Water Management - Conservation, Harvesting and Artificial Recharge PDF
Water Management - Conservation, Harvesting and Artificial Recharge PDF
Water Management - Conservation, Harvesting and Artificial Recharge PDF
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Copyright © 2008, New Age International (P) Ltd., Publishers
Published by New Age International (P) Ltd., Publishers
Increase in population and change in lifestyle has created water scarcity in many parts of the
world. Microstructures for rain water harvesting, artificial recharge and reuse of water are
becoming more and more popular to solve the local water problems, to mitigate water shortage
and improve water quality. In this book, it is attempted to fill the big gap between monitoring
and performance of actual constructed structures and theoretical design in the literature. The
three main structures for artificial recharge of groundwater viz. check dam, percolation tank
and aquifer storage recovery well, are evaluated in this book. Topics related to reuse of water
and artificial rain are also discussed in length which will be necessary in the coming period.
India has a very long coastal area, so sea water intrusion and preventive structures are very
important. This topic is also included in this book. Both the rationalized and empirical approaches
found valuable have been discussed. Many Case Studies will help the field workers to adopt
optimum design of micro-structures.
For the last several years, the authors have been associated actively with research and
teaching of the subject at the undergraduate and postgraduate level. So this book will be very
much useful for the students of water management subject at the undergraduate and
postgraduate level. It will be also very much useful to the practising engineers, farmers and
policy makers.
The authors express their sincere thanks to V. P. Parekh and Manmohan Singh for their
kind help. Thanks are also due to Mrs. Prafulla Patel and Mrs. Chetna Shah who provided
continuous encouragement for this project from its inception. Special thanks are due to
Mr. Saurabh Patel for his help in composing the manuscript.
Authors
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M. S. Patel
S ecreta ry (K )
F OREWORD
On most of the river of the world, big dams are constructed. Very few sites are left for
constructing big water storage structures. Irregular rainfall, limited rainy days has created
flood and drought situation. Microstructure becomes more and more popular to solve the local
problems, to mitigate the flood and to fight against draught. Increase population and change in
life style have increase water demand. In this situation study, analysis and design of water
conservation, rainwater harvesting, reuse of water, and artificial recharge of ground water
with the demand of time.
Groundwater being a handy resource exploited heavily and due to this reason day by day
groundwater table depleted and deterioration of groundwater quality is noticed in many parts
of the world. Existing scarcity and water quality problems experienced practically all over the
world make water harvesting a critical issue for sustainable development. India has a rich
repertoire of traditional techniques for water harvesting and it is appropriate that these practices
be evaluated and can be adopted through out the world wherever required. Many case studies
given in this book will help readers and policy-makers to select specific optimum techniques.
Water Management - harvesting, conservation and artificial recharge by Dr. A.S. Patel and
Dr. D. L. Shah is indeed a worthy contribution to the field of water management, in general
and to the education of in this field in particular. Several features make this book remarkable
among others concerned with this topic.
This book consist of various chapters such as hydrological cycle groundwater occurrence,
water losses and its prevention, water conservation, rainwater harvesting, artificial recharge
methods, their analysis and design. Many case studies of artificial recharge and rainwater
harvesting are included in this book. Some of the case studies are fully analyzed to adopt such
methods in similar situation throughout the world. Sea water intrusion is a common
phenomenon on the coastal belt. So, a special chapter on this topic describes causes, concept,
phenomenon, analysis, monitoring and structures needed for its prevention. Reuse of water
will be required at the large extent in the coming days. So, concept of reuse of water, categories
of waste water, technological innovations in the field, its reuse in different field, and case
viii Energy
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studies. The world becomes very small. Most of the countries export and import some
commodities. To produce their commodity, water consumed in the virtual water net export or
import of water (in kinds of commodity) will create a water problem. From this point of view
a concept of virtual water is also included. This chapter will guide the policy makers and
farmers to prepare water footprint of the country and the change in agriculture cropping
pattern depending upon the meteorological condition of the country. Artificial rain, reverse
osmosis, moisture harvesting from the air in desert area and desalination is also included in
this book.
On the whole, the book is well written, self contained and several aspects a unique
contribution to the field of Water Management in general and water harvesting, conservation
and artificial recharge in particular. I fully intend to recommend it to students, researchers,
and consultants.
(M.S. Patel)
Secretary (K)
ix Energy Management Contents ix
C ONTENTS
Foreword (v)
Preface (vii)
1. INTRODUCTION 1
1.1 Overview 1
1.2 Increasing Resource Demand 2
1.3 Floods and Droughts 4
1.4 Water Quality Management 6
1.5 Fresh Water Management 7
1.6 Wastewater Management 8
1.7 Recycling and Reuse of Water 8
1.8 Need for Technology Development 9
1.9 Water Conservation 10
1.10 Need of Ensuring Quality & Cost-effectiveness of Water Harvesting 12
1.11 Development of International River Basins 12
2. HYDROLOGICAL CYCLE 15
2.1 Introduction 15
2.2 Atmospheric Water 18
2.3 Precipitation 19
2.4 Surface Water 19
2.5 Infiltration 20
2.6 Groundwater 20
2.7 Evapo-transpiration 22
2.8 Recharge 23
3. GROUNDWATER OCCURRENCE 25
3.1 Introduction 25
3.2 Groundwater Occurrence 25
3.3 Source of Groundwater 26
3.4 Factors Controlling Groundwater 27
3.5 Water Bearing Properties of Soils and Rocks 27
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tremendous stress due to growing population, rapid urbanization, increase in per capita
consumption, industrial growth and other demands for maintaining ecology. It is to be stressed
that nondevelopment of water storage projects is not a viable or available option in India, due
to the large temporal variations in the river flows in Indian monsoonic climate. Tremendous
progress has been made in the field of water resources development and management and
consequent boost in agricultural production leading to self-reliance, rapid industrialization
and economic growth. In spite of that, a large portion of population still lives in sub-standard
conditions, devoid of even minimum civic amenities. Vast area under agriculture still depends
on the mercy of monsoon. The pressures on our water and land resources are continuously
increasing with rise in population and urbanization. All this demands sustainable development
and efficient management of available water resources.
1 40 0
1 20 0
P op ulation o f India (In M illion s)
1 00 0
8 00
6 00
4 00
2 00
0
1 90 1 1 91 1 1 92 1 1 93 1 1 94 1 1 95 1 1 96 1 1 97 1 1 98 1 1 99 1 2 00 1 2 01 1
Y e ars
been an additional pressure on agriculture resulting in an increase in net sown area from 119
million hectares in 1951 to 142 million hectares in 1997; high cropping intensity has also resulted
in an increased demand for water resources. Domestic water need in the urban areas has also
grown notably with the current urban population at 4.5 times the population level in 1950s
(UNEP 1998). The water requirement of the manufacturing sector has increased in proportion
to the increase in the sector’s share in GDP from about 12% in 1950s to 20% in 1990s. By the
year 2050, the population is expected to reach around 160 crores, the per capita availability will
drastically reduced and our country shall be water stressed in many river basins. In planning
critical resources like water we need to plan on safer side. A close watch on an increase in
population is essential. The following Table 1.1 shows probable water availability against year.
Further, there is substantial variance in the different user sectors—agriculture, domestic
and industry, vis-à-vis their share of water demand, resource pricing structure and usage
efficiencies, which creates inter-sector competitions and conflicts. The agriculture sector, for
instance, accounts for about 95% of the total water demand with the subsidized and free
3 Energy Management Introduction 3
1850 10,000
1950 5,177
2000 1,820
regime of supply of power and water resulting in the over-exploitation and inefficient usage of
water. The high resource cost for industries, on the other hand, cross-subsidizes the water
consumed by the other sectors.
The demand for fresh water has been identified, as the quantity of water required to be
supplied for specific use and includes consumptive as well as necessary non-consumptive water
requirements for the user sector. The total water withdrawal/utilization for all uses in 1990
was about 518 BCM or 609m3/capita/year. Estimates for total national level water requirements,
through an iterative and building block approach, have been made for the year 2010, 2025,
and 2050 (Table 1.2) based on a 4.5% growth in expenditure and median variant population
projections of the United Nations. The country’s total water requirement by the year 2050
will become 1,422 BCM, which will be much in excess of the total utilizable average water
resources of 1,086 BCM. At the national level, it would be a very difficult task to increase the
availability of water for use from the 1990 level of approximately 520 BCM to the desired level
of 1,422 BCM by the year 2050 as most of the underdeveloped utilizable water resources are
concentrated in a few river basins such as the Brahmaputra, Ganga, Godavari, and Mahanadi.
Table 1.2 Water requirements for different uses (in BCM)
Flood problem in the Ganges area in Bangladesh is mainly due to over bank spilling. The
flood situation deteriorates when Brahmaputra remains in spate forcing backwater into the
Ganges. The water in the Ganges begins to rise in May and period of maximum flood is in July
and August. Occasionally September could be a month of severe flooding.
Flooding in the Brahmaputra is characterized by large-scale inundation of its banks, erosion
at various places, and conveyance of heavy silt load from upstream. In Bangladesh, the area
prone to flooding is 6.14 million ha which 42 per cent of total area of the country. The loss
caused by floods in a normal year is about US $ 175 million. In extreme situation, it may
exceed US $ 1 billion.
River basin development is a tool for social development. It supports economic growth and
improves living conditions and the quality of life. The Ganges, the Brahmaputra and the Meghna
are international rivers with its basin areas spread over China, Nepal, Bhutan, India and
Bangladesh. Its peculiar geographical location has given the rivers ample water resources; but
today no coordinated attempt has been made to utilize these. Piecemeal attempts for development
in individual countries have not been effective in solving the problems of flooding.
Presently each country has its own plans and programs for developments, including flood
control. But recent flood and other natural disasters have shown that such individual efforts
are not enough within the country.
The need for holistic development and management of the river basins are needed to
overcome the adverse effects of floods and maximize crop production with judicious use of water.
The construction of high dams in Nepal, Bhutan and India will generate not only cheap
hydropower needed for overall development but also augment the dry season flows and
mitigation of floods all the countries for the benefit of the people.
flood plains is enormous. The after effects of floods like the agony of survivors, spread of
epidemics, non-availability of essential commodities and medicines and loss of their dwellings
make floods most feared natural disaster being faced by human kind. Large-scale damages to
forests, crops & precious plants and deaths of aquatic and wildlife, migratory and native birds
in various National Parks, Delta region, low altitude hilly areas and alluvial flood plains have
always been the matter of serious concern. River Valley Projects moderate the magnitudes as
well as frequencies of floods.
Floods and drought management, therefore, form an important part of overall water resources
development and management. Water of potable quality is essential for sustenance of life.
Besides, water is required for other domestic use and for livestock. This requirement of
water though not very large, has to be met at a huge cost due to strict quality parameters and long
conveyance. Norms of water supply in Indian cities are more than in some of the developed
countries of Europe. Users need to realize value of treated water and should inculcate habit of
conservation. The existing system should be maintained and leakage prevented to the extent
possible. Lavish consumers should be charged heavily and pricing of water should be used as a
tool for demand management. Low cost technique for recycling and reuse of grey water (Bath
room and kitchen wash) and black water (Sewerage) should be developed and encouraged.
Water requirement for industries, at present is not significant. However, with continuous
urbanization and industrialization, the demand for water for industries will increase significantly.
Further practically all industries generate some waste. As of now, the performance of affluent
treatment system in the industries is far from satisfactory and this effluent is polluting our water
bodies. The industries have to stick to the norms to treat their waste accordingly. In the process
part of their demands can be met by the industries themselves with suitable treatment and
recycling. Industries generating hazardous waste may have to be located in area having suitable
sites for waste disposal, as the present practice being adopted are very detrimental to the overall
environment. Water requirements of the country would continue to grow partly due to the rise
in population and partly as a result of the improvement in the quality of life. As the developmental
efforts to meet the water requirements take shape, simultaneously the environmental issues gain
importance. Although, less evident than the more obvious quantity related problems, these are
critically important and need to be addressed to ensure sustainable development which is a
formidable challenge, but one which can be accepted and negotiated successfully.
eco-systems. Effective environmental laws to check water pollution need to be enforced with
greater vigour. The rivers and water bodies should no be used as a source for water supplies as
well as convenient sink for wastewater discharges. The rapid urbanization, industrialization
and increasing use of chemical fertilizers and pesticides etc. have made our rivers and water
bodies highly polluted. Different organizations like Central Pollution Control Board, Central
Water Commission, and Central Groundwater Board are involved in water quality monitoring.
Water quality Assessment Authority (WQAA) has been set up recently to effectively coordinate
and improve the work of water quality monitoring by various organizations. As of now there
is no established method to assess requirements of minimum flow in the rivers. Perhaps, 50 per
cent of lean period flow before the structure is built over and above the committed use may be
passed on downstream of all existing and new structures.
consumption and effluent discharge patterns for industries would help to benchmark
resource consumption and increase the productivity levels per unit of water consumed.
• The availability of utilizable water resources, demand levels and consumption patterns
needs to be analyzed for different basins. Such an analysis would help in developing a
Water Zoning Atlas to guide decisions related to the sitting of industries and other
economic activities.
discarded from a process requiring higher purity to a process requiring lower purity. If required,
a simple treatment process may be interposed between the processes. Water reuse is more
economical if included at the design stage by modification of the existing system. In most of the
inland towns, in arid and semiarid areas, where suitable lands are generally available in the
nearby areas for development of irrigation, treated effluent can economically be used for
industrial effluents are used for irrigation. The water recovered from effluents is mainly used
for less important uses like gardening and cleaning. It is necessary to improve the production
technology, and low or no waste technology needs to be adopted. Though, such technologies
may be costly at the initial stage, it would prove economical in the long run. The municipal
wastewater and industrial effluent are being treated up to tertiary level and used for various
purposes other than drinking by various industries and cities. For example, in Chennai the
Chennai Metro Board is providing 30 mld treated municipal wastewater to Ennore Thermal
Power Plant for recycle and reuse for cooling and other purposes. Likewise in Bombay, many
of the industrial houses are using the recycled industrial effluent for purposes such as
airconditioning, cooling etc. In Pondicherry Ashram, the wastewater from housing complexes
and community’s toilets are recycled and reused for horticulture purposes and irrigation. State
Governments may create Urban Development Fund for Urban Infrastructure development
and the same can also be used for setting up of pilot projects for waste reuse, recycling and
resource recovery.
per unit of water and land. Following measure may also be considered for adoption through
intensified efforts of academicians and field technologists.
Deficit Irrigation is the scheduling method applied under a restricted water supply, when
irrigation does not fully meet the evapo-transpiration requirements of the crop and where
certain stress conditions are allowed. The specific objective is to optimize yields and incomes
by allowing water to the most sensitive crop stages and for valuable crops. Strategies for deficit
irrigation may include allocation of less water to the most drought tolerant crops, irrigation
during critical growth stages of crops, planting crops so as to stagger the critical demand periods
and planting for an average or wetter than average weather year. In drought prone areas,
deficit irrigation, rather than full irrigation, can be planned as a norm, in order to distribute
the benefit of drought proofing over a larger area.
Agriculture is at threshold of commercialization. There is need to shift focus from routine
food grains production systems to newer cropping system to meet the ever-increasing demand
of pulses, oilseeds, fodder, fibre, fuel, spices, vegetables, medicinal and other commercial crops
and make agriculture an attractive and profitable business. This has become more important
today in the light of national policy of economic liberalization and export orientation of
agriculture. Crop diversification methods like crop rotation, mixed cropping and double cropping
have been found successful in many situations. Major advantages of these types of diversification
includes reduced erosion, improved soil fertility, increased yield, reduction in need for nitrogen
fertilizer in the case of legumes, and reduced risk of crop failure. Diversity of crop varieties can
enhance the stability of yield and result in water saving. Thus, generic diversity and location
specific varieties are essential for achieving sustainable production.
Raw wastewater has been in use for crops and fish production in several countries including
India without the approval of the competent authorities. Providing financial assistance and
technical guidance in improving existing practices, not only to minimize health risks but also
to increase productivity is preferable to outright prohibition. Generally, the upgrading of existing
schemes may take precedence over the development of new projects. Treatment of wastewater
in stabilization ponds in an effective and low-cost method of pathogen removal, and is, therefore,
suitable for schemes for wastewater reuse, particularly for irrigation of crops. Similarly, duckweed
ponds are quite effective in treating municipal wastewater and at the same time the harvested
duckweed is a good fish and chicken feed. As such, there is a need to develop appropriate and
cost-effective technologies, for treatment and reuse of municipal wastewater, suitable to Urban
Local Bodies for their adoption. Possible health risks to agricultural workers should, however,
be assessed thoroughly and monitored regularly. The treated wastewater should conform to
the pollution control standards where such reuse practice is adopted.
surface runoff if harvested over a large area can yield considerable amount of water for storage
and providing life saving irrigation to the crop during the dry spells in the monsoon season and
also for growing a second crop in rabi season. The major constraints that still limit the adoption
of this technology on a macro scale are, the high initial cost, and non-availability of cheap and
defective sealants for permeable Alfisols. Additionally, long breaks in the monsoon and low
intensity rains limit the runoff flow into the ponds during dry spells when water is needed
most. Despite these difficulties, small water storage ponds seem to be the most viable strategy
to stabilize productivity of the ecologically disadvantaged dry land regions. The surface runoff
from an area can also be increased by reducing the infiltration capacity of the soil through
vegetation management, cleaning, sloping surface vegetation and reducing soil permeability by
application of chemicals. To maximize profitability from the limited quantity of water stored in
small ponds, planning for its judicious use is most crucial. Research conducted at different
locations in India established that a supplemental irrigation of 5 – 10 cm at the critical stage of
crop growth substantially increases the yields of cotton, wheat, sorghum, tobacco, pearl, millet,
etc vis-à-vis no irrigation.
Therefore one has to conserve the surface runoff by different techniques, for use in fair weather.
These techniques are:
(a) Conservation by surface storage — Storage of water by construction of various water
resources projects has been one of the oldest measures of water conservation. The
scope of storage depends on region to region depending on water availability and
topographic condition. The environmental impact of such storage also needs to be
examined for developing environment friendly strategies.
(b) Conservation of rainwater — Rainwater has been conserved and used for agriculture in
several parts of our country since ancient time. The infrequent rain if harvested over a
large area can yield considerable amount of water. The example of such harvesting
techniques involves water and moisture control at a very simple level. It often consists of
rows of rocks placed along the contour of steps. Contour terraces have been found in
use in various parts of the world. Runoff captured by these barriers also allows for
retention of soil, thereby serving as erosion control measures on gentle slopes. This
technique is especially suitable for areas having rainfall of considerable intensity, spread
over large part i.e., in Himalayan area, North – East states, and Andaman and Nicobar
Island. In areas where rainfall is scanty and for a short duration, it is worth attempting
this technique, which will induce surface runoff, which can be stored.
(c) Groundwater conservation — As highlighted earlier, out of total 400 mham
precipitation occurs in India, about 45 mham percolates as a groundwater flow. It may
not be possible to tap the entire groundwater resources. The entire groundwater cannot
be harvested. As we have limited groundwater available, it is very important that we
use it economically and judiciously and conserve it to maximum possible. Some of the
techniques of groundwater management and conservation are as below:
(i) Artificial recharge — In water scarce areas, where there is a low and erratic rainfall,
there is an increased dependence on groundwater. There are various techniques
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214
There are 44 countries where at least 80 percentage of total area falls within an International
River Basins of which 7 are in Asia. In the South Asian sub-continent, there are three as
shown below:
During the past decades, conflicts have emerged over the development and management of
the shared water of International Rivers in many parts of the World. The conflict between
Bangladesh and India on the Ganges is one of them.
With increasing population and need for further economic development, the pressure on
scarce water resources will be more in the future. There is, therefore, an urgent need to identify
the existing and emerging conflicts in the basins and discuss, and resolve the issues in a spirit
of cooperation for overall development and management of the river basins.
essential for developing together for self-reliance and ecologically sustainable development for
a better future.
With increasing population and demand for food and growing concern for environmental
degradation demand for water will increase resulting in conflicts among nations sharing
international river basins.
The Ganges: The Ganges covers an area of about 1,087,300 sq. km. spread over India (860,000
sq. km.), Nepal (147,480 sq. km.), China (33,520 sq. km.) and Bangladesh (46,300 sq. km.).
The length of the main river is about 2550 km. Three major tributaries of the Ganges, the
Karnali, the Gandaki and the Kosi rise in China and flow through Nepal to join the Ganges in
India, contributing 71 per cent of the dry season flows and about 41 per cent of the annual
flows. The Ganges forms the common boundary between India and Bangladesh for about
104 km. The river then flows southeastward inside Bangladesh for about 157 km. and joins
the Brahmaputra at Goalundo. The recorded maximum and minimum flows in the Ganges at
Hardinge Bridge were 76,000 cumec and 263 cumec.
The Brahmaputra: The Brahmaputra has a total catchments area of 552,000 sq. km. spread
over China (270,900 sq. km.), Butan (47,000 sq. km.), India (195,000 sq. km.) and Bangladesh
(39,100 sq. km.). The Brahmaputra originates in the Himalayan range and collects snowmelt
and runoff form the catchments lying in China. Bhutan, India and Bangladesh. The river after
entering Bangladesh flows southward and continues to its confluence with the Ganges near
Aricha. The total length of the Brahmaputra is about 2900 km. up to Aricha. The recorded
maximum flow in the Brahmaputra at Bahadurabad was 98,300 cumec while the minimum
was 2,860 cumec.
The Meghna: The Barak, headstream of the Meghna rises in the hills of Manipur in India.
Near the Indo-Bangladesh border, the Barak bifurcates into two rivers: the Surma and the
Kushiyara which again join together at Ajmirigonj in Bangladesh. The combined flow takes
the name of Meghna and flows in a southwesterly direction to meet the Padma at Chandpur.
Below Chandpur the combined flow is known as the lower Meghna. The total length of the
river is about 902 km. of which 403 km. is in Bangladesh. The total catchments area of Meghna
is 82,000 sq. km. out of which 47,000 sq. km. and lie in India and Bangladesh respectively. The
recorded maximum discharge of the Meghna at Bhairab Bazar was 19,800 cumec.
2 HYDROLOGICAL CYCLE
2.1 INTRODUCTION
Water is the most widespread substance to be found in the natural environment. Water exists
in three states: liquid, solid, and invisible vapour. It forms the oceans, seas, lakes, rivers and
the underground waters found in the top layers of the Earth’s crust and soil cover. In a solid
state, it exists as ice and snow cover in polar and alpine regions. A certain amount of water is
contained in the air as water vapour, water droplets and ice crystals, as well as in the biosphere.
Huge amounts of water are bound up in the composition of the different minerals of the
Earth’s crust and core.
To assess the total water storage on the Earth reliably is a complicated problem because
water is so very dynamic. It is constantly changing from liquid to solid or gaseous phase,
and back again. It is usual to estimate the quantity of water found in the so-called
hydrosphere. This is all the free water existing in liquid, solid or gaseous state in the
atmosphere, on the Earth’s surface and in the crust down to a depth of 2000 meters.
Current estimates are that the Earth’s hydrosphere contains a huge amount of water —
about 1386 million cubic kilometers. However, 97.5% of these amounts are saline waters
and only 2.5% is fresh water. The greater portion of this fresh water (68.7%) is in the
form of ice and permanent snow cover in the Antarctic, the Arctic, and in the mountainous
regions. Next, 29.9% exists as fresh ground waters. Only 0.26% of the total amount of
fresh waters on the Earth is concentrated in lakes, reservoirs and river systems where
they are most easily accessible for our economic needs and absolutely vital for water
ecosystems.
These are the values for natural, static, water storage in the hydrosphere. It is the
amount of water contained simultaneously, on average, over a long period of time — in
waterbodies, aquifers, and the atmosphere. For shorter time intervals such as a single year,
a couple of seasons, or a few months, the volume of water stored in the hydrosphere will
vary as water exchanges take place between the oceans, land and the atmosphere. This
exchange is usually called the turnover of water on the Earth, or the global hydrological
cycle, as shown in Fig. 2.1.
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2 9.9 % Fre sh
9 7.5 % G ro un d w ate r
S a line
W a te r
0.3 % Fres hw a ter Lakes and 0.9 % Oth er Includ ing
R iver S torage. On ly this soil m oisture, sw am p
potion is renew ab le w ate r a nd pe rm afrost
Solar heat evaporates water into the air from the Earth’s surface. Land, lakes, rivers and
oceans send up a steady stream of water vapour; this spreads over the surface of the planet
before falling down again as precipitation. Precipitation falling on land is the main source of the
formation of the waters found on land: rivers, lakes, groundwater, and glaciers. A portion of
atmospheric precipitation evaporates; some of it penetrates and charges groundwater, while the
rest — as river flow — returns to the oceans where it evaporates: this process repeats again and
again. A considerable portion of river flow does not reach the ocean, having evaporated in the
endotherm regions, and those areas with no natural surface runoff channels. On the other hand,
some groundwater bypasses river systems altogether and goes directly to the ocean or evaporates.
Quantitative indices of these different components of the hydrological cycle are shown in Figure
2.2. Every year the turnover of water on Earth involves 577,000 km3 of water. This is water that
evaporates from the oceanic surface (502,800 km3) and from land (74,200 km3). The same amount
of water falls as atmospheric precipitation, 458,000 km3 on the ocean and 119,000 km3 on land.
The difference between precipitation and evaporation from the land surface (119,000 – 74,200
= 44,800 km3/year) represents the total runoff of the Earth’s rivers (42,700 km3/year) and
direct groundwater runoff to the ocean (2100 km3/year). These are the principal sources of
fresh water to support life necessities and man’s economic activities.
C o n d en sa tio n
C lou d s
R u n O ff
E v ap o ra tio n Va po riz a tion
Snow
Oceans cover most of the Earth’s surface. On average, the depth of the world’s oceans is
about 3.9 kilometers. However, maximum depths can be greater than 11 kilometers. The
distribution of land and ocean surfaces on the Earth is not homogeneous. In the Southern
Hemisphere there is 4 times more ocean than land. Ratio between land and ocean is almost
equal in the Northern Hemisphere. Geographers recognize three major ocean basins: Pacific;
Atlantic; and Indian.
The water found in the ocean basins is primarily a byproduct of the lithospheric solidification
of rock that occurred early in the Earth’s history. A second source of water is volcanic eruptions.
The dissolved constituents found in the ocean come from the transport of terrestrial salts in
weathered sediments by leaching and stream runoff. Seawater is a mixture of water and various
salts. Chlorine, sodium, magnesium, calcium, potassium, and sulfur account for 99% of the
salts in seawater. The presence of salt in seawater allows ice to float on top of it. Seawater also
contains small quantities of dissolved gases including: carbon dioxide, oxygen, and nitrogen.
These gases enter the ocean from the atmosphere and from a variety of organic processes.
Seawater changes its density with variations in temperature, salinity, and ocean depth. Seawater
is least dense when it is frozen at the ocean surface and contains no salts. Highest seawater
densities occur at the ocean floor.
The hydrologic cycle is used to model the storage and movement of water between the
biosphere, atmosphere, lithosphere and hydrosphere. Water is stored in the following
reservoirs: atmosphere, oceans, lakes, rivers, glaciers, soils, snowfields, and groundwater. It
moves from one reservoir to another by processes like: evaporation, condensation,
precipitation, deposition, runoff, infiltration, sublimation, transpiration, and groundwater
flow.
River water is of great importance in the global hydrological cycle and for the supply of
water to humankind. This is because the behaviour of individual components in the turnover
of water on the Earth depends both on the size of the storage and the dynamics of water
movement. The different forms of water in the hydrosphere are fully replenished during the
hydrological cycle but at very different rates. For instance, the period for complete recharge of
oceanic waters takes about 2500 years, for permafrost and ice some 10,000 years and for deep
groundwater and mountainous glaciers some 1500 years. Water storage in lakes is fully
replenished over about 17 years and in rivers about 16 days.
Based on water exchange characteristics, two concepts are often used in hydrology and
water management to assess the water resources in a region: the static storage component and
the renewable waters. The static storage conventionally includes freshwater with a period of
complete renewal taking place over many years or decades such as large lakes, groundwater, or
glaciers. Intensive use of this component unavoidably results in depleting the storage and has
unfavorable consequences. It also disturbs the natural equilibrium established over centuries,
whose restoration would require tens or hundreds of years.
Renewable water resources include waters replenished yearly in the process of the water
turnover of the Earth. These are mainly runoff from rivers, estimated as the volume per unit
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Management
of time (m3/s, km3/year, etc.) and formed either within a specific region or from external sources,
including groundwater inflow to a river network. This kind of water resource also includes
the yearly renewable upper aquifer groundwater not drained by the river systems. However,
on the global scale, these volumes are not large compared with the volume of river runoff and
are of importance only for individual specific regions.
Lakes 17 years
Bogs 5 years
In the process of turnover, river runoff is not only recharged quantitatively, its quality is
also restored. If only man could suddenly stop contaminating rivers, then with time water
could return to its natural purity. Thus, river runoff, representing renewable water resources,
is the most important component of the hydrological cycle. It exerts a pronounced effect on
the ecology of the earth’s surface and on human economic development. It is river runoff that
is most widely distributed over the land surface and provides the major volume of water
consumption in the world.
2.3 PRECIPITATION
Water evaporated from oceanic surfaces (86%) combines with water evaporated from the land
(14%) to produce clouds. Seventy-eight percent of all rain falls on the oceans. The remaining
22% falls on land. Hence, the land receives a net moisture donation from the oceans.
Precipitation can be defined as any aqueous deposit, in liquid or solid form, that develops in a
saturated atmospheric environment and generally falls from clouds. A number of different
precipitation types have been classified by meteorologists including rain, freezing rain, snow,
ice pellets, snow pellets, and hail. Fog represents the saturation of air near the ground surface.
Classification of fog types is accomplished by the identification of the mechanism that caused
the air to become saturated. The distribution of precipitation on the Earth’s surface is generally
controlled by the absence or presence of mechanisms that lift air masses to cause saturation. It
is also controlled by the amount of water vapor held in the air, which is a function of air
temperature. A figure is presented that illustrates global precipitation patterns.
Precipitation is often intercepted by vegetation before it reaches the surface of the ground.
However, precipitation, which reaches the ground, follows two basic pathways: surface flow and
infiltration. Some water soaks into the subsurface through infiltration, this water moves through
the pores of the soil until the soil reaches saturation. Infiltration lessens with soil saturation leading
to surface flow. Once infiltrated, water continues to filter through soil or rock through vertical
movement called percolation. Percolation results in the movement of water from the soil layer to
the groundwater. This is usually seasonal, occurring only when the soil is saturated and when
roots and evaporation are not resulting in a net movement of soil water towards the surface.
In certain locations on the Earth, acid pollutants from the atmosphere are being deposited
in dry and wet forms to the Earth’s surface. Scientists generally call this process acid deposition.
If the deposit is wet, it can also be called acid precipitation. Normally, rain is slightly acidic.
Acid precipitation, however, can have a pH as low as 2.3.
The distribution of precipitation falling on the ground surface can be modified by the
presence of vegetation. Vegetation in general, changes this distribution because of the fact that
it intercepts some of the falling rain. How much is intercepted is a function of the branching
structure and leaf density of the vegetation. Some of the water that is intercepted never makes
it to the ground surface. Instead, it evaporates from the vegetation surface directly back to the
atmosphere. A portion of the intercepted water can travel from the leaves to the branches and
then flow down to the ground via the plant’s stem. This phenomenon is called stem flow.
Another portion of the precipitation may flow along the edge of the plant canopy to cause
canopy drip. Both of the processes described above can increase the concentration of the
water added to the soil at the base of the stem and around the edge of the plant’s canopy. Rain
that falls through the vegetation, without being intercepted, is called through fall.
the end of storm events and during ice melt in spring. It is relatively rare in natural environments
(e.g. forested), but is more common in urban and even rural areas. Through flow is the movement
of water laterally through the soil and it occurs most commonly on slopes.
Groundwater flows beneath the surface beyond the soil-moisture root zone. Excess surface
water moves through soil and rock until it reaches the water table. The water table is the
upper limit of groundwater and is the contact point between saturated and aerated rocks and
soils. Groundwater flows from areas with a higher water table to areas where the water table
is lower. There is often a distinction between shallow groundwater flowing through glacial
sands and gravels and deep groundwater flowing through underlying bedrock. An aquifer is a
permeable layer of rock, which can both store and transmit large amounts of groundwater.
Eight per cent of water travels from the land to oceans via surface flow. Ninety-five percent
of this surface flow returns to the ocean as overland flow and stream flow. Only 5% returns to
the ocean by means of slow-moving groundwater. These percentages indicate that the small
amounts of water in rivers and streams are very dynamic, whereas the large quantities of sub-
surface groundwater are sluggish.
Runoff is the surface flow of water to areas of lower elevation. On the micro scale, runoff
can be seen as a series of related events. At the global scale runoff flows from the landmasses
to the oceans. The Earth’s continents experience runoff because of the imbalance between
precipitation and evaporation.
2.5 INFILTRATION
Infiltration is the movement of water from precipitation into the soil layer. Infiltration varies
both spatially and temporally due to a number of environmental factors. After a rain, infiltration
can create a condition where the soil is completely full of water. This condition is, however,
only short-lived as a portion of this water quickly drains (gravitational water) via the force
exerted on the water by gravity. The portion that remains is called the field capacity. In the
soil, field capacity represents a film of water coating all individual soil particles to a thickness
of 0.06 mm. The soil water from 0.0002 to 0.06 mm (known as capillary water) can be removed
from the soil through the processes of evaporation and transpiration. Both of these processes
operate at the surface. Capillary action moves water from one area in the soil to replace losses
in another area (biggest losses tend to be at the surface because of plant consumption and
evaporation). This movement of water by capillary action generally creates a homogeneous
concentration of water throughout the soil profile. Losses of water stop when the film of
water around soil particles reaches 0.0002 mm. Water held from the surface of the soil particles
to 0.0002 mm is essentially immobile and can only be completely removed with high
temperatures (greater than 100 degrees Celsius). Within the soil system, several different forces
influence the storage of water.
2.6 GROUNDWATER
Groundwater is all the water that has penetrated the earth’s surface and is found in one of two
soil layers. The one nearest the surface is the “zone of aeration”, where gaps between soils are
21 Energy Management Hydrological Cycle 21
filled with both air and water. Below this layer is the “zone of saturation”, where the gaps are
filled withwater (Fig. 2.3). The water table is the boundary between these two layers. As the
amount of groundwater increases or decreases, the water table rises or falls accordingly. When
the entire area below the ground is saturated, flooding occurs because all subsequent
precipitation is forced to remain on the surface.
Through flow is the horizontal subsurface movement of water on continents. Rates of
through flow vary with soil type, slope gradient, and the concentration of water in the soil.
Groundwater is the zone in the ground that is permanently saturated with water. The top of
groundwater is known as the water table. Groundwater also flows because of gravity to surface
basins of water (oceans) located at lower elevations.
Su rface Layer
Zo ne of Aeration
W ater Table
Zo ne of Saturation
The amount of water that can be held in the soil is called “porosity”. The rate at which
water flows through the soil is its “permeability”. Different surfaces hold different amounts of
water and absorb water at different rates. Surface permeability is extremely important for
hydrologists to monitor because as a surface becomes less permeable, an increasing amount of
water remains on the surface, creating a greater potential for flooding. Flooding is very common
during winter and early spring because the frozen ground has no permeability, causing most
rainwater and melt water to become runoff.
Lake
O ce an
Im perm eable R oc k
Water that infiltrates the soil flows downward until it encounters impermeable rock (shown
in grey), and then travels laterally (Fig. 2.4). The locations where water moves laterally are
called aquifers. Groundwater returns to the surface through these aquifers (arrows), which
empty into lakes, rivers, and the oceans. Under special circumstances, groundwater can even
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flow upward in artesian wells. The flow of groundwater is much slower than runoff, with
speeds usually measured in centimeters per day, meters per year, or even centimeters per year.
Comparison of Advantages of Surface versus Subsurface Water Reservoirs:
The comparison of advantages between surface and subsurface storage are given
in the following Table (USDI 1985).
2.7 EVAPO-TRANSPIRATION
Evaporation and transpiration are the two processes that move water from the Earth’s surface
to its atmosphere. Evaporation is movement of free water to the atmosphere as a gas. It requires
large amounts of energy. Transpiration is the movement of water through a plant to the
atmosphere. Scientists use the term evapo-transpiration to describe both processes. In general,
the following four factors control the amount of water entering the atmosphere via these two
processes: energy availability; the humidity gradient away from the evaporating surface; the
wind speed immediately above the surface; and water availability. Agricultural scientists
23 Energy Management Hydrological Cycle 23
2.8 RECHARGE
Recharge is the process that allows water to replenish an aquifer. This process occurs naturally
when rainfall filters down through the soil or rock into an aquifer. Artificial recharge is achieved
through the pumping (called injection) of water into wells or by spreading water over the
surface where it can seep into the ground. The land area where recharge occurs is called the
recharge area or recharge zone.
When the withdrawal of groundwater in an aquifer exceeds the recharge rate over a period
of time, the aquifer is over withdrawal. There are two possible effects from the over withdrawal
of water from an aquifer.
First, when the amount of fresh water being pumped out of an aquifer in a coastal area
cannot be replaced as fast as it is being withdrawn, salt water migrates towards the point of
withdrawal. This movement of salt water into zones previously occupied by fresh water is
called salt-water intrusion. Salt-water intrusion can also occur in inland areas where briny
water underlies fresh water.
Secondly, in some areas over withdrawal can make the ground sink because groundwater
pressure helps to support the weight of the land. This is called subsidence. Sinkholes are an
example of this effect.
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GROUNDWATER
3 OCCURRENCE
3.1 INTRODUCTION
All that water occurs below the surface of the earth is termed as sub-surface water,
undergroundwater or simply groundwater. The role of groundwater in sustaining the race of
the man on this planet has of late acquired such an importance that presently all big and small
countries are giving top priorities to short and long-term schemes, envisaging exploration and
exploitation of groundwater reserves in their perspective regions. Groundwater is one portion
of the earth’s water. Various forms of water always move in natural circulation system, known
as the hydrologic cycle.
Seawater because of sun’s heat evaporates to the atmosphere, and by the wind it’s blown
to the above of land. In a high elevation place, these vapors will be compacted and when its
saturation point is exceeded, it falls again to the earth as rainwater. Most part of rainwater
flows at surface as surface water, such as rivers, lakes, or swamps. A small portion of rainwater
infiltrates into soil and percolates to reach saturated zone and joins groundwater. Part of water,
which infiltrates near surface, will evaporate again through plants (evapotranspiration). Direct
evaporation lasts on opened water body, whilst surface run-off will eventually gather back to
the sea, and hydrological process as mentioned above, will last over and over again.
Hydrogeology may be defined as the science of the occurrence, distribution and movement
of water below the surface of the earth, with emphasis on geology.
sometimes also distinguished which comprises uppermost thickness of the ground in which
some water is held-up while percolating downwards by the root zone of vegetable cover and
some chemicals. This water is then easily lost to the atmosphere through transpiration.
g rou n d su rfac e
s oil w ater zon e
Va do s e
In te rm e diate
a era tio n
zo n e of
w ate r
v ad o se
z on e
C a pillar y
z on e W ater table
sa tu ra tion
zo ne o f
G rou ndw a te r or
ph reatic w ater
G roundw ater in saturated zone
im p e rm ea b le ro ck
Fig. 3.1 Distribution of subsurface water. Fig. 3.2 Water in saturation zone.
The Capillary water is the water occupies capillary zone and is observed at the boundary
between the zone of saturation and zone of aeration. Capillary fringe is characteristic of fine-
grained sediments in which the water may rise much above the main water level of the zone of
saturation. Groundwater occurs in saturated zone filled in all rock interstices or fissures
(Fig. 3.2). In many cases a significant rise and fall in the level of this zone is observed as a
characteristic feature during different part of the year. Since in this zone all the openings are
completely filled with water, there is no or very little downward movement. The predominant
movement is a type of flow and is controlled by the head of the water.
A third zone of intermittent saturation is then easily recognized which marks the depths
between the zone of aeration and zone of saturation.
Although compaction might squeeze out most of the water initially present in the pores between
grains, yet some water might still be retained in the inter-granular spaces of such rocks. It is
however, of not much importance in yielding supplies for human consumption.
Juvenile Water: It is also called magmatic water. This water is derived from magma; where the
separation is deep, the term plutonic water is applied, while volcanic water is derived from
relatively shallow depth (3 km to 5 km). New water of magmatic or cosmic origin that has not
previously been a part of the hydrosphere is referred to as juvenile water.
During natural formation of rock pores, voids and interstices develop. Such originally
developed porosity is known as original porosity or primary porosity. Sedimentation and
crystallization of igneous rocks and the flocculation process in clay are responsible for the
formation of primary porosity. Secondary porosity is developed due to weathering and fracturing
of rocks, metamorphism, chemical reaction, biological processes such as animal and insect
burrowing, penetration of root system into the soil or rock layers etc. Grain size, shape,
roundness and angularity influence porosity. Uniform grain size provides considerable pore
space whereas poorly sorted grains restrict void space. This results in more porosity in well-
sorted grains less in poorly sorted grains. Cemented grains with mineral matter provide very
little pore space and consequently reduce porosity. Fractured and jointed blocks provide large
spaces for storage of groundwater. Open solution cavities also provide pore space.
However, porosity depends on the arrangement, shape and size of the grains. The average
porosities for some common soils and rocks are listed in Table 3.1.
Clay 45 – 55
Silt 40 – 50
Mixture of sand 35 – 40
Uniform sand 30 – 40
Gravel 30 – 35
Cavernous limestone 25 – 35
Sandstone 10 – 20
Vesicular basalt 5 – 10
Shale 1 – 10
Limestone 1 – 10
In other words, porosity is the capacity of the substance to store subsurface water. Storage
of groundwater depends on the porosity of the rocks or soils. All the water stored in the
subsurface layers cannot be recovered from wells. Large amounts of water are always retained
in the rock due to the peculiar capillary action forming a film around thee particles. The
volume of water available for draining out from the rocks is known as specific yield.
The volume of water retained in the rocks and not available for draining out is termed Specific
retention. Hence, the effective porosity = specific yield + specific retention. These parameters of
rocks or soils are determined with pumping and recovery tests from wells in the area.
29 Energy Management Groundwater Occurrence 29
Silt 46 8 0.08h
Clay 42 3 0.0002h
Limestone 30 14 0.94v
Dolomite 26 0.001v
Dune sand 45 38 20
Loess 49 18 0.08v
Peat 92 44 5.7v
Schist 38 26 0.2v
Shale 6
Slate 0.00008v
Tuff 41 21 0.2v
Basalt 17 0.01v
Water bearing properties such as porosity, specific retention and hydraulic conductivity
play important roles in the movement of subsurface water. Depending on their water bearing
properties, rock materials are classified as aquifers or water bearing and yielding formations.
Most aquifers are of large areal extent and may be visualized as underground storage
reservoirs. Water enters a reservoir from natural or artificial recharge. There are various types
of aquifers:
Unconfined aquifer: is a water-bearing layer where its water table is upper boundary of
aquifer itself. Groundwater in this aquifer type is called as unconfined of free groundwater,
since water pressure is equal to air pressure (Fig. 3.3). In unconfined aquifer, a water table
varies in undulating form and in slope, depending on areas of recharge and discharge.
g rou nd surface
re c ha rg e
a rea g rou n d
sur face p ie zo m etric p erche d w ate r tab le
sur face w a te r tab le
a rte sia n
w e ll w e ll
flow in g w a te r
w e ll ta b le im p erm e ab le strata
u nco nfin ed
a qu ifer
con fine d con fining
im p e rm ea b le stra tu m w a ter ta ble
a qu ifer
stra ta
Uunconfined
nc on fin ed aAqu
quifer
ifer
adjacent aquifers and, where sufficiently thick, may constitute an important groundwater
storage zone; sandy clay is an example.
Fig. 3.5 Pores between grains. Fig. 3.6 Colluvium - boulders and cobbles
A very unusual stack of very large rounded mixed with sand and mud in a
boulders left by Pleistocene glaciers. debris flow deposit. Very porous sediment
The lack of sediment or cement that can transmit a lot of groundwater,
between grains allows groundwater but the mud and sand fill the pores
to pass through the pores more easily. and make the rate of water flow, slow.
Young volcanic deposits: are deposits of volcanic product, consist of unconsolidated and
consolidated materials. Groundwater fills in either interstices of unconsolidated materials or
fissures of consolidated rocks. These deposits are distributed adjacent to volcano areas.
Limestone: is originally marine deposit with carbonate contents, which due to geologic process
is being uplifted to the surface. Here, groundwater occurred in fissures, cavities and solution
channels (Figs. 3.7, 3.8 and 3.9). This rock crops out in areas where formerly, there was sea.
Owing to geologic, physical and chemical processes, in several areas it formed a particular
morphology, known as karst. Limestone varies widely in density, porosity, and permeability,
depending on degree of consolidation and development of permeable zones after deposition.
Openings in limestone may range from microscopic original pores to large solution caverns
forming subterranean channels sufficiently large to carry the entire flow of a stream.
33 Energy Management Groundwater Occurrence 33
Sandstone: sandstone and conglomerate are cemented forms of sand and gravel. These
sedimentary rocks show great variation in their water yielding capacity, which is chiefly
controlled by their texture and nature of cementing materials. Coarse-grained sandstone with
imperfect cement may prove as excellent aquifers (fig. 3.10).
fault
zone of fractu re
Fig. 3.9 Solution by acidic water flowing Fig. 3.10 Cement between grains decreases
along cracks and bedding planes enhances the permeability of sedimentary rocks,
the permeability of limestone beds. compared to non-cemented sediments.
Igneous rocks: igneous rocks are either intrusive or extrusive in nature. The intrusive igneous
rocks are dense in texture with all the component minerals very closely knitted so that very
little interstices are left. These would be barren of groundwater under normal conditions, but
sometimes fissures and cracks capable of holding some reserves traverse them. The extrusive
rocks exhibit great variation in their water bearing properties. The composition of rocks and
their mode of formation from lava as well as the nature of the original topography are factors,
which generally define the water bearing capacity of these rocks (Figs. 3.11 and 3.12).
Metamorphic rocks: metamorphic rocks behave as poor sources and sites for wells unless
joints and other cracks traverse these on a large scale. Metamorphic rocks like schist; shale and
gneisses, which are often foliated and highly fractured, may prove exceptionally good aquifers.
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But marble and quartzite are normally almost impermeable except along original bedding if the
same is not completely destroyed during metamorphism.
Fig. 3.11 Columnar joints (vertical) and lava Fig. 3.12 Cracks, both horizontal and vertical,
tubes form in many basalt flows and make are common in massive igneous and metamorphic
these geologic formations very permeable. rocks. Areas with many of these fractures
can pass a great deal of groundwater.
equ ipotentia l
d ecen d ing co ol s urface w a te r
line
h h ot sp ring
dm
dq
p erm e ab le
dq HEAT zon e
h-dh
dl
dq dq flow line
coolin g m agm a cham ber
Fig. 3.13 Groundwater flow net. Fig. 3.14 A thermal spring system.
Groundwater flow generally moves from recharge to discharge area and might appear to
the surface due to various factors.
