Influence of Unsaturated Hydraulic Properties on Infiltration from Circular Surface Areas

The effects and interactive effects on infiltration of parameters in the Brooks-Corey equation for defining the hydraulic properties of unsaturated soils are investigated by analyzing the results of numerical solutions of the unsaturated flow characteristics resulting from water applied on a circular surface area. The soil parameters are allowed to vary continuously as a function of depth. The parameters that have been allowed to vary separately and in pairs are: (1) The pore size distribution exponent, (2) Pb- The bubbling pressure, (3) Sr- The residual saturation, (4) n- The soil porosity and (5) Ko- The saturated hydraulic conductivity. The conclusions are: (1) heterogeneity of the soil defined by allowing any parameter to vary with depth has a significant effect on all infiltration characteristics, (2) there is a minor to insignificant interaction between the soil parameters, and (3) the additive law of effect can be used to determine the composite effect of several soil parameters varying simultaneously

Unsaturated Transient Flow Through Heterogeneous Soils: Numerical Solutions and Analyses of Three-dimensional Axisymmetric Flows

This study deals with unsaturated, unsteady water movement through hetergeneous porous media. The specific problem investigated is the transient three-dimensional sxisymmetric flow resulting from water being applied on a horizontal circular area. The heterogeneity of the soil is described by allowing any or all of the five parameters in the Brooks-Corey equations to be any continuous function of depth. Methodologies for obtaining numerical solutions to the resulting nonlinear partial differential equation and its associated initial-boundary value problem have been developed an dimplemented in a computer program. The numerical solution is based on the Crank-Nicolson method of finite differencing and the solution to the resulting system of non-linear algebraic equations for each time step is by the Newton method combined with the line successive over-relaxation (LSOR) method. The numerical solutions provide the follwoing at each time step used: (1) the distribution of soil water saturation throughout the region, (2) the distribution of capillary pressure throuout the region, (3) the distribution of hydraulic head throughout the region, (4) the rate of infiltration if the area of application is specified at a given moisture level, (5) the extent and amount of lateral and vertical water movement, and (6) the rate of advance position of the wetting front. The solutions resulting from various variations of linearly specified heterogeneities have been studied and their influence of such quantitites are infiltration rate or intake capacities and wetting front movement, have been analyzed. To determine the effects of lateral water movement, solution results from the axisymmetric solutions have been compared with solutions from a one-dimensional vertical flow model that permitted the same specification of heterogeneity. A number of graphs are presented that illustrate influences of different soil hetergeneities. Coaxial graphs were developed to summarize the results of a number of solutions that relate the different in infiltration in hetergeneous and homogeneous soils to the variations of the five parameters in the Brooks-Corey equations. The numerical solutiosn are verified with reasonable agreement with field data at the Reynolds Creek experimental watershed obtained from experiments which duplicate the geometry of the mathematical model clostely, if not the heterogeneity, also