often develop
usually develop in the reef flat, although these can also tidal flats, presenting a facies sequence that was described in
develop on a mobile substrate (oncolites and rhodolites). Chap. 20 of this book (Fig. 20.15b). The upper part of this
Towards the lagoon, grapestone sand bodies and pelletal sequence may also consist of stromatolites, pisolites and
sediments also develop. These sandy sediments change to oncolites. The supratidal zones usually develop mangroves,
carbonate mud facies in the central zones of the lagoon. although in arid climates coastal sabkhas may also occur.
Fig. 23.13 Scheme of facies architecture of an atoll
23.6.3 Facies Architecture of Atoll Reefs 7. Embry AF, Klovan JE (1971) A Late Devonian reef tract on
Northeastern Banks Island, NWT. Can Pet Geol Bull 19:730–781
8. Guilcher A (1988) Coral reef geomorphology. Wiley, Chichester,
The distribution of the facies with respect to the reef body is 228pp
very similar to that described for the barrier reefs, except for 9. Hallock P, Schlager W (1986) Nutrient excess and the demise of
the fact that the reef structure is annular (Fig. 23.13). Thus, coral reefs and carbonate platforms. Palaios 1:389–398
in those atolls that occur in mesotidal environments, there 10. Hixon MA (1997) Effects of reef fishes on corals and algae. In:
Birkeland C (ed) Life and death of coral reefs. Chapman and Hall,
are ridges that develop detrital bodies in their upper part, New York, pp 230–248
which are interrupted by channels that develop flow deltas 11. Hopley D (1989) Coral reefs: zonation, zonality and gradients.
towards the lagoon. The reef front usually also has spur and Essener Geogr Arbeiten 18:79–123
groove systems, although these end in a slope of much 12. Hopley D, Smithers S, Parnell, K (2007) The geomorphology of
the great barrier reef, development, diversity and change.
greater depth than in most barrier reefs. Lagoon zones, Cambridge University Press, Cambridge, 532pp
however, do not usually have the intertidal systems descri- 13. Hubbard DK (1997) Reefs and dynamic systems. In: Birkeland C
bed in the near-continent zone—since there is no continent (ed) Life and death of coral reefs. Chapman and Hall, New York,
—although intertidal systems may develop in the final stages pp 43–67
14. Kench PS, Brander RW (2006a) Wave processes on coral reef
of lagoon filling. flats: implications for reef geomorphology using Australian case
studies. J Coast Res 22:209–223
15. Kench PS, Brander RW (2006b) Response of reef Island shorelines
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keep-up, catch-up and give-up. In: Proceedings of the fifth reef: West Maui Hawaii. Estuar Coast Shelf Sci 77:549–564
international coral reef congress, vol 3, pp 105–110 30. Thomson RE, Wolanski E (1984) Tidal period upwelling within
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Biol Annu Rev 53:215–295 Cambridge University Press, Cambridge, 623pp
Part IV
Coastal Evolution on a Geological Time Frame
Sleeping geology
on the isolated shore
for millions of years.
Mysterious evolving
problem solving.
“Platypus”
Mr. Bungle
Climate: Climate Variability
and Climate Change 24
all these possible causes, talk today of climate change at the

24.1 What is Climate?
popular level (and also for many scientists) has become
practically synonymous with global warming caused by
Climate is the set of atmospheric variables existing in a
humans through the emission of greenhouse gases.
given place over a long period of time [26]. Among the
variables that constitute climate are precipitation, atmo-
spheric humidity, temperature, atmospheric pressure, inso-
lation and wind. Climate should not be confused with
24.3 Climate Forcing and Climate
weather, because, although the latter is an expression of the
Mechanisms
same variables, it is considered at an immediate moment and
not over a prolonged period of time. A particular climate is
24.3.1 Explaining the Global Climate Machine
often referred to by reference to the average values of the
The 10 km of thickness of the troposphere, the lower layer
variables given above. The extreme values of these variables
of the atmosphere, represent a thin sheet with respect to the
and the probability of reaching them are also often charac-
more than 6000 km of the Earth’s radius. However, it is
terized. However, the climate actually involves the charac-
there where most of the air is concentrated and where the
terization of changes in the climatic variables over short
climatic phenomena of our planet are forged. In this layer,
periods of time (daily, monthly and annual). In this case, we
air circulation takes place in the form of convective cells.
speak of the climatic regime or climate variability.
The driving force of these are the differences in solar radi-
ation received by the Earth’s surface and the thermal
exchange between the land or water surface and the air in
24.2 What is Climate Change?
contact with it. Generally speaking, tropical regions receive
more solar energy than polar regions, and this energy is
Climate change involves any change in the statistical values
redistributed around the planet thanks to the circulation
of the aforementioned variables over the long term (at least
movements of the atmosphere and the ocean influenced by
decades). In fact, when we speak of climate change, we are
this energy gradient [26]. The excess of energy received in
referring to changes in the climatic regime, ignoring changes
the intertropical regions causes a warming of the air that
occurring over shorter periods of time, which are considered
decreases its density so that it rises. This ascent creates a
climate variability. In any case, change is an inherent char-
permanent belt of low pressure over the Equator called the
acteristic of the climate whatever the time period considered,
equatorial low or doldrums, and causes continuous rainfall
so that there has never been a period in the history of the
at these low latitudes. As this air rises, it is replaced by air
Earth in which all of the variables considered have remained
arriving from higher latitudes (trade winds). This phe-
constant. In other words, the term climate change is redun-
nomenon is known as intertropical convergence and it
dant in the same way that it would be redundant to say rising
generates a convective circulation system called the Hadley
upward or falling downward.
cells (Fig. 24.1). Between the two Tropics, and on both sides
Climate changes can be due to natural causes external to
of the Equator, there are two circulation cells that rotate in
the Earth system, such as changes in solar radiation, as well
opposite directions. This phenomenon controls the entire
as internal causes such as changes in the way the Earth
atmospheric circulation, the climatic distribution of the globe
receives that radiation (changes in the Earth’s orbit or
and its precipitation patterns. The strip of latitudes influ-
changes in atmospheric composition). On the other hand,
enced by the Hadley cells has a humid and warm climate,
changes can also be human-induced. Despite the existence of

https://doi.org/10.1007/978-3-030-96121-3_24
376 24 Climate: Climate Variability and Climate Change
with two distinct seasons (rainy and dry) based on the lati- air from the middle latitudes that circulates towards the
tudinal displacement of the cells according to the position of higher latitudes rises above the cold air that circulates
the Earth with respect to the Sun, taking into account the tilt towards the lower latitudes. This front has a wavy shape,
of the Earth’s axis. since its position varies depending on the relative wind
In the polar circles, the opposite effect occurs. Receiving speed. These undulations of the polar front are known as
less solar radiation, the air cools and densifies, circulating Rossby waves.
downward from the upper parts of the atmosphere. This At the contact between the mid-latitude cells and the
generates a high-pressure system over the Poles. The excess Hadley cells is a belt of high pressure known as the sub-
of downward air generates a convective cell where cold tropical high or horse latitudes, located around 30º in both
winds at the Earth’s surface circulate towards the lower hemispheres. These high pressures cause air to descend from
latitudes. These cells are known as the polar cells. It is the upper layers of the atmosphere. On reaching the Earth’s
evident that in the polar cells the climate is cold and dry and surface, the air is divided and deflected into each of the cells.
the lowest temperatures on the planet are produced there. Although it may seem that the distribution of these zones
The surface winds generated in both cells are affected by is constant, there is great variability in temperatures and
the Earth’s rotation and the Coriolis effect, thus deflecting precipitation in each of them throughout the year—as well as
westward. However, the mid-latitude climate is dominated between different years, since the polar front and the sub-
by the movement of the wind belts which, by way of com- tropical high occupy different positions (further north or
pensation, circulate eastward in both hemispheres. These are further south) depending on the oceanic water temperature,
the regions where the cold air masses originating in the polar which varies from one year to another in relation to solar
regions and the warm air rising from the Tropics collide, irradiation.
forming a third type of cell called the mid-latitude cells. In the contact of air masses in the horse latitudes, and also
In the contact between the mid-latitude cells and the polar in the polar front, horizontal spinning convective cells
cells, masses of air of different temperatures meet, producing induce low pressure centers. These cells always develop at
an effect called the polar front. In the polar front, the warm the contact between the atmosphere and oceanic water due to
Fig. 24.1 Global convective

atmospheric circulation cells. The
scale of the atmospheric thickness
has been amplified to show the
cell winds more clearly
24.3 Climate Forcing and Climate Mechanisms 377
the thermal exchange between the two fluids. The low The decadal cycles of solar irradiance directly influence
pressure cells generated in the horse latitudes are called the temperature distribution of the planet, and cause exten-
tropical cyclones (also hurricanes or typhoons, depending sions and retractions of the amplitude of the atmospheric
on the ocean in which they originate), while those associated cells described in the previous section. This gives rise to
with the polar front are called squalls or simply storms. climate oscillations such as the El Niño–Southern Oscilla-
Within each of these rotating cells, there is a contact zone tion (ENSO), the North Atlantic Oscillation (NAO) and
between air masses of different temperatures, called fronts. others located in different oceanic sectors. The differing
In these fronts the cold air mass is introduced under the mean temperature also has a direct influence on the tracks
warm air mass forcing it to rise and generating cloudiness followed by storms. This is true both for storms generated in
due to adiabatic decompression. The rotating cells have the the horse latitudes and those originating in the polar front.
particularity of moving across the ocean in which they form Longer solar cycles are responsible for longer-term trends
until they reach the coasts, where they enter the continent of change. For example, the cycle of minimum activity
and move over it. The climate of mid-latitudes depends inferred from the near disappearance of sunspots between
entirely on the passage of low pressure cells, which alternate 1645 and 1715 is known as the Maunder minimum. This
with the establishment of high pressure centers called period coincided with a global cooling episode known as the
anticyclones. “Little Ice Age.” A similar episode, although of lesser
In mid-latitudes, seasonal climatic differences depend on intensity, occurred between 1798 and 1832 during the Dal-
the position of anticyclones and the trajectory of low pres- ton minimum.
sure gyres. These trajectories depend in turn on the latitu- In addition to the total solar irradiation, the emission of
dinal position of the polar front and the subtropical highs. ultraviolet rays also goes through cycles that directly influ-
The evolution of the coasts of these latitudes is strongly ence temperatures. As well as direct heating, ultraviolet rays
influenced by the passage of these cyclones, which result in are responsible for the breakdown of ozone molecules in the
strong storms. upper layers of the atmosphere. A third process that signif-
icantly influences the Earth’s climate is the solar wind. Over
time, there are also significant cyclical variations in this
24.3.2 The Role of the Sun as the Main Climate process that have indirect effects on climate. An intense solar
Driver wind contributes to blocking some of the cosmic rays
coming from outer space. The arrival of more or less cosmic
It is clear from the previous sections that the origin of the rays on Earth causes changes in the production of radioac-
existence of atmospheric convection cells is insolation. In tive atoms in the upper layers of the atmosphere. This phe-
short, the Sun plays a fundamental role in the Earth’s cli- nomenon has consequences in the generation of clouds and,
mate, as it is the only source of energy that heats the Earth’s therefore, of cyclical changes in precipitation.
surface. Therefore, it can be said that the Sun is the main
driver of climate processes [20, 24]. Scientific knowledge
about the Sun allows us to state that the star is less stable 24.3.3 Internal Modes of Climate Variability:
than it may seem. The energy it emits is far from constant Short-Term Climatic Cycles
and presents seasons and storms, as well as going through
rhythms of activity that are reflected in the existence of The term internal modes of climate variability refers to
irradiation cycles. Today, it is known with certainty that changes in climate variables related to the way in which the
solar irradiation is directly linked to the existence of the planet’s surface receives solar radiation [8]. Thus, variability
phenomenon known as sunspots. related to changes in atmospheric composition, such as those
The number of sunspots varies almost daily. A continu- linked to the concentration of greenhouse gases and the entry
ous count of sunspot numbers (Fig. 24.2a) shows cycles into the atmosphere of particles from volcanic eruptions, are
varying from eight to 15 years. Measurements of the Sun’s excluded from this concept. On the contrary, these modes of
total irradiance (Fig. 24.2b) meanwhile show a remarkable variability consider the patterns of thermal exchange of the
correlation with the sunspot number curves. While solar oceans, continents and ice sheets with the atmosphere. The
irradiance data are not available beyond several decades, best-known short-period cycles of change are the ENSO and
there are sunspot number counts from the early seventeenth the NAO. Among the most studied cycles of longer duration
century (Fig. 24.2c). These data give an accurate picture of are the Pacific Decadal Oscillation (PDO) and the Atlantic
the resilience of decadal cycles over centuries, and also Multidecadal Oscillation (AMO).
allow us to observe how the amplitude of these cycles To understand how these cycles work, we can analyze the
oscillates secularly, marking other cycles of longer most studied of them: ENSO. This is a climatic pattern that
duration. consists of a cyclical change in the climatic parameters of the
Fig. 24.2 Cycles of solar

activity. a Daily number of
sunspots since 1950. b Total solar
irradiance (W/m2).
c 365 day-averaged number of
sunspots since the beginning of
records
equatorial Pacific over periods ranging from eight to cells. Thus, El Niño is linked to the occurrence of droughts
15 years. The oscillation consists of a transit between two in some places, while in others there are torrential rains and
opposite phases, one of warming of the eastern Pacific sur- extreme events such as tropical cyclones. La Niña is
face (known as El Niño) and the other of cooling of the same responsible for the same phenomena, but in different places
area (called La Niña). At one extreme, during El Niño, the [9, 32, 35]. The rest of the known oscillations have similar
ocean receives more solar radiation and overheats. The effects [10, 14, 28, 40] and all of them together cause
warming of the ocean surface (Fig. 24.3a) is transferred to extreme atmospheric phenomena at the global level
the atmosphere, which accompanies the increase in tem- (Fig. 24.4).
perature with an increase in humidity as it receives masses of The study of long-period climatic cycles is approached
evaporated water. Higher temperature and humidity imply using different methods: dendrochronology, coral growth
an increase in cloudiness and, consequently, in precipitation. phases, rhythmic lamination in sediments and speleothem
This warm and humid air mass expands towards higher growth. Any of these methods applied to a particular area
latitudes in both hemispheres, shifting the boundaries of all shows that decadal alternation of droughts and very wet
climatic zones in the same direction. At the opposite periods appear recurrently in mid-latitude areas throughout
extreme, during La Niña, the ocean receives less solar the Holocene (e.g., Cook et al. [5]; Büntgen et al. [7]).
radiation and cools (Fig. 24.3b). This cooling causes a The climatic variability produced by these short-period
temperature transfer from the atmosphere to the water and cycles profoundly affects the dynamics of coastal systems.
the air loses moisture as it cools. Consequently, climate cells For example, changes in precipitation lead to a change in the
contract and their boundaries move toward the equatorial water and sediment input regime to estuarine and deltaic
zones. systems, and also affect the sediment input to open coastal
The alternation in time of oceanic water temperature environments. Many studies have shown the relationship
oscillations accompanied by the expansion and contraction between these cycles and the change in estuarine mixing
of atmospheric cells are responsible for some extreme type, affecting suspended matter concentration, salinity,
cyclical changes observed in the contact zones between dissolved oxygen and nutrient flux.
Fig. 24.3 Distribution of temperature deviation during an ENSO cycle. a Warming of the equatorial Pacific area during El Niño. b Cooling of the
same area during La Niña. (Images from the Peruvian National Service of Meteorology and Hydrology.)
24.3.4 Earth’s Orbital Influences: Long-Term oscillations of these variables are known as Milankovitch
Climatic Cycles cycles after the Serbian astronomer who discovered them.
From an early age in school, we are taught that the Earth
In addition to the variability produced by solar activity and has two motions: one of rotation around itself and the other
internal modes, there are other changes that are produced by of translation around the Sun. This apparent simplicity hides
orbital cycles of the Earth. The repetitive cycles of the orbital variations that occur in both movements. These
Earth’s orbit affect the angle of incidence of solar radiation, variations are due to the influence of other bodies present in
thereby controlling the effects of incident solar energy. the solar system. First, the Earth’s axis of rotation about
Among these cycles are: the angle of inclination of the itself is displaced with respect to the normal movement of
Earth’s axis, the motion produced by the precession of the the orbital plane passing through the center of the planet.
equinoxes and the degree of eccentricity of our planet’s orbit The angle formed by the two axes is known as obliquity,
(Fig. 24.5). The climatic cycles induced by the periodic although it is also popularly known as the “tilt of the Earth’s

anomalous droughts and intense
rains associated to internal modes
of climatic variability
axis.” The obliquity oscillates between 22.1 and 24.3°. The circle is called eccentricity. Over time, the ellipse changes
difference between these obliquity values oscillates in cycles shape between maximum and minimum eccentricity values,
of 41,000 years. completing cycles with a period ranging from 95,000 to
Meanwhile, the axis of rotation of our planet changes its 125,000 years, and a cyclic rate of about 400,000 years.
position with respect to the orbital plane in such a way that a These changes are related to the gravitational action of the
rotation around the normal position of this plane takes place. two major planets of the solar system: Jupiter and Saturn.
This spin is known as axial precession and manifests itself in The precession, obliquity and eccentricity cycles do not
a variation in the orientation towards fixed stars such as the act in phase and combine in a non-linear way. These orbital
Pole Star (in the Northern Hemisphere) or the Southern Cross cycles directly influence the Earth’s climate. Obliquity
(in the Southern Hemisphere). The period of a precession controls the latitudes that receive the most insolation. At the
orbit ranges from 19,000 to 24,000 years, with a mean value same time, eccentricity controls the length of the seasons and
of 25,771 years. This motion is induced by the gravitational equatorial insolation [4]. Among the combined effects of
effect of the Moon as it revolves around our planet. The sum these cycles are the Pleistocene glaciations, which fit the
of the movements of precession and obliquity variation pro- eccentricity cycles almost perfectly. The influence of
duce an apparent effect of vibration of the precession trajec- Milankovitch cycles on sedimentation has been corroborated
tory. This vibration is known as nutation. by numerous studies in different sedimentary environments.
The third orbital cycle occurs in relation to the Earth’s Among them, those carried out in coastal systems are
translation around the Sun. This motion occurs in a rotation especially interesting, because the sea level movements
with an elliptical orbital path where the Sun occupies an induced by these climatic cycles are the origin of displace-
eccentric position. The degree of similarity of this ellipse to a ments of the coastline, thus generating coastal sequences.
Fig. 24.5 Orbital origin of the

Milankovitch cycles
24.3.5 The Processes of Absorption that was discussed in Sect. 10.3.1. The surficial ocean cir-
and Reflection of Solar Energy culation cells are the ocean’s response to the flow of energy
in the atmosphere from the Tropics to the polar regions,
When solar radiation reaches the Earth’s surface, whether which is influenced by the Coriolis force and the presence of
continental or ocean surfaces, a transfer of energy takes the continents. On the other hand, part of this surface water
place. In this process, the terrain of the continents or oceanic circulates at depth due to the thermohaline circulation. Both
water absorbs part of the solar energy. When the energy is currents constitute the so-called ocean conveyor belt [23].
absorbed by the oceanic water, overheating occurs, which As they circulate, ocean currents transport large masses of
directly affects the oceanic circulation processes, but also has warm water to latitudes and depths where only cold water
a response in the atmospheric circulation systems, since this would otherwise exist. Warm water currents to deep areas
excess energy ends up being transferred to the air. The contribute to heat storage in the ocean floor waters. Con-
existence of oscillations such as ENSO that are based on this versely, currents also transport cold water from higher lati-
energy transfer has been discussed in Sect. 24.3.3. tudes and depths to areas of the water surface that would be
Actually, El Niño’s warming of water is only a local warmer were it not for the arrival of these water masses. This
example of the general process of energy transfer to the phenomenon contributes to the existence of a secondary
ocean. At the global level, the absorption of solar radiation interaction between the oceanic water mass and the atmo-
from the seawater mass is the driver of the ocean circulation sphere, so that a heat exchange takes place between them to
achieve a thermal balance. This heat exchange contributes to Earth’s surface. The small solid and liquid particles that
the regulation of the Earth’s climate by reducing latitudinal function as aerosols can be released into the atmosphere by
temperature differences. natural processes such as volcanic eruptions or evapotran-
Much of the energy is reflected and makes its way back spiration from the ground, but they can also have a human
into space. The ratio between the amount of absorbed and origin, as in the case of forest fires or emissions generated
reflected energy is known as reflectance. The reflectance of through industrial activities. Each type of aerosol works in
the surface on which the Sun’s rays strike depends on the one way or another, cooling or warming the planet. In this
nature of this surface, but also on its color. In climatic terms, sense, for example, the most common aerosol, water vapor,
the reflectance of the Earth’s surface, expressed in terms of also acts as a greenhouse gas. In the opposite direction, the
the percentage reflected of the total energy received, is injection into the stratosphere of enormous quantities of
known as the albedo. Terrestrial albedo depends on the ashes and other aerosols, solid or liquid, due to volcanic
lithology of the terrain, the degree and type of vegetation eruptions is capable of producing sudden and sometimes
cover and the existence of ice cover. This last factor is of long-lasting cooling of the planet. This type of phenomenon
great importance, since ice reflects solar radiation almost deserves special attention.
completely. The presence of large ice-covered surfaces thus Following volcanic eruptions with higher explosivity,
greatly inhibits the absorption of energy and contributes to such as Plinian and Pelean eruptions, the atmosphere can
the cooling of the planet. become opaque to incoming solar radiation for prolonged
periods of time, even lasting for several years. The ashes and
other pyroclastic particles thrown into the air as a conse-
24.3.6 The Modulation of the Atmospheric quence of these explosions increase the reflection in the
Composition stratosphere of solar energy that does not penetrate the tro-
posphere. Consequently, during these periods, the planet
To reach the Earth’s surface, solar energy must pass through tends to cool down. The effect of some volcanic eruptions on
the atmosphere and, once reflected on the surface, the radi- the climate and on the temperature of the planet has been
ation must pass through the atmosphere again before finally documented on several occasions. In the nineteenth and
being scattered into outer space. The amount of solar energy twentieth centuries, the eruptions of Tambora in 1815,
absorbed or reflected by our planet is modulated by the Krakatoa in 1883, Katmai in 1912, Mount St. Helens in
atmosphere, depending on its composition (Fig. 24.6). There 1980, El Chichón in 1982 and Redoubt in 1990 were able to
are certain gases whose presence in the atmosphere prevents produce significant decreases in the Earth’s global
the reflected energy from returning to space, causing it to be temperature.
retained in the atmospheric environment. This excess energy In addition to volcanoes, other natural phenomena, such
results in an increase in atmospheric temperature. These as the diffusion of huge dust clouds from deserts, and also
gases are known as greenhouse gases (GHGs) and include human activities can produce effects similar to those of
common gases such as carbon dioxide (CO2) and less volcanic aerosols.
common gases such as methane (CH4). Greenhouse gases
absorb and release energy more efficiently than other gases
in the atmosphere, such as nitrogen and oxygen. Thus, small 24.4 A Brief History of Earth’s Climate
increases in CO2 concentrations, and even smaller increases Changes
in CH4 concentrations, have a marked effect on global
warming. Throughout its history, the Earth’s climate has changed over
The presence of greenhouse gases in the atmosphere is all timescales due to the multiple factors discussed in the
controlled by biogeochemical cycles, as they can be residues previous sections. Thus, combinations of solar radiation
of biological activity and can also be stored in the geological variations (cyclic and episodic), the Earth’s orbital cycles,
record by becoming part of stable organic structures that are atmospheric composition (and its content of greenhouse
fossilized. The abundance of these components in the gases and aerosols), as well as the different paleogeographic
atmosphere can also be increased by anthropogenic pro- configurations of the planet (due to plate tectonics) have
cesses such as fuel combustion. contributed to the existence of constant changes in the cli-
Apart from greenhouse gases, other airborne particles, mate of our planet. Sometimes, some of these effects have
called aerosols, have a bimodal effect on the Earth’s energy combined to amplify the changes towards cooling or
balance. On the one hand, they can cause atmospheric warming. Sometimes, these variables have combined to set
cooling by reflecting and dissipating incoming solar energy. in motion unique mechanisms such as the natural release of
On the other hand, they can contribute to warming by large quantities of greenhouse gases retained in sediments or
absorbing energy arriving from space or reflected at the the increase in the albedo effect of the surface of ice caps.
24.4 A Brief History of Earth’s Climate Changes 383
Fig. 24.6 Processes of