35 Energy Management Groundwater Occurrence 35
c on ta ct cem ent
s pring grou t
im p ervious
a rte sian
s pring
p erv io us
screen ope n hole
tu bu la r
s pring gravel aqu ifer
pack
Fig. 3.15 Types of gravity spring. Fig. 3.16 Examples of well formations.
Depression springs formed where ground surface intersects the water table. Contact springs
created by a permeable water-bearing formation overlying a less permeable formation that
intersects the ground surface. Artesian spring resulting from releases of water under pressure
from confined aquifers either at an outcrop of the aquifer or through an opening in the confining
bed. Tubular or fracture springs issuing from rounded channels, such as lava tubes or solution
channels or fractures in impermeable rock connecting with groundwater.
Wells: Groundwater appearing to the surface resulting from human activity may be conducted
with fully penetrated or partially penetrated to the aquifer’s thickness. Construction of well
depends on aquifer’s properties and quality of groundwater. Therefore, there are various types
of well formation (Fig. 3.16).
Shallow wells are generally less than 15m in depth and are created by digging, boring,
driving, or jetting.
Dug wells: From ancient times, dug wells have furnished countless water supplies throughout
the world. Depths range up to 20 m or more, depending on the position of the water table. Dug
wells can yield relatively large quantities of water from shallow sources of unconsolidated
glacial and alluvial deposits. In the past all dug wells were excavated by hand, and even today
the same method is widely employed. A modern dug well is permanently lined with a casing of
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36 Water Management
Management
wood staves, bricks, rock, concrete or metal. A properly constructed dug well penetrating a
permeable aquifer can yield 2500 to 7500 m3/day, although most domestic dug wells yield less
than 500 m3/day.
Bored wells: Where a water table exists at a shallow depth in an unconsolidated aquifer, bored
wells can furnish small quantities of water at minimum cost. Bored wells are constructed with
hand operated or power driven earth augers. Hand bored wells seldom exceed 20 cm in diameter
and 15 m in depth. Power driven augers will bore holes up to 1m in diameter and, under
favourable conditions, to depths exceeding 30 m.
Driven wells: A driven well consists of a series of connected lengths of pipe driven by repeated
impacts into the ground to below the water table. Water enters the well through a drive point
at the lower end of the well. This consists of a screened cylindrical section protected during
driving by a steel cone at the bottom. Diameters of driven wells are small, most falling in the
range of 10-15cms. Most depths of the wells are less than 15 m although a few exceed 20 m. As
suction type pumps extract water from driven wells, the water table must be near the ground
surface if a continuous water supply is to be obtained. Yields from driven wells are small, with
discharges of about 100 – 250 m3/day.
Jetted wells: Jetted wells are constructed by the cutting action of a downward direction stream
of water. Small diameter holes of 3 to 10 cm are formed in this manner to depths greater than
15 m. Jetted wells have only small yields and are best adapted to unconsolidated formations.
Horizontal wells: Subsurface conditions often preclude groundwater development by normal
vertical wells. Such conditions may involve aquifers that are thin, poorly permeable, or underlain
by saline water. In other circumstances, where groundwater is to be derived primarily from
infiltration of stream flow, a horizontal well system may be advantageous. Infiltration galleries
and collector wells are under the category of horizontal well. An infiltration gallery is a horizontal
conduit for intercepting and collecting groundwater by gravity flow. Galleries normally
constructed at the water table elevation, discharge into a sump where a pump lifts the water to
ground surface for use. Collector wells are normally constructed to draw water for cities and
industries located near rivers. Groundwater pumped from collector wells tapping permeable
alluvial aquifers has often proved to be a successful solution. If located adjacent to a surface
water source, a collector well lowers the water table and thereby induces infiltration of surface
water through the bed of the water body to the well. In this manner, greater supplies of water
can be obtained than would be available from groundwater alone. The large area of exposed
perforations in a collector well causes low inflow velocities, which minimize incrustation,
clogging, and sand transport. Polluted river water is filtered by its passage through the
unconsolidated aquifer to the well. Yields vary with local conditions; the average yield for a
large number of such wells approximate 27,000 m3/day. Collector wells can also function in
permeable aquifers removed from surfacewater. Several such installations gave an average
yield of about 15,000 m3/day.
In order to know about the discharge of well, pumping test should be conducted. Its principles
are to pump out groundwater from a well with a certain constant discharge and observe
37 Energy Management Groundwater Occurrence 37
drawdown of groundwater level during pumping (Fig. 3.17). From the result of observation
specific capacity of well are known — a volume of water which is resulted, in a unit volume if
water level in well is declining in a unit length (for example liter/second per meter drawdown).
Apart from that, pumping test may calculate aquifer’s parameters such as hydraulic conductivity
value. Groundwater drawdown in a single well is different with drawdown of multiple wells.
Drawdown in multiple wells will influence between each other, depends on wells’ distance
(Fig. 3.18).
S = dra w do w n d raw d ow n
c urve s fo r Q 1 s fo r Q 2 s fo r Q 3
Fig. 3.17 Effect of pumping test. Fig. 3.18 Drawdown effect on multiple wells pumping.
In an area where many wells tap the groundwater from the same aquifer, pumping will
form a cone of depression. If it happens in a coastal area, seawater encroachment may occur —
brackish or saline water flows to the land. Meanwhile, if this condition lasted in a confined
aquifer with clay layer as its confining bed, a land subsidence potentially occurs.
identifying linear features, such as lineaments representing fractures, faults, shear zones, which
are usually the zones of localization of groundwater and certain geomorphic features such as
alluvial fans, valley fills, palaeo-channels etc. often form good aquifers as well established
perspective groundwater zones in a region.
Topographical survey: In this survey, surface map is prepared and grid lines are laid on the
ground and reduced levels are determined for each of the grid points.
Hydrogeological studies: In this survey, response of rainfall pattern is studied on water level
fluctuation and total quantity added annually by rainfall in the upper unconfined aquifer is
computed. The Central Groundwater Board, Ministry of Water Resources has published a
hydrogeological map of India. This map illustrates the overall hydrogeological parameters of
the region. The occurrence and abundances of groundwater in a given terrain mainly depends
on the water holding capacity of the lithological types and their associated structural features,
which enable the rocks to allow the surface water to percolate and accumulate in the subsurface
horizons. The distribution of groundwater directly depends on the nature of vertical and
lateral extent of rock types, their interconnected structural elements and the weathered profile
capable of yielding percolation of surface and subsurface water. In hydrogeological investigation
well inventory plays a vital role. Well inventory studies provide information on groundwater
conditions of an area than do other hydrogeological aspects. A well inventory study includes
the dimensions of existing wells, soil type, lithology, structural features, water level fluctuations,
depth of wells, length of water column, mode of extraction of water, quality of water etc. A
hydrogeological map of given area is to be prepared on the basis of such hydrogeological factors
as surface water bodies, their distribution and extent, available well inventory details and
water table contours. Aquifers are to be delineated with reference to the water table, lithological
contacts, extent and attitudes of structural features etc., recharge and discharge basins of
groundwater. These studies are carried out in order to ascertain the success of water supply
project dependent upon the aquifers traced by geological and geophysical investigations. The
study involves an evaluation of:
(i) Quantity of water that the aquifer in question receives from different sources in given
periods.
(ii) The porosity, thickness and width of aquifer.
(iii) The permeability parameters of the aquifer which are necessary for defining the rate
of flow of water through the ground, and the quantity of water lost from the aquifer to
other formations through seepage, springs and by evaporation and transpiration.
(iv) The scope for recharge or replenishing the aquifers through natural and artificial
methods and economics involved in the same.
Geophysical survey: Geophysical investigations play an important role in hydrogeological
studies. These are most successful when used in combination with geological methods.
Geophysical investigations are usually carried out after studying the geology and hydrogeology
of an area. They are employed to understand the nature of the subsurface, lithology, thickness
and depth of the water bearing horizons. Electrical, magnetic, induced polarization, seismic
magnetic and gravity methods are the most important geophysical methods used in exploration.
39 Energy Management Groundwater Occurrence 39
These methods make use of the physical properties of electrical conductivity, magnetic
susceptibility, elasticity and density. These physical properties differ depending on the rock
type, structure, and degree of water saturation, physical, chemical and mineralogical changes.
Electrical methods are extensively used for the exploration of subsurface water.
Geoelectric monitors are deployed to evaluate electrical properties of the aquifer system
leading to determination of saturated thickness in subsurface. In this method, electrodes are
inserted in the ground and connected in a circuit to a source of electrical energy. Under such
circumstances, current flows from one electrode, passes through the ground and leaves through
the other electrodes. The depth to which the current penetrates depends upon the distance
between the two outer electrodes. Thus, it makes penetration to great depths possible by
increasing the spacing between the electrodes. The variations in the value of resistivity with
depth are plotted. The resistivity curves thus obtained are then interpreted for the presence of
water. For accurate interpretation, however, detailed knowledge of stratification is very
necessary. The range of resistivity generally encountered in various soils and rocks is given in
Table 3.3 hereunder:
Table 3.3 Resistivity range of various formations
Resistivity
Material
(Ohm-m)
4.2 EVAPORATION
Many areas of the world are arid or semiarid. The problem caused by the loss of water stored
in lakes and reservoirs for irrigation and domestic use by evaporation during summer months
is acute and perennial, and the loss is enormous. Table 4.1 shows the estimation of water
surface area available for water evaporation control by monolayer films. The evaporation loss
of water is of the order of 1.32 × 1012 gallons.
Table 4.1 Estimation of water surface area available for water evaporation
Area of arid, semiarid and long dry spell regions of India 2,00,000 sq. km
Estimated water area where film application may be feasible (10% of above) 2,000 sq. km
Evaporation loss of water over this per year (Estimated depth of 3 meters) 6×109 m3
(1.32 × 1012 gallons)
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42 Water Management
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Evaporation is the process in which a liquid changes to the gaseous state at the free surface,
below the boiling point through the transfer of heat energy. Consider a body of water in pond.
The molecules of water are in constant motion with a wide range of instantaneous velocities.
An addition of heat causes this range and average speed to increase. When some molecules
possess sufficient kinetic energy, they may cross over the water surface. Similarly, the atmosphere
in the immediate neighbourhood of the water surface contains water molecules within the
water vapour in motion and some of them may penetrate the water surface. The net escape of
water molecules from the liquid state to the gaseous state constitutes evaporation. Evaporation
is a cooling process in that the latent heat of vaporization (at about 585 cal/g of evaporated
water) must be provided by the water body. The equivalent molecular weight of air is 28.95
and that of water vapour is 18, i.e., water vapour is 62% lighter than air. This helps water
vapour to rise into the atmosphere to a height where it condenses. Importance of evaporation
and its potential can be gauged from water budget of continents and oceans (Table 4.2).
Table 4.3 Average values of losses for North and South India for various months of the year
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Losses for North India 70 90 130 160 270 240 180 140 140 130 90 80
(mm)
Losses for South India 100 100 180 230 250 180 150 150 150 130 100 100
(mm)
Average annual rainfall in India is about 1120mm, which is equal to 370 million hectare-m
of water. Total runoff by all the rivers of the country is 170million hectare-m. If annual ground
water recharge is 37million hectare-m is also lost to atmosphere and transpiration. Part of the
37million hectare-m is also lost to atmosphere as transpiration. The factors affecting evaporation
are: (i) vapour pressures at the water surface and air above, (ii) air and water temperature,
(iii) wind speed, (iv) atmospheric pressure, (v) quality of water and (vi) size of water body.
43 Energy Management Water Losses 43
Heat storage in waterbodies: Deep-water bodies have more heat storage than shallow ones.
A deep lake may store radiation energy received in summer and release it in winter causing
less evaporation in summer and more evaporation in winter compared to a shallow lake exposed
to a similar situation. However, the effect of heat storage is essential to change the seasonal
evaporation rates and the annual evaporation rate is seldom affected. Different evaporating
surfaces like soil, barren land, forest area, houses and lakes affect evaporation to the extent
they have the potential. Black cotton soils help to evaporate the soil water faster than red soil
because such soils have the potential to absorb incoming radiation more effectively. Evaporation
from wet soil is faster and it reduces gradually as soil becomes drier.
Measuring Evaporation
It is rather impossible to measure evaporation directly in the field. Evaporation from water
surface is estimated by different methods and its values are correlated to field data. While
estimating evaporation from open storages, it is necessary to know seepage that occurs from
the bed of the reservoir. Not much information about the determination of loss of water from
storages that can be attributed solely to seepage from the bed and slides is available. In India,
attempts have been made to develop seepage meters. A seepage meter (Fig 4.1) developed by
the Irrigation Research Institute, Poondi, Chennai, was installed in the deeper section of Buderi
Tank and seepage loss through its bed measured. The device consist of two cylindrical pan,
1.2294m diameter and 0.43m high with a hole of 38.10mm diameter in the center and short
metal pipes of about 101.60mm in length welded to the holes to project outside from the bottom.
The later pipes serve to connect the pans to each other with the help of a rubber hose. One of
the pans is inverted and rammed into the bed such that at least 228.60mm of its sides penetrate
into the soil, the other pan with its open end facing upwards is supported on a framework
above first pan with its bottom at least 228.60mm below the water surface of the tank. The top
pan is covered by a lid to prevent loss of water due to evaporation, and water is poured into it
to the same level as that in the tank on the outside of it. When the water from the bottom pan
seeps through the bed of the tank, the water level in the top pan gets lowered correspondingly
and thus serves to indicate directly the loss of water due to seepage from the tank bed. It has
been reported that consistent values could not be obtained.
Fr am e w ork L id fo r the p an
s up po rtin g To p pa n 10 1.6 m m B,
th e to p pa n 0 .45 7 2m m h igh
0 .45 7 2m m
M etal
m etal p ipe
c la m p
R u bb er
h ose
B o ttom p an 1 01 .6m m
Ta n k be d
2 28 a nd 0 .457 2m m h ig h
mm
O p en a nd d rive n a t
lea st 22 9m m in to th e
g rou nd
At the Irrigation Research Institute, Roorkee, attempts were made to improve the seepage
meter developed by Regional Salinity Laboratory, Soil Conservation Service Riverside,
California, by replacing the plastic bag by a constant head vessel (Fig. 4.2) to measure seepage
in channels. The seepage meter essentially consists of seepage cup, constant head vessel and
swivel head joint. The seepage meter before use was standardized. The value obtained by a
seepage meter is to be multiplied by a coefficient greater than one for less pervious soil and less
than one for more pervious soils.
6 .4m m tub e
G ra duated tu b e P
T
G T
C o nsta nt h ea d ve sse l
1 .5 24 m
0.3 m
Q
0 .05 m V a lv e V 1 3m m p ip e
S
P las tic tube 1 3m m H S w iv el he a d
O pera ting h ea d
0 .3 1 m
6 .4m m × 1 3m m
stiffe ne r
A irvalve 6 .4 mm B
3 2m m B
6 :1
1 3m m
0.1524m
S e ep a ge c up
The methods available to estimate evaporation losses from surfaces of large water bodies
are:
1. Evaporation pans
2. Empirical equations
3. Water balance method
4. Energy budget method
5. Mass transfer method
1. Evaporation Pans: Evaporation measurement using pans is the most reliable and the
best ofall the available methods. An evaporimeter as specified by IS: 5973 – 1970 for Indian
conditions is a pan of 1.22m in diameter and 0.255m deep. It is a modified version of the US
Weather Bureau class A pan since the latter is made of galvanized iron and is not painted white
outside. The Indian Standard pan is made up of 0.90mm thick copper sheet with hexagonal
wire netting of galvanized iron mesh covering it to protect its water from birds. The details of
IS specified pan are given in Fig. 4.3. The pan is placed over a wooden platform of 10cm height
so that circulation of air is possible all around the pan. This also helps to thermally insulate the
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46 Water Management
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pan completely from ground. Water level in the pan is recorded by a point gauge arrangement
placed inside a stilling basin. Normally, an evaporation pan is placed along with other weather
measuring instruments for recording humidity, temperature, rainfall, wind speed and other
parameters. Measurement is taken at least once a day by adding water to the pan by a calibrated
cylindrical glass jar to bring the water level to the previous position. This gives directly the
evaporation depth over the time lapse. If there is rainfall exceeding the depth of evaporation,
then water is taken out of the pan in the same way by the measuring jar and knowing the
depth of rainfall from the rain gauge the evaporation depth is found out by subtraction.
C lam p
a rrang em e n t
T he rm om e te r
S tillin g w e ll
W ire m e sh c o ver
0 .9 m m c op p er sh e et 2 55 m
P o in t ga ug e 25 mm
W ood en
b ase
1 00 m m
1 22 0 m m
US Weather Bureau Class A Land Pan – It is standard pan of 1210mm diameter and 255mm
depth. The depth of water is maintained between 18cm and 20cm (Fig. 4.4). The pan is normally
made of unpainted galvanized iron sheet. The pan is placed on a wooden platform of 15cm
height above the ground to allow free circulation of air below the pan. Measuring the depth of
water with a hook gauge in a stilling well makes evaporation measurements.
Colorado Sunken Pan – This pan, 920mm square and 460mm deep is made up of unpainted
galvanized iron sheet and buried into the ground within 100mm of the top (Fig. 4.5). The
chief advantage of the sunken pan is that radiation and aerodynamic characteristics are similar
to those of a lake.
W ater le vel
sam e a s G L
W ater le ve l in p an
50 GL
50
2 55
4 60
GL 1 50
1 21 0 D ia
W ood en
s up p ort (S Q ) 9 20 S q
Fig. 4.4 US Weather Bureau Class A Land Pan. Fig. 4.5 Colorado Sunken Pan.
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48 Water Management
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#2. Calculate the daily lake evaporation from the following data from a class – A pan.
Assume pan coefficient as 0.80.
Rainfall (mm) 10 0 19 4 10
Solution: Daily pan evaporation is the sum of the rainfall and the water added or taken out
from the pan. Calculation is carried out daily in the following table.
12/8/03 –6 19 13 10.40
2. Empirical Equations: A large number of empirical equations are available to estimate lake
evaporation using commonly available meteorological data. Most formulae are based on the
Dalton-type equation and can be expressed in the general form E = K. f(u) (es – ea). Where E
is lake evaporation in mm/day, es is saturated vapour pressure at the water – surface temperature
in mm of mercury, ea is actual vapour pressure of overlying air at a specified height in mm of
mercury, f(u) is wind speed correction function and K is coefficient. The term ea is measured
at the same height at which wind speed is measured. Other commonly used empirical evaporation
formulae are as shown in Table 4.5.
Meyer’s formula LM
E = 1+
U OP
.C.(e s – e a ) U is monthly mean wind speed in km/h
USA, small N 16 Q at 9m aboound. C = 0.36 for large
lake, 1915 deep lakes and 0.50 for shallow lakes.
Rhower’s formula E = 0.77 (1.465 – 0.000732 P) × P is the mean barometric reading in mm
USA, 1931 (0.44 + 0.0733 U) (es – ea) Hg and U the mean wind velocity at
0.6m above ground in km/h.
Penman’s formula E = 8.9 (1 + 0.15U) (es – ea) U is measured at 2m above ground level.
England, Small lake
USBR formula E = 0.833 (4.57 t + 43.3) E is mm/month, t mean annual
temperature in oC.
Contd...
49 Energy Management Water Losses 49
Wind speed at any height h1 up to 500 m above ground is calculated using the (1/7)th
1/7
h
power law given as Uhi = Uh 1 , where Uh is the wind speed measured at height h.
h
Among all the above equations, Meyer’s formula is widely used for the computation of lake
evaporation.
#3 A reservoir with average surface spread of 5.0 km2 in December has the water surface
temperature of 30°C and relative humidity of 40%. Wind velocity measured at 2.0m above the
ground at a nearby observatory is 15 km/h. Calculate average evaporation loss from the reservoir
in mm/day and the total depth and volume of evaporation loss for December.
Solution: For water surface temperature of 30°C, the saturation vapour pressure
es = 31.81 mmHg. (Ref: Table 4.6)
Relative humidity (RH) = 40% = 0.40
To use Meyer’s equation, wind speed is to be converted to a height of 9 m above ground by
(1/7)th power law, U (at 9 m above ground level) = 15× (9/2)1/7 = 18.6 km/h.
Saturation water pressure of air ea = es × RH = 31.81 × 0.40 = 12.724 mmHg.
Using Meyer’s equation, evaporation loss is computed as :
E = C 1+
LM U OP FG
(e s – e a ) = 0.40 1 +
IJ
18.6
(31.81 – 12.724) = 16.51mm / day
N 16 Q H 16 K
Depth of evaporation in December = 31 × 16.51 = 511.81 mm.
Volume of evaporated water from the reservoir for December will be
(320.5 × 5.0 × 106) × 10–3 =2.559 mm3 = 255.9 ha.m.
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50 Water Management
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Temperature Saturation Vapour Pressure es Slope of Plot between (1) and (2)
(o C) (mmHg) (millibar)
3. Water Balance Method: Water balance or water budget method balances all the incoming,
outgoing and stored water in a lake or reservoir over a period of time. The equation in its
simplest form is SInflow – SOutflow = Change in storage + Evaporation loss. Or
E = 5I – 5O ± ,S. It can be more generalized by taking all the factors of inflow and outflow.
Above equation can be written as: E = (P + Isf + Igf) – (Osf + Ogf + T) + 5S, where P is the
precipitation, Isf the ground water inflow, Osf the surface water outflow, Ogf the ground water
outflow, T the transpiration loss, DS is the change in storage. Measurement of all quantities is
possible except Igf, Ogf and T. Therefore, this equation fails to give accurate results since ground
water inflow and outflow are very difficult to measure for a lake or reservoir. It may give fairly
good result if considered annually but should not be used for daily estimation of evaporation.
This equation is good for theoretical considerations or may be applied to watertight lakes
located on impervious rocks for budgeting annual water.
4. Energy Budget or Energy Balance Method: Like water balance, energy balance or energy
budget for lakes or reservoirs can be carried out to calculate lake evaporation. This method
uses the conservation of energy by incorporating all the incoming, outgoing and stored energy
of a lake in the following form.
51 Energy Management Water Losses 51
Increased
hea t ene rg y
of w ater (H l )
(H if) H ea t tak es
(H lf ) out of system
by flow of wa ter
Above equation is known as Bowen’s ratio, defined as the ratio between heats lost by
conduction to heat lost by evaporation. Estimate of β can be made from the relation
(Ts – Ta )
β = c.p 100(e – e )
s a
Where p is atmospheric pressure in millibars, Ts and Ta are the water surface and air
temperature in o C, c is a constant varying between 0.58 and 0.66 (average value being 0.61),
es and ea are the saturation vapour pressure at water surface and air temperatures in millibar.
From above equation, we get Hs = β . ρ . LH . E
Therefore, He + Hs = ρ LH (1+β) E
(H e – H s )
or, E=
ρL H (1 + β)
(H li + H si – H so – H lo – H i – H if – H lr – H gf )
Therefore, E =
[ρL H (1 + β)]
Values of radiation from sun and sky (Hli + Hsi) are available for different latitudes. Reflected
solar radiation is dependent on factors like spectral wavelength and turbidity of water and air.
For water, it can be taken between 5 to 15% of incident radiation. Neglecting Hsi, net effect of
all the long wave radiation Hlr is given in calories per square centimeter per day as the sum of
incoming long wave radiation from atmosphere Hli plus reflected long wave radiation – Hlo
and long wave radiation emitted by water – Hlr as
Hlr = Hli – (Hlo + Hlr) = (1 – r) Hli
The incident solar energy is calculated by the equations proposed by Penman (1948) as
Hli = (0.18 + 0.55n/N) Io, Where Io is the solar radiation received at earth’s outer surface
in (cal/cm2-day), n is the actual number of bright sunshine hours, N is the possible maximum
number of hours of sunshine at the place. Io converted to mm of evaporable water/day. The
net outgoing thermal radiation expressed by Penman is given as:
Hnet = σ T 4 [0.56 – 0.092 ea0.5] (0.1 + 0.90n/N), in which σ is the Stefan–Boltzmann
constant = 2 × 10–9mm of water/day, T is the water surface temperature in °Kelvin, Hif can
Wsh.H e .Te
be calculated from the relation Hif = , in which Wsh is the specific heat of water in
LH
cal/g o C. Hn can be calculated from the relation Hn = Hli (1 – r) – Hnet
Net energy added into lake water, Hif is measured by knowing all the volume of water in
flowing and coming out of the lake and their corresponding temperatures during the period of
water budget. This term should sum all channel inflows and outflows, evaporation, condensation,
rainfall, seepage and other losses. The term increase in stored heat energy of water for the lake or
reservoir is a difficult parameter to obtain, which can be computed by knowing precisely the
53 Energy Management Water Losses 53
average temperature of lake water and the volume of water at the beginning and end of the
budget period. Application of the energy budget principle gives good results for watertight lakes
and it may give highly erroneous and confusing results for other lakes.
5. Mass Transfer Method
This method is based on theories of turbulent mass transfer in boundary layer to calculate the
mass water vapour transfer from the surface to the surrounding atmosphere. Accuracy
estimation of the amount of water vapour transferred to atmosphere from a lake surface is still
investigated. With the use of quantities measured by sophisticated instrumentation, this method
can give satisfactory results. The equation proposed by Thornthwaite and Holzman (1939)
takes the following form:,
0.000119(e i – e 2 )(u 2 – u 1 )
E= where E is m/sec, u2 and u1 are the velocities of wind in m/
L F h IO
p × M ln G J P
2
N H h KQ
1
sec at heights h2 and h1 m respectively, e2 and e1 are vapour pressure of air in pascal (Pa) at
height(s) h2 and h1, p is mean atmospheric pressure in Pa (1 N.m2 = 1 Pa; 1 kPa = 10 mb)
between lower height h1 and upper height h2. Height h1 is taken close to water surface level.
4.3 TRANSPIRATION
Plants absorb water from the soil through minute root hairs at the tips of their rootlets. Mineral
salts are also absorbed in very dilute solution, using water as the vehicle. The solutions are
transported through roots and stems to the leaves where plant food is produced from the sap
and carbon dioxide absorbed from the atmosphere, using the energy from the sun operating
chlorophyll. These plant foods, again using water as the vehicle, are distributed through the
plant for cell growth and tissue building. Most of the water absorbed through the roots is
discharged from the plant as vapour in the process known as transpiration. As much as 99%
of the total water received by a plant through its roots is lost to the atmosphere by this process.
Evapotranspiration: while transpiration takes place, the land areas in which plants stand
also lose moisture by the evaporation of water from soil and water bodies. In hydrology and
irrigation practice, it is found that evaporation and transpiration processes can be considered
advantageously under one head as Evapotranspiration. Evapotranspiration also uses the term
consumptive use to denote this loss. For a given set of atmospheric conditions,
Evapotranspiration obviously depends on the availability of water. If sufficient moisture is
always available to completely meet the needs of vegetation fully covered the area, the resulting
evapotranspiration (PET). Potential evapotranspiration no longer critically depends on soil
and plant factors but depends essentially on climatic factors. The real evapotranspiration
occurring in a specific situation is called actual evapotranspiration (AET). If the water supply
to the plant is adequate, soil moisture will be at the field capacity and AET will be equal to
PET. If the water supply is less than PET, soil dries out and the ration AET/PET would be less
than 1.0. A relation between AET/PET and available moisture can be developed for different
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54 Water Management
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types of soils on the basis of experimental results. For the same AET/PET ratio, sandy soil has
more available moisture than clayey soil. In other words, for the same percentage of available
moisture, ratio of AET/PET will be less for sandy soil than clayey soil (Fig. 4.7).
1.0
W ilting
point
C la
so i y e y
l
Sa ndy
Ratio AE T/P ET
soil
0.5
Fie ld
capacity
0
100 75 50 25 0
Pe rc entage o f av ailable m o isture
Fig. 4.7 Comparison of AET/PET ratio for sandy and clayey soils.
Measurement of Transpiration/Evapotranspiration
Transpiration
Most measurements are made with a “Phytometer” a large vessel filled with soil in which one
or more plants are rooted. The only escape of moisture is by transpiration (the soil surface is
sealed to prevent evaporation) that can be determined by weighing the plant and the container
at desired intervals of time. By providing aeration and additional water a phytometer study
may be carried through the entire cycle of a plant. It is virtually impossible to simulate natural
conditions and therefore the results of phytometer observations are mostly of academic interest
55 Energy Management Water Losses 55
to the hydrologist. Transpiration ratio (TR) is the ratio between the amount of water consumed
and the dry matter produced (exclusive of the roots, sometimes only the grains).
before and after the experiments over the periods of days. Knowing all other quantities of
equation, Et can be computed. To produce results very close to field, soil conditions, moisture
content, plant types and the methods of water application should be properly chosen such
that they represent the surrounding natural condition. The vegetation around the lysimeter
should be the same as that inside in order to avoid disturbing border effects. To the same end,
the depth of lysimeter should not be less than 1.5m and area not less than 1.0 sq. m. Lysimeter
are expensive to maintain and time consuming.
0 .6 to 3.3 m
1 .8 to 3.3 m
A Lys im e te r
2. Climatic Approach: Several empirical techniques have been developed for estimating
potential evapotranspiration from readily available climatic data. Some empirical and
theoretical equations are derived on the basis of regional relationship between measured Et
and climatic factors. The following methods are the combination of some empirical, analytical
and theoretical approaches.
Blaney – Criddle Method: Blaney and Criddle (1962) proposed an empirical relation, which
is used largely by irrigation engineers to calculate crop water requirement of various crops.
Estimation of potential evapotranspiration (consumptive use) is carried out by correlating it
with sunshine temperature. Sunshine at a place is dependent on latitude of the place and
varies with month of the year. Table below gives the values of percentages of monthly daytime
for use in Blaney – Criddle equation. PET for a crop during its growing season is given by
Pet = ΣK.F; where F = (0.0457Tm + 0.8128) P.
Here K is the monthly crop coefficient to be determined from experimental data, F the
monthly consumptive use factor, PET the potential evapotranspiration in cm, Tm the mean
monthly temperature in °C, P is the monthly percentage of hours of bright sunshine in
the year.
57 Energy Management Water Losses 57
Table 4.7 Monthly daytime percentage hours (P) to be used by blaney – Criddle formula
North
Latitude Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
(Deg.)
0 8.5 7.66 8.49 8.21 8.50 8.22 8.50 8.49 8.21 8.50 8.22 8.50
5 8.32 7.56 8.47 8.29 8.66 8.40 8.68 8.60 8.23 8.42 8.06 8.30
10 8.13 7.47 8.45 8.37 8.81 8.60 8.86 8.71 8.25 8.34 7.91 8.10
15 7.94 7.36 8.43 8.44 8.89 8.80 9.05 8.83 8.28 8.26 7.75 7.88
20 7.74 7.25 8.41 8.52 9.15 9.00 9.23 8.96 8.30 8.18 7.58 7.66
25 7.53 7.14 8.39 8.61 9.33 8.23 9.45 9.09 8.32 8.09 7.40 7.42
30 7.30 7.03 8.38 8.72 9.53 9.49 9.67 9.22 8.33 7.99 7.19 7.15
35 7.05 6.88 8.35 8.83 9.76 9.77 9.93 9.37 8.36 7.87 6.97 6.86
40 6.76 6.72 8.33 8.95 10.02 10.08 10.22 9.54 8.39 7.75 6.72 6.52
45 6.42 6.54 8.30 9.09 10.33 10.47 10.57 9.75 8.41 7.60 6.42 6.13
50 5.98 6.30 8.24 9.24 10.68 10.91 10.99 10.00 8.46 7.45 6.10 5.65
55 5.42 6.01 8.16 9.41 11.13 11.53 11.56 10.34 8.52 7.25 5.65 5.03
60 4.67 5.65 8.08 9.65 11.74 12.34 12.31 10.70 8.57 6.68 4.31 4.22
Table 4.9 Monthly crop coefficient factor K to be used for blaney – cridle method
Value of K 1.1 0.65 0.65 0.90 0.65 0.70 0.75 0.80 1.20
Range of K 0.85- 1.3 0.5-0.75 0.5-0.75 0.8-1.0 0.5-0.9 0.65-.075 0.65-0.85 0.7-1.0 1.1-1.4
#4 Use Blaney–Criddle method to calculate consumptive use (PET) for rice crop grown from
July to September in Maharashtra at a latitude 20 N from the following data taken from a nearby
observatory. Find the net irrigation demand for rice using the given rainfall during crop period.
Rainfall, (mm) 15 20 10
Sol: For rice crop, monthly crop coefficient K of equation may be taken as 1.10. Mean
monthly sunshine hours for latitude of 20N for the months of July, August and September are
obtained from Table and tabulated below.
Blaney–Criddle Method of Computation of Consumptive Use of Rice Crop for Example
Mean Monthly % Monthly Effective Depth of
Month Monthly (P) of Day Consumptive K PET Rainfall at Irrigation
Temp. Time Hours Use Factor (4) × (5) 80% Demand
(Tm) from Table (F) (cm) (6)-(7)
(cm)
1 2 3 4 5 6 7 8
Jul 13 7.74 10.89 1.1 11.98 1.20 10.78
Aug 16 7.25 11.19 1.1 12.31 1.60 10.71
Sep 25 8.41 16.44 1.1 18.00 0.80 17.28
pressure vs. temperature curve at mean air temperature, Ea is the drying power of air which
includes wind velocity and saturation deficit and is estimated from the relation:
Ea = 0.002187 (160 + u2) (es – ea); where u2 is the mean wind speed in km/day measured
2m above the ground, es is saturation vapour pressure at mean air temperature in mm Hg, ea is
actual vapour pressure in the air in mm of mercury and H is the daily net radiation in mm of
evaporable water and is estimated from the energy budget theories using the relation:
H = Ha (1 – r) (0.29 cosφ + 0.55n/N) – σT4 (0.56 – 0.092 ea ) (0.10 + 0.9 n/N); where
Ha is the extraterrestrial solar radiation received on a horizontal surface in mm of evaporable
water per day, φ the latitude of the place where PET is to be computed, r is the reflection
coefficient whose values for close crops may be taken as 0.15 – 0.25, for barren land
0.05 – 0.45 and for water surface 0.05, n is the actual duration of bright sunshine which is a
function of latitude and is an observed data at a place, N is the maximum possible hours of
bright sunshine available at different location, σ is the Stefan-Boltzman constant =
2.01 × 10–9 mm/day, Ta is the mean air temperature in °K = (273+o C) and ea is the actual
vapour pressure in mm of Hg. The wind speed measured at any other height z can be reduced
0.143
Et (Cu) is the evapotranspiration and Ep is the pan evaporation. Et/Ep = k is the consumptive use
coefficient. For dark vegetation plants, k should be taken higher for the same group and for
lighter crop, it is lesser. Tall plants have higher value of k than small plants of same degree of
greenness and density.
Values of k (Average)
% of Crop Group
Growing A B C D E F G Rice Wheat Cotton Maize
Season L P P L
1 2 3 4 5 6 7 8 9 10 11 12 13
0 0.20 0.15 0.12 0.08 0.90 0.60 0.50 0.80 0.14 0.30 0.22 0.40
5 0.20 0.15 0.12 0.08 0.90 0.60 0.55 0.90 0.17 0.40 0.22 0.42
10 0.36 0.27 0.22 0.15 0.90 0.60 0.60 0.95 0.23 0.51 0.23 0.47
15 0.50 0.38 0.30 0.19 0.90 0.60 0.65 1.00 0.33 0.62 0.24 0.54
20 0.64 0.48 0.38 0.27 0.90 0.60 0.70 1.05 0.45 0.73 0.26 0.63
25 0.75 0.56 0.45 0.33 0.90 0.60 0.75 1.10 0.60 0.84 0.35 0.75
30 0.84 0.63 0.50 0.40 0.90 0.60 0.80 1.14 0.72 0.92 0.58 0.85
35 0.92 0.69 0.55 0.46 0.90 0.60 0.85 1.17 0.81 0.96 0.80 0.96
40 0.97 0.73 0.58 0.52 0.90 0.60 0.90 1.21 0.88 1.10 0.95 1.04
45 0.99 0.74 0.60 0.58 0.90 0.60 0.95 1.25 0.90 1.10 1.03 1.07
50 1.00 0.75 0.60 0.65 0.90 0.60 1.00 1.30 0.91 1.00 1.08 1.09
55 1.00 0.75 0.60 0.71 0.90 0.60 1.00 1.30 0.90 0.91 1.08 1.10
60 0.99 0.74 0.60 0.77 0.90 0.60 1.00 1.30 0.89 0.80 1.07 1.11
65 0.96 0.72 0.58 0.82 0.90 0.60 0.95 1.25 0.86 0.65 1.05 1.10
70 0.91 0.68 0.55 0.88 0.90 0.60 0.90 1.20 0.83 0.51 1.00 1.07
75 0.85 0.64 0.51 0.90 0.90 0.60 0.85 1.15 0.80 0.40 0.93 1.04
80 0.75 0.56 0.45 0.90 0.90 0.60 0.80 1.10 0.76 0.30 0.85 1.00
85 0.60 0.45 0.36 0.80 0.90 0.60 0.75 1.00 0.71 0.20 0.73 0.97
90 0.46 0.35 0.28 0.70 0.90 0.60 0.70 0.90 0.65 0.12 0.62 0.89
95 0.28 0.21 0.17 0.60 0.90 0.60 0.55 0.80 0.58 0.10 0.50 0.81
100 0.20 0.20 0.17 0.60 0.90 0.60 0.50 0.20 0.51 0.10 0.40 0.70
#5 Use Hargreaves method to calculate crop water requirements for paddy to be grown
from January 10 to March 30. Class A pan evaporation values for the months are 11, 12
and 14 cm respectively. Rainfall during the three months can be taken as 10, 15 and 30mm.
Calculate the gross irrigation requirement at the head of field if irrigation efficiency is 85%.
61 Energy Management Water Losses 61
Solution: Referring above Table 4.10 for rice, value of k for the percent of growing season are
found and entered in column 5 of Table below. Et values are computed in column 6. Crop
period for paddy is taken as 80 days from January 10 to March 30.
No. of Rainfall Net irri.
Days Pan During Requirement Gross irri.
Date Up to % Growing Et the = col. 6 – Requirement
Evaporation K
Mid Season = k. Ep month 80% × col = col. 8 /
Ep (cm)
Point (cm) 7. (cm) Efficiency
1 2 3 4 5 6 7 8 9
4.4 INTERCEPTION
The losses occur on account of evaporation of water caught and held in suspension by
vegetation. When it rains over a catchment not all the precipitation falls directly onto the
ground. Before it reaches the ground, a part of it may be caught by the vegetation and
subsequently evaporated. The volume of water so caught is called interception. The adhesive
force between the water drops and the vegetation holds back the drops of water against gravity
until they grow in size to over weigh and slip down. The intercepted precipitation may follow
one of the three possible ways:
1. It may retain by the vegetation as surface storage and returned to the atmosphere by
evaporation; a process called interception loss.
2. It can drip off the plant leaves to join the ground surface or the surface flow, called
through fall, and
3. The rainwater may run along the leaves and branches and down the stem to reach the
ground surface, called stem flow.
Interception loss is solely due to evaporation and does not include transpiration, through
fall or stem flow. Factors on which interception depends are: (a) intensity and duration of
storm, (b) density of trees, (c) types of trees and other obstructions, (d) season of the year and
(e) wind velocity at the time of precipitation.
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The amount of water intercepted in a given area is extremely difficult to measure. It depends
on the species composition of vegetation, its density and also on the storm characteristics. It is
estimated that of the total rainfall in an area during a plant growing season the interception
loss is about 10% to 20%. Interception is satisfied during the first part of a storm and if an area
experiences a large number of small storms, the annual interception loss due to forests in such
cases will be high, amounting to greater than 25% of the annual precipitation. Quantitatively,
the variation of interception loss with the rainfall magnitude per storm for small storms is as
shown in Fig 4.9. It is seen that the interception loss is large for a small rainfall and levels off to
a constant value for larger storms. For a given storm, the interception loss is estimated as:
Ii = Si + Ki. E. t. where Ii = interception loss in mm, Si = interception storage whose value
varies from 0.25 to 1.25 mm depending on the nature of vegetation, Ki = ratio of vegetal
surface area to its projected area, E = evaporation rate in mm/h during the precipitation and
t = duration of rainfall in hours.
1 00
80
In te rce ptio n L oss a s
Pe rc e ntage R a infall
B e ech tree s
60
40
20
0
0 5 10 15 20 25 30
R a infa ll (m m )
It is found that coniferous trees have more interception loss than deciduous ones.
Also, dense grasses have nearly same interception losses as full-grown trees and can
account for nearly 20% of the total rainfall in the season. Agricultural crops in their
growing season also contribute high interception losses. In view of these, the interception
process has a very significant impact on the ecology of the area related to silvicultural
aspects and in the water balance of a region. However, in hydrological studies dealing
with floods interception loss is rarely significant and is not separately considered. The
common practice is to allow a lump sum value as the initial loss to be deducted from the
initial period of the storm.
Horton (1919) proposed a straight-line relation between precipitation P in mm and total
interception loss Ii for ash tree in the following form: Ii = 0.38 + 2.3P
Depending on the vegetal cover and precipitation, a general form of equation for
interception loss can be written as: I i = a.P + b (1 – e –p/b); where a and b are constants
which depend on the factors of infiltration loss, a varies between 0.01 and 0.2 and b
between 2.5 and 38% of rainfall, P is the precipitation depth in mm. When the intensity
of rainfall is 25-mm/h interception rates vary between 15% for soybean crop and 57%
for tall grass.
63 Energy Management Water Losses 63
4.6 INFILTRATION
It is well known that when water is applied to the surface of a soil, a part of it seeps into the
soil. This movement of water through the soil surface is known as infiltration and plays a very
significant role in the runoff process by affecting the timing distribution and magnitude of the
surface runoff. Creation of hydrogen bond between soil particles and the water initiate the
infiltration process. The adhesive force of attraction between soil and water, the surface tension,
capillary and gravitational forces help to force more water between the pores of soil particles
as more water is added to the system due to rain. Further, infiltration is the primary steps in
the natural groundwater recharge.
Infiltration is the flow of water into the ground through the soil surface and the process
can be easily understood through a simple analogy. Consider a small container covered with
wire gauze as in Fig. 4.10. If water is poured over the gauze, a part of it will go into the
container and a part overflows. Further, the container can hold only a fixed quantity and
when it is full no more flow into the container can take place. This analogy, though a highly
simplified one, underscores two important aspects, viz., (i) the maximum rate at which the
ground can absorb water, the infiltration capacity and (ii) the volume of water that it can
hold, the field capacity. Since the infiltrate water may contribute to groundwater discharge
in addition to increasing the soil moisture, the process can be schematically modeled as in
Fig. 4.11. This figure considers two situations, viz, low-intensity rainfall and high-intensity
rainfall, and is self-explanatory.
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L ow inte ns ity H igh in ten sity
ra in fall ra in fall
S urfa ce
In pu t ru no ff
Infiltra tio n
S p ill
S oil
m o isture
sto rag e
ca p ac ity
W ire
g au ze
P erc ola tio n to
to storag e g rou nd w ate r
Infiltration capacity is the maximum rate at which a given soil can absorb water under a
given set of conditions at a given time. At any instant the actual infiltration ft can be equal to
infiltration capacity f0 only when the rainfall intensity is greater than f0, otherwise actual
infiltration will be equal to the rate of rainfall. This can be observed during low intensity
rainfall when there is no surface runoff produced due to precipitation. Once water enters into
the soil, the process of transmission of water within the soil known as percolation takes place,
thus removing the water from near the surface to down below, charging the groundwater
reservoir. Infiltration and percolation are directly interrelated. When percolation stops,
infiltration also stops. During any storm, infiltration is the maximum at the beginning of the
storm, decays exponentially and attains a constant value of fc as the storm progresses.
infiltration rate to the extent, temperature does, and therefore, temperature can be considered
as the only vibrant climatic factor affecting infiltration.
Rainfall intensity and duration: During heavy rainfall, the topsoil is affected by mechanical
compaction and by the inwash of finer material. This leads to faster decrease in the rate of
infiltration than with low intensities of rainfall. Duration of rainfall affects to the extent that
when the same quantity of rain falls in n number of isolated of a continuous one, the infiltration
will be higher in the former case.
Human activities: When crops are grown or grass covers a barren land, the rate of infiltration
is increased. On the other hand construction of roads, houses etc reduce infiltration capacity
of an area considerably.
Depletion of groundwater table: Position of groundwater should not be very close to the
surface for infiltration to continue. The quantity of infiltrated water entering into the soil
should be drained out fully from the topsoil zone so that there is some space available for the
infiltrated water to store during next rain.
Quality of water: Water containing silt, salts and other impurities affect the infiltration to the
extent they are present. Salts present affect the viscosity of water and may also react chemically
with soil to form complexes, which obstruct the porosity of soil, thereby affecting infiltration.
Silts clog the pore spaces retarding infiltration rate considerably.
Vegetation: Soil covered with vegetation has greater than barren land. Because of growth and
decay of roots and bacterial activities, dense natural forest provides good infiltration than
sparsely planted crops.
Grain size of soil particle: Other factors remaining the same, infiltration rate is directly
proportional to the grain size diameter. When swelling minerals like illite and montmorillonite
are present in soils, the infiltration rate reduces.
Catchment parameters: A correlation between the drainage density and infiltration can be
established for various basins. Such curves exhibit negative correlation. When the drainage
density increases, infiltration capacity decreases.
Field Measurement Using Infiltrometers
Single tube infiltrometer: This is a simple instrument consisting essentially of a metal cylinder,
30 cm diameter and 60 cm long, open at both ends. This cylinder is driven into the ground to
a depth of 50 cm (Fig. 4.12). Water is poured into the top part to a depth of 5 cm and pointer is
set to mark the water level. As infiltration proceeds, the volume is made up by adding water
from burette to keep the water level at the tip of the pointer. Knowing the volume of water
added at different time intervals, the plot of the infiltration capacity versus time is obtained.
The experiments are continued till a uniform rate of infiltration is obtained and this may take
two to three hours. The surface of the soil is usually protected by a perforated disc to prevent
formation of turbidity and it’s setting on the soil surface. Sufficient precautions should be
taken to drive the cylinder into the ground with minimum disturbance to the soil structure.
The major criticism is that water spreads out immediately beyond the bottom of the cylinder
that does not represent a true condition in the field.
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Double tube infiltrometer: To overcome the objections of a single ring infiltrometer a set of
two concentric hollow cylinders of same length are used (Fig. 4.13). Water is added to both the
rings to maintain the same height. Reading of the burette for the inner cylinder is taken as
infiltration capacity of the soil. The outer cylinder is maintained to prevent spreading of water
from the inner one. The important disadvantages still prevalent in these types of infiltrometers
are: (i) the raindrop — impact effect is not simulated, (ii) the driving of the tube or rings
disturbs the soil structure, and (iii) the results of the infiltrometer depend on some extent on
their size. Larger diameter infiltrometers give more accurate and always lesser value of infiltration
than smaller diameter type.
O u ter rin g
In ne r rin g
GL
G .L .
Fig. 4.12 Single tube infiltrometer. Fig. 4.13 Double tube infiltrometer.
