Rainwater Harvesting and

Watershed Management

Some Facts about Water

• Only 2.5% of the world’s water is freshwater and most of this are in the form of polar ice-caps.

• Water use has increased by 70% since 1970• A recent report by Credit Suisse stated that by 2025 18 countries

will experience water demand beyond supply capabilities• It takes up to 5000 lt of water to produce 1kg of rice.• Every square mile of developed land causes 16 million gallons of

rain water to directly enter the rivers on a rainy day!• Each person uses about 150 litres of water every day. About 60

litres of this is for toilet flushing• Toilet flushing is the single largest user of household water, 30-

40%, up to 90% for offices.

What is Water harvesting??

• Water harvesting is the capture, diversion,and storage of water obtained from differentfreshwater sources for plant irrigation,domestic purposes, industrial purposes,groundwater recharge and other uses.

Rainwater harvesting [RWH]

• It is a type of water harvesting.• It can be defined as the system of collection

and concentration of rain water and its runoff and its productive use for :-

a) Irrigation of annual crops pastures and trees.b) Domestic and livestock consumption.c) Groundwater recharge.

Need For Rainwater Harvesting• Major parts of our country have been facing continuous

failure of monsoon and consequent deficit of rainfall over thelast few years.

• Also, due to ever increasing population of India, the use ofground water has increased drastically leading to constantdepletion of ground water level causing the wells and tubewells to dry up.

• In some places, excessive heat waves during summer create asituation similar to drought.

• It is imperative to take adequate measures to meet thedrinking water needs of the people in the country besidesirrigation and domestic needs.

• Out of 8760 hours in a year, most of the rain in India falls injust 100 hours.

Rainwater can be harvested in a variety of ways:

Rainwater can be harvested in a variety of ways: • Directly from roof tops and stored in tanks. • Monsoon run off and water in swollen streams

during the monsoon and storing it in underground tanks.

• Water from flooded rivers can be stored in small ponds.

• Collection and transfer of rainwater into percolation tanks so as to facilitate discharge into ground.

Components of RWH

Catchment

Delivery

Storage

Models of RWHThere are two main models of rainwaterharvesting done in India:-

• RURAL MODEL.• URBAN MODEL.

Rural model of RWH• Rural areas generally use traditional methods of

rainwater harvesting.• Main motive of rainwater harvesting in these

areas is to facilitate irrigation for agriculture anduse of water for domestic and drinking purposes.

• Nowadays practices are also been followed to asto recharge groundwater levels.

• Many of the traditional structures includeTankas, Nadis, Talabs, Bavdis, Rapats, Kuis,Virdas, Kunds, Khadins, Johads etc.

BawodiTraditional step wells are called vavadi in Gujarat, or baoris or bavadis in Rajasthan and northern India.

KundsCovered undergroundtank, developedprimarily for tacklingdrinking waterproblems.

Khadin Bund

Urban Model of RWH• More modernized system of rainwater

harvesting.• The main components of the urban model are:-a) Roof catchmentb) Guttersc) Down piped) First flush pipee) Filter unitf) Storage tankg) Collection pit.

Components of Urban RWH models

Storage Tank Pipe System

Advantages

• RWH provides a good supplement to other water sources thus relieving pressure on other water sources.

• It can supply as a buffer and can be used in times of emergency or breakdown of public water supply systems.

• Helps reduce the storm drainage load and flooding in the cities.

• It is a flexible technology and can be built to require meets of any range. Also the construction, operation and maintenance is not very labour intensive in most systems.

Advantages• Prevents water wastage by arresting run off as well as prevents soil

erosion and mitigates flood.• Sustains and safeguards existing water table through recharge.• Arrests sea-water intrusion and prevents salination of ground

water.• Rainwater harvesting can reduce salt accumulation in the soil

which can be harmful to root growth. When rainwater percolatesinto the soil, it forces the salts down and away from the root zonearea. This allows for greater root growth and water uptake, whichincreases the drought tolerance of plants.

• Rain-water is a clean and pure source of drinking water whichrequires minimal chemical treatment as the amount of pollutantsare not much.

Disadvantages• In terms of complex constructions, there is a requirement for high

costs, trained professionals. • Maintenance costs may add to the monetary burden. • If not maintained properly then it can cause various problems in

terms of algal or bacterial growth. • Tanks if not constructed properly might result in leakages and

metal tanks may also lead to problems such as corrosion harming the water quality.

• All these factors might prove harmful and result in various kinds of health issues.

