Effective Green-Ampt Parameters for Two-Layered Soils

The Green-Ampt method is a physically based model for partitioning rainfall into surface runoff and infiltration. This method is widely used in infiltration practice because of its simplicity and the ease of obtaining the required hydraulic soil properties. The method assumes that the soil is homogeneous. This, however, limits its application to layered soils. In this paper, a simple procedure for applying the Green-Ampt method to two-layered soils was examined under both steady and unsteady rain. For a given design storm, the maximum saturated depth of the top layer was estimated and was used to identify whether the soil profile behaved as a single-layered or two-layered profile. For a two-layered soil profile, the overall effective Green-Ampt parameters were then estimated considering different parameters such as rainfall characteristics, the hydraulic properties of both layers, the thickness of the top layer, and the maximum saturated depth. The cumulative infiltrated volumes with effective Green-Ampt parameters were compared with MIKE SHE simulation results based on the Richards equation with two-layered soils for different layer thicknesses and rainfall hyetographs. The results showed that the proposed simple procedure for estimating the effective soil parameters using the Green-Ampt method showed a good agreement with that computed using the Richards equation in terms of the volume of infiltration water. This approach is expected to provide researchers and engineers a more practical tool in estimating infiltration in two-layered soils than what is presently available.