Chapter4-环境水文学

1、March 26, 2009,Principle of Hydrology, BNU,1,Chapter 4 Infiltration and Groundwater,Prof. Zongxue XU,March 26, 2009,Principle of Hydrology, BNU,2,Objective,Infiltration mechanism Groundwater flow Darcys law,March 26, 2009,Principle of Hydrology, BNU,3,Infiltration,Horton Law: f: infiltration rate fc

2、: infiltration capacity fo: initial infiltration capacity k: constant,March 26, 2009,Principle of Hydrology, BNU,4,Infiltration Capacity,Factors to affect infiltration process Slope up to a limiting value Initial moisture content Rainfall intensity,March 26, 2009,Principle of Hydrology, BNU,5,Method

3、s to Estimate Infiltration Capacity,-index method Definition: The average rainfall intensity above which the volume of rainfall equals the volume of runoff Main problem: without considering the variation in f with time,March 26, 2009,Principle of Hydrology, BNU,6,Soil Moisture,Antecedent precipitati

4、on index USA Soil moisture deficit UK,March 26, 2009,Principle of Hydrology, BNU,7,Antecedent Precipitation Index,Basic assumption Soil moisture is depleted at a rate proportional to the amount in storage in the soil Basic equation I0: initial value of index It: index value at time t K: a recession

5、constant with a value between 0.85 and 0.98,March 26, 2009,Principle of Hydrology, BNU,8,Soil Moisture Deficit (SMD),Evapotranspiration occurs Soil moisture deficit Soil moisture deficit (Antecedent precipitation)-1 Soil moisture deficit (Runoff)-1,March 26, 2009,Principle of Hydrology, BNU,9,Catche

6、ment Wetness Index (CWI),Catchment wetness index (CWI):,March 26, 2009,Principle of Hydrology, BNU,10,Groundwater,Definition: Rainfall that infiltrates the soil and penetrates to the underlying strata Factors affecting groundwater The liquid density and viscosity The media through which the liquid m

7、oves The boundary conditions,March 26, 2009,Principle of Hydrology, BNU,11,Several Definitions,Viscosity: A measure of the shear strength of a liquid Kinematic viscosity: The ratio of absolute viscosity to density Porosity The ratio of total voids to the total volume of soil,March 26, 2009,Principle of Hydrology, BNU,12,Darcys Law,Basic assumptions: The material is homogeneous and isotropic There is no capillary zone, There is a steady state of flow,March 26, 2009,Principle of Hydrology, BNU,13,Darcys Law,i: Hydraulic gradient A: Area K: Permeability coefficient,March 26, 20