Rain Water Harvesting - SSWM
PrefaceWe, the human beings, are largely dependent onwater for our survival. Although water is as important forsurvival of human beings as much as food, air etc. but wehardly pay any attention for its economical use andconservation of this precious resource.Due to indiscriminate pumping of ground water, thewater table has already gone down abnormally and if we donot wake up even now then our future generations may haveto face severe crisis of water. The rains are important sourceof water and if we can harvest rain water, the scarcity ofwater can be eliminated altogether. Therefore, it is ourbounden duty to conserve the rain water in the form of rainwater harvesting.The book on “Rain Water Harvesting” is an attemptby IRICEN to propagate the concept of rain water harvestingwhich can be effectively implemented in our office andresidential establishments. It is hoped that this will serve asa helpful guide to the field engineers.Shiv KumarDIRECTORIRICEN, Pune
AcknowledgementThe rapid development of cities and consequent populationexplosion in urban areas has led to depletion of surface waterresources. For fulfillment of daily water requirement, indiscriminatepumping of ground water is being resorted to, leading to loweringof ground water table. At the same time the rain water is notbeing conserved which ultimately goes waste. To avoid thisimbalance, conservation of rain water in the form of rain waterharvesting is the only solution.Rain water harvesting can be effectively implemented inour office and residential complexes for conservation of rain water.The subject has assumed lot of significance in the presentscenario. This has been included in Indian Railway Works Manual2000 vide correction slip no. 10 dated 17.02.05 also. Thispublication is an attempt to compile all the relevant informationregarding various methods commonly in use. These methodscan be used by field engineers for designing and implementingRain Water Harvesting systems.Efforts have been made to make the book more useful forthe field engineers. In this effort, the IRICEN staff and facultyhave contributed immensely, notably among them are Mrs.Gayatri Nayak and Shri Sunil Pophale. I am particularly thankfulto Shri N.C.Sharda, Senior Professor/Works for his valuablesuggestions and proof checking and Shri Praveen Kumar,Professor/Computers for providing logistic assistance for printingof the book.Above all, the author is grateful to Shri Shiv Kumar,Director, IRICEN for his encouragement and suggestions forimproving the publication.A.K. GuptaProfessor/TrackIRICEN/Pune
CONTENTSCHAPTER-1 GENERAL1.01.11.21.31.41.51.6IntroductionHydrologic cycleAdvantages of rain waterRain water harvestingNeed for rain water harvestingAdvantages of rain water harvestingRain water harvesting potentialCHAPTER-2 METHODS OF HARVESTING RAIN WATER2.1Rain water harvesting methods2.1.1 Storing rain water for direct use2.1.2 Recharging ground water aquifers fromroof top runoff2.1.3 Recharging ground water aquifers withrunoff from ground areas2.2Components of rain water Catchment areaCoarse mesh/leaf screenGutterDown spout/ConduitFirst flushing deviceFilterSettlement tankStorage tank
CHAPTER-3 RECHARGING SUBSURFACE AQUIFERS3.1Methods of recharging subsurface aquifers3.1.1 Through recharge pit3.1.2 Recharge through abandoned hand pump3.1.3 Recharge through abandoned dug well/open well3.1.4 Through recharge trench3.1.5 Recharge through shaft3.1.6 Recharge trench with boreCHAPTER-4 CASE STUDY4.14.2IntroductionRain water harvesting at IRICEN hostelCHAPTER-5 QUALITY OF WATERReferences
CHAPTER 1GENERAL1.0IntroductionWater is the most common or major substance onearth, covering more than 70% of the planet’s surface. Allliving things consist mostly of water. For example, thehuman body is about two third water. World wide distributionof water is given in table 1.1. Of the total volume of water,only 2 percent (over 28,000,000 Km3) is fresh water, whichcan be used for consumption and for agriculture as given intable 1.2. The average runoff in the river system of India hasbeen assessed as 1869 km3. Of this, the utilisable portionby conventional storage and diversion is estimated as about690 km3. In addition, there is substantial replenishableground water potential in the country estimated at 432 km3.The per capita availability of water at the national level hasreduced from about 5,177 m3 in the year 1951 to the presentlevel of 1,869 m3. For improving per capita water availabilityin the country, replenishment of ground water resources is anecessity which can be done very effectively through rainwater harvesting.Table 1.1 World-wide Distribution of WaterS.No.1234567Water typeVolume(1000 km3)Ocean1,370,323Ground water (fresh &saline)60,000Glaciers24,000Lakes and reservoirs280Soil moisture85Atmospheric water14River water1.2Total 1,454,703.21Percentageof Total 0.000
