Simulation of surface runoff using hydrodynamic model

A two-dimensional hydrodynamic model, named CHRE2D, is developed for simulating surface runoff in watershed. The model is based on the solution to shallow water equations (SWEs) using the Godunov-type finite volume method. The novelty of the model is a stable and accurate algorithm to calculate flow velocities in cells of very shallow flow depth. Stability analysis shows that the friction terms in the momentum equations are stiff when flow depth is very small (e.g., 10^-3 m). In this study, the velocities in those cells are calculated by the diffusion wave approximation (DWA). This leads to a perfect balance between the surface gradient and the friction terms and prevents the occurrence of stiffness. Furthermore, the model possesses the well-balance property for both overland and channel flow. This allows the use of the original digital elevation model (DEM) data without removing topographic depressions. The model has been tested and verified by three experimental and one field cases including the rapidly varied dam-break flow and the sheet flood in arid regions. Simulated flow depth, velocity, and discharge hydrographs were compared with available measurements in two experimental testing cases. Since the resolution of the DEM significantly affects the modeling results of flow depth for field applications, only the simulated hydrograph was compared with the observation. The simulated results demonstrate that the model is highly capable of simulating both hydrodynamic and hydrological flow processes.