Techniques of Rain Water Harvesting to Increase Ground Water Levels - Free Essay Example

Sample details Pages: 3 Words: 1038 Downloads: 8 Date added: 2017/09/12 Category Advertising Essay Did you like this example? RAIN WATER HARVESTING AND ARTIFICIAL RECHARGE OF GROUND WATER RAJASTHAN CONTEXT by Dr. S. K. GUPTA Scientist ‘D’ Central Ground Water Board Western Region, Jaipur Rain water harvesting and Artificial recharge of ground water Rainwater harvesting is the technique of collection and storage of rain water at surface or in subsurface aquifer, before it is lost as surface run off or as evaporation. The artificial recharge to ground water is a process by which the ground water reservoir is augmented at a rate exceeding that under natural conditions of replenishment utilizing suitable civil construction techniques. IdentificationofArea Basic requirements for artificial recharge of ground water are: †¢Availability of non-committed surplus monsoon run off in space and time. †¢Identification of suitable hydrogeological environment and sites for creating sub-surface reservoir through cost-effective artificial recharge techniques. †¢Areas where availability of ground water is inadequate in lean months. †¢Areas where groundwater levels are declining on regular basis. †¢Areas where salinity ingress is taking place. ScientificInputs ?Hydrometeorological Studies ?Hydrological Studies ?Soil Infiltration Studies ?Hydrogeological Studies ?Geophysical Studies Chemical Quality of Source Water Assessment of sub-surfacestoragespacefor artificialrechargeofgroundwater Thesubsurfacestoragespaceforartificial recharge in terms of volume of water which can be accommodatedisestimatedbytakingintoaccount theareaofpotential zone, depthtowaterbelow3m groundlevelandspecificyieldoftheformation. RAINFALL †¢149 TO 1 141MM †¢DECREASES NW †¢ERRATIC †¢DROUGHTS Similartothevariationsinhydrogeologicalframework, theartificial rechargetechniquestoovarywidely. The artificial recharge techniques can be broadly categorisedasfollows: A. Directsurfacetechniques †¢Flooding †¢Basinsorpercolationtanks †¢Streamaugmentation Ditchandfurrowsystem †¢Overirrigation ArtificialRechargeTechniques B. Directsubsurfacetechniques †¢Injectionwellorrechargewell †¢Rechargepitandshaft †¢Dugwellrecharge †¢Boreholeflooding †¢Naturalopenings,cavityfillings C. Combinationsurfacesub-surfacetechniques †¢Basinorpercolationtankswithpitshaftorwells. D. IndirectTechniques †¢Inducedrechargefromsurfacewatersource †¢Aquifermodification Inareaswithundulating topography, water from stream or canal is divertedtoshallow, flat bottomed and closely spaced ditches or furrows to provide maximumwater contact area for recharge. The water contact area seldom exceeds 10 percen t of the total echargearea. Generally three patterns of ditch andfurrowsystemare adopted. Lateral Ditch Pattern DendriticPattern Contour Pattern Ditch and Furrow Method SiteCharacteristicsandDesignGuidelines (a) Althoughthis methodis adaptable toirregular terrain. thewatercontact areaseldomexceeds10 percentofthetotalrechargearea. (b) Ditchesshouldhaveslopetomaintainflowvelocity andminimumdepositionofsediments. (c) Ditches should be shallow, flat-bottomed, and closelyspacedtoobtainmaximumwatercontact area. Widthof0. 3to1. 8m. aretypical. (d) Acollectingditchtoconveytheexcesswaterback tothemainstreamchannelshouldbeprovided. Don’t waste time! Our writers will create an original "Techniques of Rain Water Harvesting to Increase Ground Water Levels" essay for you Create order PercolationTanks(PT)/SpreadingBasin †¢ThesearethemostprevalentstructuresinRajasthan asameasuretorechargethegroundwaterreservoir bothinalluvialaswellasinhardrockformations. †¢Percolationtanksbenormallyconstructedonsecond tothirdorderstreamsincethecatchmentsoalsothe submergenceareawouldbesmaller. †¢Thesubmergenceareashouldbeinuncultivableland asfaraspossible. †¢Percolationtankbelocatedonhighlyfracturedand weathered rock for speedy recharge. In case of alluvium,thebouldaryformationsareidealforlocating PercolationTanks. †¢Thebenefittedareashouldhavesufficient