Chapter4-环境水文学

March26,2009PrincipleofHydrology,BNU1Chapter4InfiltrationandGroundwaterProf.ZongxueXUMarch26,2009PrincipleofHydrology,BNU2Objective•Infiltrationmechanism•Groundwaterflow•Darcy’slawMarch26,2009PrincipleofHydrology,BNU3Infiltration•HortonLaw:–f:infiltrationrate–fc:infiltrationcapacity–fo:initialinfiltrationcapacity–k:constantktcceffff)(0March26,2009PrincipleofHydrology,BNU4InfiltrationCapacity•Factorstoaffectinfiltrationprocess–Slopeuptoalimitingvalue–Initialmoisturecontent–RainfallintensityMarch26,2009PrincipleofHydrology,BNU5MethodstoEstimateInfiltrationCapacity•Φ-indexmethod–Definition:Theaveragerainfallintensityabovewhichthevolumeofrainfallequalsthevolumeofrunoff–Mainproblem:withoutconsideringthevariationinfwithtimeMarch26,2009PrincipleofHydrology,BNU6SoilMoisture•Antecedentprecipitationindex–USA•Soilmoisturedeficit–UKMarch26,2009PrincipleofHydrology,BNU7AntecedentPrecipitationIndex•Basicassumption–Soilmoistureisdepletedatarateproportionaltotheamountinstorageinthesoil•Basicequation–I0:initialvalueofindex–It:indexvalueattimet–K:arecessionconstantwithavaluebetween0.85and0.98ttKII0March26,2009PrincipleofHydrology,BNU8SoilMoistureDeficit(SMD)•Evapotranspirationoccurs•Soilmoisturedeficit•Soilmoisturedeficit∝(Antecedentprecipitation)-1•Soilmoisturedeficit∝(Runoff)-1March26,2009PrincipleofHydrology,BNU9CatchementWetnessIndex(CWI)•Catchmentwetnessindex(CWI):SMDAPICWI5125544332215.05.05.05.05.05dddddPPPPPAPIMarch26,2009PrincipleofHydrology,BNU10Groundwater•Definition:Rainfallthatinfiltratesthesoilandpenetratestotheunderlyingstrata•Factorsaffectinggroundwater–Theliquid–densityandviscosity–Themediathroughwhichtheliquidmoves–TheboundaryconditionsMarch26,2009PrincipleofHydrology,BNU11SeveralDefinitions•Viscosity:–Ameasureoftheshearstrengthofaliquid•Kinematicviscosity:–Theratioofabsoluteviscositytodensity•Porosity–TheratiooftotalvoidstothetotalvolumeofsoilMarch26,2009PrincipleofHydrology,BNU12Darcy’sLaw•Basicassumptions:–Thematerialishomogeneousandisotropic–Thereisnocapillaryzone,–ThereisasteadystateofflowMarch26,2009PrincipleofHydrology,BNU13Darcy’sLaw•i:Hydraulicgradient•A:Area•K:PermeabilitycoefficientkAiQMarch26,2009PrincipleofHydrology,BNU14March26,2009PrincipleofHydrology,BNU15