design of water conservation system through rain
DESCRIPTION
Water conservation through rain water harvestingTRANSCRIPT
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DESIGN OF WATER
CONSERVATION SYSTEM
THROUGH RAIN WATER
HARVESTING: AN EXCEL SHEET
APPROACH
Learnium School, Learnium School, Learnium School, Learnium School, New Delhi, INDIANew Delhi, INDIANew Delhi, INDIANew Delhi, INDIA
2007200720072007
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EditorEditorEditorEditor Nainshree Gupta Sukhmani Ashok
SupervisorSupervisorSupervisorSupervisor Mehmet Akif Erdogan
AdvisorAdvisorAdvisorAdvisor Er. Sirajuddin Ahmed
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ABSTRACT
Water is one of the most important constituents of our planet and most vital reason for
existence of life on the earth. Unfortunately it is being adversely affected both in terms
of quality and quantity by human activities.
Potable water, which is hardly 0.1% of all the water available on the planet, the scarcity
of water is increasing day by day and it is considered to be more threatening than
climate change.
India like semi arid countries is very soon likely to experience “Water Stress
Condition”. There are no more fresh water sources to exploit, therefore conservation of
water is only a practical solution to this mega problem.
Rain is primary source of fresh water but most of the rainwater goes back to ocean
without being properly used. The rapid urbanization has further aggravated the urban
runoff problem causing regular flooding in cities during rainfall season and depletion of
ground water table. The mushrooming of concrete jungles and network of road and
paved areas has literally sealed the top surface of land and blocked the natural path of
water infiltration to the aquifers in urban area.
Rainwater harvesting is an engineering solution to water problem of urban area
especially in semi arid region.
A very simple and user friendly excel program is developed to calculate the critical
rainfall intensity, annul rainwater harvesting potential and optimum volume of recharge,
cost of recharge structure, volume of water required to store for dry days, and cost of
storage. A help sheet is also developed to make this program easy to use without any
subject knowledge. Two case studies at micro and meso scale for design of rainwater
harvesting through recharge well were demonstrated using self-developed excel
program.
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CONTENTCONTENTCONTENTCONTENT
ABSTRACT 3
CONTENT 4
1 Introduction 6
1.1 Importance of potable water 6
1.2 Water scenario 7
1.3 Scarcity of water 7
1.4 Need for water conservation 9
1.5 Objectives of the project 11
2 Impact of urbanization 12 2.1 Infiltration of water 12
2.2 Water consumptions 13
2.3 Urban flood 13
2.3 Ground water table 13
3 Water harvesting 15 3.1 Concept of water harvesting 15
3.2 Different modes of water harvesting 17
4 Rain water harvesting 20
4.1 Advantages of Rainwater Harvesting in Indian Climate. 21
4.2 Different modes of Rainwater Harvesting 22
4.3 Rural Rainwater Harvesting 24
4.4 Urban Rainwater Harvesting 25
5 Basic Concept of Hydrology and Design of Rainwater Harvesting
System 26
5.1 Hydrological Parameters 26
5.2 Assessment of Critical Discharge 29
5.3 Assessment of Annual Potential of Rainwater Harvesting 30
5.4 Development of Excel based Design Calculator 30
6 Case Study 34 5.1 Learnium School (micro level) 34
5.2 Jamia Millia Islamia Central University (meso level) 36
7 Conclusion 37
8 Bibliography 39
List of Figures
1. Hydrological Cycle 6
2. Distribution of Water on Globe 7
3. Water Scarcity Region 8
4. Severe Drought 9
5. Aquifer System 14
6. Different Water Harvesting Practices in India 16
7. View of Baoli in Delhi 17
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8. Khadin Method of Water Harvesting 18
9. Zing Water Harvesting Structure 19
10. Different View of Rain Water Harvesting Using Storage Tank 22
11. Schematic Diagram of Rain Water Harvesting by Recharge Pit 22
12. Schematic Diagram of Recharge Trench 22
13. View of Recharge Trench in Packing Area 22
14. Section of Recharge Well 24
15. Schematic View of Urban Recharge System 24
16. Rainfall Intensity Duration Curves 25
List of Tables
1. Regional, Values of Imperical Constants 27
2. Coeffient of Runoff for Different Ground Cover 28
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1. INTRODUCTION
1.1 Importance of Potable Water
Water is one of the most abundantly
available substances in nature. It is an
essential constituent of all living organism,
animal, plants and a biotic part of earth.
Water, the most vital resource of life on
this planet is also being adversely affected
both in terms of quality and quantity by
human activities.
Water cannot be produced or added as and
when required by any technological means.
The total fresh and seawater content of the
earth is essentially fixed. Although man has
been able to modify to a certain extent the
pattern of availability of the fresh water with respect to time and space, but the total availability
of water has remained the same probably over millions of years. The circulation of fresh water
over the earth can be represented by a continuous process, under the influence of solar energy,
whereby water follows a cycle of evaporation from the earth’s surface (mainly from oceans),
condensation, precipitation, flow over the land surface and below it and returning back to the
oceans. In this hydrological cycle, the surface and ground water flow is the vital part as far as
human needs are concerned.
The world is running out of potable water. A major policy initiative to guarantee freshwater, as a
human need is required. According to Jeffery Sachs of the UN’s Millennium Project, the world
simply has “no more rivers to take water from”, and a major water shortage crisis that ravishes
millions may be more serious and alarming than climate change. Without a change in personal
lifestyles and a proper water policy from the governments, the achievement of global ecological
sustainability is not possible. In developing countries like India, not only the water supply but
also even the food production is threatened. Most industries of the economic booms have largely
been built upon the use of unsustainable water and other resources – “a deck of cards waiting to
fall”.
Rainwater is a free source of nearly pure water. It can be used to supply potable (drinkable)
water and non-potable water. For non-potable uses, like watering landscapes, it is ready for use
as it falls from the sky. For potable uses, rain-water must be treated to remove or kill disease
causing organisms present in it. For drinking purposes, rainwater must go through several steps:
screening, settling, filtering, and disinfecting. The screening prevents leaves and other debris
from entering the storage tank. The settling in the storage tank helps remove fine particles of dirt
and dust by allowing them to settle to the bottom of the tank. The filtering can remove sediment
and contaminants, and trap particulate matter depending on the type of filters used. Disinfecting
with chlorine, ozone, or ultraviolet light kills micro-organisms.
Fig 1 Hydrological Cycle
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1.2 Water Scenario
Almost 85 percent of the rainwater falls directly
into the sea and never reaches the land. The
small remainder that precipitates on the land fills
up the lakes and wells, and also keeps the river
flowing. For every 50,000 grams of ocean water
only one gram of fresh water is available to
mankind making it a scarce and precious
commodity.
Water covers about three quarters of the earth’s
surface. The total volume of water has been
estimated to be more than 1400 million Km3 ,
enough to cover the entire earth with a layer of
300 m depth. About 97.0% of this water is in
the oceans. Of this 3.0% that is fresh, 79% lies
frozen in the Polar Regions. Thus, all the
remaining water in the lakes and rivers, in under
ground reservoirs and in form of the moisture in
the atmosphere, soil and the vegetation, amounts to only about O.6% of the total. Of this 0.6%
(that is liquid fresh water), only 53 % is available in the form of river and lake water.
Surprisingly it is the salt water of the oceans that is the ultimate source of fresh water on this
earth.
About 113,000 cu. km. of fresh water is generated annually by the global hydrological cycle, out
of which 72,000 cu. km. is lost to evaporation, leaving only 41,000 cu. km available for use.
India has a total annual availability of renewable fresh water of 2.085 million m3, lower than
Brazil (6.949), Russia (9.465), Indonesia (2.530), the USA (2.478) and China (2.427). The
economical use of water must be promoted both in the developed and the developing societies.
Agriculture accounts for 80 percent of all water use in the developing societies.
India’s per capita water availability in 2004 was 2000 m3 compared with 110,000 for Canada,
9900 for US and 4400 for Japan. These countries have been able to harness large parts of their
water resources through proper management. Unfortunately, we have not been able to make
proper utilisation of our water resources, leading to tremendous water stress in many parts of
India. As of today, the country is experiencing chronic water shortages, and the affected area is
likely to increase significantly by 2025. We cannot afford to overlook the genuine need for
optimal utilisation of water resources. Proper management and utilisation of water resources
have become a major global issue with significant implications for population planning, welfare,
social stability and peace.