numberof wellsandcultivablelandtodeveloptherechargewater. Detailedhydrologicalstudiesforrunoffassessmentbe doneanddesigncapacityshouldnotnormallybemore than50%oftotalquantumofrainfallincatchment. Check Dam, Cement Plug, Nala Bund Aseriesof small bundsare made across selectednala sectionssuchthat theflow of surface water in the streamchannel isimpeded and water is retained on pervioussoil/rocksurfacefor longe r period. Nala bunds are constructed across biggernalasofsecondorder streams in areas having gentler slopes. Analabund actslikeamini percolation tank. Horizontal Section of Nala Bund Vertical Section of Nala Bund †¢Thetotal catchment of thenalashouldnormallybe between40to100Hectares. The rainfall in the catchment should be 1000 mm/annum. †¢Thewidthofnalabedshouldbebetween5and15m andthedepthofbedshouldnotbelessthanImetre. †¢Thelandsdownstreamof CheckDam/Bundshould haveirrigablelandunderwellirrigation. †¢Therockstrataexposedinthepondedareashouldbe adequatelypermeabletocausegroundwaterrecharge. †¢Normallythefinal dimensionsof theNalabundare: length10to15m,height2to3mandwidthIto3m. Site Characteristic and Design Guidelines This is constructed across small streamto conserve streamflowswithpractically no submergence beyond streamcourse. Theboulders locallyavailablearestoredin asteelwire. Theheightofsuchstructures s around 0. 5 mand is normallyusedinthestreams with widthof about 10to15 m. The cost of such structures is around Rs. 10000toRs. 15000. The excesswater overflowsthis structurestoringsomewater to serve as source of recharge. Gabion Structure Inalluvial aswell asinhardrock areas, therearethousandsof dug wells which can be used as structuresforartificial rechargeof groundwater. Stormwater, tank water, canal water etc. can be divertedintothese structures to directlyrechargethedriedaquifer. The recharge water is guided throughapipetobottomof well belowthe water level to avoid scoringof bottomandentrapment ofair-bubblesintheaquifer. Dug Well Recharge Recharge through Dug Well ?Tobedugmanuallyifthestrataisofnon-caving nature. ?Ifthestrataiscaving,properpermeableliningin theformofopenwork, boulderliningshouldbe provided. ?Thediameterof shaft shouldnormallybemore than2mtoaccommodatemorewater. ?Intheareaswheresourcewaterishavingsilt,the shaft shouldbefilledwithboulder, gravel and sandfrombottomtohaveinvertedfilter. ?Theinjectionpipeshouldbeloweredbelowthe waterleveltoavoidthis. Recharge Shaft Recharge through Shaft Vertical Recharge Shaft a. Without injection well ?Ideallysuitedforwaterlevels(upto25mbgl) ?Effectiveintheareasoflessverticalnaturalrecharge. Copiouswateravailablecanbeeffectivelyrecharged. ?Effectivewithsilt water also(usinginvertedfilter consistingoflayersofsand,gravelandboulder) ?Therateofrechargewithinvertedfilterrangesfrom7- 14Ipsfor2-3meterdiameter. b. With injection well Inthistechniqueat thebottomof rechargeshaft a injectionwell of100-150mmdiameterisconstructed piercingthroughthelayersofimpermeabl ehorizonto thepotential aquiferstoberechargedabout 3to5 meterbelowthewaterlevel. †¢Ideallysuitablefordeepwaterlevels(25m). †¢Aquiferisoverlainbyimperviousthickclaybeds. †¢Injectionwellcanbewithorwithoutassembly. †¢TheInjectionwellwithassemblyshouldhavescreen nthepotentialaquiferatleast3-5mbelowthewater level. †¢Theinjectionwell without assemblyisfilledwith graveltoprovidehydrauliccontinuitysothatwateris directlyrechargedintotheaquifer. ?The injectionwell without assemblyis verycost- effective. ?Theefficiencyisveryhighandrateofrechargegoes evenupto151psatcertainplaces. Vertical Shaft with Injection Well Rainwater Harvesting Structure, Collectorate Building, Jaipur Lateral Recharge Shaft ?Ideally suited for areas where permeable sandy horizoniswithin3meter belowgroundlevel and continuesuptothewater level under unconfined conditions. ?Copiouswateravailablecanbeeasilyrechargeddue olargestorageandrechargepotential. ?Siltwatercanbeeasilyrecharged. ?2to3meterwidean d2to3meter deeptrenchisexcavated, length ofwhichdependsonthevolume ofwatertoberecharged. ?Withandwithoutinjectionwell. Theinjectionwellsareadvantageouswhenlandis