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1、UndergroundwaterOfalltheearthswater97%isfoundintheoceans2%inglaciersonly1%onl.Ofthis1%almostall(97%)isfoundbeneaththesurfacecalledsubsurfaceundergroundwater.Mostofthiswatereventuallyfindsitswaybacktotheseaeitherbyundergr

2、oundmovementbyrisingintosurfacestreamslakes.Thesevastundergroundwaterdepositsprovidemuchneededmoisturefdryareasirrigateddistricts.Undergroundwateractsinsimilarwaystosurfacewateralsoperfminggeomphicwkasanagentofgradation.

3、Eventhoughmanhasbeenawareofsubsurfacewatersinceearliesttimesitsnatureoccurrencemovementgeomphicsignificancehaveremainedobscure.Recentlyhoweversomeanswershavebeenfoundtotheperplexingquestionsaboutundergroundwatersrelation

4、shiptothehydrologicalcycle.1.SourceofUndergroundWaterSincethedaysofVitruviusatthetimeofChristmanytheieshavebeenpresentedtoexplainthelargevolumeofwaterunderneaththeearthssurface.Onetheywasthatonlytheseacouldprovidesuchlar

5、gequantitiesthewatermovingundergroundfromcoastalareas.Vitruviuswasthefirsttorecognizethatprecipitationprovidedthemainsourceofsubsurfacewateralthoughhisexplanationsofthemechanicsinvolvedwerenotveryscientific.Histheynowfir

6、mlyestablishedistermedtheinfiltrationtheystatesthatundergroundwateristheresultofwaterseepingdownwardsfromthesurfaceeitherdirectlyfromprecipatationindirectlyfromstreamslakes.Thisfmofwateristermedmeteic.Averysmallproptiono

7、fthetotalvolumeofsubsurfacewaterisderivedfromothersources.Connatewateristhatwhichistrappedinsedimentarybedsduringtheirtimeoffmation.Juvenilewateriswateraddedtothecrustbydiastrophiccausesataconsiderabledepthanexamplebeing

8、volcanicwater.2DistributionofSubsurfaceWaterDuringprecipitationwaterinfiltratesintotheground.Undertheinfluenceofgravitythiswatertravelsdownwardsthroughtheminutepespacesbetweenthemit(3)CapillaryFringeImmediatelyabovethewa

9、tertableisaveryshallowzoneofwaterwhichhasbeendrawnupwardsfromthegroundwaterreservoirbelowbycapillaryfce.Thedepthofthiszonedependsentirelyonsoiltexturesoilswithminutepespacesbeingabletoattractmewaterfrombelowthansoilswith

10、largepespaces.Inthelattertypesofsoilthemolecularfcesarenotabietospanthegapsbetweensoilparticles.Thussy~ilsseldomexhibitanextensivecapillaryfringemergingfromsoilwaterthroughtothezoneofsaturation.(b)ZoneofSaturationThezone

11、ofsaturationistheareaofsoilrockwhosepespacesarecompletelyfilledwithwaterwhichisentirelydevoidofsoilair.Thiszoneistechnicallytermedgroundwatereventhoughthetermbroadlyincludeswaterinthezoneofaeration.Theupperlimitofthezone

12、ofsaturationisthewatertablephreaticsurface.Itisdifficulttoknowhowdeepthegroundwaterzoneextends.Althoughmostgroundwaterisfoundintheupperthreekmofthecrustpespacescapableofwaterretentionextendtoadepthof16km.Thisappearstobet

13、heupperlimitOfthezoneorockflowagewherepressuresaresogreatthattheycloseanyinterstitialspaces.Theupperlevelofthesaturatedzonecanbecompletelyplottedbydiggingwellsatvariousplaces.Studiessuggesttwoquiteinterestingpoints.(i)Th

14、ewatertablelevelishighestunderthehighestpartsofthesurfacelowestunderthelowestpartsofthesurface.Hillsmountainshaveahigherlevelphreatiesurfacethanvalleyslakes.Thereasonfthisisthatwatercontinuallypercolatingthroughthezoneof

15、aerationliftsthewatertablewhileseepagefromthegroundwaterzoneintocreekslakeslowersthelevel.(2)Thedepthofthe“WatertableDeiowthelsurfaceisgreatestinuplareaswherethewatermovesquitefreelydownhillundergravity.Closetostreamslak

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