1.3 Scarcity of Water
The situation is critical in developing countries as the gap between the water demand and the
supply has been continuously widening. This has led to an increased emphasis on the optimal
management of the available resources. Rigorous planning and management of water resources
is required for long term sustainable resource development. The need for optimal management
of existing water resource systems as well as the optimal development of the new ones is now
universally acknowledged. Water resource systems are an important part of the infra-structure of
Fig 2: Distribution of Water on Globe
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every country, particularly the developing ones. In addition to the basic purpose of supporting
life, they serve a multitude of water uses such as the water supply, hydropower generation,
recreation, irrigation, flood control, navigation and wild life maintenance. India is likely to
experience “WATER STRESSES” from this year i.e. 2007 onwards. It will be pertinent to shift
the thrust of the policies from “water development to sustain water development”. Half a
century back, the high level of sub soil water was a major problem of Delhi – the Government
had an exclusive division to install large number of tube-wells to compound the water to
Yamuna to lower the ground water level. Today the problem is exactly the opposite. The water
table has gone down to such as extent that we are desperately trying to recharge the aquifers.
Human interference with the environment has made rains more irregular, since the natural cycle,
is disturbed. The quantity of rainfall is becoming erratic, reduced and uncertain. Hence, a need
for conservation is felt much more than ever before. The rise of urban development, amenities,
and luxury is driving to high per-capita consumption of water. It is therefore necessary to
conserve and augment the renewable natural ground water resources as a last chance for
survival, realizing that natural resources are not unlimited if they are exploited beyond certain
limits.
A vital element of this shift in strategy is the increasing importance of water harvesting and
artificial recharge of ground water. With industrialisation, urbanisation and rising living
standards, non-agriculture uses of water are increasing exponentially. The rapid developments
of cities and
population explosion in urban areas have, led to the depletion of available surface water
resources. Now, the available water resources are at far then distance, from the cities, forcing
the municipal corporation to spend higher capital expenditure and longer time for planning and
execution for the conveyance of water. This has also resulted into over exploitation of surface
sources like wells for drinking and industrial use, resulting in the dropping of water levels and
drying up of bore wells or sea-water intrusion because of the imbalance of inflow and outflow
Fig 3: Water Scarcity Region
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equation for sub-surface water. The key aquifers in India are being over-pumped, and the soil is
growing saltier through contamination with irrigation water.
It is a well known fact that whenever the environment is degraded in the form of pollution or
drying up of water sources, it is the poor who suffer the most. Even though they have much less
water demand than the rich, they suffer most because they live on the undeveloped lands. The
government has constraints of funds to employ high technological solutions; the private sector
may not be interested since it is not be a profitable venture. For these poor people, water scarcity
means death or utter misery.
1.4 Need of Water Conservation
Do we need to conserve water? Water
conservation means controlling, protecting,
managing and planning for the wise use of our
water resources. Economically, conversation is
very important, since the water is getting more
expensive. It’s costing us more to supply, to
treat, to dispose off and to treat again. The
energy required to meet these demands is
enormous, carrying with it an environmental
price tag. Just because the water is available
does not mean that we have to use it with such reckless abandon. Studies have shown
that our household water use could be reduced by 50% without significantly changing
our lifestyle.
Fig 4: Severe Drought
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According to the estimates, a leaking faucet dripping one drop per second can amount to 25
litres per day and to more than 10,000 litres per year. That is enough water to wash more than
65 loads of clothing; have 140 five-minute showers, or enough to wash 40 cars. Over the years,
rising populations, growing industrialization, and expanding agriculture have pushed up the
demand for water. Efforts have been made to collect water by building
dams and reservoirs and digging wells; some countries have also tried to
recycle and desalinate (remove salts) water.
Our religious texts and epics give a good insight into the water storage
and conservation systems that prevailed in early days. In the forests,
water seeps gently into the ground as vegetation breaks the fall. This
groundwater, in turn, feeds wells, lakes, and rivers. Protecting forests
means protecting water ‘catchments’. In ancient India, people believed
that forests were the ‘mothers’ of rivers and worshipped the sources of
these water bodies.
One of the oldest water harvesting systems in India is found about 130
km from Pune, along Naneghat in the Western Ghats. A large number
of tanks were cut in the rocks to provide drinking water to tradesmen
who used to travel along this ancient trade route. Each fort in the area
had its own water harvesting and storage system in the form of rock-
cut cisterns, ponds, tanks and wells that are still in use today. A large
number of forts like Raigad had tanks that supplied water. In the
ancient times, houses in parts of western Rajasthan were built so that
each had a rooftop water harvesting system. Rainwater from these
rooftops was directed into underground tanks. This system can be seen
even today in all the forts, palaces and houses of the region.
Underground baked earthen pipes and tunnels to maintain the flow of
water and to transport it to distant places, are still functional at
Burhanpur in Madhya Pradesh, Golkonda and Bijapur in Karnataka, and Aurangabad in
Maharashtra.
The most important step in the direction of finding solutions to issues of water and
environmental conservation is to change people’s attitudes and habits.
There are numerous methods to reduce such losses and to improve soil moisture. Some of them
are listed below.
1. Mulching, i.e., the application of organic or inorganic material such as plant debris,
compost, etc., slows down the surface run-off, improves the soil moisture, reduces
evaporation losses and improves soil fertility.
2. Soil covered by crops, slows down run-off and minimizes evaporation losses. Hence, fields
should not be left bare for long periods of time.
3. Ploughing helps to move the soil around. As a consequence, it retains more water thereby
reducing evaporation.
4. Shelter belts of trees and bushes along the edge of agricultural fields slow down the wind
speed and reduce evaporation and erosion.
5. Planting of trees, grass, and bushes breaks the force of rain and
helps rainwater penetrate the soil.
6. Fog and dew contain substantial amounts of water that can be
used directly by adapted plant species. Artificial surfaces such
as netting-surfaced traps or polyethylene sheets can be exposed
to fog and dew. The resulting water can be used for crops.
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7. Contour farming is adopted in hilly areas and in lowland areas for paddy fields. Farmers
recognise the efficiency of contour-based systems for conserving soil and water.
8. Salt-resistant varieties of crops have also been developed recently. Since these grow in
saline areas, the overall agricultural productivity is increased without making additional
demands on freshwater sources. Thus, it is a good water conservation strategy.
9. Transfer of water from surplus areas to deficit areas by inter-linking water systems through
canals, etc.
10. Use of efficient watering systems such as drip irrigation and sprinklers will reduce the water
consumption by plants.
1.5 Objectives of the Project
The main objective of this project is to study the scenario of potable water on regional
and global basis and develop an excel sheet for design of rain water recharge well using
simple and minimum input. Specific objective are as follows:
1. To study the water scenario on regional and global basis
2. To study different means of water conservation
3. To asses the impact of urbanisation of water resources
4. To study the different modes of rain water harvesting and its historical perspective.
5. To understand the basic concepts of hydrology for optimum design of rain water
harvesting.
6. To develop user friendly excel sheet for design of rain water recharge well
7. To implement this design by carrying out case study on micro and meso scale.
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2. IMPACT OF URBANIZATION ON GROUND WATER
Multiple hydrological problems are growing due to the rapid urbanisation. During the last fifty
years the entire demography has changed as majority of population from villages has shifted to
urban area all over the world The United Nations estimates indicate that in the mid 1990s, about
43 per cent of the world population lived in urban areas. With the urban population growing two
and a half times faster than its rural counterpart, the level of urbanisation is estimated to already
cross the 50 per cent mark in 2005. United Nations projections further show that by 2025, more
than three- fifth of the world population will live in urban areas (U. N. 1993). India’s urban
population is also growing with international trend. The percentage of urban population has
grown from 17% in 1951 to 28.65 % in 2000.
The growth of the cities has affected urban hydrology and utility services by following different
ways
Hindrance in natural infiltration of Rain-water
Excessive pumping out of ground water to meet the water requirement of inhabitants
Due to this increased groundwater pumping in the metropolitan cities is that most of the pumped
water ends up in the sanitary sewer system. The flow rates of wastewater being treated by the
municipal authorities have increased lockstep with this urban development.
A major problem from the greater urban impervious area is the increase in storm water runoff to
the near-by river and drains, causing frequent occurrence of urban flood (Mumbai –2005)
The combined effect of this altered hydrology at macro scale will lead to more frequent and
severe flooding in the city rivers, during the wet periods. During the drought periods, water
levels are often too low for recreation, Lower water tables in the shallow aquifer have led to a
decline in the flow of local springs that maintain dry weather base flow in streams.