Table 1.2 World-wide Distribution of Fresh WaterS.No.123456Water typeVolumePercentage of(1000 km3)Total 40.0501.20.00428,253.2100.00GlaciersGround waterLakes and reservoirsSoil moistureAtmospheric waterRiver waterTotalThe harvested rain water can also be used directlyfor various purposes, which will improve per capita wateravailability substantially.1.1Hydrologic cycleThe never-ending exchange of water from theatmosphere to the oceans and back is known as thehydrologic cycle (Fig. 1.1). This cycle is the source of allforms of precipitation (hail, rain, sleet, and snow), and thus ofFig. 1.1 Hydrologic cycle2
all the water. Precipitation stored in streams, lakes and soilevaporates while water stored in plants transpires to formclouds which store the water in the atmosphere.Currently, about 75% to 80% of conventional watersupply is from lakes, rivers and wells. Making the mostefficient use of these limited and precious resources isessential. Otherwise, scarcity of water will be faced by ourfuture generations. This includes using appliances andplumbing fixtures that conserve water, not wasting water, andtaking advantage of alternative water sources such asgreywater reuse and rain water harvesting.1.2Advantages of rain waterThe rain water’s environmental advantage and purityover other water options makes it the first choice, eventhough the precipitation cycle may fluctuate from year toyear.Environmental advantageCollecting the rain that falls on a building and usingthe same for various purposes is a simple concept. Sincethe rain you harvest is independent of any centralizedsystem, you are promoting self-sufficiency and helping tofoster an appreciation for this essential and preciousresource. The collection of rain water not only leads toconservation of water but also energy since the energy inputrequired to operate a centralized water system designed totreat and pump water over a vast service area is bypassed.Rain water harvesting also lessens local erosion and floodingcaused by runoff from impervious cover such as pavementand roofs, as some rain is instead captured and stored.Thus, the storm water run-off, the normal consequence ofrain fall, which picks up contaminants and degrades ourwater ways, becomes captured rainfall which can then fulfill anumber of productive use. Policymakers would have toreconsider present assumptions regarding impervious coverand consequent run-off management strategies when rainwater harvesting systems are installed.3
Qualitative advantageA compelling advantage of rain water over other watersources is that it is one of the purest sources of wateravailable. Indeed, the quality of rain water is an overridingincentive for people to choose rain water as their primarywater source, or for specific uses such as wateringhouseplants and gardens. Rain water quality almost alwaysexceeds that of ground or surface water as it does not comeinto contact with soil and rocks where it dissolves salts andminerals and it is not exposed to many of the pollutants thatoften are discharged into surface waters such as rivers, andwhich can contaminate groundwater. However, rain waterquality can be influenced by characteristics of area where itfalls, since localized industrial emissions affect its purity.Thus, rain water falling in non-industrialized areas can besuperior to that in cities dominated by heavy industry or inagricultural regions where crop dusting is prevalent.Rain water is soft and can significantly reduce thequantity of detergents and soaps needed for cleaning, ascompared to typical municipal water. In addition, soap scumand hardness deposits disappear and the need for a watersoftener, often an expensive requirement for well watersystems, is eliminated. Water heaters and pipes will be freeof deposits caused by hard water and will last longer. Rainwater’s purity also makes it an attractive water source forcertain industries for which pure water is a requirement.Thus, industries such as computer microchip manufacturingand photographic processing would certainly benefit from thissource of water.1.3Rain water harvestingFor our water requirement we entirely depend uponrivers, lakes and ground water. However rain is the ultimatesource that feeds all these sources. Rain water harvestingmeans to make optimum use of rain water at the placewhere it falls i.e. conserve it and not allow to drain awayand cause floods elsewhere.4
The rain water harvesting may be defined as thetechnique of collection and storage of rain water at surface or insub-surface aquifer before it is lost as surface run off. Theaugmented resources can be harvested whenever needed.1.4Need for rain water harvestingWater is one of the most essential requirement forexistence of living beings. Surface water and ground water aretwo major sources of water. Due to over population and higherusage levels of water in urban areas, water supply agencies areunable to cope up demand from surface sources like dams,reservoirs, rivers etc. This has led to digging of individual tubewells by house owners. Even water supply agencies haveresorted to ground water sources by digging tube-wells in orderto augment the water supply. Replenishment of ground water isdrastically reduced due to paving of open areas. Indiscriminateexploitation