absorption, reflection and the
greenhouse effect
There is ample evidence in the geological record to recon- However, the Pleistocene glaciations were not the only ones
struct the successive changes in climate that occurred during in the history of the Earth, and not even the most dramatic.
this history (Fig. 24.7). In this section we will analyze the Starting from the beginning, but also moving to the most
most significant among them. dramatic of climate changes, there was a time in the Pre-
Certainly, when speaking of dramatic changes in climate, cambrian when the entire planet remained frozen for more
the first thing that comes to mind are the Pleistocene than 90 million years. This is the period known as the
glaciations (Pt in Fig. 24.7). During this period, there were Cryogenian, between 650 and 560 million years ago (Cr in
four glacial periods separated by interglacial stages, with a Fig. 24.7). There is geological evidence that the oceanic
cyclicity of 100,000 years. It is evident that this value of water mass froze to a depth of 1000 m from the Poles to the
cyclicity coincides with the periodicity of the cycles of Equator. This geological interval is popularly known as
eccentricity of the Earth’s orbit, so it follows that the “Snowball Earth.” The mechanisms that led to such a radical
glaciations were mainly related to this phenomenon. glaciation are not yet well understood, but most hypotheses
Fig. 24.7 Curve of averaged temperature throughout Earth’s history, showing the main glacial periods and the extreme hot events
that attempt to explain them involve a feedback of external non-explosive basaltic eruptions. The lava flow would have
and internal effects that contributed to the total cooling. The heated the ocean floor to the point of releasing huge amounts
most plausible hypothesis is related to several initial factors: of methane hydrate stored there. As discussed in the previ-
(1) the Earth was at a time of maximum eccentricity and ous section, methane is a much more potent greenhouse gas
obliquity; (2) the continents were concentrated in the than CO2. Once water saturation in this dissolved gas is
intertropical zone; and (3) the oceanic circulation was reached, enough methane would be released into the atmo-
interrupted, doing extreme the thermal contrast. Under these sphere to explain the temperature rise observed in the oxy-
conditions, there was a concentration of ice at the Poles gen isotopic analysis.
which increased the albedo effect. The coincidence of high There are also several episodes of global warming caused
albedo and poor thermal redistribution by the ocean currents by increased atmospheric CO2 concentrations. These
fed back into the drop in temperatures and the growth of occurred in the Upper Devonian (390–359 million years ago;
ocean ice masses. Once the glaciers reached tropical lati- Ds in Fig. 24.7), the Middle–Upper Triassic (245–208 mil-
tudes, the greenhouse gases could not counteract the heat lion years ago; Tr in Fig. 24.7), the Upper Cretaceous (100
loss and the ocean eventually froze completely. million years ago; Cs in Fig. 24.7) and the Paleocene–
This time interval was the second known major glacia- Eocene (60–45 million years ago; PE in Fig. 24.7) periods.
tion, since an extreme glacial period was recorded 730 None of these episodes reached temperatures as extreme as
million years ago (the Sturtian glaciation, St in Fig. 24.7). the Permian, but they were much higher than that observed
However, it is not proven that this first glaciation was able to today. In particular, the last was one of the most rapid global
freeze the Earth completely. What is well known is that our warmings ever recorded in Earth’s history. In a period of less
planet froze almost completely again during the Ordovician, than 100,000 years, the global temperature rose several
about 447 million years ago (Or in Fig. 24.7). In this case, degrees.
the glaciation was preceded by a drastic drop in atmospheric In each case, these episodes of extreme climate caused
CO2 levels. However, the study of oxygen isotopes shows mass extinctions. However, the end of all of them meant an
that the period of glaciation was much shorter, not exceeding explosion of life and a multitude of new beings appeared,
1.5 million years. which quickly recolonized all the ecological niches of the
Some scientists believe that, with a complete glaciation, planet.
our planet could have been frozen forever, since the enor- In addition to the climatic changes of natural origin
mous albedo effect would completely prevent the retention described in the previous paragraphs, there is currently suf-
of energy in the atmosphere. So, what were the mechanisms ficient instrumental and geological evidence to suggest that
that contributed to the thawing? On the one hand, the CO2 we are immersed in a global change influenced by human
emitted by the volcanoes would increase its concentration in activity. There is a broad scientific consensus on the influence
the atmosphere. On the other hand, the dry environment of the increase in atmospheric concentrations of CO2 of
linked to the presence of ice would prevent the existence of industrial origin on the global increase in temperatures. Other
rain and, therefore, no amount of CO2 could be used in the voices affirm that it is possible that solar activity trends are
formation of carbonic acid to be stored geologically through the cause of global warming, although with a notable influ-
weathering. In addition, the absence of a liquid water body ence of human activity accelerating the rate of change (e.g.,
meant that CO2 could not be stored in the form of carbon- Lüning and Vahrenholt [24]). Apart from the scientific dis-
ates, either. All these mechanisms together led to a cussion on the degree of influence of solar activity and
thousand-fold increase in atmospheric CO2 concentration in humans, what is undeniable is that the rate at which this
just 10 million years. As atmospheric warming freed some global change is occurring far exceeds that observed in the
areas from ice, the decrease in the albedo effect fed back into Paleocene–Eocene, since it is occurring on the scale of cen-
the system in the opposite direction, increasing thawing. turies and not on the scale of thousands of years as occurred
Meanwhile, perhaps the geothermal thawing of the areas in the case of changes related to natural causes.
near the volcanic foci also played an important role.
In contrast, there have also been times of extreme global
warming. The most extreme of these occurred at the end of 24.5 Effects of Climate Changes on the Coast
the Permian, 250 million years ago, when the average tem-
perature of the planet rose by 5° and caused one of the All coastal systems studied in this book are susceptible to
largest mass extinctions in Earth’s history (Pr in Fig. 24.7). changes in climate—both short-term changes that fall under
During this period, the polar ice caps melted completely. climate variability and those that occur in the long term. The
This warming was mainly due to causes related to atmo- intensity and direction of wind, the size and origin of waves
spheric composition. In this case, the most plausible (fairweather and storm), the magnitude of weather surges,
hypothesis relates the onset of this rise to an increase in the amount of precipitation, water and sediment discharges
24.5 Effects of Climate Changes on the Coast 385
from rivers, water temperature, the path and velocity of Holocene (e.g., Scanes et al. [31]). On the other hand, in
ocean currents, turbidity and water quality, and the distri- terms of macroorganisms, thermal change may also con-
bution of organisms are all controlling factors in the tribute to the modification of the distribution of
dynamics of coastal environments, and all of them are sediment-disturbing species in sheltered coastal environ-
controlled by the climate. ments such as lagoons and tidal flats. Similarly, the distri-
Today, there are numerous data instruments collecting bution of plants that colonize subtidal environments
information at fixed stations and on board satellites that (mudflats and mangroves) may also be modified by varia-
show changing trends for many of the abovementioned tions in thermal ranges [25].
parameters. However, these instrumental records are limited Of all coastal environments, reefs will certainly be the
in time and only record changes over a few decades. The most directly and indirectly influenced by thermal changes.
geological record can, however, provide data for much As these environments are directly related to the growth of
longer periods. In this sense, data obtained from boreholes in organisms, the response of the system to thermal changes is
present-day coastal sediments provide records for thousands immediate. A warming of the coastal waters has a direct
of years, while rock sequences can do so for intervals of impact on the algae that are symbiotically related to corals.
millions of years. In many cases, this type of data has been A disappearance of the algae leads to a bleaching of the reef
used for paleogeographic, paleoecological and paleoclimatic that continues with ecological deterioration and ends with
reconstructions that allow us to interpret quite accurately the the death of the corals. Indirectly, the increase in water
changes that occurred in coastal systems over periods of the temperature influences its ability to dissolve gases. Warmer
past as a consequence of climate variations (e.g., Cronin and water increases its concentration of dissolved CO2 and thus
Walker [11]; Bacino et al. [1]; Rice et al. [29]). increases its acidity, preventing coral growth [3].
Looking ahead, dynamic modeling studies based on In more recent times, the sedimentary record shows that
climate-dependent changes in hydrological parameters allow many species of organisms inhabiting coastal systems have
us to understand trends in change and to predict the future undergone major shifts in their geographic distribution in the
behavior of coastal environments as a function of current last century, driven by thermal change. Looking ahead,
climate change. For example, there are growing efforts to seawater temperatures are expected to increase in the coming
project estuarine responses to thermal change [18], but many decades due to greenhouse gases. This warming could lead
other efforts are focused on modeling changes in sediment to continued changes in the distribution of species of all
transport patterns (e.g., Samaras and Koutitas [30]). types of organisms (animals and plants) with low tolerance
The impacts of climate change on coastal systems can to temperature changes [17].
affect some variables that are discussed below: temperature
(global and regional), regional precipitation, wind and storm
regimes, sedimentary processes and sea level rise [8]. 24.5.2 Precipitation
Any change in climate implies a modification in rainfall

24.5.1 Temperature patterns at the regional level. In turn, rainfall patterns have a
direct influence on river water and sediment flow. Thus,
Temperature variations are the most obvious of all climate circulation, water mixing systems and sediment dispersal
changes. Most climate changes have been recorded as ther- associated with river mouths such as deltas and estuaries are
mal changes and are easily analyzed using oxygen isotopes profoundly modified. Within these systems, the modification
(d18O). It is true that these variations control the functioning of these processes leads to a direct change in the physico-
of the coast as an ecosystem. However, the influence of chemical properties of water, such as salinity, dissolved
thermal changes on the dynamics of coastal systems is not so oxygen or nutrients that condition the ecological develop-
obvious. On the one hand, many groups of microorganisms ment of the communities that inhabit these systems [33]. In
that inhabit coastal areas, such as foraminifera, ostracods, general terms, it can be stated that the current change pre-
dinoflagellates, diatoms and radiolarians, were affected by sents a clear trend towards the global eutrophication of flu-
the modification of their biogeochemical cycles during the viomarine systems (e.g., Howarth et al. [19]).
thermal changes that occurred during the Pleistocene [22]. Changes in rainfall do not only affect coastal systems
The distribution and relative abundance of these organisms associated with river mouths. The modification of sediment
can be used as paleoclimatic indicators in coastal sediments inputs brought about by precipitation changes also affects
and can contribute to making paleoclimatic reconstructions coastal systems open to waves, since these also receive
based on sedimentary records. There are some examples of inputs from the mainland via rivers. An increase in precip-
such studies showing the modifications of estuarine itation is usually accompanied by an increase in the rate of
dynamics induced by temperature changes during the sedimentation in terrigenous coastal systems, which will be
better nourished. However, other coastal systems sensitive to ecological point of view (e.g., Paerl et al. [27]). Some of
high rates of siliciclastic input will be adversely affected. An these effects can become long-lasting through processes such
example of such systems is reefs, which would be dimin- as the opening of new inlets in barrier island systems or the
ished by the increased water turbidity that accompanies deepening of river mouth channels [2, 12]. Large storms can
increased precipitation. also affect coastal wetlands during storm surges, contributing
to a short-term increase in sedimentation rates [6] or the
deposition of cheniers.
24.5.3 Wind Regime and Storms
Climate changes imply a variation in the extension of the 24.5.4 Sedimentary Processes
climatic cells and a displacement of their limits. This nec-
essarily entails an important change in the wind regime and, The sedimentary dynamics of coastal systems are profoundly
with it, in the wave regime. There are documented cases of affected by climate. The climate-influenced factors discussed
rotations in the direction of the prevailing winds that have above (temperature, precipitation, and wind and wave
influenced coastal dynamics by changing the direction and regime) are primarily responsible for the dynamic func-
intensity of coastal drift, or the depositional/erosional tioning of coastal systems. Thus, the influences of climate on
regime. On the other hand, a warming or cooling of the each of these factors have a direct effect on sedimentary
ocean surface directly influences the process of storm gen- processes. The three phases of the sedimentary cycle (ero-
eration, as well as the intensity that these can reach. This sion, transport and sedimentation) modify their degree of
type of phenomena can be preserved in coastal facies in the action and their distribution in space and time in response to
form of “tempestites,” but also in the form of erosive sur- these changes.
faces or changes of direction in the berm lines observed in One of the main direct effects is related to variations in
prograding systems such as wave-dominated deltas or precipitation and river flow, since these two variables largely
strandplains. control the volume of sediment input to coastal environ-
With respect to current climate change, there is talk about ments. But there are also other effects on input caused by
an increase in the frequency and intensity of storms [41]. temperature variations. For example, an increase in tem-
The number of tropical storms (Fig. 24.8) seems to have perature and the resulting decrease in glacier ice mass
increased in recent decades [25, 39], but so have storms completely modifies the sediment input to fjords [36].
associated with Rossby waves at the polar front acting at In sheltered systems such as deltas, estuaries, lagoons,
higher latitudes [38]. The increase in these storms is tidal flats or marshes and mudflats, the combined variations
expected to alter the seasonal sediment balance in open in temperature and river flow not only influence the volume
coastal systems and increase coastal erosion in these regions. of sediments, but also their nature. As for siliciclastic sedi-
In addition to the direct effects of waves on the water- ments, their distribution depends to a large extent on the
front, the surge that accompanies storms causes flooding, dynamics of the turbidity maximum. These clouds of sus-
and produces water renewal in coastal systems protected pended matter are controlled by river flow, which in turn is
from wave action such as lagoons, estuaries and deltas [13]. controlled by the precipitation regime. Changes in estuarine
In many cases, these events cause beneficial effects from an mixing conditions imply changes in the dynamics of these
turbidity clouds. For example, an increase in freshwater flow
is usually accompanied by a change in mixing conditions.
The change from saline wedge conditions to well-mixed
ones leads to a marked increase in the volume of flocculated
material, making the sediments in the central part of estu-
aries finer and more cohesive [16]. This phenomenon may
also influence the type of diffusion that occurs at the mouths
of distributary channels at the front of deltaic systems.
Within a closed system, not only clastic sediments are
deposited, but also the accumulation of organic matter has a
significant influence. This organic matter comes from the
remains of organisms (animal and plant) and from floccu-
lation processes. These processes, in turn, depend on
climate-influenced parameters such as temperature, salinity,
Fig. 24.8 Number of tropical storms per year in the North Atlantic and turbidity and light penetration. A large part of this organic
Eastern Pacific oceanic areas since 1995, showing the increasing trends matter comes from the productivity of microalgae fed by
24.5 Effects of Climate Changes on the Coast 387
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watershed-coast systems: a case study using an integrated state-of-the-art climate change projection. Coast Eng 83:65–71
approach. Int J Sedim Res 29:304–315
Relative Sea Level: Eustatism and Tectonics
25
25.1 Why Sea Level Movements Are Relative 25.2.1 Global Changes in the Volume of Ocean
Waters
The coast is the place where the sea meets the continent. It is
Most eustatic movements are associated with variations in
obvious that the location of this meeting place depends on
the volume of water in the oceans. Thus, an increase in
the height of the water level as well as on the height of the
volume will be in response to a rise in sea level and, con-
terrain. Both of these change over time. Sea level move-
versely, a decrease in sea level will be in response to a loss
ments in absolute terms can have the same effects on the
of volume. Assuming that the total mass of water in the
coast as vertical land movements. In fact, the coast will
world has remained constant over the last few hundred
undergo displacements towards the continent or towards the
million years, there are several possibilities that could cause
sea in response to movements in both elements, or the
the volume of ocean water to vary.
combination between them. When we study a given coast,
The most obvious cause for the change in the mass of
we always speak of relative movements because what we
water contained in the oceans is the change of state of this
observe are the results of the net movement, without
water. That is, when a significant part of the water is
knowing whether it is the sea or the land (or both) that is
transformed into ice, the volume of water remaining in the
moving [28]. Determining the causes of these movements
liquid state decreases, and vice versa [16]. This phenomenon
invariably requires more detailed study.
directly links eustatic changes to global climate changes.
While relative sea level changes are observable at the
Specifically, glaciations are the most frequent phenomenon
regional level, the study of global changes always requires a
that originates this type of eustatic movement, which is why
comparison of the results obtained on different coasts. In this
this is called glacioeustatism.
way, it is possible to discriminate between changes that are
The best known glacioeustatic variations are those related
due to land movements (local) and those that are actually
to the four glacial periods that occurred during the Pleis-
due to absolute sea level movements (global). At least five
tocene. These variations involved rises and falls of more
global and four regional processes influence the relative sea
than 100 m (Fig. 25.1). The present position of the sea level
level position on any given coast [6]. The contribution of
and the development of all today’s coastal systems are linked
each factor is different for each coast. The causes of these
to the last of these rises, as a consequence of the melting of
changes, as well as the effects on the coast of these changes,
the Würm glaciation and the subsequent stabilization over
will be discussed separately in this chapter.
several thousand years. The total disappearance of polar ice
associated with periods of extreme warming, such as those
occurring at the end of the Permian or during the Paleocene–
25.2 Global Movements: Eustatism
Eocene, meant a rise in water levels up to several tens of
Eustatism is the phenomenon that causes absolute rises and meters above the present level.
On the other hand, there are causes that can vary the mass
falls of the sea level and, therefore, takes place globally.
Eustatic variations can be associated with different geolog- of water stored in continental areas. In addition to glaciers,
ical phenomena, although it is estimated that these phe- this water may be retained in lakes, aquifers and permafrost.
Water retention in continental areas varies with climate.
nomena can be attributed to two types of origin: (1) variation
of the volume of water in the oceans and (2) deformation of A drier climate transfers water to the oceans, causing the
the receiving basin. mean sea level to rise. Conversely, a humid climate increases

https://doi.org/10.1007/978-3-030-96121-3_25
390 25 Relative Sea Level: Eustatism and Tectonics
Fig. 25.1 Glacioeustatic changes

during the Pleistocene
the level of water retained on the continents and lowers the 25.2.3 Effects on Coastal Systems
sea level [20].
Minor variations in the volume of ocean water that are not Considering only eustatic movements (that is, assuming
associated with the oceanic water mass may also be related local tectonics that do not modify the vertical position of the
to climate. For example, the volume of liquid water varies continents and in the absence of the effects of sedimentation
with changes in temperature (thermal expansion). Generally and erosion), a rise in sea level implies a landward dis-
speaking, water density increases as temperature decreases placement of the coast [25]. Under the same assumption, a
[33] while, on the contrary, a warming implies an increase in fall in sea level would imply a seaward displacement of the
volume. As an example, an increase of 1 °C in an ocean coast.
4000 m deep would imply a vertical rise in sea level of An absolute rise in sea level leads to transgressive con-
60 cm [21]. ditions and results in inundation and landward migration of
These eustatic variations are directly linked to climate coastal environments (Fig. 25.3a). If the rise is slow and
variations and their causes were analyzed in detail in progressive, the facies superposition will respect Walther’s
Chap. 24 of this book. Law with the facies in reverse order, placing the deeper
facies on top of the shallower ones. However, if the ascent is
abrupt, depth conditions change rapidly and may go from
25.2.2 Changes of Shape and Size of Oceanic very shallow to deeper environments, lacking intermediate
Basins terms, without respecting Walther’s Law.
Conversely, an absolute sea level fall leads to regressive
The dynamics related to plate tectonics introduce horizontal conditions and results in emersion of coastal environments
stresses in the oceanic crust that produce changes in the and seaward progradation of systems (Fig. 25.3b). In the
morphological configuration of the seafloor. On the one offshore seafloor, a rise in sea level will lead to a transition to
hand, the opening of some ocean basins while others are deeper conditions, while a fall will lead to a transition to
narrowing can modify their capacity to store water. On the shallower conditions. Thus, the deeper facies will be located
other hand, horizontal stresses related to the expansion of the on top of the shallower facies. If subsidence occurs slowly,
ocean floor can be transformed into vertical movements in the facies will be arranged in the order established by
the vicinity of subduction zones and mid-ocean ridges. The Walther’s Law; however, if sharp pulses of subsidence
bathymetric position of the ridges may also undergo changes occur, intermediate terms may be missing.
due to the arrival of magmatic masses to the reservoirs Of all the eustatic movements in the history of the Earth,
located beneath them, or because of periods of more intense the one that followed the melting of the Würm transgression
volcanic effusion. In this situation, there may also be is the one that gave rise to the starting point for the evolution
upwelling of the seafloor related to the increase in mean rock of all present-day coastal systems. This is the upwelling
temperature (thermal expansion and contraction). known as the Holocene transgression (or Flandrian trans-
These deformations in the shape and size of ocean basins gression). This rise occurred at a rate that exceeded 2 cm per
produce sea level changes on a global scale (Fig. 25.2). year at its peak [6].
Although in absolute terms these phenomena can produce After a stabilization period lasting more than 4500 years,
eustatic movements of several tens of meters, in general the the mean sea level has started to rise again, reaching a rate of
rate at which they occur is very slow, in the order of cen- 3.1 mm/year in recent decades (TOPEX website). This is a
timeters per century. new eustatic change due to thermal expansion of water and
25.2 Global Movements: Eustatism 391
Fig. 25.2 Eustatic changes due to vertical movements of the oceanic bed. The figure indicates two mechanisms of tectonic sea level rising. The
inverse movements of sea level fall may be produced by thermal contraction and tectonic relaxation
interpreting seismic profiles in terms of relative sea level

position. During these years, exploration for energy resources
had led to the study of several continental margins through-
out the world, and by the end of that decade, valuable
information was available. The first curve of eustatic cycles
was proposed by Vail et al. [31]. This was based on the study
of seismic profiles of passive continental margins in a variety
of regional tectonic settings. For the establishment of the
global eustatic curve, the authors discriminated between sea
level movements that appeared in all basins (global cycles)
and those that appeared only in some of them (regional tec-
tonic movements). To establish the magnitude of the global
changes, they averaged the magnitudes observed in all the
basins studied, taking into account their tectonic framework.
During the following decade, many authors made efforts
to improve that curve. That task was much easier for more
Fig. 25.3 Effects of eustatic sea level movements. a Sea level rise.
b Sea level fall modern sedimentary formations. Chappell and Shackleton
[5] produced the first high-resolution global eustatic curve for
the last 250,000 years using data from a series of New
melting of land glaciers. The effect on current coastal sys- Guinea rift terraces. It was the same team of authors, this time
tems is diverse [15]. In barrier island systems, the rise means led by Haq [17], who proposed an improved curve of eustatic
that dune systems are frequently being overtopped by cycle for the most recent periods of Earth’s history
washover events. Many dune ridges have already disap- (Fig. 25.4). As these authors worked for an oil company, the
peared and islands are undergoing landward migration by curve was named on behalf of their organization as the Exxon
shifting over sediments of the inner systems [32]. In estu- Curve. It is a curve in permanent revision, since this group
aries, sea level rise is leading to a change in water mixing permanently collects information from seismic profiles,
patterns and a shift of the salt wedge upstream (e.g., Murphy boreholes and stratigraphic sections, from the most diverse
et al. [18]; Hong and Shen [24]. In other coastal wetlands, parts of the world, and maintains an updated data bank to
changes in tidal circulation are modifying some of the check and modify previous proposals. The most accurate
parameters controlling organic sedimentation, such as Exxon curve covers the time interval for the last 255 million
nutrient distribution or dissolved oxygen [4]. Other coastal years, from the Upper Permian to the present day. Data
systems that are highly dependent on organic activity, such available for earlier time intervals have allowed curves to be
as marshes, mangroves or reefs, need to achieve vertical proposed, but not to a similar degree of accuracy.
growth rates to compensate for the rate of sea level rise in
order to avoid inundation.
Advanced box 25.1 Global eustatic movements: the 25.3 Regional Movements: Uplift
Exxon curve and Subsidence
Since the development of sequence stratigraphy, one of the
main interests of geologists has been the establishment of a In addition to the eustatic changes that can be produced by
global eustatic curve through Earth’s history. In the 1970s, oil tectonic activity, there are other tectonically induced changes
company geologists had established the principles of at the regional level that can be much more rapid and also of
Fig. 25.4 Curve of eustatic sea

level movements for the last 255
million years (built with data by
Haq et al. [17])
greater magnitude. As a consequence of local tectonic the sediment pores leads to a decrease in fluid pressure,
activity, the floor of ocean basins can rise or sink [12]. which facilitates grain accommodation and contributes to
subsidence [26].
25.3.1 Causes of Regional Movements