2.1 Infiltration of Water
The rapid urbanization has also introduced reduction in the original permeable ground surface
due to the construction of pavements, roads, and buildings. Storm water drains are laid to drain
the rain water as quickly as possible to nearby natural stream, river or sea to avoid flooding of
grounds and disruption in traffic. These surfaces and quick disposals give no time for rain water
to percolate into the natural ground to replenish the water in sub-surface aquifer, causing the
dropping of water levels or drying up of wells. These problems include lowered groundwater
levels both in shallow as well as deep aquifers due to the combination of less rainfall infiltration
into the ground, and greater groundwater pumping by municipalities. According to an estimate,
the runoff increase by urbanisation is almost equal to the rate of urbanisation.
Infiltration capacity depends on many factors such as soil type, moisture content, organic matter,
vegetative cover, season, air entrapment, formation of surface seals or crusts etc. Porosity
determines storage capacity and also effective resistance to flow. Thus infiltration tends to
increase with porosity. Vegetation cover increases infiltration as compared to the barren soil by
retarding surface flow giving the water additional time to enter the soil. The root system makes
the soil more pervious and the foliage shields the soil from raindrop impact and reduces rain
packing of surface soil. Infiltration of water through surface takes place generally over small
periods of time, while the process of redistribution of the soil water goes on for most of the time
and therefore predominates.
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2.2 Water Consumptions
Water consumption is directly proportional to the financial status of the society. Higher income
group consumes more water as compare to low income residents. The use of dish-washers,
washing machines and bathing showers etc encourage higher water consumption. The value of
water consumption per capita increases from 135 to 270 depending on the financial status of the
people. Since the people living in the metropolitan area, have higher income, so is then water
consumption rate.
Urbanisation, especially in the developing countries has directly increased pressure on urban
water recourses. Municipal authorities are neither equipped nor efficient to quench the ever
increasing thrust of the rapid urbanisation. Most of the time, due to an insufficient or non-
availability of potable water by municipal supply, the inhabitant, have to bore their own private
tube wells to pump out water to meet their requirements. Some municipal authorities are putting
further strain on ground water by exploiting it to meet the industrial, commercial and other
municipal requirements.
2.3 Urban Flood
Recently the urban flood has become a major devastating problem in the metropolitan cities of
India. The ever growing impermeable area of mega cities in the form of roofs, road, parking
area, hard landscape and paved areas convert almost all quantity of rainfall into runoff. Improper
design of drainage system and common use of non-biodegradable packaging materials,
polythene bags and discarded solid waste on roads and pavements further decrease the carrying
capacity of the drainage system.
Excessive runoff finds it very difficult to quickly pass through the existing drainage system and
hence water gets impounded for several hours, sometimes upto days. The volume of excessive
runoff is so high that the shallow parts of the city get flooded causing severe problem for traffic
and other amenities.
2.4 Ground Water Table
Groundwater is the water located beneath the ground surface in soil pore spaces and in the
fractures of geologic formations. A formation of rock or soil is called an aquifer when it can
yield a usable quantity of water. The depth at which soil pore spaces become fully saturated
with water is called the water table. Groundwater is recharged from the surface. Some times it
flows to rivers supplementing its water The natural discharge of ground water often occurs at
springs, or it can form oasis or wetlands. Groundwater is also often withdrawn for agricultural,
municipal and industrial use by constructing and operating extraction wells.
Groundwater is naturally replenished by the surface water from precipitation, streams, and rivers
when this recharge reaches the water table. It is estimated that the volume of groundwater is
fifty times that of surface freshwater; the icecaps and glaciers are the only larger sources of fresh
water on earth.
Groundwater makes up about twenty percent of the world’s fresh water supply, which is about
0.61 percent of the entire world’s water supply.
A comparison of water levels from 1960 to 2001 shows that the water levels in major parts of
Delhi are steadily declining because of over-exploitation. During 1960, the ground water level
was by and large within 4 to 5 meters, and in some parts even water logged conditions existed.
During 1960-2001, the water levels have declined by 2- 6 m. in most part of the alluvial areas.
The decline of 8-20 m. has been recorded in south-west district and in south district it has been
8-30 m. If this trend continues it is predicted that water scarcity will become a major problem in
the near future.
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Fig 5: Aquifer System
The combined effect of this altered hydrology has led to more frequent and severe
flooding in the metropolitan area and nearby surface water resources such as river and
lakes during rainy seasons. The water level goes too low during Dry periods thus
significantly affecting the buffering capacity of the aquifer. An aquifer is a subterranean
geologic unit (or layer) of permeable material (like sand and gravel) that is capable of
providing usable quantities of water to a well. Aquifers can be confined or unconfined.
A confined aquifer has a low permeability confining layer (an aquitard), such as clay,
above it that restricts the upward and downward movement of the water. If a confined aquifer follows a downward grade from its recharge zone, groundwater can become pressurized
as it flows. This can create artesian wells that flow freely without the need of a pump. The top of
the upper unconfined aquifer is called the Water table, where water pressure is equal to
atmospheric pressure.
Lower water tables in the shallow aquifer have led to a decline in the base flow to local rivers in
dry weather which is a direct source of clean water to the cities at its bank.
One of the biggest challenging aspects of urbanization is to mitigate the impact of impervious
surfaces that cause groundwater reduction in infiltration rates and increase in surface runoff
volumes to surface waters. Low-impact of this modified urban hydrology can be made by :
� Preserving natural areas with highly permeable soils
� Minimising soil compaction during development.
� Restoring permeability of disturbed soils.
� Using permeable hard capes.
� Routing runoff from impervious surfaces to infiltration practices.
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3.0 WATER HARVESTING
3.1 Concept of Rain Water Harvesting
Water harvesting in its broadest sense can be defined as the “collection of runoff for its
productive use”. Runoff may be harvested from roofs and ground surfaces as well as from
intermittent or ephemeral watercourses such as fog, dew and snow.
Water harvesting techniques which harvest the runoff from roofs or ground surfaces fall under
the term: Rainwater Harvesting , whereas all systems which collect discharges from the water
courses are grouped under the term: Floodwater Harvesting
To facilitate the presentation of the various types of water harvesting techniques, the following
four groups of water harvesting can be distinguished. A brief description of these water
harvesting techniques along with sub-types is given below:
1. Rainwater harvesting: It is defined as a method for inducing, collecting, storing and
conserving local surface runoff for agriculture in arid and semi-arid regions (Boers & Ben-
Asher 1982). Three types of water harvesting are covered by rainwater harvesting.
a) Water collected from roof tops, courtyards and similar compacted or treated surfaces is used
for domestic purpose or garden crops.
b) Micro-catchments water harvesting is a method of collecting surface runoff from a small
catchments area and storing it in the root zone of an adjacent infiltration basin. The basin is
planted with a tree, a bush or with annual crops.
c) Macro-catchments water harvesting, also called harvesting from external catchment, is the
case where runoff from hill-slope catchments is conveyed to the cropping area located at hill
foot on flat terrain.
2. Flood water harvesting: It can be defined as the collection and storage of creek flow for
irrigation use. Flood water harvesting, also known as ‘large catchments water harvesting’ or
‘Spate Irrigation’, may be classified into following two forms:
a) In case of ‘floodwater harvesting within stream bed’, the water flow is dammed and thus,
inundates the valley bottom of the flood plain. The water is forced to infiltrate and the
wetted area can be used for agriculture or pasture improvement.
b) In case of ‘floodwater diversion’, the wade water is forced to leave its natural course and
conveyed to nearby cropping fields. It is practiced in Africa and Middle East Asian regions
3. Groundwater Recharge: It is a rather new term and employed to cover traditional as well as
unconventional ways of ground water extraction. Qanats systems, underground dams and
special types of wells are few examples of the groundwater harvesting techniques.
Groundwater dams like ‘Subsurface Dams’ and ‘Sand Storage Dams’ are other fine
examples of groundwater harvesting. They obstruct the flow of ephemeral streams in a
river-bed; the water is stored in the sediment below ground surface and can be used for
aquifer recharge. Sand filled reservoirs have the following advantages:
(1) Evaporation losses are reduced,
(2) No reduction in storage volume due to saturation
(3) Stored water is less susceptible to pollution, and
(4) Health hazards due to mosquito breeding are avoided.
4. Fog and dew harvesting: They are forms of precipitation. Due to fine size of fog droplets
and their low velocity of descent (ranging from 1 cm/s to approximately 5 cm/s), moisture is
carried readily by breezes of even low velocity. Hence, fog harvesting requires a nearly
vertical surface as catchments area for its collection. In contrast, dew harvesting requires an
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horizontal surface. A gravel layer is commonly used in agricultural areas as a means of
maintaining soil moisture by dew harvesting, while minimizing evaporative losses and
increasing soil temperature. In the evening, the
gravel layer cools and remains so in the early
morning, when water vapour condenses onto the
gravel creating droplets, which pass between the
gravel particles and reach the soil surface,
moistening the soil. Fog and dew harvesting is
practised in Gansu Province, in northwest China,
where melons are cultivated with water supplied
using dew harvesting techniques. These farms are
well known as the ‘gravel fields for melons’ in China (UNEP, 1982).