Solution:
Time Time Cumulative Infiltration Depth (cm) Rate of
Hr – min Difference Time Point Gauge Difference Cumulative Infiltration Remark
(min) (min) (min) Reading Depth I=(5)/(2) × 60
1 2 3 4 5 6 7 8
10-31 - - 14.5 - - -
1 00
C um u la tiv e In filtra tion D e pth (cm )
10
0.514
y = 1.2 t
0 .1
1 10 1 00 1 00 0
Figure # 6 (i)
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20
18
14
12 0.514
y = 1 .2 t
10
0
0 50 1 00 1 50 2 00 2 50
Figure # 6 (ii)
35
30
R a te o f Infiltra tio n (cm /h r)
25
20 0.486
I = 0 .6 16 8 t–
15
10
0
0 20 40 60 80 1 00 1 20 1 40 1 60 1 80 2 00
C u m ulative Tim e (m in)
Figure # 6 (iii)
Fd = Pd – SRD – Sol, where Fd is the depth of infiltrated water in mm, Pd the simulated
measured rainfall depth in mm, SRD the measured surface runoff depth in mm, Sol the depression
storages, surface detention, abstraction and other losses in mm. When steady state is reached,
the analytical run is carried out, the volume Sol being no more effective, the constant rate of
infiltration is calculated from the relation Fd = (Pd – SRD). When rainfall stops, runoff from the
plot continues and the values of depression storage plus surface detention can be measured from
the recession between stop of rainfall and the last drop of water flowing out of the plot as runoff.
Block furrow method: The method consists of blocking the furrows at two ends, unit distance
apart so as to assess the volume storage difference in the furrow in relation to time. The
instrument includes a float mechanism and a water stage recorder. In this method, PVC plates
are inserted at a spacing of 1 m. Water is applied from the tank into furrow regulating it in such
a way that water level in furrow remain constant through out the test. Thus, water test from
the furrow due to infiltration is refilled by supply tank. To measure the rate of infiltration the
fall of the level of water in the supply tank is measured by piezometer for a fixed interval of
time. The volume of water lost can also be calculated for the same interval of time. Equivalent
depth of infiltration is obtained by multiplying the difference of piezometric reading with ratio
of water supply to water applied.
Volume of water supplied = πr2h .
Volume of water applied = spacing of furrow in cm × 100
r = radius of supply tank in cm.
A graph can be plotted between the rate of infiltration and cumulative time, and also
between the depth of water in tank and time. The depth versus time curve will be a parabola.
dy
Let the equation of curve be y = α. tβ. To obtain rate of infiltration I = = α.β.tβ–1
dt
B LO CK F UR R OW INF ILTR O ME T ER
FIE L D C H A N N E L
B LO C K E D B Y S T E EL P LA T E
S P A C IN G O F
W
FURROW
1m
PIE Z O M E T E R
S U P P LY TA N K
VA LV E
S T E EL P L AT E
h
1 5 C M B E L LO W
FURROW
W AT E R B O T TO M
S U P P LY P IP E
HOOK GAUG E
FURROW
1 m LE N G TH
B LO C K
S T E EL P L AT E
#7 Following data collected on a farm for blocked furrow infiltrometer test. Diameter of a
drum of supply tank = 30.8 cm and spacing of furrows are 70 cm; obtain the equation for
cumulative infiltration depth y versus cumulative time T and rate of infiltration.
Time Piezometer Reading in Supply
Remark
Hr-min Tank (cm) 26.8
9 – 06 26.8
9 – 08 21.1
9 – 10 15.0
9 – 12 11.2 / 25 Refilling
9 – 15 17.1
9 – 20 26.3
9 – 25 15.7
9 – 50 13.4
10 – 00 22.7
11 – 50 6.4
71 Energy Management Water Losses 71
Solution:
1 2 3 4 5 6 7 8 9
9–06 – – 26.8 – – – –
.774
y = 0 .43 t0
0 .1
1 10 1 00 1 00 0
C u m u la tiv e T im e (m in )
Figure # 7(i)
30
25
C u m u la tiv e Infiltra tio n D e pth (c m )
20
15
0.774
y = 0 .4 3 t
10
0
0 20 40 60 80 1 00 1 20 1 40 1 60 1 80
C u m u la tiv e T im e (m in )
Figure # 7(ii)
35
30
R ate of In filtra tion (c m /h r)
25
20 –0 .22 6
I = 0 .3 32 8 t
15
10
0
0 10 20 30 40 50 60 70
C u m ulative Tim e (m in)
Figure # 7(iii)
73 Energy Management Water Losses 73
π × (15.4 )2 × h
Therefore, y′ = = 0.1064 h
70 × 100
Now from graph of cumulative depth versus cumulative time, y = α . tβ
Therefore, log y = log α + β log t
Y = c + mx
dy
From log – log graph equation, I = =α . β . t β – 1
dt
α = 0.43
Now, y = α.tβ = 0.43 . t0.774
dy
I= =0.43 × 0.770 × t0.774–1 = 0.3328 × t–0.226
dt
Inflow–outflow method: This method is also known as volume balance method. It is considered
to be the most satisfactory one because it gives the average infiltration value by compensating
various errors, inherent in the furrow, arising out of soil heterogeneity, furrow cross sectional
difference, cracks and puddling effects. The cylinder infiltrometer is used for basin and border
irrigation. Inflow–outflow method is most conventional for furrow.
In this method, the furrow is divided into a number of sections and Parshall’s flumes or
other suitable water measuring devices are installed at each station to measure the flow rate.
The furrow cross sectional profile is determined at the representative locations in the test
section with a point gauge before admitting water. The furrow spacing is measured from the
center of the water in the test section and the depth of flow at different points at definite
time intervals are also reckoned. From the above measurements, it is possible to obtain the
furrow cross sectional area and wetted perimeter. The average value of wetted perimeter
multiplied by length of the test section gives the wetted area. Furrow irrigation is determined
by following relationship.
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Accumulated infiltration
Accumulate depth on depth =
Wetted areaof cross section
With the help of point gauge of even section, profile of head and sides is to be calculated.
The point gauge is called the profilometer. Consider average profile for experiment because at
particular section we are not able to know the exact depth and the depth is also not constant
throughout the length of furrow.
Now, in order to get relationship between the infiltration depth (y) and time (t) the power
relationship is assumed between them.
y = α.t β
log y = log α + β log t
Plot the graph of y versus t on log – log graph paper. The intercept on y axis gives log (α)
and slope of the line gives β.
After getting equation of infiltration depth, infiltration rate can be found out as
dy
I= = α.β.tβ – 1
dt
0 m 20 m 40 m 60 m 80 m 1 00 m
PA RSHA LL FLUM E FO R D IS CH ARGE M EASUR EM EN T
X
F IE LD C H A N N E L
0 m
20 m
40 m
P LA N
60 m
TEST
FURRO W
80 m
1 00 m
S E C T IO N
W AT E R S U R FA C E P R O F IL E
0m 2 0m 4 0m 6 0m 8 0m 1 00 m
S E C T IO N X -X
Stream Size Distance Advance Time Wetted Perimeter Furrow Cross-sectional Area
(lit/min) (m) ‘t’ (min) (cm) Corresponding to Average Depth
of Flow (cm2)
20 3.5 21.3 93.00
Solution:
Stream Size Distance Advance Time Accumulated Wetted Furrow Cross-sectional
(lit/min) (m) ‘t’ (min) Inflow Perimeter Area Corresponding to
(lit) q × t (cm) Average Depth of Flow
(cm2)
1 2 3 4 (1 × 3) 5 6
0 .1
0 .1 1 10 1 00
A d van ce T im e (m in)
Figure # 8 (i)
4 .5
4
A c cu m u la ted D ep th of Infiltra tio n (cm )
3 .5
2 .5
0.56
1 .5 y = 0 .6 t
0 .5
0
0 5 10 15 20 25 30
A dv a nc e T im e (m in )
Figure # 8 (ii)
Sample calculation:
1. Accumulated inflow = q × advance time = 74 × 3.5 = 259.0 lit
2. Accumulated storage = cross-sectional area × distance = 93 × 20 × 100 = 186000
cm3 = 186 lit
3. Wetted area = wetted perimeter × length from upstream end of furrow = 21.3 × 20
× 100 = 42600 cm2
4. Accumulated infiltration = accumulated inflow – accumulated storage = 259 – 186
= 73 lit = 73,000 cm3
5. Accumulated depth of infiltration = (accumulated infiltrated volume/wetted area) =
(73,000/42,600) = 1.71 cm
y = 0.6 t0.56
Take t = 6.83
y = 0.6 (6.83)0.56 = 1.76 from graph and from table
y = 1.65
per cent error = [(1.76 – 1.65)/1.76 × 100] = 6.25%
equation y = 0.6 t0.56
5 WATER CONSERVATION
5.1 INTRODUCTION
The term conservation has been widely used in different fields. Economists consider
conservation as managing the resources in such a way that maximum human needs will be
satisfied. The water conservation can be considered as prevention against loss of waste.
Technically, this can be achieved by putting the water resources of the country for the best
beneficial use with all the technology available in hand. As far as India is concerned, in most of
the places, there is a rainfall during monsoon months and very little rain during other months.
The monsoon rainfall often comes in pattern, which leaves some drought period in between.
For this drought period, conservation of water is necessary. Conservation of water in drought
prone area will help in providing more irrigation for development of agricultural potential of
these areas.
(ii) Rainfall cistern system: In a rainfall cistern system, runoff collected from roof tops
of the houses is used for various purposes including irrigation in droughts of short
duration of 10 to 15 days.
(iii) Weather modification: Modifying suitable clouds artificially can augment the rainfall
in areas. Weather modification can be of much use when shortage in water supply is
acute. Even a small contribution from seeding is helpful and economically acceptable
in such critical situations.
Effective Use of Surface Runoff: Manipulation of vegetative covers, soils, snow and other
measures in a watershed can jointly increase water yield. Water losses from large bodies can be
minimized by using some chemicals like aliphatic alcohols, acetyl alcohol etc. Floating blocks
of wax and certain light material like rubber can also be used as evaporation suppressant. In
one such experiment at Stevens Creek Reservoir in Australia hexadeconal chemically known
as acetyl alcohol was used. Though this chemical is cheaper and does not impart any colour,
odor, or biological activity to the water still there is a scope for research in this field. At Aji –
I reservoir near Rajkot in Gujarat state of India, acetyl alcohol in the form of powder was used,
which gave very successful results. Due to the above treatment, the average saving in
evaporation losses was found to be of the order of 16.5%.
Improving Groundwater Storage: The groundwater is used by pumping from aquifers. For
groundwater, a hydrologic equilibrium must exist between all water entering and leaving the
basin or aquifer. The equilibrium can be maintained by artificial recharge. In artificial recharge,
it is tried to spread water on more and more area for deep percolation into the ground. The
spreading of water may be done by flooding water in a relatively flat area, constructing basins
by excavation or by construction of dykes or small dams.
Soil Conservation: Erosion is the detachment and transportation of the soil, which will affect the
plant growth. It necessitates need of soil conservation. Soil and water conservation of agricultural
land are somewhat same which include contour farming, mechanical measures such as contour
bunding, graded bunding, bench terracing on steep slopes and run off harvesting storage.
Reduction of Seepage: By lining of canals and channels seepage can be reduced, leading to saving
of water. According to US Department of the Interior Bureau of Reclamation, different lining like
hard surface lining, buried membrane linings, earth linings can be practiced for this purpose.
where aquifers for such storages are available and these do not entail higher lateral
dispersion losses. Subsurface dams can also be constructed in such schemes to prepare
limited aquifers and thereby raise the level of storage, reducing subsequent pumping.
Subsurface dams or underground check dams have been constructed across streams
or rivulets in water deficient areas to hold groundwater and recharge the adjoining
limited aquifers. One of the outstanding applications of this method was recharge of
the aquifer (adjoining Talaji rivulet near the town Talaji, Gujarat, India) where
significant water level rises were registered after the limited monsoons. The main
advantage of this method is that loss of valuable lands and forest areas due to surface
submergence can be avoided. Unlike in the case of surface storages, the evaporation
losses are minimal. This method consists of managing the available reservoir in
conjunction with other reservoirs by drawing water for consumption such that the
aggregate area exposed to evaporation especially in summer months is minimum.
(f) Minimizing exposed water surfaces through storage management or integrated reservoir
management.
Biological Methods: There are many locations requiring phreatophyte control to reduce
non-beneficial consumption of water by plant growth of little economic value. Salt cedar, willows
and cottonwoods not only consume large amount of water but they also aggravate meandering
thus causing further water loss. Techniques of phreatophyte control are being perfected and
continued research proposes further improvements. A major difficulty however is that effective
control generally requires repeated treatment with resulting high costs. Possibly this may be
relieved by management techniques that will result in grasses becoming established in place of
the phreatophytes.
Chemical Method: These methods although useful to certain extent and have been used
successfully in some areas, cannot be used for the entire water surface available in the country.
One of the novel methods used for reducing the evaporation from water surface is the chemical
method. There are some compounds called long chain fatty alcohol, which when put on water
surface spread spontaneously and form a monomolecular film. This technique of spreading
monomolecular films for suppressing water evaporation has been tried on a large scale in
Australia for the first time in early 50s using monomolecular films of cetyl alcohol. This water
evaporation retardant was also called hexadecanol having a formula C16H33OH. This is a white
waxy crystalline solid compound generally available in flakes or powder form and is derived
from tallow sperm oil. Its specific gravity 0.85 and melting point 50°C. The monomolecular
film formed by hexadecanol on water surface is only about 0.015 micron in thickness. Another
long chain fatty alcohol called stearyl alcohol having a formula C18H37OH is also used with
cetyl alcohol. Cetyl alcohol was mainly used as a retardant. In some cases cetostearyl alcohol
i.e. mixture of cetyl and stearyl alcohols were used as effective evaporation retardants.
These chemicals can be dispersed in different forms:
(i) Solution using suitable solvents.
(ii) Fine powder, as molten liquids or as slurry.
81 Energy Management Water Conservation 81
Application in the form of solution has several advantages: (i) spreading rate is fast; it is
independent of temperature and slightly affected by increasing chain length of alcohol, (ii)
relatively small amounts of solution are needed to generate a film, and (iii) being in liquid
form, continuous application is simplified.
The disadvantages are: (i) the solution cannot be used in late full winter and spring, and
(ii) the cost of the solvent would be prohibitive unless suitable wind activated dispensers
could be developed.
In emulsion form, the advantages are: (i) it yields a satisfactory spreading rate and high
evaporation suppression ability, (ii) the unit material cost is much lower than in solution, and
(iii) ease in dispensing with a wind activated screw dispenser. The disadvantages are:
requirement of an emulsifier which is to be cleared by health authorities, and total cost of
material and transportation might be higher than for power.
will be at a pressure 40 dynes/cm. Riedeal used monolayer of fatty acids and found that
the evaporation reduction depends on the film pressure or surface concentration. R.
McArthur and Durham from their studies demonstrated that the efficiency of the monolayer
to reduce evaporation increased with dosage as expressed in multiples of the theoretical
quantity needed to form monolayer up to a maximum value after which a constant efficiency
was reached.
Polymorphism
Polymorphism is the property possessed by certain chemical compounds of crystallizing in
several forms, which are generally different. Two properties of long chain n¾alcohols in the
application of the materials to reservoir surfaces for retarding evaporation are the spreading
rate of the monolayer as it forms from the floating alcohol crystal and permeability of the
monolayer to water vapour molecules. Both these properties depend in part on the chain
length of the alcohol. The spreading rate also depends on which polymorph of the alcohol is
present. The polymorphic changes of alcohols, in turn, occur at temperature, which depends
on the chain length.
Film Pressure
The film pressure should be of the order of 40 dynes/cm because evaporation reduction is the
greatest in that range and substantially decreased effectiveness results from lower film pressure.
Maintenance of optimum film pressure with additional material is complicated by temperature
effect. To obtain high efficiency in evaporation reduction, it is necessary that, as the temperature
changes, first to generate a fully compressed layer at the highest possible degree of compression
by continuous supply of fresh retardant material to compensate for loss due to attrition, etc.
Effect of Impurities
Effective life of alkanol film depends on its continued existence in the liquid condensed state.
Bodies that cause solidification on the film are therefore detrimental. Dust, carbonaceous matter
and possibly algae solidify on the film and if the contaminants have sufficiently high specific
gravity, they cause the film to sink.
The film destroying impurities most commonly met in practice are proteins arising from
aquatic life and carbonaceous dust. The spreading front of the solvent, if alcohol is dispensed
in solution form, helps to clean protein deposits off the water surface. The effective life of the
monolayer is, therefore, shorter on the reservoir water than on tap water.
Effect of Wind
There are several factors influencing the survival and effectiveness of monolayer of which
wind can be considered the most important. The rate of movement of monolayer is a function
of the wind velocity. With winds 24 to 32 km/h, it appears impracticable to maintain any
appreciable coverage. On the basis on the experiments conducted in Australia, it is stated that
for wind up to 8 km/h evaporation saving has been 40% or more. When wind velocity is 24
km/h or more, no saving can be effected.
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5.5 EQUIPMENTS
Following are the main equipments required:
Floating Rafts: This dispensing unit consisting of a drum of capacity 181.83 liters installed on a
floating raft 2.49 m × 2.49 m in size (Fig 5.1). The raft is constructed of light material, about
38.10 mm thick over six floating drums. Attached to the floating raft is a frame carrying a drum
of capacity 18.18 liters, which is kept floating on the surface. The delivery unit comprises of a
control valve and a delivery tube, which draws the solution from the 181.84 liters drum, with its
delivery and kept 76.20 – 152.40 mm below the water surface by the float drum of 18.18 liters
capacity. The number of raft dispensers depends upon the shape and extent of water spread.
Ve n t
L evel g auge C o ntrol valve
(o ptio na l)
Filter
L ug w e ld ed
to d rum
P ivo t
Floa t
W ater le ve l
P.V.C . tube
a tta ch e d to flo at
R a ft disp e ns er
Shore Dispensing Unit: This type of dispensing unit consists of 181.84 liters drum installed
on a portable stand made of mild steel angles (Fig 5.2). These are placed on the periphery of
the water spread to deliver the solution at the shoreline. The position and location of these
depend on extend of water spread and direction of wind.
L e ve l ga u ge o ptio na l
W in d va ne
Ve n t
Boat: One ordinary rowboat or motorized one for towing the floating rafts, and for going over
the water spread for testing the surface pressure is required.
Meteorological Equipments: Temperature of air and humidity are measured by using
maximum and minimum thermometers, wet and dry bulk thermometers or any other type of
hygrometer. These thermometers being housed in standard Stevension screen. Anemometers
either direct reading or recording type, measure temperature of water.
1.0 Name of the organization Karnataka Engineering Research Institute, Junagadh Irrigation Division
Krishnarajasagar
2.0 Address Karnataka Engineering Research Institute, Junagadh Irrigation Division,
Krishnarajasagar, India Junagadh, India
3.0 Name of reservoir Kukkarahalli Tank Khodiyar Irrigation Scheme
3.1 Total capacity at
(a) FRL (WS 66.77 Ha) Max depth 10.67m 38.22 Mm3
(b) Sill level ---- Nil
3.2 Levels at
(a) 75% Capacity Not available RL 24.16 Mm3
(b) 50% Capacity Not available RL 16.11 Mm3
4.0 Total losses including 2.893 Mm3/day 4.26 Mm3
seepage loss
4.1 (a) Method of estimation which methods have been adopted at By pan evaporimeter
of evaporation loss Karnataka Research Institute,
(b) Comparative study Krishnarajasagar By standard of CDO
of different method
4.2 Method for estimation of Only savings effected per day has been By V Notch
seepage losses found out by eliminating seepage loss
5.0 Evaporation loss
(a) In winter season Nil 2.688 Mm3 in Rabi season
(b) In summer season Only savings effected per day has been 1.578 Mm3 after Rabi season
found out
6.0 Seepage loss at
(a) FRL Seepage loss has been eliminated 0.05m per month (CDO
Standard)
(b) Intermediate level — 0.05m average per month
7.0 Retardant used for Cetyl alcohol surface treatment with Cetyl alcohol
reduction of evaporation chemical retardant
loss with method and experience
8.0 Saving in evaporation loss Not available 10% (3.22 Mm3)
8.1 % of total capacity of
reservoir
8.2 % of summer capacity of Not available 26.29%
reservoir
9.0 Year and period of study Feb, April, May 1962 28/4/1988 to 14/6/1988
10.0 Meteorological data Not available Not available
pertaining to period of
study
87 Energy Management Water Conservation 87
1.0 Name of the organization Water Resources Department, Gujarat Hindustan Zinc Limited
2.0 Address Bhavnagar Irrigation Division, Pan Hindustan Zinc Limited,
Wadi, Bhavnagar, India Zinc Smelter, Udaipur, India
3.0 Name of reservoir Malan irrigation Scheme Udaisagar lake
3.1 Total capacity at
(a) FRL 11.44 Mm3/FRL 104.26 m 29.73 Mm3 / FRL 551.83 m
(b) Sill level 0.00 mcft 93.90 m 3.54 Mm3 at 544.43 m
3.2 Levels at
(a) 75% Capacity 103.26 m 550.75 m
(b) 50% Capacity 102.03 m 549.50 m
4.0 Total losses including 0.65 Mm3 0.7618 Mm3
seepage loss
4.1 (a) Method of estimation Thin film by Cetyl stearyl alcohol Pan evaporation
of evaporation loss measurement
(b) Comparative study if Not done Not done
different method
4.2 Method for estimation of Assumed 0.12% per day Seepage is nil being
seepage losses impervious bed of the lake
5.0 Evaporation loss
(a) In winter season 1.26 m without WER chemical, and 0.2685 Mm3 (21/1/87 to 28/2/87)
(b) In summer season 1.02 m using WER chemical 0.4933 Mm3 (1/3/87 to 15/6/87)
6.0 Seepage loss at
(a) FRL Not available Not available
(b) Intermediate level 0.28 m in summer Here seapage log has to be
given not the capacity
7.0 Retardant used for reduction Cetyl alcohol in powder form (dusting Retardant used was ACILOL
of evaporation loss with from boat) TA – 1618 WER
method and experience
8.0 Saving in evaporation loss
8.1 % of total capacity of Not available 0.80% (0.22772 Mm3)
reservoir
8.2 % of summer capacity of 9.15% Not available
reservoir
9.0 Year and period of study 1/3/1988 to 31/5/1988 21/1/87 – 15/6/87
10.0 Meteorological data Wind velocity: 11.17 km/h Wind velocity – 15 – 20 km/h
pertaining to period of Temperature: Max. Min & Max Temp – 6°C & 46°C
study 1800 hrs – 37.87°C
D B Temperature 800 hrs – 28.50°C Relative humidity – 14% to 60%
1800 hrs – 34.70°C Panevaporimeter – 10% to 47%
W B Temperature 800 hrs – 23.00°C Wind direction – Towards east
1800 hrs – 27.00°C Lake temperature – 5°C to
45°C Rainfall - Nil
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Following table gives a list of countries where Cetyl alcohol was successfully used.
Sr. Percentage
Country Observations Remark
No. Saving Effected
1 Australia Reservoir of areas from 2 to 20 acres 20 to 70%
2 Japan Evaporation pans over a period of three 53% OED paste
months in summer
3 USA USA Laboratory experiments 13 to 60%
4 Australia (CSIRO) — 52%
5 USA 100000 gallons capacity aerator tank 30 11% Sept 14 to 23 & Oct
feet diameter and 14 feet deep 11 to 18
33% August 30 to Sept 7
6 South Dakota Pactola 14%
7 Nairobi Reservoir area 6.5 acres 30%
8 Tabora, Tanzania Reservoir of 105 acres water spread 30%
9 Malaya — 11%
10 Spain Reservoir areas 31 acres 35% 4% solution in
white spirit
31% 35% solution
kerosene
Type of Soil First Foot, Per Cent Pounds Per cu. ft Second Foot, Percent
Clay soil contained 33.91 26.79 26.60
with a fine, dry clay loam to a depth of 0.5 inch to 0.75 inch, the daily loss was then at the rate
of 6.33 tonnes per acre per day for the naked surface, but only 4.54 tonnes and 2.4 tonnes for
the mulches, respectively.
There is thus left no room to doubt the efficacy of dry earth mulches, as conservators of
soil moisture, but it should be said that not all soils are equally effective in their power to
diminish evaporation.
Influence of Vegetation
Organic matter: The influence of vegetation upon infiltration and soil water storage is
particularly due to the effect of organic matter on and in the soil and plant roots. Measurements
have shown a positive correlation between the quantity of organic matter present in the soil
and its water holding capacity. Increased soil porosity and water absorbing capacity have been
found to follow forest planting in fields formerly cultivated.
Plant roots: Channels left by decayed roots also perform an important function in percolation
and storage of water.
Plant and animal life: The soil under a relatively undisturbed forest and range cover is the
home of much animal life. In the process of nutrition, the worms pass great quantities of soil
and organic debris through their bodies, thereby together with bacterial action, promoting
91 Energy Management Water Conservation 91
humification and the incorporation of organic matter with mineral soil. All such life, plant and
animal influence the moisture intake and moisture holding capacity of the soil, either directly
or indirectly. Any modification of the plant cover and surface soil by cultivation, burning or
overgrazing induces conditions unfavorable to the optimum development of these soil fauna
and flora and results in a reduction in the capacity of the soil to take up water.
Sheltering: Vegetation shades the ground and minimizes wind movement. The effect tends to
reduce evaporation and snow melting rates. It is found that evaporation of water from snow in
forest areas may be only about one third as fast as from open areas. Also snow-melting rates
have been observed to be as much as one third more rapid in the open than in the forest.
Stream temperature: D R Dewalle et al., (1977) have demonstrated that (i) maximum daily
water temperatures near inlet in the unshaded reach increase almost linearly with distance,
and (ii) farther from the inlet, maximum water temperatures increase exponentially and approach
an equilibrium condition.
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6 RAIN WATER HARVESTING
6.1 INTRODUCTION
According to the National Drinking Water Mission, a village is classified as a problem village if:
• The source of water i.e., a well or hand pump is located at a distance of more than 1.4
km from habitat.
• The source dries up during the summer months.
• The source has inadequate supply. The Government norm for adequate supply in
rural areas is 40 liters/capita/day and 30 liters/cattle/day.
• If the source contains total dissolved solids/arsenic/fluoride/iron in concentrations
above their permissible limit.
According to Agarwal (2000), the number of such problem villages identified in 1972 was
150,000 and out of these, 94,000 were provided a source of drinking water by 1980, as per
Government records. The number of remaining problem villages should then have become
56,000. However, a separate inventory showed that the total number of problem villages had
now become 231,000 in the same year 1980. Again according to Government reports, 192,000
villages were provided a source by 1985, but 140,975 villages remained without a source. Out
of these, by 1997, the problems of 110,371 villages were apparently addressed, but still the
number of remaining problem villages was 61,747 instead of 30,604 which one can obtain
through simple subtraction.
This bewildering and confusing statistical jugglery is a sad reflection on the failure of the
methodology used till now in solving the problems, which have also increased manifold over
the years. It also means that:
• The solutions found to problem villages were not sustainable.
• Some new villages which were earlier having an adequate source have turned
‘problematic’, possibly because of over-exploitation and
• The increasing practice of tapping deeper aquifers has led to problems of drinking
water quality.
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94 Water Management
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One important point to be noted is that in all the Government machinery approaches so
far, the methodology adopted was to locate what was already provided for by nature if possible,
at the problem village itself, or otherwise provided through expensive pipelines from elsewhere,
where the natural source was available at that point in time.
There was hardly any attempt at creating a new source at the problem village itself through
harvesting and conserving the precipitation endowment received annually.
The second reason was that the Government efforts failed at the operation and maintenance
level. This happened because the people were not involved in the process of solving the problem.
The people were neglected and in turn they neglected the upkeep of the sources made available
by the Government department.
Rain water roof catchment systems (RRCS) as existing in many individual homes of the
states mentioned were also surveyed and studied. Among the north–eastern states of India,
Arunachal Pradesh, Nagaland, Mizoram, Manipur, Meghalaya, Assam and Sikkim, RRCS are
accepted particularly in those places where the homes are scattered and the piped water supply
system could not reach individual homes. In contrast, the RRCS cannot be applied in densely
populated areas, where there are many industries/factories or excessive traffic load is causing
to precipitate acid rains. In all the states as mentioned the average rainfall is of the order of
1500 – 3000 mm and there is no concentration of industries.
There are areas where there is no problem with groundwater quality, or where the water
table in the monsoon season does not rise up to ground level. In such areas, it is desirable and
cheaper to recharge the collected precipitation into the groundwater reservoir through a
percolation pit in the ground or through an existing open well or a tube well. However in
areas where the groundwater quality is poor due to excess occurrence of dissolved salts/fluoride/
arsenic or due to anthropogenic pollution, surface storing in sumps or other storage structures
becomes a necessity. Sumps are also the only option for storing the roof harvested water in the
case of a hilly terrain, having slopes or a laterite cover, as in such areas, aquifers having adequate
storage capacity are generally absent.
If roof water harvesting is practiced on a large scale in an urban area, then it also helps in
reducing the severity of floods, which follow a heavy downpour. Similarly if it is used for spot
recharging by large number of households, then it helps in restoring the water table and also
in improving the quality of water. Another benefit accruing from roof water harvesting in an
urban area is that it reduces the demand on the municipal water supply system that in general
is inadequate to meet the needs of each and every household.
G u tte r
Stora ge Tan k
Ta p
H o le in gu tte r
Ta r
D o w n P ipe
S cre en ing
G u tte r
D o w n P ipe
S ec o nd p iece o f ru bb e r w ra p pe d
o n o utside of dra in p ip e
F le xib le jo in t fo r do w n P ip e
The Roof Area: To collect rainfall, the roof must be constructed of appropriate material such
as corrugated metal, clay tile and locally available materials; also have sufficient surface area
and be adequately sloped to allow run-off.
Corrugated metal is light in weight, easy to install and requires little maintenance. However,
it may be expensive or unavailable in isolated areas where rainwater roof catchment system
may be most applicable.
Clay tiles make good surfaces and are usually cheaper and longer lasting than sheet metal
because they can be produced locally. However, the manufacturer of clay tiles requires a good
source of clay and fuel for firing. The disadvantage of tile is their weight. A strong roof support
structure is required for supporting the tiles. Roofs constructed of thatched materials such as grass
and palm leaves have proved to be inexpensive and durable. The disadvantage of thatched roofs is
that the run-off contains organic matter, is yellowish in colour and smells of decomposed leaves.
For this reason, thatched roofs should be used in conjunction with a simple filtration device.
The Gutter System: Effective guttering is an important part of the rainwater roof
harvesting system. Water must be efficiently conveyed from the roof to the tank to meet
the homeowner’s demands. A good gutter material should be lightweight, water resistant
and easy to join. To reduce the number of joints and thus the likelihood of leakages, a
material that is available in long, straight sections is preferred. Metal gutters are most
durable and require the least maintenance. However, they are the most expensive.
Regardless of the material selected, the gutter should be large enough to channel water
from heavy rains without overflowing. A gutter with a cross-section of 100 sq. cm is usually
98 Energy
98 Water Management
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sufficient to meet this requirement. The minimum recommended depth is 7.0 cm for any
gutter. The gutter should be placed at a uniform slope to prevent water from pooling or
overflowing. The slope should be about 1 cm per meter. To collect the water running off
during light and heavy rains, the roof should overhang the gutter by 1 or 2 cm. The gutter
should extend beyond the roof edge by about 7 cm.
The Storage Tank: A satisfactory storage tank is the most important part of the rainwater
roof water harvesting system. It is difficult to construct and must be a durable device, hence it
is the most expensive component of the system. The materials used are masonry, concrete,
ferro-cement, plastic, metals sheet etc. The design stage of the project involves sizing the storage
tank. There are a number of methods that can be used to determine tank volume.
Dry Season Demand versus Supply: This approach considers the length of the dry period
as a design constraint. The tank is designed so that it accommodates the household demand
around during the dry season. For this reason, the method is most appropriate where there is
a definite wet/dry period during the year.
The length of the dry period can be estimated by:
• Asking farmers and residents about the longest drought they remember.
• By estimating from official weather analysis data the number of consecutive dry months
per year. The dry season demand versus supply method should also consider the
maximum drought length in light of its probability of occurrence.
The dry season demand versus supply gives only a rough estimate of supply and demand.
However, it does not take into account variations in annual rainfall patterns. A better method
of tank sizing involves the Mass Curve Analysis Technique.
Mass Curve Analysis: A more accurate method of sizing a tank involves an analysis of data
using the mass curve technique. Successful use of the technique requires approximately 10
years’ data.
First, an approximation of the run-off coefficient is required. Some rainwater will be lost during
collection. This amount is represented as a fraction called the run-off coefficient. This is not a
precise value but is estimated on the basis of the type of roof, the condition of gutters and
piping, and the evaporation expected from the roof and tank. Approximate runoff coefficient
values are:
The Filter: Whenever it is apprehended that water may contain dust or other organic matter
from the roof, simple filtration device using crushed charcoal, sand and gravel or coconut
fibers or some combinations thereof as media may be installed over the storage tank.
99 Energy Management Rain Water Harvesting 99
The less use of rain water for latrine is due to the fact that many rural houses do not have
latrine inside their houses and they use jungle/bushes for defecation.
For drinking water, many people carry water from public hydrants or springs, though
they are located at long distances and nowhere, it was found that the people use directly
rainwater collected in the storage tank. Either they boil the water or use some water filter
available in the market.
Only in Tripura in few houses, there is arrangement of adding bleaching powder solution
in the filter; though it is being done in a very irregular way.
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Instead of disinfecting all the water stored in the storage tank, it is desirable to disinfect
only that portion of water, which will be consumed for drinking and cooking. So covered
storage vessel inside the house is required.
ROO F
G u tte r
P V C P ipe 75 m m D ia , 1 .2 m Lo ng
F iller
1 00 cm
1 20 cm
R e m ova ble E n d C ap
W ash o ut valve
GL
3 0 cm
A irven t P ip e
C o ver
R a inw a te r Pipe
E a rth e r P o t fille d
w ith Lim e U n de rg ro un d
Stora ge ta nk
(3 .0 × 2.20 × 1 .5 0 m )
Table 6.3 Roof size for generating runoff of 10,000 liters in a locality having seasonal rainfall of 500 mm.
4 Thatch 40 50
Assuming an average rainfall of 500 mm and the per capita requirement of potable water
for domestic use as 20 liters/person and family of five, the storage required to provide
requirements for 100 days (summer season) is 10,000 liters. The roof area required for generating
this amount of runoff in the case of roofs of different types is given in Table 6.3.
These calculations are for storage sump. The roof area is to be increased by about 30% in
cases where the harvested roof water is used for recharging the local aquifer. This is because
only about 70% of the recharged water can be recovered through pumping.
The roof area will proportionately increase or decrease if the local rainfall is less or more
than the 500 mm value used in this model calculation. In general, the non-monsoon period
rainfall amounts to 15% to 20% of the total annual rainfall. The rainfall value used for the
calculations in Table 6.5 is for the monsoon season. Any shortfall in the average annual rainfall
by 15% to 20% will not therefore reduce the total runoff stored in the 10,000-liter tanks.
However, it is advisable, especially in the case of low rainfall areas that the roof area be kept
20-25% larger than that calculated using the average seasonal rainfall. Such a step would
compensate for the effect of low precipitation in drought years.
and is also promoting this practice to alleviate water insufficiency. It is also engaged in
demonstrating how water harvesting can be put into actual practice. The CSE building is
located on a 1000m2 plot. Residents are practicing both surface storage and recharge of the
rain endowment received on their plot since 1999, Figs. 6.4 to 6.8.
A b an d on ed b ore w e ll
C h eck b un d
U n de r g ro un d
w a te r ta nk
S o ak w a ys
Fig. 6.4 Schematic diagram of water harvesting system at CSE, New Delhi (Renade, 2000)
Fig. 6.4 Shows map of the building and compound area of the CSE, New Delhi showing
various components of an integrated water harvesting system (Ranade, 2000).
F ilter b ed su m p
6 0 cm × 60 c m × 6 0 cm
P erfo rate d/
h on ey co m b ed
2.5 - 5 m d ee p
b ric kw o rk
1 0 m d ee p
B ric kb a t filte r m ed ia
Fig. 6.5 Schematic diagrams of a recharge pits and a soakway (Ranade, 2000).
104 Energy
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f
Run n of
o ff Ru
P e rfora te d p ip e
F ilter b ed
R e cha rge du g w e ll
Fig. 6.6 Recharging a dug well with run-off water (Ranade, 2000).
Pe rfo ra ted
cove r
Brickbat filter
m ed ia
1 - 1.5 m
0.5 - 1 m
Fig. 6.7 Arrangement for percolation of water accumulated near a compound wall (Ranade, 2000).
Filtratio n tan k
Filter be d
R e cha rge d ug w e ll
Fig. 6.8 Recharging a dug well with harvested roof water (Ranade, 2000).
105Energy Management Rain Water Harvesting 105
The annual average rainfall in Delhi is 600 mm or 0.6 m. The total water endowment of
the CSE premises is therefore 600,000 liters. They have used a combination of surface storage
and various types of recharge devices such as an abandoned bore well and several soak ways.
A soak way is a bore well having a diameter of about 30 cm and depth of 3 to 10m and is cased
with a perforated pipe. A soak way may be filled with filter media such as brick fragments,
gravel and coarse sand. A small sump is built at the top of the soak way to prevent a gush of
water in the soak way (Fig. 6.5). The annually harvested water quantity is estimated as 366,000
liters or 65% of the received rainfall. CSE claims that during the last two monsoon seasons not
a single drop of rainwater drained out from their premises, even after a heavy downpour. We
may therefore assume that the remaining 35% of the endowment is used in soil moisture
replacement, evapotranspiration by garden plants, and natural recharge or evaporation loss.
The total cost of installing the various units excluding cost of pre-existing underground water
tank and pond is estimated at Rs. 36,000.
Example 2: Water-born bacteria and viruses are rampant during the monsoon season. Slum
dwellers are particularly prone to cholera, diarrhea and other water-born diseases. Provision
of clean water is very important. Tamil Nadu chapter of the National Water Harvesters Network
has developed a water harvesting structure of 3000 liters capacity on a tenement building in
Kuil Thotam, a slum area of Chennai, using a roof area of 1.85m × 1.85 m. Chennai has an
annual average rainfall of 1200 mm and receives some rainfall every month. Some clean water
can get collected in the Sintex tank (Fig. 6.9). Over 1500 liters of water was collected in the
Sintex tank during the first few rain showers in actual practice. The harvested water was
subjected to laboratory tests and found to be of potable standard.
ip e
rp
te
wa
R a in w ate r p ipe R
O p en spa ce
S an d
S m a ll P eb b le
b ed
M e d iu m P eb b le
b ed
F iltra tio n Ta n k
F iltration Tan k
D e ta il
Fig. 6.9 Roof water harvesting system at a slump tenament in Kuil Thotam, Chennai (Khurana, 1999).
106 Energy
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A commonly raised quarry by those intending to install facilities for recharging the harvested
water is about the rate at which the runoff from roof or ground level will be accepted by the
local aquifers. This is a difficult question to answer generally. The hydraulic conductivity (k)
of soils or aquifer material is a key parameter, which varies very widely. For example, clean
gravel has k values ranging between 1 and 100 cm/sec while the k value for sandy loam ranges
between 0.003 to 0.005 cm/sec and that of clay can be less than 0.00001 cm/sec. Soils are
mixture of gravel, sand, silt and clay whose proportions in the soil vary from place to place.
The best way to know the infiltration rate is by a trial experiment. It is also advisable to
provide buffer storage Ranade type figure (Fig. 6.5). This will ensure that the runoff after a
heavy storm does not overflow the recharge pit.
In spite of limitations, the village ponds, the bulk water requirement for half the year is met
from them. Small groundwater mound formed under the pond bed, used to partially supply
through wells dug in the pond bed. This traditionally practiced rainwater-harvesting structure
served water supply since ages. During scarcity years, some deepening of ponds is made, but it is
being done on a haphazard manner, does not help much.
Pond Lining
The limitations of the traditional ponds, especially the quality deterioration and seepage losses
could be completely stopped by using plastic membrane. The simple technique has proved
effective. The evaporation loss could be checked by use of chemical retardants and adopting
system of multiple ponds system (compartments). Limitation of the depth factor has to be
accepted and required storage could be built by increasing the length and breadth of the pond.
Of course, the places where salty water table is at greater depth, pond storage can be increased
even with less open surface, and thereby reducing the evaporation loss. Such favorable locations
may not be provided with plastic lining, provided the rate of salt contamination from sediments
is within limits. Plastic lining is a rather costly proposition, however, it envisages the use of
local water resources and regular maintenance is almost negligible.
This technology involves lining of the walls and floor of the pond, tank reservoir with
tough, wide-width low-density polyethylene (LDPE) film. These LDPE films are available in
widths of 4 to 12 m and thickness 100 to 250 microns. These films meet specifications as per
IS: 2508 – 1984. This film has excellent water barrier properties, very good blend of physical
properties such as tensile impact strength coupled with good weatheribility and chemical
resistance properties. These films also prevent the inherent salinity of the soils and saline
groundwater from seeping into pond or tank and starts contamination. The construction of
plastic lined pond includes excavation work, screening work for removing big boulders and
sharp-edged gravel, which could damage the plastic film, dressing of sides and beds so that
lining is not punctured, laying plastic film on beds and sides, brick lining on the sidewalls, soil
filling on the floor, inlet system and distribution system. At present, 19 villages of Bhal area of
Gujarat have 20 such plastic lined ponds (Fig. 6.10).
M on son
W in te r
S u m m er
L aye r of
B lac k S o il
L .D .P.E . F ilm
lay er B rick lining
Fig. 6.10 Water harvesting by means of brick and plastic lined ponds.
108 Energy
Water Management
Management
The study of biological contamination was limited to the investigation of the presence of
total coliforms. Samples from 500 rainwater cisterns were tested. 135 out of 500 samples
contained coliforms and 365 samples contained zero coliforms. The total coliform colony counts
revealed through sample testing are presented in Table 6.5. It reveals that 27% of the cisterns
water in the West Bank is contaminated by coliforms and did not meets WHO drinking water
standards, while 73% is not contaminated and meets WHO drinking water standards. Despite
this finding, it may still be concluded that cisterns water in general is safe and of good quality
for drinking and domestic uses.
Table 6.5 Total coliform counts in 100 ml samples of cistern water in the West Bank
1 – 10 25 5.0
11 – 20 38 7.6
21 – 30 30 6.0
31 – 40 17 3.4
41 – 50 10 2.0
>50 15 3.0
the women can help in mobilizing support for the rainwater collection system raising the
initial capital. Women and children also can contribute most of the labour. The engineer should
collect information on existing catchment technologies and discuss the community the
usefulness of water supplied by a roof system. The community’s need for communal versus
individual catchment system should be evaluated.
The project engineer must also compile a resources inventory of local skills, materials and
experience that can be used in rainwater roof catchment system. Materials, which are easy to
obtain by local people who know how to work with the materials, will result in a rooftop
system that is cheap and simple to build and repair. To make the system widespread, some sort
of financial help is to be given to the villagers. This can be in the form of subsidy or low
interest loan. The Government or local societies can come forward for this so that the whole
burden is not put on the beneficiary itself.
Rainwater collection system, though implemented in many parts of north – eastern states,
is not gaining popularity because the owners do not properly maintain the system. The
water collected in this system is not of standard quality and mainly used for other purposes
except drinking and cooking.
ARTIFICIAL RECHARGE
7 METHODS
7.1 INTRODUCTION
The term Artificial Recharge refers to transfer of surface water to sub-surface aquifers through
human intervention. Augmentation of groundwater resources through artificial recharge can
be considered as an activity, which supplements the natural process of recharging the aquifers
through percolation of a fraction of the rainfall through the soil to the water table. Artificial
recharge thus becomes relevant in a situation witnessed by India, where the rainfall is seasonal
and is not spread uniformly over the year and quantum of natural recharge is inadequate to
meet the increasing demand on groundwater resources.
be used for improving the quality of groundwater in areas where it is brackish or contains toxic
chemicals such as fluoride and arsenic, in concentrations above their permissible limits.
Recharge
Artificial recharge of groundwater can be achieved with surface infiltration system (basins,
spreading facilities), wells trenches, pits, shafts etc. Surface infiltration systems require the
availability of adequate land with permeable soils, vadose zones without restricting layers that
produce excessive perched mounds and unconfined aquifers of sufficient transmissivity to
prevent undue occurrence of groundwater mounds. Also, Vamoose zones and aquifers should
be free from undesirable chemicals (contaminated areas, pollution plumes) that can move
with the recharge flow system to where they are not wanted.
Where suitable conditions for surface infiltration systems do not exist or aquifers are confined,
recharge can be accomplished with wells, pits or shafts. Water source for recharge include any
excess surface water from streams, irrigation canals, aqueducts and storm water runoff.
For unpolluted water, the only pretreatment that may be necessary before infiltration is
sediment removal, as it can be accomplished with pre-sedimentation basins (with or without
use of coagulants) or vegetative filtration in overland flow type systems.
113Energy Management Artificial Recharge Methods 113
Sustainability
Recharge systems using clean water should be completely sustainable. Clogging of the surface
where infiltration takes place will occur because of biological activity and/or accumulation of
suspended solids. For surface infiltration systems such clogging can readily be remedied by
periodic drying and cleaning of the infiltration system (removing the clogging layer by shaving
or scraping the surface). For well recharge, remedy of clogging is more difficult and adequate
pretreatment of the water is necessary to prevent clogging as much as possible. Frequent pumping
of the recharge well (5 minutes each day, for example) to reverse the flow may prevent or
delay clogging. Periodic redevelopment of the well by surging, jetting or other techniques may
keep well clogging under control.
Considerations
The type of the artificial recharge system that can be developed at any specific site is controlled,
to a large degree, by the geologic and hydrologic conditions that exist at that site.
Site selection criteria, in addition to economic considerations, should include at least the
following:
(1) Source of recharge water
(2) Chemical and physical characteristics of the recharge water
(3) Availability of an aquifer suitable for artificial recharge
(4) Thickness and permeability of the material overlying the aquifer, if any
(5) Thickness and permeability of the aquifer
(6) Chemical characteristics of water in the aquifer
(7) Proximity of the potential recharge site to an appropriate well field cone of depression
(8) Water level differences between the aquifer and the recharge site
(9) Topography
Mainly there are three main categories of artificial recharge as listed below.
(A) Direct methods.
(B) Indirect methods.
(C) Incidental methods.
(A) Direct Methods: Direct methods of recharge can further be subdivided into two main
categories as surface methods and sub-surface methods.
