Physically-based distributed model for coupled surface runoff and subsurface flow simulation at the catchment scale

The interactions between surface and subsurface hydrologic processes are important in many waterresource applications and require modeling approaches capable of treating these processes in an integrated manner. We describe a distributed, physically-based model that couples a three-dimensional subsurface flow module to a DEM-based one-dimensional surface routing module and resolves in a detailed manner the exchange of flux and head information between the two regimes. The coupled model can treat flow in saturated and variably saturated porous media, surface runoff, channel flow, and storage in lakes and other topographic depressions. The algorithm that handles the exchange between the surface and subsurface components is described in detail, and an illustrative test case is presented.