Snow, being another form of precipitation, can also be harvested to provide an alternative
supply of freshwater. Applications of the traditional snow harvesting technology to augment
drinking water supplies can be found in Takhar Province, Afghanistan.
3.2 Water Harvesting Practices in India
Water has been harvested in India since antiquity, with our ancestors perfecting the art
of water management. Many water harvesting structures and conveyance systems
specific to the eco-regions and culture has been developed. They harvested the raindrop
directly from roof tops, and collected water and stored it in tanks built in their
Qanats, widely used in Iran, Pakistan,
and North Africa and even in Spain,
consists of a horizontal tunnel that taps
underground water in an alluvial fan,
brings it to the surface due to
gravitational effect. Qanat tunnels have
an inclination of 1-2% and a length of up
to 30 km Many are still maintained and
deliver steadily water to fields for
agriculture production and villages for
Fig 6: Different Water Harvesting practices in India
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courtyards. From open community lands, they collected the rain and stored it in artificial
wells. Monsoon runoff was also harvested by capturing water from swollen streams
during the monsoon season and stored it various forms of water bodies. Harvesting from
flooded rivers was also practiced in ancient India.
A few of traditions of water harvesting are described below.
Dighis – Emperor Shahjahan (1627-58 AD) first shifted the city from the Aravalli hills towards
the plains of the Yamuna. But he made sufficient arrangements to meet the water needs of the
new palace, the army, and the common people. His system of Shahjahani canals and dighis was
probably the best creation of the time.
In the main city, the canal charged dighis and wells. A dighi was a square or circular reservoir of
about 0.38 m by 0.38 m with steps to enter. Each dighi had its own sluice gates. People were not
allowed to bathe or wash clothes on the steps of the dighi. However, one was free to take water
for personal use. People generally hired a kahar or a mashki to draw water from the dighis. Most
of the houses either had their own wells or smaller dighis on their premises. In the event of canal
waters not reaching the town and the dighis consequently running dry, wells were the main
source of water. Some of the major wells were Indara kuan near the present Jubilee cinema,
Pahar-wala-kuan near Gali-pahar-wali, and Chah Rahat near Chhipiwara (feeding water to the
Jama Masjid).
Baolis
Traditional step wells are called vav or vavadi in Gujarat, or baolis or bavadis in
northern India. The construction of step wells date from four periods: Pre-Solanki
period (8th to 11th century CE); Solanki period (11th to 12th century CE); Vaghela period
(mid-13th to end-14th century CE); and the Sultanate period (mid-13th to end-15th century
CE). A major reason for the breakdown of this traditional system is the pressure of
centralisation and agricultural intensification.
Fig 7: View of Baoli in Delhi
18
The sultans of Delhi patronized concept of baolies, constructed and maintained many large
baolis (step wells). Gandak-ki-baoli (so named as its water has gandak the Indian name of
sulphur) was built during the reign of Sultan Iltutmish. The water of this beautiful rock-hewn
baoli is still used for washing and bathing. Adjacent to this, there are the ruins of other baolis
like Rajon-ki-baoli, a baoli in the Dargah of Kaki Saheb, and a caved baoli behind Mahavir
Sthal. During this period baolis were built in other parts of the city too.
Tankas
Tankas (small tank) are underground tanks, found traditionally in most Bikaner houses. They
are built in the main house or in the courtyard. They were circular holes made in the ground,
lined with fine polished lime, in which rainwater was collected. Tankas were often beautifully
decorated with tiles, which helped to keep the water cool. The water was used only for drinking.
If ever there was less than normal rainfall and the tankas did not get filled, the water from
nearby wells and tanks was obtained to fill the household tankas. In this way, the people of
Bikaner were able to meet their water requirements. The tanka system is also found in the
pilgrim town of Dwarka where it has been in existence for centuries. It continues to be used in
residential areas, temples, dharamshalas and hotels.
Khadin
Khadin, also called a dhora, is an ingenious construction designed to harvest surface runoff
water for agriculture. Its main feature is a very long (100-300 m) earthen embankment built
across the lower hill slopes lying below gravely uplands. Sluices and spillways allow excess
water to drain off. The khadin system is based on the principle of harvesting rainwater on
farmland and subsequent use of this water-saturated land for crop production.
First designed by the Paliwal Brahmins of Jaisalmer, in western Rajasthan, in the 15th century,
this system has great similarity with the irrigation methods of the people of Ur (present Iraq)
around 4500 BC, and later of the Nabateans in the Middle East. A similar system is also
reported to have been practised 4,000 years ago in the Negev desert, and in southwestern
Colorado 500 years ago.
Fig 8: Khadin Method of water harvesting
19
Bengal’s Inundation Channel
Bengal once had an extraordinary system of inundation canals. Sir William Will Cocks, a
British irrigation expert who had also worked in Egypt and Iraq, claimed that inundation canals
were in vogue in the region till about two centuries ago. Floodwater entered the fields through
the inundation canals, carrying not only rich silt but also fish, which swam through these canals
into the lakes and tanks to feed on the larva of mosquitoes. This helped to check malaria in this
region. According to Will cocks, the ancient system of overflow irrigation had lasted for
thousands of years. Unfortunately, during the Afghan-Maratha war in the 18th century and the
subsequent British conquest of India, this irrigation system was neglected, and was never
revived. The major features of the irrigation system were broad and shallow canals, carrying the
crest waters of the river floods, rich in fine clay and free from coarse sand and irrigation was
performed by cuts in the banks of the canals, which were closed when the flood was over.
Zings
Zings are water harvesting structures
found in Ladakh. They are small tanks, in
which collects melted glacier water.
Essential to the system is the network of
guiding channels that brings the water
from the glacier to the tank. As glaciers
melt during the day, the channels fill up
with a trickle that in the afternoon turns
into flowing water. The water collects
towards the evening, and is used the next
day. A water official called the churpun
ensures that water is equitably distributed
Fig 9: Zing Water Harvesting Structure
20
4.0 RAIN WATER HARVESTING
Rainwater, which is easily available and is the purest form of water, would be an immediate
source to augment the existing water supply by “catching water wherever it falls”. Rainwater
Harvesting has emerged as a viable alternative to traditional perennial sources of water in the
hilly areas, in places where the level of fluoride and arsenic is above permissible limits and in
urban areas facing water shortage and flooding during monsoons.
Rainwater Harvesting (RWH) is the process of collecting and storing rainwater in a scientific
and controlled manner for future use. Rainwater harvesting in urban areas include
Roof top rainwater harvesting
Rainwater harvesting in paved and un-paved areas (open fields, parks, pavement landscapes
etc.)
Rainwater Harvesting in large areas with open ponds, lakes, tanks etc.
4.1 Advantages of Rain Water Harvesting in Indian Climate
Rain is the first form of water that we know in the hydrological cycle, hence is a primary source
of water. Rivers, lakes and groundwater are all secondary sources of water. In present times, we
depend entirely on such secondary sources of water. In the process, we forgot that rain is the
ultimate source that feeds all these secondary sources, and remain ignorant of its value. Water
harvesting also signifies the value of rain, and to make optimum use of the rainwater at the place
where it falls.
Rainwater is one of the purest sources of available water. Its quality always exceeds that of
ground or surface water. It does not come into contact with soil or rocks where it can dissolve
minerals and salts. Nor does it come into contact with many of the pollutants that are often
discharged into local surface waters or contaminate ground water supplies. However, rainwater
quality is influenced by where it falls. Rainfall in areas where heavy industry or crop dusting is
prevalent, may not have the same purity as rain falling in other areas.
Rainwater is soft. It can significantly lower the quantity of detergents and soaps needed for
cleaning. Soap scum and hardness deposits do not occur. There is no need for a water softener
as there often is with ground water. Water heaters and pipes are free of the deposits caused by
hard water and should last longer. The first rainfall of the season should be bypassed or avoided
for harvesting because most of the pollutant gasses present in the atmosphere get dissolved in
the raining water.
Rainwater harvesting promotes self-sufficiency and fosters an appreciation for water as a
resource. It not only promotes water conservation but also conserves energy. Local erosion and
flooding from impervious cover associated with buildings is lessened as a portion of local
rainfall is diverted into collection tanks.
