One‐dimensional steady state infiltration in heterogeneous soils

The effects of heterogeneity on one‐dimensional, steady state infiltration are studied using numerical simulations where the soil hydrologic properties are assumed to be spatial stochastic processes. Analytical solutions to one‐dimensional, steady state infiltration in heterogeneous soils are developed and applied to the stochastic random fields. The effects of spatial variability of parameters of an exponential unsaturated hydraulic conductivity model on the soil‐water pressure profiles are examined. The amount of variation in pressure heads is found to vary with infiltration rates and mean pressure heads, while the cross‐correlation between parameters is shown to have important influences on the value of the head variance. An inverse procedure is developed to determine the effective hydraulic conductivity parameters. The effective parameter is found to vary with mean pressures. Effective hydraulic conductivities and pressure head variances estimated from the numerical simulations were compared with those obtained from a spectral method by Yeh et al. (1985a, b, c). A unit mean gradient approach was used to estimate the effective unsaturated hydraulic conductivity, and the result shows that this approach is adequate for heterogeneous soils.