River Deltas

Ostia is one of the most extensively excavated cities of the Roman period. The port-city of Rome, which today lies 4km from the coastline, was established in a very constrained environment at the mouth of the River Tiber. Based on a review of the geoarchaeological and archaeological research at Ostia, 4 new cores analysed through palaeoenvionmental methods, and 21 new radiocarbon dates, we propose a new model of the fluvio-coastal landscape of Ostia from its origin: (1) the coastline shifted rapidly westward between the 8th and the 6th c. BCE followed by a slow progradation and possible erosion phases until the end of the 1st c. CE; (2) the castrum of Ostia (c. late 4th–early 3rd c. BCE) was founded away from the river mouth but close to the River Tiber; (3) between the 4th and the 1st c. BCE, the River Tiber shifted from a position next to the castrum, below the northern Imperial cardo of Ostia, to 150m to the north; (4) a possible harbour was established to the north of the castrum during the Republican period; (5) the city expanded and a district was built over the harbour and the palaeochannel between the Republican period and the beginning of the 2nd c. CE, showing that Ostia was a dynamic and resilient city during that time. Finally, we suggest the possibility to combine urban fabric analysis (the orientation of the structures) and palaeoenvironmental analysis for reconstructing the evolution of the city in relation to the fluvio-coastal mobility.

This study examines the long-term interactions between the well-known Roman city of Ostia and a river meander. Located at the mouth of the Tiber river, Ostia was a major harbor city that connected Rome to the Mediterranean Sea. Based on aerial photography and borehole analysis, the paleodynamics of the Fiume Morto's paleomeander are understood to be linked to the urban evolution of the city of Ostia. Four periods of evolution have been identified as a result of this interdisciplinary work: (1) the foundation of Ostia's urban center, in the 4th to 3rd century BC, occurred when the meander already existed; (2) between the 4th century BC and the 3rd century AD, human/environmental interactions contributed to the compound growth of the meander that possibly eroded an important Roman road linking Ostia to Rome; (3) from the Imperial period until the meander was cut off in AD 1557–1562, the constricted meander channel at the apex led to the stability of the downstream river channel; (4) the cutoff of the paleomeander was completed in 1562, leading to the filling of the paleochannel. These successive phases of channel evolution mark changing fluvial risks from the Roman period to today.

Deltaic processes of the Mississippi River Delta have been severely limited by artificial river levees, which prevent overbank flows during Spring floods. To counteract the effects of severing the connection between the river and the delta, focus has been placed on reconnecting the river to the delta by the creation of artificial outlets or diversions. The Caernarvon Freshwater Diversion and the Bohemia Spillway are two legacy diversions located on the east bank of the Mississippi River south of New Orleans.
The Caernarvon Freshwater Diversion was designed to deliver up to 8000 cfs from the Mississippi River. The sediment load in the diverted water is carried into the Caernarvon Diversion outfall area known as the Big Mar Pond. Turbidity measurements were taken from December 2009 through 2012 and used to calculate the total suspended solids (sediment load) delivered to the receiving basin. In total, approximately 264,000 yd3 of sediment was delivered to the receiving basin. Often, the diversion is not operated when sediment spikes are present and therefore does not maximize potential sediment capture. Despite this variability in operation of the diversion, and the fact that the Caernarvon Diversion was built to minimize sediment capture, there has been enough accumulation in some areas to permanently support emergent wetland plant life on a new sub-delta. Total wetland growth of the sub-delta in Big Mar Pond from 1998 to 2011 was 600 ac. Of this total, 581 ac were new growth since 2004. This pattern is similar to that documented for other larger diverted flows, such as the Wax Lake Delta, where there is an initial delay in wetland growth as mineral soil platforms vertically accrete to a threshold on which emergent vegetation can survive.
Bohemia Spillway was created in 1926 by the removal of existing artificial river levees, thereby allowing unencumbered flow across the river's natural levee during high river stages. In 2011, the Mississippi River watershed experienced an historic flood similar to the 1927 flood which provided an ideal opportunity to investigate and study the hydrology of the Spillway. Field surveys were conducted to measure the magnitude of the overbank flow into the Spillway and a Mississippi River flow survey was conducted using Acoustic Doppler Current Profiler (ADCP) measurements. These surveys indicate that the Spillway passed 30,000 to 50,000 cfs at peak flow. Current land loss rates in the Bohemia Spillway are negligible, perhaps due to receiving inputs of freshwater, nutrients, and sediment during high river events.
It is instructive to compare the natural processes of overbank flow, sediment delivery, and deltaic land building of the two river outlets, although neither of the outlets was built for these purposes. The first three decades of discharge through the Bohemia Spillway were higher than the long-term average, and probably had greater sediment concentrations than the post-1950 sediment load, which was reduced by dams located upriver. The landscape response for the Bohemia Spillway and the Caernarvon Diversion has similarities and differences. The Bohemia Spillway has not built a delta, but it has infilled some canals, and more importantly, has prevented the pattern of indirect wetland loss due to canals, or "interior" wetland loss due to relative sea level rise or other more regional processes. In spite of the delta development, the Caernarvon Diversion area has regionally lost wetlands since its operation began with large wetland losses occurring during Hurricane Katrina. Overall, the Bohemia Spillway wetlands are more resilient.
The history of the Bohemia Spillway does suggest sustainability may be achieved by high discharges and high sediment concentrations early in the life history of the outlet followed by years of lower discharge as the diversion becomes a tool for wetland maintenance rather than wetland building. The need for the later phase of maintenance can be also inferred from the Caernarvon Diversion pre-history. Because the Mississippi River levee was intentionally breached at Caernarvon during the 1927 flood a large sediment pulse was deposited, followed by a 65-yr hiatus in regular sediment input before the Caernarvon Diversion became operational. This hiatus undoubtedly contributed to subsequent regional land loss during Hurricane Katrina in 2005. For both Bohemia Spillway and the Caernarvon Diversion, there are clearly some benefits in reconnecting the river to the marsh.