Rainwater harvesting provides fresh water to local horticultural use. Even the simplest methods
provide benefits. The water customer benefits from lower bills and the community achieves
long-term benefits which reduce groundwater use and promote soil conservation. With the
increased environmental concern and sustainability, the implementation of a rain water system
on campus of school and university will not only reduce its ecological footprint, but also set the
stage for future sustainable developments
Once Cherrapunji was famous for the largest volume of rainfall in the world. Today ironically, it
experiences acute water shortages. This is mainly the result of extensive deforestation and lack
of proper methods of conserving rainwater. There has been extensive soil erosion and often,
despite the heavy rainfall and its location in the green hills of Meghalaya, one can see stretches
of hillside devoid of trees and greenery. People have to walk long distances to collect water.
21
Area surrounding the River Ruparel in Rajasthan, the story is different – this is one of the best
examples of proper water conservation. The water level in the river began declining due to
extensive deforestation and agricultural activities along the banks and, by the 1980s, a drought-
like situation began to spread. Under the guidance of some NGOs (non-government
organizations), the women living in the area were encouraged to take the initiative in building
johads (round
ponds) and dams to hold back rainwater. Gradually, water began coming back as proper
methods of conserving and harvesting rainwater were followed. The revival of the river has
transformed the ecology of the place and the lives of the people living along its banks. Although
this site does get even half the rainfall received by Cherrapunji, but proper management and
conservation have made the area receive water more than in Cherrapunji.
Advantages of rainwater harvesting can be summarized as below:
• Provide drinking water
• Increase groundwater recharge
• Reduce storm water discharges, urban floods and overloading of sewage treatment plants
• Reduce seawater ingress in coastal areas.
• Save energy in pumping of water by raising the water table.
4.2 Different modes of Rain Water Harvesting
The storage of rain water on surface is a traditional technique and the structures used were
underground tanks, ponds, check dams, weirs etc. Recharge to ground water is a new concept of
rain water harvesting. The techniques of rain water harvestings can be classified as
I. Storage of rainwater on surface for future use.
II. Recharge to ground water.
Storage tanks: – Rain water can be stored in tanks for harvesting the roof top rain water.
These tanks may be constructed on the surface as well as under ground by utilising local
material. The size of the tank depends upon the availability of runoff and water demand. After
proper chlorination, the stored water may be used for drinking purpose.
22
Recharge Pits: – Rain water can also be
infiltrated into the ground water. Recharge pits are
constructed for recharging the shallow aquifers.
These are constructed 1 to 2 m. wide and 2 to 3 m.
deep which are back filled with boulders, gravels
& coarse sand. The size of filter material is
generally taken as below:
Coarse sand : 1.5 – 2 mm
Gravels : 5 – 10 mm
Boulders : 5 – 20 cm
The filter material should be filled in graded form.
Boulders at the bottom, gravels in between &
coarse sand at the top so that the silt content that
will come with runoff will be deposited on the top
of the coarse sand layer and can easily be removed. If clay layer is encountered at shallow
depth, it should be punctured with an auger hole. The auger hole should be refilled with fine
gravel of 3 to 6 mm size.
Trenches: –These are constructed when the permeable strata
is available at shallow depth. The trench may be 0.5 to 1 m.
wide, 1 to 1.5m. deep and 10 to 20 m. long, depending on the
availability of water. These are back filled with filter
materials.
Existing abandoned dug
wells may be utilised as
recharge structure after
cleaning and desalting the
same. Similarly, existing
hand pumps may also be
used for recharging the
shallow / deep aquifers, if the availability of water is limited.
Abandoned tube wells should be redeveloped before use as
Fig 12: View of Recharge
Trench in parking area
Fig 13: Schematic diagram
of recharge trench
Fig 10: Different View of Rainwater Harvesting using storage tank
Fig 11: Schematic diagram rain water
Harvesting by Recharge pit
23
recharge structure. For removing the silt contents, the runoff water should pass either through a
desalting chamber or filter chamber.
Recharge Wells/Shafts:- For recharging the shallow aquifers which are located below clayey
surface at a depth of about 10 to 15 m, recharge shafts of 0.5 to 3 m. diameter and 10 to 15 m.
deep are constructed depending upon the availability of runoff. These
are back filled with boulders, gravels and coarse sand. For lesser diameter shafts, the reverse
/ direct rotary rigs are used and larger diameter shafts may be dug manually. In upper portion of
1 or 2 m depth, the brick masonry work is carried out for the stability of the structure.
Lateral shafts with bore wells:-: For recharging the upper as well as deeper aquifers,
lateral shafts of 1.5 to 2 m. wide & 10 to 30 m. long (depending upon availability of
water with one or two bore wells) are constructed. The lateral shafts are back filled
with boulders, gravels & coarse sand.
Pressure Injection System:- In this recharge technology, rainwater is first properly filtered
and stored in an underground storage tank. To reduce the volume of storage tank, water is
pumped directly into the aquifer by means of a well developed tube well. The pumping pressure
can be regulated by using water level sensors in the storage tank. This system is usually
practiced in large hotels and apartment with less open space. The recurring cost of water
pumping makes it less economically viable.
4.3 Rural rainwater harvesting:
Storage of rainwater on the surface for future use should be the main objective of the rainwater
harvesting in rural area India, since plenty of land is available. The average population of an
Indian village is approximately 1200 (year 2000) and India’s average rainfall is about 1170 mm.
Even if only half of this water is planned to be captured, an average Indian village needs 2.7
hectares of land to harvest 15.8 million litres of water. The annual water consumption for
average Indian village for cooking and drinking is estimated to be 15.3 million litres. If there is
a drought, and the rainfall levels dip to half the normal, the land required would rise to a mere
5.4 hectares.
The area of land needed to meet the drinking and cooking water requirement of an average
village will vary depending on the population of the village and metrological characteristic of
the region.
24
Fig 14: Section of Recharge Well
4.4 Urban rainwater harvesting:
Recharge of ground water (aquifer) should be the goal of rain water harvesting in the
urban area. Recharge well, trenches, pit and pressure injection system. Water harvesting
can be done from micro scale i.e. single dwelling unit to meso scale i.e. sector level. The
surface area required for rainwater harvesting structure is hardly 1-2% of total land and
cost incurred is not more than 1% of the total construction cost of building. It is neither
the availability of the land nor the cost but the will which is a major constraint for
rainwater harvesting in urban area.
Fig 15 Schematic View of Urban recharge Well
25
5.0 BASICS CONCEPTS OF HYDROLOGY AND DESIGN OF
RAINWATER HARVESTING SYSTEM
For proper design of drainage and recharge pit, it is very important to estimate the most
probable rainwater discharge that is likely to enter the system. Rainwater harvesting is basically
designed for storm runoff, therefore the assessment of peak rate of flow, i.e. discharge, is very
important.
The peak rate of run-off that is produced from particular catchments depends on numerous
factors such as return period, intensity and duration of rainfall, permeability of catchments
surface area, shape and size of catchments area, length of drainage system, and climatic
conditions. The precise assessment of peak runoff is not possible because of the involvement of
so many variables. Therefore, the runoff cannot be exactly determined by a mathematical
equation. Many empirical formulas are commonly used for prediction of duration of rainfall,
corresponding intensity and runoff.
It can be simply observed that higher is the duration less would be the intensity of the rainfall.
The duration of drizzling is always longer as compare to downpour. Higher the return period,
i e. recurrence interval more would be the intensity of rainfall of same duration.
5.1 Hydrological Parameters
Return period
In rainwater harvesting design, the probability of occurrence of a particular rainfall (intensity) is
very important. This information can be obtained by frequency analysis of the point rainfall
data. The annual average probability of occurrence of a rainfall whose magnitude is equal to or
in excess of, a specified magnitude (intensity), is known as “Recurrence Interval” and donated
as “P”. Engineers often use the reciprocal of annual average probability “Return period”
designated as “T”
PT
1= ............. (1)
Where
T = Return period
P = recurrence Interval
Return period represents the average interval
between the occurrence of rainfall magnitude of
equal to or greater than specified magnitude.
The unit of return period is a year If return
period of particular rainfall x intensity is 5 year
at particular point then it implies that on an
average the rainfall intensity of equal to x or
greater than x would occur once in five years
and its probability to occur in a year is (1/5) i.e.
0.2. As the return period increases, the intensity
of rainfall of particular duration will increase.
