Comparing Depth-Integrated Models to Compute Overland Flow in Steep-Sloped Watersheds

On steep-sloped watersheds, high-intensity, short-duration rainfall events are the leading causes of flash floods. Typical overland flow analysis assumes sheet-like flow with a shallow water depth. However, the natural creek beds in steep watersheds produce complex and intense flows with a shallow depth and high velocity. According to the hydrodynamical modeling processes for open channel turbulent flow, calculating rainfall-induced overland flow becomes a complex task. Steep topography requires a highly refined numerical mesh, which demands a more complex simulation process. Depth-integrated models with distributed parameters provide useful methods to capture the behavior of steep watersheds. This study investigates the watershed’s overland flow behavior by varying turbulent flow parameters and monitoring possible model errors. The refined modeling places a heavy demand on numerical solvers used for simulating the overland flow motion. This paper examines different depth-integrated model solvers applied to artificial watersheds and compares results produced by the different solver types. This study found that the Shallow Water Equation solutions produced the most consistent and stable results, with the Local Inertia Approximation solutions performing adequately. Adding Large Eddy Simulation to these solutions tended to overcomplicate Shallow Water solutions but generally improved Large Eddy solutions. The Diffuse Wave Equation solutions produced erratic results, losing stability and accuracy as watershed slopes steepened and flow paths became complex.