A seepage face model for the interaction of shallow water tables with the ground surface: Application of the obstacle-type method

This paper presents a model to simulate overland flow genesis induced by shallow water table movements in hillslopes. Variably saturated subsurface flows are governed by the Richards equation discretized by continuous finite elements on unstructured meshes. An obstacle-type formulation is used to determine where saturation conditions, and thus seepage face conditions, are met at the ground surface. The impact of hillslope geometry, boundary conditions, and soil hydraulic parameters on model predictions is investigated on two-dimensional test cases at the metric and hectometric scales. The obstacle-type formulation is also compared with a more detailed model coupling subsurface and overland flow, the latter being described by the shallow water equations in the diffusive wave regime.