Simulazione in continuo dei processi idrologici in un ripido bacino naturale con suoli poco profondi

A coupled groundwater-channel flow distributed model has been developed for the continuous simulation of the basic hydrologic processes in a 123 km2 steep basin with shallow surface soil. The aim was to analyze and simulate the streamflow generation processes at the basin scale in natural vegetated environments. Finite difference schemes have been used in order to solve conservation equations of both the 2-D saturated subsurface flow and of the 1-D kinematic surface flow in the channel network extracted from the Digital Elevation Model (DEM). Taking into account inadequate knowledge of space distribution of soil and climatic parameters at the basin scale, the model has been developed by minimizing the number of parameters and by using the topographic data in distributed form. Thus, because of the high hydraulic conductivity of the surface soil, only the “saturation excess” mechanism of runoff production from variable source areas has been considered. Parameter sensitivity analysis showed the prevailing influence of soil storage capacity and conductivity. Analysis of space grid resolution has shown the inadequacy of using a grid discretization greater than 100 m. 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, and 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.