• The system is very much rainfall dependent and hence if there are problems with the rainfall in the area, it may not be very effective.

Future of Rainwater Harvesting

• Rainwater harvesting systems serve as analternative decentralized water source especiallyin the age when groundwater supplies aredepleting and municipal water infrastructuresare facing high replacement costs.

• The use of decentralized rainwater harvestingsystems is growing nationally andinternationally, especially in industrial countrieslike Asia, Europe and the US.

• Roof Rain Water Harvesting• Land based Rain Water Harvesting• Watershed based Rain Water harvesting

• For Urban & Industrial Environment –• Roof & Land based RWH

• Public, Private, Office & Industrial buildings• Pavements, Lawns, Gardens & other open spaces

RWH – Methodologies

RAIN WATER HARVESTING TECHNIQUES :

There are two main techniques of rain water

harvestings.

• Storage of rainwater on surface for future use.

• Recharge to ground water.

The storage of rain water on surface is a traditional

techniques and structures used were underground

tanks, ponds, check dams, weirs etc

Recharge to ground water is a new concept ofrain water harvesting and the structuresgenerally used are :-

Pits :- Recharge pits are constructed forrecharging the shallow aquifer. These areconstructed 1 to 2 m, wide and to 3 m. deepwhich are back filled with boulders, gravels,coarse sand.

• Trenches:- These are constructed when the permeable stream is available at shallow depth. Trench may be 0.5 to 1 m. wide, 1 to 1.5m. deep and 10 to 20 m. long depending up availability of water. These are back filled with filter materials.

• Dug wells:- Existing dug wells may beutilised as recharge structure and watershould pass through filter media beforeputting into dug well.

Appropriate Technology

Water conservation

and groundwater

recharge techniques

Water harvesting cum

supplementary

irrigation techniques

Hand pumps :- The existing hand pumps may beused for recharging the shallow/deep aquifers,if the availability of water is limited. Watershould pass through filter media beforediverting it into hand pumps.

Recharge wells :- Recharge wells of 100 to 300mm. diameter are generally constructed forrecharging the deeper aquifers and water ispassed through filter media to avoid choking ofrecharge wells.

Recharge Shafts :- For recharging the shallowaquifer which are located below clayey surface,recharge shafts of 0.5 to 3 m. diameter and 10 to15 m. deep are constructed and back filled withboulders, gravels & coarse sand.

Lateral shafts with bore wells :- For recharging theupper as well as deeper aquifers lateral shafts of1.5 to 2 m. wide & 10 to 30 m. long dependingupon availability of water with one or two borewells are constructed. The lateral shafts is backfilled with boulders, gravels & coarse sand.

Spreading techniques :- Whenpermeable strata starts from topthen this technique is used. Spreadthe water in streams/Nalas bymaking check dams, nala bunds,cement plugs, gabion structures or apercolation pond may beconstructed.

Rain Water Harvesting?.

Rain Water Harvesting RWH- process of collecting, conveying

& storing water from rainfall in an area – for beneficial use.

• Storage – in tanks, reservoirs, underground storage-

groundwater

• Hydrological Cycle

Harvesting System

Broadly rainwater can be harvested for two purposes

•Storing rainwater for ready use in containers above or

below ground

•Charged into the soil for withdrawal later (groundwater

recharging)

Source: A Water Harvesting Manual For Urban Areas

Rain Water Harvesting?

• RWH - yield copious amounts of water. For an average rainfall

of 1,000mm, approximately four million litres of rainwater can be

collected in a year in an acre of land (4,047 m2), post-

evaporation.

•As RWH - neither energy-intensive nor labour-intensive

•It can be a cost-effective alternative to other water-accruing

methods.

• With the water table falling rapidly, & concrete surfaces and

landfill dumps taking the place of water bodies, RWH is the most

reliable solution for augmenting groundwater level to attain self-

sufficiency

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The roof catchment are selectively cleaner when compared to the ground level

catchment• Losses from roof catchment are minimum• Built & Maintained by local communities• No Chemical contamination & only required

filtration• Available at door step with least cost

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Rain water harvesting systemThe typical roof top rain water harvesting system comprises

• Roof catchment• Gutters• Down pipe & first flushing pipe• Filter Unit• Storage Tank

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Roof Catchment

The roof of the house is used as the catchmentfor collecting rain water. The style constructionand material of the roof effect its suitability as acatchment, Roofs made of corrugated iron sheet ,asbestos sheet, Tiles or Concrete can be utilizedfor harvesting the rain water

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GuttersGutters are channels fixed to the edges of roofall around to collect & transport the rainwaterfrom the roof. Gutters can be made in semi-circular and rectangular shape with cementpipe, plain galvanized iron sheet, PVC pipes,bamboos etc. Use of locally available materialreduce the overall cost of the system.