Usually high value of return period, say five
years, is considered for a sensitive area,
hospitals, important offices, high value
residential area. For low value residential
area this value can be taken as one year. Fig 16: Rainfall intensity and duration curves
26
Rainfall Intensity
Intensity can be defined as the rate of rainfall per unit time. It gives an analytical idea of
how fast and slow rain is falling. Drizzling is a low intensity rainfall and downpour is
very high intensity rainfall. Unit of rainfall intensity is cm/hour. The intensity of rainfall
changes continuously throughout the storm (rainfall) period. The rainfall intensity is
average value over the period of time. If it rains 40 mm in a particular one hour giving
an average rainfall rate as 40 mm/hour However during that particular hour at some time
the rainfall intensity will exceed 40 mm/hour while at other time it will be much less
than 40 mm/hour. This value is directly used in the design of drainage system and
recharge storage pit.
The Duration of Rainfall
The period for which a particular rain falls, is known as its duration. There is an inverse
relationship between rainfall intensity and duration. As the duration of a storm increases
its intensity will decrease.
Time of Concentration
It is a fundamental hydrology parameter and used to compute the peak discharge for catchments.
The peak discharge is a function of the rainfall intensity of particular return period and duration.
Time of concentration is the longest time required for the a water to travel in catchments and
reach to outlet point (in our case, roof top and length of drain to recharge pit). The mathematical
equation used for calculation of time of concentration requires inputs for the longest
watercourse length in the watershed (catchments area (L), the average slope of that watercourse
(S). The average value of slope will be different for different surfaces e.g. Roof, road, lawn,
drain etc. Usually L and S can be obtained from architectural drawing of the building and if
drawings are not available then by assessment.
The Tc is generally defined as the time required for a drop of water to travel from the most
hydro- logically remote point in the sub-catchments to the point of collection
A time of concentration value is essential to determine critical intensity of rainfall because
maximum discharge will occur for rainfall intensity of duration equal to the time of
concentration. Time of concentration can be calculated by using following formula
385.077.00195.0 −= SLTC ............. (2)
where:
Tc = Time of concentration in minutes
L = overland flow length in m
S = average slope of the overland area.
This equation has been adopted from Kirpich 1940 (Soil and water conservation Engineering by
Glenn O. Schwab John Wiley). If the slope of overland flow surface is different for different
portion of overland flow then we can use the following formula
385.077.0
1
0195.0−
=
∑= ii
n
i
C SLT ............. (3)
where:
Tc = Time of concentration in minutes
27
Li = overland flow length of ith stretch in m
Si = average slope of the ith stretch of overland flow.
n = no. of different stretches
Prediction of Rainfall Intensity
As discussed above, that peak discharge for rainwater harvesting would the resulted by rainfall
of the duration equal to concentration time of specified return period. Since the rainfall intensity
is directly proportional to the return period and inversely proportional to rainfall duration, apart
from many metrological parameters
= M
TTFunctioni
c
,1
,. ............. (4)
where:
i = rainfall intensity in cm/hour
Tc = the time of concentration in minutes
T = return period
M = Metrological parameters
It is almost impossible to predict the rainfall intensity for a particular duration and return period
in general by a single mathematical equation. Use of empirical equation at meso scale (region
wise) gives more accurate and probable results since they are developed on the basis of more
than last 100 years of metrological data
( )n
x
aD
KTi
+= ............. (5)
where
i = rainfall intensity (cm/hour)
D = Duration of rainfall (hour)
T = Return period years
K, x, a and n are constants for given catchments (region) and depend on the local metrological
data. Central Soil and Water Conservation Research and Training Institute, Dehradun has given
values of these constant , which are region specific.
Table 1: Regional, Values of Imperical Constants
Region K x a n Annual
Rainfall
(mm)
Bhopal 6.93 0.189 0.5 0.878 785
Nagpur 11.45 0.156 1.25 1.032 802
Chandigarh 5.82 0.16 0.4 0.75 617
Delhi 5.82 0.16 0.4 0.75 617
Bellary 6.16 0.694 0.5 0.972 415
Raipur 4.68 0.136 0.15 0.928 515
28
5.2 Assessment of Critical Discharge
The conversion of rainfall into runoff inversely depends on permeability of the surface.
The higher permeable surfaces like the lawn or gardens, have low runoff as compared to
the impermeable surfaces such as roof top, balconies etc. The ration of runoff and
rainfall for particular surface is defined as runoff coefficient of that surface. Table below
gives the average value of coefficient of runoff for different types of surfaces.
Table 2: Coeff of Runoff for Different Ground Cover
Ground Cover
Rational Runoff Coefficient
for FAA Method, c (Corbitt,
1999; Singh, 1992)
Average value for
design purpose
Forest 0.05 – 0.25 0.15
Lawn 0.05 – 0.35 0.20
Cemeteries 0.1 – 0.25 0.25
Cultivated land 0.08-0.41 0.25
Unimproved
area 0.1 – 0.3
0.25
Meadow 0.1 – 0.5 0.3
Pasture 0.12 – 0.62 0.35
Residential area 0.3 – 0.75 0.55
Industrial area 0.5 – 0.9 0.7
Brick street 0.7 – 0.85 0.75
Business area 0.5 – 0.95 0.75
Asphalt street 0.7 – 0.95 0.8
Concrete street 0.7 – 0.95 0.85
Roof 0.75 – 0.95 0.9
There are various empirical formulae for the calculation of storm water runoff. Most of these
formulae such as Burkling-Ziegler formula, Dicken’s formula, Ryve’s formula, Inglis formula
and nawab Jung Bahadur formula are much suited for larger catchments of their native locations
Rational formula gives quite reliable results for smaller catchments area. It can be used only up
to catchments area of 400 hectares. For assessment of runoff in rainwater harvesting design,
rational formula is universally used. Mathematically it can be defined as
KiAQ **= ............. (6)
where
Q= Rate of runoff
A= Catchments area contributing runoff
I = Rainfall intensity
K = Coefficient of runoff
29
5.3 Assessment of Annual Potential of Rainwater Harvesting
It can be defined as average quantity of water that can be harvested annually. The harvesting
potential can be very easily determined if the average annual rainfall, area of the catchments and
its coefficient of runoff is known. Mathematically it can be written as
KPAV **= ............. (7)
where
V= Volume of rain water harvested
A= Catchments area contributing runoff
P = average annual rainfall
K = Coefficient of runoff
The minimum distance between a pumping well and recharge tube well.
There are no criteria as such about the minimum distance between pumping well and recharge
well. Recharging wells are generally of shallow depths which means that they are in the
fluctuation zone of water levels.
Highly turbid and silt mixed water shall not be allowed to enter into the recharge structures. A
grit catch basin should be provided immediately before the recharge structure to avoid highly
turbid water entering into it. A, low height usually of 2 –3 inches baffle walls may be
constructed as silt traps which remove the silt from the storm water. Periodic cleaning of storm
water drains shall be carried out to remove the plastic bags, leaves etc which chokes the
entrance of recharge structures.
Recharge rate of tube wells.
The recharge rate of a recharge tube well is a factor of transmissivity of aquifer system which in
turn depends upon geo-morphological characteristic of an aquifer. Another factor which also
plays important role is the depth to water levels in an area. Thus the recharge rate varies from
place to place. Usually this value is neglected in design calculation.
Design for filters
Three types of filters are available to be used in recharge structures.
Gravity filters
These are the most widely used filters. In these filters, three layers consisting of coarse sand
/fine gravel of 2-4 mm size, gravel of 5 – 10 mm size and boulders of 5-20 cm size are placed
one above the other. Coarse sand /pea gravel shall be placed at the top so that the silt content
that will come with runoff will be deposited on the top of the coarse sand/ pea gravel and can
easily be removed. For smaller roof area, pit may be filled with broken bricks /cobbles. These
filter beds require minimum maintenance, except periodic scrapping of fine clay and silt
deposited on the filter bed. Silt deposited on the filter media should be cleaned regularly by
removing the top deposited silt. Once in a year the top 5-10 cm sand /pea gravel layer should
also be scrapped to maintain the constant recharge rate through filter material. Thickness of
these layers varies from 0.3 to 0.50 m depending up on the silt load of the storm water.
30
On–line filters (Dewas Filters)
The filter is of 1.0 to 1.2 m length and is made up of PVC pipe. Its diameter should vary
depending on the area of the roof, 15 cm if roof top area is less than 150 sqm and 20 cm if area
is more. The filter is provided with reducer of 6.25 cm on both sides. The filter is divided into
three chambers by PVC screens so that filter material is not mixed up. The first chamber is filled
up with gravel (6-10 mm), middle chamber with pebbles (12-20 mm) and last chamber with
bigger pebbles (20-40 mm).
