Infiltration analysis in unsaturated soil slopes

This paper describes a simple model which can be used to estimate the time needed for a wetting front to develop in an unsaturated soil slope. The model is an extended form of the traditional Green-Ampt method. The first extension recognises that ponding of water cannot occur on a soil slope. It further allows the user to indirectly account for antecedent rainfall conditions by separating slopes into two categories depending on their initial suction profiles. In the first category, where the initial suctions are large, the rate of the development of the wetting front depth is controlled by the rainfall intensity. In the second, where the initial suction is low, the time taken for a wetting front to develop to a given depth depends on the infiltration capacity of the soil. In the final section of the paper results from the new model are compared to numerical predictions of wetting front depth in a fine sand slope.