of ground water results in lowering of water tablerendering many bore-wells dry. To over come this situation borewells are drilled to greater depths. This further lowers the watertable and in some areas this leads to higher concentration ofhazardous chemicals such as fluorides, nitrates and arsenic. Incoastal areas like Chennai, over exploitation of ground waterresulted in seawater intrusion thereby rendering ground waterbodies saline. In rural areas also, government policies onsubsidized power supply for agricultural pumps and piped watersupply through bore wells are resulting into decline in groundwater table. The solution to all these problems is to replenishground water bodies with rain water by man made means.1.5Advantages of rain water harvesting(a)(b)(c)(d)(e)(f)Promotes adequacy of underground waterMitigates the effect of droughtReduces soil erosion as surface run-off is reducedDecreases load on storm water disposal systemReduces flood hazardsImproves ground water quality / decreases salinity(by dilution)(g) Prevents ingress of sea water in subsurface aquifersin coastal areas5
(h) Improves ground water table, thus saving energy(to lift water)(i) The cost of recharging subsurface aquifer is lowerthan surface reservoirs(j) The subsurface aquifer also serves as storage anddistribution system(k) No land is wasted for storage purpose and nopopulation displacement is involved(l) Storing water underground is environment friendly1.6Rain water harvesting potentialThe total amount of water that is received in the form ofrainfall over an area is called the rain water endowment of thatarea. Out of this, the amount that can be effectively harvested iscalled rain water harvesting potential.Area of catchment x Amount of rainfall rain water endowmentAll the water which is falling over an area cannot beeffectively harvested, due to various losses on account ofevaporation, spillage etc. Because of these factors the quantityof rain water which can effectively be harvested is always lessthan the rain water endowment. The collection efficiency ismainly dependent on factors like runoff coefficient and first flushwastage etc.Runoff is the term applied to the water that flows awayfrom catchments after falling on its surface in the form of rain.Runoff from a particular area is dependent on various factors i.e.rainfall pattern and quantity, catchment area characteristics etc.For determining rainfall quantity, the rainfall data preferably for aperiod of at least 10 years is required. This data can be collected6
from meteorological department. For determining the pattern ofrainfall, the information may be collected either frommeteorological department or locally. The pattern of rainfall in aparticular cathcment area influence the design of rain waterharvesting system. In areas where rainfall is more but limited tovery short period in a year, big storage tanks would be requiredto store rain water, if we are collecting rain water in storagetanks for direct use. In such areas, it is preferable to use rainwater for recharging of ground water aquifers, if feasible, toreduce the cost of rain water harvesting system.Runoff depends upon the area and type of catchmentover which it falls as well as surface features. Runoff can begenerated from both paved and unpaved catchment areas.Paved surfaces have a greater capacity of retaining water on thesurface and runoff from unpaved surface is less in comparison topaved surface. In all calculations for runoff estimation, runoffcoefficient is used to account for losses due to spillage,leakage, infiltrations catchment surface wetting andevaporation, which will ultimately result into reduced runoff.Runoff coefficient for any catchment is the ratio of the volume ofwater that run off a surface to the total volume of rainfall on thesurface. The runoff coefficient for various surfaces is given intable 1.3.Table 1.3 Runoff coefficients for various surfacesS.No.123456Type of catchmentRoof catchmentsTilesCorrugated metal sheetsGround surface coveringsConcreteBrick pavementUntreated ground catchmentsSoil on slopes less than 10%Rocky natural 0.0-0.30.2-0.5Source : Pacey, Amold and Cullis, Adrian 1989, Rainwater Harvesting : The collection of rainfall and runoff in ruralareas, Intermediate Technology Publications, London p 55.7
Based on the above factors, the water harvestingpotential of site could be estimated using the followingequation:Rain Water harvesting potential Amount of Rainfallx area of catchment x Runoff coefficientThe calculation for runoff can be illustrated using thefollowing example:Consider a building with flat terrace area (A) of 100sqm located in Delhi. The average annual rainfall (R) in Delhiis approximately 611mm. The runoff coefficient (C) for a flatterrace may be considered as 0.85.Annual water harvesting potentialA x R x Cfrom 100 m2 roof 100 x 0.611 x 0.85 51.935 cumi.e. 51, 935 liters8