scarce. Hydraulicallytheeffectivenessof inductionof waterininjectionwellisdeterminedby: (a) PumpingRate (b) Permeabilityofaquifer (c) Distancefromstream (d) Naturalgroundwatergradient (e) Typeofwell Artificial Recharge Through Injection Wells Inalluvialareasinjectionwellrechargingasingleaquifer ormultipleaquiferscanbeconstructedtonormal gravel packedpumpingwell. Aninjectionpipewithopening againsttheaquifertoberechargedmaybesufficient. However, in case of number of permeable zones separated by imperviousformations, a properly designed injection well with inlet pipeagainst eachaquifer toberechargedneedto be constructed. The injectionwellsasameans of artificial recharge are comparativelycostlierand require specialised techniques of tubewell construction and supported by operation and maintenance to protect therechargewell fromclogging. It is an indirect methodof artificial recharge involving pumping from aquifer hydraulically connected from surface water, toinducerechargeto hegroundwater reservoir. In such methods there is actuallynoartificial buildup of groundwaterstoragebut only passage of surface water tothepumpthrough anaquifer. Inthissense,itis more a pumpage augmentation rather than artificialrechargemeasure. Induced Recharge from Surface Water Source a. NaturalFlowb. Flowpatternwithpumpingwell Agroundwater damisasub-surfacebarrier across streamwhichretardsthenatural groundwaterflowof thesystemandstoreswaterbelowgroundsurfaceto meetthedemandsduringtheperiodofneed Ground Water Dams or Sub-Surface Dykes or UndergroundBandharas(UGB) Artificial Recharge Through Underground Bandhara Therooftoprainwatercanbeconservedandusedfor artificial recharge of groundwater. This approach requiresconnectingtheoutlet pipefromroof topto divertthewatertoeitherexistingwell/tubewell/borewell or specially designed wells. The urban housing complexesor institutional buildingshavelargeroof area and can be utilised for harvesting roof top rainwater torechargeaquifer. Threemost important componentswhichneedtobeevaluatedfordesigning therainwaterharvestingstructuresare: Roof Top Rain Water Harvesting ?Hydrogeologyofthearea ?Areacontributingforrunoff ?Hydrometeorologicalcharacters Recharge structures should be designed based on vailabilityofspace,availabilityofrunoff,depthtowater- tableandlithologyofthearea. AssessmentofRunoff Therunoff shouldbeassessedaccuratelyfordesigning therechargestructureandmaybeassessedbyfollowing formula: Runoff=catchmentareaxRunoffcoefficientxRainfall RunoffCoefficients Runoff coefficient playsanimportant roleinassessing therunoff availabilityandit dependsuponcat chment characteristics. Table-1showsavailabilityof rainwater throughrooftoprainwaterharvestingandtable-2shows generalvaluesofrunoffcoefficient. Design Criteria of Recharge Structures Recharge Pit ?Suitable for building having roof area of about 100 sq. etersinalluvial areaswhere depthtowaterlevelisshallow. ?Generallyof1-2mwideand2-3 mdeepwhicharebackfilled with boulders, gravels and sandfrombottomupwardwith 1-10. 5mthickness. Theshape of pit can be circular, rectangularorsquare. ?Therainwaterenteringthepit shouldbefreefromsilt, waste/ debris. ?Theupperhalfofthepitshould bekept enteringforcollecting rain water for artificial recharge. Recharge Trench ?Suitable for building having roofareaof200-300sq. mand where permeable strata is availableatshallowdepth. ?Ifmaybe0. 5to1mwide, 1to 1. 5mdeepand10to20mlong dependinguponavailabilityof watertoberecharge These are back filled with boulders, gravelsandcoarse sandfrombottomupward. ?Toplayer of sandshouldbe cleaned periodically to maintainre chargerate. Recharge through Hand Pump ?Suitableforbuildinghaving roofareaofabout150sqm. ?Abandoned/in use existing handpumpcanbe used. Therainwaterfromrooftop is channelised to hand pumpusingabout 100mm diameterpipe. ?Hand Pump in use is providedwithonewayvalve inthe rainwater pipe to prevententeringofairinthe liftingpipe of handpump duringpumping. ?Afilter pit isprovidedfor filteringsilt fromrainwater beforeenteringhand. Recharge through Dug well / Shaft / Tube well