STOCHASTIC MODELING OF LARGE-SCALE FLOW IN HETEROGENEOUS UNSATURATED SOILS

A simulation experiment is used to test the stochastic theory of unsaturated flow proposed by Mantoglou and Gelhar (1987a, b, c). Tension means and variances derived from this theory are compared to tension distributions obtained from a detailed three-dimensional model developed by Ababou (1988). The synthetically generated unsaturated hydraulic conductivity functions used in the detailed model vary significantly over relatively small distances. Results from a simulated infiltration event indicate that the stochastic theory's predictions reproduce the overall trend of the heterogeneous tension distribution. Deviations from the predicted mean generally lie within confidence intervals derived from the predicted variance. The stochastic theory predicts less vertical moisture movement and somewhat more horizontal spreading than a comparable deterministic analysis. This reflects the fact that the effective hydraulic conductivity function used in the stochastic approach is anisotropic. The magnitude of this anisotropy increases with increasing tension.