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Down PipeIt is the pipe which carries the rainwater fromthe gutters to the filter & storage tank. Downpipe is joined with the gutters at one end &the other end is connected to the filter unit ofthe storage tank. PVC or GI pipe of 50mm to75mm (2 to”) are commonly used for downpipe. Bamboo can be also used whereveravailable and possible

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First Flush PipeDebris, dust & dirt collect on the roof duringnon rainy periods when the first rain arrive. Afirst flush system arrangement is made toavoid the entering unwanted material into theFilter media & storage tank. This is a simplemanually operated arrangement or semi-automatic system with a valve below the ‘T’junction

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Filter UnitThe filter unit is a container or chamber filledwith filter media such as coarse sand,charcoal, coconut fiber, pebbles & gravels toremove the debris & dirt from water thatenters the tank. The filter unit is placed overthe storage tank or separately. It may be ofFerro cement filter unit, Aluminum, Cementrings or Plastic bucket etc.

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Storage Tank

It is used to store the water that is collected from the roofthrough filter. For small scale water storage plasticbuckets, jerry cans, clay or cement jars, ceramic jars,drums may be used. For larger quantities of water, thesystem will require a bigger tank with cylindrical orrectangular or square in shape constructed with Ferrocement or cement rings or plain cement concrete orreinforced cement concrete or brick or stone etc. Thestorage tank is provided with a cover on the top to avoidthe contamination of water from external sources. Thestorage tank is provided with pipe fixtures at appropriateplaces to draw the water to clean the tank & to dispose ofextra water. A provision for keeping the vessel to collectthe water is to be made.

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Size of Storage Tank

• Based on

– No. of person in the House hold

– Per capita water requirement

– No. of days for which water is required

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Water available from Roof

Annual rainfall (in mm) x roof area (in sq. m) x co-

efficient of run off for roof

co-efficient of run off

GI sheet 0.9

Asbestos 0.8

Tiled 0.75

Plaster on bricks/ Concrete 0.7

Watershed Management• What is a watershed??• Watersheds can be defined as a geo-hydrological

unit draining to a common point by a system ofdrains. All lands on earth are part of onewatershed or other. Watershed is thus the landand water area, which contributes runoff to acommon point.

• For example, the watershed of a lake wouldinclude not only the streams entering that lakebut also the land area that drains into thosestreams and eventually the lake.

Water Shed

Water shed

Water Shed

Watershed Management – Definition• The process of creating and implementing plans,

programs, and projects to sustain and enhancewatershed functions that affect the plant, animal, andhuman communities within a watershed boundary.

• Watershed management is the integrated use of land,vegetation and water in a geographically discretedrainage area for the benefit of its residents, with theobjective of protecting or conserving the hydrologicservices that the watershed provides and of reducingor avoiding negative downstream or groundwaterimpacts. Fresh water, and freshwater ecosystems, is themost basic components of watershed management.

Need for Watershed Management.• In spite of sufficient rainfall, people have to

depend upon tankers for their domestic watersupply in summers in most of the areas. This ismainly due to large runoff which is responsiblefor water loss as well as soil loss of the land.

• A raindrop, when flows along the slope, carriesthe loose soil along it. In this case the topmostlayer of soil is lost rapidly. Due to high intensityrainfall, it is estimated that, more than 100 tonsof soil is lost .

Objectives of Watershed management• To control damaging runoff and degradation and thereby conservation

of soil and water.• To manage and utilize the runoff water for useful purpose.• To protect, conserve and improve the land of watershed for more

efficient and sustained production.• To protect and enhance the water resource originating in the watershed.• To check soil erosion and to reduce the effect of sediment yield on the

watershed.• To rehabilitate the deteriorating lands.• To moderate the floods peaks at downstream areas.• To increase infiltration of rainwater.• To improve and increase the production of timbers, fodder and wild life

resource.• To enhance the ground water recharge, wherever applicable.

Watershed Development• Watershed development refers to the

conservation, regeneration and the judicioususe of all the resources (Natural and Human)Within a watershed.

