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1、GROUNDWATERFLOWMODELSC.P.KumarScientist‘E1’NationalInstituteofHydrologyRoorkee–247667(Uttaranchal)1.0INTRODUCTIONTheuseofgroundwatermodelsisprevalentinthefieldofenvironmentalscience.Modelshavebeenappliedtoinvestigateawidevarietyofhydrogeologicconditions.Morerecently,groundw
2、atermodelsarebeingappliedtopredictthetransportofcontaminantsforriskevaluation.Ingeneral,modelsareconceptualdescriptionsorapproximationsthatdescribephysicalsystemsusingmathematicalequations;theyarenotexactdescriptionsofphysicalsystemsorprocesses.Bymathematicallyrepresentinga
3、simplifiedversionofahydrogeologicalsystem,reasonablealternativescenarioscanbepredicted,tested,andcompared.Theapplicabilityorusefulnessofamodeldependsonhowcloselythemathematicalequationsapproximatethephysicalsystembeingmodeled.Inordertoevaluatetheapplicabilityorusefulnessofa
4、model,itisnecessarytohaveathoroughunderstandingofthephysicalsystemandtheassumptionsembeddedinthederivationofthemathematicalequations.Groundwatermodelsdescribethegroundwaterflowandtransportprocessesusingmathematicalequationsbasedoncertainsimplifyingassumptions.Theseassumptio
5、nstypicallyinvolvethedirectionofflow,geometryoftheaquifer,theheterogeneityoranisotropyofsedimentsorbedrockwithintheaquifer,thecontaminanttransportmechanismsandchemicalreactions.Becauseofthesimplifyingassumptionsembeddedinthemathematicalequationsandthemanyuncertaintiesinthev
6、aluesofdatarequiredbythemodel,amodelmustbeviewedasanapproximationandnotanexactduplicationoffieldconditions.Groundwatermodels,however,evenasapproximations,areausefulinvestigationtoolthatgroundwaterhydrologistsmayuseforanumberofapplications.Applicationofexistinggroundwatermod
7、elsincludewaterbalance(intermsofwaterquantity),gainingknowledgeaboutthequantitativeaspectsoftheunsaturatedzone,simulatingofwaterflowandchemicalmigrationinthesaturatedzoneincludingriver-groundwaterrelations,assessingtheimpactofchangesofthegroundwaterregimeontheenvironment,se
8、ttingup/optimisingmonitoringnetworks,andsettingupgroundwaterprotectionzones.Themod