Pressure filters
These filters consist of the sand through which water is being injected with pressure. These
types of filters are fitted with pumps to pressurize the water through filter chamber. Main
disadvantage of these filters is that they require energy for operation and these filters need to be
back washed periodically to remove the finer material so that the rate of filtration is maintained.
5.4 Development of Excel based Design Calculator
Following are the parameters required for the design of rainwater Harvesting System
• Return period the values can be taken from 0.5 year to 5 year depending on significance
• Concentration time is the main criteria for selecting the duration of rainstorm for the design
of rain water harvesting system. 15 minute is minimum value of rainfall duration for
design purpose.If the concentration time is greater than 15 minutes then it is considered as
duration of rainfall for design purpose.
• Average annual rainfall
• Detail of catchments area (Architecture layout plan with detain of existing drainage system)
• Runoff coefficient of different surfaces of layout plan
• Depth of water table
• Potable water requirement
• Peak intensity of rainfall,
• Average coefficient of runoff
• Type of sub geological formation
The decision whether to store or recharge water depends on the rainfall pattern of a particular
region. In a region where rainfalls through out the year, barring a few dry periods, a small
domestic sized water tank for storing rainwater can be used. The storage tank capacity for the
area should be in no case greater than its annual average rainwater harvesting potential in other
regions where total annual rainfall occurs only during three to four months of monsoon, the
water collected during monsoon has to be stored throughout the year which means that the huge
volumes of storage container are required. So it is feasible to use rain water to recharge ground
water aquifers rather than for storage.
The main objective of the developed software is to make the complicated meteorological and
engineering calculation simple and fast. The program has very few inputs such as physical
parameter of the building, return period and meteorological region and population. Based on
these input programme it self calculate the design meteorological parameter such as
1. Duration of Rainfall / Concentration Time
2. Critical Rainfall Intensity
3. Number of Dry Days
4. Potable water of given population for requirement dry days
31
5. Annual rainwater harvesting potential
6. Critical discharge for design of drainage system
7. Volume of recharge well with storage capacity
8. Optimum size of recharge well (Diameter and depth)
9. Numbers of recharge well
10. Cost of recharge well including box hole
11. Volume of water available for storage
12. Cost of water storage for potable purpose.
The software will be a very useful tool for popularizing the optimum design and estimation of
cost of water harvesting recharge structure. Following are working windows of the Excel Sheet
Program.
Help Sheet
32
Data Input Sheet
Designed Sheet
33
6.0 CASE STUDY
The following two case studies have been performed. First case study is of micro level that is of
a single house hold building or apartment comprises of one single roof. This case study is done
to demonstrate the simplicity of excel calculator and its wide applicability. The example of
Learnium School located at south Delhi is taken as micro level case study. For meso level case
study the example of Jamia Millia Islamia is considered. It is one of the central universities of
India spread over a large area. The campus of the university consists of different buildings and
land use patterns such as road, parking area, lawn etc.
One manual sample calculation is done to demonstrate different mathematical steps and formula
involved in the design of rain water harvesting system.
6.1 Micro Level (Learnium School, New Delhi)
Physical Parameters
Name of Building: Learnium School
Climatological Location Delhi Region
Type of Building Single unit
Type of Surface Roof (Flat)
Surface Area (13.97 X 19.89) =277.86 m2
Distance of farthest point on roof from vertical drain 24.3m
Slope of roof 0.002
Length of drain for harvesting structure 5.6 m
Slope of drain ‘ 0.01
Coefficient of Runn-off 0.9
Metrological Data
Return period 2 Years
Annual Rainfall 617 mm
Value of K, x, a and n for Delhi region from table No. 2
Calculation of critical rainfall duration
385.077.0
1
0195.0−
=
∑= ii
n
i
C SLT
In this case
n 2
L1
24.3
L2
5.6
S1
0.002
S2 0.01
By substituting theses values in above equation we get
Tc = 2.92 minutes
Since Tc calculated is less than 15 minutes therefore design value of T
c would be taken as 15 minutes
Region K x a n
Delhi 5.82 0.16 0.4 0.75
34
Calculation of critical rainfall intensity
( )n
x
aD
KTi
+=
In this case
K 5.82
X
0.16
a
0.4
n
0.75
By substituting theses values in above equation we get
i=67.37 mm/hour
Calculation of annual rainwater harvesting potential
KPAV **=
In this case
A 277.86 m2
P
617 mm
K
0.9
By substituting theses values in above equation we get
V= 154296 lts
Assessment of critical discharge for harvesting structure
KiAQ **=
In this case
A 277.86 m2
i
67.37 mm/hour
K
0.9
By substituting theses values in above equation we get
Q = 16847 lit/hour
Calculation for Size of Harvesting Structure
Volume of water required to be stored for ground water recharging
V = Q*TC
In this case
Q 16847 lit/hour (14.601 m3/hour)
TC
15.0 minutes (0.25 hour)
By substituting theses values in above equation we get
Vw =4.212 m3
Providing 50% extra volume to compensate for the space occupied by filter media in recharge well
Vrecharge well
= 1.5 *4.211 = 6.32 m3
Dimension of Harvesting Recharge well
35
Considering it as cylinder and minimising the parameter for required volume
Depth =2.78 meter (including 0.3 meter as free board)
Diameter= 1.8 meter (Min. dia)
Estimated Cost of Harvesting Structure
Cost (INR) = (Volume of Harvesting Structure * Cost per unit volume +25,000)* No. of Harvesting Unit
= ((π*(1.8)^2*2.789/4)*5000+25000)*1=135657/- (INR)
Critical Volume of water storage required for dry days
No. of dry days*Population *Potable water requirement per capita+20% losses
=1.2*(245*200*15)= 88200 lts
If annual rainwater harvesting potential is equal to or greater than critical volume of water storage
required for dry days than provide storage equal to the critical volume otherwise provide storage equal to
annual rainwater harvesting potential. In this case annual rainwater harvesting potential is less then
critical volume for dry season; therefore we will provide storage equal to154296 lts
Estimated Cost of Water Storage Tank
Cost (INR) = (Volume of Water Storage Tank * Cost per unit volume)
=154296*3.5=540035/- (INR)
6.2 Meso Level (JAMIA MILLIA ISLAMIA (Central University))
Total Area = 205 Acre (8,29,942 sqm.)
Total floor area = 1,24,330, sqm.
Roof area = 25,919 sqm.
Lawn/Playing fields/Parks = 5,28,649 sqm.
Road/Paved Area = 48,810 sqm.
Forest Cover = 2,26,564 sqm.
Climatological Location = Delhi Region
Type of Building = Multiple units
Type of Surface = Roof (Flat)
Slope of roof = 0.002
Slope of drain = 0.01
Coefficient of Runn-off = 0.9
The University is divided into three zones I, II and III. Each zone is further divided into different blocks
such as A, B, C depending on location and vicinity of the buildings to the purpose rainwater recharge
wells. The detail of these zones including roof area, type of surface, length of flow of water on roof and
length of rain are given in the following tables.