25.3.2 Effects on Coastal Systems
The processes leading to ocean floor uplift or downfall can
have several origins. Uplift can be related to: (a) elastic Vertical land movements have the same effect as eustatic
deformation due to compressive tectonic processes; (b) iso- movements. A rise of the continent will have the same
static readjustment; and (c) thermal expansion. The downfall response as a fall in sea level, and will result in a loss of
process is known as subsidence and can also have several depth and the superimposition of shallower environments
origins: (a) tilting due to extensional tectonic processes; over deeper ones (Fig. 25.5a). Conversely, subsidence will
(b) isostatic subsidence; (c) thermal shrinkage subsidence; have the same effect as a rise in absolute sea level, and will
and (d) compressional subsidence of older sedimentary cause the floor to sink, resulting in a deepening and relo-
formations due to the loading of upper sediments. Isostatic cation of coastal systems to the continent (Fig. 25.5b).
upward and downward movements are often regulated by
the gain or loss of mass in the ice caps. This phenomenon is
known as glacio-isostatic rebound and is due to the vis- 25.4 Combined Tectonics and Eustatism
coelastic response of the Earth’s mantle to mass variations in
the large ice sheets [13]. Continental uplift and downfall by Relative sea level changes refer to variations in sea depth at a
isostasy can also occur at locations associated with orogenic given point during a specific time interval due to the com-
fronts. An orogeny always implies a crustal thickening that bined action of regional tectonic movements and eustatism.
leads to an isostatic subsidence response. Similarly, a crustal
thinning by extension or by erosion of a mountain range has
as a response an isostatic readjustment of elevation [29].
Loading subsidence is much more common in smaller
areas. Some coastal environments characterized by rapid
sedimentation and high sedimentary input are capable of
generating sedimentary bodies that overlap one another over
a short space of time. For this reason, many deltas, for
example, have accumulated thick aggradational and
progradational bodies during the Holocene. Such rapid
sedimentation does not guarantee that the sediments adopt
the highest degree of packing during the depositional pro-
cess. The vertical accumulation of successive sediment
bodies implies an increase in weight on the lower bodies,
which forces them to optimize their space by increasing their
packing and decreasing their volume. This loss of volume of
the lower bodies has the effect of sinking the surface [1].
Sometimes, the loss of groundwater, oil or gas contained in Fig. 25.5 Effects of regional land movements. a Uplift. b Subsidence
25.4 Combined Tectonics and Eustatism 393
Thus, relative sea level rise may be due to eustatic rise Advanced Box 25.2 Ocean surface topography
(Fig. 25.6a), subsidence (Fig. 25.6b) or a combination of Until the middle of the twentieth century, geologists spoke
both. Among the possible combinations for relative sea level of sea level as if the ocean had an equipotential surface
rise to occur are: eustatic rise accompanied by subsidence adapted to the geoid. It was assumed that this novel sea level
(Fig. 25.6c), rapid subsidence accompanied by slow eustatic varied only on very short timescales due to wave action,
subsidence (Fig. 25.6d) and rapid eustatic rise accompanied surges and tides, but that it maintained an average position.
by slow tectonic rise (Fig. 25.6e). The highest rates and It was assumed that the level varied in the long term because
magnitudes of relative uplift will occur in the third case, of eustatic changes, but when it changed it did so simulta-
when eustatic uplift and subsidence coincide. neously all over the world. However, the beginning of the
On the contrary, a relative sea level fall is an observable use of topographic instruments on satellites orbiting the
effect whose cause can be found in a eustatic lowering Earth completely changed this perception.
(Fig. 25.7a), a tectonic uplift (Fig. 25.7b) or a combination Spacecraft in orbit around the planet carry precision
of both phenomena. Within these, combinations may occur: instruments that make very close measurements of the
eustatic subsidence accompanied by tectonic uplift Earth’s topography and also of the height of the ocean sur-
(Fig. 25.7c), rapid eustatic uplift accompanied by slow face. Specially designed radar altimeter systems are used to
eustatic subsidence (Fig. 25.7d) and rapid eustatic fall make extremely accurate measurements of the altitude of the
accompanied by slow subsidence (Fig. 25.7e). ocean surface. These instruments achieve an accuracy of less
An episode of relative sea level stand will result from than 3 cm. Both land and ocean topography are processed
absolute stability or when both phenomena counteract each and characterized in the same way. Normally, both are
other. expressed as a positive or negative height relative to the
The response to a relative rise in sea level is the process geoid—i.e., above or below this theoretical surface. In the
of migration of coastal systems towards the continent, gen- sea, the geoid would be the shape of the sea surface if there
erating a deepening sequence. Conversely, the effect of a were no topography—i.e., what was hitherto called “sea
relative fall is the process of migration of coastal systems level.” It is clear that the marine topography measured by
seaward, generating a shallowing sequence. From the point satellite instruments is an instantaneous topography. There-
of view of the geological record, these are the effects we see. fore, it is necessary to process the values obtained to elim-
That is why geologists always speak of relative rise and fall. inate the effect of short-term variations such as those from
Some authors have even questioned whether eustatic tide and wind [3]. The result obtained is a relief that shows
movements act in isolation without the effect of regional elevated and depressed areas on the ocean water surface
tectonic movements [23]. (Fig. 25.8).
Fig. 25.6 Possible combinations

of processes resulting in a relative
sea level rise
Fig. 25.7 Possible combinations

of processes resulting in a relative
sea level fall
Fig. 25.8 Mean dynamic ocean

surface topography obtained for
the period 1992–2008 (adapted
from Andersen and Knudsen [2])
Since the beginning of the twenty-first century, NASA probe was launched in 2008 and operated until 2016, when
has launched three satellites capable of measuring ocean Jason-3 was launched, which continues its work today.
surface topography. The first of these was TOPEX/Poseidon, The existence of sea surface relief is due to three types of
which operated from 1992 until the fall of 2005. In 2001 cause: (1) gravity differences; (2) atmospheric and oceanic
Jason-1 was launched, which continued measurements until circulation; and (3) thermal expansion and contraction of
the launch of the Jason-2 mission (OSTM/Jason-2). This water. The establishment of ocean surface topography is
25.4 Combined Tectonics and Eustatism 395
important for the study of ocean circulation and tides. These accumulation/erosion rates was analyzed graphically by
observations are also used to establish interannual, decadal Curray [8]. According to this author’s criteria, transgressions
and longer-term weather patterns. Changes in the position of and regressions can both take place under different condi-
these highs and lows of ocean surface relief imply that tions of sedimentation, erosion or relative sea level move-
eustatic changes need not occur simultaneously or be of the ments. Thus, four types of transgression and four types of
same magnitude around the world. regression are distinguished (Fig. 25.9).
In the case of regressions, these can occur under erosional
conditions as long as there is a decrease in sea level at a rate
25.5 Transgressions and Regressions that exceeds the rate of erosion (RI). More commonly,
however, regressions occur under depositional conditions.
Relative movements of sea level are manifested in the Depositional regressions usually occur under conditions of
coastal fringe as advances or retreats of the coastline that are relative sea level fall accompanied by sedimentary accu-
known as transgressions and regressions. The term trans- mulation (RII and RIII). In these cases, the preservation of
gression is applied to an encroachment of the sea onto an regressive depositional sequences depends on the relation-
emerged zone, implying a landward advance of the coast- ships between the rate of fall and the rate of sedimentation.
line. In contrast, a regression is defined as a retreat of the When the rate of relative sea level fall exceeds the rate of
sea, so that a previously submerged area becomes part of the sedimentation, mixed depositional regressions (RII) occur,
continent, with a shift of the shoreline seaward. in which new coastal sedimentary bodies can develop, dis-
The phenomena of transgression and regression are most connected from the previous ones, which are hanging in the
clearly manifested in coastal environments, where a minimal emerged zone. If, on the other hand, the rate of input exceeds
variation of the coastline means an abrupt modification of the rate of fall, a discontinuous depositional regression (RIII)
sedimentation conditions and a horizontal displacement of occurs, in which new coastal bodies develop in the form of
sedimentary environments. However, transgressions and an offlap, resting on the previous ones. Regressions can also
regressions can also be deduced from the observation of occur only by sedimentary accumulation under a stable sea
deposits in deeper locations, such as shelf environments, by level or even with a slightly rising relative sea level. These
studying the variability of sediment bathymetric conditions. are depositional regressions (RIV). In this case, the coastal
It should be noted that the existence of transgressions and bodies develop an offlap system that materializes in the
regressions does not depend only on relative sea level progradation of the coastal systems.
movements. The balance between erosional and accretionary Transgressions also occur in a wide range of possibilities.
processes, and the rates of erosion or accretion with respect There are transgressions whose cause is directly linked to
to the rates of relative sea level movement, are the real erosional processes under stable conditions of relative sea
drivers of transgressive and regressive movements. For level (TI) or by a rise accompanied by erosion (TII). How-
example, with a stable sea level, we can obtain a trans- ever, the situation in which coastal sequences can be pre-
gression by erosional invasion of the sea or a regression by served occurs when transgressions are accompanied by a
progradation caused by sedimentation. The combination of more or less active depositional regime. Under conditions of
the rhythms of relative sea level movements and sedimentary accretion, the rate of relative sea level rise must
Fig. 25.9 Transgression–

regression diagram of Curray [8]
following the combinations of the
velocity of relative sea level
changes and the
erosional/depositional rates
exceed the rate of accretion. When the rate of rise is small depositional filling of estuaries (wave- or tide-dominated)
and is exceeded by the rate of accumulation, depositional after a period of relative sea level stability. Conversely,
transgressions (TIII) occur, and under these conditions the estuaries always develop from a situation of relative sea
coastal systems move towards the continent, overlapping level rise and marine invasion of river valleys.
one another and forming an onlap geometry that materializes In systems where fluvial influence is minimal, strandplain
the process of retrogradation. On the contrary, when the environments predominantly originate on well-fed, wave-
relative rate of rise exceeds the rate of accumulation, a dis- dominated coasts during regressive processes associated
continuous depositional transgression (TIV) occurs. with relative sea level stability or lowering. These systems,
Coastal systems subjected to depositional transgressions given their high sediment availability, evolve easily under
and regressions evolve by developing transgressive and transgressive conditions, although part of the sediment in
regressive sedimentary sequences (deepening and shallow- their frontal region can be reworked by the waves to build
ing sequences). In general terms, it can be said that sedi- new systems in their migration landwards.
mentary environments are transformed into each other by In non-river-dependent but tidally influenced systems,
superimposing their facies in the form of third-order such as tidal flats and barrier islands, sediment availability is
sequences (depositional sequences). There is a transition not as high as in the case of strandplains. This means that
scheme between the most typical sedimentary environments under transgressive conditions the available material has to
developed on clastic coasts [9]. In this scheme (Fig. 25.10), be reworked to build new systems (Fig. 25.11a). This process
the transition between fluviomarine systems, such as deltas is known as rollover [30]. The cohesive character of the tidal
and estuaries, through transgressions and regressions can be sediments, located in the most protected part of the systems,
observed. Transitions between other systems not associated makes them better preserved in the transgressive sequences.
with river mouths and dominated by waves and tides can The speed of the transgression may sometimes be greater
also be observed. than the capacity to rework material and the rate of input
As for the systems developed at river mouths, this scheme (transgressions type TIV). Then, the coastal bodies become
explains why deltas are associated in the scientific literature disconnected from each other and move upwards towards
with regressive systems. They are systems that are easily the continent (Fig. 25.11b). Under these conditions, the
built during processes of relative sea level fall, since the river bodies may be submerged so rapidly that they are subjected
must make its way to the new coast, developing the delta to the low-energy regime characteristic of deeper zones and
from the reworking of submarine materials from the previ- the coastal sequences may be preserved. This process is
ous stage. However, deltas can also be constructed following known as overstepping [8].
Fig. 25.10 Scheme of evolution

of sedimentary environments
under transgressions and
regressions
25.6 Preservation Potential of Coastal Sequences Under Sea Level … 397
Fig. 25.11 Possible models of

shoreline retreat as a response to a
transgression (adapted from
Mellett and Plater [22])
spared the more erosional processes. In this context, tidal

25.6 Preservation Potential of Coastal deltas, as well as estuaries, are particularly susceptible to
Sequences Under Sea Level Movements erosion because they develop in depressions in the terrain.
These depressions tend to be occupied by river valleys
The preservation potential of coastal sequences depends where runoff from more or less permanent channels will
entirely on the conditions under which transgressions and circulate and rework the sediment towards the new
regressions occur in relation to the reworking capacity of shoreline.
active coastal processes. The following sections discuss the Under conditions of sea level rise, sequences will pre-
possibilities for sequences developed in coastal environ- serve better or worse according to the relationships between
ments to be preserved in the geological record. These pos- the rate of rise and the rate of input. When the relative rise is
sibilities depend largely on the type of environment and its slow, the shoreline can be prograded if the accretion rate is
dynamics in relation to the rate of transgressions and sufficiently high, according to a depositional regression
regressions. model (RIV). In this case, the preservation potential of the
entire assemblage will be maximal [19].
In the opposite case, when the rate of accumulation does
25.6.1 Preservation Potential of Beaches not compensate for the rate of rise, a marine transgression
and Barrier Systems will occur, in which the preservation potential will depend
on the transgressive model that is developed (rollover or
Considering relative sea level movements, it is necessary to overstepping).
address the problems posed by regressions and transgres- In the case of a rollover transgression, there is a total or
sions on the preservation potential of barrier island systems. partial reworking of the coastal facies depending on the
The same processes that act by reworking the sediment relationship between the rate of rise and the reworking
during periods of stability also act during periods of relative capacity of the coastal agents. Under conditions of slow rise
movement. The preservation of the depositional record in and high reworking capacity, the entire system is reworked
these barrier systems depends largely on the type of sea level to migrate towards the coast and the preservation potential is
movement that follows deposition [14]. null. When the rise is moderate, the inland systems are
A relative drop in sea level tends to preserve the systems overtopped by sea level. At first, this implies an increase in
in the short term, as the sediments remain out of reach of the tidal prism and further development of tidal deltas.
coastal reworking processes. However, in the long term, However, if the wave reworking capacity is greater than the
coastal deposits are exposed to subaerial erosion processes. input, the systems subjected to the wave are reworked to
Under these conditions, some part of the systems may be move the barrier island towards the mainland. Under these
conditions the preservation potential of back-barrier facies, 25.6.3 Preservation Potential of Estuaries
such as lagoons, tidal flats, wetlands and flow deltas, is much
greater than that of wave-influenced facies, such as beaches In transgressive contexts, when river valleys are invaded by
and ebb deltas [11]. This may be one explanation for the the sea, morphology and slope have a significant influence
paucity of fossil examples of these systems. on the establishment of the tidal prism that will regulate
Finally, if an overstepping process occurs, the maximum sedimentation in estuarine systems. Generally speaking,
preservation potential is reached, since the deposits of the estuaries become larger with smaller coastal gradients and
complete system are fossilized by deeper marine deposits. larger tidal ranges [9]. When incised valleys are trans-
gressed, changes in valley shape can occur which can
influence trends in the character of tidal sedimentation. In
25.6.2 Preservation Potential of Tidal Flats this sense, the potential for preservation of estuarine
and Wetlands sequences will depend on the geometry of the valley as it is
inundated, as well as the volume of fluvial and marine
Preservation of intertidal sequences is also highly dependent sediments during transgression. On the other hand, as estu-
on relative sea level movements following sedimentation. aries move landward, parts of the sequences may be
Thus, the minimum preservation potential occurs when reworked by the more energetic agents. For example, in
sedimentation is followed by a fall in sea level that exposes wave-dominated estuaries, the barriers that enclose the
the facies to continental agents which eventually dismantle estuary are subject to strong wave reworking processes.
the entire sedimentary edifice. Conversely, the maximum When this occurs, these barriers may or may not be pre-
preservation potential occurs under conditions of rapid rel- served, according to the same criteria discussed in
ative sea level rise, since the sequences are submerged and Sect. 25.6.1. Regardless of the type of estuary, in the
fossilized by sediments generated in lower energy innermost domain the river-dominated sequence may also be
environments. destroyed by erosional incision of tidal and/or fluvial chan-
During a moderate relative sea level rise, preservation nels [9, 11]. Thus, in wave-dominated estuaries, the central
depends on sedimentary input. Thus, under conditions of part of the estuary may be the only section preserved in the
insufficient input, these environments may be partially face of a transgression.
reworked to feed the environments that would be placed in In regressive contexts, the preservation potential may be
increasingly higher topographic positions; under these con- higher if sea level changes are minimal and depositional
ditions, the preservation of deepening sequences is rare. In regression occurs (RIV type regression). During relative sea
this sense, the subtidal channel-fill facies prove to be the level lows, the preservation potential is usually low, since
most preservable, as they are protected by the rest of the the valley is usually occupied by the fluvial system and
facies which overlie it and are potentially most easily eroded fluvial incision processes usually erode and dismantle the
[10]. Many examples of fossil tidal flats are represented only estuarine sequences. When this occurs, in many cases only
by these facies. The magnitude of the intertidal facies is what is deposited on the margins is preserved.
usually finer, as it is generally equal to the tidal range of the
coast where it was generated.
If, on the other hand, the input is sufficient, changes in the 25.6.4 Preservation Potential of Deltas
rate of relative sea level rise may be reflected in the
preservation of cyclical series of the Milankovitch frequency During transgressive conditions, the preservation of deltas is
band (parasequences). In these cases, a repetition of an maximal. This is the reason why deltas are one of the best
elementary shallowing sequence consisting of subtidal, represented coastal environments in the geological record.
intertidal and supratidal facies may develop. However, not all sedimentary sub-environments present in
Finally, if the rate of transgression is slow, preservation deltas are preserved to the same extent. Of all the deltaic
depends on the location of the barrier island. If the plain is environments, those associated with the delta plain have the
on the backside of a barrier island system, the entire system highest preservation potential, while the deltaic frontal bars
may be reworked by waves and not be preserved. If, on the have the lowest because they are more exposed to occasional
other hand, the plain is in a sheltered bay and the rate of erosion events. The preservation potential of deltaic systems
input offsets the rate of relative sea level rise, very strong also depends on the type of delta. In principle, river-
sequences are usually preserved. dominated deltas have the highest preservation potential,
In any case, there are numerous examples of preserved since coastal agents (tides and waves) are capable of
tidal flats in the geological record, which suggests that these reworking the frontal sectors of the delta. Subsidence phe-
systems in general have good preservation potential. nomena related to sediment compaction are responsible for
25.6 Preservation Potential of Coastal Sequences Under Sea Level … 399
the existence of relative rise and stabilization of the sea level 4. Cahoon DR, Hensel PF, Spencer T, Reed DJ, McKee KL,
and for the generation of an accommodation space that is Saintilan N (2006) Coastal wetland vulnerability to relative
sea-level rise: wetland elevation trends and process controls. In:
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dominate the system. In this context, channel incision can 5. Chappell J, Shackleton NJ (1986) Oxygen isotopes and sea level.
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9. Dalrymple RW, Zaitlin BA, Boyd R (1992) Estuarine facies
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the rates of terrigenous input, turbidity, substrate type and 11. Davis RA, Clifton HE (1987) Sea-level change and the preserva-
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12. Dokka RK (2006) Modern-day tectonic subsidence in coastal
related to the relative proximity of continental areas. An Louisiana. Geology 34:281–284
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14. Fisher AG (1961) Stratigraphic record of transgressing seas in light
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Paleoceanography
26
26.1 Introduction 26.2 What is Paleoceanography?
Changes in climate and sea level movements throughout Paleoceanography was conceived as the “science that studies
Earth’s history have been accompanied by major changes in the past characteristics of the ocean.” However, with the
the oceans. On the one hand, there is evidence of numerous entry on the scene of plate tectonics, it underwent a change
modifications in the environmental characteristics (physical, in its conception. It is now defined as the “science that
chemical and biological) of ocean waters. On the other hand, studies the past characteristics of the oceans.” This change
plate tectonics have provided a changing framework of the of definition may seem only a nuance, but it hides more
physiography and dimensions of the oceans over geological important assumptions: that the present oceans have not
time. Changes in the position of the continents must nec- been the only ones throughout the Earth’s history.
essarily have been accompanied by variations in ocean cir- A more precise definition would include the study of the
culation, which help to explain many of the physical and following characteristics: physiography, physical and
chemical changes observed in the geological record. These chemical properties of water masses, ocean circulation pat-
environmental changes have often been accompanied by terns at different depth levels and biological communities.
ecological modifications in the biosphere. The physical, From this perspective, paleoceanographic studies are heavily
chemical and biological characteristics of ocean water have weighted with quantitative measurements based on the
been recorded as markers in the sediments of the ocean floor markers of the sedimentary record mentioned in the previous
at different stages of geological history. section. In today’s oceans, these quantitative studies can be
In this regard, it should be noted that the oceanic circu- addressed from the Mesozoic to the present, since the oldest
lation regime is coupled with that of the atmosphere. For this sediments and oceanic crust in the current oceans are of
reason, paleoceanography and paleoclimatology are sciences those ages. However, the study of marine and coastal sedi-
that go hand in hand in many studies. Thus, many of the ments of older ages that outcrop in some mountain ranges
climate changes in the past have been studied through geo- can provide data on ocean basins that have disappeared as
chemical and paleontological markers in the sediments of the far back as the Precambrian.
ocean floor [2]. The methodology of paleoceanographers to
make accurate use of some of these markers is an advance of
the last four decades. The development of scientific deep 26.3 A Brief History of the Science
drilling programs and the analytical capability of both geo-
physical (seismic and magnetic) and geochemical data have Drilling techniques were born in the 1940s and underwent
been growing in recent decades. As a result, an increasingly rapid development into the late 1950s. During the beginning
long time series of data regarding the present-day oceans has of the next decade, ocean drilling began, and numerous
been obtained. In parallel, the application of the knowledge undisturbed cores were obtained from deep seafloors. The
obtained in today’s oceans to the geological record of study of sediments accumulated in the form of long
ancient ocean basins, now deformed, has made it possible to sequences in these cores allowed the characterization of the
obtain data on oceans that have already disappeared. chemical and ecological properties of the ocean in periods
This chapter will analyze some of the data that paleo- prior to the present time. These could be considered the
ceanography can contribute to the study of Earth’s history events that led to the birth of paleoceanography as a disci-
and, above all, how the changes in the coupled ocean–at- pline of marine geology. However, it was not until some
mosphere system have been reflected in the ancient coasts. 15 years later that Van Andel et al. [24] used the term for the