A – I: Surface Methods: In this method of recharge, water is applied on the permeable ground
surface where it infiltrates into the unsaturated zone to reach slowly the undergroundwater
table. Surface techniques, especially spreading techniques of artificial recharge are most widely
used because of their economy and easiness in operation. Various types of spreading techniques
are as follows:
• Basins
• Furrows and ditches
114 Energy
Water Management
Management
→
Stre am
F en ce , as req uire d →
→ In ta k e struc tu re s
→
O u tfa ll
M e asu rin g →
→ →
→
→ → 2 M a in te na nce road s o n le vee s
→ 1
→
2 → 1 2 → 1
→ → 1 R e cha rg e B as in
2 In te rb asin C on tro l
s tru ctu res
Strea m M ea surin g
G a te An d D e vic e
. 1 P rev ailin g G ro u nd Slo pe G en e rally G rea ter Th a n 3 %
M ea surin g No D itc h C u tle ts
D e vic e tc h .2 If R e qu ired
Di
No
h
it c
.3
o. 4
7
D C o llecting
No
D itc h N o .
h No
D itch
5
hN
S u pply D itch
ch
o.
lo w
D it c
hN
D it
D itc
et F
D it c
S he
A lte rna tive D ivers ion
a s R eq u ie d
W ire B o u nd C h ec k D a m s as R eq uired
S u pply D itch
D itch
D ra in
O rigina l G ro un d w ater Table
2 q0
z
q0 s0 q0
o rig in al
q0 q0 g rou nd w te r
ta ble
H g alle ry
H0
L 2w L
Q0 Q0 Q0
n n
s0
o rig in al
g rou n dw a te r
H tab le
H0 circ u la r b attery
r o f w e lls
L 2ρ L
Fig. 7.5 Artificial recharge with a spreading pond surrounded by a concentric battery of wells.
116 Energy
Water Management
Management
C o ntrol D itc h
Str eam
DS A . LAT E R A L B ITC H PAT TR E N
DS
DS
m
ea
S tr
B . D O N D R IT E D ITC H PATT ER N
Strea m
ow
Fl
of er
t h at
Pa of W
lo w
a nk
rB
rF
ve
Ri
ve
Ri
k
an
rB
ve
Ri
H O O K LE V E E FIN G ER B IK ES
offers few difficulties. With slight modifications, it may also be applied for artesian aquifers
when the confining layer on top is thin. For confined aquifers covered by thick deposits of less
pervious material, recharge must be accomplished by injection wells, having their own problem
and possibilities. The simplest construction of parallel spreading ditches and infiltration galleries
is shown in Fig. 7.4, where the coefficient of transmissivity, kH, of the aquifer as well as the
maximum allowable drawdown, So, are determined by the local geo-hydrological conditions.
The other factors indicated in this figure, q0, L and w, must be chosen such that the purposes
of the recharge scheme are fulfilled, that is to say, an adequate detention time of the recharge
water in the sub-soil and no rapid clogging of the spreading basins. When it is provisionally
assumed that both the spreading basin and the gallery for groundwater recovery fully penetrate
the saturated thickness of the aquifer, these requirements may be formulated mathematically as
(a) detention time
T = pHL/q0 or q0 = pHL/T
(b) drawdown
S0 = [q0 / (kH)] L or q0 < kHSo
(c) entry rate
ve = q0 / w or q0 < ve w
The last requirement can always be satisfied by increasing the width of the spreading
basin, while the first two requirements give as length and flow rate
L= kS o T/ p q o = (H / T) kS o pT = H kS o P / T
With shallow aquifers composed of fine sand, H and k will be small, calling for a short
length and a low flow rate, which can best be accomplished with the scheme of Fig. 7.3.
With deep aquifers built up of coarse sand and high values of H and k, the length and, in
particular, the flow rate may be much greater. The scheme of Fig. 7.3 may again be used, but
in plan it tends to be rather square, leading more or less automatically to the recharge scheme
of Fig. 7.5, here consisting of a spreading pond surrounded by a circular battery of wells for
recovery of groundwater.
Spreading in shallow phreatic aquifer: The design procedures to be used in this case can
best be demonstrated with an example (Huisman, 1985). Consider an aquifer composed of fine
sand with a coefficient of permeability k = 0.12 × 10–3 m/s, a porosity p = 0.38, a saturated
thickness, Ho, before spreading of 15 m, a maximum allowable rise of water table equal to S0 =
2 m, giving together an average saturated thickness during spreading of H = 16 m. A capacity
Q0 = 30×106 m3/year or 0.951 m3/s is sought, with a detention time T = 8 weeks or 4.84 ×
106 s and a maximum allowable entry rate ve = 0.4 m/day or 4.63 × 10–6 m/s. This gives as
length and flow rate (Fig. 7.4).
2 × 69.5 × 10–6
2w = = 30.0 m
4.63 × 10–6
and the combined length of the spreading basins
0.951
B= = 6840 m
2 × 69.5 × 10–6
the total area between the infiltration galleries equals
A = 6840 × [30.0 + (2 × 55.3)] = 0.962 × 106 m2
This area could also have been calculated directly:
Q oT QT
A= + o = (0.757 × 106) + (0.205 × 106) = 0.962 × 106 m2
pH ve
The amount of water in dynamic storage, that is, in the pores of the formation between the
original and the present water table is
V=p S0 (L + 2w) B, of which a fraction, µ/p, can be used. With, for instance, µ = 0.25
and the other factors as assumed before,
V = 0.25 × 2 × (55.3 + 30.0) × 6840 = 0.292 × 106 m3, allowing an interruption in the
spreading operations for a period, t = V/Qo = (0.292 × 106)/0.951 = 0.307 × 106 s or 3.6
days.
This period will seldom be adequate to let a wave of polluted river water pass the point of
intake. The calculations given above have the attraction of being simple and straight forward,
but they have strongly simplified reality, demanding at this point a number of corrections. The
first simplification is the assumption of a constant saturated thickness, H, in the calculation of
the drawdown, So
So = [qo/(kH)]L = 2.0 m
Taking into account the variations in water table elevation as well as the recharge by
available
-9
rainfall, P (say 400 mm/year or 12.7 x 10 m/s), with the notation of Fig. 3a, the
following as a correct calculation
2q 0L PL2
(H0 + S0′)2 – H02 = –
k k
and for the case under consideration S′0 = 2.01 m, a negligible difference compared with
the value of 2.0 m originally assumed.
119Energy Management Artificial Recharge Methods 119
The second simplified concerns the assumption that the spreading ditch fully penetrates
the saturated thickness of the aquifer and does so over a width 2w. To correct this, the spreading
ditch is first replaced by a fully penetrating one of zero width, increasing the flow length by an
amount w and giving an additional drawdown
qo
∆S1 = w= 0.51 m
k(H0 + S0 )
Replacing this ditch by the real one gives, the additional drawdown as
2q 0 H + So
∆S2 = ln 0 = –0.21 m
πk 2w
together
The third simplification involves the finite length of the spreading ditch. When the area
available has a more or less square plan, the total length of the spreading ditches, calculated at
6849m, must be broken up into 6 units, each of a length B = 1140 m. This gives a ratio of B
over L equal to 1140/55.3 ~– 20 and, a weighted average reduction in drawdown by a factor of
1
(2α2 + 4α3) = 1.04, thus ΣS0 = 2.31/1.04 = 2.22 m
6
When the increase in drawdown from 2.0 to 2.14 m is not acceptable, the foregoing calculations
must be made a new, starting from a value of S0 equal to 1.85 m, as indicated in Fig. 3a. The
piezometric level inside the gallery is less than that which corresponds with H0 = 15 m, but this
does not affect the groundwater tables outside the recharge area. With a number of spreading
ditches parallel to one another, the capacity of the gallery equals 2 × 69.5 × 10–6 = 139 × 10–6 m3
m–1 s–1, giving for a circular drain of 0.5 m outside diameter the additional drawdown due to partial
penetration as
q H 139 × 10 –6 FG IJ
∆S = 0 ln =
15
ln = 0.83 m
π k Ω π(0.12 × 10 )
–3
H K
π × 0.5
to which must be added the entrance resistance caused by clogging. Finally, it should be noted
that, at the outset of the calculations, a spreading ditch fully penetrating the saturated thickness
of the aquifer over a width 2w has been assumed. Replacing this ditch by the real one slightly
lowers the minimum detention time, but with regard to the improvement in water quality
during underground flow, this decrease is more than compensated by an increase in average
detention time, roughly by a factor (L+w)/L to 6.2×106s or 10 weeks.
Spreading in deep phreatic aquifer: The difference in spreading operations for deep and
shallow aquifers is not a principal one, but only concerns the layout of the spreading area.
Again, this can best be clarified with an example, assuming in this case that Qo = 30 × 106 m3/
year = 0.951 m3/s, k = 0.4 × 10–3 m/s, p = 0.38, µ = 0.32, ve = 5 cm/h = 13.9 × 10–6 m/s,
120 Energy
Water Management
Management
L= kS0T/P = 332.5 m
2q 0 H0 + S0
∆S2 = ln 2w = 0.11 m
πk
ΣS0 = 5.03 + 0.39 + 0.11 = 5.53 m
For a single spreading ditch, bounded at both sides by parallel infiltration galleries with
reduction factors for additional flows around the far ends, reducing ΣS0 to 4.69 m, or well
below the maximum allowable value of 5m.
In the case considered above, the recharge area has a width of 719 m and a length of 1256
m, thus approaching a square plan. This points to the possibility of a circular battery of wells,
as shown in Fig 3b. With the notation of this figure, the design criteria become
(a) Detention time, neglecting the soil mass below the spreading pond:
T = pHπ [ (ρ + L)2 – ρ2]/Q0
(b) Drawdown, composed of two terms: S0 = S1 + S2, with S1 as the flow resistance from
the rim of the spreading pond to the concentric battery of wells, calculated from
Q0 FG ρ + LIJ ; and S
(H0 + S1)2 – H02 = k In H LK as flow resistance below the spreading pond,
π 2
Q0
calculated from S2 = 2 kH α, with α tabulated as follows
π
2ρ/H 0.01 0.1 1 10 100
α 308 27.6 1.58 0.088 0.0088
121Energy Management Artificial Recharge Methods 121
V = µ S0 π ρ2 z
ρ
µS 2 πrdr
V = µS0π
bL + ρg – ρ2 2
2 ln bL + ρg / ρ
and in the case under consideration V= 0.927 × 106 m3, allowing an interruption in operating
operations of no less than 11.3 days.
As a regards the pumping equipment of the wells for groundwater recovery, the additional
drawdowns of point abstraction and partial penetration should be taken into account. With
122 Energy
Water Management
Management
say, 40 wells, the individual capacity equals 23.8 × 10–3 m3/s and the intervals between wells
99 m. With a screen length of 20 m (p = 20/60 = 0.333) and an outside diameter of the gravel
pack of 2r0 = 0.60 m, this gives
∆Spa =
23.8 × 10–3
ln
FG 99 IJ= 0.63 m
2π × 0.4 × 10 × 60
–3 H
2π × 0.3K
23.8 × 10–3 1 – 0.333 L(1 – 0.333) × 20 O
∆Spp = ln M
2π × 0.4 × 10–3× 60 0.333 N 0.30 PQ = 1.20m
to which must still be added the additional resistance caused by clogging of the well screen
and gravel pack.
F lo w
w e ll P L AN H .F.L
M a x W a te r Le ve l
N O N -G ATE D
CH ECK D AM
S ee pa g e P erv io u s B ed
S ee pa g e
C R O SS -S E C TIO N
F lo w
S lot fo r O p en in g
P L AN M a x W a te r Le ve l
w e ll
C ATE D
CH ECK D AM
P erv io u s B ed
S ee pa g e
w e ll C R O SS -S E C TIO N
STREAM
C o ntro llin g G ate
F ee de r C an a l
E a rth e n Bu nd
W ell
S e e pa g e
P L AN
W ater Le vel
E a rth e n Bu nd
W ell P e rm e ab le B ed
C R O S S -S E C T IO N S e e pa g e
Tank is a general term used for surface water storage of moderate size. The storage may
have come into being due to interception of rainwater in a natural depression or a man-
made excavation. Such waterbodies are popularly called ponds. Alternatively water storage
may be done by closing the openings of a natural saucer shaped landform by constructing
bunds sized embankments. The storage so constructed is called a tank. The tank bunds
are mostly constructed with earth to keep cost of construction low and commensurate
with the benefits envisaged.
124 Energy
Water Management
Management
Water storages of large size not called tanks but they are referred to as reservoirs. Such reservoirs
are formed in the river valleys by constructing a barrier or a data using masonry, concrete or earth
depending upon site conditions. Technically bund is a miniature form of a dam.
Due to simplicity in construction it was a very popular mode of conserving rainwater. In
South India where river flows are monsoon fed tank assumes special importance. In the plains
of Uttar Pradesh, West Bangal and Orissa as also on the plateaus of Madhya Pradesh tank can
be extensively practiced.
Network of Tanks
The tank system may exist with each tank as a separate entity or in the form of a group of
tanks in a series or tanks with inter-connection. In tank system, following types of network
exist:
(i) Isolated tanks;
(ii) Tanks with inter-connection; and
(iii) Tanks in series.
Isolated tanks: When a tank is fed by an independent free draining catchment and also when
the surplus flows do not form network inflow into another tank, the tank system is called
isolated tank system. Mostly large and medium-large tanks are constructed as isolated tanks
with independent catchment area. Also in the plains and on plateau land tanks exist in isolation.
Tanks with inter-connection: Sometime a group of tanks may be so situated that they could
be inter-connected to receive flows through, as well as deliver flows to, other tanks in the
group severally. It thereby implies that the tanks have a combined catchment. Any surplus
received by a tank from the catchment lying above is transferred to other tanks. Depending
upon prevailing hydro-meteorological condition the tanks are capable of feeding each other in
reverse. Thus optimum water utilization is achieved.
Tank in series: Such tanks are located alongside the river drainage channels. They are fed by
inflow drains and serviced by escape or outflow drains. The tanks in upper reaches get their
supplies from the catchment through inflowing drains. It then lets its surplus flow down
through an escape or outflow drain, which contributes to the inflow of the tank lower down
in the series. Thus while the uppermost tanks have substantial free catchment, the tanks
lower down have limited free catchment falling between two tanks. The tanks lower down in
series get inflows immediately after rainfall from their free draining catchments. But supplies
from already intercepted catchment are received only after the upper tanks existing in southern
125Energy Management Artificial Recharge Methods 125
States of the country from series network. The advantage of this system is that, surplus water
from the upper tank does not go waste but is picked up by the lower tanks. Thus optimum
water gets conserved.
It, however, suffers from one disadvantage relating to safety. Since each tanks has vast
combined catchment, in case of breach in the upper tank, lower tanks also become prone to
severe flooding endangering safety of the tank bund. To avoid this, breaching sections are
provided at appropriate places in each tank.
Definitions
Before proceeding with the subject matter it is worthwhile to understand the terms commonly
used for tank.
(i) Free catchment: Catchment area is defined as that area, which always contributes the
surplus rainwater, received by it to the natural drainage grid present in the area. It is this
area, which is responsible for maintaining flow in the natural drainages like rivers. When
the catchment lying above any storage structure like a tank bund or a dam is not
intercepted by another structure then it is called free catchment of that structure.
(ii) Breaching section: Overtopping of tank bund by floodwater is dangerous to the safety
of the bund. Hence every precaution is taken to avoid its overtopping. To achieve this
object, a natural saddle on the periphery of the tank is selected. In the saddle, an ordinary
retaining wall is constructed. Its height is kept higher than full tank level but lower than
top of the tank bund. When the water level in the tank rises dangerously the rushing
water breaches the periphery of the tank at this section. Thus the tank is protected and
breach is localized to predetermined sections. If such a location is not available naturally
breaching section may be constructed at a suitable site away from the bund.
(iii) Escape channel: The floodwater rushes out of the breached section. To carry the
outflow safely, channel of adequate capacity is provided below the breaching section.
It is called and escape channel. By diverting water in the escape channel safely of the
tanks on the downstream in a series network is ensured.
(iv) Full tank level (FTL): It is that level up to which water is stored in the tank for
utilization during fair weather. Normally full tank level (FTL) is governed by the top
of the escape or surplus weir. As soon as water level starts rising above this level,
water starts spilling over the weir.
(v) Maximum water level (MWL): It is the level up to which the water may get stored
temporarily in the tank during high flood inflows. The maximum water level (MWL)
depends upon the waterway provided to pass flood discharge safely. The top of bund
is generally kept above this level by keeping adequate free board.
Tank Bunds
Tank bund is an embankment of low height. Generally it is made of earth. Since earth of
various types is available, tank bunds may be constructed using principles adopted for
construction of earth dams. Generally tank bunds of three types are constructed. They are:
126 Energy
Water Management
Management
(a) Homogeneous Type: (Tank bund of Type A) In construction of this type uniform and
homogeneous material is used. It is constructed with relatively flat side slopes from
consideration of stability. Most of the bunds belong to this type (Fig. 7.10).
L in e o f S atura tion
2 :1 H o m og en e ou s 2 :1
M ateria l
When the height of tank bund is more than 5 meters the section is modified suitably with
seepage checking trenches, blankets, toe drains. Design principles of earth dams are dealt with
subsequently in this book.
(b) Zoned Type: (Tank bund of Type B) When earth of different types is locally available
the bund may be constructed by dividing the section in different zones (Fig. 7.11).
F.T.L .
2 :1 P I P 1 ½ :1
G rit
cut-off
Im p erviou s R o ck L a ye r
Outer zone is generally made of pervious material. The inner zone is made of impervious material.
(c) Diaphragm Type: (Tank Bund of Type C) Many times zoning is done by providing a
central core wall, called diaphragm. It is generally constructed with masonry or concrete
(Fig. 7.12).
F.T.L .
M aso nry 1½ : 1
2:1 core w a ll
P e rvio us zo ne
P e rvio us
Im p erviou s Stratu m
In such types the diaphragm is taken quite deep in the foundation preferably up to
impervious stratum.
Table 7.1
Height of Bund above Deep
Bed (Meters) Free Board (Meters) Top Width (Meters)
The side slope of Tank bund is kept quite flat. 2:1 (Horizontal: Vertical) is a common slope.
However for lesser heights steeper slopes may be adopted.
Like earth dams the upstream face of the tank bund is generally given stone pitching. It is
also called revetment. Thickness of the pitching may vary from 0.3 to 0.6 meters. A toe is also
provided to support the sloping face. General arrangement is shown in Fig. 7.13.
H .F.L Top o f b un d
Ston e P itch in g
G ra ve l laye r
Toe
Storage capacity of a tank: Storage capacity of a tank can be calculated using trapezoidal
formula. It is stated as:
V = H/3 (A1 + A2 + A1 – A 2 )
Where V is volume of space enclosed between two adjacent contours.
A1 & A2 are the areas enclosed in two contours.
H is contour interval.
This method is useful in finding capacity in two successive contours only. But since
tank bunds are of small heights the method is quite useful. The effective or utilization
storage in a tank is the volume between level of sill of the outlet or lowest sluice and full
tank level.
128 Energy
Water Management
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Escape Weirs
It is already mentioned that tanks are small storage works constructed to meet local requirements.
Obviously attempt is not made to contain full runoff coming down from the catchment area. It
is therefore necessary to make suitable arrangement to pass down excess water beyond Full
Tank Level (FTL) safely. Structure constructed to provide passage to excess water is called
escape weir. It is also called tank surplus weir. The water starts spilling over the weir as soon
as tank is filled up to its crest. However temporarily due to rush of incoming water the level in
the tank rises above F.T.L. The new level reached is called Maximum Water Level (MWL). It
depends on the extent of flood. For design purposes M.W.L. is calculated taking into account
maximum flood discharge likely to occur and the waterway available at the site of the escape
weir. The surplussing or spilling water is carried down through a channel, which is generally
a natural drainage and has enough capacity.
Selection of site for a tank weir: Following points may be taken into consideration while
selecting a site for a tank weir: -
(i) Tank weir performs the function of surplussing excess flow. Therefore it is preferable
to locate the weir in a natural saddle away from the tank bund.
(ii) To carry surplus flows existence of a well-defined escape channel is very necessary at
a site selected for construction of a weir.
(iii) The saddle, where Natural Surface Level (NSL) is approximately same, as full tank
level (FTL) should be given first preference.
(iv) Hard foundation if available at the site reduces the cost of construction of bed
protection works.
(v) When a site away from tank bund is not available, as far as possible weir may be
located on one end of the tank bund.
(vi) Surplus weir may be housed in the body of the tank bund only as a last resort.
(vii) Care should be taken to see that escape channel carrying surplussing water is not
likely to damage cultivated areas.
Types of weirs: Escape weirs constructed in tank irrigation system is similar to a diversion
weir or an anicut constructed across the river channel. It may be constructed either with
masonry or rockfill or concrete depending upon availability of construction material and site
conditions.
Masonry weirs: This type of weir is most commonly used in a tank irrigation system. Masonry
weirs are generally constructed with vertical drop and are designed as gravity weirs. Self-
weight of the body wall is the only restoring external force and it counteracts all dislodging
forces like water pressure, uplift etc. On the body wall of the weir dam stones may be erected
to enable extra storage. Depending upon the site conditions, masonry weirs may be constructed
in three ways as given below.
(a) Masonry weir with horizontal floor: In this type of weir, vertical drop is given as
shown in Fig. 7.14.
129Energy Management Artificial Recharge Methods 129
D am stone
F.T.L
M asonry Tauls
C oncrete
C urtain
This type is suitable when on the downstream side hard rock is available in the foundation
and the height of the weir is less than one meter or so.
(b) Masonry weir with depressed floor: This type is similar to one explained above except
that the downstream apron is depressed below the ground level. Fig. 7.15.
D a m Ston e
F.T.L
G.L. 4:1
Talus
A p ron
By depressing the apron below ground level a sort of stilling pond is formed. It helps in
dissipating the energy of water spilling over the crests of the weir. This type of arrangement is
generally used for weirs with greater heights say more than 2.5 meters. They are then designed
like a fall.
(c) Masonry weir with stepped floor: When the topography is such that there is no
space for constructing horizontal or depressed horizontal apron, weir with stepped
apron may be constructed as shown in Figure 7.16. It is something like steps and is
suitable for low heights of body wall.
F.T.L.
B o dy w a ll
M as o nry
N .S .L.
Step s Talus
Rockfill weirs: It is constructed with dry rock fill if such material is locally available in sufficient
quantity. Fig. 7.17.
F.T.L.
1 IN 4 1 IN 2 0
S ton e a p ron
To support the rock fill masonry retaining walls are constructed as shown in the fig. 7.17
Top surface of the weir is plastered. This type of weir acquires a very big section because the
slopes are quite flat.
Concrete weirs: Typical profile is shown in Fig. 7.18. The weir is constructed with reinforced
concrete to make the section monolithic. This type is constructed mostly where foundations
are pervious.
In this type of weir, a sloping glacis is provided on the downstream side. It helps in creating
a hydraulic jump on the sloping face. When hydraulic jump is created the energy of flow is
dissipated. Thus the bed is protected below the weir.
F.T.L
.
1 IN 5 D /S G la cis
1 IN 4
B ou lde r
S he et p ile s pitch ing
M is catchment area in sq km
C is a constant
= 6.74 for areas within 24 km from coast
= 8.45 for areas with in 24-161 km from coast
= 10.1 for limited hilly areas.
This formula can be applied for a free catchment. For a tank in series or interconnected
tanks the formula needs correction. Modified formula is
Qm = CM2/3 – Cm. Mm2/3
Where Mm is the catchment area in sq km intercepted by upstream tank
Cm is new coefficient, which varies from 0.2 to 0.33.
Waterway of the weir: The weirs constructed are generally broad crested weirs and the
formula, which gives discharge over broad crested weir, can be used. Generally velocity of
approach is neglected. The discharge formula is in the form –
Q = C.L.H3/2
L = Q / C.H3/2
Where L is length of weir in meters
H is design head over weir; it is given by (MWL – FTL) in M
C is a constant
= 1.84 for weir crest up to 0.9 m width.
= 1.66 for weir crests more than 0.9 m width.
= 1.66 for crests with dam stones.
= 1.47 for crests with d/s sloping face.
Length of apron: Usually length of horizontal downstream apron is kept 2(D+H) from toe
of body wall. Here D is height of the body wall above floor and H is maximum water head over
the crest of the wall. A further factor of safety of 1.5 is provided when important areas lie
below the surplus weir. Then length is kept 3(D+H).
Length of stone talus or pitching: Generally 3(D+H) to 5(D+H) length of stone pitching
is provided on the downstream of apron in continuation. Greater length is provided for weaker
foundation material.
To restore the lost area under storage and to increase the tank area there is urgent need to
rehabilitate and modernize the age – old tanks. Rehabilitation can be achieved by desilting the
tank. Modernization involves strengthening and raising height of bund, improvement of
surplussing arrangement, minimizing evaporation losses.
Design Problems
# 1: Free catchment of an isolated tank is 50 sq km. Average annual rainfall recorded is 100
cm, nearly 80% of which occurs in a short period of two months and the rest is distributed
over balance period. Taking dependability of average year rainfall to be 60% calculate the
gross storage capacity required for the tank. Assume that only 30% of the rainfall flows down
as surface run-off. Also calculate design flood likely to be generated by the catchment. Area is
within 80 km from coast.
Step 1: Average annual rainfall = 100 cm
For calculating storage capacity, we may use only that part of runoff, which occurs
in the rainy season because it is stated that balance rainfall is distributed over a 10
month period and may produce insignificant runoff. It will be accommodated in
vacant space of the tank.
100
Effective rainfall = 80 × = 80 cm
100
Step 2: In the question dependability level is given to be 60% of average flow,
60
Dependable rainfall = 80 × = 48 cm
100
Step 3: Runoff factor is given to be 30% of rainfall
30
Runoff expected at bund site = 48 × = 14.40 cm
100
14.40
or Gross storage capacity required = ×50 × 1000 × 1000
100
= 7.2 × 106 cubic meters
Step 4: Design flood can be calculated using Ryve’s formula
Q = C M2/3
Where Q is peak flood in cubic meters
C can be taken to be 8.45
M is 50 sq. km
Q = 8.45 × 502/3 = 114.68 cubic meters
#2: In the catchment of problem 1, another tank has been constructed on the upstream.
Free catchment of new tank is 10 sq km. Calculate modified gross storage capacity and design
flood as also percent reduction for the existing tank. Assuming that upstream tank releases 1/
5th of its runoff.
Step 1: Free catchment of the existing tank= 50 – 10 = 40 sq km
133Energy Management Artificial Recharge Methods 133
Intercepted catchment = 10 sq km
Runoff in tank = 14.40 cm (from step 3 of problem 1)
Step 2: Modified runoff into existing tank
= Runoff from free catchment +1/5 (runoff from intercepted catchment)
= 5.76 × 106 + 0.288 × 106
= 6.048 × 106
7.2 –6.048
Step 3: % reduction in storage = × 100 = 16%
7.2
Step 4: Modified design flood is given by using the relation Qm = C.M2/3 – Cm. Mm2/3
Where Cm = 0.2 C and Mm is 10 sq km
Qm = 8.45 × 502/3 – 0.2 × 8.45 × 102/3
= 114.68 – 7.84
= 106.84
Step 5: % Reduction
114.68 – 106.84
In design flood = × 100 = 6.84 %
114..68
B un d Tren c h
P LA N V IE W
B un d Tren c h
S E C T IO N A L V IE W
E m b an km en t
S he e t F low
R e tu rn C a n al
am
S te
D ire ctio n o f F low
L ow P erm ea b ility
M a terial
S cre en
P erm ea b le M ate ria l
L ow P erm ea b ility
M a terial
Unfortunately, pits used for storage or treatment of liquid wastes provides a significant
source of inadvertant recharge, which leads to complex and widespread problems of groundwater
pollution. Examples include sewage treatment lagoons, industrial waste holding or disposal
ponds and oil field brine evaporation pits, to mention only a few of an exceedingly large number
of practical situations.
Recharge shafts (Fig. 7.25) are generally deeper and of smaller diameter than pits. Their
purpose is also to penetrate low permeability layers. Shafts may be lined or unlined, open or
filled with coarse material and large or small. They are constructed by hand, with draglines
and backhoes or are drilled or bored where the recharge water contains sediment, shafts may
become plugged fairly rapidly.
Commonly, recharge shafts are used in conjunction with pits (Fig. 7.26). Both suffer from
decreasing recharge rates with time due to the accumulation of fine-grained materials and to
the plugging effect brought about by microbial activity. Rates through recharge pits may be
maintained by periodically allowing the facility to become dry or by scraping and removing the
accumulated material from the sides and bottom. Shafts are less easy to maintain owing to
their smaller diameter and greater depth. In some cases, the coarse material used to fill the
shaft must be replaced.
C a na l o r Po n d level
2w
z’ 0
z0
sp sc s’ 0
H0
L w H L L+w
Fig. 7.27 Spreading ditch above the Fig. 7.28 Spreading ditch above the
groundwater table. groundwater table.
For parallel and circular systems respectively, the head loss here is given by
Sp =
q0
L, Sc =
Q0
ln
L+ρ FG
; Z0 =
IJ
1 q0
w; Z0 =
Q0
.
kH 2πkH ρ H 2 kHK 2πkH
With finer grained aquifers on the other hand, the air present in the pores of the
formation will be dissolved and carried on by the downward percolating recharge water,
while re-supply of air from the ground surface will be too limited to maintain an unsaturated
zone. A closed body of groundwater will thus be formed, shown in Fig. 7.28. For a clean
ditch without clogging, its necessary width is given by (Vermeer, 1974):
2q 0 4 – πkz ′0/(2q )
2w′ = + (H0 + S′0)e 0
k π
q
with S′0 = 0 (L+W)
πk
whereas for a clean circular pond without clogging (Fig. 7.29), the necessary diameter, 2ρ, may be
Q0 LM F
L+ρ IJ OP
+ α , with α is a function of
N GH
calculated by trial and error from S0 = S1+S2 = ln
2πkH ρ K Q
2ρ/ . For instance, Q=20 × 106 m3/year = 0.634 m3/s, k = 0.4 × 10–3 m/s, H = 50 m, L + ρ =
H
500 m, the distance from the ground surface to the groundwater table S0 = 10 m and moreover, so
138 Energy
Water Management
Management
Qn Qn
n n
2ρ
L+H
B ed
S tr ea m
W a ter ta ble
G R O U N D W AT E R F LO W
R eg io na l
W ate r ta ble SUBSURE P h re atic A q uife r
DYKE
K
IM P ER M E A B L E R O C
G ro un d s urfac e G ro un d s urfac e
W atertab le W atertab le
R ive r
R ive r
Im p e rm ea ble Im p e rm ea ble
(a) (b )
Fig. 7.31 Induced recharge resulting from a well pumping near a river
(a) Natural flow pattern (b) Flow pattern with pumping well.
140 Energy
Water Management
Management
Fig. 7.32 Induced recharge resulting from a collector well on stream bed.
1
q0 =qa + qn; qn = PW + (kHS0/W)
2
In these formulas, W is the wetted circumference of the river bed in contact with the
aquifer, ve the maximum allowable value for the average entry rate of river water into the sub-
soil, p the pore space, H the saturated thickness and k the coefficient of permeability of the
aquifer, T the minimum acceptable detention time, P the amount of residual rainfall and S0 the
maximum value of the drawdown, S, which increases linearly with the distance from the
bounding rivers. With regard to the requirements for the detention time and drawdown, no
compromise is possible, giving for the interval L
141Energy Management Artificial Recharge Methods 141
or L=
FG q IJ k S T
a
Hq +q K p
a n
0
L = 0.9 ( k / p)S0T
0.4 ¥ 10–3
L = 0.9 ¥ 1.5 ¥ 6 ¥ 106 ª 85.38 say 85 m
0.4
Starting from this value, the requirements for the detention time and drawdown give
0.40 ¥ 22 ¥ 85
qa < or qa < 124.67 × 10–6 m3m–1s–1
6 ¥ 106
q0 < 0.4 × 10–3 × 22 × 1.5/85 or q0 < 155.29 × 10–6 m3m–1 s–1 and with
qn =
FG 1 ¥ 16 ¥ 10 –9 IJ
¥ 6000 + [0.4 × 10–3 × 22 × (1.5/6000)]
H2 K
= (48 × 10–6) + (2.2 × 10–6)
qn = 50.2 ×10–6 m3/ms
qa < (155 × 10–6) – (50 × 10–6) or qa < 104.8 × 10–6 m3m–1s–1
or qa < 105 × 10–6 m3m–1s–1
As the smaller of the two values for qa, this is the deciding one, giving with a river width of,
for instance, 40 m an average entry rate into the sub-soil equal to
ve = 105 × 10–6/40 = 2.62 × 10–6 m/s
or 0.2 m/day, which seems quite acceptable. For a city of 100 000 inhabitants, with a daily
consumption of 20 000 m3 or on average 0.23 m3/s, the gallery yield of 133 × 10–6 m3m–1s–1
means a length of bank infiltration equal to
0.262
B= _ 1690 m
155 ¥ 10–6
for which it will not be difficult to find an appropriate place. Slightly better results in theis
respect could be obtained by a small reduction in the value of L, from 90 to 84 m, increasing
the gallery yield to 143 × 10–6 m3 m–1 s–1 and decreasing the required gallery length to 1600 m.
Without saying so expressly, the calculations carried out so far are based on a one-
dimensional flow pattern, showing only horizontal flow lines perpendicular to the river. Such
142 Energy
Water Management
Management
a flow net would indeed be present when the length of the gallery parallel to the river is
infinite and when both the gallery and the river fully penetrate the saturated thickness of the
aquifer and, moreover, do so with vertical sides. This, however, will never be the case, slightly
changing the results obtained above.
For the water flowing directly beneath the water table, the detention time will be somewhat
smaller than the value of Td assumed so far, but for all other flow lines the detention time will
be longer, giving an average value appreciably above the design value. Due to a greater length
of flow and to the presence of vertical flow components, the drawdown, S0, will increase by
∆s. With a fully penetrating gallery of zero width in the centre of the river, the length of flow,
L, increases by Ω/ 2, augmenting the drawdown to
q0 q W
So = L , by ∆S1 = 0
kH kH 2
Replacing the fully penetrating gallery by the real one gives as additional drawdown due to
partial penetration
∆S2 = [q0/(πk)] ln (H/Ω)
For the correct example quoted above
155 ¥ 10–6
S0 = ¥ 85 = 1.50m
0.4 ¥ 10–3 ¥ 22
155 ¥ 10–6 40
∆S1 = = 0.35m
0.4 ¥ 10–3 ¥ 22 2
∆S2 =
155 ¥ 10–6
ln
22 FG IJ
= –0.07 m
p ¥ 0.4 ¥ 10–3 40 H K
ΣS0 = 1.50 + 0.35 – 0.07 = 1.78 m
It should be noted, moreover, that according to Fig. 7.33, the entry of river water is
concentrated near the shoreline. In extreme cases, clogging will occur here, shifting the recharge
towards the centre of the streambed, thus increasing the length of flow and the drawdown. To
prevent this as much as possible, the design rate of entry should be chosen small.
Due to the finite length of the gallery and the additional inflow around the far ends, the
capacity for the same drawdown will be larger, equal to αΒq0 with α equal to
B/L 2 5 10 20 50 100
α 2.29 1.65 1.39 1.23 1.13 1.07
For the same capacity, the drawdown will correspondingly be smaller. In the example
mentioned above,
143Energy Management Artificial Recharge Methods 143
∆S′ =
155 ¥ 10–6 FG 22 IJ
–3 ln =0.30 m.
p ¥ 0.4 ¥ 10 H
p ¥ 0.6 K
re sidu al
ra in fall P
q0 = qa + q0
so
Ω qn
qs
L
W
The influence of clogging cannot be calculated, but it is wise to anticipate a value of 0.5 –
1 m, keeping in mind that cleaning of the gallery is impossible.
The calculations made so far are based on a constant water level in the bounding rivers.
When these water levels vary, a change in groundwater levels will also occur, influencing the
ratio between artificial and natural groundwater abstracted. In the case where the river shows
a sinusoidal variation (Fig. 7.33), z = z0 Sin (ωt), then assuming that W is so large that mutual
interference may be neglected, the variation in river water abstraction, qa, equals
∆qa =
FG
wmkH Z 0e –aL Sin wt – aL +
1 IJ
p , with a =
1
wm / ( kH )
H 4 K 2
With the example described before, µ= 0.30, yearly fluctuations and Z0 = 1.5 m
2p
∆qa = 6
¥ 0.30 ¥ 8 ¥ 10–3 (1.5e -84 /517 ) = ± 28 ¥ 10-6 m 3m -1s -1
31.54 ¥ 10
144 Energy
Water Management
Management
With a steady state river water abstraction equal to qa = 101 × 10–6 m3 m–1 s–1, this amount
will now vary between 73 × 10–6 m3 m–1 s–1 and 129 × 10–6 m3 m–1 s–1, making 51 to 90% of
the gallery yield, q0, of 143 × 10–6 m3 m–1 s–1.
maximum water level and two right angle elbows are fitted at this level. At upper end one
additional pipe of about one meter is fitted which will act as an air escape pipe. In order to keep
pipe in position, a masonry foundation of 1.0 m × 1.0 m × 1.0 m is constructed. By this
method, whenever the water surface reaches at maximum water level the surplus water will
enter the pipe and reaches to aquifer. (Figs. 7.35 & 7.36).
A
P ipe u p to
p erm e a ble la ye r
Fig. 7.35 Groundwater recharge by diverting surplus water of pond into well.
Trench connecting
natural drain or stream
ra ck
Cart T
Strea m or River
Stream bed
Wire mesh Air vent pipe
Strainer
(perforated) pipe Gravels
Holes provided
for air escape
R e ch arg e B o re
G ra ve l 6 0 cm
M e ta l 6 0 cm
R u bb le 11 .2
.2 00 cc m
m
Straine r P ip e
P ipe le ad
u pto p e rv iou s
stra ta
G ro und w ater R ec h arg ing by C on stru ctin g S oak P it in riv er B e d
Because of the influence of finite length, this value must be divided by α2. With B/L = 4,
α2 = 1.17. This result, however, must still be augmented by the influence of point injection;
while noting that Qinj = 2Q0,
∆S0′ =
2Q 0
ln
FGb IJ
, and with r0 = b/200,
2πkH H
2πr0 K
∆S0′ = 6.9209 Q0/(2πkH)
Together S0 = (S′0/α2) + ∆S′0 =17.6613 Q0/(2πkH) or 7% above the correct value.
According to the calculations given above, the capacity of the outer injection wells is 12%
above and of the inner wells 5% below the average value. These differences are higher when
the ratio L/b increases. For L=4b and a more or less square recharge scheme, they amount to
+20% and –11%. When, during operation, clogging of the injection wells occurs, these
differences will decrease.
Increasing the injection head to overcome the clogging of the formation surrounding the
well screen has little influence on the cost of operation, but it may result in soil cracks through
which the recharge water flows upward to the ground surface. To investigate this danger, Fig.
7.42 shows the pressure distribution in the sub-soil before and during injection. From soil
mechanics, it is known that the vertical grain pressure equals the difference between the soil
pressure and water pressure:
σg = σs – σw
Using the notation of Fig. 7.42, the smallest grain pressure occurring at the top of the
artesian aquifer equals, before injection,
σg =ρs gA – ρw g (A – D), with ρs and ρw as the mass densities of soil and water, respectively.
The horizontal grain pressure normal to the vertical planes is smaller by a factor α
σgh = α σg
and will, during injection, decrease by an amount ρw g (S0 + Sc ), where Sc is the increase
of the injection pressure, S0, by clogging. Together these give
150 Energy
Water Management
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α = tan2 45
FG –f IJ
H 2 K
with ϕ as the angle of internal friction. For sand, this angle varies between 30° and 40°, thus
α = 0.33 to 0.22. Using the lowest value and assuming for water saturated sand ρs=2ρw, one
finally gets
S0+Sc < 0.22 (A+D)
Meaning that for D = 0, the water level inside the well may not rise more than 0.22A
above the ground surface or with, for instance, A = 20 m, not more than 4.4 m above the
Q0
ground surface. In the example given above, S0 = (16.5)
2pkH
Assuming Q0 = 0.02 m3/s and kH = 0.03 m2/s, then S0 = 1.75 m, giving for the rise, Sc, in
the injection head due to clogging Sc = 4.4 – 1.75 = 2.65 m, which is a rather small value.
The changes in the injection head may also be caused by variations in the temperature, Tr,
of the recharge water. In temperature climates, Tr = T0 + Tc Sin(wt) which variations
propagate through the aquifer with little damping but a large delay. Neglecting this damping
altogether, it gives for the temperature at a distance x down stream of the line of recharge wells
Tx = T0 + Tc Sin (ωt – δx)
The average temperature over the flow length L, thus becomes
L
Ta =
1
z 1FG IJ FG1
Tx dx = T0 + [2 / dL]sin dLTc sin wt – dL
IJ
L0 2 H K H 2 K
ρa C a ω T
with δL = d
ρw C w p
1.5
Slo p e
l
ne
an
Ch
FAR M
5 0 cm Sa n d lay er
M a ter lay er 5 0 cm
S oa k cha nn e l G ra ve l layer 1 m
2 .0 m
s0 s c2
groundwater table
before injection
a qu ifer
w e ll sc re en
g ra ve l pac k
san d trap
Fig. 7.48 Installation of piezometers for the identification of injection well clogging.
154 Energy
Water Management
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Presence of air bubbles: During injection, air bubbles may be entrained by the free fall of the
water when the injection pipe ends some distance above the water level in the well casing and
may come out of solution when the water pressure drops below atmospheric. In water at rest,
air bubbles with diameters between 0.1 and 10 mm rise at velocities of 0.3 – 0.4 m/s, meaning
that injection with higher flow rates carries them downward, through the well screen openings
into the gravel pack and surrounding formation. Here, they clog the pores between the individual
grains, causing an additional resistance, which in its turn decreases the injection capacity and
the amount of air supplied. On the other hand, the air bubbles present will dissolve into the
water flowing by, together meaning that already after a short time an equilibrium situation is
brought about and no further increase in injection head occurs (Fig. 7.49). The entrainment
of air can easily be prevented by carrying the supply to some distance below the static water
level in the well. In the upper part of this pipe, water pressures below atmospheric would still
occur, unless at the lower end an orifice is installed, giving such a flow resistance that everywhere
a water pressure 1 – 2 m positive is maintained. With the pressure diagram of Fig. 7.50, this
flow resistance can easily be calculated.
sc
air
bacteria
tim e
When the valve in the supply pipe of Fig. 7.50 is used to reduce the capacity of this particular
well, it should be realized, however, that an additional lowering of the pressure would occur.
The solubility of air in water decreases with rising temperature, meaning that air bubbles
will also evolve when cold recharge water is mixed with warm groundwater. For a temperature
increase of 10o C, the solubility decreases by a factor 0.8. This can be compensated, however,
by a pressure increase from 1 to 1.25 atm, so that no difficulties will arise when the top of the
well screen is more than 2.5 m below the water level in the well. This is always the case.
As already mentioned, clogging by air bubbles is easily recognized by a sharp increase in
the injection head directly fter recharge operations starts, reaching its maximum value already
after some hours (Fig. 7.49). When the operation is stopped, the water in the well will, moreover,
foam due to escaping air bubbles.
Presence of suspended matter: Clogging by suspended matter manifests itself by an increase
in the injection head, Sc, which, for a particular well and recharge water, grows linearly with
time (Fig. 7.49), while it is proportional to the square of the capacity. This can easily be explained
by assuming cake filtration to occur, the cake having a constant coefficient of permeability, k’,
while its thickness, t, increases by the deposition of suspended matter present in a gravimetric
concentration, c, in the recharge water. For a fully penetrating well in an aquifer of depth H,
this gives with the notation of Fig. 7.51.
Q r +l Q0 r l Q (k k′) r0 + l
Darcy – Sc = 2 pk0H ln 0r 2 kH ln 0 + = 0 ln
r 2 kk H
′ 0 π 0 π ′ r0
c
Continuity – Q 0 dt = 2 Π(r 0 + l)Hdl(p p )′ , where ρd is the mass density of the deposits
ρd
and (p – p′) the decrease in pore space. Integration between the limits t = 0, l = 0 and t = t,
l = l gives, after rearranging terms,
156 Energy
Water Management
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2
r0 + l 1 Q 0ct
r = + (p p )Hr 2
0 π ′ 0 ρd
By substitution
Q 0 (k k′) Q 0 ct
Sc = ln 1 +
4 πkk′H π (p p′)Hr 2
0 ρd
r + l 1 l l
ln 0 = +r ≈ r
r0 0 0
kk′ Q 20 ct
Sc =
kk′(pp′)ρd 4 p2 r02 H2
Assuming that p′ and thus k′/k has some minimum values, Sc may be simplified
to Sc = α [Q20 ct/(4π2r20H2)], where α is a constant.
With the entrance rate
ve = Q0 /2 π r0 H
this may be further simplified to
Sc = αve2 ct
once the value of α has been determined for an existing well, operating with a particular
recharge water, the clogging rate for the other wells in the same formation using the same
recharge water, but having a different capacity, diameter or depth of penetration, can easily be
calculated. The results, however, cannot be used for other aquifers or other types of recharge
water as now the values of k′, p′, ρd and thus α are changed in an unknown way. Even the
influence of the concentration, c, of suspended particles in the same recharge water is less
straightforward than would follow from the formula given above. Cases are known where c
was drastically reduced by pre-treatment, using chemical coagulation, flocculation, settling
and filtration, without a noticeable change in the clogging rate. Afterwards, this has been
explained by considering the untreated water to contain negatively charged particles, which
are difficult to retain by the negatively charged sand grains in the formation, leading to deep-
bed filtration and a low clogging rate. After treatment, the remaining particles had a positive
charge and were easily captured by the negatively charged sand grains, resulting in cake
filtration and, notwithstanding the much smaller amount, in about the same rate of clogging.
The pre-treatment, incidentally, still had advantages as the small amount of penetration allowed
a more rapid and more complete removal of the clogging by cleaning. To evaluate the influence
157Energy Management Artificial Recharge Methods 157
of pretreatment, only tests in situ can give reliable results, while filtration tests in the laboratory
are only a poor substitute.
Another problem is that for waters with a low suspended matter content, drinking water
for instance, there is no relation between turbidity and clogging rate, making evaluation of
field tests rather difficult. More meaningful results in this respect can be obtained with
membrane filter test, whereby the water to be investigated is filtered at a constant head (2 atm)
and a constant temperature (10o C) through a membrane with a specified diameter (42 mm),
having very fine openings (0.45 µm). With the notation of Fig. 7.52.
D
con sta nt z 0
cak e, pe rm ea b ility k ’
m em b ran e
Q l z π
β + k o r Q = D2
0
z0 = 1 l
πD2 ′
β+ 4
4 k
′
c l
continuity Q dt = πD 2dl
ρd 4
ρd l
β+ dl
cz 0 k′
dt =
ρd k′ l 2 2
β + β
t = cz 2
0 k ′
159Energy Management Artificial Recharge Methods 159
tubidity
(FT U)
M FI
1.6
1.4
100
1.2
1.0
0.8
10 0.6
M FI
0.4
turbidity 0.2
1
0 5 10 15 20 25 30 35 40
3+
Fe (m g/l)
Fig. 7.54 Decrease of turbidity and MFI by rapid filtration as a function of the iron dose.
1 00 2
M FI (s/l )
10
Fig. 7.55 Relation between clogging rate and membrane filter index.