Zone-I
S.NO NAME OF BUILDING TOTAL
AREA (M2) Type of Surface Length of
Flow Length of
Drain
Block A-I
1 Faculty of Engg 2500 Roof 79 98
2 Faculty of Humanaties & languages 379 Roof 44 124
3 S.R.K. Hostel 500 Roof 56 75
4 Examination Building 560 Roof 29 38
5 Center for Management 450 Roof 24 18
6 Faculty of B. Arch 708 Roof 44 34
Block B -I
1 Auditorium 226 Roof 32 88
2 Mass Communication 444 Roof 87 94
36
3 Administration Building 411 Roof 35 109
4 New Administrartion Building 1200 Roof 38 87
5 Guest House 356 Roof 42 76
Zone-II
S.NO NAME OF BUILDING TOTAL
AREA (M2) Type of Surface Length of
Flow Length of
Drain
Block A-II
1 T.T. College 880.05 Roof 87 49
2 Law Faculty 285 Roof 23 185
3 T.T.C (Extn) 276 Roof 35 68
4 Mujeeb Bagh Qtrs. 525 Roof 24 196
Block B-II
1 Jamia Enclave 601 Roof 18 86
2 Lecturers Qtrs. 117 Roof 17 94
3 Working girls Hostel 643 Roof 53 42
4 New Girls Hostel 458 41 86
Block C-II
1 J.S. Qtrs. 296 Roof 23 125
2 C-29 Hostel 125 Roof 15 106
3 J.S. Qtrs. 283 Roof 34 86
4 J.S. Qtrs. 472 Roof 68 76
5 J.S. Qtrs. 540 Roof 76 94
Zone-III
S.NO NAME OF BUILDING TOTAL
AREA (M2) Type of Surface Length of
Flow Length of
Drain
Block A-III
1 Gymnasium 580 Roof 13 81
2 Canteen 191 Roof 12 42
3 Social Science block 275 Roof 36 68
4 Student union office 123 Roof 16 63
5 Maths Deptt. Building 425 Roof 23 46
6 Science faculty Building 379 Roof 36 76
7 New Commerce Building 1500 Roof 78 123
8 N.C.C.Qtrs. P.O. Teacher office etc. 323 Roof 16 36
Block B-III
1 Work shop Building 449 Roof 13 49
2 Extn. Part +Lab 730 Roof 11 56
3 Polytechnic 300 Roof 29 35
Block C-III
1 Science block 425 Roof 46 78
2 Central Library 766 Roof 68 54
3 Islamic study Centre 165 Roof 9 23
4 Mosque 520 Roof 47 89
Block D-III
1 Class rooms of Middle School 560 Roof 56 135
2 Canteen + others 160 Roof 10 132
3 School Hostel 836 Roof 78 112
4 School Building 425 Roof 62 93
5 Lab 250 Roof 35 62
6 New Building near museum 219 Roof 33 146
Block E-III
37
1 Workshop (building Deptt) 220 Roof 76 136
2 Nursery School 102 Roof 23 28
3 FINE- ART Faculty 567 Roof 68 76
4 Building Deptt. 352 Roof 21 156
5 Class room Higher Secondary School 760 56 45
Block F-III
1 J.S. Qtrs. 450 Roof 16 189
2 Pink House. Sartaj Hostel 780 Roof 62 24
3 Kellat Hostel 540 Roof 45 145
Note: Ground water contaminate has high probability if runoff water from unclean and
contaminated surfaces such as road, parking area, playing fields are directly injected to water
table. For runoff water from such surfaces can be stored in open funds and allow to infiltrate
through natural process not by infiltration well. Therefore for this case study only roof top
surface is considered.
7.0 CONCLUSION
The exponential growth of population in urban area and increase in per capita water
demand has put severe stresses in fresh water resources of the world. It is more
prominent and critical in semi acid region.
Water conservation, water reuse, and harvesting of water are very important and
essential for sustainable development. Each drop of fresh water save and use properly
will go a long way in quenching the thirst and desire of human civilization. The GOD
has provided us sufficient bounty in form of water to meet the requirement of each of
us.
Rain water harvesting is one of the oldest and commonly used technology in India. Rainwater
harvesting appears to be one of the most promising alternative for supply of fresh water
in the face of increasing water scarcity and escalating demands water harvesting also
present an opportunity for the augmentation of water supplies using this technology.
There are many advantages of rainwater harvesting schemes that make it an attractive
option for highly urbanized cities such as Delhi. With the implementation and
popularization of the rainwater schemes in semi arid regions, following benefits are
likely to accrue.
1. Raising of ground water level at the sites
2. Reduction in flooding of roads
3. Smooth flow of traffic during rainy days
4. Prevention of choking of storm water drains
5. Aesthetically pleasing environment will be available at the flyovers
6. Tubewells will be saved from further deepening
7. Saving in energy required for lifting ground water would be achieved
The main object of this project was to develop an user friendly excel sheet for design
and cost estimate of rainwater harvesting system for individual houses an institution
level. The major object has been successfully achieved and demonstrated in two case
studies at micro and meso level.
38
Summary of Design Calculation Using Excel Sheet for Jamia Millia Islamia (Central University) Case Study
NAME OF BLOCK
TOTAL AREA (M2)
Annual Rainwater Harvesting
Potential (L)
Critcal Discharge in (L/hour)
Critcal Rain
Water Volume
(L)
Volume of Recharge Well (m3)
Dimension of Recharge Well
No of Units
Cost of Recharge Well (INR)
Volume of Potable Storage Tank (L)
Cost of Storage
Tank (INR)
Zone-I Diameter Depth
Block A-I 5097 2830364 309045 66420 99.63 3 2.65 6 731189 2830364 9906274
Block B -I 2037 1464326 159888 29984 44.98 3 2.42 3 345999 1464326 5125141
Total 7134 4294690 468933 96404 144.61 9 1077187 4294690 15031415
Zone-II
Block A-II 1966 1091748 119207 27970 41.95 3.5 2.48 2 285350 1091748 3821116
Block B-II 1819 1010091 110291 19368 29.05 3.5 2.3 2 271315 1010091 3535317
Block C-II 1716 952895 104046 19865 29.8 3.9 2.8 1 181214 952895 3335132
Total 5501 3054734 333544 67203 100.8 5 737879 3054734 10691565
Zone-III
Block A-III 3796 2107919 230162 43824 65.74 3.9 2.8 3 543639 2107919 7377716
Block B-III 1479 821289 89676 12427 18.64 3.5 2.3 1 135658 821289 2874510
Block C-III 1876 1041743 113747 19840 29.76 3.9 2.8 1 181044 1041743 3646100
Block D-III 2450 1360485 148550 30335 45.5 3.5 2.66 2 299721 1360485 4761698
Block E-III 2001 1111155 121326 24423 36.63 3.5 2.3 2 271315 1111155 3889044
Block F-III 1770 982881 107320 22321 33.48 3.5 2.3 2 271315 982881 3440084
Total 13372 7425472 810781 153170 229.75 11 1702691 7425472 25989152
G. Total 26007 14774896 1613258 316777 475.16 25 3517758 14774896 51712132
39
8.0 BIBLIOGRAPHY: 1. “Rain Water Harvesting - A New Water Sources” by Jan Gerston: National Wild Flower
Research Centre.
2. Artificial Recharge in Delhi Area “Central Ground Water Board”.
3. Artificial Recharge in Delhi Area, Central Ground Water Board, Northern Water Region
Chandigarh.
4. Dovlopment & Augmentation of Ground Water Resourses in NCT of Delhi.
5. Ground Water Recharging Peoples participants in Jamnagar Region, Prof. G.G. Parthasarthi and
A.S. Patel, Indian Water Works ASSOCIATES Jan 1997.
6. Guide on Artificial Recharge to Ground Water “by Central Ground Water Board” Ministry of
Water Resourses.
7. Guide on Artificial Recharge to Ground Water, Central Ground Water Board, Ministry of water
resourses,New Delhi 2000.
8. Gupta O.P.Lal, J.J, and Gupta, V(2005) “ Need for Rain Water Harvesting to Mitigate Water
Crises of Delhi “ Journal of Indian Buildings Congress,Vol12, No.1
9. Indian Metrological Department (Monthly and Annual Rainfall Data).
10. Kesari, P, and Singh,S.K.(2005) “ Sustainable Development of Ground Water in Delhi through
Rain Water Harvaisting” , Journal of Indian Buildings Congress Vol12,No.1
11. Mahi, S.P. and Prakash, O.(2005)”Artificial Recharge to Grounder Water in Railway Residential
Complex in Delhi “ Journal of Indian Buildings Congress Vol.12, No.1
12. Manual on Rain Water Harvasting and Conservation: CSO, CPWD,Govt of India
Publication,New Delhi
13. Master Plan of Jamia Millia Islamia (Central University)
14. Pal, S, and Sharma,S.K.(2005) “ Rain Water Harvesting and Artificial Recharge “ Journal of
Indian Buildings Congress, Vol.12 No.1
15. Rain Water Harvesting and Conservation Manual, Government of India, C.P.W.D. Nirman
Bhawan, New Delhi (2002)
16. Rain Water Harvesting Mannual for Urban Areas, Center for Science and Envirmental,
Tughlakabad Institutional AREA, New Delhi.
17. Rain Water Harvesting System : Report; CGWB, Ministry of Water Resourses, Govt. of India,
New Delhi
18. Ralegoankar, R.v., Gupta,R,Singh,D(2005) “ Economic Modlling for Rainwater Harvasting
Scheme” Journal of Indian Building Congress Vol.,12 No.1
19. Roof Top Rain Water Harvesting for Augmentation Ground Water Storage in NCT Delhi
“Central Ground Water Board” Ministry of Water Resourses.
20. Singh,S.(2005) “ Water Management in Cantonments” Journal of Indian Buildings Congress,
Vol.12 No.1
21. Soil and water conservation by Glenn D. Schwali Delmar D. Fangmeir, William J. Elliot by John
Wiley & Son Inc.
22. http://www.cgwaindia.com
23. http://www.csestore.cse.org.in
24. http://www.gdrc.org.
25. http://www.hinduonnet.com
26. http://www.rainwaterharvesting.org