https://doi.org/10.1007/978-3-030-96121-3_26
402 26 Paleoceanography
first time, and it was not until five more years passed that Over the next 20 years, the efforts of the first international
Schopf [19] wrote the first manual of this discipline. drilling program with a purely paleoceanographic predefined
In the 40 years since that first manual, it can be said that aim would materialize: the Ocean Drilling Program (ODP).
there has been a consolidation of this science, as well as a This program was carried out on the JOIDES Resolution
change of perspective and objectives. Indeed, in the initial (Fig. 26.2a) until 2003 and conducted 110 expeditions,
approaches to it, both Schopf and his immediate competitor, drilling more than 2000 boreholes in different locations
Kennett [12], overlooked one of the main applications of the throughout the world’s oceans.
knowledge obtained about the oceans of the past: the From 2003, the ODP was replaced by the Integrated
knowledge of the paleoclimate. Ocean Drilling Program (IODP). This program was much
Today, most of the efforts of paleoceanography teams are more ambitious, involving 26 countries and employing more
devoted to the interpretation of climate evolution, taking into advanced technology. The JOIDES Resolution was
account the close link between ocean and atmosphere and revamped to adapt it to new needs, and the Japanese vessel
with the aim of predicting future climate trends [8]. Chikyu (Fig. 26.2b), with much more specialized facilities,
In this sense, the international collaboration carried out joined the campaign. From its entry into operation, the IODP
through scientific drilling programs has allowed access to had conducted 52 expeditions by 2013.
data in realms that would have been unthinkable at the At the end of 2013, the IODP partners renewed their
beginning of this science. In short, these data have been a collaboration through a new program called the International
giant step forward in the understanding of the oceanic–cli- Ocean Discovery Program (also IODP). This program,
matic system and the history of the Earth [11]. In fact, the which will be active until 2023, has a much more open plan,
first drilling campaigns that provided data on the ocean floor in which research teams from the 24 participating countries
were not carried out with a paleoceanographic objective. The can propose missions with specific objectives. At the time of
Mohole project, developed in 1961 by the United States, was this book’s publication, the program had completed 30
aimed at understanding the geological nature of the oceanic missions with 346 soundings.
crust up to the Mohorovicic discontinuity, at the transition But ocean drilling programs cover only a small part of
with the upper mantle. Earth’s history in the knowledge of the oceans. Actually,
It was the Deep Sea Drilling Project (DSDP), which ran information from the oceans prior to the present has to be
from 1966 to 1983, that began to address the study of ocean studied in the rock record of ancient sediments that were
floor cores, with an objective much closer to what is now deposited in those paleoceans [23]. Research in this regard
considered paleoceanography. This project, developed has been much less systematic than ocean drilling programs,
entirely on the Glomar Challenger (Fig. 26.1), carried out although in recent decades many papers on sedimentary
numerous surveys over 17 years in the Atlantic, Pacific and rocks of ancient formations that had been approached from a
Indian Oceans, as well as in the Mediterranean and Red purely geological point of view have been revised to obtain
Seas. The valuable data provided by these results contributed information from a paleoceanographic perspective. In this
to refining the approach to this science, in addition to way, it has been possible to obtain information on the
achieving an improvement in drilling techniques. composition of now-extinct oceans such as the Panafrican
Fig. 26.1 The first

oceanographic explorations:
Glomar Challenger (1968–1983)
working on a survey for the Deep
Sea Drilling Project (DSDP)
26.3 A Brief History of the Science 403
The main paleothermal indicator is the isotopic fraction-

ation of oxygen. This technique makes use of the isotopic
ratio d18O/d16O of oxygen that exists in crystalline mole-
cules formed in a given period of the Earth and contained in
sediments. It has been shown that the curves of this isotopic
ratio obtained in the shells of deep-sea foraminifera are
parallel to the thermal curves [5]. In particular, this indicator
is used by analyzing the air in bubbles contained in ice or
mineral inclusions, as well as in calcite molecules precipi-
tated in the environment or in shells. These studies are based
on three premises: (1) the isotope ratio has been changing
throughout Earth’s history in equilibrium with temperature,
(2) carbonates in shells precipitate in equilibrium with water;
and (3) the isotopic variation since deposition has been
negligible.
Paleosalinity analysis methods are very diverse and could
be grouped into three sets: geochemical, mineralogical and
paleontological. Between them, up to 11 control parameters
can be used to deduce salinity. The following are used as
geochemical indicators: boron, bromine, strontium, gallium,
sulfur and carbon isotopes. The following can be used as
Fig. 26.2 Oceanographic vessels employed by the ODP and IODP mineralogical indicators: clay minerals, glauconite, phos-
programs. a JOIDES Resolution. b Chikyu. (Photographs by
JAMSTEC/IODP.) phates, amino acids and manganese nodules. Paleontological
methods are based on the ecological behavior of aquatic
organisms and the fact that organisms need to be in osmotic
(Proterozoic), Mirovia (Neoproterozoic), Iapetus (Paleo- balance with their environment. Thus, the concentration of
zoic), Rheic (Paleozoic), Panthalassa (Paleozoic, lower salts in their cells must be equal to that of the water in which
Mesozoic), Paleo–Tethys (Carboniferous–Triassic) and they are immersed. The mere occurrence of certain genera
Tethys (Permian–Eocene). Many chemical and environ- can therefore be used as an indicator of paleosalinity.
mental characteristics of these oceans, including their pale- However, in this regard it should be noted that there are two
oclimatic context, have already been unraveled. However, types of organisms with respect to their tolerance to salinity:
other features, such as the oceanic circulation systems of the euryhaline (with high tolerance to salinity changes) and
times when these oceans were active, are yet to be stenohaline (with low tolerance). In this case, it is the
investigated. stenohaline organisms that provide the most information.
Sometimes, the application of the different methods gives
disparate results, so it is always advisable to make several
26.4 Different Paleoceanographical Foci approaches.
Salinity and temperature variations in today’s oceans
Paleoceanography, like oceanography, is nowadays carried have been used for climate reconstruction, since there is a
out with a multidisciplinary approach. However, in both close relationship between these properties and the volume
sciences there are different perspectives that result in dif- of ice at the Poles, and also with the rate of evaporation of
ferent specialized disciplines. oceanic water [21].
26.4.1 Hydrographic Paleoceanography 26.4.2 Physical Paleoceanography

The reconstruction of the ancient hydrography of the oceans The discovery of the thermohaline circulation was the result
requires the characterization of the physicochemical prop- of the first German oceanographic campaigns [25], yet it was
erties of the water masses. Thus, the study of paleotemper- not until the last decade of the twentieth century that the
ature and paleosalinity can be approached through a variety knowledge of these currents was combined with the surface
of geochemical and paleontological indicators of ancient ocean circulation to define the “global conveyor belt” and its
sediments that provide quantitative data on these properties close relationship with the terrestrial climate [4]. It is now
[7]. known that, since the opening of the Atlantic Ocean after the
breakup of Pangea, this system of currents has undergone siliciclastic material input to ocean basins. In this sense,
variations over time. For example, it is known with certainty desert dust clouds fall into the ocean and sediments are
that the deep waters of the Atlantic were much warmer redistributed by ocean currents. The trace of these particles
during the Miocene [26]. However, there is intense debate can be followed in deep ocean sediments and thus be used as
about how these changes in temperature of deep water an indicator of the amplitude of atmospheric circulation
masses affect the overall circulation system [22]. cells. Variations in the concentration and grain size of desert
One of the techniques that has been used to approximate dust particles in sediment cores can be used as a paleocli-
the intensity of these currents has been grain size methods. mate indicator [22]. The distribution of other elements from
Since current velocity is reflected in the size of grains that the continent (e.g., pollen, spores and other organic particles)
can be transported and then deposited, some authors have in bed sediments can be used in the same way [7].
used grain size variations in deep ocean basins to identify The climate variations and changes described in Chap. 24
changes in the current system. The first attempts to apply have been mostly verified through their reflection in the
this methodology were made by McCave et al. [14], who sedimentary sequences of the ocean floor. In this sense, cli-
interpreted variations in the North Atlantic. Subsequent mate cycles induced by orbital changes (Milankovitch cycles)
attempts have been made in other oceans to correlate and are clearly reflected in the cyclicity of pelagic sediment
detect changes in the overall system. laminae. Hays et al. [9] were the first to demonstrate these
relationships, which had already been proposed in an elabo-
rate hypothesis by Köppen and Wegener [13]. The identifi-
26.4.3 Ecological Paleoceanography cation of climatic cycles of Milankovitch frequency in
Mesozoic, Paleozoic and Precambrian ocean floor sediments,
As discussed in the previous sections, benthic microfossils now deformed, has extended the knowledge of climate vari-
contained in ocean floor cores have been widely used as ations to very remote epochs of the planet’s geological past.
indicators of paleosalinity and paleotemperature. In addition
to this, planktonic and benthic microfossil associations have
provided valuable information on the environmental and 26.4.5 Oceanic Paleophysiography
ecological conditions of the oceans. Currently, the distribu-
tion of planktonic foraminifera on the ocean floor is adapted A consequence of the change in the position of the conti-
to the temperature distribution of the water masses, which in nents due to plate tectonics has been the constant change in
turn follows the pattern of ocean currents. This type of oceanic physiography. Thus, paleophysiography is closely
pattern has been used to reconstruct these ecological con- linked to global paleogeography. In present-day oceans, the
ditions in ancient sediments since their discovery [10] to the information provided by the distribution of magnetic
present day [18]. anomalies of ocean floor basalts has made it possible to
There are other geochemical indicators that are excellent establish with remarkable precision the physiography of the
markers of ecological characteristics such as biological oceans at different periods of the Earth’s history since the
productivity, nutrient content and dissolved CO2. In this beginning of the Mesozoic [15]. From a physiographic point
respect, biogenic barium, some radiogenic isotopes (e.g., of view, this period represents the transition from a single
carbon, phosphorus and nitrogen), concentrations in some large ocean basin at the end of the Paleozoic to the current
compounds (e.g., nitrates and ammonium) and the ratio physiography consisting of an ocean mass divided into dif-
between different alkenones are useful in determining eco- ferent smaller oceans.
logical properties [7]. Alkenones are long-chain organic Paleomagnetic indicators have been shown to be excel-
compounds produced by planktonic algae that have been lent markers of the position of continental masses and, by
preserved in sediments for at least the last 120 million years extension, of the physiography and position of the oceans in
[16]. pre-Mesozoic times. In this way, the position of the conti-
nents with respect to the magnetic poles influenced the
entrance inclination of the magnetic beams to the terrestrial
26.4.4 Climatic Paleoceanography surfaces according to latitude. It should be noted that the
magnetic minerals of igneous rocks are oriented according to
Chapters 10 and 24 of this book, as well as the previous the magnetic beams of the Earth’s field, generating a prop-
sections, have emphasized the relationships between atmo- erty known as remanent magnetization. Thus, the latitude
spheric and oceanic circulation in climatic cycles of different of a rock (and the continent in which it is embedded) at the
amplitudes. time of its formation can be known by knowing the angle of
Atmospheric circulation, in addition to being the main the magnetic minerals with respect to the horizontal
driver of ocean circulation, is an important source of (Fig. 26.3).
26.4 Different Paleoceanographical Foci 405
Fig. 26.3 Different angles of

interaction of magnetic field
beams with the Earth’s surface
according to latitude
The knowledge of the orientation due to the remaining accompanied by subsidence due to thermal contraction. As
magnetization in igneous formations of the same age (and in the bed depth increases, both the lysocline and the CCD are
successive epochs) in all continents has made it possible to successively crossed and the calcareous mudstone facies are
reconstruct the position of the continents (and the physiog- replaced by abyssal red clays or siliceous mudstone facies
raphy of the oceans) for the times prior to the formation of (radiolarites and diatomites). The presence in a paleocean of
Pangea. This method has been used to discover the existence this facies sequence gives an idea of the timing of these
of oceans prior to the present ones, as well as their changes depth changes and provides insight into their evolution [24].
in extension throughout geological history. The average CCD level is currently at 4500 m. However,
Not only the dimensions and location of the ancient being temperature-dependent, compensation levels vary in
oceans can be analyzed through gauges, but also their depth. depth in space and time. On the one hand, latitude has been
The dissolution of calcite and aragonite crystals depends on found to introduce significant changes in CCD depth in all
temperature and pressure and thus on depth. In this way, present-day oceans [3]. On the other hand, the depth for the
there is a certain depth at which aragonite is dissolved, same latitude has changed over geological time in all oceans
which is called the lysocline. Similarly, when calcite dis- [1], Fig. 26.4. So, it has changed in time, but also in space—
solves, in this case at greater depths, it reaches the so-called the position of the CCD is estimated to have varied between
calcite compensation depth (CCD). Consequently, calcium 3500 and 5500 m.
carbonate grains from pelagic rain can only reach the bed
when the depth is shallower than these dissolution levels.
The presence or absence of aragonite and calcite (or fossils 26.5 Past Oceans
of both compositions) in ocean floor sediments can be used
as an indicator of paleodepth [17]. Throughout the Earth’s history, plate tectonics have caused
One of the phenomena discussed in Chap. 25 has a sig- continental masses to migrate, collide, be fragmented and
nificant influence on variations in the position of the ocean then move apart again. In this process, numerous oceans
floor relative to carbonate compensation depths: thermal have appeared, evolved and disappeared. In parallel, sedi-
subsidence. The oceanic crust generated at the ridges is ments deposited in the coastal systems surrounding these
above the compensation levels. In areas close to the ridges, oceans have consolidated and deformed, becoming part of
the warm ocean floor is elevated and calcareous muds the sedimentary record among the system tracts deposited
accumulate there. However, when the emission of new on the continental margins. Some of these paleocean sys-
oceanic crust moves these beds away from the ridge, a tems and their influence on their coasts are characterized
process of crustal cooling inevitably occurs. This cooling is below.
Fig. 26.4 Evolution of the

calcite compensation depth
(CCD) in the main present-day
oceans during the last 150 million
years (adapted from
Arthur et al. [1])
– Mirovian Ocean – Panafrican Ocean

Mirovia was probably the first ocean in the history of our When the breakup of Rodinia began during the late
planet. Its name comes from the Russian word mirovoy, Proterozoic, a rifting process opened a new oceanic basin
meaning “global.” This name was assigned to the only on the southwestern facade. This basin eventually
ocean on Earth during the Neoproterozoic, between 1 became the Panafrican Ocean. This ocean was located
billion and 750 million years ago. This large ocean sur- for more than 100 million years between the Laurentia
rounded the first megacontinent that grouped all emerged and Gondwana supercontinents (Fig. 26.5b). The
lands, named Rodinia (Fig. 26.5a). This must have had occurrence of a subduction zone on its northern margin
extensive coastlines associated with passive margins caused its closure before the beginning of the Phanero-
where transgressive and regressive coastal sequences zoic Eon, during the process of collision of the two
with significant preservation of tidal signatures were well continents to form a new supercontinent called Pannotia.
recorded [6]. The coasts of the Panafrican Ocean would change from
Fig. 26.5 Ancient oceans during

the Proterozoic ages. a The
Mirovian Ocean during the late
Proterozoic. b The Panafrican
Ocean closing during the opening
of the Panthalassic Ocean in the
Neoproterozoic (Scotese [20])
26.5 Past Oceans 407
trailing-edge coasts to collision coasts. Coastal sequences the Greek, “all the Earth”). Panthalassa then became the
were preserved in the tectonic accretionary prisms during huge global ocean that surrounded Pangea until the early
the collision. Mesozoic (Fig. 26.6a). The coastal systems developed
– Panthalassic Ocean around the Panthalassic Ocean are as diverse as those
The Rodinia breakup process continued with the gener- developed today around the Pacific Ocean. Many of these
ation of a second rifting in the Neoproterozoic. In this systems have been preserved in Andean-type subducted
case, it culminated in the emergence of a ridge where the margins.
emission of oceanic crust was much more significant than
in the case of the Panafrican Ocean. This opening process – Iapetus Ocean
gave rise to a new ocean called the Panthalassic Ocean or From the end of the Proterozoic, the megacontinent
simply Panthalassa (Fig. 26.5b). Etymologically, the Rodinia continued to break up into smaller and smaller
term comes from a Greek word meaning “all seas.” continents. Between these continental fragments, smaller
Panthalassa continued its opening process throughout the oceans appeared which remained open until the forma-
Paleozoic, until it succeeded in bringing all the continents tion of Pangea at the end of the Paleozoic. The Iapetus
back together into a megacontinent called Pangea (from Ocean was among these oceans. Iapetus was formed by
Fig. 26.6 Ancient oceans during

the Paleozoic and Mesozoic ages.
a Panthalassa, Paleo–Tethys,
Iapetus and Rheic Oceans during
the middle Ordovician.
b Panthalassa, Paleo–Tethys and
Rheic Oceans during the early
Devonian, before the collision to
build Pangea. c Oceans
(Panthalassa, Paleo–Tethys and
Tethys) during the beginning of
the disintegration of Pangea in the
early Jurassic
the separation of a supercontinent in the Southern emit oceanic crust, starting the opening of the Tethys. Over
Hemisphere about 600 million years ago. This ocean the next 60 million years, the ridge generated the force that
extended between Laurentia, Baltica and Avalonia uplifted the Cimmerian islands isolating the old Paleo–
(Fig. 26.6a). One of the extensions of this ocean was the Tethys from the new Tethys (Fig. 26.6c). As a result of this
Tornquist Sea, located between Avalonia and Baltica and process, the new ocean replaced the old one by displacing
connecting Iapetus with Paleo–Tethys. the Cimmerian islands northward and causing them to col-
This ocean closed as the continents that formed its lide with Laurasia. At the end of the Tethys Ocean process, it
margins converged during the Caledonian orogeny, ended up occupying the same position as the Paleo–Tethys.
forming the continent called Euramerica (also Laurus- A similar process occurred between the Tethys, the Indian
sia). The ocean disappeared between the Cambrian and Ocean and the Mediterranean Sea. After the breakup of
Ordovician, about 400 million years ago. The sediments Gondwana, the continents of India, Arabia and Africa
of its coastal systems were incorporated into the Cale- moved northward, closing Tethys as the Indian Ocean
donian, Akkadian and Taconic mountain chains, in the opened and the Mediterranean became isolated. As a con-
Euramerica continent. sequence of the closure of Tethys, its marine and coastal
– Rheic Ocean deposits were deformed to form the Himalayan and Alpine
Another of the oceans that developed in the Paleozoic mountain ranges during the Alpine orogeny.
between the approaching continents was the Rheic
Ocean. This was located between the supercontinent
Gondwana and the smaller continents separating it from References
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continued to exist even after the closure of Iapetus with 1. Arthur MA, Dean WE, Schlanger SO (1985) Variations in the
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Broecker WS (eds) The carbon cycle and atmospheric CO2: natural
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– Paleo–Tethys Ocean 2. Barnes CR (1999) Paleoceanography and paleoclimatology: an
The third of the great oceans that separated the Paleozoic Earth system perspective. Chem Geol 161(1):17–35
3. Berger WH, Be AWH, Sliter WV (1975) Dissolution of deep-sea
continents was the Paleo–Tethys. Throughout the lower carbonates: an introduction. Special Publication of Cushman
Paleozoic, this ocean extended north of Gondwana and Foundation 13
was bounded on the northwestern edge by the continents 4. Broecker WS (1991) The great ocean conveyor. Oceanography
of Laurentia, Baltica and Siberia (Fig. 26.6a). Later, in 4:79–89
5. Emiliani C (1955) Pleistocene temperatures. J Geol 63:538–578
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Older Coasts
27
of Australia [12] represented by the Upper Mount Guide

27.1 Introduction
Group (−1800 My, the transition between the Meso- and
Neo-Proterozoic of West Africa [9, 37] in the Pelel and
Ancient oceans and paleocontinents have combined to form
Dindefelo Formations of the Segou-Madina Kouta Group
coastal systems throughout Earth’s history. Many of these
(−1200–750 My); and the Neo-Proterozoic of Australia [36]
coastal systems have been preserved in the sedimentary
in the Elatina Group (0.6 Ga).
record as stratigraphic formations corresponding to different
All the tidalites described, whatever their age or location,
geological periods. There is an abundance of scientific lit-
have a number of common characteristics. Notably, the total
erature on many of these formations, especially those in
absence of organisms with shells in these very early stages
Europe, North America and Australia. Compiling the
of the Earth makes these facies totally devoid of fossils. By
information on all of these ancient coastal systems would be
the same token, there is also a paucity of trace organics and
an endless task, well beyond the scope of this book. How-
bioturbation. This fact results in a maximum preservation of
ever, it is possible to synthesize the main characteristics of
physical structures. At the stratotype level, the tidalites are
the most significant coastal systems of each geological
characterized by the presence of parallel tidal bundles
period. This chapter analyzes some of the coastal environ-
(Fig. 27.2) and herringbone cross-stratifications (Fig. 27.3a).
ments that have contributed to a better understanding of the
At the outcrop scale, tidalites are organized in repetitive
functioning of the Earth system at some key moments in the
parasequences. Each of these sequences is formed by sub-
history of our planet.
tidal bars of sandstones with herringbone-type
cross-stratification that may even present tidal bundles in
the cross lamellae (Fig. 27.3b). Over these, finer sandstones
27.2 Precambrian Tidalites with decimeter-scale herringbone laminations develop, and
over these appear the finely laminated sediments with tidal
Among the most striking coastal geological records are those bundles. The finely laminated layers are usually covered by
found in tidalites. These are coastal facies with an ripples (Fig. 27.4a and b). The sequence may culminate in
unequivocal signature that identifies them as sediments layers with bacterial mats (microbially induced sedimentary
deposited by tidal processes. Tidalites are usually charac- structures, MISS; Fig. 27.4c) affected by desiccation cracks
teristic of open tidal flats, but can also occur in environments (Fig. 27.4d). Each of these sequences can range in thickness
protected behind barriers and in those associated with other from 0.5 to 12 m and may represent subtidal, intertidal and
systems such as deltas or estuaries. Although tidalites have supratidal facies succession. The repetition of parasequences
been preserved from all periods of Earth’s history, perhaps is due to the presence of subsiding pulses.
the most significant are the Precambrian tidalites [13]. The abundance of tidalites from these early periods of the
Known examples of tidalites preserved in the Precam- Earth’s history has been attributed to the shorter distance
brian record span nearly all of the Archean and Proterozoic between the Moon and the Earth, meaning greater tidal
eons (Fig. 27.1). The oldest formations are Archean and are ranges, which would be characteristic of macrotidal coasts
found in South Africa [11, 14]. These are formations of the [13]. However, many authors agree on the similarity of these
Moodies (−3250 My) and Witwatersrand (−3000–2800 My) tidal signatures with those that currently appear in tidal flats,
Groups. More recent examples are in the Paleo-Proterozoic ruling out the possibility of generation on megatidal shores.

https://doi.org/10.1007/978-3-030-96121-3_27
412 27 Older Coasts
this context, the dismantling of the new orogenic reliefs

provided a good supply of siliciclastic sediment to the coasts
surrounding the megacontinent. Several deltaic and estuarine
systems developed along the coasts of this new continent,
whose supratidal fringes were associated with extensive
swamps and marshes. These swamps were the ideal envi-
ronments for the formation of the coal that gives its name to
the main geological period of this time. However, these
environments were not only capable of producing coal, but
also other natural resources such as petroleum and uranium.
A good example of this type of environment is recorded
in the Río Genoa Formation, within the Tepuel Group
(Chubut, Argentina). In this example, the detailed sedi-
mentological column correlation study allowed the identifi-
cation of all the delta plain, delta front and prodelta
environments of a river-dominated (lobated) delta developed
over the shallow platform facies of the Mojón de Hierro
Formation [2]. The Río Genoa Formation consists of
1200 m of mostly sandy facies that include some gravel
intercalations, thick shale bodies and abundant coal layers.
Fig. 27.1 Geological timetable of the Precambrian eon, indicating the
The sandy facies contains numerous sedimentary structures
age of the best documented examples of Precambrian tidalites
such as meter-scale cross-stratifications (planar and trough),
and current and wave ripples. The facies include a rich fossil
record of marine plants and invertebrates that contributed to
27.3 Late Paleozoic Deltas the biostratigraphic and paleoecological interpretation.
In addition to several distributary channels separated by
The late Paleozoic (Carboniferous and Permian) was a levees, there are numerous prograding bar-finger sands
favorable time for the development of extensive siliciclastic developed over the fine-sediment prodelta facies. The com-
coastal systems. During this interval, the final stages of the plete sequence shows the presence of autocycles of progra-
Variscan orogeny were taking place, and the collision of the dation and abandonment that are attributed to the existence
great continents to form Pangea was coming to an end. In of switching phenomena of the distributaries and deltaic
Fig. 27.2 Tidalites of the