During well injection, the physical and chemical environment of the recharge water changes,
by which dissolved impurities may be transformed into suspended ones. Small amounts of iron
and manganese present in any recharge water may fall out by contact flocculation or may be
precipitated, together with carbonates, by changes in pH and redox potential, again resulting
in clogging by suspended impurities. The removal of clogging by suspended matter can easily
be obtained by well cleaning, but it is seldom 100% effective.
Growth of bacteria: Bacteria are also suspended matter, but their combined volume is extremely
small. With, for instance, 100 bacteria/cm3, each with a volume of 2 µm2, the suspended matter
content of the recharge water equals 0.2 parts per billion, from which no clogging needs to be
feared. Bacteria, however, are living things and multiply rapidly. In time t, their number growths
from n0 to n according to
160 Energy
Water Management
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n = n0 e0.693t/Td
with Td as the doubling time. With an entrance velocity ve, the number passing the wall of the
borehole in time dt equals
dN = ve no dt
In time t, this number increases to
dN = veno e0.693t / Td dt
giving at a time T after injection starts
T
N=
0
z
v e n o e0.693t / Td dt = v n Td
e o
0.693
d i
e0.693t / Td –1
. ¥ 1016 ¥ 2 ¥ 10–18
11
l= = 4 ¥ 10–2 m = 4 cm
0.55
after some time completely sealing the wall of the borehole. Real situations in the meanwhile
are less dramatic, as the calculations given above pre-suppose an unlimited food supply. This
food, however, is only present in small amounts in the recharge water, meaning that already
after short time equilibrium situation arises, where the available food is used to maintain the
population at a constant number (endogenic respiration) and no further growth occurs. During
this endogenic phase, bacteria need about 0.03 kg BOD per day and per kg of dry matter
conforming to a volume of roughly 10 l. With an entrance rate of 1 m/h and recharge water
with a BOD of 5 mg/l the food supply equals 0.120 kg BOD m-2 day-1, which is able to maintain
indefinitely a 40 mm thick layer of bacteria.
From the description given above, it will be clear that the rise, Sc, in the injection head due
to bacterial clogging reaches its maximum value already after some days (Fig. 7.49). When
large amounts of biodegradable matter are present in the injection water, a complete sealing of
the well may occur within 1 or 2 weeks. Bacteria preferably grow where their food supply is
most abundant, that is, in the well screen openings and the gravel pack when present and here
the resistance will be concentrated (Fig. 7.48). Growth of bacteria can be prevented in two
ways: (i) by removing their food prior to injection, for instance, by a preceding slow sand
filtration; (ii) by killing the bacteria with chlorine, maintaining inside the well a residual of 1 –
2 ppm.
Clogging caused by bacteria can easily be removed by burning them away with chlorine.
Some operators prefer to do this once or twice a year instead of the continuous chlorination
161Energy Management Artificial Recharge Methods 161
mentioned above under (ii). Bacterial clogging disappears by it when the well is taken out of
service and the food supply stops. The ensuing putrefaction, however, may impart a horrible
taste to the water present in the formation.
Reactions involving the recharge water: For completeness, it may be recalled that reactions
between the two types of water can only occur at the start of the injection process, at the
interface between the recharge water and the displaced native groundwater. In fine-grained
formations, this mixing zone is narrow and no adverse effects need to be feared. In coarse
grained and fissured rock formations, an appreciable amount of mixing may take place, but
here the openings are so large that the reduction in permeability by the deposits formed is
again small. The most important reaction follows the mixing of anaerobic groundwater
containing ferrous iron with aerobic recharge water, producing insoluble ferric oxide hydrates.
To be doubly safe, the recharge operations proper could be preceded by an injection of anaerobic
water, pushing the zone of possible reactions to such a distance away from the well that the
increase, Sc, in the injection head is always negligible.
The adverse effects between the recharge water and the aquifer material mainly concern
the swelling and dispersion of clay particles, present as silt in the formation. This clay consists
of small negatively charged threads, plates or flocs, kept together by positively charged ions, in
particular, by those having a multiple charge. In aquifers containing fresh water, the swelling
of clay particles and the reduction of pore space occur when the ratio between Ca2++ Mg+
and Na++K+ is reduced and/or the ionic strength is lowered. This can probably be prevented
by choosing another type of recharge water or by adding CaCl2 to the recharge water. It may
further be reduced by a pre-flush with water containing high amounts of CaCl2. When fresh
water is injected into a saline aquifer, the processes of mixing and cationic exchange produce
a zone of advancing water with the low ionic strength of fresh water and the high SAR value
of saline water. This combination strongly reduces electrostatic bonding and produces the
swelling and dispersion of clay particles when present. The dispersed clay particles are entrained
by the flowing water over considerable distances, but sooner or later they are captured in the
converging spaces between adjoining sand grains, thus decreasing pore space and permeability.
Flushing with CaCl2 to increase the bonding strength is again a preventing measure, but it is
not always effective. Polyvalent metal ions give better results, but they may not be applied in
drinking water practice.
The cleaning of wells clogged by the swelling and
dispersion of clay particles in the surrounding aquifer has only very limited effects.
Mechanical jamming: With a dual-purpose well, the direction of flow reverses periodically,
which might lead to a decrease in pore space, lowering the permeability of the formation in the
immediate vicinity of the well (mechanical jamming). The influence on the rise Sc in the injection
head can be calculated in the same way as indicated below:
Q 0 (k k′) r0 + l
Sc = ln
2 πkk′H r0
162 Energy
Water Management
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automatically, but it requires the presence of a pump and possibility of discharging the dirty
water. With dual-purpose wells, this is seldom a problem, but with single purpose wells, the
installation of a submersible pump with discharge piping may be rather expensive.
Notwithstanding their low efficiency, air lift-pumps, as shown in Fig. 7.56, may now be more
economical proposition with the added advantage of low maintenance costs. However, pumping
lowers the groundwater table and a small-saturated thickness, which are otherwise very well
suited for artificial recharge. In some cases, this problem can be solved by installing a battery
of, for instance, eight small-diameter recharge wells at a distance of, say, 3 m around the injection
well to be cleaned.
air
groundwater table
during injection
during back-pum ping
Fig. 7.56 Air lift pump for a regular cleaning of injection wells.
More intensive hydraulic methods: When the cleaning method is not feasible or not effective
in the long run, more vigorous means must be applied. Scrubbing with brushes removes deposits
on the inside of a well screen and casing. Slots in the well screen may be cleaned with powerful
water jets directed horizontally outward, as shown in Fig. 7.57. These jets also agitate and
clean the inside of the gravel pack, while a submersible pump removes the liberated clogging
simultaneously. To clean the outside of the gravel pack and the formation wall, large values of
the entrance velocity, ve, are necessary, which can be obtained by treating the screen section
by section, for instance as shown in Fig. 7.58. This is particularly effective when the gravel
pack has been clogged by, for instance, bacterial growth or iron deposits, but due to short
circuiting (Fig. 7.59) it is of less help to remove clogging at the formation wall.
These clogging, mainly originating from suspended solids in the recharge water, cling
tenaciously to the grains of the formation and are very difficult to dislodge. Straight pumping,
even at high entrance rates, has often little effect and the best way to liberate them is the
creation of flow reversals. Once they are free, they can easily be pulled through the gravel
pack and screen openings into the well and out through the pump. Flow reversals can be
affected in different ways, but in the case under consideration the use of compressed air, as
shown in Fig. 7.60, is most simple and effective. The operation starts with the air cock open
and the three-way valve turned so as to deliver air down the air line. The combination of drop
pipe and inside airline operates as a regular air lift pump, abstracting water from the well and
out through the discharge pipe. After the water has become clear, free of suspended matter,
the supply of air is cut off and the water in the well is allowed to regain its static level.
to p um p
su bm ersible pum p
w ell screen
gravel pa ck
form ation w all
ve
electric motor
aqu ifer
rubber cuff
Fig. 7.58 Cleaning a well Fig. 7.59 Short-circuiting Fig. 7.60 Cleaning of injection
Section by suction. during sectional cleaning. wells using air.
The air cock is now closed and the three way valve is turned so that the air supply is
directed down the bye pass to the top of the well. This air forces the water out of the casing
165Energy Management Artificial Recharge Methods 165
and back through the screen openings into the formation, agitating the sand and loosening the
clogging. After the water level has been lowered to the bottom of the drop pipe, the air will
escape upward through this pipe, without the danger of air clogging the formation. The air
cock is now opened, allowing a rapid rise of the water level in the well and inflow of groundwater
at high velocities. This inflow is further promoted by directing the air supply down the airline
to pump the well. The procedure is repeated several times, until the pumped water has become
clear and no more debris can be drawn into the well. Sometimes it is necessary to remove the
washed-in material by boiling, to keep the well screen active over its full length. From the
description given above, it will be clear that hydraulic cleaning is a rather complicated operation,
taking 1-2 days to perform. Keeping injection wells operable in this way is therefore only an
acceptable proposition when the intervals between cleaning are long, e.g. more than one year.
Chemical cleaning: In some cases, the clogging material is so strongly attached to the grains of
the gravel pack and surrounding formation, that the shear stresses created by hydraulic cleaning
are inadequate to dislodge them. The surging described above must now be preceded by chemical
treatment of which the most important are: (1) Chlorine or chlorine compounds, such as sodium
hypochlorite (NaOCl) or calcium hypochlorite [Ca(OCl)2], to burn away deposits of bacterial
slimes. Moreover, they kill the bacteria present and when the distance over which this occurs is
large, subsequent growth of bacteria is greatly retarded. (2) Acids, such as hydrochloric acid
(HCl), sulphuric acid (H2SO4) or sulphamic acid (NH2SO3H), to dissolve deposits of calcium
carbonate, magnesium hydroxide and iron and manganese oxide hydrates, which moreover act
as cementing agents forming thick encrustations around the well screen. (3) Polyphosphates to
disperse deposits of iron and manganese oxide hydrates, silt and clay particles.
This page
intentionally left
blank
8 CASE STUDIES
8.1 IN SITU WATER HARVESTING FOR DRINKING WATER SUPPLY AT
CHERRAPUNJI, MEGHALAYA
Cherrapunji has the dubious distinction of being one of the highest rainfall places in the
world and still suffering a shortage of drinking water supply in the pre-monsoon months.
The situation is prima facie paradoxical as it indicates water scarcity in the midst of super
abundance of precipitation.
Cherrapunji is located on the southern fringe of the Shillong plateau, on an E-W trending
escarpment at an altitude of 1310 m. Traditional water supply to the town is through the
spring issuing from surrounding hills. The annual rainfall is about 11,000 mm, most of it
coming in the period June to September. The local rock is limestone. These escarpments are
devoid of any soil cover because of the intensity of rainfall and consequently have hardly any
vegetative cover. It is claimed that the discharge from the springs has declined but no one has
actually measured this. The reason for scarcity, therefore, seems to be an increase in population
and per capita consumption.
Roof water harvesting, introduced by the public health engineering department of
Meghalaya, comprises the collection of rainwater from house rooftops through gutters, its
filtration and subsequent storage above the ground in a reservoir with an average storage of 7
cu.m. These systems are designed to supply 10 liters per capita per day for 90 days. The life
span of the system is about 15 years with the costs worked out to Rs. 14,000 per cubic meter
in the year 1991.
The alternative technology comprising in situ water harvesting is described here. Pits of
size 10m × 10m × 10m at elevated sites close to a cluster of 10 –12 houses can be constructed.
The cost of such a pit, with concrete lining, reinforced concrete roofing with inlet holes,
distribution pipelines, two transient storage galvanized iron tanks etc. based on the 1990-91
rate schedule of PHED of Meghalaya, works out much cheaper than the system developed by
the PHED. In addition, such situ systems are able to supply water at a rate of 40 lpcd throughout
the year to an estimated population of 60 persons living in this cluster of 10 – 12 houses. This
water supply will be by gravity flow as in the case of the water supply from springs. The
dissolved solids and iron content will be lower than the permissible limits. It may require
168 Energy
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chlorinating treatment for organic contamination but this also happens with water supplied
by the PHED (Athavale, 2001).
Other options for improving the water supply situation for Cherrapunji town are gully
plugging, creating open wells in streambeds and storing the water in abandoned limestone
quarries and augmentation of spring discharge by constructing horseshoe shaped subsurface
impervious barriers below the discharge point (Athavale, 1991).
continuously for about 250 days was probably sustained because of contemporaneous
withdrawal from the aquifer through nearby irrigation wells.
In Mehsana area, artificial recharge experiments through the spreading method were also
conducted using canal water. A spreading channel of 3.3 meters width, 400 meters in length
with 1:1 side slope was constructed and the canal water was fed for 46 days. The recorded
buildup in water level of 3.5 to 5.0 cm was observed up to 15 m from the recharge channel and
about 20 cm at a distance of 200 m. A recharge rate of 260 cubic meters per day was estimated
using an infiltration rate of 17 cm/day. Dissipation in recharge mound (1.42 in) was observed
in 15 days.
Another experiment using a recharge pit (1.7 in × 1.7 in × 0.75 in) to study the feasibility
of recharging the shallow aquifers was conducted at Dabhu in central Mehsana area. Canal
water was used for the experiment and the pit was covered to prevent dust deposition and
evaporation losses. It was reported that during the recharge phase of 60 days, the recharge was
at the rate of 17.3 cubic meters per day with an infiltration of 0.5 m/day. A rise of 4.13 m in the
water level was observed at a distance of 5 meters from the recharge pit. Both these recharge
methods were effective in alluvial areas.
Artificial recharge through pressure injection technique was tried on a pilot scale using
groundwater from a phreatic aquifer for a short period in the Mehsana alluvial aquifers. Tiwari
and Srivastav (1983) have reported the results of this experiment. The source well was located
in Saraswati River and the water was carried to an injection well at a distance of 130 meters by
a 10 cm (diameter) pipeline. On-line flowmeter and pressure gaugeswere fitted to monitor the
flow rate and cumulative quantity and to record the pressure developed during the injection
experiment. The injection recharge experiment was conducted with 8 liters per second (lps)
rate for about an hour. The injection rate was increased to 12 lps and the test was continued
for 90 minutes. A drastic reduction in recharge rate (3 lps) was reported and the cause of
reduction was attributed to back pressure, due to clogging of the injection well. Due to well
clogging, the water level could not reach its initial static level even after eight days. Though in
this case, the silt free shallow groundwater was used for recharge, the observational results
clearly indicate the necessity of understanding probable clogging problems, which may arise
due to many other factors apart from silt entry.
Studies on control of salinity in coastal Saurashtra using the spreading and injection methods
have indicated that the recharge pit and the injection shaft can affect recharge at the rate of
192 and 2600 cubic meters per day respectively. Canal water was used for these recharge
studies. It was reported that problems in land acquisition in this highly developed area make it
difficult to select suitable sites for spreading structures.
The Gujarat Water Resources Development Corporation conducted pressure injection test,
for a short period, in 1974 near Ahmedabad city. Processed water from the city water works
was injected for 72 hours in a deep tube well and a pressure varying between 80 and 100 psi
was applied with a rate of 45 liters per second.
170 Energy
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Sama Chhani
Particular Unit
OW TW OW TW
Aquifer TypeUC SC UC SC
Wells No.4 33 - 39
Depth m 10-17 50-70 - 60-100
Diameter mm 3000 150-200 - 200-250
SWL (1999) m 8-10 15-30 20-25 -
Pump Hp 5 5-15 - 30
Discharge lpm 30 300-600 - 800-1500
Quality B B B B, Su
Use D D, I - D, I
Three exploratory bores of 200mm diameter and 30 – 45m depths, one each on the bank of
the existing village tank have been taken for the study of aquifer material, water level and
quality. The bores were converted into shallow tube wells by providing blind/slotted PVC
casing and gravel pack. They were used for determining permeability by pump out tests.
Recharge tests were carried out by adding clean water from outside source.
The bore at Sama, drilled up to 32m depth encountered two aquifer layer; 10.5-21.0m and 16.0-
30.0m depth. These have been provided with 110mm PVC slotted pipes. The top 10.5m is yellow
silty soil and the two aquifers have been separated by 8m thick (18-26m depth) yellow silty clay.
171Energy Management Case Studies 171
The bore at Chhani encountered two aquifer zones; first, 18m thick (10-28m depth) and second,
13m thick (33-43m depth) of fine to medium sand and gravel deposit. The top soil of clay, silt and
sand mixture was encountered up to 10m depth. The yellow silty clay, with kankar of 5m thickness
(28-33m depth) separates the two-aquifer zones. While developing the hole, the lower 10m thick
zone between 33 and -43m depth has been provided with 110mm PVC slotted pipe.
Permeability and Recharge Tests: Permeability tests for Chhani and Sama tanks were
carried out by pumping water at a constant rate and measuring steady state drawdown in
exploratory bores.
An observation of in-situ tests permeability tests and recharge tests are as shown in Table 8.2.
Table 8.2 Recharge and permeability tanks
Based on topographical survey, contour maps and area capacity tables were prepared for
each tank. FRL and area capacity at two tanks are given in Table 8.3.
Table 8.3 FRL, area and capacity of tanks
Computer Modeling of Chhani Tank: To carry out recharge study for Chhani tank area, the
computer model is developed using MODFLOW software developed by US Geological Survey.
The study area is discretised into a grid of 114 rows and 119 columns with variable size.
Minimum spacing of 9.5m is selected in tank area and the grid spacing was increased away
from tank area near constant head boundary. The aquifer is considered as confined with
bottom RL as –6.0m and top RL +4.0m. It is assumed that constant head boundary exists
about 800m away from tank boundary.
The results of pumping test were confirmed by model test. For a 37 lpm pumping of a well
located at row –53 and column –35 and using permeability value of 4.67 m/day, the drawdown
was computed by model as 1.15m as compared to observed drawdown of 1.34m. Hence
permeability of 4.6 m/day is considered for recharge modeling.
Based on available water in the tank and capacity of recharge wells, 20 wells recharging at
a rate of 50 lpm are feasible.
In recharge modeling, 20 wells of 50 lpm steady state recharge were considered surrounding
the tank periphery. The static water level was considered as RL 7.0m. After the simultaneous
172 Energy
Water Management
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recharge from all 20 wells the resulting water level was obtained by model. The contours of
water levels are shown in Fig. 8.1. A cross sectional view showing water level mound across
tank area is shown in Fig. 8.2. The results indicate that maximum water level of 14.7m is
achieved near recharge wells. An average water level below tank area is found to be 14.12m.
7.5
200 0
7.0
8.5
1 800
8.0
7 .0
9.5
9. 0
7. 5
8 .5
0
1 600
8.
10 .5
7.5
11.0
8.5
7.0
5 11 .5
0.
0
9.
1 12 .0
12 .5
14 00
13 .0
8 .0
13 .5
9 .5
.5
12
9. 0
11 .0
1 20 0
12 .0
10 .5
11 .5
1 2.5
9 .5
11 .5
1 3.5
1 0.5
11 .0
1 2.0
13 .0
1 00 0
1 3.5
.0
9.0
1 2 13
.5
80 0
8 .0
8.5
.0
12
7 .0
1 1 .5
6 00
11.0
10 .5
7 .5
9.0 9 .5
8.
400
0
8 .5
7 .0
200
7.5
0
0
20 00 18 00 16 00 14 00 12 00 10 00 80 0 60 0 40 0 20 0
38 37-0 FR L 36-5
GL GL
34 33-0
10
RE CH ARG E W E LL
3
14-7 14-12
1 RE CH ARG E MO UND
0 20 0 40 0 60 0 80 0 10 00 12 00 14 00 16 00 18 00 20 00 22 00
D istan ce (m )
Fig. 8.2 Cross section xx showing water level rise due to recharge in Chhani tank.
173Energy Management Case Studies 173
Computer Modeling of Sama Tank: To carry out recharge study for Sama tank area, another
computer model is developed. The study area is discretised in to a grid of 109 rows and 91
columns with variable size. Minimum spacing of 10m is selected in tank area and the grid
spacing was increased away from tank area near constant head boundary. The aquifer system
is considered as two confined aquifer layers as shown in Table 8.4.
The permeability value is adopted from calculation based on field recharge tests. It is
assumed that constant head boundary of 9.0m exists about 800m away from tank boundary.
In recharge modeling, 10 wells of 30 lpm steady state recharge were considered surrounding
the tank periphery. As aquifer system is comprised of two layers, it is considered that each
well is recharging water at a rate of 27 m3/day in top layer and 15 m3/day in bottom layer.
The static water level was considered as RL 9.0m. After the simultaneous recharge from all
10 wells, the model obtained the resulting water level. The results indicate that maximum
water level of 28m is achieved near recharge wells. An average water level below tank area
is found to be 25.5m.
Recharge Scheme: It is proposed that water from village tank will be used for recharge through
recharge wells. The available water for storage is considered as volume of water between FRL
and sill outlet pipe, which leads water, through filter unit to recharge well. Net available recharge
water is considered 80% of total volume, allowing 20% evaporation losses. As all tanks bed
comprise of clay layer, seepage losses are considered negligible. The filter unit is designed as
slow sand filter with filtration rate of 3.5 lit/min.
Recharge rate is estimated by recharge test in an exploratory bore at each tank. Number of
recharge wells possible at each tank is worked out by dividing net volume of recharge water by
recharge capacity exchange of well at each site.
Chhani Tank: SWL at exploratory bore was 30.8m below GL. Recharge rate observed at
exploratory bore was found to be 37 lpm with 16.3m head i.e. recharge water level 14.5 below
GL. Considering that inlet pipe from the tank will approximately be at GL, recharge head can
be increased to 25m with recharge level 5.8m below GL. The difference of 5.8m between GL
and recharge level is necessary to accommodate filter bed unit of about 2.7m height and pipe
losses to supply recharge water from tank to recharge well through filter bed unit by gravity. It
is estimated that recharge rate will be 50 lpm with 25m head.
Area of filter bed will be 50/3.5 = 14.3 m2. An area of 20m2 is provided to allow for
reduction in capacity due to clogging. Area of 4m × 5m is provided for filter bed. 4m × 1m
dry chamber is provided for installation of control valve and water meter.
174 Energy
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Filter bed to provide with 2 layers of sand (0.4m), 2 layers of graded gravel (0.3m) and one
layer of gravel (0.4m) for laying 100m slotted PVC pipe. Recharge well comprising of 200m
hole, 100mm blind/slotted casing and gravel pack.
Volume of water available between FRL 36.5m and outlet pipe sill at RL 33.0m is 468920m3
(604120 – 135200). Net volume available allowing 20% for evaporation losses will be 468920 ×
0.8 = 375000m3.
During three monsoon months, there will be overflow. Hence storage will be needed for 9
months i.e. 270 days with recharge rate of 50 lpm i.e., 72 m3/day, number of wells will be
375000/(270 × 72) = 19.29 say 20 wells.
There can therefore be 20 recharge wells around periphery of tank, at locations, depending
on demand of users.
Rise of water level at recharge well is up to RL 14.7m as against maximum possible RL of
33.0 i.e. sill of outlet pipe of filter unit. Additional recharge would have been possible if available
water from tank was larger. Total recharge from Chhani tank will be 72 m3 per day. If domestic
water supply requirement is considered as 100 liter/capita/day, this can meet requirement of
720 persons.
Sama Tank: SWL was 3.4m below GL. Recharge rate at exploratory bore was 14 lpm at 3.4m
recharge head i.e. recharge level just at GL. As exploratory bore was just at bank of tank, GWL
was converted to tank water level. A minimum 3m difference is necessary between outlet pipe
sill level and recharge level so as to provide filter bed unit and recharge by gravity head. The
exploratory bore site is not suitable for actual recharge well. The recharge well location has
therefore to be at some distance away from tank where GWL is about 10m lower than outlet
pipe sill. By this way, larger recharge will be available. It is informed that recharge rate can be
increased to 30 lpm if recharge head is increased from 3.4m to 7.0m. FSL of tank is 36.3m
outlet pipe sill is provided at RL 34.0m.
Filter bed area will be 30/3/5 = 8.0 m2. However 12.0 m2 (4m × 3m) is provided for
probable clogging of filter bed. 4 × 1m dry chamber is provided to install control valve and
water meter. Filter bed is provided with 2 layers of sand (0.4m), 2 layers of graded level (0.3m)
and one layer of gravel (0.4m) for laying 100 mm slotted PVC pipe. Recharge hole comprising
of 200m hole, 100 mm blind/slotted PVC pipe, with gravel pack. Volume of water between FRL
36.3 m and outlet pipe sill 34.0 is 152870 – 37540 = 35,330 m3. Net volume available for
recharge is 0.8 × 135330 = 108300 m3. During three monsoon months tank will overflow
and hence storage will be needed to be used for nine months only. Recharge rate per well is 30
lpm (43.2 m3/day). Number of recharge wells feasible = 108,300/ (43.2 × 279) = 9.2 say 10.
Therefore, 10 recharge wells around periphery of Sama tank are feasible. They may be
provided at location depending on demand of users. Rise of water level at recharge well is up
to RL 28.0m as against maximum possible RL of 34.0m i.e. sill of outlet pipe filter unit.
Additional recharge would have been possible if available water from tank was larger. Total
recharge from Sama tank will be 43.2 m3 per day. If domestic water supply requirement is
considered as 100 liter/capita/day, this quantity can meet requirement of 432 persons.
175Energy Management Case Studies 175
S IP H O N F O R A R T IF IC IA L R E C H A R G E E X P ER IM E N T
V IL L A G E : K A N D U K U R U D IS T R IC T: A N A N TA P U R S TAT E : A N D H R A P R A D IS H
EARTH EN BU N D
A A
K A N D U K U R U TA N K
A
A
DUG CUM
BOR EW ELL
2 .5 C m o f P V C P I P E F O R S IP H O N
PLA N
The amount of water harvested from water harvesting scheme depends upon the frequency,
intensity and duration of rainfall, catchment characteristics, rainwater harvesting method used
and response of the system that depends on maintenance and operation of the structure. How
long the supply could last depends upon size of storage and water demand. The quality of
harvested water depends upon design of structure, operational procedures and on education
and sensitization of users on water quality issues.
Use of Kunds is an ancient practice of water harvesting in Thar Desert. The Kunds were
and still are owned mostly by community and some privately. The first known construction of
a Kund in western Rajasthan was during 1607 AD by Raja Sursingh in village Vadi-Ka-Melan.
In the Mehrangarh Fort in Jodhpur, a Kund was constructed during the regime of Maharaja
Udai Singh in 1759 AD. During the great famine of 1895-96, construction of Kunds was taken
up on a wide scale. Unfortunately use of Kunds as rainwater harvesting structures declined
thereafter owing to availability of water through community and other schemes. Though
such schemes have provided drinking water at a high cost for human consumption, cattle
have suffered as they are fed with the available low quality groundwater. Some of the problems
related to Kunds are deterioration in quality water with time making it unacceptable,
178 Energy
Water Management
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development of cracks and hence seepage from catchment area and tank, soil erosion due to
improper location/construction of structure, inadequate/sub optimal design, construction and
maintenance of structure, silting of catchment area due to shifting sand dunes and failure of
cleaning the catchment surface before the onset of monsoon etc.
Recently with lot of emphasis on rainwater harvesting, hundreds of such Kunds were
built in Churu district under the drought relief works. Many more projects for construction of
such Kunds are under active consideration. It is thought that with technical inputs for design,
construction and maintenance of these Kunds they can be developed as sustainable, reliable
and economical sources of water with improved quality.
Study area: Churu district is located in the North Eastern Rajasthan and is bounded by
Ganganagar and Hanumangarh district in North, Sikar, Jhunjhunun and Haryana state in the
east, Nagaur in south and Bikaner district in west. It lies between latitude 27°25¢10¢¢ to
28°59¢20¢¢ north and longitude 73° 37¢30¢¢ to 75° 40¢30¢¢ east. Average altitude is about 400 m
from mean sea level. Climate of area is absolutely dry with scanty rainfall. It is very hot during
summer and very cold during winter. Annual rainfall of various blocks (tehsils) of 2000 to
2003 as well as normal rainfall is given in Table 8.5.
There are very few wells in this area for irrigation purpose. The wells, Kuias, Johad and
Kunds are used for drinking purpose. The water table depth is comparatively shallow towards
eastern half of the district (33 to 56 m). It is deeper towards western half and ranges between
40 and 115.44 m. Practically there is no river in the district, however, in extremely high rainy
events Kantli river enters in the extreme southern peripheral village of Rajgarh block.
The undulating sand dunes and sandy plains represent the entire district. Fairly open and
flat plains have also been observed in Rajgarh and Sujangarh blocks of the district. Isolated
hillocks of considerable height and restricted extension have also been observed towards
southeastern part of the district at Gopalpura, Dungras, Balera, Rndhisar and Biramsar.
However, one or two small hillocks of granite are also exposed towards extreme north of
Rajgarh block at village Galar in block, Rajgarh and village Sandan in block Sujangarh.
The main water bearing formation in the district are younger and older alluvium of
quaternary age, tertiary sandstone, Nagaur sandstone, Bilara limestone and Jodhpuri sandstone.
179Energy Management Case Studies 179
The groundwater in the district occurs under semi confined to confined conditions. The
occurrence of perched waterbodies above saturated zone has also been found in some part of
Churu, Rajgarh and Taranagar block. These bodies have very limited potential of groundwater.
The pH of soil is normal (8 to 8.7) and conductivity of soil is good.
Methodology: In order to analyze the present structures, data were collected from 81 existing
old as well as recent structures in Churu district. Of these, 13 structures were constructed
prior to 1960, 23 were constructed between 1960 and 1980, 1 was from 1980 to 2000. Cost of
many of the old structures was not available, however those of last year varies from
approximately Rs. 20,000 to 100,000 depending upon the size of structure.
The life of Kund and the user’s financial condition play a major role in selection of
dependability factor. For drinking water purpose, less risk and so higher dependability factor is
considered as compared to the irrigation projects. Table 8.6 shows the size of storage tank for
different diameter of paithan considering dependability factors of 90% and 70% and runoff
coefficient 0.85.
Dependability factor 90% 70% 90% 70% 90% 70% 90% 70%
On the basis of data collected of different Kunds, an analysis of their paithan area and
catchment area was made. Figure 8.5 shows the points for each combination of paithan area
in ft and storage tank capacity in liters. As can be seen, there are wide variations on storage
capacity for same size of paithan. For example, for 50 ft2 of paithan area, storage tank capacity
ranging from 32,795 lit. to as high as 269,185 lit. was found. The capacity of tank varied
with local mason or person who designed it and was mostly based on their past experience.
A linear trend line shows some correlation between paithan size and storage tank capacity
but correlation is not very strong with R2 (coefficient of determination) value of only 0.42.
Correlation equation is:
Storage tank capacity in liters = 2328.9 × Paithan diameter in ft – 32435 (Fig. 8.5)
180 Energy
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5000 00
4500 00
S iz e o f s te era g ew a y tan k
4000 00
3500 00
y = 2 328.9 × .32435
2
3000 00 R = 0.42 05
2500 0
2000 00
1500 00
1000 00
5000 0
0
0 10 40 60 80 100 120 140 160
S ize o f P a lth an , ft
With this equation average capacity of storage tank works out to 14,100 liters for 20 ft2
paithan area and 84,000 for 50 ft2 paithan area, which indicates that most of the time,
storage tanks are traditionally designed for less than 50% dependability factor, still some
of the tanks were much below the desired storage capacity of 90% dependability factor.
For example a 40 ft paithan area tank was found with the storage capacity of only 2,800
liters.
A similar analysis of slope indicated that the slope of catchment area varied with
construction material used, finish of catchment area, and the person who undertook the work
of Kund. The slopes varying from 0.75% to 5% were found in existing structures.
The above analysis indicates that some guidelines should be made for optimal design of
such Kunds for the future projects to conserve the rainwater at a high efficiency. Also, the
structures need certain considerations for ensuring a better maintenance of the quality of
water stored. Some recommendations based on the present study are as follows:
1. The paithan size must be calculated based on the required capacity of storage tank,
design annual rainfall, dependability factor and tunoff coefficient as suggested above.
2. The demand of water consideration should be based on I S recommendation. The
Kund for individual family of 5 members normally should be 20,000 or 22,000 liters
capacity.
3. Slope 1.5% is recommended for paithan.
4. The storage tank of the Kund should be constructed at the one end of paithan in case
Kund is constructed for drinking water purpose. This will ensure better quality of
stored water, as the users themselves would not contaminate the paithan.
5. A small ditch should be provided at the bottom of Kund to remove water. This will
facilitate proper cleaning of tank from time to time.
6. Over flow arrangement for first flush (for drinking water Kunds) should be made.
7. Enough funds should be earmarked for maintenance of Kunds as it was found that in
absence of maintenance the paithan and tanks leaked and so the Kunds become useless.
181Energy Management Case Studies 181
8. Since the cost of Kund per liter of water decreases as the size of Kund is increased,
efforts must be made to construct large capacity Kunds for more number of users.
However it is found that the maintenance of such structures is poor, so efforts must
also be made to ensure proper maintenance of such structures.
9. To promote the economic development of the village community and employment
generation Kund water can be used for horticulture purpose.
10. In Churu district groundwater contains alarming quantity of fluoride. If Kund water
is mixed with groundwater, it can bring some respite for man and cattle. The Kund
can be designed for a family with a due consideration given to the demand for cattle.
Roof Top Rain Water Harvesting Storage cum Artificial Recharge to Check the Gradual
Lowering of Piezometric Water Surface of the Ground Sources as well as Improvement
of Groundwater Quality in and around DUMDUM: South Dumdum Municipal area is
probably the most densely populated area of all the municipal bodies in West Bengal. It has
experienced a steady growth in the last 250 years. People from different parts of the country
have come here in search of livelihood. A major influx of people occurred after the partition of
Bengal and settled indiscriminately wherever they found space. The present population of
South Dumdum Municipal area is about 450000. On account of growth of unplanned settlement
in and around Dumdum, the availability of civic amenities is becoming scarce everyday. One
such problem is acute scarcity of safe drinking water. The supply of water from groundwater
source is more than 33500 kiloliters per day through big and small diameter tube wells as well
as private tube wells. This figure is increasing with the expansion of urban complexes, rise in
population and industrial development.
To cope up with the increasing demand, groundwater is being withdrawn indiscriminately
in the city that in turn is posing serious threat to the safety of the city structure due to gradual
lowering of piezometric surface in the range of 5 – 10 meters in the city. Moreover, the availability
of groundwater in the lean period is also a great concern. The aim of this project is to explore
the possibility of augmentation of groundwater resource in the area by roof top rainwater
harvesting cum storage cum artificial recharge of groundwater. We felt that this is specifically
needed in the area because though average rainfall in the area is high but due to non-availability
of suitable surface area for percolation, the run off is maximum and percolation of rainwater is
less. Moreover, rain water being the purest form of water, can improve the quality of
groundwater that is getting deteriorated day by day.
Objective: The main objective of the project was to assess the possibility of sustainable
development of groundwater in the area where natural percolation of rainwater is very limited
due to non-availability of suitable surface area conducive for percolation due to extensive
urbanization. The South Dumdum Municipal authorities initiated the pilot project of “Roof
Top Rainwater Harvesting – Storage cum Artificial Recharge” at the municipal office building
at Nagar Bazar, Kolkata. The basic idea is to catch the surface run off from the rooftop through
a piping network system, i.e. collecting from the roof and getting it connected to the collection
cum recharge storage pit for onward transmission to the injection well newly installed for the
artificial recharge.
182 Energy
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Study of the lithological log of the tube wells constructed in the area indicates that beneath
a thick clay bed (35 – 45m) there occurs an aquifer of moderately good groundwater potential
down to the depth of 45 – 150 m with thin intervening clay layers. This aquifer is being exploited
by a large number of tube wells, as a result of which the groundwater level (piezometric surface)
has been lowered considerably in the last two decade. The present disposition of piezometric
surface of groundwater is around 15 m below ground level. It is reported that in the last two
decades there has been a significant drop of piezometric surface level in the tune of 5 to 9 m in
this area. Since the aquifer is composed of medium to coarse-grained sand of moderate permeability,
the water harvesting potential is quite high in this aquifer.
Considering different hydrometeorological, hydrological and hydrogeological aspects, it was
decided to construct roof top rain water harvesting system with primary objective to recharge to
groundwater in the underlying aquifer and to create storage of rainwater of 20000 liters capacity
for utilization for the purpose like washing of pavements, car washing, gardening etc.
Based on the size of the roof area, available rainfall in the monsoon months and roof
catchment efficiency, it is considered that a total quantity of 4, 50,560 liters can be available
from rainwater harvesting of the rooftop of the building. Allowing a storage facility of 20000
liters in the storage tank that has been created, rest of the harvested rain water would be
recharged to groundwater.
The other objective was to examine the possibility and extent of qualitatively and
quantitatively improvement of the groundwater that is deteriorating increasingly. A monitoring
well is placed at a distance of 100 feet down gradient for surveillance purpose.
Profile of Area: The boundary of the area has always been expanding since its birth. The area has
railway track as its western boundary from Patipukur to Bediapara, Baguiati canal as its eastern
boundary, Clive House as its northern boundary and Dakshindari as its southern boundary.
Latitude and longitude of city : 22°28′00′′ : 22°37′30′′
80°17′30′′ : 88°25′00′′
Climate :
Type of climate : Tropical sub-humid to humid
Maximum Temperature : 40.3° C
Minimum Temperature : 10° C
Rainfall:
Average Annual Rainfall : 1600 mm
Distribution of Rainfall :
January 17.60 mm July 308.70 mm
February 29.40 mm August 320.50 mm
March 35.38 mm September 241.00 mm
April 50.00 mm October 117.60 mm
May 126.40 mm November 32.34 mm
June 273.42 mm December 7.35 mm
183Energy Management Case Studies 183
Geological formation: The area is located on the lower deltaic plain of the Ganga Bhagirathi
delta. It is covered by the sediments deposited by the river system flowing through it during
quaternary period. The succession of sediments of Quaternary age consists of clay, silt, fine —
medium to coarse sand and occasional gravel and pebbles. Both recent and Pleistocene sediments
have been deposited successively by the Ganga River as the flood plain deposits. From the
study of litho logical logs generated from boreholes drilled by different agencies, it can be
concluded that the lithological sequence is topped by a clay layer of 30 – 60 thickness in this
area. The top clay layer is followed by fine to medium sand layers of clay and sand bed. The
floor of the quaternary deposits in this area may be fixed at depth between 296m and 414m
below ground level. Two horizons of pit have been observed in the boreholes between 2 -5m
and 12m and 12.6m during the metro railway excavations. The litho log of area is characterized
by the occurrence of a clay bed in the upper part of the sedimentary column and another clay
bed at bottom. Both the upper and bottom clay beds are dark grey in colour, sticky and are
plastic to semi-plastic in nature. A conspicuous feature is the occurrence of fine to coarse sand
horizon mixed occasionally with gravel and sandwiched between clay beds.
The continuity in the sequence of sand, which forms the aquifer material, is broken by the
occasional occurrence of clay lenses of limited lateral extent. The entire sandy sediment up to
a depth of 150 meters is on an average moderately well sorted. The borehole lithologs indicate
the occurrence of yellow to brownish coloured sand in the depth span of 20 to 80 m, which
suggests oxidizing condition of deposition. The colour of the sediments occurring below the
above horizon varies from grey to light grey which appears to have been deposited under
reducing conditions.
Hydrogeology: Quaternary sediments having a sequence of clay, silty clay, sand and sand
containing gravel underlie SDDM area. The upper layer is underlined by coarse clastic
consisting of sand, fine medium and coarse grain mixed with gravel in some places. These
coarse clastics form the aquifer. The shallow aquifers that are available within less than 20
meters level are water table aquifers.
The sediments exhibit typical deltaic deposition showing facies variation at a few places
having sand and pebbles from the aquifer materials. The most prolific water bearing formation
is available within 60 – 180 meters consisting of fine to medium sand of 20 – 40 meters thickness.
However, in places brackish water aquifers capped the freshwater aquifers.
The piezometric surface of fresh water aquifer on the central part of the city has been
lowered by 5 – 9 meters over the last four decades and as a result of which the flow direction
of groundwater has changed from southerly to easterly and south easterly direction. This is
due to over extraction of groundwater compared to natural recharge.
The deeper aquifer in SDDM area is recharged from northern and western part of the area
outside Kolkata where these sand beds are exposed almost near to the surface. These areas are
mainly in Kanchrapara – Kalyani – Ranghat – Shantipur area in Nadia District in North. The
near surface aquifers of these areas that get recharge mainly from the rainfall and this water
infiltrates into the deeper aquifers of SDDM area.
184 Energy
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With the progress of urbanization, the groundwater withdrawn has been increased to an
alarming extent. The depletion of the piezometric head has been registered most prominently
in SDDM area.
As in some areas of SDDM has been a major decliment of piezometric head observed and
the groundwater exploitation can’t be stopped, the need for artificial recharge of this aquifer is
strongly felt.
Rooftop Rainwater Harvesting: From the record, it has been observed that the static water
level (SWL) has dropped from 8.84m below ground level in 1994 to 13.85m below ground
level in 2004, i.e. in the last ten years the SWL has lowered by more than 5 meters. This is
indeed an alarming situation and unless augmentation of groundwater is done through
rainwater harvesting, both the quality and quantity of groundwater in the area is bound to be
affected adversely.
Keeping above in mind and office of the Councilors of South Dumdum Municipality, Kolkata
entrusted the job of roof top rainwater harvesting cum artificial recharge of groundwater at
the office building of the Municipality. Rainwater harvesting potential of the building was
carried out as per the following details:
Average rainfall per annum: 1600 mm
Rain water collection efficiency = rainfall (mm) × collection efficiency
= 80% of maximum rainfall = 1280 mm
Available roof top area in the office building is 550 m2
Height of rainfall = 1.28 m
Volume of rainfall = Area × height of rainfall = 704 m3
Coefficient of roof catchment = 0.8
Coefficient of evaporation, spillage and first flush = 0.8
Harvested potential = 704 × 0.8 × 0.8 = 450.56 m3 = 450560 liters
Work done:
• All the rainwater drop pipes were connected in Ring Main System with a slope towards
the collection pit.
• SWR water drop pipes of 100 mm were connected horizontally in 150 mm diameter
pipes with inclination that was reduced to 100 mm diameter pipes for gaining velocity
up to the collection pit. Strainer has been provided for arresting unwanted solids,
leaves/straws etc. Arrangement for flushing the first rainwater has been provided before
rainwater enters the collection pit by providing suitable valves.
• 150 mm diameter SWR pipes drawn from collection pit to the recharge pit.
• Overflow pipe for recharge pit has been provided.
• An air vent above the tubewell is also to be provided.
• Sinking of 150 mm diameter tubewell upto a drilled depth of 105 meters and lowered
depth of 99 meters BGL by providing PVC casing pipes and ribbed screens having
185Energy Management Case Studies 185
1 mm slot width. The discharge of the newly sunk tube well had been recorded to be
15100 Imperial gallons per hour. During the heavy monsoon period, it has been observed
that the tube well sunk for artificial recharge of groundwater is capable of recharging
all the water that overflowed to the well from the storage tank.
• The total cost of the completed project — Rs. 421,572/-.
Artificial Recharge Experiment for Underground Storage of Water Based on Siphon
Principle
The principal source of natural replenishment to aquifers is infiltration from precipitation.
This annual replenishment of aquifers is limited to a small fraction of precipitation due to
runoff and evaporation. The situation is even worse in arid and semi-arid regions like Gujarat,
where the loss due to evaporation is high. As a result of rapid development in agriculture and
industry during the last two decades, demand for water in Gujarat has increased enormously.
In absence of available surface water supplies, the groundwater reservoir has been subjected
to large-scale exploitation through an increasing number of tube wells by both government
and private agencies. This heavy withdrawal of groundwater has resulted in lowering the
water level at an alarming rate in parts of north Gujarat. One of the methods of remedying the
situation is artificial recharging of aquifers in this region. A recharge scheme involving
purification of water through the upper sand layers in the Sabarmati riverbed and its direct
injection to a tube well on the riverbank through a siphon arrangement was suggested by
Physical Research Laboratory, Ahmedabad. The construction of tube wells and other
arrangements were done by Gujarat Water Resources Development Corporation.
Experimental Details: A 350 mm diameter shallow gravel packed tube well (depth 21,34
m) was constructed in the riverbed of Sabarmati River adjacent to the fair weather bridge
linking Gandhinagar with Ahmedabad via Hansol. This well taps the unconfined aquifer in
the riverbed between 6.04 and 21.34 m below riverbed level. This well (source well) is used
to supply adequate quantity of naturally filtered river water. The water from the source well
flows into a deep tube well (depth 238 m), (hereafter called injection well) tapping confined
aquifers below 74 m depth. A schematic diagram showing the arrangement of source well,
injection well, connecting siphon pipe and observation well at the site of experiments is
shown in Fig. 8.6.
The injection recharge experiments was started at 10.53 hours on 29th May 1977 and
continued till 15.55 hours on 7th June 1977, when it was stopped for studying the dissipation
or recharge mound. The priming of the siphon was adopted by evacuating the siphon pipe
using a water ring type vacuum pump of capacity 50 m3/minute. During the period of experiment
water level fluctuations in (i) injection well and (ii) the observation well was regularly monitored
at suitable intervals. Recharge rate during a given interval was computed from the readings
shown by a flow meter on the siphon pipe.
186 Energy
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Fig. 8.6 Schematic diagram of siphon, source well, injection well and observation well
(suggested by J F Mistry 1988).
Data Analysis: Before the start of recharge test, difference in water level between the sources
well and injection well was 7.06 m. This represents the net available head (HT) in the present
system. After the recharge was started on 29th May 1977 (at 10.53 hours), water levels in
injection and observation wells were monitored at suitable intervals. At steady state, the
following conditions were observed:
Recharge rate (Q) = 590 lpm
Build-up in the injection well (HB) = 5.18 m
Drawdown in the source well (HD) = 0.70 m
Build-up in the observation well = 1.15 m
Head loss due to flow in siphon (HS) including
velocity head (HV) = HT – (HB+HD) = 1.18 m
According to Todd (1959), if water is admitted into a well, a cone of recharge is formed
which is similar in shape but is reverse of a cone of depression surrounding a pumping well.
Assume aquifer formula used during pumping also valid during recharge. The average values
of coefficient of transmissivity (T) and storage (S) estimated from the recharge data are
540 m2/day and 3 × 10–5 litres respectively. Using these values of T and S in Theis formula to
be 2.89 m, compared to an observed build up of 5.18 m in the injection well. This gives an
injection well efficiency = 56%.
The radius of influence is estimated by using slope (∆St) of time build up plot and constituting
the distance build up plot using ∆Sr = 2∆ St.
187Energy Management Case Studies 187
Using the formula for steady uni-directional flow in a leaky artesian aquifer (Huisman, 1972),
the permeability (k) of the unconfined aquifer in the riverbed is estimated to be 70 m day.
It was earlier shown that at steady recharge rate, loss of head due to flow of water through
the siphon (i.e. Hs + Hv) is 1.18 m. However, for recharge rate of 590 lpm through 200 mm
diameter siphon pipe the velocity head is only 5 mm and hence not considered. Using tables
based on William and Hazen’s formula for estimating head loss through a 200 mm diameter
standard pipe, the equivalent length of the siphon pipe for the observed head loss of 1.18 m
works out to 1180 m. This, when compared with the actual, 75 m length of siphon pipe indicates
the extent of head loss due to: (i) Entrance, (ii) two 90° bends, (iii) pipe joints and welding,
(iv) sluice valve, (v) flow meter, (vi) sudden contraction and expansion (there is 2 m segment
of 150 mm diameter pipe in the line), (vii) several ups and downs and (viii) exit of water etc.
