Application of the Green-Ampt Model to infiltration under time-dependent surface water depths

The performance of the Green-Ampt model for infiltration problems where the depth of water above the ground surface is varying with time is investigated. In order to yield infiltration rates that agree with those predicted by the Richards equation for flow in a homogeneous, nondeforming, and nonhysteretic soil the effective suction head parameter in the Green-Ampt model must be considered a function of time, surface water depth, initial moisture content, and soil type. However, when a constant value of the effective suction head is assumed, the response of the Green-Ampt model to variations in surface water depth is qualitatively equivalent to the response of the Richards model. The effectiveness of a number of definitions of the suction head parameter that have been proposed in the literature is investigated. While the differences in predicted infiltration rates and cumulative infiltration obtained by using the different definitions are, in general, of marginal significance, the best choice of the value of the effective suction head depends upon the particular problem to which the model is being applied.