Stenian Pelel Formation,
Segou-Madina Kouta Group
(West Africa)
27.3 Late Paleozoic Deltas 413
lobes. In any case, it is a highly constructive delta with high

rates of progradation and aggradation. The vertical repetition
of sequences is controlled by local subsidence phenomena in
a stable sea level framework, although two eustatic uplifts
have been identified during the Permian.
A very similar system has been described in the
Anyang-Hebi coal basin in Henan Province, North China. In
this case, 76 boreholes were studied, in addition to the series
raised in open-pit workings [30]. The deltaic series is laid out
across an unconformity overlying Ordovician carbonate
rocks and beneath siliciclastic rocks of Triassic age. The
entire sedimentary succession was formed after continental
uplift occurred at the end of the early Paleozoic by the col-
lision between the North China plate and the Siberian plate.
At the base of the sequence are the offshore facies, which
mainly consist of alternating black shales (with bivalves,
gastropods and brachiopods) and carbonates with abundant
corals, crinoids, brachiopods, foraminifera and bryozoans
(Fig. 27.5a). Overlying the offshore facies are the prodelta
facies, which consist of black shales with rhythmic lamina-
tion and, above them, the delta front facies consist of a
coarsening-upwards sequence of black shales and
Fig. 27.3 Tidal structures of the Tonian Dindefelo Formation, medium-grained sandstones with abundant flaser structures
Segou-Madina Kouta Group (West Africa). a Herringbones. b Tidal and small-scale herringbones (Fig. 27.5b). In the delta plain
bundles in the cross-bedding
facies, depositional facies corresponding to the different
Fig. 27.4 Sedimentary structures

of the upper terms of the tidal
sequence in the Dindefelo
Formation, Segou-Madina Kouta
Group (West Africa). a Straight
crested ripples. b Linguoid
ripples. c Microbially induced
sedimentary structures. d Mud
cracks
414 27 Older Coasts
sub-environments can be distinguished. The distributary parasequences including the coal layers (Fig. 27.6a) and
channel facies consist of lithofacies sequences that range in even the clinoforms of prograding units of the delta front
thickness from 3 to 10 m and are composed of fine-grained (Fig. 27.6b) are observed.
sandstones (Fig. 27.5c) with abundant decimeter-scale
cross-laminations (ripples). The levee facies consists of the
same sandstones that are interbedded with shale laminae 27.4 Late Jurassic–Early Cretaceous Reefs
with carbonaceous traces (Fig. 27.5d and e). The interdis- and Carbonate Coasts
tributary swamp facies consist of carbonaceous shales and
coal layers (Fig. 27.5f). During the Jurassic and Cretaceous periods, most of Gond-
These facies are repeated in regressive sequences that wana (South America and Africa), the southern half of North
form parasequences, reaching total thicknesses of between America and southern Europe were in intertropical latitudes.
1000 and 10 m. As in the case of the Río Genoa Formation, In these periods, there was a general tendency towards
the repetition of parasequences has been attributed to sub- extensional processes, since the fragmentation of Pangea
sidence pulses separated by periods of stability. It is this was taking place through rifting processes that gave rise to
subsidence that led to the deposition of a large repetitive new marine basins. This process was especially intense in
succession that allows the exploitation of the coal beds. Europe, which was fragmented during the Jurassic in the
Late Paleozoic deltaic successions similar to the two form of numerous islands separated by shallow seas
discussed in this chapter are repeated in different basins of (Fig. 27.7a). The migration of continents associated with the
the world. Some examples have been described in the opening of the Atlantic pushed the continental masses of
Appalachians [26], Scotland [20], Wales [19], Germany Europe toward lower latitudes during the Cretaceous
[35], Poland [25], Spain [7], Ukraine [23], Southern Africa (Fig. 27.7b). The coasts of these seas, being at intertropical
[5] and India [3], among other places. In many of the out- latitudes, were conducive to the development of reefs and
crops where these sequences have been found, the delta plain carbonate shores.
Fig. 27.5 Sedimentary facies

observed in the Anyang-Hebi
coalfield sequences. a Carbonate
offshore facies. b Small-scale
flasers interpreted as prodelta
facies. c Fine-grained sandstone
facies of the distributary channels.
d Cyclic laminated sandstone and
shale facies from levees. e Shaley
sandstones with coal traces.
f Coal facies from
interdistributary swamps.
Photographs by Li et al. [30]
27.4 Late Jurassic–Early Cretaceous Reefs and Carbonate Coasts 415
Fig. 27.6 Different aspects of

deltaic sequences at an outcrop
scale. a Coal beds in a delta plain
sequence (Namurian Basal Grit
Formation, Wales, UK).
b Prograding sequence in a delta
front facies (Westphalian
Millstone Grits, Wales, UK)
During the Jurassic period, the distribution of reefs (Fig. 27.7b) and microbial reefs (Fig. 27.7c). In addition,
increased significantly. The cause of this increase was in there are mixed-type reefs (Fig. 27.7d). Coral facies domi-
response to several factors, not only those linked to the nate the reefs of the Iberian basins. These reefs include a
latitudinal distribution of the coasts of that period. The wide variety of coral facies that reflect a diversity of envi-
development of carbonate systems has usually been related ronments associated with the reef bodies.
to times of highstand [28]. Throughout the Jurassic, the sea Siliceous sponge-dominated reefs occur abundantly in the
level was rising, so that in the late Jurassic it was in a global basins of southern Germany (south of the Swabian paleo-
position that reached 150 m above the present level. In the continent). These spongiolithic reefs are often associated
early Cretaceous, the level dropped rapidly by about 70 m with microbial mats and algal crusts. Such reefs occur in a
and then rose again by about 20 m above the maximum coastal belt on the north-European margin of the Tethys
Jurassic level. This high sea level position caused extensive from Romania to Portugal and also on the southwestern
areas of the continental zones to be flooded, increasing the margin of the Tethys (the Atlas Mountains of Morocco).
habitat surface for biohermal organisms and reducing the Sometimes spongiolithic reefs also occur in association with
source areas of terrigenous sediment and, consequently, the coralline facies. Then, they manage to form large reef bodies
volume of siliciclastic sediment. Moreover, the high atmo- that may outcrop at some distance from the coast, forming
spheric CO2 levels of the late Jurassic and early Cretaceous topographic elevations and reef patches. The distribution of
exhibited a climatic optimum that was related to these high facies in these mixed reefs is closely linked to the bathy-
marine levels. This climatic optimum caused tropical seas to metry and the distribution of energies in the environment. In
extend above tropical latitudes, reaching 40° latitude. These these systems there are also abundant detrital facies, which
environmental conditions seem to explain the increase in are linked to bioclastic shallows, washovers and aprons, as
reef environments during these periods better than the radi- well as oolitic tidal deltas [29].
ation of reef-forming organisms. In any case, all these fac- Microbial crusts may be present in the above types of
tors acting together led to the appearance of a large number reef, where they combine with siliceous sponges and corals
of different types of reefs linked to different paleogeographic to build large reef structures. But in addition, microbes can
contexts. also build reefs on their own. In these periods, thrombilitic
In Europe, regional studies of different reefs from this reefs dominate, which can exceed 30 m in height. Throm-
period of Earth’s history have identified three types of reef bolites are similar to stromatolites in their external form, but
[27]: coral reefs (Fig. 27.8a), siliceous sponge reefs their inner structure is not laminated. Pure microbial reefs
416 27 Older Coasts
[32]. Examples of Pleistocene barrier islands are more

abundant. Systems of these ages have been characterized in
the Port Dunford Formation in South Africa [22] and on
Mockhorn Island in Virginia, USA [16]. In most cases, the
unconsolidated character of the facies allows observation of
the three-dimensional architecture at outcrop scale, as well as
measurement of the migration directions of the bedforms
from the dip of the cross-bedding.
Many of the preserved systems have common charac-
teristics. Among them is a similar architecture between
barrier/beach/dune bodies and barrier/lagoon/tidal plain
bodies. Barrier sequences are characterized by the presence
of medium to very coarse sands composed of siliciclastic,
bioclastic or mixed grains. Whatever the composition, they
are generally constituted of very mature sediments due to the
continuous wave reworking. The structures characteristically
preserved in these facies are planar, trough (Fig. 27.9a),
swaley (Fig. 27.9b) and hummocky cross-stratifications.
Regardless of the dominant lithology, the presence of layers
with a high concentration of shells is common. These layers
have lenticular geometry, suggesting that they are accumu-
lated by storms. Sometimes, the barrier sequences are
composed of pebbly sandstone facies, also very mature
texturally. In such cases, the characteristic internal structure
is seaward-sloping parallel laminations or low-angle
landward-sloping cross-stratifications. Barrier sequences
may be capped by dune facies. The lithology of these facies
corresponds to very well-sorted fine to coarse sands of sili-
ciclastic or bioclastic origin. When bioclasts are present,
they usually belong to foraminiferal shells or fragments of
Fig. 27.7 Paleogeographic map of the distribution of reefs (red circles)
mollusks with very light shells. The dune facies character-
in the carbonate platforms (light blue) of the late Jurassic (a) and early
Cretaceous (b) istically show very complex cross-stratifications (Fig. 27.9c)
and root bioturbation is often extensive (Fig. 27.9d).
The back-barrier/lagoon sequences are dominated by the
with coralline and spongiolithic influence are greatly abun- presence of clayey sediments rich in organic matter. These
dant in the Mesozoic basins of Iberia. In this context, sediments usually have a massive aspect, although they may
thrombilitic reefs may even occur in environments with a also appear laminated. Sometimes they are cut by bioclastic
high influence of siliciclastic input [29]. debris lenses that correspond to tidal channel bed sediments.
Towards the uppermost part of the sequence, flaser/
wavy/lenticular structures usually appear, and everything is
27.5 Cenozoic Barrier Islands generally topped by peat layers. All facies show a high
degree of bioturbation (Fig. 27.9e), with galleries of the
There are numerous examples of barrier island systems from Ophiomorpha and Thalassinoides types frequently present.
all periods of the Cenozoic. Eocene barriers are well repre- In areas where outcrops allow the contact between these
sented in the Claiborne, Jackson and Wilcox Group Forma- two types of sequences (barrier and lagoon) to be seen, the
tions of Texas (e.g., Fisher et al. [17]; Davies and Ethridge lagoon sequences may be covered by washover facies
[8]; Dickinson [10]; Galloway [18]; Johnston and Johnson (Fig. 27.9f) and dunes, especially in the case of transgressive
[24]; Hamilton [21]), as well as in the Misoa Formation in sequences.
Venezuela [1]. Oligocene barriers are also represented in the Cenozoic sequences are not usually deformed by com-
Frio Formation of Texas [4]. A good Miocene example has pressional tectonic processes, although they may be tilted
been studied in the Cohansey Formation in New Jersey, USA due to extensional processes. Their sediments may also be
[6]. More recently, a Pliocene sandy barrier system has been affected by early diagenetic processes such as partial disso-
characterized in the Spartizzo–Scandale Formation in Italy lution of bioclasts, carbonate cementation and neomorphism.
27.5 Cenozoic Barrier Islands 417
Fig. 27.8 a Mid-Jurassic branching coral facies in Portugal (Pho- Jurassic thrombolite in the Central High Atlas, Morocco (Photograph:
tograph: Francisco Félix [15]). b Lower Jurassic spongiolite in the Mannani [31]). d Mixed siliceous sponge–microbialite mound in
Central High Atlas, Morocco (Photograph: Mannani [31]). c Lower Portugal (Photograph: Reolid and Duarte[34])
Fig. 27.9 Facies of Cenozoic

barrier island systems. a Planar
cross-bedding and sea-inclined
parallel-bedding characteristic of
beach facies of a Miocene
formation (SW Spain). b Swaley
cross-bedding in the same
formation. c Complex
cross-bedding characteristic of
coastal dune facies of a Pliocene
formation (W Morocco). d Detail
of root bioturbation in the same
formation. e Burrowed muds
characteristics of lagoon facies in
a Miocene formation (SW Spain).
f Bioturbated lagoonal muddy
sands covered by cross-bedded
washover pebbly sands in a
Pleistocene formation (SW Spain)
418 27 Older Coasts
Despite the obvious similarities, it appears that the 14. Eriksson KA, Turner BR, Vos RG (1981) Evidence of tidal
Cenozoic sequences preserved in facies are markedly dif- processes from the lower part of the Witwatersrand Super-
group. Sed Geol 29:309–325
ferent from the systems functioning today. On the one hand, 15. Félix F (2021) Bank of images of science's house in Portugal.
the depositional facies of many of the environments present https://www.casadasciencias.org/imagens
in today’s systems have not been well preserved in the fossil 16. Finkelstein K (1992) Stratigraphy and preservation potential of
examples. For example, the facies of the most wave-exposed sediments from adjacent Holocene and Pleistocene barrier-island
systems, Cape Charles, Virginia. In: Fletcher III CH and
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Part V
The Humans in the Coast: Interaction Problems
and Coastal Management
I made jetties so they’d catch all the sediment,

removed the rocks and every impediment,
but the tide’s rising high to wash away
my island in the night.
“The island”
Bad Religion
Human Impacts on Coastal Systems
28
the atmosphere. On the one hand, this means the emission

28.1 Introduction
of greenhouse gases from the combustion of hydrocar-
bons and, on the other hand, the emission of certain
The majority of the population of most of the world’s
aerosols that contribute to global warming and the pro-
countries are based in coastal areas, a fact that has been true
gressive rise in sea level.
throughout history [4]. However, since the second half of the
twentieth century, human activity has had a greater and
With these considerations in mind, it seems clear that,
faster impact on coastal dynamics. Part of this increased
when humans occupy the coast, they invariably alter the
impact on the coast is due to the development of beaches for
natural environment. Human-induced alterations to coastal
recreational use, but it should not be forgotten that most
dynamics can range from minimal to disastrous and, over
economic activity is also located around coastal systems.
decades, the effects have depended more on chance than on
The protection of human assets requires constant interven-
planning.
tions on the natural environment for a variety of reasons—
for example, to avoid sediment losses, to replenish sediments
or to artificially create new beaches. However, these actions
are not the only ones, nor are they the most important ones,
28.2 Direct Human Interventions
that are carried out by humankind on the coasts. If we
on the Coast (Coastal Engineering)
consider the factors responsible for sediment dynamics on
In many areas of the planet, coastal areas have been
the coast that were studied in Chap. 3 (Fig. 28.1), we see that
over-occupied without any prior planning or understanding
humans can intervene directly or indirectly in all of them.
of the dynamics of the coastal segment in which the con-
structions were carried out. It is true that many of these
• The most direct impact that humans exert on the coasts is
actions took place before we had the knowledge we have
the modification of the patterns of action of hydrodynamic
now about the coast. However, even today, when we do
agents on the coastal fringe. These interventions include
have sufficient knowledge, wide stretches of coastline con-
the construction of groins, jetties, breakwaters and sea-
tinue to be occupied due to political decisions that do not
walls that modify wave refraction patterns. In addition, the
take this knowledge into account at all. When we speak of
restriction of intertidal surfaces by preventing natural
human constructions on the coast, the presence of housing
drainage in estuaries, deltas and tidal flats modifies their
developments and tourist facilities quickly comes to mind;
tidal prism. This alters the energy balance at their mouths.
however, in addition to these, port facilities and numerous
• The least studied of these interventions is the impact that
industrial complexes are also found on the coast. In short,
humans can exert on the continental input to the coasts by
the coast has become an important enclave for human eco-
damming rivers and destroying coastal dunes. This gen-
nomic activities. As a consequence, related infrastructures
erates a sediment deficit that contributes to the erosion of
have for decades themselves been threatened by ordinary
coastal front systems. Conversely, the creation of artificial
coastal processes and even more by high-energy events such
beaches through the forced contribution of sand intro-
as storms [9]. Because of this, coastal engineers have been
duces a cumulative modification.
forced to build structures for the protection of human
• The human influence on climate has been a matter of
property. The influence of these activities on the natural
debate in recent decades. Today it is assumed that the
dynamics of the coast is analyzed below.
climate is changing due to anthropogenic emissions into

https://doi.org/10.1007/978-3-030-96121-3_28
424 28 Human Impacts on Coastal Systems

influence of human activities on
different components of coastal
dynamics
28.2.1 Building Rigid Structures outflowing longitudinally into the adjacent sector. Thus,
excess sand accumulates on this side of the groin. Con-
The coast is a changing and flexible environment. This versely, in the downdrift zone, the longitudinal inputs of
flexibility is often incompatible with the presence of human sediment are cancelled out, generating a sediment deficit that
constructions on the coast. Indeed, this is why engineers makes this section erosive.
have created different rigid structures that try to stabilize the Where groin combs are present, transverse rather than
position of the coastline. Several types of structures have longitudinal dynamics dominate. The groins compartmen-
been created by coastal engineers for this purpose. Some are talize the beach into multiple sediment circulation cells
perpendicular to the coastline, while others are parallel, and (Fig. 28.3a). In this way, sand can only transit between
some structures even consist of a complete fortification of different cells when it is eroded during storms and trans-
the coastline. ported transversely to deeper areas. Of particular interest is
One of the structures that engineers have classically used the situation that occurs when groins are arranged too close
to slow down coastal erosion has been groins (or groynes). together, as each cell between two groins can behave like a
Many beaches, especially those located in front of centers of reflective beach, generating strong undertow currents in its
coastal urbanization, have been converted into a succession central sector [3]. These undertow currents can draw sig-
of groins in the form of a comb. In other examples, in order nificant volumes of sand into the shore face beyond the
to reduce the mobility of the channels that interrupt coastal length of the groins. From this area, the sand can return to
continuity (tidal inlets, river mouths or even artificial harbor the foreshore of the adjoining cell when a fair weather wave
channels), jetties have been built on the margins of these acts obliquely to the shore. A situation that is particularly
channels. sensitive to coastal erosion occurs when there are steps in the
Groins and jetties exert a similar effect. As constructions subtidal zone that prevent sand from returning to the fore-
perpendicular to the coastline, they constitute a barrier to shore zone.
longitudinal sedimentary bypassing (littoral drift). The This behavior shows that the presence of groin combs
presence of one of these structures compartmentalizes the does not completely prevent beach erosion. In order to
coastal fringe by dividing sediment circulation cells. From a prevent the transverse transport of sand into deeper areas,
dynamic point of view, each structure divides two zones engineers can extend the apex of the breakwater with a
with different behaviors on either side (Fig. 28.2) and causes longitudinal structure giving it a T-shape (Fig. 28.3b). This
a change in the wave refraction pattern. On the updrift side type of construction partially prevents the transport of sand
of the groin, the desired effect is accumulated sediment, into deeper areas, but also prevents the entry of sand into the
while on the downdrift side a zone of divergence of wave cell. The construction of such structures is often accompa-
trains is generated [7]. The accumulation of sediment in the nied by artificial nourishment of the cells between the groins,
updrift segment is achieved because the groin prevents sand which function as small pocket beaches.
28.2 Direct Human Interventions on the Coast (Coastal Engineering) 425

dynamic modification of the wave
trains by a rigid structure built in
a perpendicular direction from the
coastline and its effect on the
sedimentary patterns. Examples
shown are of a single groin and
two parallel jetties. Images
Landsat from Google Earth
Breakwaters (or exent dams) are constructions created increase in both zones of drift outputs and this, therefore,
by linear rock piles, typically less than 100 m in length, marks their erosive behavior.
which are placed parallel to and separated from the beach. In many cases, these breakwaters are designed in a seg-
The distance from the breakwater to the shore is calculated mented manner—i.e., several breakwaters are constructed
using the surf distance. Like the groins, these structures separated by gaps. The design of the length of the gaps in
modify the wave action on the coast, damping the waves and relation to the distance of the breakwater from the coastline is
affecting the refraction pattern in such a way that wave fundamental to understanding the dynamic functioning of the
divergence zones are generated on one side or on both sides stretch of coastline that will be protected by the breakwater
of the structure, with a convergence zone behind it [13]. Normally, the beach area acquires a profile with a
(Fig. 28.4). Behind the structure, the sediment volume succession of concave forms in front of the hollows and
increases due to drift inputs from the two adjacent cells. convex forms behind the breakwaters. Sometimes the accu-
However, the generation of these two wave divergence mulation of sand in the area protected by the breakwaters can
zones outside the protection of the breakwater means an even reach the structure, which becomes a kind of tombolo.
Fig. 28.3 Examples of multiple

rigid structures dividing
circulation cells in a beach.
a Comb of straight groins.
b Multiple T-shaped groins.
Images Landsat from Google
Earth
In other examples, the development of long stretches of constructed, but can also be easily removed. A more per-
coastline has eliminated the line of dunes in order to build manent way of constructing a seawall is by cladding. In most
promenades. At other times, although the promenades were cases the revetments are built with rocks extracted from
built after the first line of dunes, they were designed without quarries close to the shore (Fig. 28.5b); however, when this is
prior planning and were installed in clearly erosive areas, so not possible, revetments can be built with precast concrete
that after their construction the line of dunes was eroded. blocks. The most radical form of seawall is the erection of a
Whatever the causes, in many cases the promenades or the vertical concrete wall (Fig. 28.5c).
buildings themselves are exposed to wave action, which Normally, these structures protect the buildings behind
attacks them especially during high-energy events. In these them, but they do not prevent the erosion of the sediments in
cases, one of the solutions commonly adopted is the com- front of them. On the contrary, the presence of these struc-
plete protection of the shoreline by building seawalls. tures increases the effect of wave reflection and often causes
Another use of seawalls is to stop or slow down the retreat of the beaches in front of them to be completely dismantled
the cliffs, especially when there are developments located on [11]. It should be noted that the reflection produced by rock
the cliffs that are threatened by such retreat. In this case, the revetments is less than that caused by vertical concrete walls.
stabilization of some sections of cliff is associated with a To minimize the effect of reflection on frontal beach erosion,
decrease, or even cancellation, of the contribution that the engineers have devised the creation of revetments with
littoral drift supplies from the cliff to other adjacent sectors irregularly shaped concrete blocks which create large gaps
of the coast. that disperse wave reflection in many directions, so that the
Seawalls can be constructed in a number of possible ways. reflected waves counteract each other.
Sometimes they consist solely of wooden stakes driven into The presence of sea walls has another influence on the
the waterfront, stacked sandbags, or a combination of both sediment balance by preventing the entry of eroded sediment
(Fig. 28.5a). These structures are also called bulkheads. In volumes from the supratidal zones into the system,
this case, it is a temporary structure that is easily and quickly increasing the sediment deficit of these beach segments.

dynamic modification of the wave
trains by a rigid structure built
parallel to the coastline and its
effect on the sedimentary patterns,
with an example of a real case.
Image Landsat from Google Earth
On the other hand, these structures are frequently attacked the changes that these structures will have on the dynamics of
and destroyed by waves during storms. In this case, less rigid the natural system. The models applied by the engineers focus
structures such as wooden stakes, sandbags and rock revet- on the calculation of the design and the dimensions that the
ments behave less uniformly against collapse caused by the structures must have in order to resist the action of the pro-
disappearance of the sand supporting the structure and are cesses in terms of durability and resilience. The principles
more easily reconstructed than vertical concrete walls. governing these approaches can be summarized as follows:
Some of the economic activities that humans carry out on
the coast are directly embedded in the tidal systems. For • A large part of human infrastructure and natural resources
example, activities such as fish farming or the salt industry are located in coastal areas.
require the occupation of extensive intertidal areas of coastal • The coasts are highly valued as recreational areas.
systems such as lagoons, deltas or estuaries. • Coastal wetlands are ecologically rich.
• The boundary between land and sea is a permanent
Advanced Box 28.1 Geologists Versus Engineers on danger zone.
Coastal Protection • Coasts are easily modifiable.
The anthropic structures that modify coastal systems are
designed by coastal engineers according to principles that The conclusion drawn from the sum of all these consid-
prioritize functionality and do not always take into account erations is that the coast must be protected.