Steps Involved in Watershed Development

• Human Resource management• Soil and land management• Water management• Crop management• Afforestation• Rural energy management• Livestock management

Human Resource Management• Training is essential to enhance the technical ,

social and managerial capacity of workers,especially the NGO’s and VWC’s involved inthe watershed development

• The NGO staff, village watershed committeeand watershed committees have beenprovided training through on field’ hands on’structured and farmer to farmer extension

Soil and Land Management• Soil Management: The soil Conservation

methods should be adopted in the catchmentarea. The erosive power of natural agents(Wind, Rain) and erodibility properties of thesoil combine to causes oil erosion

• The process gets accelerated with increase inslope of the land surface and retarded bydecreasing in the slope

Soil Management• The soil erosion can be decreased by

intercepting the erosive power of rain andwind with vegetation cover, by increasing theroughness of land surface by different tillageoperations by decreasing the slope of land byadopting practices like bunds, terraces, andother such structures.

Conserving Soil and Water• Contour - Contour trenches trap rain water,

enable it to percolate to underground aquifersand break the speed of fast moving water

• Gully control - Gully plugs help to control theflow of water, sedimentation and rechargeground water aquifers.

• Stone bunds - Building stone and nala bundsacross the slope arrest the flow of water andcontrol erosion in areas where soil work is notpossible.

Contour Bunds Stone Bunds

Check Dams Gully Control

Vegetation Cover

Bunds

Bunds

terraces

Land Management• If the agriculture land is undulated the water is

lost by trapping, so the agricultural land shouldbe properly levelled to obtain uniform growth ofplants with optimum uniform quantity of water

• The deep ploughing by tractors is much efficientto retain water and to get maximum yield withoptimum supply of water.

• Along the slops of hills area contours, bunds, orterrace bunds should be constructed at differentlevels which arrest the sediments and serve asdetention basin for heavy runoff season.

Deep Ploughing

Water Management• Benefits may be obtained by utilizing

minimum volume of water, so the watermanagement is a science of propermanagement of water by the cultivators

• •Methods of water management• Reservoir management.• Conveyance system management.• Application of right amount of water

Reservoir Management• The Reservoir management involves the

method of reducing evaporation losses (use ofchemicals like cethyl alcohol), absorption andpercolation losses (by making reservoirImpervious by techniques like grouting)

Conveyance System Management• The canals should be lined to reduce seepage

losses

Application of right amount of water• The right amount of water should be applied to the

land which is just sufficient to meet the waterrequirement of crop.

• Eg. Different crops require different quantity of waterto come to maturity

• The amount of water required by them is known asdelta i.e. ht of water measured in cm required by thecrop

• Sugarcane-120 cm• Rice -120 cm• Cotton 50 cm

Crop Management• The crop management should be practices for

maintaining the fertility of the lands forobtaining maximum yield with minimum supplyof water, correct method of irrigation

• •Border strip method-for wheat, vegetables• •Furrow methods-for cotton, sugarcanes• •Basin methods-For orchards• •Sprinkler methods-for groundnuts, vegetables• •Drip method-for all types of crops.

Furrow Irrigation

Basin Method

Sprinkler Method

Drip Method

Afforestation• Planned growth of trees in wasted, restricted

area is a valued aspect of greening. Theseconservation measures can reduce soil erosion

Rural Energy Management• Prevention of local environment degradation

by replacing traditional fuel sources byrenewable energy sources.

• This reduces the agony of rural women• It mitigates the indoor air pollution

Traditional methods of cooking food

Renewable energies• Bio gas plant• Solar cookers• Solar panels

Livestock management• The live stock population in the watershed

comprises of cows, bullocks, buffaloes, sheep,goats, and camels, the live stock ownernormally provides water to large animalseither in the home or the animals are taken tofarmwells. Water availability situation, is alsofound to be affecting livestock population. Sonecessary steps should be taken to grow thepopulation of live stock provide them foodand shelter and health.

Live stocks• Drinking water• Health care for live stocks

Shelters

Water Shed community

Advantages/Future Of WSM• Watershed Development program is a revolutionary

program aimed at fulfilling the water needs in the waterscarce areas.

• In areas where there is inadequate water supply watershedmanagement offers an ideal solution.

• It helps in utilizing the primary source of water andprevents the runoff from going into sewer or storm drains,thereby reducing the load on treatment plants.

• If we take steps to encourage each drop of rainfall topenetrate in the ground at the point where it strikes earth,it will result in addition of one drop to our useful watersupply and subtraction of one drop from a potential flood.

Water Shed Community

Thank You