The ancient lagoon of Ostia played a key role in the development of the cultures of central Italy and
especially that of Rome. The evolution of its environmental history and its partial transformation into a
saline body of water during Antiquity remain as poorly known to archaeologists and historians as to
geologists and geographers. A high chronostratigraphical resolution palaeoenvironmental study has been
carried out on a sediment core. It is based on multi-proxy analysis and pays particular attention to ostracods,
which are very useful palaeoenvironmental indicators in marginal marine environments. Our
study has unveiled five evolution phases of the landscapes in the countryside of Ostia: (1) between the
6th and the middle of the 2nd millennia BC a lagoon open to the sea was formed; (2) the lagoonwas then
subject to marine and fluvial influences,; (3) between the middle of the 2nd and the beginning of the 1st
millennia BC, a marshland formed, indicating either a period of limited flooding or a shifting of the
branch of the Tiber; (4) during the first part of the 1st millennium BC, the lagoon became again connected
to the sea. In this area, its depth at the time of the founding of Ostia varied between 3.5 m and
4.5 m (below ancient sea level), which suggests that it could have served as a naturally sheltered place on
the coast; (5) from the middle of the 1st millennia BC to the 19th century AD, the lagoon probably
remained connected to the sea and progressively silted, until it disappeared in the 19th century.

Flowing through Mongolia and Russia, the Selenga River is the main tributary to Lake Baikal, the world’s largest and deepest freshwater lake. The massive wetlands of the Selenga River Delta (SRD) on Lake Baikal perform important functions, including maintaining local and regional biodiversity and improving water quality. However, there exists a paucity of habitat and relevant ecological data for monitoring system-level changes. In this study, we characterized the rich habitat heterogeneity of the SRD using advanced 8-band multispectral satellite imagery coupled with a vegetation association algorithm and relatively extensive field surveys to analyze the spatial pattern of the system at multiple scales, from habitatspecific (e.g., Dense Floating Vascular habitats [Nymphoides sp.]) to coarser scales (e.g., Emergent Herbaceous; Aquatic Bed; Unconsolidated Bottom). We achieved an overall classification accuracy of 86.5 %for 22 wetland and aquatic habitat classes at the finest scale and greater than 91 % accuracy for broad vegetation and aquatic classes at more generalized scales. Our study provides the first detailed multi-scale characterization of the SRD for the conservation and management of the system and establishes baseline information for future change detection analyses.

In deltaic areas, riverine and coastal waters interact; hence, these highly dynamic environments are particularly sensitive to climate change. This adds to existing anthropogenic pressures from irrigated agriculture, industrial infrastructure, urbanization , and touristic activities. The paper investigates the estimated future variations in the dynamics of surface and coastal water resources at a Mediterranean deltaic environment for the twenty-first century. Therefore, an Integrated Deltaic Risk Index (IDRI) is proposed as a vulnerability assessment tool to identify climate change impact (CCI) on the study area. For this purpose, three regional climate models (RCM) are used with representative concentration pathways (RCPs) 4.5 and 8.5 for short-term (2021-2050) and long-term (2071-2100) future periods. Extensive numerical modeling of river hydrology, storm surges, coastal inundation, water scarcity, and heat stress on irrigated agriculture is combined with available atmospheric data to estimate CCI on the Nestos river delta (Greece). The IDRI integrates modeling results about (i) freshwater availability covering agricultural demands for three water consumption scenarios, i.e., a reference (REF), a climate change (CC), and an extended irrigation (EXT) scenario, combining river discharges and hydropower dam operation; (ii) inundated coastal areas due to storm surges; and (iii) heat stress on cultivated crops. Sustainable practices on irrigated agriculture and established river basin management plans are also considered for the water demands under combinatory scenarios. The differentiations of model outputs driven by various RCM/RCP combinations are investigated. Increased deltaic vulnerability is found under the RCP8.5 scenario especially for the long-term future period. The projected IDRI demonstrates the need for integrated water resources management when compared with risk indexing of individual water processes in the study area.

Although remote sensing technology has long been used in wetland inventory and monitoring, the accuracy and detail level of wetland maps derived with moderate resolution imagery and traditional techniques have been limited and often unsatisfactory. We explored and evaluated the utility of a newly launched high-resolution, eight-band satellite system (Worldview-2; WV2) for identifying and classifying freshwater deltaic wetland vegetation and aquatic habitats in the Selenga River Delta of Lake Baikal, Russia, using a hybrid approach and a novel application of Indicator Species Analysis (ISA). We achieved an overall classification accuracy of 86.5% (Kappa coefficient: 0.85) for 22 classes of aquatic and wetland habitats and found that additional metrics, such as the Normalized Difference Vegetation Index and image texture, were valuable for improving the overall classification accuracy and particularly for discriminating among certain habitat classes. Our analysis demonstrated that including WV2’s four spectral bands from parts of the spectrum less commonly used in remote sensing analyses, along with the more traditional bandwidths, contributed to the increase in the overall classification accuracy by ~4% overall, but with considerable increases in our ability to discriminate certain communities. The coastal band improved differentiating open water and aquatic (i.e., vegetated) habitats, and the yellow, red-edge, and near-infrared 2 bands improved discrimination among different vegetated aquatic and terrestrial habitats. The use of ISA provided statistical rigor in developing associations between spectral classes and field-based data. Our analyses demonstrated the utility of a hybrid approach and the benefit of additional bands and metrics in providing the first spatially explicit mapping of a large and heterogeneous wetland system.