Modeling Saturated‐Unsaturated Water Flow in Soils

Abstract

A model for the transient one‐dimensional water movement in the saturated‐unsaturated zone using a finite difference method with stochastic inputs is developed. Hysteresis in the soil water retention and hydraulic conductivity‐ versus‐moisture content relationship is incorporated. The model considers layered geologic formations with each layer having different parameters. Monte Carlo simulation, together with the nearest neighbor model, is used to incorporate the stochastic nature of hydraulic conductivity into the flow model. Outputs of the flow model include pressure head, water content, and the watertable elevation. Two Monte Carlo simulations of 100 realizations each are made for a 12‐day simulation period. Input standard deviations of the log saturated hydraulic conductivity are assumed to be 20% and 40% of the mean of log saturated conductivity for the two Monte Carlo runs, respectively. The standard deviations of the water‐table elevation and pressure head increase with an increase in the standard deviation of log saturated hydraulic conductivity. The model is applied to predict a long‐term water‐table fluctuation, and the predicted water table agrees well with the observed one.