Head loss due to all these, affects the recharge rate of system adversely. In suitably designed
siphon, it is possible to reduce this head loss significantly as has been shown later, to achieve
a higher recharge rate through the system.
The efficiency of the injection well is observed to be about 56%. For economical recharging
operation, it is desirable to have wells with as high efficiency as possible. In practice, it may not
be difficult to construct wells with 75 – 80% efficiency. Increased efficiency of the injection
well will result in lesser build-up in the injection well, which in turn results in an increased
available head for siphon and ultimate increase in the recharge rate. In the following we estimate
the increase in recharge rate for assumed well efficiencies and improved low resistance PVC
siphon keeping other parameters of the experiment constant.
Using the values of coefficient of transmissivity (T = 540 m 2 /day) and storage
(S = 3 × 10–5 litres) as determined from the recharging test, steady state build-up (HB) for
various injection well efficiencies (56%, 70%, 80% and 90%) has been calculated for different
recharge rates. This formula has been used in these calculations. Steady state draw down (HD)
in source well for different recharge rates have been estimated using the value of 18 hydraulic
conductivity (K = 70 m/day) estimated earlier from the recharge test. Source well efficiency
is assumed 100%.
The loss of head in the siphon (Hs) can be easily reduced to 30% of its present value by
reducing the number of bends, welded joints etc. and by using a continuous non-collapsible 200
mm diameter PVC pipe. It can be seen from Fig. 3 (P 203 JFM) that in the improved system
steady state rate of recharge at Hansol may be expected to be 680 lpm for 56%, 800 lpm for 70%,
890 lpm for 80% and 970 lpm for 90% injection well efficiency. The expected recharge rate in
Ahmedabad (for a minimum available head of 25 m) by using this system will be higher than
2170 lpm for 56%, 2500 lpm for 70%, 2700 lpm for 80% and 2990 lpm for 90% injection well
efficiency. It may be noted that in estimates made above, the value of Transmissivity and available
head considered are lower than those estimated by Sharma and Desai (1974) at Ahmedabad (T
= 745 m2/day) and HT > 30 m) and therefore the projections made are in fact conservative.
Consequent upon increase in recharge rate, the velocity of water across the screens, in
both injection and source well will increase. In order to minimize corrosion and to reduce, any
possible suction of silt from the source well it is desirable to increase the open area of screens.
188 Energy
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This may be easily done by increasing the well diameter and changing the design of slotted
section and artificial filter.
As the remedy was to be designed for a single well, privately owned by Kanha Project, the
cost effectiveness of the remedy was of foremost importance. Hence solutions such as the
method of “pump and treat” in order to contain the contaminant plume were not feasible. So,
the technique of artificial recharge was selected as a remedial measure and a recharge well
190 Energy
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The outcome of the study will provide an insight of the existing situation and can also be
used to aid in decision making for planning issues such as issues related to remediation of the
contaminated aquifer, water resources development, health hazards, etc.
Table 8.7 Groundwater quality of discharge well under study before and after
introduction of the recharge well
U N IF O R M
FLOW
SO URC E S IN K
x
Q G
Fig. 8.10 Estimation of composite stream function for source, sink and uniform flow.
m 0.8 ¥ 10 –4 40 ¥ 10 –6
Ψ = – 2 θ2 = – q1 = – q1
sink
π 2p p
192 Energy
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Table 8.4: Stream functions for source, sink & uniform flow
40 ×10 `6 40 × 1 0`6
‘y’ w.r.t. origin ;u =4y × 10–6 ; w= ` θ1 ;w= θ2
π π
Deg Rad m m2 /sec m2 /sec m2 /sec
S1 q1 q2 S2
a a
rS rS
0.8 ¥ 10–4
= 3.6 1+
3.14 ¥ 4 ¥ 10–6 ¥ 3.6
= 5.9908 m
≈
– 6.0 m
Hence co-ordinates of the two stagnation point w.r.t. origin are (–6,0) and (6,0)
193Energy Management Case Studies 193
P¢
r1 h r2
(p
p/2 -a
)
a a
a a
rs
phU o
h = a cot
m
3.14 × h × 4 × 10–6
h = 3.6 × cot
0.8 × 10 –4
By trial and error, the value of h is 4.38 m
Analytical Result
Distance of stagnation point w.r.t. origin , rs = 6.0 m
Maximum height of Rankine oval body, h = 4.38 m
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PERFORMANCE INDICATORS
OF ARTIFICIAL RECHARGE
9 STRUCTURES
9.1 INTRODUCTION
Groundwater use for domestic, industrial and agricultural purposes in India has been growing
steadily over the years. The report of the Groundwater Resources Estimation Committee
(GWREC) has indicated that in India during the period 1952 – 1992, the number of dug wells
increased from 3.86 million to 10.12 million, while the number of shallow tube wells increased
from 3000 to 5.38 million. The total area irrigated by groundwater increased from 6.5 million
ha. in 1951 to 35.38 million ha. (gross) in 1993. Of the 716 blocks in the country, 250 (3.5%)
are “overexploited” while 179 (2.5%) are “dark” (GWREC 1997).
A substantial portion of the hard rock belts of India, area is experiencing acute conditions
of groundwater overexploitation as a result of phenomenal increase in the rates of abstraction
of groundwater, particularly by the agricultural sector which far cruised the recharge rates.
Groundwater resources in the hard rock areas face the twin problems of overexploitation and
groundwater pollution. Steep lowering of groundwater levels and the consequent decrease in
well yields has started affecting even small rural communities, creating social tensions between
neighboring villages and even among individuals within the same village.
While insufficient availability of groundwater is one side of the problem, the deteriorating
quality of groundwater is the other side, equally vexing. Pollution of groundwater due to
external contaminants produced by industrial, urban and agricultural activities is quite well
documented (Bhatnagar and Sharma, 2001); overexploitation of groundwater that leads to
lowering of groundwater levels also leads to increasing content of total dissolved solids (TDS)
in groundwater.
A major problem encountered in developing groundwater resources in hard rock areas is
the sharply declining groundwater levels, leading to the formation of overexploited pockets.
Bore wells drilled in hard rocks often become unproductive as the weathered / partly weathered
rocks as well as the shallower water bearing fracture zones progressively become desaturated.
In such areas, bore wells are drilled deeper year after year with the hope of encountering deep
fracture zones leading to mining of groundwater, since there is no replenishment of the deep
fracture zones taking place.
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Now that overexploitation exists in many parts of India, it is worthwhile to briefly examine
as to what constitutes an overexploited area and the indicative hydro-geological parameters
characterizing such areas. The report of GWRDC (1997) recommends that using the ratio of
net draft to total utilizable groundwater resources can assess the level of groundwater
development in area. Areas with stage of groundwater development less than 65% are classified
as “white” those with 65% but less than 85% “grey” more than 85% but less than 100% as
“dark” as and more than 100% as “overexploited”. The report further adds that over exploited
areas show significant long-term decline in both pre and post-monsoon groundwater levels.
An area may be classified as overexploited if one or more of the following hydrogeological
features are encountered:
• When groundwater levels do not recover to their original levels on a long-term basis
• When discharge exceeds recharge by an appreciable volume
• When shallow aquifers progressively become unproductive
• When groundwater is pumped from depths greater than that to which adequate recharge
currently takes place
• When the natural gradient is reversed and remains so throughout the year.
In order to counter the overexploitation of hard rock aquifers, the concept of rainwater
harvesting and artificial recharge to the groundwater system has lately caught the imagination
of technocrats dealing with water resources as well as lay public. It is well known that artificial
recharging of aquifers has in many cases resulted in a remarkable recovery of groundwater
levels locally in the vicinity of artificial recharging structures, at least in the first few years of
their construction.
The most common artificial recharge structures are percolation ponds, check dams, sub–
surface dykes, spreading basins and injection wells.
Out of these structures a detailed study of performance of percolation tanks, check dams
and dual purpose wells (ASR wells) was carried out by the author in Saurashtra region of the
Gujarat State of India. The details are described in this chapter.
The ever-increasing demand for water and the deteriorating quality of available groundwater
resources have already precipitated a major water crisis in the Saurashtra region of Gujarat.
The region receives approximately 500 mm average annual rainfall, lion’s share of which is
received during the monsoon season (Mid – June to September). Due to the high year–to–
year variation in the annual rainfalls, the region is heavily prone to droughts.
Over the past few years, local water harvesting and groundwater recharge have emerged
as a major strategy in Saurashtra to mitigate the impact of the recurring droughts, which are
manifested by severe shortage of water for irrigation and drinking, and fodder scarcity. Many
NGOs in the region and government agencies had constructed nearly 1400 percolation tanks
in the region. It is important to analyze the impacts of these interventions, before advocating
them as a viable approach for addressing water scarcity, and drought proofing.
Performance Indicators of Artificial Recharge Structures 197
197Energy Management
A study was undertaken to analyze the hydrological impacts of the local recharge. Sites
were selected for detailed keeping in view the unique geological settings of the areas where
these structures are located. Water levels in the percolation tanks, check dams, ASR wells, and
surrounding observation wells were taken at 15-day intervals. Based on the data gathered,
recharge rates and efficiency of percolation tanks are calculated. Based on the recharge rate
estimates, performance indicators for the recharge systems were estimated. The paper presents
the results of the study with regard to the following: [1] maximum rise in the water mount and
the duration of rise; [2] radius of influence of percolation tanks; and [3] recharge rate and the
recharge rate equation.
Management
Sr. Village Location Soils/Topography Geology Remark
No. Taluka Dist. Latitude Longitude
District Km North East
(4) Chhalla Rupavati Percolation Tank: Population of the village is 1088. The work was
started on 20/4/96 and was completed on 27/5/96. The construction involves earth
work of total 30,500 cubic meters. As a result of this good quality of water is available
in adjoining wells. Local stones available free of cost and cement of worth Rs.16,000
has been used for the work. Thirty-five tractors were engaged for 2092 hours.
Nature of Water Mound Developement
Taking reduced levels in the area of the tanks was the contour map of percolation tanks
developed. With the help of the contour map area v.s elevation, volume stored v.s elevation
and volume stored vs. area graphs were developed. Out of this the graphs of Hamirpura
percolation tank is as follow:
H am ir p u ra P e rc o la tio n Ta n k
Villa g e : H a m irp u ra Ta . : M o r b i D is t. : R a jk o t
9 8 .5
98
9 7 .5
97
9 6 .5
96
9 5 .5
0 50 00 10 000 15 000 20 000 25 000
2 G - 5 .4
A re a (m )
10 0 Vo lu me v /s E le v a tio n
9 9 .5
99
E le v a tio n (m )
9 8 .5
98
9 7 .5
97
9 6 .5
96
9 5 .5
0 50 00 10 000 15 000 20 000 25 000 30 000 35 000 40 000
2
Vo lu me v /s A re a (m ) G - 5 .5
25 000 Vo lu me v /s A re a
20 000
E le va tio n ( m 2 )
15 000
10 000
50 00
0
0 50 00 10 000 15 000 20 000 25 000 30 000 35 000 40 000
3
Vo lu me s to re d (m ) G - 5 .6
Water level fluctuation in the surrounding observation wells were observed continually at
15 day interval for a whole year and water mound and decay graphs were developed for all the
ponds. Out of these for Hamirpura percolation tank is given in Fig. 9.2 as below:
H a m ir pu r a Pe rc o la tio n Ta n k
96 2 7 -0 9 -9 7
95 2 5 -1 0 -9 7
94 2 2 -11 -9 7
W a te r L e ve l R .L . ( m ) 93 2 0 -1 2 -9 7
92
91
90
89
88
87
-1 0 0 0 -5 0 0 0 50 0 10 00 15 00
D ista nc e (m )
27-Jul
21-Sep
8-Feb
8-Jun
28-Jun
21-Jul
23-Aug
20-Sep
7-Feb
30-Nov
29-Nov
18-Apr
Date
To obtain the equation of recharge rate a graph of cumulative days vs. recharge rate was
plotted on log – log graph paper for Hamirpura percolation tank as shown in Fig. 9.4a, b and c.
R echarge Rate G raph for Year 19 96
R echage rate mm/Day
10 0
10
1
1 10 10 0 10 00
C umulative D ays
Fig. 9.4 (a)
Contd...
Performance Indicators of Artificial Recharge Structures 201
201Energy Management
10
1
1 10 1 00 1 00 0
C um ulative Days
(b)
10
1
1 10 1 00
C um ulative D ays
(c)
Fig. 9.4 Graphs for recharge rate calculation.
1 2 0 .0 0
1 0 0 .0 0
8 0 .0 0
% 6 0 .0 0
4 0 .0 0
2 0 .0 0
0 .0 0
J ul
J ul
9 6 Ju n
Sep
Sep
Sep
Aug
9 7 Ja n
Aug
9 8 Ja n
Aug
Dec
Dec
M ar
M ar
J ul
Fe b
Fe b
Oct
Oct
Oct
Apr
Jun e
Year/M onth
Effect on Quality
Water samples of surrounding wells were taken and analyzed. Total dissolved solids vs.
distance of observation wells are plotted in (Figs. 9.6 a & b), showing clear cut reduction in
TDS due to recharge.
M a y -9 7
E ffe ct o n TD S M a y -9 8
C hh alla R u pava ti P erc o lation Tan k
18 00 Villa g e :- C hh alla R u pava ti Ta :- D hrol D is t:- Ja m nag a r
16 00
14 00
12 00
10 00
80 0
60 0
40 0
20 0
0
0 . W.3 0 . W.2 0 . W.1 P.T. 0 . W.4 0 . W.5 0 . W.6 0 . W.7 0 . W.8
-6 1 0 -3 8 9 -2 1 7 23 1 32 2 63 7 78 0 90 0
Contd...
Performance Indicators of Artificial Recharge Structures 203
203Energy Management
O c t9 7
O c t-9 8
10 00
90 0
80 0
70 0
60 0
50 0
40 0
30 0
20 0
10 0
0
0 . W.3 0 . W.2 0 . W.1 P.T. 0 . W.4 0 . W.5 0 . W.6 0 . W.7 0 . W.8
-6 1 0 -3 8 9 -2 1 7 23 1 32 2 63 7 78 0 90 0
(b)
Fig. 9.6 Effect of percolation tank on TDS.
Table 9.2 Maximum water mound rise at different distances in observation wells
Table 9.5 Recharge rate equations from log-log graph cumulative days v/s recharge rate
Water Management
Village Location
Sr. Taluka Dist. Latitude Longitude Soils / Topography Geology Remark
No. District Km North East
Management
1. Chokil 20° 0′30′′ 70°15′ Fine, montmorillonitic Deccan trap of cretaceoecocene Constructed by
Mendarda 10 (calcareous) hyperthermic vertic age volcanic in nature having Swadhyay Parivar
Junagadh 22 ustochrepts. thickness of 7 to 26 m. Below it in 1993. Desilting
Moderately shallow, fine soil on compact trap is encountered. carried out every year
very gently sloping alluvial
plain (with mounds)
2. Arnhi 20°50′ 70°10′10′ Clayey, montmorillonitic, (calcar- Deccan trap of cretaceoecocene Constructed by
Uplete 22 eous), hyperthermic, paralithic age volcanic in nature having Premjibhai in 1996
Rajkot 95 vertic ustochrepts. Well drained, thickness of 9 to 19 m. Below it
gently sloping, dissected alluvial compact trap is encountered.
plain
3. Sutrapada 22°50′ 70°20′ Fine, loamy, mix (calcareous), Miliolite limetone, 15 to 40 m 3 km from Arabian
Veraval 22 ustochrepts. typic ustochrepts. depths are highly carveneous in sea cost constructed
(Patan) Well drained, fine clayey soils nature form, local aquifer by Swadhyay Parivar
Jamnagar 120 on very gently coastal plain Yielding saline quality of water.
Recharge Rate
A survey was conducted to find out reduced level in and around check dams and contour
maps were prepared. From the contour map graphs of cross sectional distance vs. elevation
were prepared. Cross-section areas at different distances were also plotted and area of each
cross-section were found out, from which average area is calculated. A table of reduced levels
and corresponding cross-section area, width, perimeter, water spread distances from check
dam were tabulated. With the help of these tables and weekly observations at check dams the
total water loss and evaporation was found out from this wetted area and recharge rate were
calculated. The equations of the recharge rate were found out in similar way as done for the
percolation tanks.
40 0
37 5 0 75 15 0 30 0
1
30 0 O W 12
22 5 (1 7 5 , 2 4 5 ) 2
OW 8
15 0 OW 5 OW 7 (5 4 5 , 1 9 2 )
3
(11 , 1 4 0 ) (3 2 0 , 1 6 7 )
75 O W 10 OW 5 OW 6
0 (-2 0 6 , 2 1 ) (6 7 , 2 1 ) (1 9 0 , 3 2 )
-7 5 0 OW 1 OW 9
Ow2 (-2 6 , - 9 4)
-1 5 0 (3 6 2 , 1 0 5 )
2 (-1 8 8 ,-1 51 )
-2 2 5 1
OW 3
(-1 9 2 ,-1 63 ) OW 4
-3 0 0
(3 8 ,-3 2 2 )
-3 7 5
-4 5 0 3
-5 2 5
-6 0 0
67 5
-7 5 0
-8 2 5
-9 0 0
-3 0 0 -2 2 5 -1 5 0 -7 5 0 15 0 22 5 30 0 37 5 45 0 52 5 60 0 67 5 75 0
Water level fluctuations in 12 observations wells for 2 years were observed and reduced
water level was calculated. Water level maps for water mound rise and decay were prepared
and were plotted for 3 cross-sections as shown below.
208 Energy
Water Management
Management
90
89
88
87
86
85
84
-2 0 0 -1 5 0 -1 0 0 -5 0 0 50 10 0 15 0 20 0 25 0 30 0 35 0
D istan ce (m )
93
0 4 -0 8 -9 7
92
0 1 -0 9 -9 7
91
2 0 -1 0 -9 7
90
89
R .L.in m .
88
87
86
85
-4 0 0 -3 0 0 -2 0 0 -1 0 0 0 10 0 20 0 30 0 40 0 50 0 60 0 70 0
D istan ce (m )
90
89
88
R .L.in m .
87
86
85
-2 0 0 -1 0 0 0 10 0 20 0 30 0 40 0
D istan ce (m )
Fig. 9.7 a, b c Water mound development graphs for Chokli check dam.
Performance Indicators of Artificial Recharge Structures 209
209Energy Management
93 2 3 -0 2 -9 8
92 2 0 -0 4 -9 8
91
90
89
R .L . in m .
88
87
86
85
84
83
-2 0 0 -1 5 0 -1 0 0 -5 0 0 50 10 0 15 0 20 0 25 0 30 0 35 0
93 2 0 -1 0 -9 7
1 5 -1 2 -9 7
92
2 3 -0 2 -9 8
91
2 0 -0 4 -9 8
90
89
R .L. in m .
88
87
86
85
84
-4 0 0 -3 0 0 -2 0 0 -1 0 0 0 10 0 20 0 30 0 40 0 50 0 60 0 70 0
89
R .L. in m .
88
87
86
85
84
-2 0 0 -1 0 0 0 10 0 20 0 30 0 40 0
D istan ce (m )
Fig. 9.8 a, b, c Water mound decay graphs for Chokli check dam.
210 Energy
Water Management
Management
S rtrapa da C hec k D am
Villa g e :- S utrapad a Ta .:- Ve rav al D is t:- Jun ag ad h
E ffe ct o n TD S
16 00 A p r. 9 7
Oct 9 7
14 00 A p r. 9 8
Oct 9 8
12 00
10 00
80 0
60 0
40 0
20 0
0
O W -2 O W -3 O W -6
1 .5
0 .5
0
O W -5 O W -6 O W -4 C .D . O W -1 O W -2 O W -3
O b s e rv atio n W e lls
Le ft R igh t
Fig. 9.10 Effect of recharge on fluoride for Hathigadh Khara check dam.
Performance Indicators of Artificial Recharge Structures 211
211Energy Management
3
M a y -9 8
O c t-9 8
2 .5
2
F lo ur ld e s (p p m )
1 .5
0 .5
0
O W -2 O W -4 O W -1 C .D . O W -6 O W -5 O W -3
O b s e rv a tio n W e lls
U /S Sid e D /S Sid e
Table 9.8 Maximum water mound rise at different distances in observation wells
for Chokli check dam (1996 - 98)
Upstream Side (m) Downstream Side (m)
Dist. from CD (m)
150 200 300 400 100 150 200 300 400 50 0
Mound Height developed (m) 1.2 1.1 0.87 0.1 4.2 4.0 3.6 1.5 0.5 0.2
Table 9.10 Recharge rate equations from log-log graph cumulative days v/s recharge rate
Name of Intercept on y-axis
Slope of Graph, > Average Equation
Check Dam (Recharge Rate), =
1996 1997 1998 1996 1997 1998 = >
Chokli 70 68 64 -0.10 -0.92 -0.065 67.33 -0.086 I = 67.33 T0.086
Arnhi 60 58 55 -0.261 -0.183 -0.171 57.67 -0.205 I = 57.67 T-0.205
Bhiyal 41 43 65 -0.022 -0.031 -0.18 49.66 -0.078 I = 49.66 T-0.078
212 Energy
Water Management
Management
(Aquifer Storage Recovery) wells. As they are dual purpose wells, due to surveying and desilting
effect, their discharging rate is not reduced considerably. The quality of water is improved
which improves the quality of soils also. As a result, so many farmers have earned additional
income of Rs.20,000 per annum each.
Mithapur A.S.R. Well :This village is on bank of Madhuvanti river. One farmer has laid a
pipe line by excavating more than 8.0m average in rocky area (by help of explosive) and
recharged his well. The district panchayat has constructed one check dam in upper region.
The well gets recharged upto the month of February from this reservoir. Due to this recharge
the quality and water level of surrounding wells are also improved considerably. Formally the
well becomes dry in the month of February. Now water is available throughout the year and
farmer is able to take three crops in a year.
Goraj A.S.R. Well: This village is just 8 km from Arabian sea coast. More than 200 dug wells
are constructed by farmers. Nearly all are recharged in monsoon. In the well under study,
water is diverted from tributary of river. The porosity of calcarious lime stone in this region is
high. As a result intake capacity of well is excellent so farmers have agreed for Warabandhi for
diverting stream water into wells. Varabandhi for recharging wells might have been practiced
for the first time in the world.
Sajantimba A.R.S. Well: This village is in Liliya taluka, a floride-affected area of Amreli
district. To study the effect of recharge on fluride, water analysis of surrounding and recharge
wells are collected and analysed in water supply and sewage board laboratory at Bhavnagar.
214 Energy
LOCATION, SOILS, TOPOGRAPHY AND GEOLOGY
Water Management
Table 9.13 Location, soils, topography and geology for A.S.R. wells
Village Location
Sr.
Management
Taluka Dist. Latitude Longitude Soils/Topography Geology Remark
No.
District Km North East
1. Khadvanthil 22° 0′30′′ 70°30′ Clayey, montmorillonitic (calcar- Deccan trap of cretaceoecocene An ope well recharge
Gondal 23 eous), hyperthermic paralithic age volcanic in nature having from farm runoff
Rajkot 55 vertic ustochrepts. Very gently thickness of 9 to 20 m. Below it since 1993
sloping dissected alluvial plain compact trap is encountered.
with moderate erosion
2. Mithapur 21°30′ 70°20′ Clayey, montmorillonitic, (calcar- Deccan trap of cretaceoecocene A well recharge from
Mendarda 12 eous), hyperthermic, paralithic age volcanic in nature having the river Madhuvanti
Junagadh 43 vertic ustochrepts. Well drained, thickness of 8 to 25 m. Below it directly by laying 30
gently sloping, dissected alluvial compact trap is encountered. cm dia. pipeline
plain
3. Goraj 21°15′ 70°0′ 30′′ Fine, loamy, mix (calcareous), Miliolite limetone, 10 to 45 m Warabandhi for
Mangrol 8 ustochrepts. typic ustochrepts. depths are highly carveneous in recharging wells form
Well drained, fine clayey soils nature form, local aquifer strom water drains.
Jamnagar 64 on very gently coastal plain Yielding saline quality of water.
4. Sajantimba 21°48′ 71°27′ Fine, montmorillonitic (calcareo- Decan trap of creataceoecocene Located on tributory
Lilya 10 us) hyperthermic vertic of 15 to 20 m depth becomes of Shetrunji river.
Amreli 57 ustochrepts. Moderately shallow, compact at depth having max. Fluoride affected area.
fine soils onfine soils on very depth more than 150 m contains
gently sloping alluvial plain fluoride contents
(with mounds)
Performance Indicators of Artificial Recharge Structures 215
215Energy Management
87
85
83
81
79
77
75
3 0-A p r 1 9-Jun 0 8-A u g 2 7-S e p 1 6-N o v 0 5-Jan 2 4-F eb 1 5-A p r 0 4-Jun 2 4-Jul
D ate
2 0.4 6
20 1 9.5 8
1 8.6 9
15 1 5.7 8 1 6.8 9
10
5
0 .2 0 .61 1 .3 2 .49 3 .43
0
1 99 4 O ct. 1 99 5 O ct. 1 99 6 O ct. 1 99 7 O ct. 1 99 8 O ct.
M ay M ay M ay M ay M ay
Year
Fig. 9.13 Water level fluctuation from 1994 – 98 in Khadvanthali ASR well.
16 00 T D S -M a y
14 00 T D S -O ct. 13 20
12 00 12 10
10 00 10 00 10 72
80 0
60 0 61 3 67 0
51 0 59 0
40 0
20 0
0
O .R .W 20 3 O .W .-1 51 6 O .W .-2 72 0.O .W .-3
5 O ct.
4 pe rm issible lim it
3
2
1
0
W e ll
A .S .R .
O W -1 .
O W -2 .
O W -3 .
(18 6m )
(60 0m )
(62 0m )
(b) Effect on Flouride C onten t in A .S.R . W ell
1.6
1.4
Florid e (p pm )
1.2
1
0.8
0.6
0.4
0.2
0
M a y-9 7
M a y-9 8
O ct-9 7
O ct-9 8
M o nth / Year
7 M a y '98
6 O ct '98
pe rm issible lim it
5
Floride (pp m)
4
3
2
1
0
0 10 0 20 0 30 0 40 0 50 0 60 0 70 0
Summary of Results
From the foregoing discussion, following conclusions emerge.
(i) The height of water mound developed in A.S.R. wells in miliolite limestone is 8.4 m as
compared to A.S.R. wells in weathered trap 6.1 m but radius of influence are 530 m
and 570 m and period of development of water mound is 100 days and 120 days whereas
period for decay is 200 and 220 days, respectively indicating miliolite limestone greater
permeability. Water mound height in limestone is higher but less life period.
(ii) Silting in percolation tanks and check dams not only decreases the storage capacity
but also reduces recharge rate as seen from following results.
(iii) Recharge structures have effect upto greater extent on downstream as compared to
upstream as seen from following results.
Radius of Influence
U/S D/S
Percolation Tank Miliolite limestone 1100 1300
Gaj limestone 780 1000
Weathered basalt rock 720 1100
Check Dam Weathered basalt rock 430 550
(iv) The T.D.S. values, which is a quality parameter is remarkably less at the vicinity of
recharge structure and increases alongwith the distance of the structure. This is due
to dilution caused by recharge.
(v) Monitoring one check dam and one aquifer storage recovery well in flouride
contaminated area indicated a significant decrease in flouride content, which proves
that recharge methods are effective in reducing effects of flouride.
220 Energy
Water Management
Management
(vi) The values of linear and volumetric efficiencies are nearly the same for all percolation
tanks and check dams. This can also be taken as performance indicator of successful
recharge effort.
(vii) The percolation tanks and check dams are said to be successful if the efficiency is
more than 70% and said to be effective if it is more than 80%.
(viii) The desilted percolation tanks and check dams have very long life, it can not be predicted
but the life of percolation tanks and check dams is 6 to 7 years. So it is better to desilt
the existing percolation tanks and check dams than to construct new one.
(ix) Recharge rate is maximum (30.25 mm/day) in miliolite limestone, medium (24.47 mm/
day) in Gaj limestone and minimum (20.40 mm/day) in weathered basalt rock.
Recharge rate equations for percolation tank are
I = 86.5 T–0.125 for miliolite limestone
I = 41 T–0.113 for Gaj limestone
I = 34.67 T–0.89 for weathered basalt rock
This indicates recharge structures are more effective in miliolite limestone.
From the above, one can deduce that for success of any recharge structures in Saurashtra
region following serves as the performance indicators.
(a) Height of water mound formed
(b) Areal extent of water spread both upstream and downstream of the structure.
(c) Linear and volumetric efficiency
(d) Water quality parameters such as TDS and Flouride
(e) Management of recharge structure
Given a scenario like Saurashtra, it is needless to say that though the water is trapped in an
unconfined aquifer, it is only through the recharge efforts; water is made available in difficult
periods either during a draught cycle or in summer. This itself speaks volumes of the recharge
efforts put in by the people of Saurashtra.
10 SEA WATER INTRUSIONS
10.1 INTRODUCTION
At present, 6 out of 10 people live within 60 km of the coast and by the end of 2020 more than
two-third of the population of developing countries, i.e. around 4,000 million people, will live
in the vicinity of the sea. For ages, mankind is attracted to these areas because of the availability
of an abundance of food (e.g., fisheries and agriculture) and the presence of economic activities
(e.g., trade, harbors, ports and infrastructure). Due to increasing concentration of human
settlements, agricultural development and economic activities, the shortage of fresh groundwater
for domestic, agricultural, and industrial purposes becomes more striking in these coastal zones,
resulting in seawater intrusion and related deterioration of the water quality.
During the latter part of 20th century there has been a widespread increase in urbanization.
As many major cities in the developing world are situated on the coast, and many lie on
unconsolidated aquifers, this has placed increasing importance on coastal unconsolidated
aquifers for water supply. As little as 2% seawater in freshwater can render the water non-
potable, and saline water has been reported to be the most common pollutant in fresh
groundwater (Todd (1980)). The problem of seawater intrusion requires the application of
specific management techniques.
The term sea water intrusion specifically describes the situation where modern seawater
displaces, or mixes with, freshwater within an aquifer in response to a change in the hydro-
geological environment. The expression is, however, frequently used to describe any case
where waterbodies of differing salinities occupy the same aquifer system. The most common
processes responsible of salinization in coastal aquifers are:
1) Present-day (active) seawater intrusion due to overpumping and upward displacement
of the freshwater-saline interface.
2) In the case of confined aquifers, the natural geochemical evolution of groundwater
along a particular flow-path may result in a progressive increase of salinity. If the
aquifer is made of partly flushed marine sediments, groundwater may acquire a
chemical signturel (either sodium chloride or calcium chloride facies) similar to
the observed trend in the case of seawater intrusion. Refreshing of aquifers may
lead to important.
222 Energy
Water Management
Management
3) Changes in water chemistry due to cation exchange in coastal aquifers (Appelo and
Postma, 1994).
4) Dissolution by groundwater of evaporitic minerals interbedded in the stratigraphic
column. Intense pumping may force groundwater leaching of low permeability horizons
containing soluble salts.
5) Upward leakage from a deeper confined aquifer into a shallow phreatic water-bearing
horizon may also result in a marked increase of salinity.
6) Irrigation returns flow or infiltration of industrial wastewaters or sewage.
7) Infiltration from estuaries or artificial canals containing brackish waters. In this case,
three different water types may be interacting in the aquifer.
8) Presence of connate, trapped brines or brackish waters mixed in different proportions
with shallow groundwater.
9) Incorporation of sea salt spray into infiltrating waters in the soil layer.
In the simple case of direct seawater intrusion or a simply mixture of two water types, the
mixing proportions of the two end-members (e.g. seawater and fresh groundwater or river
water from an estuary) can be derived from a simple linear relationship. This approach can be
followed using a series of physical, chemical or isotopic parameters, as long as there is sufficient
contrast (in the chemical or isotopic contents) between the two types of waters, and the
parameters are conservative. Among these parameters, the most commonly used are: electrical
conductivity, chloride, bromide, sodium, oxygen- 18, deuterium, etc.
L A N D SU R FA C E
W AT ER TA B L E
h S EA L E V E L
FR E S H W AT E R z
S EA FL O O R
S ALT W ATE R
IN TE R FA C E
Already at this moment, many coastal aquifers in the world, especially shallow ones,
experience an intensive salt water intrusion caused by both natural as well as man-induced
processes (Oude Essink, 2000a).
Human interferences, such as mining of natural resources (water, sand, oil and gas)
and land reclamation (causing subsidence) threaten coastal lowlands. Consequently,
salinities of surface water systems increase and land degradation occurs because soils
become more saline. As a result, poor crop yields are produced due to salt damage and
indigenous crops might be substituted by more salttolerant crops. If even the salt-tolerant
223Energy Management Sea Water Intrusions 223
crops cannot withstand the high salinities, the population might eventually migrate from
the barren land and resettle in more fertile arable territories, which could cause social
commotions. In addition, coastal aquifers within the zone of influence of mean sea level
(M.S.L.), are threatened by an accelerated rise in global mean sea level. This rise in global
mean sea level, 50 cm for the coming century as the present best estimate, could even
more jeopardize vulnerable coastal aquifers than they are threatened today. Subsequently,
the salinization of coastal aquifers will accelerate. This could mean a reduction of fresh
groundwater resources. In addition, the present capacity of the discharge systems in several
coastal lowlands may be insufficient to cope with the excess of seepage water, especially in
those coastal areas, which are below M.S.L. This seepage will probably have a higher
salinity than at present.
Effects
H um an activities salt w a te r in tru sio n C ountermeasures
- q ua n tita tive
g ro u nd w ater extra ctio n in crea s e se e pa ge e xtraction sa line g ro un dw a te r
-q u a lita tive
la n d re cla m a tion in filtra tion s urface w ater
d ecrea se g ro un dw a te r re s ou rce s in u nd ation lo w -lying a rea s
m in in g -g a s
salt d am a ge c rops p hysical b a rrie rs
-o il
d eg rad atio n e cosystem s in crea s e n atura l recha rg e
-s an d
lo w e rin g g ro un dw a te r leve l
The present distribution of fresh, brackish and saline water in the subsoil has developed in
geologic history and has been and still is affected by several natural processes but also by
human intervention. Brackish and saline groundwater can be found in coastal areas, but also
further inland. Features that affect coastal aquifers are summarized in Fig. 10.2. Obviously,
from a hydro-geological point of view, the most interesting coastal areas are the hydro-geologic
systems with sedimentary deposits (‘a porous medium’), rather than hydro-geologic systems
consisting of hard rocks.
Here it is important to define what is meant by saline water. Terms relating to the degree of
salinity were suggested by the USGS.
Table 10.1 Classification of saline water
Terms describing degree of salinity as used by USGS
Brine >35000
quality of groundwater is in question, the salinity or total dissolved solids (TDS) is considered.
An advantage of using TDS is that a rapid determination of TDS is possible by measuring the
electrical conductivity of a groundwater sample.
The concentration of dissolved solids is subdivided into negative (anions) and positive
ions (cations), see table 10.2. For instance, ocean water consists of 11 main components:
Since in coastal groundwater chloride (Cl–) is the predominant negative ion, which is
moreover investigated intensively, the interest is often focussed on the chloride distribution.
When, in fact, only changes in the chloride distribution are simulated, the distribution of
all dissolved solids is meant. In other words, the distribution of chloride ions is considered
to represent the distribution of all dissolved solids. As such, a proportional distribution of
all dissolved solids, which is present in ocean water, is also assumed to be present in
groundwater under consideration.
The applied classification of fresh, brackish and saline groundwater based on chloride
concentrations according to Stuyfzand (1993) is presented in Table 2.2. Obviously, there are
various other classification systems possible, e.g. because the definition for fresh groundwater
depends on the application of the groundwater. For instance, the drinking water standard in
the European Community equals 150 mg Cl—/l (Stuyfzand, 1986), while according to the
World Health Organisation, a convenient chloride concentration limit is 200 mg Cl–/l (Custodio
et al., 1987). A chloride concentration equal to 300 mg Cl–/l indicates the taste limit of human
beings according to ICW (1976), while Todd (1980) gives 100 mg Cl–/l as the limit when salt
can be tasted. Livestock can endure higher concentrations: up to 1500 mg Cl–/l may be accepted,
in case the chloride concentration stays constant.
(The three components with low concentrations are Strontium (± 8 mg/l), Barium
(±5 mg/l) and Fluoride (±1 mg/l).
IONS mg/l
Table 10.3 Classification into eight main types of fresh, brackish or saline groundwater
Chloride Concentration
Main Type of Groundwater
(mg Cl–/l)
h se a h
fresh
fresh O u tflo w
Fa c e
hf H hf S ea h
H
Hf Calculated
Interface
H
Hs
sa lin e A c tu a l In te rfa c e
sa lin e
= = ( H- s)/ Hf Hf
Fig. 10.3 The Badon Ghijben-Herzberg principle: a fresh-salt interface in an unconfined coastal aquifer.
areas where groundwater levels are lowest. Hydraulic head (often simply referred to as “head”)
is a measure of the total energy available to move groundwater through an aquifer, and
groundwater flows from locations of higher head (that is, higher energy) to locations of lower
head (lower energy). The distribution of hydraulic head within an aquifer is determined by
measuring ground-water-level elevations in observation wells that are open to a small interval
of the aquifer. The groundwater level (elevation) at each well, most often is reported as meters
above or below sea level. The upward direction of some of the groundwater flow paths near
and beneath the ocean in the aquifer system indicates that groundwater heads in the deeper
part of the flow system are above sea level near the coast.
Fresh groundwater comes in contact with saline groundwater at the seaward margins of
coastal aquifers. The seaward limit of freshwater in a particular aquifer is controlled by the
amount of freshwater flowing through the aquifer, the thickness and hydraulic properties of
the aquifer and adjacent confining units, and the relative densities of saltwater and freshwater,
among other variables. Because of its lower density, freshwater tends to remain above the
saline (saltwater) zones of the aquifer, although in multilayered aquifer systems, seaward-
flowing freshwater can discharge upward through confining units into overlying saltwater. In
general, saltwater is defined as water having a total dissolved-solids concentration greater than
1,000 milligrams per liter (mg/L). Seawater has a total dissolved-solids concentration of about
35,000 mg/L, of which dissolved chloride is the largest component (about 19,000 mg/L).
The freshwater and saltwater zones within coastal aquifers are separated by a transition
zone (sometimes referred to as the zone of dispersion) within which there is mixing between
freshwater and saltwater (Figs. 10.4). The transition zone is characterized most commonly by
measurements of either the total dissolved-solids concentration or of the chloride concentration
of groundwater sampled at observation wells. Although there are no standard practices for
defining the transition zone, concentrations of total dissolved solids ranging from about 1,000
to 35,000 mg/L and of chloride ranging from about 250 to 19,000 mg/L are common indicators
of the zone. In general, the term “transition zone” implies a change in the quality of ground
water from freshwater to saltwater, as measured by an increase in dissolved constituents such
as total dissolved solids and chloride.
Within the transition zone, freshwater flowing to the ocean mixes with saltwater by the
processes of dispersion and molecular diffusion. Mixing by dispersion is caused by spatial
variations (heterogeneities) in the geologic structure and the hydraulic properties of an aquifer
and by dynamic forces that operate over a range of time scales, including daily fluctuations in
tide stages, seasonal and annual variations in groundwater recharge rates, and long-term changes
in sea-level position. These dynamic forces cause the freshwater and saltwater zones to move
seaward at sometimes and landward at sometimes. Because of the mixing of freshwater and
saltwater within the transition zone, a circulation of saltwater is established in which some of
the saltwater is entrained within the overlying freshwater and returned to the sea, which in
turn causes additional saltwater to move landward toward the transition zone (Fig. 10.4). The
horizontal (or lateral) width of the transition zone can be narrow or very wide. The vertical
thickness of the transition zone also varies among aquifers, but generally is much smaller than
the horizontal width and is limited by the total thickness of the aquifer.
229Energy Management Sea Water Intrusions 229
Figure 10.4 Salt Water Intrusion in a Coastal Aquifer: a) balance between fresh water
and static salt water and b) circulation of salt water from the sea to the zone of diffusion and
back to the sea (modified from Henry, 1964).
For the convenience of illustrating freshwater-saltwater interactions as simply as possible
and facilitating simplified scientific analysis of these interactions when possible, the freshwater
and saltwater zones often are assumed to be separated by a sharp boundary that is referred to
as the freshwater-saltwater interface, such as those shown in Fig. 10.4. Although the depth to
this interface is quite variable, it can be estimated approximately under some circumstances by
using a technique known as the Ghijben - Herzberg relation.
The variety of geologic settings, aquifer types, and hydrologic conditions along the Atlantic
coast has resulted in many patterns of freshwater-saltwater flow and mixing in coastal aquifers.
Following are some case studies that illustrate some of the important freshwater-saltwater
environments that exist in aquifers along the Atlantic coast and highlight the many variables
that control the natural occurrence and flow of freshwater and saltwater in coastal aquifers.
The case studies progress from the glacial aquifer of Cape Cod, Massachusetts (Fig. 10.5),
which is representative of shallow, single-layer aquifers, to two of the most productive regional
aquifer systems in the United States—the Northern Atlantic Coastal Plain aquifer system that
extends from Long Island, New York, through North Carolina, and the Floridian aquifer system
that extends from South Carolina to Alabama. These are thick, multilayered aquifer systems
that underlie thousands of square miles.
230 Energy
Water Management
Management
Fig. 10.5 Patterns of the freshwater-saltwater transition zone at three sites in the Cape Cod aquifer,
Massachusetts.
In addition, the transition zone is also increasing as a result of the circulation of brackish
water due to inflow of saline groundwater (mixing with fresh groundwater due to hydrodynamic
dispersion), the tidal regime and human activities, such as (artificial) recharge and groundwater
extraction at high and variable rates (Cooper et al., 1964).
–fx2 – 2C1x + 2C 2
H=
k(1 + α )α
h = αH
q = f x + C1
In many shallow phreatic aquifers, the freshwater body originally touches the impervious
base, thus creating a salt water wedge of length L, see Fig. 10.8. The corresponding boundary
conditions are:
x = 0: q = q (q = –fW) .→ C1 = q
0 0 0
x = 0: H = 0 ® C2 = 0
where
• W = width of the coastal aquifer up to the water divide (L),
• q0 = natural groundwater outflow at the coastline x=0 (negative sign) (L2 T –1).
Saline groundwater is stagnant. The length of the salt water wedge L is:
x=L:H=D
where D = thickness of the aquifer (L). The equations of this case become:
–fx 2 – 2q o x
H=
k(1 + α )α
h = αH
q = fx + q0
q0 = – fW
2
L=
–q o
–
FG q IJ
o
–
k 2
D (1 + α)α
f HfK f
For example, if W=3000 m, f=1 mm/day, α=0.020, k=20 m/day and D=50 m, then the
length of the salt water wedge L is 175.1 m.
dh
(I) Darcy: Q = – 2πrk(H+h)
dr
(II) Continuity: dQ = f2πrdr ⇔ Q = fr2π+C1
dh dH
(III) BGH: h = αH ⇔ =α
dr dr
Combining these equations gives:
dH C
–2k(H+αH)α = fr+ r1
dr π
C 1 C
fr + 1 fr 2 1 ln r + C
r 1 2 π 2
HdH = – 2k(1 π) dr ⇔ H2 = 2k(1 )
+α α 2 +α α
235Energy Management Sea Water Intrusions 235
A confined aquifer is enclosed by two aquicludes. The three equations involved are
(Fig. 10.9).
dh
(I) Darcy : q = – kH
dx
(II) Continuity : q = q0
(III) BGH : h = α (H + A)
where
• q0 = fresh groundwater flow from recharge in the uplands, per unit coast length (L2T–1),
• A = height of the sea level with respect to the top of the aquifer (L).
dh qo
Combining the equations: – kH = qo ⇔ HdH = – dx
dx ka
1 2 –q o x –2q o x
H = +C⇔H= + 2C
2 ka ka
Example 10.4: Salt Water Wedge in a Confined Aquifer
The freshwater body touches the impervious base, thus creating a salt water wedge
(Fig. 10.10). The corresponding boundary condition is:
x=0;H=0→C=0
dH Q0
–2πrkHα = Q0 ⇔ HdH = – dr
dr 2pkar
1 2 Q ln r – Q 0 ln r
H = 0 +C ⇔ H = + 2C
2 2kαπ kap
In areas where saline groundwater is present below fresh groundwater, the interface
between fresh and saline groundwater may rise when piezometric heads are lowered due
to well extraction. This phenomenon is called interface upconing (Fig. 10.12). Here the
interface is horizontal at the start of pumping i.e. at t = t0. Especially in overpumped
areas, e.g. in a semi-arid zone, upconing of saline groundwater has become a serious threat
to domestic water supply. Solutions are often difficult to invoke as water is scarce in these
238 Energy
Water Management
Management
areas and illegal extractions are not easily to be stopped. As a result of the extraction and
the lowering of the piezometric heads in the fresh and saline groundwater zone, the interface
will rise. In case of a continuous extraction of fresh water, the interface will rise until it
reaches the pumping well. From that moment, the quality of the extracted groundwater
deteriorates, and the pumping has to stop. When the pumping is stopped, the denser saline
water tends to settle downward and to return to its former position. In order to avoid or to
limit these negative effects, one should keep the extraction rate, and so the lowering of the
piezometric head, below a certain limit. After reducing the extraction significantly, the
interface may descend to its original position, though at a very slow pace. Another solution
is to replace the extraction well to a location where saline groundwater is positioned at
greater depth from the well.
(Fig. 10.13), e.g., by reducing the width of the sand-dunes along the coastline where
fresh groundwater resources are situated and by diminishing the length over which
natural groundwater recharge occurs. Both events may lead to a decrease in fresh
groundwater resources.
• Rivers and estuaries will experience an increased salt water intrusion in case of sea
level rise, if the river bed elevation can not match with sea level rise. Because the
sediment load at many river mouths is reduced significantly these last decades among
others due to human activities (building dams, sand-mining), quite some rivers and
estuaries are expected to have an increased salt water intrusion. This could threaten
adjacent aquifers along rivers and estuaries from which groundwater is extracted.
Furthermore, the backwater effect of sea level rise would also decrease the safety
against flooding over large distances upstream the river mouth. Especially areas adjacent
to rivers with valley slopes only slightly steeper than river slopes have to be protected
by embankments.
• Coastal aquifers within the zone of influence of M.S.L. can be threatened by sea level
rise (Fig. 10.13). Intrusion of salt water is accelerated into these aquifers, which could
result in smaller freshwater resources (Oude Essink, 1999b, 2000a). Furthermore,
seepage will increase quantitatively in those areas and this seepage could contain more
saline groundwater. In consequence, crops may suffer from salt damage and fertile
agriculture land might change into barren land. In addition, the mixing zone between
fresh and saline groundwater will be shifted further inland. Extraction wells, which
were previously located beyond the salinization zone, will then be situated in areas
where upconing of brackish or saline groundwater can easily occur. This can be
considered as one of the most serious effects of sea level rise for every coastal aquifer
where groundwater is heavily exploited.
