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Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,*,CE 394K.2 Hydrology,Infiltration,Reading AH Sec 5.1 to 5.5,Some of the subsequent slides were prepared by Venkatesh Merwade,1,Darcys Law,K,= hydraulic conductivity,q,= specific discharge,V,=,q/n,= average velocity through the area,2,Richards Equation,Recall,Darcys Law,Total head,So Darcy becomes,Continuity becomes,Soil water diffusivity,3,Infiltration,General,Process of water penetrating from ground into soil,Factors affecting,Condition of soil surface, vegetative cover, soil properties, hydraulic conductivity, antecedent soil moisture,Four zones,Saturated, transmission, wetting, and wetting front,depth,Wetting Zone,Transmission,Zone,Transition Zone,Saturation Zone,Wetting Front,q,4,Philips Equation,Recall Richards Equation,Assume K and D are functions of,q, not,z,Solution,Two terms represent effects of,Suction head,Gravity head,S Sorptivity,Function of soil suction potential,Found from experiment,5,Infiltration into a horizontal soil column,x,0, = ,n,for t = 0, x 0, = ,o,for x = 0, t,0,Equation:,Boundary conditions,6,Measurement of Diffusivity by Evaporation from Soil Cores,Air stream,q = soil water flux = evaporation rate,q,x,7,Measurement of Diffusivity by Evaporation from Soil Cores,8,Numerical Solution of Richards Equation,(Ernest To),9,Implicit Numerical Solution of Richards Equation,x (i),t (j),i-1 i i+1,j,j -1,10,Implicit Numerical Solution of Richards Equation,11,Matrix solution of the equations,12,13,f,14,F,15,Definitions,solid,Pore with,air,Pore with,water,Element of soil, V,(Saturated),Element of soil, V,(Unsaturated),16,Infiltration,Infiltration rate,Rate at which water enters the soil at the surface (in/hr or cm/hr),Cumulative infiltration,Accumulated depth of water infiltrating during given time period,17,Infiltration Methods,Horton and Phillips,Infiltration models developed as,approximate solutions,of an,exact theory,(Richards Equation),Green Ampt,Infiltration model developed from an,approximate theory,to an,exact solution,18,Hortonian Infiltration,Recall Richards Equation,Assume K and D are constants, not a function of,q,or,z,Solve for moisture diffusion at surface,f,0,initial infiltration rate,f,c,is constant rate and k is decay constant,19,Hortonian Infiltration,20,Philips Equation,Recall Richards Equation,Assume K and D are functions of,q, not,z,Solution,Two terms represent effects of,Suction head,Gravity head,S Sorptivity,Function of soil suction potential,Found from experiment,21,Green Ampt Infiltration,Wetted Zone,Wetting Front,Ponded Water,Ground Surface,Dry Soil,22,Green Ampt Infiltration (Cont.),Apply finite difference to the derivative, between,Ground surface,Wetting front,Wetted Zone,Wetting Front,Ground Surface,Dry Soil,23,Green Ampt Infiltration (Cont.),Wetted Zone,Wetting Front,Ground Surface,Dry Soil,Integrate,Evaluate the constant of integration,24,Green Ampt Infiltration (Cont.),Wetted Zone,Wetting Front,Ground Surface,Dry Soil,See:,Nonlinear equation, requiring iterative solution.,25,Soil Parameters,Green-Ampt model requires,Hydraulic conductivity, Porosity, Wetting Front Suction Head,Brooks and Corey,Effective saturation,Effective porosity,26,Ponding time,Elapsed time between the time rainfall begins and the time water begins to pond on the soil surface (,t,p,),27,Ponding Time,Up to the time of ponding, all rainfall has infiltrated (,i,= rainfall rate),Potential,Infiltration,Actual Infiltration,Rainfall,Accumulated,Rainfall,Infiltration,Time,Time,Infiltration rate,f,Cumulative,Infiltration,F,28,Example,Silty-Loam soil, 30% effective saturation, rainfall 5 cm/hr intensity,29,
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