A conceptual model for infiltration and redistribution in crusted soils

Treating the crust as a single layer, a simplified but accurate infiltration and redistribution model for a crust-topped soil profile is developed. The method is an extension of an earlier infiltration and redistribution model for homogeneous soil profiles. The crust is conceptually subdivided into regions associated with surface water content and interface water content, respectively. The extension of the wetting front into the subsoil is described by the homogeneous soil method described earlier. Two ordinary differential equations are written which match pressure heads and fluxes at the soil interface and are solved by a Runge-Kutta technique. The model is tested against the results of the Richards equation with variations in the key variables of capillary lenght scale and saturated hydraulic conductivity for both soil and crust and for cases where ponding occurs both in the crust region and after wetting has entered the subsoil region. In all cases the profile water contents and infiltration rates are very reasonably simulated.