seawall construction. a Using
wooden stakes and geotextile
bags of sand. b Rock revetment.
c Concrete vertical walls
At the end of the twentieth century, these approaches (1) Coastal erosion problems do not exist until the presence
were strongly contested by coastal geologists, represented by of human infrastructure forces us to measure them.
the figure of Orrin Pilkey, one such geologist at Duke (2) The construction of anthropogenic structures on bea-
University, North Carolina, USA. Geologists understand that ches reduces their flexibility and causes erosion.
most of the time engineers only consider whether a structure (3) The interest of the owners should not be confused with
can be built, but they never consider whether that structure the natural interest.
should be built or not. The consequence is that the structures, (4) Once you start stabilization, you can’t stop.
although costly, often have unexpected and undesirable (5) The cost of saving a property is in the long run much
effects on adjacent coastal areas. Pilkey enunciated what are higher than the price of the property itself.
known as “the six truths about the coast” [12]: (6) To save the coast, you end up destroying it.
Pilkey’s truths are controversial, but perhaps they were the limitations often offered by the lack of a suitable site for
the starting point for the development of the integrated dredging the sands for nourishing, means that sometimes
coastal zone management (ICZM) concept that governs the suboptimal sediment is used for beach replenishment. Even if
principles of coastal occupation today. the sediment used has an adequate mean grain size, where
there is poor sorting the finer sizes are usually washed by
waves and wind and are easily extracted from the system.
28.2.2 Beach Replenishment This, in addition to a loss of material volume, leads to a
decrease in the quality of the sediment on the beaches, as only
Many coastlines in front of major tourist resorts or cities are the residual fractions remain as a lag.
highly erosive. The demand for beaches for recreational use The erosion of the sediment added by regular replenish-
has led many governments to devote a significant budget to ments has a clear influence on the feeding of the adjacent
the artificial replenishment of these beaches. The artificial non-nourished sectors. On the one hand, the erosion of part
contribution of sand to beaches is known as replenishment of these sediments can mean an increase in sedimentation
or nourishment (Fig. 28.6). rates in the shoreface sectors in front of the replenished area.
The choice of grain size usually takes into account the On the other hand, on beaches with a strong longshore
sedimentological characteristics. Normally, the grain size component, neighboring beaches may also see an increase in
used is intended to be above the entrainment threshold of the sand input due to littoral drift.
dominant wave, in order to as far as possible avoid continued Although these inputs constitute an increase of material
erosion [5]. This, in practice, means the use of an average size into the coastal system, it is an ephemeral input. Since the
coarser than the natural diameter of the replenished beach dynamic equilibrium of the beach is not modified, the input of
[14]. However, other grain-size parameters such as sediment this material does not produce changes in the sediment bal-
sorting are often not taken into account. This, together with ance. This means that if the dynamic agents provoke a
Fig. 28.6 Beach replenishment

operations
negative balance on this stretch of coast, it will continue to pick up the sand to rebuild the dune (Fig. 28.8a). Complete
have erosive behavior even after the artificial contribution of dismantling of the foredune ridge will constitute a decrease in
sand. Thus, replenishment is never a definitive solution to an the potential for input to the beach from the mainland, and
erosion problem, but only a temporary one, and the beach will thus a decrease in the overall sediment volume of the coast.
have to be nourished again in the short or medium term [6]. In addition, the absence of a foredune line leaves coastal
The cost of beach replenishment in many developed buildings exposed to the direct action of storm surges. It
countries runs to hundreds of millions of dollars per year. In should be remembered that storm surges also occur during
many cases, this investment is beneficial because the money conditions of meteorological surges. This endangers the
returned to the state in the form of taxes from the tourism coastal buildings themselves. Recent studies have shown
industry exceeds the initial costs. However, more often than that beaches where the dunes have been removed are much
not, the money is not returned and is a sunk cost [8]. Given more vulnerable (Fig. 28.8b) and have a more pronounced
that replenishments have to be carried out periodically, most erosive character [9].
of the time, in the long term, the investment in protecting a
stretch of beach through nourishment costs far more than the
value of the property it is intended to protect [12]. 28.2.4 Modifications of Tidal Prisms
in Restricted Environments
Advanced Box 28.2 Artificial Coasts
For most of the twentieth century, human actions on the In inland coastal systems such as lagoons, deltas and estuaries,
coasts were limited to protecting coastal systems with rigid extensive intertidal areas are impounded for uses involving
works or sediment replenishments. The development of agriculture, aquaculture (Fig. 28.9a) and saline activities
complex harbor infrastructures and the appearance of con- (Fig. 28.9b) or industrial waste piling (Fig. 28.9c). The
struction techniques that allowed building underwater led to restriction of surfaces that were previously inundated and
large port areas being reclaimed from the sea by the mixed exposed by water implies a decrease in the tidal prism. This
use of rigid structures filled with sedimentary material reduction of the tidal prism in turn implies a decrease in the
(Fig. 28.7a). This gave birth to the first artificial shorelines. tidal flows drained during each tidal cycle, and thus a decrease
The increase in port trade at the end of the twentieth century in the velocity of currents entering and leaving these systems.
led to an increased need for storage space in many major In any of the tidal channels of these systems, the reduction
harbors, which began to expand their facilities by reclaiming of the mean current velocity will lead to sedimentation and
land from the sea in this way. Thus, ports such as New York loss of flow. This effect is not a significant change in the case
(USA), Rotterdam (the Netherlands) or Barcelona and of natural systems, although the loss of draft may affect nau-
Algeciras (Spain) were extended with artificial land. tical activities when there is a harbor in these environments.
The area where the greatest changes due to the reduction of the
The extreme point of artificial shoreline construction tidal prism are observed is at the mouth of the tidal drainage
came with the emergence of entire islands with extensions of channels. In these areas are located environments such as tidal
tens of square kilometers for luxury developments off the deltas (in lagoons and estuaries) or frontal bars (in deltas),
coast of the United Arab Emirates. These artificial shorelines whose equilibrium depends on the balance of forces between
have been designed with unique shapes such as palm trees tidal currents and waves. The loss of velocity of the tidal
(Fig. 28.7b). In this case, engineers have designed the arti- currents will allow greater wave dominance, which is reflected
ficial land revetment with wave-spreading structures to have in a landward displacement of the frontal lobes. This phe-
a minimal effect on wave reflection. nomenon can lead to the closure of inlets if the decrease of the
tidal prism is significant and, in the case of harbors within the
systems, constant maintenance dredging is required. This
28.2.3 Destruction of the Foredune Systems dredging activity also induces modifications of the tidal current
velocities, since it implies an increase of the flow section.
The destruction of coastal dune systems for aggregate or
beachfront development has been common in the past dec-
ades, and is still common in many developing countries. 28.3 Human Modifications of the Fluvial
From a dynamic point of view, there is a strong interaction Sediment Supply to Coastal Systems
between the foredune and the beach equilibrium. The fore-
dune is the sand reserve of the coast and provides protection Humans can influence the inputs that reach the coast from
for the mainland from extreme erosional effects. Thus, the the mainland by modifying the sedimentary supply from
dune is eroded during storms, but its sand feeds the nearshore rivers. These changes directly affect the sedimentary balance
and remains there until dynamic conditions favor the wind to of a coastal cell.
28.3 Human Modifications of the Fluvial Sediment Supply to Coastal Systems 431
Fig. 28.7 Examples of artificial

coasts. a Esplanade docks of the
Algeciras harbor (S Spain).
b Artificial island of Palm
Jumeirah (Dubai)
Fig. 28.8 Comparison of two

nearby beaches after the same
storm. a Beach with a partially
eroded foredune. b Beach without
foredune where the storm waves
destroyed the sea promenade
Fig. 28.9 Intertidal surfaces

restricted by human uses. a Fish
farms. b Industrial salt pans.
c Industrial waste stockpile
28.3.1 Building of Dams into Rivers can be regulated by the partial opening of gates so that rivers
maintain an ecological discharge; however, each dam means
Countless rivers around the world, regardless of their size, a cutoff of sedimentary material. The efficiency of some of
have been regulated in order to store water for urban, agri- these dams in retaining sediment is as high as 100% in some
cultural or industrial consumption (Fig. 28.10). The pres- cases [17].
ence of a reservoir implies an alteration of the natural flow of On the other hand, each dam represents a significant
water and sediment downstream of the dams. Water flows decrease in the source area of coastal systems. Thus, river
28.3 Human Modifications of the Fluvial Sediment Supply to Coastal Systems 433
Fig. 28.10 Dam totally cutting

the path of water and sediments in
a small river
Fig. 28.11 Images showing the

strong retreat at the front of the
Ebro River Delta (NE Spain) after
the building of 70 dams, most of
them between 1955 and 1970
basins with a high number of dams are no longer con- It is not only the river mouth systems that suffer from
tributing significant volumes of sediment to the coastal sediment deficit, but also the adjacent coasts. Shorelines at
systems developed at their mouths. It is estimated that more the margins of river mouths are often fed with river sedi-
than a quarter of the sediment delivered by rivers globally ments transported by littoral drift. Sometimes these shores
has been retained in their reservoirs [15]. adjacent to river systems continue to receive sediment from
This decrease in sediment input implies a change in the the erosion of the delta front. However, erosion and long-
morphodynamics and sediment balance of river mouth sys- shore current often fail to supply sediment at a sufficient rate,
tems (estuaries and deltas). In estuaries, the water mixing and beaches also begin to retreat.
patterns are modified, as less freshwater is received. The
mixing zone shifts towards the river and there is usually a
tendency for the degree of mixing to increase as the volume of 28.4 Human Influence on Global Climate
flocculated material increases. In general, the sediment in the
central part of estuaries becomes finer and more organic [16]. After studying the effect of atmospheric greenhouse gases on
In deltas, the reduced arrival of sediment in bed load global warming in Chap. 24, we can conclude that the
implies a change in the morphology and dimensions of the increase in these gases has taken place due to the use of
delta front bars. In general, the reduced supply of fluvial fossil fuels since the Industrial Revolution of the nineteenth
sands to the delta front is accompanied by a retreat due to century. The increase in atmospheric CO2 levels due to
erosion and subsidence, as fluvial sediments no longer anthropogenic causes has different impacts on the coastal
compensate for the wave transport capacity and land subsi- system. These effects have been summarized by Masselink
dence (Fig. 28.11). There are numerous well-documented et al. [10], taking into account that many of these effects may
examples of this effect in many rivers in the Mediterranean have a local character, while others have a global character.
(Po and Ebro), Atlantic (Guadiana and Senegal), Indian
(Indus and Ganges–Brahmaputra) and Pacific (Mekong, Red • Increase of dissolved CO2 in seawater: acidification of
River) [2]. coastal water with negative effects on coral reefs.
• Increase in seawater temperature: effect on eutrophication
of coastal wetlands; impact on coastal reefs through coral
28.3.2 Changes in River Catchment bleaching.
• Modification of the wind regime: effects on the generation of
Human-induced changes in the fluvial catchment area are a dunes and on the directions in which waves reach the coast.
main cause of modification of the sediment supplied by the • Increased number of storms and wider temporal distri-
rivers to the coastal systems. In this context, deforestation of bution: effects on increased erosion.
wide continental areas may cause a dramatic increase in • Increased wave size: effect on increased erosion.
erosional processes and the consequent increment of sedi- • Changes in river flow: effects on sediment input to coastal
ment introduced by rivers in estuarine or deltaic systems. As systems.
an example, many deltas developed on the Mediterranean • Sea level rise: long-term effects on the evolution of
coasts prograded quickly during the last 6,000 years since coastal systems.
the vegetation of their basins were eliminated [1]. Another
clear example has been described in the Iberian Peninsula, The consequence of most of the effects is transgression,
where the massive construction of ships that followed the accompanied by increased erosion and vulnerability of
discovery of America was necessarily accompanied by the coastal systems, as they are subjected to a change in the
cutting down of trees from the vast forests of the interior of maritime climate that tends to increase the energy of
the continent. Estuaries tend to respond to this increased hydrodynamic processes.
sediment input by increasing their fill rate, while deltas
normally respond by generating prograding cycles on the
delta front. References
Conversely, reforestation can reduce the rates of sediment
supply from rivers to the coastal systems. This process has 1. Anthony EJ, Marriner N, Morhange C (2014) Human influence
also been described by Anthony et al. [1] as occurring in and the changing geomorphology of Mediterranean deltas and
many Mediterranean deltas during the last 50 years. The coasts over the last 6000 years: from progradation to destruction
phase? Earth Sci Rev 139:336–361
studied deltas responded to this decrease in contributions 2. Besset M, Anthony EJ, Bouchette F (2019) Multi-decadal
with setbacks caused by coastal erosion. Consequently, variations in delta shorelines and their relationship to river
many coastlines associated with these systems had to be sediment supply: an assessment and review. Earth Sci Rev
protected by structures. 193:199–219
References 435
3. Bowen AJ, Inman DL (1969) Rip currents 2: laboratory and field 12. Pilkey OH (1981) Geologists, engineers and a rising sea-level.
observations. J Geophys Res 74:5479–5490 J Coastal Res Northeast Geol 3:150–158
4. Carter RWG (1988) Coastal environments: an introduction to the 13. Pope J, Dean JL (1986) Development of design criteria for
physical, ecological, and cultural systems of coastlines. Academic segmented breakwaters. In: Proceedings of the 20th coastal
Press, London, 617 pp engineering conference. American Society of Civil Engineers,
5. Dean RG (1974) Compatibility of borrow material for beach fills. pp 2144–2158
In: Proceedings of the 14th coastal engineering conference. 14. Simoen R, Verslype H, Vandenbossche D (1988) The beach
American Society of Civil Engineers, pp 1319–1330 rehabilitation project at Ostend, Belgium. In: Proceedings of the
6. Dean RG (1983) Principles of beach nourishment. In: Komar PD 21st coastal engineering conference. American Society of Civil
(ed) Handbook of coastal processes and Erosion. CRC Press, Boca Engineers, pp 2855–2866
Raton, USA, pp 217–232 15. Syvitski JPM, Kettner A (2011) Sediment flux and the Anthro-
7. Dunham JW (1965) Use of long groins as artificial headlands. In: pocene. Philos Trans Royal Soc A: Math Phys Eng Sci 369:957–
Coastal engineering, Santa Barbara specialty conferences. Amer- 975
ican Society of Civil Engineers, pp 755–762 16. Ve ND, Fan D, Vuong BV, Lan TD (2021) Sediment budget and
8. Houston JR (1996) International tourism and US beaches. Coastal morphological change in the Red River Delta under increasing
Eng Res Centre (CERC) 96(2):1–3 human interferences. Marine Geology 431:106379
9. Komar PD (1998) Beach processes and sedimentation. 17. Vörösmarty CJ, Meybeck M, Fekete B, Sharma K, Green P,
Prentice-Hall Inc., Englewood Cliffs, New Jersey, 429 pp Syvitski JPM (2003) Anthropogenic sediment retention: major
10. Masselink G, Hughes MG, Knight J (2003) Introduction to coastal global impact from registered river impoundments. Global Planet
processes and geomorphology. Routledge, London, 416 pp Change 39:169–190
11. McDougal WGM, Krauss NC, Ajiwibowo H (1996) The effects of
seawall on the beach. Part II, numerical modeling of supertank
seawall tests 12: 702–713
Coastal Changes and Coastal Hazards
29
– Exposure is the location of a vulnerable person or

29.1 Introduction
infrastructure in a place where it can be reached by a
hazard.
Throughout this book it has become clear that the coast is a
– Risk is the real possibility of a hazardous process
place of permanent change. “If there is one thing about the
affecting people or human infrastructure. Risk is classi-
coast that does not change, it is change.” Many of these
cally defined as hazard vulnerability exposure.
changes are cyclical, but others are permanent. Sometimes
– Disaster is an event that has caused a lot of damage or
coastal evolution has specific trends that can be known and
destruction—i.e., a destructive reality that has already
assessed, making future changes predictable. All this vari-
happened is considered a disaster.
ability is generically known as coastal change.
Humans have to consider that their activities on the coast
In the above terms, if any of the variables affecting risk
must allow for the flexibility that the coast requires. How-
(hazard, vulnerability or exposure) is zero, then the risk is
ever, a significant percentage of the population of civilized
zero. For example, if a hazard threatens an area vulnerable to
countries lives within the influence of coastal change.
that hazard but that area is not exposed, there is no risk. If a
Houses, hotels, flats, port infrastructure, power plants,
hazard threatens an exposed area, but that area is not vul-
industries, refineries, recreational areas and military bases
nerable, the risk is also zero. The problem is that the people
occupy an enormous expanse of coastal segments. And this
living along our coasts are extremely vulnerable to coastal
occupation has increased in the first decades of the
change and its hazards, but they are also exposed to it. It is
twenty-first century. In Spain, for example, the build cost per
currently estimated that some ten million people around the
square meter has multiplied by five in the last 20 years,
world are directly affected by the effects of coastal change
despite the economic crisis. The point is that all this occu-
associated with events such as storms (where high wave
pation has been carried out without respecting, and in many
action is coupled with coastal flooding due to storm surges).
cases without even taking into account, coastal changes.
This number increases for populations at risk from tsunamis.
Coastal change is perceived as a hazard by humans,
There are numerous studies in the scientific literature that
because people and their constructions are vulnerable to
document, assess and model coastal change, hazards, vul-
these changes. However, there is no real possibility of
nerability and risk to human exposure to these processes.
coastal change affecting humans if there is no exposure to it
These studies include research into historical coastal change,
(Fig. 29.1). In the previous sentence, the concepts of hazard,
geological structure, the dynamic functioning of coastal
vulnerability and exposure are conflated. These are different
processes, the influence of sediment input and mobility, the
concepts, but they are linked to each other. Two other words
influence of sea level and how extreme storm events affect
that are often associated with these concepts are risk and
sedimentation. Social studies are also included, such as the
disaster, which also have different meanings.
history of occupation of coastal regions and the impacts of
coastal change on these populations [22].
– Hazard is the probability of a situation occurring that is
Disasters are occurrences when all the adverse conditions
perceived as a threat to humans. In terms of coastal
of hazard, vulnerability and exposure have come together to
geology, it is the potential of a coastal process to affect
produce events that have severely affected certain coastal
humans.
populations, producing a high economic cost and sometimes
– Vulnerability is the fragility of the natural environment
costing human lives. Many of these disasters, such as those
or of human beings to the potential damage that this
associated with Hurricane Katrina in 2005 or the tsunami in
hazard could produce.

https://doi.org/10.1007/978-3-030-96121-3_29
438 29 Coastal Changes and Coastal Hazards
result is that, today, more and more developments are being

attacked by marine processes, especially in the context of
rising sea levels accompanying global change.
Irrespective of the debate between the cause of hazards
(natural vs. human), it seems clear for the management and
use of coastal zones that there are problems related to two
types of phenomena: continuous phenomena and eventual
phenomena. These risks are discussed separately below.
29.2 Slow-Rhythm Coastal Changes

Fig. 29.1 Diagram showing the relationships between hazard,
vulnerability and exposure to determine risk Certain coastal processes occur on the coast at a very slow
rate. These are known as continuous phenomena. Such
processes do not pose a risk to human life, as the slow pace
Indonesia in 2004, have been marked in the collective allows humans to get to safety. However, these phenomena
memory by the great damage they caused and the impact of do pose a risk to property. Sea level rise and coastal erosion
the images that were broadcast around the world by the fall into this category. Both phenomena are related to climate
media. change [17].
In some studies, disasters have been classified from a
social science point of view. Thus, natural disasters and
human disasters have been differentiated [11]. These 29.2.1 Sea Level Rise
authors describe “disasters that are caused by the action of
natural phenomena beyond human control.” This category It is now commonly accepted that sea level is rising. The
includes disasters related to climatic phenomena (storms causes of this rise are well known and are related to climate
and coastal flooding) and tsunamis. Human catastrophes are change, which is evolving towards global warming. The
described as those in which humans are the main cause. origin of this warming is attributed to the greenhouse effect
These include chemical pollution disasters. A third category that has resulted from the extensive use of fossil fuels over
could also be included, in which humans can act as a cat- the last two centuries. In both hemispheres, the retreat of
alyst by accelerating or increasing the effects of a natural continental ice masses has been observed, accompanied by a
disaster. This third category would include catastrophic slow increase in oceanic water mass [1]. In addition, global
transformations of coastal dynamics. Today, this approach warming implies an increase in ocean water volume due to
has been strongly contested to the point that some studies thermal expansion.
deny the existence of natural catastrophes on the coast [8]. A few decades ago, there was controversy over the
The main argument used is that catastrophes would not magnitude of sea level rise, with differences ranging from
occur if humans had not occupied these areas (exposure). 1 mm/year to 2 cm/year, depending on where the measure-
By this criterion, a coastal phenomenon acting on an area ment took place [2]. Today, there are global measurement
without humans would never produce a catastrophe. From networks that estimate mean sea level variations at many
this point of view, all coastal disasters would belong to the coastal locations around the world. Estimating the magni-
third type described above. tudes of sea level rise at each of these locations requires at
It follows from this argument that human development is least 30 years of observations. Some stations such as Balti-
one of the main problems in the genesis of coastal risk. We more (USA) store data from more than 110 years of records,
began this chapter by pointing out that building on the coast accumulating a 425 mm rise since 1902 [20]. The average
eliminates the natural flexibility to adapt to coastal change. estimate of sea level rise must compare the magnitudes
The construction of houses in flood-prone areas makes them observed at stations around the globe. In parallel, satellites
high-risk zones because the buildings are extremely vul- recording the dynamic topography of the ocean surface have
nerable, but they are also exposed to coastal processes in accumulated global data since 1993 (see Advanced box 25.2
general and to more energetic ones in particular. To con- in Chap. 25 of this book). Historical rates of rise of
struct buildings in areas that can be reached by storms is to 1.8 mm/year over the last century are now accepted. These
put not only the buildings at risk, but also the lives of the rates have accelerated to 3.1–3.4 mm/year when averaged
people who occupy them. It is now known that certain areas from satellite data [3], but they may have increased even
of the coast are vulnerable to coastal processes, and yet more if the last decade is considered separately, reaching
buildings continue to be constructed there anyway. The values of 4.6 mm/year (Fig. 29.2).
29.2 Slow-Rhythm Coastal Changes 439
Fig. 29.2 Graph of the averaged

sea level evolution from satellite
observations since 1993 (NASA
Goddard Space Flight Center)
It is not only eustatic rise that is influencing coasts. The will be introduced into the estuarine inlets and preserved
effects of subsidence coupled with eustatic rise are acceler- within them.
ating the rate of relative rise in some of the world’s most Reef systems are also expected to be inundated. The
densely populated areas [12]. On the African coasts of the preservation of reef systems and their position will depend
Mediterranean and the coasts of India, China, Korea and on the relationship between coral growth capacity and the
Japan, the relative rate of rise is between 10 and rate of sea level rise. In general terms, reefs are responding
15 mm/year, and in some areas, such as the islands of to sea level rise with vertical accretion, sometimes accom-
Indonesia or the Philippines, rates can even exceed panied by migration towards the mainland.
20 mm/year. All these processes that have been developing naturally in
The immediate effect of this sea level rise, if not com- all previous periods of Earth’s history are now seriously
pensated for by sediment inputs, is a migration of the affecting humans [7, 15]. Urban or industrial areas that
coastline towards the continent. This migration implies mainly develop on coastal plains, such as barrier islands or
inundation of inland coastal areas (Fig. 29.3a) and an the interior of fluvio–tidal systems are being affected by
increase in the depth of intertidal and subtidal littoral marine inundation (Fig. 29.3b).
systems.
Under these conditions, coastal systems adapt to the rise
through new trade-offs between dynamic processes and 29.2.2 Coastal Erosion
sediment input, which depend on the particular coastline and
the environments that develop along it [6]. For many cliffs, Coastal erosion is the retreat of the coastline due to a neg-
particularly those made of less resistant materials, sea level ative sediment balance. We have seen that, in coastal
rise is accompanied by an increase in the rate of retreat. dynamics, there are oscillation margins that include seasonal
In general, barrier island systems move landward through and inter-annual periods of alternating erosional and depo-
rollover and overstepping processes. In both cases, the rise is sitional conditions. However, this section is not referring to
accompanied by an increase in overwash processes. Many of these periodic erosive moments, but to prolonged periods of
these systems are now losing their characteristic geometry as continuous erosion. Any coastal system can be subject to
the dune systems are destroyed by wave action, using their erosion. Rocky shores are the most erosive of all the systems
sedimentary material to build washovers over the barrier studied (Fig. 29.4a), but beaches in front of barrier islands
island systems. (Fig. 29.4b), deltas and estuaries are also susceptible to
At river mouths, the coastal plains are flooded according erosion. Continuous erosion can be measured by comparing
to the rates of rise. If the rate of sediment aggradation out- the shoreline in the same month between different years.
weighs the rate of rising, there may not be much transfor- More continuous measurements—e.g., monthly—allow the
mation in these environments. However, if the rate of duration of erosion–accumulation cycles and the return
vertical accretion is less than the rate of rising, the marshes periods of point erosion events to be determined more
and mangroves associated with estuaries and deltaic plains accurately. There are numerous works in which shoreline
can be expected to be inundated and drowned. As estuaries displacement and linear erosion rates are determined by
are invaded by the sea, tidal exchange at river mouths will remote sensing using geographic information systems (GIS;
increase. In this case, much of the sediment from the barriers e.g., [4]). However, these works do not allow for
Fig. 29.3 Results of sea level