It is important to recognize that impacts of sea level rise must be considered in relation to
impacts of human activities. It is very likely that not sea level rise, but human activities will
cause a severe salinization of most coastal aquifers in the future. A reason for this assumption
can, among others, be deduced from the time lag between causes and effects. Sea level rise
takes place progressively. The time characteristic of sea level rise is in the order of decades. On
the other hand, the time characteristic of human activities, such as groundwater extraction
projects, is in the order of years. Before negative impacts, such as upconing, are recognized, it
may be too late to take countermeasures.
sa lin e sa lin e
grou nd water grou nd water
natural groun dwa ter recharg e natural groun dwa ter recharg e
sh oreline
retre at
se a ,x
lev el
rise
sa lt wa ter we dg e
sa lt wa ter we dg e sh ift of wedge
natural groun dwa ter recharg e natural groun dwa ter recharg e
se a ,x
low-lying
lev el area
low-lying rise
area
activities and move to other places. A shift to more salt resistant crops could enlighten the
need to extract groundwater of high quality. Finally, in some areas (e.g. tropical islands),
desalinization of saline water could relieve the stress on groundwater resources though at
the expense of high-energy costs.
Recent increases in global population, together with enhanced standards of living, have
created greater demand on water resources, requiring improved groundwater management.
Any new groundwater development should take into account the possibilities of saline intrusion,
and ensure adequate control, with prevention of saline intrusion being seen as the ideal. Any
intrusion carries with it the risk that the matrix of the aquifer will become contaminated,
causing a permanent loss of freshwater storage capacity. The impact of saline intrusion on the
Nile delta is described in a case study.
Where the possibility of intrusion exists, appropriate monitoring procedures should be
routinely carried out. A network of sampling piezometers should be established to monitor
heads and salinity changes along the coastal fringe.
Actual methods for controlling saline intrusion vary widely according to geology, extent of
the problem, water use, and economics. They generally rely on the principle that, in order to
limit seawater intrusion, some freshwater outflow above the saline wedge must be maintained.
They can be broadly divided into methods relying on barriers and those dependent on aquifer
management; some of these are discussed briefly below.
Barriers: Barriers to saline intrusion include recharge mounds, abstraction troughs, and
physical barriers.
Abstraction Troughs: An abstraction barrier is created by maintaining abstraction along a line
of wells close to the coast. This creates a pumping trough, with seawater flowing inland to the
trough, and freshwater flowing seaward. The fresh water can then be utilized by inland wells.
Recharge Mounds (Injection Barrier): This approach uses recharge wells to maintain a pressure
ridge along the coast. The injected water flows both landward and seaward. Ideally high quality
fresh water is required for recharge, necessitating the development of a supplemental source.
Physical Barriers: An impermeable subsurface barrier may be created through the vertical
extent of the aquifer, parallel to the coast. The barrier may be constructed of various materials
including sheet piling, puddled clay, cement grout, or bentonite. The approach is best applied
to small-scale problems.
Aquifer Management: Aquifer management i.e. modification of pumping, is generally carried
out on a regional scale. Modification requires changes in operational practices.
Control of Pumping: Modifying pumping practice and/or well system through reduction of
withdrawal rates and/or adequate relocation of extraction wells. The desired extraction rate
should preferably be extracted by well-distributed shallow wells to prevent excessive upconing.
In most situations, groundwater withdrawal for domestic, agricultural and industrial water
supply has not been reduced during periods of droughts, so that salt water intrusion tends to
occur anyway. In the case where an aquifer is underlain by saline fluid, upconing can be
limited by proper design and operation of wells (Bowen (1986)). For example, wells should be
as shallow as is feasible, and should be pumped at a low, uniform rate. Riddel (1933) suggested
that a multiple well system with small individual pumping rates was preferable to a high capacity
single well. Another alternative is an infiltration gallery (i.e. horizontal well) which has been
reported to help reduce the upconing that can result from heavy pumping by a vertical well
(Das Gupta (1983)). However, these are expensive to install, and similar benefits may be
obtained by utilizing several shallow wells.
243Energy Management Sea Water Intrusions 243
Redistribution of Pumping: Relocating pumping wells inland may help to re-establish fresh
water outflow. Some schemes to reduce the effects of saline intrusion in the Chalk of Great
Britain have utilised two sets of boreholes, one inland and one coastal (Headworth and Fox
(1986)). The coastal wells are pumped during periods of high groundwater levels when outflow
is large, with the inland wells being used during periods of low water levels.
The present countermeasures to prevent and/or retard salt water intrusion due to the
negative effects of human activities resemble the possible solutions to counteract the effects of
a relative sea level rise on the salinization process. In fact, sea level rise is basically the same as
equally lowering the land surface and thus the phreatic groundwater level. Nowadays, dramatic
lowering of the piezometric heads due to excessive overpumping already occurs in many
groundwater systems around the world, see table 1.2. It is obvious that, for those systems, the
impact of a (relatively small) sea level rise (e.g. 0.5 m per century) on the groundwater system
will be of marginal importance compared to the effect of an increase in withdrawal rate. The
economic feasibility of countermeasures should be investigated. For instance, it is recommended
to derive the optimum position of well lines and rates of extraction or infiltration. Moreover,
the countermeasures should be adapted and optimized in the course of the realization of the
measure, based on changes in the salinity of the subsoil.
Listed below are a number of Alternative seawater barriers which have been proposed.
Slurry Walls: The construction of a slurry wall involves the cutting of a bentonite slurry
stabilized trench. This is accomplished using a large backhole excavator suplemented by a
clam shell (a large tool operated by a crane for the purposes of digging). The ditch is then
backfilled with a mixture of soil-bentonite, a mixture of cement-bentonite, or plastic concrete
materials that, when stabilized, forms an impervious barrier to seepage. Because of the need to
cut a trench using heavy equipment, this prodedure has limitations with respect to disturbances
of existing utilities which are often located near the ground surface.
Grout Curtains: Grout curtains are constructed by drilling 2- to 6-inches diameter holes along a
single line or multiple parallel lines. Grout is then injected into the holes under pressure to fill
the surrounding soil pores or rock fractures. By placing these holes on a tight enough spacing
(typically 3 to 10 feet spacing), a grout barrier of variable thickness is created. Grout curtains can
be installed to most any depth and can be surgically injected to treat specific depth zones.
Air Injection: Air injection is used in the development of oil and gas fields and during tunneling
to cutoff the flow of water. Compressed air injected into the groundwater attempts to cause a
piezometric rise in water level that can be used to alter groundwater gradients and flow
directions. Air entrained in soil pores causes an overall decrease in the permeability of the
aquifer which could be used to reduce flow across specific zones.
Bio Wall: This technology involves the injection of starved bacteria cultures into the pores of
the aquifer media to develop a biological subsurface plug or bio-wall. This method uses microbial
growth to fill in the void space found in all soils, thus decreasing its permeability. The wall is
maintained by periodic injection of nutrients to feed the bacteria in specific zones. This type of
wall has only been evaluated by modeling and in the laboratory.
244 Energy
Water Management
Management
In 1976, to study the effects of salinity ingress in coastal region, Government of Gujarat
had appointed a High Level Committee – I (H.L.C. - I). The area selected for preventive measures
was between rivers Madhuvanti near Madhavpur and Rawal near Una. Based on the studies
of H.L.C. – I area Government of Gujarat had appointed High Level Committee – II (H.L.C. -
II) in 1978 to study and prevent the salinity ingress problems in rest of the coastal area of
Saurashtra and Kutch. H.L.C. – II committee has divided the coastal reach into three parts:
1) Bhavnagar to Una reach.
2) Madhavpur to Malia reach.
3) Malia to lakhapat reach for Kutch region.
Consequences of Salinity Ingress
In Bhavnagar to Una reach, total 166 villages of seven coastal talukas of Bhavanagar; Amreli
and Junagadh districts are affected by salinity ingress covering an area of about 1,39,212 hectares.
4600 open wells without pump sets and 4200 wells with pump sets have gone out of order.
Total population of 2,20,000 souls was affected by salinity ingress. The break up of affected
area by various stages of salinity is as under.
Area affected by inherent salinity 87,867 ha
Area affected by seawater ingress 33,055 ha
Marshy land including tidal ingress 18,290 ha
Total 1,39, 212 ha
In Una to Madhavpur reach, total 120 villages of five talukas are affected by salinity ingress
covering an area of about 1,00,000 ha. 12,562 wells have gone saline affecting the population
of about 2,80,160 souls and irrigation land of 19,850 ha.
Area affected by seawater intrusion 86,243 ha
Marshy land 13,757 ha
Total 1,00,000 ha
In Madhavpur to Maliya reach, 248 villages are affected by salinity ingress in 13 talukas of
Junagadh, Porbandar, Jamnagar and Rajkot districts covering an area of about 4,60,120 ha.
The break up of affected area by various stages of salinity is as under.
Alluvial Ghed area coral beds, saline alluvial of Maliya 1,70,200 ha
Marshy land 99 500 ha
Area having inherent salinity 1,32,230 ha
Area having seawater ingress 17,600 ha
Area affected by seawater inundation 40,590 ha
Total 4,60,120 ha
Moreover 6,000 open wells and 5,388 wells with pump sets are affected by salinity in above area.
247Energy Management Sea Water Intrusions 247
Effect of salinity has become so severe that people and cattle actually start migrating from
coastal villages towards the nearby urban areas and are depending less and less on land for
their lively-hood.
The rate of growth in population is observed as 27 per 1000 souls as the state as a whole,
whereas in salinity-affected area of coastal strip this rate is 7 to 20.
Adverse effect of salinity is also reflected in agriculture activity along the coastal area. For
example, Mahuva taluka of Bhavnagar District, once known for its rich output of Coconut,
Banana, Guava and ‘Jamadar’ Mango plantations, has turned into shambles due to salinity.
The yield per hectare has gone down considerably affecting local market. The farmers residing
near the saline reaches are in despair. Their land value had also gone down more over fruits
have also lost their quality.
In these circumstances, an immediate implementation of integral programme of preventing
salinity ingress had become necessary in the interest of common people of the affected area.
withdrawal is not more than the annual recharge. The farmer can also be trained to go in for
crops, which can resist salinity.
Cropping Pattern
The cropping pattern of an area depends upon mainly on soil types, prevailing climate and the
irrigation facilities available.
The area between Bhavnagar to Una mainly grows the crops of Groundnut, Jowar and
Bajra in Kharif and Wheat in Rabi. The area between Madhavpur to Porbandar grows the
crops of Jowar, Gram, Wheat, Groundnut and Bajra etc. In low-lying area of Ghed Cotton is
sown in Kharif depending upon the availability of rainfall. In Jamnagar district Bjara, Groundnut
and Cotton are sown in Kharif and Wheat, Mustard, Potato, Garlic, Chilly; Lucerne etc. are
sown in Rabi depending upon rainfall available. In Morbi and Maliya talukas of Rajkot district
Cotton, Bajra, Jowar and Groundnut are sown in Kharif and Wheat in Rabi. Horticulture
crops like Coconut, Guava, Pomegranate and Mangoes are planted in Bhavnagar to Una reach.
While in Madhavpur to Maliya reach, there are no horticulture plantations found.
In order to make use of the saline water for irrigation, following table suggests guidelines
depending upon the degree of salinity and soil types. Crops like Date palm, Bor, Bamboo,
Eucalyptus, Guava, and Coconut are moderately to highly salt tolerant crops. Crops like Wheat,
Bajra, Jowar, Mustard, Cotton, Castor can withstand the salinity up to some limit.
During floods, gates are opened and regulated as per flood forecast so as to allow the flow
of the excessive flood water without creating undesirable submergence of the land in the up
stream. As soon as the flood starts receding, the gates are closed to store fresh water on upstream
side. The stored sweet water will improve the existing water supply of the affected villages
situated near Tidal Regulator. Thus villages situated in the periphery of the proposed Tidal
Regulators will be benefited by improved quality of water due to such structures.
The sweet water reservoir that will be created behind Tidal Regulator is proposed to be
used for irrigation in the surrounding command areas through lift. It will be possible to do
irrigation, three to four times during monsoon and protect Kharif crop. As the gates are
provided on the Tidal Regulators, it will be possible to fill the reservoir during every flood in
the monsoon by proper regulation of gates. Incidentally, it will also be possible to increase
recharge into the groundwater through the command area also. Thus, the recharge of sweet
water through command area will be over and above that which will take place through the
bed of the reservoirs.
The reservoir waters will improve the surrounding village wells, thereby water supply
problems of the surrounding villages will also be solved to a great extent. The lands around the
reservoirs will be leached out through use of sweet water for irrigation and will make it possible
to fetch higher yields from the same fields.
Bandhara: Bandhara is an ungated structure constructed near the mouth of the river to prevent
upland movement of tidal water in the upstream. It stores the sweet water in upland which
helps to recharge the aquifer for pushing the salt water seawards and for lift irrigation. Thus it
reduces the pressure on groundwater utilisation and over withdrawal of groundwater. Bandhara
works on the same function to prevent the tidal ingress into the land by sealing the mouth of
the river.
As per normal practice, the top of the Bhandharas shall be kept 1 meter above the highest
tide level so that the waves from the sea side will not splash above the Bhandharas and pollute
sweet water reservoirs behind them. In case where submergence does not become a problem,
the Bhandharas shall be raised even higher to store more sweet water.
It is also possible to do irrigation three to four times during monsoon from the reservoir.
This will facilitate to protect Kharif irrigation and at the same time increase recharge from
larger areas by spreading reservoir waters in the command areas through lift. The surrounding
villages will get benefit by the probable improvement in the well waters.
Bhandharas will be constructed with impervious cut off below the foundation. Such cut
off will be taken down to relatively impervious strata and will enable to prevent tidal ingress
through foundation strata directly to contaminate groundwater.
Spreading Channel (Static Barrier): Spreading channels (Static Barriers) are preferred when
existing river channels are to be used as connecting channels from upstream reservoirs to
spreading channels or when recharge is desired in narrow strip near seashore for creating
fresh water barrier to stop seawater intrusion (Fig. 10.16).
251Energy Management Sea Water Intrusions 251
Fig. 10.16 Construction of spreading channel to prevent seawater intrusion in coastal aquifer.
Linking Canal: A canal joining two or more rivers or stream in coastal region is called Linking
canal. Sometimes in the coastal region rainfall occurs over a small region due to cyclonic
storms. Because of this rainfall there might be a runoff in one river and other nearby river may
run dry. If a canal joining these two rivers is constructed then runoff water from one river can
be diverted to another river and recharge over larger area can be obtained. If in case both the
rivers get flood then also linking canal gets flooded and more area comes under freshwater
recharge. These types of canals are suitable for areas where a porous stratum, limestone layer
is situated near the upper layer (Fig. 10.17).
Radial Canal: Radial canals are constructed towards the landward side from the reservoir
created by the construction of tidal regulator or bandhara in the coastal region. Slope of the
land is towards bandhara or tidal regulator while these canals constructed towards landward
side from the reservoir. Thus depth of these canals increases as it goes away from reservoir.
Floodwater will flow in these canals and farmers of surrounding regions can take advantage of
this water and irrigate their fields, thus much more area can be benefited (Fig. 10.14).
Fig. 10.17 Map showing location of linking canal, radial canal and bandhara.
11 REUSE OF WATER
11.1 INTRODUCTION
World has witnessed rapid economical growth, urbanization, and population growth and that
has developed serious environmental concerns range from pollution largely urban and industrial,
to resource management of water, land, forests, and energy.
A common approach used to evaluate water availability is the water stress index, and is
measured as the annual renewable water resources per capita that are available to meet
needs for domestic, industrial, and agricultural use. Projections predict that in 2025, two-
thirds of the world’s population will be under conditions of moderate to high water stress
and about half of the population will face real constraints in their water supply. This includes
numerous nations with adequate water resources, but also has arid regions where drought
and restricted water supply are common (north-western China, western and southern India,
large parts of Pakistan and Maxico, the western coasts of the US and South America, and the
Mediterranean region).
It is essential that about 80% of wastewater in developing countries is used in irrigation.
The double “R” mainly reclamation and reuse of wastewater belong to concept of clean
technology and have been practiced in many parts of the world. Table 11.1 shows global data
on wastewater irrigation practice in past two decades especially in semi-arid areas of both
developed and developing countries.
Table 11.1 Global data on wastewater irrigation practice
Country & City Irrigated Area Country & City Irrigated Area
(ha) (ha)
Argentina, Mendoza 3700 Peru, Lima 6800
Australia 10,000 Saudi Arabia, Riyadh 2850
Bahrain, Tubli 800 South Africa, Johannesburg 1800
Chile, Santiago 16,000 Sudan, Khartoum 2800
China, all cities 13,30,000 Tunisha, Tunis 4450
Federal Rep of Germany 3000 Tunisha, other cities 2900
Braunschweig
Germany, Other cities 25,000 USA, Chandler, Arizona 2800
Contd.
254 Energy
Water Management
Management
Table 11.2 Status of wastewater generation (w/w), collection, and treatment in class I cities and
class II towns (million liters per day)
Type Number of W/w W/w %age of W/w %age of w/w %age of w/w
Cities/Towns Generated Collected w/w treated Treated (of Treated (of
(mld) (mld) Collected (mld) Collected) Total)
Table 11.3 Status of wastewater (w/w) generation, collection, and treatment in major
contributing states (million litres per day)
State Number of W/w generated W/w colleted % age w/w W/w treated % age w/w Treated
type Cities/Towns (mld) Collected (mlf) (mld) Collected (mld)
Gujarat Class I 21 1175.80 936.70 78.60 676 51.30
Class II 27 191.20 137.80 25
Maharashtra Class I 27 3593.40 3139.00 85.60 481.4 13.3
Class II 28.00 160.40 73.80 18
Uttar Pradesh Class I 41 1557.70 1048.90 66.70 246.2 13.4
Class II 45 275.50 174.00 -
West Bengal Class I 23 1623.10 1183.00 72.20 -
Class II 18 66.90 36.70 -
Delhi Class I 1 2160.00 1270.00 58.80 1270 58.8
Total 231 10804.00 8000.00 74.04 2716.6 25.14
Potable water has become an extremely precious commodity in many areas of India, whether
rural or urban. Pressure of growing populations in cities has increased the demand for water,
but the development of additional water resources has not kept pace. Demand and deficit for a
few major cities in India are presented in Table 11.4 below:
255Energy Management Reuse of Water 255
Table 11.4 Demand and deficit for a few major cities in India
Water has always been used and reused by man. The natural water cycle, evaporation
and precipitation, is one of reuse. Cities and industries draw water from surface streams and
discharge wastes into the same streams, which, in turn, become the water supplies for
downstream users. In the past, dilution and natural purification were usually sufficient for
such system to perform satisfactorily, but, in recent years, population and industrial growth
have made it evident that wastewater must be treated before discharge to maintain the quality
of the stream.
ti o n
a n d R R e c la m a
M u n ic
euse
R e pu rified
ip a l a
D rinkin g
r
W a te r
W a te
W a te r
Q ua lity of W a ter
nd
nttm e
In d u
U n po llute d R e claim e d
T re a tm w a te r
W a te r W a te r
r Tre a
ent
s t ria l
W a s te
Tre ated
W a te
U se
E fflue nt
W a stew a te r
T lm e S eq ue nce (N o Sc ale)
Fig. 11.1 Quality changes during municipal use of water and the concept of
wastewater reclamation and reuse. (Mc Gauhey, 1968)
Figure 11.1 shows, conceptually, the quality changes during municipal use of water in a
time sequence. Through the process of water treatment, a drinking water is produced which
has an elevated water quality meeting applicable standards for drinking water. The municipal
and industrial uses degrade water quality, and the quality changes necessary to upgrade the
wastewater then becomes a matter of concern of wastewater treatment. In the actual case, the
treatment is carried out to the point required by regulatory agencies for protection of other
beneficial uses. The dashed line in Fig. 11.1 represents an increase in treated wastewater
quality as necessitated by wastewater reuse. Ultimately as the quality of treated wastewater
approaches that of unpolluted natural water, the concept of wastewater reclamation and reuse
is generated (McGauhey, 1968). Further advanced wastewater reclamation technologies, such
as carbon adsorption, advanced oxidation, and reverse osmosis, will generate much higher
quality water than conventional drinking water, and it is termed repurified water. Today,
technically proven wastewater reclamation or purification processes exist to provide water of
almost any quality desired.
Domestic reuse offers the best recycle opportunity, but, even then, the amount of water
recycled falls short of the total amount of water used. The wastewater arriving at the treatment
plant is generally found to be less than the amount originally supplied to the municipal water
system. Losses occur, and they may be quite large in warm dry areas, where domestic reuse is
most likely to be practiced.
Another consideration is the character of the wastewater entering the renovation plant,
especially if this waste includes some industrial pollutants. Care should be taken to exclude
materials that would be detrimental to the application for which the reclaimed water is to be
used. This is especially true for the domestic reuse. Such materials may not be only those
usually considered toxic. Ordinary salt brines, for example, are undesirable if the renovated
wastewater is to be demineralized. A survey of the sewer system will determine how much of
the available wastewater could be reused. Water highly contaminated with metals or containing
a high total concentration of dissolved solids may be unacceptable Fig. 11.2. Treated wastewater
257Energy Management Reuse of Water 257
may be deliberately used in a planned way for a variety of purposes some of which are shown
in Fig. 11.3. Intentional reuse is not new, but there is a growing recognition of the need for it.
D isc h ar g e s
o f in d u s tria l w a s te s
D isc h ar g e of u n su ita b le fo r re c la m a tio n
h o u se h o ld s e w a g e
TR U N K E v e n flo w S lu d g e s
S EW E R to p la n t re tu rn e d to
W a s te rw a te r sew er
re n o v atio n p la n t C le an w a te r fo r re u s e To m u n icipa l
d is p o sa l p la n t
IN D U S TR IA L
M U N IC IPAL
W AS TE W ATER
W AS TE W ATER
M U N IC IPAL D R IN K IN G R E C R E AT IO N FIS H
N O N PO TA B LE C U LTU R E A G R IC U LT U R E IN D U S TR Y
S W IM M IN G B O AT IN G FIS H IN G IN TR A P L AN T GENER AL
S TO C K O R C H AR D S FO D D E R , FIBE R C R O PS
C R O PS C O N S U M E D
W ATE R IN G AND C R O PS AN D C O N SU M E D
A FT E R P R O C E S SIN G
V IN EYA R D S S EE D C R O P S R AW
Definitions
Municipal wastewater: The spent water of a community: it consists of water that carries
wastes from residences, commercial buildings, and industrial plants and surface or groundwater
that enter the sewerage system.
Indirect reuse: Indirect reuse of wastewater occurs when water already used one or more
times for domestic or industrial purposes is discharged into fresh surface or underground
water and is used again in its diluted form.
Direct reuse: The planned and deliberate use of treated wastewater for some beneficial purpose,
such as irrigation, recreation, industry, the recharging of underground aquifers, and drinking.
In-plant water recycling: The reuse of water within industrial plants for conservation and
pollution control purposes.
Industrial wastewater: The spent water from industrial operations, which may be treated
and reused at the plant, discharged to the municipal sewer, or discharged partially treated or
untreated directly to surface water.
Advanced waste treatment: Treatment systems that go beyond the conventional primary
and secondary processes. Advanced waste treatment processes usually involve the addition of
chemicals (biological nitrification — denitrification, the use of activated carbon), filtration, or
separation by use of membranes.
258 Energy
Water Management
Management
G r o u n d w a te r
A g ric u ltu r a l re c h a ge 1 4 %
Irr ig a tio n 1 3 % In d u stria l u s e 4 1 %
A g ric u ltu r a l
L a n d s c a p e irrig a tio n irrig a tio n 6 0 %
a n d im p o u n d m e n ts
16 %
Japan C a lifo rn ia
432 × 10 6 m 3 /ye ar
1 0 0 × 1 0 6 m 3 /ye a r
Fig. 11.4 Types and volume of wastewater reuse in California and Japan.
Contrary to the arid or semi-arid regions of the world where agricultural and landscape
irrigation are the major beneficial use of reclaimed wastewater. Wastewater reuse in Japan is
dominated by the various non-potable, urban uses such as toilet flushing, industrial use, stream
restoration and flow augmentation to create so called “urban amenities”. Figure 11.4 shows
the comparative diagrams for Japan and California, depicting the various reclaimed water uses
and the corresponding volumes per year (State Water Resources Control Board, 1990; Japan
Sewage Works Association, 1994).
259Energy Management Reuse of Water 259
Non-potable urban uses (1) Public health concerns on pathogens transmitted by aerosols,
Fire protection (2) Effects of water quality on scaling, corrosion, biological growth,
Air conditioning and fouling, (3) Cross-connection.
Toilet flushing
Potable reuses (1) Constituents in reclaimed wastewater, especially trace reservoir
Blending in water supply organic chemicals and their toxicological effects, (2) aesthetics and
Pipe to pipe water supply public acceptance, (3) health concerns about pathogen transmission,
particularly viruses.
Composition of Wastewaters
Unpolluted surface and groundwaters contain various minerals and gases depending upon the
geology and surface terrain. Use of water by a city adds a variety of materials such as grit, dirt,
oil, bacteria, fertilizer, pesticides and miscellaneous organic matter from streets or land erosion;
human waste (organic matter, bacteria, viruses, salts); laundry waste (inorganic salts,
phosphates, salts, surfactants); industrial waste (heat, inorganic salts, colour, metals, organics,
toxic materials, oils, and the product itself). Even with the myriad materials in wastewaters,
municipal wastes are 99.9% water.
260 Energy
Water Management
Management
Table 11.6 Summaries of recommended microbiological quality guidelines and criteria by the World
Health Organization (1989) and the State of California’s Wastewater Reclamation Criteria (1978)
(a) Intestinal nematodes, expressed as the arithmetic mean number of eggs per litre during the irrigation
period. (b) WHO recommends a more stringent guideline (<200 fecal coliforms/100mL) for public lawns,
with which the public may come into direct contact. (c) California Wastewater Reclamation Criteria is
expressed as the median number of total coliforms per 100mL as determined from the bacteriological
results of the last 7 days for which analyses have been completed
Contd...
263Energy Management Reuse of Water 263
A . F u ll Tre a tm e n t ( Title 2 2 )
P o ly m e r
C la rilica tio n
A lu m
S e c o n d a ry
E ffu e n t
R a p id Flo c c u la tio n
M ix
G r a n u la r
R e c la im e d C l2
M e d iu m
W a s te w a te r F iltr a tio n
C h lor in e
C o n ta c t
B a s in
B . D ir ec t Filtr atio n
P o ly m e r
A lu m
S e c o n d a ry
E fflu e nt
R a p id Flo c c u la tio n
M ix
C l2 G r a n u la r
M e d iu m
F iltr a tio n
C h lor in e
C o n ta c t
B a s in
C . C o n ta c t F iltra tio n
C l2
P o ly m e r
A lu m
S e c o n d a ry
E fflu e nt
R a p id
M ix C h lor in e G r a n u la r
C o n ta c t M e d iu m
B a s in F iltr a tio n
R e c la im e d
W a s te w a te r
Fig. 11.5 Schematic diagram of filtration systems using wastewater reclamation and reuse
expose wastewater to natural purification and dilution system. (e.g. Irrigation for agriculture,
parks, golf courses, lawns, processing and cooling water for industries, recreational water
ponds like swimming, boating, fishing etc).
Indirect reuse: Here effluent is discharged to receive water for assimilation and withdrawal
downstream. It involves natural buffer as an intermediary stage and includes greater temporal
and spatial separation of treatment and reuse. Greater time provides opportunity for monitoring
and testing water quality before use and spatial separation allows for dilution and improvement
in aesthetic property of water. (e.g. Ground water recharge, upstream disposal. Chennai
refineries Ltd., gets effluent from the city’s sewer unit plants and use it as their process water
after treating the sewage by biological and advanced treatment methods like ion exchange and
reverse osmosis).
Inadvertent/unplanned reuse: As the name suggests, occurs when water is withdrawn,
used by one party, returned to a water source (e.g. lake, river, aquifer) without specific intention
or planning to provide water for use of other parties.
Planned reuse: Involves collection and purposeful provision of wastewater for subsequent use.
Potable reuse: Planned direct or indirect reuse for some beneficial purposes (e.g. drinking,
cooking, bathing, laundry etc.).
Non-potable reuse: Inadvertent indirect reuse (e.g. fire fighting, toilet flushing etc.). Depending
upon the intended wastewater reuse application, municipal wastewater reuse is categorized
along with the potential constraints in Table 11.8.
Irrigation Reuse
Reusing of Municipal wastewaters for irrigation is the oldest and largest reuse. Advanced
treatment of wastewaters is not always required, but each potential reuse should be thoroughly
analyzed to determine the quality required. The advantages and the reuse of treated wastewater
for irrigations are:
1. Low-cost source of water.
2. An economical way to dispose of wastewater to prevent pollution and sanitary problems.
3. An effective use of plant nutrients content in wastewater.
4. Providing additional treatment before being recharge to the groundwater reservoir.
When wastewater is used for irrigation, a number of possible disadvantages have to be considered:
1. The supply of wastewater is continuous throughout the year, while irrigation is seasonal
and dependent on crop demands.
2. Treated wastewater may plug nozzles in irrigation systems and clog capillary pores of
heavy soils.
3. Some of the soluble constituents in wastewater may be present in concentrations toxic
to plants.
4. Health regulations restrict the application of wastewater to edible crops.
5. When wastewater is not properly treated, it may be a nuisance to the environment.
Current standards for irrigation water are compared to those of WHO and the USEPA for
urban reuse in Table 11.9.
Parameter India Irrigation WHO (A) EPA Food Crop EPA Non-food Crop
Recreational Reuse
Reuse of wastewater in recreational lakes is becoming increasingly popular in the arid areas of
the United States. The state of California has pioneered in recreational reuse, with several
lakes in existence for a number of years. Lakes at Santee and Indian Creek Reservoir near Lake
Tahoe are probably the best known. Tuscon, Arizona is installing recreational lakes derived
from treated wastewaters.
Wastewater used in recreational lakes must satisfy both health standards and standards
that will make the lake acceptable from the recreational purposes. Although there are no
266 Energy
Water Management
Management
national public health standards, at least one state, California, has written standards that can
be used as an example. For unrestricted recreational use, wastewater in California must be
biologically treated, chemically flocculated, filtered to produce a turbidity of not more than 10
turbidity units, and adequately disinfected. Adequate disinfection is defined as 2.2-coliform/
100 ml. The mean is determined over a 7 days period. These standards were arrived at after
several years of careful observations, including monitoring for viruses.
The public health standards cannot be used alone to define an adequate treatment system,
since they do not deal in detail with problems related to ammonia in the water. Limiting the
amount of the major nutrients (generally involves phosphorus or nitrogen, or both) can control
excessive algae growth.
For cost-estimating purposes, Fig. 11.6 shows a treatment system that should satisfactorily
produce recreational lake water. The system includes conversion of nitrogen to nitrate and
phosphorus removal down to the level of about 0.1 mg/lit, as P. Organic removal should be
excellent because of the two-stage biological treatment and filtration suspended solids in the
treated water should be almost zero.
R .A .W P R IM A R Y A C TIVAT E D B IO L O G IC A L
W AS TE W AT ER TR E ATM E N T S LU D G E N ITR IF IC AT IO N
D U A L -M E D IA TW O - STAG E
C H L O R IN AT IO N
FILT R AT IO N L IM E TR E ATM E N T
R E N O VATE D W AT ER
TO R E C R E ATIO N A L L AK E
11.7 shows a treatment that should have widespread usefulness. Nitrification could be included if
ammonia is a problem. Clarification could be carried out with lime, aluminium salts, or iron salts.
Lime, however, would appear to have several advantages over the other materials: it does not add
extraneous ions such as chloride or sulfate; it removes some heavy metals; and it produces water
that is less likely to be corrosive. If clarification were carried out with good solids control, filtration
would not be required. For the relatively small additional cost, however, its inclusion significantly
increases dependability. At Las Vegas, a system using lime treatment is followed by a holding pond
rather than a filter. The pond is very effective for solids control.
R .A .W P R IM AR Y A C T IVATE D C H E M IC A L
TR E ATM E N T SLUDGE C L A R IF IC ATIO N
W AS T E W AT ER
DUAL
C H L O R IN AT IO N M E D IA
FILT R AT IO N
R E N O VATE D
W AS T E W AT ER
Manufacturing produces large quantities of BOD. The major contributors are the chemical
industry, the pulp and paper industry, and the food processing industries. Table 11.10 lists
typical BOD and suspended solids levels produced by a variety of industries.
Table 11.10 Typical process waste strengths
Source: Sell, 1992 (sell, N J (1992) Industrial Pollution Control: Issues and Technologies. Van Nostrand Reinhold
Publishing Co. Inc, New York.
268 Energy
Water Management
Management
Pollutants of concern in wastewater, if reuse is considered, are listed in Table 11.11 where
the different classes of industrial wastewater pollutants are categorized alongwith measured
parameters and potential reuse concerns.
Source: Papadopoulus I, 1992: Rehabilitation of the areas irrigated with wastewater in the state of Kuwait. Assignment report,
World Health Organization.
269Energy Management Reuse of Water 269
Large cities generate large quantities of sewage. In most cities, the sewage is treated and
discharged as treated water. In the present situation most of the treated sewage is used for
farming. The treated sewage can also be used by industry as an alternate source of water.
Depending on the use of treated water in an industry, the secondary treated sewage may have
to be subjected to further treatment termed as Tertiary treatment. Various unit operations such
as clarification, filtration, and chemical treatment desalination may be incorporated in the
treatment scheme to produce desired quality of water for reuse. Sewage generally contains low
concentration of impurities and most of the pollutants being of organic nature. It is treated at
low cost using naturally available micro-organism and conventional methods of clarification,
filtration and chlorination. The treated sewage can be used by industries as cooling tower
make-up. In case the industry needs water with low dissolved solids, for use as process water
boiler feed water, or as replacement of raw water, the sewage after secondary and tertiary
treatment may be treated by technologies such as RO or EDR to produce high quality water.
In most cases, where industry is buying water from industrial development corporations or
state government, implementation of sewage reuse is economically viable. Sewage reuse plants
have already been adopted by industry in Chennai (Chennai Refineries Ltd., Madras Fertiliser
Ltd.), and by Rashtriya Chemical & Fertilizer Ltd., in Mumbai.
Industrial wastewater is the other source of water for reuse. As compared to sewage reuse,
the industrial wastewater reuse system is slightly expensive. This is because the industrial
waste is more completed to treat. On the other hand, operation of industrial waste reuse plant
is more dependable as constant quality wastewater is available at the outlet of existing Effluent
Treatment Plant. For ready reference a case study to indicate technocommercial feasibility of
using sewage as industrial water is given hereunder as case A.
R AW S E W A G E G R IT PA R S H A L
B AR A ER AT IO N FIN A L
3 0 0 M 3 /D AY R E M O VA L FL U M E TA N K C L A R IF IE R
S C EE R N
G R IT S LU D G E
PUMP
E XC E S S S L U D G E
S L U D G E R E C YC L E TO D R Y IN G B ED
C H L O R IN AT IO N
(H Y P O C H L O R ITE )
C L E AR P R ES S U R E A C TIVATE D
W AT E R TR E ATE D W AT ER
S AN D F ILT E R C A R B O N FILTE R
TA N K
FILT E R
PUMP
B AC K W A S H TA N K A IR SC O U R IN G
& PU M P B L O W ER
Fig. 11.8 Reuse of domestic sewage as cooling tower makeup – Case study -A
Industrial wastewater is the other source of water for reuse. As compared to sewage reuse,
the industrial wastewater reuse system is slightly expensive. This is because the industrial waste
is more complicated to treat. On the other hand operation of industrial waste reuse plant is more
dependable as a constant quality wastewater. Two case studies (Case study B and C) are presented
here to prove the point.
Case study B – Feed and treated water quality (Low TDS industrial waste water)
CO M BINED
SL UDG E C H LO R IN E
W A S TE W A T E R C O LLE C T IO N P IT FL ASH C O N TA C T TA N K
BL ANK ET
(4H R S . C S P ) M IXER C L A R IF IE R
(35 5 M 3/ H R )
F ILTE R F E E D
TR ANS FER P U M P S ( 1+ 1)
P U M P S ( 1+ 1)
S L U D G E TO
D R Y IN G B E D S
SL UDE
P U M P S ( 1+ 1)
F ILTE R B A C K W A S H
CL2
A C T IVAT E D T R E AT E D W A T E R
DU AL C H LO R IN E
C A R B O N F I LT E R S FO R REU SE
M E D IA F ILT E R S C O N TA C T TA N K
(A C P ) 35 0/ M 3 /h r
(D M F )
T R E AT E D W A T E R
P U M P S ( 1+ 1)
BA CK W AS H
BA CK W AS H
P U M P (1N o )
A IR S C O U R IN G
BL OW ER
Fig. 11.9 Low TDS industrial wastewaters reuse system – Case study - B
Case study C: Feed and treated water quality (Industrial cooling tower blowdown)
C AS E ST UD Y - (C)
POLYELECTROLYTE FILTER BACK WASH
DOLOMITE LDUE
H 2 SO 4 CHLORINE
Na2Co3
SODIUM
BISULHTTE ANTIBCALENT
VENT ALKASS
FILTRATE RO PERMEATE
MICBON DEGASS ER
TANK FILTERS FOR REUSE
& TANK 150 m 3 /hr.
BLOCK
SLUDGE TO SLUDGE
PEMP BRYINC SED
SLUDGE
PUMP
Because of the limited experience with direct reuse of renovated wastewater, there are no
standards to apply to such waters. Standards for drinking water such as those of the US Public
Health Service (1962), apply to water sources that are as free as possible from pollution. Many
in the water field believe that renovated wastewater should meet additional standards beyond
those written for large unpolluted sources. The most important areas of concern are trace
organic pollutant, metals, and pathogens, especially viruses. Analytical techniques to detect
very low concentrations of organics and virus are in an early stage of development, are expensive,
and are time consuming. Analyses for metals are sensitive and generally adequate.
One answer to the problem is to insist that the water be overtreated to a point at which
there could be absolutely no doubt of the water purity, even in the absence of adequate analytical
techniques. Such procedure may be tolerated in some cases to obtain potable water, but this
would not be possible for large volume uses.
A system such as that shown in Fig. 11.11 might be used for demineralization step; this is
very much like the advanced waste treatment plant at South Lake Tahoe, as it is presently
operated. The product water from the system will meet the quantitative values of the US
Public Health Service Drinking Water Standards. Although there is no standard for ammonia,
nitrification would be necessary to reduce the ammonia concentration to aesthetically acceptable
levels. Limited virus determinations from the Tahoe plant showed no virus recovery from the
product water. Whether demineralization would be required, or to what degree, would depend
upon the fraction of recycle and the mineral content of the make up water supply. A material
balance would have to be made for each particular situation to determine demineralization
requirements. A 40% total dissolved solids removal would probably cover most situations. Ion
exchange is shown in the diagram as the method of demineralization because it presently
appears to be as cheap as any other method and offers some degree of trace organic removal.
Since ion exchange would probably be operated to give almost total removal of minerals, not
all of the water would have to be treated. If demineralization were not included, there is a
chance that the nitrate concentration would exceed the standard of 10 mg/lit, as nitrogen. In
such cases, the necessary nitrate removal could be obtained by biological denitrification of
part of the flow.
R AW P R IM AR Y A C T IVATE D B IO L O G IC A L
TR E ATM E N T S LU D G E N ITR IF IC AT IO N
W AS T E R W ATE R
G R AN U L A R DUAL- TW O - STAG E
CARBON M E D IA L IM E
TR E ATM E N T FILT R AT IO N TR E ATM E N T
LO N R E N O VATE D
C H L O R IN AT IO N
E XC H A N G E W AS T E W AT ER
SL OW DOW N
AN D O THE R LO SE S
BU IL DING
DRA IN AG E
ROA D
GRO UND LE VEL
To determine the quality and quantity of water required for reuse in the tall buildings the
following approach is followed: An open re-circulating system is generally adopted for air-
conditioning cooling water and the amount of water to be kept re-circulating in the system is
275Energy Management Reuse of Water 275
approximately 11 liters/min for every ton of refrigeration capacity when temperature drop is
5°C in the cooling tower. For such a situation, the water lost in evaporation (E) is about 1% of
the re-circulating water.
Windage loss (W) is of the order of 0.1 to 0.3% of the re-circulating water when mechanical
draft towers are used, but increases to 0.3 to 1.0% for atmospheric towers. Blow down
requirement (B) is estimated from the following equation if maximum permissible cycles of
concentration (C) are known.
E + W(1 – C)
B= ; Where B, E, and W are in liters/min.
C –1
For trouble-free operation and minimum use of water quality control chemicals in the re-
circulating water, the cycles of concentration are generally kept at 2.0 to 3.0 and, in no case,
more than 4.0 in cooling towers such as these in Bombay. Hence, for a 100-tonnes air-conditioning
plant re-circulating 1100 liters/min of water with a temperature drop of, say, 10°C through a
mechanical draft tower where cycles of concentration are to be restricted to 2.0.
E = 2% × 1100 = 22 liters/min; W = 0.2% × 1100 = 2.2 liters/min
22 + 2.2(1 – 2)
B= = 20 litres/min (approx)
( 2 – 1)
The total make-up water requirement thus equals 44.2 liters/min (=22+2.2+20) or
63.4 m3/day for 24-hrs working of this 100-tonnes plant.
Similarly, if 3.0 cycles of concentration are permissible, the total requirement of make-up
water reduces to 47.7m3/day for 100-tonnes plant.
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12 VIRTUAL WATER
12.1 INTRODUCTION
Virtual Water: This is a concept that was developed by Prof. Tony Allan, which refers to the
volume of water needed to produce a commodity or service. For example, it typically takes
1,000 tonnes of water to produce one tonne of wheat. This represents the Virtual Water value
of wheat. As such, it is easier and less ecologically destructive, to import one tonne of wheat
than to pipe in 1,000 tonnes of water (Turton, 2000a). Virtual Water is also present in
hydroelectric power and constitutes the volume of water needed to produce a given unit of
hydroelectricity (Turton, 1998).
Virtual Water is a fascinating concept that is now being developed and refined for use by
decision-makers at the strategic level of society. Recourse to trade in times of scarcity has been
an age-old mechanism by which society has managed to cope with acute water deficit. This
mechanism is now being considered as a component of a longer-term strategy. As such, the
trade in Virtual Water has shown itself elsewhere to be economically viable, and
politically silent. A fine line exists between viable trade in Virtual Water and food aid. As
such a balance needs to be struck between economic development and foreign trade. Similarly,
post-colonial dependency is also politically risky. Therefore, a balance needs to be struck between
a policy of national self-sufficiency and food security. All policies are doomed to fail however,
if the underlying driver of water deficit is ignored. As such, water deficit is not really the
problem. It is merely the manifestation of a greater and more complex problem — uncontrolled
population growth.
consumption of meat brings along a large water footprint. Also the more food originates from
irrigated land, the larger is the water footprint. Finally, nations in warm climate zones have
relatively high water consumption for their domestic food production resulting in a larger
water footprint. At an individual level, it is useful to show the footprint as a function of food
diet and consumption patterns.
1 cup of coffee needs 140 litres of water.
1 litre of milk needs 800 litres of water.
1 kg of wheat needs 1100 litres of water.
1 kg of rice needs 2300 litres of water.
1 kg maize needs 900 litres of water.
• The production of one kilogram of beef requires 22 thousand litres of water.
• To produce one cup of coffee, we need 140 litres of water.
• The water footprint of China is about 775 cubic meter per year per capita. Only about
3% of the Chinese water footprint falls outside China.
• Japan with a footprint of 1100 cubic meter per year per capita, has about 60% of its
total water footprint outside the borders of the country.
• The USA water footprint is 2600 cubic meter per year per capita.
(Source: UNESCO-IHE - Water Footprint)
Virtual Water
Virtual water is the amount of water that is embedded in food or other products needed for its
production. Trade in virtual water allows water scarce countries to import high water
consuming products while exporting low water consuming products and in this way making
water available for other purposes [World Water Council].
Ten litres of orange juice needs a litre of diesel fuel for processing and transport, and 220
litres of water for irrigation and washing the fruit. The water may be a renewable resource,
but the fuel is not only irreplaceable but is a pollutant, too.
For example, the virtual water content (in m3/tonne) for potatoes is 160. Others examples
maize=450; milk=900; wheat=1200; soyabean=2300; rice=2700; poultry=2800;
eggs=4700; cheese=5300; pork=5900; and beef=16000.
Showing people the ‘virtual water’ content of various consumption goods will increase the
water awareness of people.
12.3 DEFINITIONS
Virtual water content: The virtual water content of a product is the volume of water used to
produce the product, measured at the place where the product was actually produced. The
virtual water content of a product can also be defined as the volume of water that would have
been required to produce the product in the place where the product is consumed. The adjective
‘virtual’ refers to the fact that most of the water used to produce a product is in the end not
279Energy Management Virtual Water 279
contained in the product. The real water content of products is generally negligible if compared
to the virtual water content.
Virtual water export: The virtual water export of a country or region is the volume of
virtual water associated with the export of goods or services from the country or region. It is
the total volume of water required to produce the products for export.
Virtual water import: The virtual water import of a country or region is the volume of
virtual water associated with the import of goods or services into the country or region. It is
the total volume of water required (in the export countries) to produce the products for import.
Viewed from the perspective of the importing country, this water can be seen as an additional
source of water that comes on top of the domestically available water resources.
Virtual water flow: The virtual water flow between two nations or regions is the volume of
virtual water that is being transferred from one place to another as a result of product trade.
Virtual water balance: The virtual water balance of a country over a certain time period is
defined as the net import of virtual water over this period, which is equal to the gross import
of virtual water minus the gross export. A positive virtual water balance implies net inflow of
virtual water to the country from other countries. A negative balance means net outflow of
virtual water.
National water saving: A nation can save its domestic water resources by importing a water-
intensive product rather than produce it domestically.
Global water saving: International trade can save water globally if a water-intensive commodity
is traded from an area where it is produced with high water productivity (resulting in products
with low virtual water content) to an area with lower water productivity.
Coping strategy: A coping strategy is the output of the decision-making elite, usually in the
form of some coherent policy or set of strategies such as water demand management, that
seeks to manage the water scarcity in some form or another (Turton & Ohlsson, 1999). A
coping strategy is the synthesis of a logical series of options that decision-makers consider,
thereby converting those options into a clearly defined policy choice with which to confront
the problems of rising levels of water scarcity in a given state or regional setting. A coping
strategy contains a logic of its own that is based on political rationality, which in turn may not
coincide with an outsider’s perception of rationality.
Problemshed: This is a conceptual unit in which the remedy for a problem can be found. In
other words, conventional wisdom would have us believe that watersheds are the unit of
management, but it is also at this level that water deficit exists.