CHAPTER 2METHODS OF HARVESTING RAIN WATER2.1Rain water harvesting methodsThere are three methods of harvesting rain water asgiven below :(a) Storing rain water for direct use (Fig. 2.1)(b) Recharging ground water aquifers, from roof toprun off (Fig. 2.2)(c) Recharging ground water aquifers with runoff fromground area (Fig. 2.3)2.1.1Storing rain water for direct useIn place where the rains occur throughout the year, rainwater can be stored in tanks (Fig. 2.1). However, at placeswhere rains are for 2 to 3 months, huge volume of storage tankswould have to be provided. In such places, it will be moreappropriate to use rain water to recharge ground water aquifersrather than to go for storage. If the strata is impermeable, thenstoring rain water in storage tanks for direct use is a betterFig. 2.1 Storing rain water for direct use9
method. Similarly, if the ground water is saline/unfit forhuman consumption or ground water table is very deep, thismethod of rain water harvesting is preferable.2.1.2.Recharging ground water aquifers from roof toprun offRain water that is collected on the roof top of thebuilding may be diverted by drain pipes to a filtration tank (forbore well, through settlement tank) from which it flows intothe recharge well, as shown in Fig.2.2. The recharge wellshould preferably be shallower than the water table. Thismethod of rain water harvesting is preferable in the areaswhere the rainfall occurs only for a short period in a year andwater table is at a shallow depth. The various methods ofrecharging ground water aquifers from roof top runoff arediscussed separately in Chapter 3.FilterationtankRechargewellFig. 2.2 Recharging ground water aquifers from rooftop run off10
2.1.3Recharging ground water aquifers with runofffrom ground areasThe rain water that is collected from the open areasmay be diverted by drain pipes to a recharge dug well / bore wellthrough filter tanks as shown in Fig.2.3. The abandoned borewell/dug well can be used cost effectively for this purpose. Thevarious methods of recharging ground water aquifers with runofffrom ground areas are discussed separately in Chapter 3.Fig. 2.3 Recharging ground water aquifers with runofffrom ground areas2.2Components of rain water harvestingThe rain water harvesting system consists offollowing basic components –(a)(b)(c)(d)(e)(f)(g)(h)Catchment areaCoarse mesh / leaf screenGutterDown spout or conduitFirst flushing deviceFilterStorage tankRecharge structure11
2.2.1Catchment areaThe catchment area is the surface on which the rainwater falls. This may be a roof top or open area around thebuilding. The quality of water collected from roof top iscomparatively much better than collection from the ground.Rain water harvested from catchment surfaces along theground should be used for lawn watering, flushing etc.,because of increased risk of contamination. This water canalso be used for recharging ground aquifers after properfiltration.The rain water yield varies with the size and textureof the catchment area. A smooth, cleaner and moreimprovised roofing material contributes to better water qualityand greater quantity with higher value of runoff coefficient.(refer table 1.3 for runoff coefficient)When roof of the house is used as the catchment forcollecting the rain water, the type of roofand theconstruction material affect the runoff coefficient and qualityof collected water.Roofs made of RCC, GI sheets,corrugated sheets, tiles etc. are preferable for roof topcollection. But thatched roofs are not preferred as these addcolour and dissolved impurities to water. Water to be usedfor drinking purpose should not be collected from roof withdamaged AC sheets or from roofs covered with asphalt andlead flashing or lead based paints as the lead contaminationmay occur in the collected water.2.2.2Coarse mesh / leaf screenTo prevent the entry of leaves and other debris in thesystem, the coarse mesh should be provided at the mouth ofinflow pipe for flat roofs as shown in Fig. 2.4.12
CoarsemeshFig. 2.4 Coarse meshFor slope in roofs where gutters are provided to collectand divert the rain water to downspout or conduits, the guttersshould have a continuous leaf screen, made of ¼ inch wire meshin a metal frame, installed along their entire length, and a screenor wire basket at the head of the downspout.( Fig. 2.5)GUTTERCONTINIOUSLEAF SCREENCOARSEMESHFILTERDOWNTAKE PIPEFOR STORAGE TANKFig. 2.5 Leaf screen13STORAGETANK
2.2.3GutterGutter is required to be used for collecting water fromsloping roof and to divert it to downspout. These are the channelsall around the edge of a sloping roof to collect and transport rainwater to the sto
certain industries for which pure water is a requirement. Thus, industries such as computer microchip manufacturing and photographic processing would certainly benefit from this source of water. 1.3 Rain water harvesting For our water requirement we entirely depend upon riv
water harvesting and conservation. Water harvesting techniques gather water from an area termed the ‘catchment area’ and channel it to the cropping area or wherever it is required. Conservation techniques conserve water within the biomass and the soil by reducing run-off and keeping the
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