rise. a Effects in a natural
environment, at Driftwood Beach,
Georgia, USA, b effects in a
coastal city, at Isla Cristina, SW
Spain
calculations of eroded volumes. The calculation of erosion transport or from inputs coming from the sea. Among
volumes requires the comparison of topographic profiles the natural causes of this deficit is the existence of
carried out at regular intervals along the coast (e.g., [24]). resistant lithologies that do not supply enough sedi-
The main cause of erosion is the existence of a negative ment to the coast. Another possible cause may be a
sediment balance in the coastal section where it occurs. This reduction in inputs in relation to climate change.
means that more material flows out of that stretch of coast – Increase in the intensity and frequency of storms:
than comes in. There are two possible causes for this sedi- this cause involves increased cumulative erosion
ment deficit to occur, and they are natural and during times of energy peaks. The overall increase in
anthropogenic. storm energy is also related to climate change.
(2) Anthropogenic causes
(1) Natural causes – Modifications of wave refraction and tidal prisms:
– Hydrodynamic erosive agents: it is usually the the existence of human constructions on the coast
waves that cause erosion. When the carrying modifies the balance between hydrodynamic agents
capacity of the waves is greater than the volume of and the way in which sediment is distributed. These
material available, the waves remove older material alterations normally lead to the appearance of seg-
from the shore. ments of coastline where a situation of permanent
– Deficit in sedimentary input: most of the time, it is the erosion occurs.
rivers that present this deficit in their input to the – River damming: this causes sediment retention in
coast, although the deficit can also come from wind inland areas and a loss of the transport capacity of
29.2 Slow-Rhythm Coastal Changes 441
Fig. 29.4 Coastal environments

under erosion with threat to
buildings. a Cliff with an
urbanized top (Azenhas do Mar,
Portugal), b Eroded beachfront
(Mazagón beach, SW Spain)
rivers to supply sediment to the coast. Both of these The effects of these erosional phenomena mean a loss of
are determining factors in generating a sediment coastal habitats, but above all the loss of recreational areas,
deficit in the coastal areas fed by these rivers. buildings and infrastructures and, in short, a loss of security.
– Artificial sand mining: building in coastal areas When a natural area is subject to erosion, the erosional
requires significant volumes of sand. On many of the process does not pose a risk, although a loss of ecosystem
world’s coasts, this sand has been obtained directly value does occur [18]. Where there are no buildings, there is
from the dunes. The extraction itself causes a deficit, no risk. However, erosion poses a serious risk to areas where
but the dune also represents a store of sand for humans have built within reach of these processes. It is
coastal dynamics, which is used by the waves during simply an increase in exposure, with people being respon-
specific moments of the annual cycle. The lack of sible for building in areas subject to erosion or even causing
such a store is often reflected in permanent erosion erosion with their infrastructure [14]. In these cases, not only
along that stretch of coastline. buildings located between the seasonal or inter-annual
oscillation margins of the coastline would be at risk, but also the energetic discharge represented by large waves and the
those located in nearby areas, taking into account the general currents associated with these waves represent a great
rate of retreat. capacity for sediment movement and an enormous destruc-
In developed countries, continuous erosion is recognized tive force for the infrastructures located on the coast
as a major problem, especially because it is considered to be (Fig. 29.5a). It should be taken into account that the surge
a phenomenon that has been increasing for decades and is that normally accompanies storms can reach up to 6 m,
still increasing. As a result, the budget allocated to correcting causing the coast to be flooded and the waves to act in areas
this impact is often very large, especially in countries that where they do not normally reach. In addition to the surge,
base their economies on tourism. On the Atlantic coast of the the passage of storms means occasional periods of high
United States, the average rate of erosion is 0.9 m per year, rainfall. In coastal systems located at river mouths, high
and it is even higher on some stretches of the Gulf of Mexico discharge situations join the surge to plug the river inlet,
coast, where it exceeds 1.8 m per year. causing fluviomarine flooding in the delta plains and estu-
There are different possible mitigation and management arine margins.
strategies to slow down these erosion processes, which will The consequences of storm action on natural coastal
be discussed in the next chapter of this book. systems are as follows:
– Intense erosion of beaches and dunes: the main effect of

29.3 High-Energy Coastal Events storms is erosion along the coast. Larger wave action
erodes at a faster rate, with sediment moving to areas
Some events concentrate an enormous amount of energy on below the closure depth, from where it can no longer
the coast in a very short space of time. This is the energy return to shore. Erosion rates in some coastal segments
generated by the movement of water masses, which is nor- can exceed 30 meters in a single day.
mally used to transport large masses of sediment, but also – Overwash processes: on barrier island ridges, the com-
has great destructive power. These coastal events cause bined action of surges and large waves can exceed the
occasional problems on the coast and pose a risk not only to height of the foredunes. Sand from the dunes can be
property but also to human life. High-energy events have reworked back towards the rear of the system, forming
two distinct origins—meteorological action and seismic washovers. At the front of tide-dominated systems, these
activity in the marine environment—and are reflected in the same processes act on the foreshore to displace coarse
arrival of severe storms and tsunamis on the coast. Both sediment onto the tidal flats, forming cheniers.
phenomena have been discussed in Chap. 13 from the point – Breaching processes: in barrier island systems, overwash
of view of the processes and the sediments they leave in the processes can concentrate at certain points, leading to the
geological record. The following sections describe the effect formation of channels that can evolve into inlets when
these processes have on coastal populations. they become embedded and deepened.
The natural coastal system can partially or fully recover

29.3.1 Extreme Storms from these storms. On the beaches, thanks to the dynamics
of ridges and runnels during periods of fair weather, the sand
Storms are one of the main threats to coastal areas, especially displaced towards the shoreface during the storm can accu-
those that are heavily occupied by humans. Storms represent mulate again in the foreshore and from there the wind can
moments of high wind force and enormous wave energy pick it up to rebuild the foredunes.
deployment, which are also accompanied by flooding due to However, these processes also cause damage to human
the meteorological surge. The sum of all these causes means infrastructure:
that storms represent moments of high erosion.
Chapter 13 considered two types of storms of different – Direct wind damage;
intensity: tropical cyclones (hurricanes or typhoons) and – Flood damage;
mid-latitude storms. In inter-tropical areas, cyclones act on – Damage caused by wave action;
the coast with winds in excess of 200 km/h. These are – Damage caused by the accumulation of sediment.
low-pressure centers surrounded by winds that spiral in a
cyclonic pattern. In mid-latitudes, storms have winds of Storms, and especially tropical cyclones, can devastate
lower intensity than in tropical areas, but the action on the entire coastal regions, causing extensive damage to prop-
coast is similar due to their longer duration. erty and people. Perhaps the most publicized cases
The action of storms on the coast is not only related to the worldwide were Hurricanes Andrew, which struck Florida
direct action of wind on infrastructures. In addition to wind,
29.3 High-Energy Coastal Events 443
Fig. 29.5 Effects of storms on

human-occupied coasts. a Storm
Eleanor acting on the coast of
Saint-Malo (NW France),
b Fluviomarine flood in Chennai
(India)
in 1992, and Katrina, which devastated New Orleans in Records now show that the frequency, duration and
2005. Andrew was a category five hurricane that cost 23 average intensity of storms are increasing due to climate
lives and caused $26.5 billion in property damage. Katrina change [10, 13]. Meanwhile, the storm season is also
was the most economically and personally damaging event expanding, with the first storms arriving earlier and staying
in the USA, with more than 2,000 deaths and more than later.
$108 billion in property damage. Although the most
media-worthy events are those occurring in the USA, there
are events as destructive as those described in densely 29.3.2 Tsunamis
populated areas of Asia. An example of this is the river–sea
flooding on the coast of southern India in 2015 Tsunamis are great waves originated by sudden movements
(Fig. 29.5b). The passage of a monsoon affected the states of the ground transferred to the water mass, usually due to
of Tamil Nadu and Andhra Pradesh with more than 300 tectonic causes (see Chap. 13). These waves are character-
fatalities, 1.8 million people evacuated and damages ized by their kilometric wavelength. The volume of water
exceeding $ 3 billion [19]. displaced by a tsunami, and the speed it reaches, are so great
that its energy is 70 million times greater than a wind wave some 27,000 deaths, displaced more than 165,000 people
of the same height. The direct action of the tsunami wave and caused economic damage in excess of $300 billion.
breaker generates damage in the frontal zone of the coast. On – Destruction of the economic system: a less obvious effect
the other hand, the encroachment of the water mass driven is the destruction of the economic system in
towards the inland areas close to the coast causes inundation tsunami-affected areas. In addition to the cost of recon-
damage. The extent of tsunami inundation depends on the struction, these areas are affected by the disappearance of
geographical configuration of the terrain according to vari- businesses that generate economic wealth and capital.
ables such as water column in relation to topography, veg- Developing countries suffer particularly badly from this
etation and the existence of other human obstacles [16]. In effect, as they lack insurance systems and credit systems.
certain regions, waves can reach areas more than 10 km
inland, especially on coastal plains. At river mouths, the There are societies such as Japan or Chile whose culture
tsunami wave can be channeled and penetrate even further and experience make them prepared for tsunamis. However,
inland. In these flat areas, additional damage can occur tsunamis are often unexpected phenomena that reach soci-
related to debris entrainment during the advancing wave, eties which are totally unprepared. There is a substantial
which is densified with a high sediment concentration. In difference in the way a tsunami affects both types of soci-
high topographic configurations of funnel-shaped valleys, eties. Two events of similar characteristics had very different
the water can pile up, amplifying the wave dimensions and consequences for the countries of Japan and Indonesia due to
reaching heights of more than 100 m. their different degrees of development and preparedness. In
The effects of a tsunami on the communities it strikes are Japan, society was prepared in terms of defensive infras-
similar to those of an extreme storm, but much greater in tructure (coastal walls), warning and evacuation systems, but
magnitude in all respects: also in educating its citizens for self-protection. All this was
lacking in the case of Indonesia. The result was that the
– Loss of human life: the tsunami with the highest death toll number of casualties in Indonesia was 100 times higher than
was the 2004 Indonesian tsunami. The total number of in Japan, despite the fact that the events affected similar
casualties has not yet been reliably counted, but is esti- populations.
mated to have exceeded 260,000.
– Loss of infrastructure: tsunamis cause the destruction of
buildings, but also of factories of all kinds, affecting fuel, 29.3.3 Other High-Energy Processes Affecting
light and water supplies. In tsunami-hit areas, the effects the Coasts
are total devastation (Fig. 29.6). All this generates very
significant economic damage. The event that has gener- Certain coasts of the world can be affected by singular
ated the most economic damage to date was the Tōhoku eventual phenomena that can cause specific imbalances in
2011 tsunami in Japan. This event, in addition to causing their dynamics. Coasts located on tectonically active margins
Fig. 29.6 Total destruction of

the city of Palu (Indonesia) after
the Tsunami of 2004
29.3 High-Energy Coastal Events 445
present a high risk of landslides, both in the emerged area tidal height at the time of the event. However, some studies
and in the submerged area. In the case of emerged areas, based on hydrodynamic modeling of possible long-term
these landslides are usually associated with steep coasts such scenarios estimate that, in certain coastal areas, a moderate
as cliffs and bluffs. The occurrence of this type of phe- rise of tens of centimeters could double the risk of being hit
nomenon causes changes in rhythm in the normal processes by a tsunami [9]. Such a scenario could occur in about
of the receding cliff. Landslides in submerged areas can 150 years.
cause tsunamis of moderate size, which do not spread across Future strategies for the defense of coastal areas will need
the oceans but can locally affect the closest coastal areas. to take these combined effects into account.
Coasts affected by active volcanism are also subject to
changes associated with magmatic activity. The emission of
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Mitigation, Coastal Policies and Integrated
Coastal Zone Management 30
retreat related to sea level rise and erosion. The action that
30.1 Introduction
causes the greatest impact is the construction of rigid
structures (groins, breakwaters and seawalls). As discussed
If one thing can be concluded from the previous chapters, it is
in Sect. 28.2.1, these structures induce an imbalance in
that human economic and social activities are permanently
coastal dynamics by modifying wave refraction patterns and
threatened by coastal processes in both the long and short
the compartmentalization of the coast into different coastal
term. In addition, the natural balance of the coast is in turn
transport cells.
threatened by these same human activities. This two-way
In addition to these, other lower impact defenses have
interaction between humans and natural processes is complex
been developed in recent times. These are known as
and requires interdisciplinary analysis to obtain an adequate
non-traditional defenses [9]:
response from coastal management institutions (Fig. 30.1).
At present, the possible responses that those responsible for
– Bulkheads: these are structures made of metal, wood or
management decisions should make to help people who are
sandbags, which extend parallel to the shore to prevent
menaced by coastal processes, but want to continue to live on
direct wave attack and transverse transport of sand to
the coast, are still under discussion. These responses must
deeper areas (Fig. 30.2a). Some of these structures are
respond to strategies that provide security for coastal com-
designed either for use at the waterfront on a temporary
munities while respecting the balance of natural systems.
basis or in inland areas protected from direct ocean wave
This chapter will look at the different measures that
attack but subjected to smaller waves or wakes.
governments in some countries are taking to address the
– Dewatering systems: these are drainage systems that
challenges posed by human coexistence with the geological
lower the water table in the frontal zones of the beach by
hazards induced by coastal change. Some of these measures
extracting water from the pores of the sand. In this way,
include the adoption of specific coastal policies and pro-
part of the water from the swash is absorbed by the pores,
grams. Recently, the comprehensive approach that these
reducing the volume of water drained superficially by the
policies require is being addressed through an integrated
undertow. This decrease implies a lower velocity and,
coastal zone management (ICZM) strategy.
therefore, a lower erosional capacity.
– Hardening dunes: this consists of locating a hardened
core inside the foredunes. Sometimes the installation is
30.2 Mitigation
done by artificially constructing the dune over a concrete
On many coasts around the world, the intersection of geo- core, and sometimes the artificial design contains irreg-
ular structures designed to increase wind friction by
logical processes, vulnerability and exposure produces an
unacceptable risk to the coastal community. In these areas, growing the dune over it. During storms, waves can erode
coastal managers have typically employed coastal protection the dune front, uncovering the rigid core that acts as a
classic defense. After the storm, the wind can rebuild the
measures to reduce risk. These measures together are known
as mitigation. On many occasions, mitigation has been dune again.
justified as a form of risk reduction for the environment, but – Sand-filled geotubes: these are large bags of strong,
porous fabric that can be filled with sand (Fig. 30.2b).
the truth is that most of the time these measures are aimed at
protecting human uses of the coast. Geotubes are designed to behave as rigid structures,
Chapter 28 of this book discussed some of the solutions although they have the advantage that they can be easily
removed by cutting the fabric when no longer needed.
that engineers propose to mitigate the effects of coastal

https://doi.org/10.1007/978-3-030-96121-3_30
448 30 Mitigation, Coastal Policies and Integrated Coastal …
zones should always follow a proper planning process based

on knowledge of the dynamics of geological processes.
From this perspective, if it is known that there are processes
of continued erosion or threat of encroachment by sea level
rise or storm or tsunami attack, the decision should be not to
build. Proper siting of coastal constructions is considered the
best defense (Fig. 30.3a). Sometimes, humans decide to
build in a risk zone but adapt their structures to that expo-
sure. One way of doing this is by elevating structures
(Fig. 30.3b). However, many coasts have already been built
inappropriately. Especially in the second half of the twen-
tieth century, many civilized countries massively populated
coastal areas without any prior planning or adequate
knowledge of the geological processes of the coastline. In
such instances, it is often the case that the long-term costs of
protecting the built environment are greater than the value of
the construction itself. In such cases, relocation should be
Fig. 30.1 Interaction between natural and human processes (social and considered.
economic) that give rise to the need for integrated coastal management When a development is built in an area exposed to coastal
for sustainable development
hazards, the action of extreme events is unavoidable, despite
mitigation and protection measures. In these cases, human
preparedness measures are needed to mitigate the effects of
Sometimes, these geotubes are installed as resistant cores the most severe events. If coastal flooding cannot be avoi-
in the dunes by mixing this solution with the one ded, it is essential that water drainage systems be kept clear.
described above. Generators and electricity transformers should be located on
– Viscous drag mats: these are covers composed of high ground to avoid flooding. Trees susceptible to toppling
high-strength plastic sheets woven into a carpet that is should be kept away from power lines. Apart from the
fixed to the seabed in deep areas of the waterfront. The protection of property, above all, efforts should be made to
plastic fronds create turbulence that interrupts the keep human lives safe. The establishment and marking of
undertow of the waves and thus reduces erosion. This safe areas and evacuation routes is vital. It is ultimately of
solution is not suitable for the nearshore, but works very paramount importance to educate the population at risk
well in deeper waters, and is often used to protect sub- about self-protection measures in order to minimize loss of
merged infrastructure in these areas. They have the dis- life [9].
advantage that they degrade over time and contribute to Such measures should be established on the basis of
microplastic pollution. decisions taken according to coastal strategies and policies.
– Biotextile covers: these are covers made of biodegradable Ideally, these policies should be framed within an integrated
material that increase the resistance of the soil, favoring coastal management (ICM) program. These aspects will be
the growth of plants on a stable substrate. They are spread discussed below.
over dune systems and backshore areas, and also over the
shores of inland systems (tidal channels and lagoons), to
cushion the direct impact of waves on the sand. Some- 30.3 Coastal Policies
times, the biotextiles are formed into bags that are filled
with sand and distributed over the site to be protected. Decision-making about human development on the coast, as
Over time, the biotextile degrades and disappears, leaving well as the measures taken to protect it, is set within a policy
only natural vegetation. framework. The set of measures taken to make coastal
communities sustainable, to reduce human impacts on nat-
Another mitigation measure adopted from an engineering ural resources and to minimize natural impacts on people
point of view is beach nourishment. These types of measures and their infrastructure are called coastal policies. These
have also been extensively discussed in Sect. 28.3.1. measures are informational, economic and legislative in
Apart from these mitigation actions that attempt to reduce nature (Fig. 30.4) and should, in theory, be aimed at making
vulnerability, there are non-engineering ways to combat the coast a desirable and safe place to live.
coastal risk by reducing exposure: pre-construction planning Coastal policies should be formulated by governmental
and relocation. Theoretically, the occupation of coastal authorities at different territorial levels. These policies
30.3 Coastal Policies 449
Fig. 30.2 Some non-traditional

mitigation measures. a Bulkheads
made of sand bags, b operations
to install a sand-filled geotube in
the core of a hardened dune
should provide an orientation and/or a general legislative environmental state of the coastal ecosystem and the
framework for all bodies and institutions involved in the consequences that different measures may have on the
management and development of the coastal zone, offering system.
security to the citizen user of the coastal zone. – Coordination between all parties involved is the basis for
Not many countries have clearly established coastal sustainable development in the coastal zone. The pro-
policies—this is especially true in developing countries, but grams should help to identify concordances and contra-
they are also absent in many developed countries. Three dictions between the actions proposed by the various
examples where coastal policies are already in place can be policies and promote arbitration in the event of conflicts.
highlighted: the USA, the European Union and Australia. – Cooperation between different actors must be organized
Although each of these areas has its own particularities, all and maintained. There must be fluid communication
of the policies studied have three key underlying principles: between the different sectors of economic activity, as well
as between the different levels of territorial administra-
– Appropriate policies can only be based on knowledge. tion. Similarly, a continuous exchange of information is
Decisions must be made on the basis of complete and recommended, from the scientific community to the
comprehensible information on the dynamics of the administrative level and the community level, and vice
geological processes that cause coastal change, the versa. In this way, the programs will establish appropriate

adaptation to the coastal hazards
by planning. a Siting the first line
of promenade and buildings
behind the foredunes, b Elevating
the structure of a building
procedures, working methods and forums to ensure dia-

logue between those involved. This cooperation ulti-
mately leads to the development of a general sense of
responsibility.
30.3.1 USA Policies
The National Coastal Zone Management Program (CZMP)

was introduced in 1972 and is a world pioneer [10]. This is a
federal law that encourages state laws to balance economic
development with environmental protection. The objectives
of the CZMP are as follows:
– Protection of natural and cultural resources.

– Improvement of coastal water quality.
Fig. 30.4 Scheme showing the different interactions of the natural – Protection of people and property against natural coastal
environment, society and economy in influencing decisions on coastal hazards.
policies
30.3 Coastal Policies 451
– Guarantee of public access to marine and coastal areas. protection of Europe’s coasts there is the 2002 EU Recom-
– Prioritization of the development of uses dependent on mendation on Integrated Coastal Zone Management.
the coast. The Marine Strategy Framework Directive (MED) is the
– Revitalization of the promenades. first EU law specifically aimed at protecting the marine
environment and its natural resources. A framework direc-
It is not a binding law. It is a program that states vol- tive means a law at the European level to which the national
untarily adhere to when enacting their own laws. Although it laws of the member states must be adapted on a mandatory
is not mandatory, 34 of the 35 coastal states currently sub- basis within a certain period of time. In this way, the MED is
scribe to it. The administration and coordination between the a European legislative framework for the sustainable use of
coastal management programs of the different states is the marine waters whose objectives are set in accordance with a
responsibility of the National Oceanic and Atmospheric strategy that has a regional focus.
Administration (NOAA)’s Office of Coastal Management. However, for coastal zones there is no framework
This office is tasked with guiding administrations to bring directive, but only a simple recommendation. The 2002
federal consistency to state programs [12]. Standardization ICZM Recommendation defines the principles of good
of state programs requires that they include: coastal planning and management. The objectives of this
document are:
– Delimitation and mapping of the coastal zone.
– Definition of permissible land and water uses within the – To provide information on the factors favoring or disfa-
coastal zone. voring sustainable coastal zone management.
– Inventory of areas of special interest (economic, cultural, – To encourage the exchange of information between
historical and ecological). actors involved in the management and use of Europe’s
– Identification of actors and local authorities. coastal zones. This debate should generate a consensus
– Defining the methods by which the state will regulate on appropriate measures to stimulate ICZM at the Euro-
land and water uses and implement its policies. pean level.
– Description of the institutional arrangements and
authorities through which the program will be imple- The non-binding nature of this document has made it easy
mented (there are five types of institutional arrangements for member countries to continue to fail to adapt their leg-
recognized by the CZMP). islation to what is indicated by this recommendation. Thus,
– Definition of planning processes for the siting of instal- despite its existence, coastal planning activities and urban
lations of community interest. development decisions continue to take place under arbitrary
– Establishment of methods to assess erosion and make criteria and in a non-unified manner for the entire European
decisions on coastal protection and restoration. territory. This leads to inefficient use of coastal resources,
contradictory claims on the use of space, inadequate pro-
tection measures and, ultimately, missed opportunities for
sustainable coastal development.
30.3.2 European Union Policies
Unlike in the USA, there is no single European model of 30.3.3 Australian Policies
coastal management or program that firmly regulates the
coastal policies of member states [2]. The protection of In Australia, there is also no federal legislation or national
coasts and marine waters was initially addressed by legis- strategy governing the coastal policies of the different states
lating on some partial aspects affecting marine and coastal [7]. Of the seven Australian states, only four have coastal
areas. Thus, fisheries were regulated through the Common management legislation (New South Wales, Queensland,
Fisheries Policy (CFP), and coastal water quality control South Australia and Victoria). Of these four, three of them
through the Water Framework Directive (WFD). But these have put legislation in place within the last decade. Only one
laws, although useful for the protection of marine waters, of them is devoting any budget to coastal risk zone mapping.
only contribute to the protection of specific issues without The agencies that are supposed to undertake planning and
having the integrative character that coastal policies require. development by implementing coastal policies went into
With this in mind, the European Union has more recently clear decline from 2003 and were virtually non-functional by
adopted two instruments, one for the protection of marine 2010 [5, 8]. However, all states have developed coastal
areas and the other specifically for coastal areas. For the policies. If there has been coherence between the policies of
protection of the marine environment, the Marine Strategy the different states, it is because the policies were established
Framework Directive came into force in 2008, while for the under the same basic principles. It is only since 2016 that the
Australian government has begun to realize the importance of the Coastal Zone, all within the limits set by natural
of having a strategy for climate change adaptation and dynamics and carrying capacity.” (European [6]).
mitigation of coastal vulnerability. When the term ICZM is analyzed word for word, the
above definition is explicitly reflected [14]. The term man-
agement refers to the ultimate goal of the process. Although
30.3.4 Other Countries it is management, it actually refers to a process involving
research, information gathering, planning and
The previous sections make it clear that the laws regulating policy-making. In this sense, planning is understood as a
coastal policies in the most advanced economic systems strategic development that enables the adoption of appro-
have more shadows than light. Nevertheless, in the last priate policies. Management involves not only
decade, steps have been taken towards a homogenization of decision-making and the establishment of concrete mea-
policies not only in these countries, but also in other nations sures, but also the monitoring of the results obtained with the
outside the West. For example, the Russian Federation has measures taken and the adaptation of new measures to these
had a coastal management program for the fishing industry results. The word integrated refers to the need to link
since 1959 and a law for the protection of coastal areas of multiple sources of information and diverse interests to
ecological interest since 1995. In 2002, it regulated the achieve objectives. In this way, it is necessary to integrate:
protection of wetlands in a coastal zone management scientific and technical information on the marine and inland
framework, and in 2006 it issued a law on the protection of processes found on the coast, the needs of users, the needs of
biodiversity in integrated marine and coastal zone manage- the different economic and social involved sectors, the
ment. These laws are national in scope and enforceable, competences of the different levels of administration
although they are aimed solely at the protection of natural (Fig. 30.5). In this process, the participation of all parties
areas and do not regulate human development in coastal involved (scientists, economic agents, social agents,
areas or mitigation measures. It should be noted that the administrative and political agents) is essential.
Russian Federation has thousands of kilometers of unoccu- It should be noted that, from an administrative point of
pied coastline. view, there is no precise delimitation of the coastal zone.
Another example of Eastern countries with coastal policy Thus, the term coastal zone is not applied in the same sense
legislation is China. China established a marine and coastal as described in Chap. 2 of this book. From a management
management law in 1982 that gave local administrations the point of view, the coastal zone is a band of land as well as
ability to manage their coastal concerns. This law basically sea, and can be defined using different criteria based on the
recognized the inability of the central administration to deal interrelationships between humans and the natural environ-
with local problems on a coastline of more than 20,000 km. ment [1]. These criteria vary depending on geographical
For decades, local authorities have had neither the technical characteristics, dynamic behavior, the influence of human
knowledge, nor the means, nor the money, to meet the activities on the coast or administrative boundaries. In each
challenges of curbing coastal environmental degradation. management unit (countries, states, regions or communities),
Moreover, many local authorities have prioritized economic the seaward limit of the coastal zone may vary from tens of
development over environmental sustainability. However, meters to the outer limit of territorial waters. The same is
the economic development and international openness of the true for the landward boundary, where the coastal zone can
last two decades have allowed for better funding of envi- be understood as just the fringe affected by coastal pro-
ronmental policies and international cooperation. This has cesses, or the band up to several kilometers inland where
been reflected in improved coastal management measures social and economic uses are related to the presence of the
[4]. coast.
30.4 Integrated Coastal Zone Management 30.4.1 The Evolution of ICZM
“Integrated Coastal Zone Management (ICZM) is a The beginnings of coastal occupation are full of cases in
dynamic, continuous and iterative process designed to pro- which constructions and uses were made without any prior
mote sustainable coastal zone management. ICZM seeks, planning. It is only in the last decades that coastal planning
over the long term, to balance the benefits of economic activities have started to be developed in some countries.
development and human uses of the Coastal Zone, the However, even when planning did exist, decisions were
benefits of protecting, preserving and restoring the Coastal taken on a sectoral basis, without an overall strategy and
Zone, the benefits of minimizing loss of human life and with hardly any links between the plans made by different
property, and the benefits of public access to and enjoyment sectors (urban, port, tourism and so on). This lack of a global
30.4 Integrated Coastal Zone Management 453
Fig. 30.5 Process of integration