Sectoral water efficiency: The Sectoral Water Efficiency (SWE) is the ratio of water consumed
within a given economic sector (expressed as a percentage of total national water consumption)
in relation to contribution of the same economic sector to overall GDP (expressed as a percentage
of total GDP) (Sectoral Water Efficiency = Sectoral Water Consumption as %: Sectoral
Contribution to GDP as %) (Turton, 1998:7).
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Water deficit: This refers to the prevailing condition that exists when the consumption of
freshwater within a given social entity exceeds the level of sustainable supply (Turton, 2000b).
Water scarcity: This is the condition that exists when the demographically induced demand
for water exceeds the prevailing level of local supply, meaning that supply-sided augmentation
becomes necessary (Turton & Meissner, 2000).
20 0 20
W a ter D e m an d
A nn ual W ater D em an d
(th ousan ds)
15 0 15
Popu lation
(m illion m )
3
10 0 10
P o p lu tio n
50 5
19 30 19 60 19 90
Year
Fig. 12.1 Growth of Windhoek’s population and water demand (after Jacobson et al., 1995). This can
be thought of as being the visible fraction of water demand.
This is typical of the problem being faced by urban water supply schemes so the literature
is rich with examples. While this is clearly an important aspect of water resource
management, it does not tell the full story and as such can be misleading to strategic
decision-makers. This is where the invisible water fraction becomes relevant. Ohlsson
(1999) provides an insight into the problem by showing a breakdown of water needs for
one human being expressed in liters of water per day. In terms of this analysis, one
human being can survive on 2-5 liters per day for drinking purposes; between 25 and
100 liters per day are needed for domestic use such as sanitation services, washing of
clothes and cooking utensils, etc; and between 1,000 and 6,000 liters per day are used
for food and biomass production. From this it is evident that the volumes of water that a
local authority would need to supply — the so-called visible fraction of water consumption
— is in the order of 27-105 liters per person per day. This falls into absolute insignificance
when compared to the invisible fraction of water consumption for the same person,
which according to Ohlsson (1999) ranges between 1,000 and 6,000 liters per day
(depending on where that person lives and what type of diet is taken as being normal).
Stated differently, at the lowest end of the scale, the invisible water fraction (for food) is
37 times greater than the visible fraction. At the highest end of the same scale, the
invisible fraction of water in the form of food is a staggering 57 times greater than the
visible fraction. This nuance is largely ignored in the literature.
This can be understood by means of a simpler illustration. Let us take the basic water
requirement (BWR) as 50 liters per person per day. Let us then accept that a healthy diet
consists of 3000 calories of food per person per day. We know that on average, it takes
around one liter of water to produce one calorie of food. This translates to 3000 liters of
water per person per day for the invisible fraction of water for food production, which is
a staggering 60 times greater than the visible fraction of water consumption. Therefore
in order to ensure an adequate supply of food and water for one person for a year, a
1
whopping 1113 tonnes of water is needed of which a mere th (18 tonnes) is related to
60
the visible fraction.
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3. We need to take yet another fundamental fact into consideration. This is related to
the Sectoral Water Efficiency (SWE) of agriculture versus industry. Ohlsson (1999)
states that a reasonably acceptable global benchmark figure for agricultural water
consumption is 65-70% of the total water abstractions in a given country. This will
obviously vary from country to country, largely as the result of agricultural
dependence. In developing countries this can be higher. An acceptable international
benchmark for industrial water abstraction is in the order of 20-25% of the total
water abstraction in any given country. Of this a small fraction (9%) is consumptive
use, with the rest being recaptured via treatment and recycling technologies and
therefore made available for other economic purposes or activities. The world
benchmark for household water abstraction is only 5-10% of the total water
abstraction in any given country. So, in terms of pure abstraction alone, agriculture
is by far the largest user of water in any given economy.
Thus, in general terms, the agricultural SWE is low whereas the industrial SWE tends
to be high. In fact water that is diverted away from agricultural use into the industrial
and urban domestic sectors, can produce 70 times more economic value for given
volume of water (Ohlsson, 1999).
Table 12.1 Selected SWE statistics for four SADC member states during 1995 (after Turton 1998)
4. Having noted that an industrialized economy tends to be more water efficient, another
critical aspect also becomes relevant to this guide. This different SWE characteristic
allows the notion of economic gearing to be brought to bear on the problem of water
deficit. This in turn implies a better water use pattern, and in particular, the ability to
generate foreign currency with which to finance Virtual Water imports.
5. The latter issue of social stability gives us a clue as to the existence at strategic levels of
yet another critically important aspect, namely the social ability to adapt to changing
levels of water deficit.
available to the strategic-level decision-maker. It is this fact alone, that has mitigated
against the confidently prophesied water wars in the Middle East (Allan, 1998).
2. By reaching into the problemshed for a solution, vast quantities of Virtual Water become
available at reasonable (usually subsidized) prices, with the added advantage of being
environmentally sustainable. The current global grain surplus sees Virtual Water that
has been harvested from the soil profiles of water abundant countries, often at highly
subsidized rates, becoming a viable means of balancing local-level water deficits. During
times of drought, countries often resort to importing grain or foodstuffs. This time-
tested remedy has always been available to governments in water stressed regions.
The only difference between this normal coping strategy, and a Virtual Water-based
solution, is the fact that the former is a once off act, whereas the latter is a deliberate
policy choice.
3. There is a definite conceptual difference between a country that uses Virtual Water as
a rational coping strategy and a country that relies on food aid for survival. Japan, for
example, does not grow all of its own food, but Japan is certainly not aid-dependent.
Botswana and South Africa are shifting away from a policy of national-self-sufficiency
in food to one of food security instead. The difference between a country that has a
rational coping strategy based on Virtual Water and an aid-dependent country is
therefore the ability to pay.
4. A rational coping strategy that is based on the merits of virtual water implies a fundamental
re-think of the policy of national self-sufficiency in foodstuffs. In fact, a Virtual Water
paradigm is based on a policy of food security instead, with a strong and diversified economy
with which Virtual Water imports can be paid for in a sustainable manner. This does not
imply that a new form of post-colonial political or economic dependence is being accepted.
It does imply however, that a balance needs to be struck between the relative merits (and
demerits) of national self-sufficiency versus food security. For example, South Africa as a
diversified political economy was forced to adopt a national self-sufficiency policy as the
result of apartheid-induced sanctions. This implied massive mobilization of water for
irrigation purposes, to the extent that environmental sustainability became a key issue.
Virtual water is therefore environmentally friendly, and as such ought to be supported by
environmental NGOs and special interest groups as a fundamental component of sustainable
development in water deficit regions of the world.
5. Virtual water is politically silent (Allan, 2000). It is therefore never expected to become
front-page news in any country that uses it as a coping strategy. In fact, research shows
that where it is used, the political decision-makers concerned can keep up the necessary lie
that water deficit is not a problem for economic growth and social stability.
6. Virtual water is not a universal panacea of all water-related problems however. This
fact needs to be appreciated as well. While water deficit can be balanced at the strategic
level of a given country, it will not necessarily relate to food security at the household
level of society.
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7. Virtual water can become a powerful tool for balancing the water budget at a regional
level. This is particularly useful within the context of SADC, where development is
spatially uneven and where water distribution patterns do not match economic
development patterns. As such, by considering a virtual water paradigm as a
fundamental driver of intra-regional trade and development, it cans fast-track
agricultural and economic development in a more equitable and sustainable way.
argumentation can be made for export of virtual water. Import of water-intensive products by
some nations and export of these products by others include what is called ‘virtual water
trade’ between nations.
CWR[n,c]
SWD[n,c] = ..........(1)
Cγ[n,c]
287Energy Management Virtual Water 287
R e f. cro pe v ap otr an sp .
C lim atic param eters -1
E o [m m da y ]
C ro p w ate r re q uirem en t
C W R [m 3 h a ]
-1
Calculation of Virtual Water Trade Flows and the National Virtual Water Trade Balance
Virtual water trade flows between nations have been calculated by multiplying international
crop trade flows by their associated virtual water content. The latter depends on the specific
water demand of the crop in the exporting country where the crop is produced. Virtual water
trade is thus calculated as:
VWT[n , n ,c,t] = CT[n ,n ,c,t] × SWD[n ,c]
e i e i e .......(4)
in which VWT denotes the virtual water trade (m3yr–1) from exporting country ne to importing
country ni in year t as a result of trade in crop c. CT represents the crop trade (ton yr–1) from
exporting country ne to importing country ni in year t for crop c. SWD represents the specific
water demand (m3 tonnne–1) of crop c in the exporting country. Above equation assumes that
if a certain crop is exported from a certain country, this crop is actually grown in this country
(and not in another country from which the crop was just imported for further export).
Although a certain error will be made in this way, it is estimated that this error will not
substantially influence the overall virtual water trade balance of a country. Besides, it is
practically impossible to track the sources of all exported products.
The gross virtual water import to a country ni is the sum of all imports:
The gross virtual water export from a country ne is the sum of all exports:
GVWE[n ,t] = ∑VWT[n ,n,c,t]
e e i .......(6)
n,c
i
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The net virtual water import of a country is equal to the gross virtual water import minus the
gross virtual water export. The virtual water trade balance of country x for year t can thus be
written as:
NVWI[x,t] = GVWI [x,t] − GVWE [x,t] .......(7)
where NVWI stands for the net virtual water import (m3yr-1) to the country. Net virtual water
import to a country has either a positive or a negative sign. The latter indicates that there is net
virtual water export from the country.
As an index of national water scarcity, we use the ratio of total water use to water availability:
WU
WS = ×100 .......(9)
WA
In this equation, WS denotes national water scarcity (%), WU the total water use in the
country (m3yr-1) and WA the national water availability (m3yr-1). Defined in this way, water
scarcity will generally range between zero and hundred percent, but can in exceptional cases
(e.g. groundwater mining) be above hundred percent. As a measure of the national water
availability WA we take the annual internal renewable water resources, that are the average
freshwater resources renewably available over a year from precipitation falling within a
country’s borders (Gleick, 1993).
The water dependency (WD) of a nation is calculated as the ratio of the net virtual water
import into a country to the total national water appropriation:
NVWI
×100 if NVWI ≥ 0
WD= WU+NVWI .......(10)
i f NVWI<0
The value of the water dependency index will vary per definition between zero and hundred
percent. A value of zero means that gross virtual water import and export are in balance or
that there is net virtual water export. If on the other extreme the water dependency of a
nation approaches hundred percent, the nation nearly completely relies on virtual water import.
As the counterpart of the water dependency index, the water self-sufficiency index is
defined as follows:
WU
×100 if NVWI ³ 0
WSS= WU+NVWI .......(11)
100 i f NVWI<0
The water self-sufficiency of a nation relates to the water dependency of a nation in the
following simple way:
WSS = 1 – WD .......(12)
The level of water self-sufficiency (WSS) denotes the national capability of supplying the water
needed for the production of the domestic demand for goods and services. Self-sufficiency is hundred
percent if all the water needed is available and indeed taken from within the own territory. Water
self-sufficiency approaches zero if a country heavily relies on virtual water imports.
FAO Penman- Monteith equation for calculating reference crop evapotranspiration. The
CropWat model calculates crop water requirement of different crop types on the basis of the
following assumptions:
(1) Crops are planted under optimum soil water conditions without any effective rainfall
during their life; the crop is developed under irrigation conditions.
(2) Crop evapotranspiration under standard conditions (ETC), this is the evapotranspiration
from disease-free, well-fertilised crops, grown in large fields with 100% coverage.
(3) Crop coefficients are selected depending on the single crop coefficient approach, that
means single cropping pattern, not dual or triple cropping pattern.
Climatic Data
The climatic data needed as input to CropWat is taken from FAO’s climatic database ClimWat,
which is also available through FAO’s web site. The ClimWat database contains climatic data
for more than hundred countries. For many countries climatic data are available for different
climatic stations.
Crop Parameters
In the crop directory of the CropWat package sets of crop parameters are available for 24
different crops. The crop parameters used as input data to CropWat are: the crop coefficients
in different crop development stages (initial, middle and late stage), the length of each crop in
each development stage, the root depth, and the planting date. For the 14 crops where crop
parameters are not available in the CropWat package, crop parameters have been based on
Allen et al. (1998).
Crop Yields
Data on crop yields is taken from the FAOSTAT database, again available through FAO’s
website.
Crops for which crop parameters have been taken Crops for which crop from parameters
from FAOs CropWat package have been taken Allen et al. (1998)
Fig. 12.3 National virtual water trade balances over the period 1995-1999
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Green coloured countries have net virtual water export. Red coloured countries have net
virtual water import.
National virtual water trade balances over the period 1995-1999 are shown in the coloured
world map of Fig. 12.3. Countries with net virtual water export are green and countries with
net virtual water import are red.
Some countries have net export of virtual water over the period 1995-1999, but net import
of virtual water in one or more particular years in this period (Table 12.4). There are also
countries that show the reverse (Table 12.5).
Table 12.3. Top-30 countries of virtual water export and top-30 countries of virtual water import (over
1995-1999).
Table 12.4. Countries with net export of virtual water in the period 1995-1999 that have however net import
in particular years. A ‘minus’ indicates a negative virtual water trade balance (i.e. net export of virtual
water). A ‘plus’ indicates a positive virtual water trade balance (i.e. net import of virtual water)
Brazil – + – – –
Syria – – – – +
Greece – – – + –
Sudan – + + + –
United Kingdom + + – + +
Burkina Faso – + + – –
Benin + – – – –
Slovakia – – + – –
Ecuador – – – + –
Bulgaria – + + – –
Cuba + – – + –
Finland – – – – +
Yugoslavia – – + – –
Uganda – – + + +
Papua N. Guinea – – + – +
Bahamas + – – – –
Montserrat – – – – +
Tajikistan + – – – –
Cameroon – – + + –
Martinique – + + + +
Pakistan – – + – +
Solomon Islands – + – + +
Central Africa – + – + –
Samoa – – – + –
Wallis Island – + + + +
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Table 12.5 Countries with net import of virtual water in the period 1995-1999 that have however net export
in particular years. A ‘minus’ indicates a negative virtual water trade balance (i.e. net export of virtual
water). A ‘plus’ indicates a positive virtual water trade balance (i.e. net import of virtual water)
6 .0 E+ 11
2 .0 E + 11
5 .0 E+ 11
4 .0 E+ 11 1 .5 E + 11
3 .0 E+ 11 1 .0 E + 11
2 .0 E+ 11
5 .0 E + 1 0
1 .0 E+ 11
0 .0 E+ 0 0 0 .0 E + 0 0
19 95 19 96 19 97 19 98 19 99 To ta l 19 95 19 96 19 97 19 98 19 99 To ta l
Fig. 12.4 Gross virtual water import into and Fig. 12.5 Gross virtual water import
export from the United States in the into and export from Canada in the
period 1995-1999 (m3yr –1). period 1995-1999 (m3yr –1).
3 .0 E + 11 2 .0 E+ 11
E x p o rt 1 .8 E+ 11 E x p o rt
2 .5 E + 11 Im p o rt Im p o rt
1 .6 E+ 11
1 .4 E+ 11
2 .0 E + 11
1 .2 E+ 11
1 .5 E + 11 1 .0 E+ 11
8 .0 E+ 1 0
1 .0 E + 11
6 .0 E+ 1 0
4 .0 E+ 1 0
5 .0 E + 1 0
2 .0 E+ 1 0
0 .0 E + 0 0 0 .0 E+ 0 0
19 95 19 96 19 97 19 98 19 99 To ta l 19 95 19 96 19 97 19 98 19 99 To ta l
Fig. 12.6 Gross virtual water import into Fig. 12.7 Gross virtual water import into
and export from Thailand in the and export from India in the
period 1995-1999 (m 3yr –1). period 1995- 1999 (m3yr –1).
1 .6 E+ 11 5 .0 E+ 11
E x p o rt 4 .5 E+ 11 E x p o rt
1 .4 E+ 11
Im p o rt Im p o rt
4 .0 E+ 11
1 .2 E+ 11
3 .5 E+ 11
1 .0 E+ 11 3 .0 E+ 11
8 .0 E+ 1 0 2 .5 E+ 11
2 .0 E+ 11
6 .0 E+ 1 0
1 .5 E+ 11
4 .0 E+ 1 0
1 .0 E+ 11
2 .0 E+ 1 0 5 .0 E+ 1 0
0 .0 E+ 0 0 0 .0 E+ 0 0
19 95 19 96 19 97 19 98 19 99 To ta l 19 95 19 96 19 97 19 98 19 99 To ta l
Fig. 12.8 Gross virtual water import into Fig. 12.9 Gross virtual water import into
and export from Australia in the and export from Sri Lanka in the
period 1995-1999 (m3yr –1). period 1995-1999 (m3yr –1).
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Fig. 12.10 Virtual water trade balances of 13 world regions over the period 1995-1999. Green coloured regions
have net virtual water export; red coloured regions have net virtual water import. The arrows show the largest net
virtual water flows between regions (>100 Gm3).
1000
E x p o rt
Im p o rt
800
600
400
200
0
Ce ntra l Ce ntra l Ce ntra l Ea stern Middle No rth No rth Oc eania FS U So uth So uth So uth Western
A frica Ame ric a and So uth Eu ro pe Ea st Afric a Ame ric a Ame ric a Ea st Asia Eu ro pe
Asia
Fig. 12.11a Gross virtual water import and export per region in the period 1995-1999 (Gm3).
297Energy Management Virtual Water 297
1000
500
-500
-100 0
-150 0
Ce ntra l Ce ntra l Ce ntra l Eastern Middle No rth No rth Oc eania FS U South South South Western
A frica Ame ric a and So uth Euro pe East Afric a Ame ric a Afric a Ame ric a East Asia Euro pe
Asia
Fig. 12.11b Net virtual water import per region in the period 1995-1999 (Gm 3).
CONCLUDING REMARKS
Here virtual water trade related to crop trade between nations mentioned. Also other goods
contain virtual water, for instance meat, dairy products, cotton, paper, etc. In order to get a
complete picture of the global virtual water trade flows, also other products than crops have to
be taken into account. For instance, the virtual water trade balance of the Netherlands drawn
in the current study suggests that this country has an incredibly high net import of virtual
water, due to the large import of feed for the Dutch bio-industry. The balance will look quite
differently if we would take into account the export of virtual water that relates to the export
of meat from the Netherlands.
Knowing the national virtual water trade balance is essential for developing a rational
national policy with respect to virtual water trade. But for some large countries it might be as
relevant to know the internal trade of virtual water within the country. China for instance,
relatively dry in the north and relatively wet in the south, domestic virtual water trade is a
relevant issue.
298 Energy
Appendix : I Crop water requirements (m3/ha) (source: crop wat model)
Water Management
Country Banana Barley Bean Ground Maize Potato Sugar Vegetables Onion Rice Wheat Cotton
Green Nut Cane Dry Seed
Management
Afghanistan 6800 3770 3540 3890 3340 2980 12740 4040 — 5900 4350 7410
Australia 8970 4030 2670 5930 4380 5790 18520 1190 6620 8600 4730 8710
Bangladesh 7050 3520 3260 4600 3350 3420 13460 3300 — 8200 4260 8300
Brazil 7730 4220 2250 4830 3480 4400 14250 3180 6630 7800 3320 6680
Canada 7120 3560 2200 3180 3170 3130 12830 2950 6920 6200 3740 4872
China 6180 4100 4120 4960 3600 4070 9870 2920 6680 6800 4040 6780
Germany 7120 3560 2200 3180 3170 3130 12830 2460 6590 6900 3740 3880
India 8610 3780 5190 6930 4720 4820 20300 5460 6400 9880 6910 9190
Indonesia 8640 4180 3020 5010 4850 6170 16480 2680 5170 9300 3950 7080
Israel 13070 8800 — 5980 6350 4780 24710 4400 6160 12000 6100 11920
Italy 6630 4850 3530 5370 2460 5500 18920 4070 6710 6400 6540 8752
Japan 6400 3650 2980 4620 3160 2410 10100 2810 6190 7600 3760 6510
Korea 6600 2460 2980 3370 2190 2300 10600 3790 6820 6570 3820 7020
New Zealand 6570 3640 2120 3540 3250 6290 12850 2430 5740 — 3030 6110
Singapore 7810 3560 3180 4950 4250 4480 15020 3050 6820 — 4150 8930
South Africa 8970 4030 2670 5930 4380 4680 18520 4490 — — 4730 8710
Sri Lanka 8970 5590 4570 6870 6640 6930 15780 5140 — — 8730 —
UK 7120 3580 2200 3180 3170 3290 12830 2450 3780 5900 3740 —
USA 6570 3640 2120 3180 3170 3290 12830 2450 4830 8600 3740 6210
CREATION OF SWEET
13 WATER
13.1 ARTIFICIAL RAIN
There is a river in the sky a complex, swirling, tumultuous river of air and water. Sometimes
we cannot see the water, when it is in the form of vapor. At other times, airborne droplets of
water gather in clouds, which, of course, can be seen. We should not assume that clouds
contain water and the surrounding air does not, because the surrounding air carries vapor,
which often flows into the cloud. And, also, clouds dissolve into vapor and fade away. But the
clouds we see with our eyes contain water brought along a step in the process of becoming
rain. With clouds we can have rain. Without clouds we cannot. But with clouds we do not
necessarily have rain. The droplets of water often fail to take the further step of becoming
raindrops, accretions of water become heavy enough to fall to the ground.
This exasperates the farmer — when lush clouds, apparently containing a great deal of
moisture, float over his dry fields and fail to precipitate out even one small part of the moisture
carried by and flowing into these clouds. Cloud census studies have shown that seasons with
considerable cloud cover can also be dry seasons.
Why? Can we coerce the droplets into becoming drops heavy enough to fall onto the
ground? Can we haul down needed moisture from sky?
A FEW YEARS AGO many of us thought we had been theorized that minute particles of
dust, present throughout the atmosphere, were a necessary ingredient of rain, something for
the droplets to cluster on and grow. In 1946, Dr. Vincent J. Schaefer, of the General Electric
Co., sprinkled particles of dry ice from an airplane and produced precipitation. A little later Dr.
Bernard Vonnegut of General Electric ran onto silver iodide as the ideal particle or crystal. A
few experiments produced seemingly awe-inspiring results.
And so, “scientific rainmaking” came into being. The scientific basis of it was “artificial
nucleation” — that is, the supplying of artificial nuclei or particles to clouds thought to lack
sufficient natural nuclei.
A comment on terminology should be inserted at this point. The word “rainmaking”
seems to imply the creation of water, whereas so-called rainmakers cannot produce water
that does not already exist in the air. Perhaps “rain increasing” should be used. Further, the
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phrase “Weather control” implies a management of the elements beyond present conception.
Perhaps “weather modification” states more accurately what we can now visualize. The
terms “rainmaking” and “weather control”, however, have become common and are more
easily recognized.
Artificial nucleation is tied in with the ice crystal theory. According to the theory, natural
ice crystal formation occurs at quite low temperatures (– 40° F). Presumably the crystals grow
by attracting other moisture particles until they become heavy enough to fall out of the clouds
as snow, which melts on the way down and becomes rain.
Dropping dry ice (carbon dioxide) on clouds cools areas of those clouds and starts the
process of crystal formation. The effect can be substantial if the clouds are near the temperature
at which ice crystals form naturally.
Supplying nuclei to clouds does not cool them, but with nuclei the ice crystal formation
occurs at higher temperatures — that is, below freezing but closer to the freezing level. Some
natural nuclei or dust particles start the process at temperatures between –40° and 5°. But
crystals of silver iodide (artificial nuclei) start it between 5° and 25°.
Therefore, silver iodide not only can start rainfall in clouds too warm for natural rainfall
production but also can increase rainfall in clouds already producing small amounts by
nucleating the warmer lower sections.
Another method of producing rainfall is of interest, although not of commercial importance.
In warm regions, non-freezing clouds release rain, obviously by some other process than the
formation of ice crystals.
It is commonly believed that precipitation results when larger than normal water droplets
fall relative to other droplets, collecting enough smaller ones to grow to raindrop size large
enough to fall out of the cloud. The answer lies in providing the larger droplets.
Such clouds, found in the Southern States and farther north in the summer, have been
successfully seeded by water sprayed from airplanes.
But airplanes cost money to operate and flying them into storm clouds can be dangerous.
The large commercial “cloud – seeders” therefore do not use dry ice or water but rely on silver
iodide, which can be released from ground generators. The minute crystals drift away from
the generators and presumably get sucked into the updrafts of storm clouds.
Experts suggest that rainmaking is a pretty big business, even with its uncertainties.
The study indicates that the rainmakers really have modified the weather significantly
an assumption that a majority of scientists familiar with the subject do not go along with
wholeheartedly. Most of them seem to agree that nucleating agents can modify weather in
certain circumstances. Some think these circumstances occur frequently enough so that man
can change the whole pattern of water distribution, with a tremendous impact on the economy.
Others are skeptical of large–scale effects. Most of them say: “A lot more has to be learned
about the rainmaking process before we can tell”.
301Energy Management Creation of Sweet Water 301
The rainmakers answer the argument by saying that nature is an inefficient rainmaker,
with only about 1 percent of a cloud’s moisture falling to the ground in an ordinary storm. By
supplying more nuclei they may increases this efficiency up to 2 percent. Such amounts are
insignificant, they say, and the vast streams of moisture floating in the sky will replenish the
clouds almost immediately.
Whatever the merits of this, rainmaking, viewed on a grander scale, may indeed increase
substantially the amount of mineral–free water available for man’s use.
FOR ONE THING, it seems perfectly obvious that many airborne streams of moisture
escape the land and give much of their water back to the seas. Rainmaking might make it
possible for us to take better advantage of the rain potential of these airborne streams before
they get away. For another thing, it has been suggested that precipitating moisture out of
clouds at earlier stages of storm development might speed up the hydrologic cycle and establish
a new rainfall regime. This would mean more use and reuse of air-borne moisture.
But even if rainmaking could not increase the net amount of moisture on the ground, it might yet
affect the distribution of this moisture in such a way as to produce tremendous economic benefits.
DOES IT REALLY WORK? That is the question farmers ask. Scientists reply that it does
in certain circumstances.
Seeding with dry ice and water admittedly has modified clouds and has produced
precipitation. Silver iodide can do the same.
But scientists disagree as to whether the more economic method of seeding clouds by
means of ground generators produced, or can produce, the substantial increases in rain and
snowfall claimed by the private “cloud-seeders”.
The problem of evaluation is inherent in the ground–generator method. Seeding with dry
ice or water, the operator can usually turn around and see the results. The seeded clouds often
change from and precipitation falls before his eyes. But when he releases silver iodide from a
generator he cannot see the material. Does the generator produce the right–sized crystals? Do
they get into the storm clouds in the right quantities at the right altitude? Does the silver
iodide retain its effectiveness or does it decay because of temperature, pressure, or exposure to
ultraviolet rays. There can be many a slip between the cup and the lip.
The fact that he seeds during storm situations, usually when at least some rain fall naturally,
makes visual observation impossible in most cases and makes measurement of any manmade
increase extremely complicated.
And so, instead of seeing the cause and effect, he has to guess. And he has to attempt a measurement
of the manmade increase by means of statistical evaluation. He has to compare the “target area”
rainfall with rainfall of past years or, more commonly, with rainfall received in adjacent areas.
Statistical analyses – usually provided by the cloud–seeder himself and imperfectly
understood by the layman – can often show spectacular and convincing results. But sometimes
figures the statistical people can bury good results in a pile of figures. Thus, there is controversy.
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The analyses themselves get complicated, but the problem of analysis can be stated quite simply.
When the target area gets more rain than outside areas, say three control areas labeled “A”
“B” and “C,” the cloud-seeder usually satisfies his clients. Yet the center of a storm may have
passed over the target area to produce the result naturally and the cloud-seeder may have done
nothing.
When the target area gets more rain than A and B, but less than C, the clients may nurse a
small doubt or two. And when the target area gets less than A, B, and C — then they become
skeptics. Yet in both cases the cloud-seeder may have increased rainfall on the target area over
the amount, which would have fallen naturally.
Rainfall results in the target areas usually fall within the realm of historical variation. We
can always suspect therefore, that increases are only accidental. If we only knew how much
rain would have fallen naturally, we can never know and we have to satisfy ourselves with a
statistical substitute.
A study of an entire river basin in the United States, based on physical assumptions
considerably more modest than some cloud-seeders have asserted, showed a benefit — cost
ratio of 20 to 1. Obviously experiments in certain areas—possibly mountain areas where air
movements showed into the clouds and where temperatures should be more favorable—these
should show a higher benefit — cost ratio. Experiments in some areas should prove to be more
nearly marginal.
Experiments in the United States have attracted a great deal of interest in foreign countries.
At least 26 countries, on every continent except Antarctica, have carried out experiments in
recent years.
Farmers in South Africa have used rockets to disperse silver iodide at high altitudes, the
purpose being to reduce hail damage. Farmers in the Bayonne region of France have used
ground generators for the same purpose. The theory of hail prevention is that, by precipitating
out moisture at earlier stages, cloud seeding can prevent large hail–producing storms from
developing. The same theory applies to lightning prevention and thus has interest for fighting
forest fires. Some cloud-seeders in the United States like hail–prevention projects because
while farmers do not always want more rain they almost always want to prevent hail if they
can. Thus such projects sometimes get a steadier financial support.
Formosa and Sweden have undertaken projects to increase hydroelectric power. Owners
of sugar plantations is Cuba have financed rain–increasing projects despite an average of more
than 1200 mm inches of rainfall a year. Additional rainfall means additional sugarcane for
them.
Much of the work in foreign countries has been of high caliber. But it still has not supplied
the answers.
Analysis of experiments will produce some answer helpful to farmers and other water
users in deciding whether weather control activities are a good bet or not. But the real and
positive answers will come from further research into rainfall processes. The sky is wild,
303Energy Management Creation of Sweet Water 303
unpredictable laboratory; research in weather is difficult and often frustrating. All the same,
science moves inexorably onward, learning more and more about the possibilities for modifying
or controlling weather.
Perhaps these possibilities will narrow down to certain limited applications. It is conceivable,
though, that weather control can become a regular feature of crop production.
Russian Air Force used this technique on 9th May 2005, to prevent rain on Moscow city
celebrating freedom festival. A group of eleven planes of Air Force of Russia flying at a high
3000m – 8000m spray silver iodie, liquid nitrogen and dry ice in air at 50 to 150 km away from
Moscow city. Due to this spray rainfall before the cloud reach to Moscow city. The event was
very important, as leaders from 53 countries were present in this celebration.
O SM O SIS
W h e n flu id s o f d iffere n t c o n c e ntra tio n s in
a v e s s el are se p a rate d b y a m e m b ran e , the
d ilute s o lutio n w ill flo w th ro ug h th e m e m b r an e
in to th e c o nc e n tra te d s o lu tio n .
F re s h w a te r S e a w a ter
M e m b ra ne
Fig. 13.1 Principle of osmosis.
F re s h w ate r Sea
w a ter
M em b ran e
Fig. 13.2 Osmotic pressure.
P re ss ure
F re s h w ate r S e a w ater
M em b ran e
reverse osmosis system is employed with some pre-treatment and post treatment. The pre-
treatment is required to remove suspended solids, colloids, metals, etc. to avoid fouling and
choking of the membrane surface which otherwise reduces the water flux. Post-treatment
usually consists of pH-adjustment and chlorination or depends upon end–product reuse.
Most reverse osmosis systems in use today employ semi–permeable “asymmetric membranes”
made from cellulose acetate or polyamide, or “composite membranes” made with a dense thin
polymer coating on a sulfone support film. The dense rejecting skin of the composite membranes
can be up to 10 times thinner than the skin of the cellulose acetate membranes.
The rejection of the dissolved species depends not only on the size of the rejected species,
but also on the chemistry of the membrane and the rejected species. The rejection of low
molecular mass is generally low with the asymmetric cellulose acetate and polyamide membranes
while with composite membranes; moderate to good rejections can be obtained with many
intermediate and even low molecular mass organics.
The percent rejections tend to be constant over a wide range of concentrations while only
the applied pressure will have to be varied. The concentration in the water passing through
the membrane will be proportional to the concentration retained. The higher the fraction of
feed which passes the membrane, that is, the higher the “recovery” of water, the higher will be
the concentration in the product water. The retained water is often termed the “concentrate”
and the product water the “permeate”.
H IG H M EM B R A N E
P R E SS U R E A S S E M B LY FR E SH
PUMP W AT E R
S A L IN E
F E E D W AT E R P O ST.
PRE- T R E AT M E N T
T R E AT M E N T
S TA B ILIZ E D
F R E S H W AT E R
B R IN E
D IS C H A R G E
(3) Permeation rate of water per unit pressure gradient which determines the size of
equipment per unit production rate of potable water.
(4) Membrane durability which determines the replacement rate of membrane.
(5) Capability of being fabricated with high surface to volume ratio (hollow fibers, thin films).
(6) Wide operating range
: (a) Ion content of water source.
: (b) Pressure
: (c) Temperature
: (d) Operating pH – range
(7) Resistance to chemical agents, heat and biological attack.
(8) Low cost.
(9) Versability to fit different requirements.
Indeed a large variety of membranes have been developed. The different membranes
available are:
(1) Cellulose acetate membranes.
(2) Polyamide membranes.
(3) Thin film composite membranes.
(4) Dynamic membranes.
Table 13.1 Comparison of different membrane modules
Parameters Limitations
Turbidity Less than 1 NTU
Free chlorine Nil
Iron, manganese Less than 0.05 ppm
Bacteria and organics Nil
Oil and grease Nil
Temperature Less than 45° C
Silting index Less than 4.0
pH 3 to 10
Parameters Results
TDS, ppm 38,926
Turbidity, NTU 30
pH 8.2
P-Alkalinity as CaCO3, ppm NIL
MO-Alkalinity as CaCO3, ppm 116
Chloride as chloride ppm 21,500
Chloride as CaCO3, ppm 30,315
Total hardness as CaCO3, ppm 6800
Calcium hardness as CaCO3, ppm 1050
Magnesium hardness as CaCO3, ppm 5750
Sulphate as sulphate, ppm 3000
Contd.
309Energy Management Creation of Sweet Water 309
Parameters Results
Sulphate as CaCO3, ppm 3120
Silica (dissolved) as SiO2, ppm 1.2
Corrected conductivity at 25°C µmhos/cm 61800
Residual chlorine, ppm —
Free CO2 as CO3 ppm 15
Free CO2 as CaCO3, ppm 17
It clearly seems from the above two tables (Table 13.2 & 13.3) of requirement of Reverse
Osmosis feed water and sea water analysis, that extensive pretreatment before the actual Reverse
Osmosis process is very essential. The pretreatment comprises of coagulation, sedimentation,
filtration, chlorination and dechlorination. The pretreatment or unit operation is a costly process
but is a must for running Reverse Osmosis process very smoothly. If the cost of the total
Reverse Osmosis process is say 10 Rs. / lit, the approximately 7 Rs. / lit is the unit operation
cost and rest 3 Rs. / lit is the cost Reverse Osmosis process. As a total solid contains of the
seawater is very high (38,000 – 42,000 ppm) a very high pressure (60 – 65 Kg / sqm) is
required to have the reliable results of the Reverse Osmosis effluents.
As per the requirement of the Reverse Osmosis feed water, the primary treatment to the
Sea water is given by
(1) Chlorination followed by coagulation and flocculation with FeSO4, cation polyelectrolyte
and recirculation of settled sludge.
(2) Sedimentation and filtration.
(3) Activated carbon filter.
(4) Micron cartridge filter.
The post-treatment degasification by degassifier.
Following are the pretreatment units
(1) Flash mixer.
(2) Sludge blanket type clariflocculator with sludge recirculation system.
(3) Rapid gravity dual media filter.
(4) Sludge collection sump and disposal system.
(5) Activated carbon filter (ACF).
(6) Chemical dosing system.
(7) Micron cartridge filter (MCF).
The high pressure pump is provided with suction and discharge pressure gauges to indicate
respective pressure and pressure switches at the suction and discharge of pumps to prevent
the pump from operating in the event of low suction or high discharge pressure. There are
residual chlorine analyzer, pH meter, temperature indicator in common suction header while
temperature indicator and high pressure switch at common discharge header.
Data:
Nos. : 3 working + 1 standby.
Capacity (cu.m/hr) : 215
Head (kg./sq.cm) : 64.35
Liquid to be handled : Filtered Sea Water
Type : Multistage Centrifugal Horizontal.
Motor:
Nos. : Four
kW / rpm : 600 / 2975
Supply Voltage : 6600 V, 3 Phase 50 Hz
Energy recovery turbine (ERT): This system is provided to take advantage of highpressure
energy of high-pressure pumps. The highly pressurized rejected water is fed into reverse pump
type turbine which in turn produces rotation power output used to assist main electric motor
in driving the high pressure pump thus saving a very considerable proportion of power to
drive the pump.
This system is directly coupled with motor shaft. Reverse Osmosis rejected water is fed to
it. It is provided with actuated globe valves at suction and globe valve at discharge. The discharge
water is sent to reject storage tank.
Data:
Nos. : 3 working + 1 standby.
Material of construction : DUPLEX – SS
Capacity (cu.mt/hr) : 135
Inlet pressure (psig) (min./max.) : 850/900
Liquid to be handled : RO Reject Water.
Reverse osmosis unit: RO unit is provided to reduce dissolved solids from the RO feed water
and to get the purified water (permeate water). The permeate water is then passed through
degassifier. The reject water is then passed through the energy recovery turbine to save the
considerable amount of electric power.
RO feed water, under high pressure, enters into pressure tubes of the RO unit which
passes through the RO membrane elements. The permeate travels through the header whereas
the concentrated reject water, which contains very high dissolved solids passes through Energy
Recovery Turbine (ERT) and then collected in reject water storage tank. The reject water is
used for backwash of Activated Carbon Filter (ACF) and Rapid Sand Filter (RSF).
311Energy Management Creation of Sweet Water 311
The Reverse Osmosis Unit consists of three stream (A,B & C). Each stream consists of
four sub-streams of six pressure tubes each in single pass array. Each pressure tube contains
six membranes elements which are interconnected inside the pressure tubes with help of “O”
rings placed in the interconnectors.
Data:
No. of stream : Three (RO – A / B & C)
No. of substream : Four (RO – A / B / C – 1/2/3/4)
No. of pressure tubes : Six/Substream
Membrane type : 8040 HYS SWCI
No. of membrane element : Six/Pressure Tube
Total no of pressure tube : 72
Total no of membrane element : 432
Length and size of pressure tube : 12.4m
Flow array : Single pass
Max. feed flow (cu.mt/hr) : 53.7
Operating pressure (kg/sq.cm) : 64.35
Max. permeate flow (cu.mt/hr) : 15.3
Degasser tower (DGT): Degasser tower is an atmospheric tower provided for removal
of residual gases like carbon dioxide. It is made from mild steel rubber lined (MSR/L)
internally and provided with polypropylene pall rings supported on MSR/L coated tray.
To distributes the incoming water from the top header the lateral type of distribution
system is provided.
The bottom tray distributes the draft of low-pressure air from the blower from top and
going upwards. Packing is provided to increase the surface area by breaking the water.
312 Energy
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Data:
Nos. : Two
Diameter (mm) : 1400
Height (mm) : 3000
Material of construction : MSR / L
Type of packing : Polypropylene pall rings
Degasser air blower: Degasser air blower is provided for blowing the air the bottom of degasser
tower and carbon dioxide from permeate water is removed by this blown up air.
Data:
Nos. : Two + Two standby
Type : Centrifugal
Capacity (cu.m/min) : 46.2
Head (mm WC) : 50
Motor:
Nos. : Four
kW / rpm : 1.5 / 1400
Supply voltage : 3 Phase. 415 V AC, 50 Hz
Caustic soda (NaOH) dosing system: Caustic soda (NaOH) may be dosed in the permeate
water after degasification to increase the pH of water to make it suitable for further use.
Sometimes it may happen that pH of the RO feed water is acidic and hence the permeate water
is also having low pH value. This low pH value water is not suitable for further domestic,
drinking or other use and hence if the permeate water is having low pH value then only
caustic dosing system is need based applicable.
Permeate storage tank (PRST): Permeate storage tank is provided with an inlet for degassed
water, outlet leading to overflow, drain connections and level indicating transmitter, permeate
transfer pump suction, permeate flushing pump suction.
To pump the degassed water from permeate storage tank permeate transfer pump is provided
with pressure gauge and non – return valve at the discharge line.
Data:
Nos. : One
Material of construction : MSR / L
Diameter (mm) : 3600
Length on straight (mm) : 5000
Liquid to be handled : Degassed permeate water
Pump:
Nos. : Two + One standby
Type : Horizontal centrifugal
Capacity (cum / hr) : 93
Liquid to be handled : Degassed permeate water
313Energy Management Creation of Sweet Water 313
Motor:
Nos. : Three
kW / rpm : 7.5 / 2915
Supply voltage : 3 phase, 415 V Ac, 50 Hz
Reject water storage tank (RJST): Reject water storage tank is provided to store the reverse
osmosis rejected water which can be used for back washing of activated carbon filters and
rapid gravity dual medial filter by operating the rejected water transfer pumps.
Data:
RJST
Nos. : One
Dimensions (mm) : 12500 × 8000 × 2500 LWD
Material of construction : RCC
Pump:
Nos. : Two + Two standby
Type : Vertical turbine
Capacity (cum / hr) : 265
Liquid to be handled : Rejected water
Motor:
Nos. : Four
kW / rpm : 30 / 1500
Supply voltage : 3 Phase, 415 V Ac, 50 Hz
Cleaning system: To remove foulants from the RO membrane element and to fill up the
pressure tubes with disinfectant solution, cleaning system is provided. Cleaning system comprises
the following.
(1) Cleaning solution tank (CST)
(2) Cleaning solution pump.
(3) Micron cartridge filter.
(1) Cleaning solution tank: Cleaning solution tank is provided with high-speed mixer, gauge
glass type indicator, overflow and drain piping.
Data:
Nos. : One
Material of construction : MSR / L
Diameter (mm) : 1600
Depth (mm) : 2600
Liquid to be handled : Cleaning solution
Agitator:
Nos. : One
Type : Top mounted three blade propeller type.
314 Energy
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Motor:
Nos. : One
kW / rpm : 1.50 / 925
Supply voltage : 3 Phase, 415 V Ac, 50 Hz
(2) Cleaning solution pump: Pump is provided to recirculate cleaning solution from the tank
to the micron cartridge filters to reverse osmosis elements and back to the tank. Pump is
complete with suction discharge valves and piping and pressure gauge.
Data:
Nos. : One + One standby
Type : Horizontal centrifugal
Capacity (cu.m/hr) : 55
Head (kg/sq.cm) : 3.0
Liquid to be handled : Cleaning solution
Motor:
Nos. : Two
kW / rpm : 15 / 1470
Supply voltage : 3 Phase, 415 V Ac, 50 Hz
(3) Micron cartridge filter: The micron cartridge filter is provided for removing the suspended
particles from the cleaning solution upstream of the Reverse Osmosis unit during cleaning Solution
application. The filter cartridge must be replaced when differential pressure across the cartridge
filters approaches 1 kg /sqcm or when the flow rate reduces, which ever occurs earlier.
Data:
Nos. : One + One Standby
Material of construction : MSR / L
Diameter (mm) : 400
Height on straight (mm) : 1150
Filtration size (micron) : 10
Nos. of element in each : 14
Operating Consideration for RO
Observe the following general operating points in day use of RO system.
1. Check the RO flow adjustment at least once in every shift and readjust if needed.
2. Check the chemical dosing and readjust if required.
3. SHMP dosing is very important to inhibit the formation of scale within the RO
membrane element so analyze the brine sample and adjust the dosing accordingly.
315Energy Management Creation of Sweet Water 315
4. For solving any operational problem during normal use maintain the log sheet
accurately.
5. Regular visual inspection, repairs of any leaks, cleaning and touch of painting should
be done for preventive maintenance.
6. Do not operate RO system at reduced capacity.
Change in Parameters After RO Process
After Reverse Osmosis process significant changes found in the following parameters.
1. Flash C ha m ber
2. C ond e nse r
3. Tre stle
4. S ea W ater S u m p
5. O u tp ut Fres h W ate r
Lo catio n : K av aratti
C ap acity : 1,00 ,0 00 liters/day
W arm Water Tem pe rature : 28 °C
C old Water Tem perature : 13 °C
C old Water Intake : 35 0m d epth
FLASH C HAMB ER
VA CUUM
WAT ER VA POU R PU MP
DE NISTE R
SH ELL & TUBE
CON DEN SER
COL D WAT ER
DISC HARG E FR ESH PU MP
WAR M W ATE R
PU MP WAT ER PU MP
PU MP
Though the concept was known for a long time, due to practical difficulties, it was never attempted.
This approach of providing water is extremely useful for islands like Kavaratti where there
is no other source of fresh water and the environment is extremely fragile.
This opens a new vista for setting up much larger barge mounted desalination plants to
address our ever-increasing need for potable water.
The Apparatus
The present model occupies an area of about 0.7 square meters. Major parts are of aluminum.
It has two frames. The upper frame fitted with a glass, rests above the lower base with the help
of hinges. Lower frame, made of aluminum sheet has thermocol insulation. Fine sand is spread
above the aluminum sheet. Row water enters the system through low-head distribution pipes
and soaks the sand layer to its field capacity. The upper glass frame, like a windowpane, fits
correctly on the lower base. Using a few ‘C’ clamps, it is made airtight.
Solar Distillation
Sunlight falling through the glass panel heats up the sand. Water slowly evaporates and the
vapour condenses on the inner side of the glass sheet.
The still is kept at an angle such that, the condensed vapour slowly flows out of the outlet
of the still. This is then transferred to a utensil through a pipe.
10 Litres a Day
After a thorough survey, it was found out that an average family could manage their drinking
and cooking needs with 10 liters of water per day. Five panels would be required to provide
318 Energy
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this much of water. The cost would be around Rs. 3000. According to Planet Kerala worksmen,
these stills can be made out of locally available materials by any person with some basic
fabrication aptitude. Once installed, there is no recurring or maintenance cost. Rewashing of
deposited salt and maintenance is very simple and easy. For the cloudy days in monsoon a
guiding angle made of alummium at the lower side of the glass panel is provided for catching rain.
It is time for the government and NGOs to adopt such system for pilot studies. A couple of
stills can be installed in houses where family members can take interest and observe the results
carefully. Subsequently, amendments improvements can be made in the panels after obtaining
the vital feedback.
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Allan J A (1999) Global systems ameliorate local droughts: Water, Food and Trade. Paper presented
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I NDEX
A Estuaries 239
Evaporation 41
Control 79, 85
(A.S.R.) Wells 212
Pans 45
Aquiclude 31
Evapotranspiration 22, 53, 55
Aquifers 21, 30, 212
Aquifuge 31
Aquitard 31 F
Artificial Rain 299
Artificial Recharg 111, 116, 144, 168, 170, 175, 185, 188 Factors Affecting
Evaporation 43
B Infiltration 64
Transpiration 54
Bored Wells 36 Farm Ponds 152
Floods 4
C Fresh–Saline Interface 226, 230
Fresh-Salt Interface 235
Desalination 317
H
Driven Wells 36
Droughts 4 Horizontal Wells 36
Dug Wells 35 Hydrological Cycle 15, 26
E I
R W