Simulation of ground-water flow in steep basin with shallow surface soil

A coupled groundwater-channel flow distributed model has been developed for the continuous simulation in a 123 km2 basin. The aim was to analyze the streamflow generation processes in natural vegetated environments. Finite difference schemes have been used in order to solve conservation equations of the 2-D saturated subsurface flow and the 1-D kinematic surface flow. Because of the high hydraulic conductivity of the surface soil, only the “saturation excess” mechanism of runoff production has been considered. Parameter sensitivity analysis showed the overriding influence of soil storage capacity and conductivity. A grid discretization greater than 100 m produces hydraulic conductivity greater than physically meaningful, which considerably increases as the space-grid step increases. Results indicate that the model can satisfactorily simulate the hydrologic behavior of the catchment after fitting the three parameters of surface hydraulic conductivity, effective porosity, and evapotranspiration losses. These are done after calculating the conductivity as a function of the height of the water table. The simulation efficiency has varied from 87% in the first five-year calibration period to 85.8% in the subsequent five-year validation period.