of components to develop an
adequate coastal zone
management program [3]
vision of planning and management led, during the period of One of the most evolving aspects of the ICZM concept
greatest human development on the coasts, to an inefficient was its focus. While the initial focus was on environmental
use of resources. This meant that human activities came into conservation, later trends have shifted towards economic
clear conflict with the evolution of the natural environment development and solving human conflicts [15].
and the geological processes menacing human constructions.
In response to these threats, humans built coastal defenses
that further altered the dynamic equilibrium of the coast. 30.4.2 Future ICZM
Moreover, human uses began to conflict with each other, and
there were also inconsistent decisions and claims of some In addition to the conflicts already described in the coastal
sectors over others. All this created a problematic framework zone, there are now future challenges such as sea level rise
that meant a period of missed opportunities for sustainable and increased storms related to climate change. Although it
coastal development [14]. is now widely recognized that developing ICZM is the best
Within this framework, the entry into force in 1972 of way for nature and human use to coexist, most ICZM
the US Coastal Zone Management Program (CZMP) was a applications have been carried out at local and regional
milestone, as it was able for the first time to bring together levels. As demonstrated in the section on coastal policies, at
a comprehensive strategy for human uses of the coast the national and supranational levels the legal coverage of
within the framework of knowledge of natural coastal these policies has not been sufficiently developed. Even in
processes. Since the creation of this program, the concept the case of the United States, the program promotes the
of management has been shifting towards increasingly policies but does not enforce them, and therefore does not
integrated approaches, as more and more countries have have the status of law. In the European Union, ICZM is
joined in the establishment of ICZM-compliant strategies. contained in a recommendation and has not even acquired
After 20 years of policy development within an ICZM the status of a framework directive, which would oblige all
framework, this approach was endorsed by the global member countries to develop binding ICZM laws.
community at the United Nations Conference on Envi- It is true that, at the regional level, laws have been
ronment and Development in Rio de Janeiro in 1992. developed to promote ICZM. Also, at the international level,
Since then, further steps have been taken, although most agreements have been signed to develop this management
national or supranational ICZM strategies, even in the system. For example, in 2011 the Protocol on ICZM in the
most advanced countries of the world, do not have the Mediterranean was put in place, as a legally binding agree-
status of law and are merely recommendations. Even so, ment signed by 21 countries located in Europe, Africa and
many specific coastal regions have adopted ICZM strate- the Middle East. This agreement obliges the European Union
gies to develop coastal area development planning. In to elevate the recommendations on ICZM to the level of a
some areas, such as the north coast of the Dominican framework directive. The development of these directives
Republic, they have thus achieved a coexistence of reefs obliges the signatory countries to adopt policies under the
and beaches with industrial and agricultural zones in which ICZM prism. This vision will promote the sustainable
important tourist complexes have been incorporated development of the coast and ensure coherence of coastal
(Fig. 30.6). strategies and policies.
Fig. 30.6 Panoramic view of Puerto Plata (Dominican Republic). A local plan of ICZM was applied to allow the coexistence of the natural
environment with different human uses
In regions where integrated management is in place, there previously occupied zones, or the adaptation of new con-
is a tendency to subsequently carry out sustainability mea- structions (floating buildings or ones raised on pillars). All
surements to check the success of the program. These local factors must be taken into account in each case. It will
measurements are usually complex because they have to take not be easy, but without an adequate ICZM it will be
into account many variables; so, indices have been designed impossible.
to quantify the state of sustainability following the measures
undertaken. The indices provide an overview, albeit sim-
plified, and also allow comparison between different areas References
under integrated management, and are therefore considered a
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Part VI
Final Remarks
The most dedicated research the data,

this info tempo is gatherin momentum.
A thousand rounds of ammo
one of them was spent in Applied science...
“Knock, Knock”
GZA
Future Trends in Coastal Geology
31
development and use of new techniques to improve coastal

31.1 Introduction
knowledge; and (3) contributions to environmental diagno-
sis, showing the effects of some human actions on the coast,
Throughout the chapters of this book, the state of current
mainly focused on planning sustainable coastal manage-
geological knowledge about the coast has been discussed.
ment. These same three lines of study highlight the probable
This knowledge is the result of the last 50 years of research,
trends for the next years, especially in the context of climate
which in turn built on the concepts and principles described
change.
by the pioneers of this science from the end of the nine-
teenth century. The existence of many scientific journals, as
well as publishers dedicated to the dissemination of the-
matic monographs on coastal geology issues, has con-
31.2 Studies on Coastal Dynamics,
tributed to the remarkable increase in detailed knowledge of
Geomorphology and Sedimentology
many coastal systems, both regionally and thematically.
The general guidelines of knowledge on the dynamic func-
But, in addition, the study methodologies that have been
tioning of coastal systems are already firmly established. In
established during these years, and the specific techniques
addition, the main aspects of coastal geomorphology and
that have been developed, have allowed coastal geologists
sedimentology are well studied from a thematic point of
to delve into aspects that could not be observed before.
view. However, much remains to be understood in different
Some of these techniques are among the greatest scientific
ways. Here are the main trends that must be among the
advances today and also herald trends for the immediate
future research to respond to the immediate challenges.
future.
The chapters that make up the last part of this book have
shown us that this science becomes especially vital when
31.2.1 Underground Records and Architectural
applied to human problems on the coast. Although the entire
Studies
book has focused mainly on coastal geology issues, these
chapters show us that coastal study in recent times requires
A large part of the published studies has been centered on
an interdisciplinary approach. Even under this approach,
the surficial distribution of sediment. Studies about sedi-
knowledge of active geological processes plays a key role.
mentary sequences have been mainly focused on some
Likewise, the study of sedimentary sequences of Holocene
specific environments such as barrier islands, but others
coastal environments allows us to observe their evolution
including estuaries have received less attention from this
over thousands of years. This knowledge of evolutionary
perspective. Future geological research must focus more
trends is the key to understanding the fragile equilibrium of
closely on the stratigraphic record, especially regarding the
coastal systems, and the human beings occupying the coasts
three-dimensional architectural disposition of the sedimen-
must be aware of the evolutionary trends of natural systems
tary facies. These further studies could contribute to deter-
in order to achieve sustainable development policies in an
mining geometries of sedimentary bodies (Fig. 31.1) and,
ICZM framework.
superimposing a sediment chronology, could help to
The main contributions of coastal geologists in the last
understand possible slight sea level movements in the last
decades fit into three key lines of research: (1) contributions
5000 years. These studies must also be the basis for better
to the general knowledge of the coasts from a dynamic,
interpretation and understanding of ancient stratigraphic
geomorphological, sedimentological and environmental
coastal sequences by applying the uniformitarian principle.
point of view; (2) contributions about pure methodological

https://doi.org/10.1007/978-3-030-96121-3_31
460 31 Future Trends in Coastal Geology
Fig. 31.1 3D architectural scheme based on linked vibracores and seismic profiles of the central part of a mesotidal wave-dominated estuary
(Odiel Estuary, SW Spain)
31.2.2 Study of Coastal Events 31.2.4 Upscale and Downscale Studies
Coastal events are important energetic and destructive pro- Once the mesoscale dynamics of many coasts have been
cesses that have impacted our coasts in the past, but will also characterized, it is necessary to change the scale in both
menace us in the future. It will be important for future directions. On the one hand, more detailed and specific
guidelines to develop detailed studies about the effects of studies on a microscale would be useful to understand small
each one of the storms and tsunamis that may reach the nuances in processes and sedimentary distribution. In this
coasts in the future. It is also necessary to recognize the sense, detailed sedimentological studies (e.g., facies analy-
records of past events in order to establish event catalogues sis) will contribute to understanding short-term evolutionary
and determine return periods. This integrated knowledge cycles and trends in specific coastal sedimentary environ-
will be the best tool for developing correct predictions and ments. On the other hand, studies carried out in adjacent
minimizing future damage. areas must be connected on a macroscale to understand some
of the problems in a wider context.
31.2.3 Extension of Studies to the Submarine

Areas of the Coast 31.2.5 Basic Studies on the Coasts
of Developing Countries
Until now, geological study has largely focused on the
emerged part of the coastal systems. However, the coast is The main advances in studies on coastal geology have been
an integrated system and to get an adequate knowledge developed in only a couple of dozen countries. So, the coasts
about dynamic processes, and also about geomorphology of the USA, Canada, Western Europe, Russia and Australia
and sedimentology, it is necessary to extend the studies to are the best known from a coastal geology perspective. In
the sub-littoral areas. For this purpose, some of the new addition, the state of knowledge of other developed countries
techniques as described in the following section should be of South America and Asia, including Argentina, Brazil,
adopted. Chile, Japan and South Korea, is also high. However, the
31.2 Studies on Coastal Dynamics, Geomorphology and Sedimentology 461
coasts of the rest of the world’s countries remain practically internal structure of sandy barriers and littoral dunes in the
unstudied. These countries have developed human occupa- land portion of the coast. The combination of facies
tion of the coast without planning and without knowledge descriptions obtained by coring, and the information of the
about their coastal systems, resulting in problems for their geometry of sedimentary bodies obtained by using these
buildings and infrastructure, increasing risk of damage and methods, will contribute to establishing 3D architectural
subsequent conflicts. Increasingly urgently, these countries facies models in many coastal environments (Sect. 31.2.1).
need to develop studies on the geological functioning of
their coastal systems.
31.3.3 Remote Sensing
31.3 Studies on Methodological During the last two decades, the digital treatment of data
Development and Use of New from remote sensing (satellites, airborne sensors and drones)
Techniques has developed in an exponential way. Presently, most of the
coastal evolution that accompanies the dynamic changes of
The development of methodologies emerging from new the world’s coasts is studied through the use of these tech-
technologies has been a revolution for coastal geology. niques. It is foreseeable that the current accelerated techno-
Chapter 6 of this book described the main techniques that are logical development that we are experiencing will lead us to
beginning to be applied to coastal geology studies. These the discovery of increasingly sophisticated and precise
techniques are advancing at a very rapid pace and are remote sensing techniques. At the same time, the use of
expected to be implemented as a priority in the coming analysis software through online platforms will facilitate
years, and will help to widen knowledge of coastal systems. more widespread applications and more generalized use.
31.3.1 Sensors for Process Measurements 31.3.4 Bathymetric and Topographic Methods
During the last years, a new generation of sensors for New acoustic and laser techniques, including side scan sonar
measuring processes has been incorporated in the equipment or multibeam echosounders such as aerial and drone LIDAR,
used by coastal geologists. The best examples of these have allowed high-resolution bathymetric and topographic
include wave gauges, tidal stations, wave radars and Doppler records to be obtained. These records are contributing to
current meters, instruments capable of making continuous elaborate digital terrain models (DTM) that integrate ter-
measurements and recording them in data loggers. These restrial and underwater datasets. The DTM results provide a
devices provide geologists with datasets that will contribute very useful tool in coastal areas to understand certain geo-
to our understanding and ability to quantify a variety of morphological features. The comparison of high-resolution
short-term processes which until now were beyond our DTM of different dates allows us to quantify rates of erosion
capacity to see. The application of these kinds of records and deposition in coastal environments, thus aiding deter-
during subsequent years will allow to recognize the mination of volumes and surfaces (eroded and filled by
long-term trends of many coastal processes. This will be sediments).
especially helpful in the changing framework of Earth’s
climate.
31.3.5 Numerical Models
31.3.2 Geophysical Methods Modeling of hydrodynamic and sedimentary processes is a

new tool which is now being used by geologists to under-
Recent years have seen a growing trend in the use of stand the functioning of coastal systems (Fig. 31.2).
acoustic techniques such as high-resolution seismic profiles Uncalibrated models have proved an excellent method to
to complete the geomorphological and sedimentological identify the cause of past effects, but also to get a prediction
underwater and underground information of coastal systems of future actions on the coast. In the future, the use of these
(Fig. 31.1). These methods have been widely and success- models in coordination with the datasets obtained by using
fully used by marine and petroleum geologists in deeper the previously described measuring techniques will allow
areas. The technical development of cheap, smaller and more accurate calibration of the models. These models will then
versatile equipment will contribute to extending the studied be able to develop reliable predictions which can help
areas to the subtidal areas of the coast. In the same way, coastal managers to take the best decisions and adopt nec-
ground penetration radar is being used to characterize the essary policies.
462 31 Future Trends in Coastal Geology
Fig. 31.2 Vectors and magnitudes of longshore transport obtained from a numerical model (Guadiana Delta front, SW Spain)
integrated in a map of general vulnerability. Normally, the

31.4 Environmental Studies and Integrated mapped element is an index (coastal vulnerability index, or
Coastal Zone Management CVI). The most important part of these maps considers the
degree of exposure to the main coastal hazards; then, they
The beginnings of coastal geology studies were prompted by could be considered maps of risk rather than maps of
the work of coastal engineers, since the first aim of these vulnerability.
studies was to adapt the coast to human requirements. In
fact, the only book entitled Coastal Geology before this one
was written by an engineer from this perspective. When 31.4.2 Conceptual Modeling
geologists began to study the coast, pure science was
focused on the correct understanding of the natural coastal Conceptual models are conceived as a method for visualiz-
system. Now, situated between the scientific aspects studied ing integrated and interpreted data. There are different con-
by coastal geologists are the consequences on coastal ceptual models that could be applied in coastal geology, but
dynamics caused by the structures built by the civil engi- the most interesting for coastal managers are those that
neers. This present state of the subject means a new focus is synthesize processes and sedimentary transport as a response
necessary so that the knowledge can be applied to ICZM. In to modifications in the parameters (natural or human) that
order to develop the best criteria to take decisions, it will be cause the coast to evolve. In this way, conceptual models are
necessary to study the followings areas. a useful way to convey resource information to political
bodies, since such systems of representation can be com-
prehensible to experts and non-experts alike.
31.4.1 Mapping Vulnerability
At this moment, a priority objective of main coastal areas is 31.4.3 Interdisciplinary Studies and Debates
the development of detailed maps of degree of vulnerability
to coastal hazards. These kinds of charts are not only needed After European Union directives such as Horizon 2020 and
for natural environments, but especially for the US programs that have included the CZMP, scientists have
human-occupied coasts. There is not a general agreement tended to adopt a transversal and interdisciplinary vision of
about the aspects, variables and parameters that have to be their studies. Taking into account these new rules, coastal
considered to elaborate a map of vulnerability. Nowadays, geologists are obliged to incorporate the vision of geogra-
social, economic, cultural, biological and dynamic factors phers, oceanographers, biologists, ecologists, archaeologists,
are all recognized as being equally important. Nevertheless, coastal engineers, mathematicians, physicians, geochemists,
the main efforts to map coastal vulnerability are currently economists, social scientists and lawyers in building
focusing on geological hazards. Vulnerability maps for multi-visionary teams capable of analyzing any aspect of the
individual hazards can be done, but they can also be future ICZM.
31.5 Science for Society and Citizen Science 463
31.5 Science for Society and Citizen Science Another effective tool for coastal geology is citizen sci-
entific communication. This concept refers to a broader and
The last challenge that needs to be addressed is to carry the more inclusive way of communicating science, where vol-
knowledge to society at large. Since the entire population is unteers engage in citizen scientific journalism. This is a
and will be affected by coastal processes in the future, system of dissemination in which the data collected, ana-
coastal scientists are strongly encouraged to communicate lyzed by citizens and prepared by scientists are also com-
their discoveries to the public. Therefore, it is no longer municated by the citizen. This process ensures both
enough to write in scientific publications, but communica- reliability and transparency.
tions that a non-technical audience can understand are nee- All these developments of citizen science are especially
ded, as well as reports in webpages and social media. useful in the debate and exchange of information between
The concept of citizen science goes far beyond the professionals, researchers, economic agents, society and
transmission of scientific results to citizens. Citizen science policy makers, when it comes to aspects involved in for-
is scientific research involving non-specialists and involving mulating and enacting ICZM.
them in the work of scientists and technicians. In the most However, citizen science has so far mainly been a process
practical form of citizen science, users are responsible for the whereby people join projects designed and conceived by
collection and/or analysis of data, as well as the process of scientists. Currently, there are forms of citizen science in
dissecting the results by researchers. Citizen science is which the citizen contribution is also incorporated into the
especially useful for coastal geology, as coastal users are project approach. In this way, initiatives such as the European
most frequently present during the action of coastal pro- Platform for Citizen Science (https://eu-citizen.science/)
cesses, which can be measured and photographed by them. provide an open forum for the exchange of knowledge, tools,
In this sense, a widespread use of new technologies, such as training and resources for citizen scientists. The objective of
simple applications installed on smartphones, will contribute this space is not so much for citizens to participate in sci-
to a broader participation of citizens in scientific data col- entific data collection, but, beyond that, it transforms the way
lection. Thus, citizens can actively contribute to the devel- citizen science projects are conceived and developed.
opment of science, sharing their knowledge and their own
tools and resources to increase experimental data volume.
The participants, while adding value to science, acquire local 31.6 Concluding Remark
and thematic knowledge framed in an improvement of their
vision of the scientific methodology. This way of working is Ultimately, coastal geologists have to focus on the future by
very valuable, especially when it comes to an issue as linked addressing challenges that will become increasingly difficult,
to the development of their lives as coastal geology. In short, especially in the context of a post-pandemic economic crisis
citizen science applied to coastal geology is an effective way that considerably limits investment in research. However, we
of promoting scientific education and environmental edu- will address this task with our best weapons: effort and
cation, while generating useful knowledge that can be passion.
applied by local managers.

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Juan A.

More information about this series at https://link.springer.com/bookseries/15201

ISSN 2510-1307 ISSN 2510-1315 (electronic)

Part I Geological Approaches to the Coast

2.5.3 Storm and Tsunami Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

6.2.3 Instruments for Measuring Tidal and Ocean Currents . . . . . . .... 56

Part II Coastal Processes

8.5 Tidal Currents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

12.4 Bioclastic Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

Part III Coastal Systems: Dynamics, Facies and Sedimentary Models

15.3 Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191

17.4.3 Dynamics of Longitudinal Bars . . . . . . . . . . . . . . . . . . . . . . . . . 238

19.4.3 Flood-Tidal Deltas . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280

21.5 Depositional Facies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 320

23.3 General Morphology, Associated Environments and Forms . . . . . . . . . . . . 358

Part IV Coastal Evolution on a Geological Time Frame

25.6 Preservation Potential of Coastal Sequences Under Sea Level

Part V The Humans in the Coast: Interaction Problems and Coastal

29.3 High-Energy Coastal Events . . . . . . . ................... . . . . . . . . 442

Part VI Final Remarks

Coast through it all

the erosional features that appear on the already deposited

© Springer Nature Switzerland AG 2022 3

Fig. 1.1 Erosional coast: cliffs

Fig. 1.2 Depositional coast:

Fig. 1.3 Illustration of an

Fig. 1.4 Chart of Otaheite, 1769,

Fig. 1.5 Houses built on the

air interact.” This deﬁnition is intentionally broad, since, as

Although the coast is normally deﬁned in two dimensions as

© Springer Nature Switzerland AG 2022 13

Fig. 2.1 Graphic deﬁnition of

2.2 A Datum Issue

Fig. 2.2 Statistical levels

Table 2.1 Hydrographical Hydrographical datum Countries

Fig. 2.3 a Location of tidal

Fig. 2.4 Vertical relationships

2.3 Coastal Framework 2.3.2 Consolidated Versus Unconsolidated

coastal areas. That is the cause of the presence along the

2.4.4 Recreational Use

Some of the problems described above are the product of the

Subsidence is a slow sinking of coastal lands due to multiple

2.5.7 Changes in Ecological Structure

The uncontrolled exploitation of many coastal ecosystems or

changes at short time intervals are not reflected in that

© Springer Nature Switzerland AG 2022 25

previous paragraph. The sediment supply by rivers repre-

1. Berger A, Loutre MF, Laskar J (1992) Stability of the astronomical

4.1 Introduction 4.2 Coastal Landforms

© Springer Nature Switzerland AG 2022 31

Fig. 4.1 Main coastal landforms.

Fig. 4.2 a Main coastal forms

Fig. 4.3 Some depositional

Fig. 4.4 Some depositional

Washover fans Lagoons

Fig. 4.5 Main clastic coastal

Swamps and marshes 4.4.1 Genesis Under Relative Sea Level

4.4 Classifications of the Coast 4.4.2 Origin of Processes