Numerical dissipation and parameter values in the distributed hydrological modeling’

A coupled subsurface-channel flow distributed model has been applied for the continuous simulation of the basic hydrologic processes in a small mountain basin, in order to investigate the effects of the numerical resolution on parameter evaluation and on simulation results. Finite difference schemes have been used to solve conservation equations of the 2-D saturated subsurface flow and the 1-D kinematic surface flow. Simulation tests developed in terms of space and time-steps have highlighted that the truncation error in the finite difference approximation of groundwater flow equation, produces a numerical dissipation which grows as the space-step grows. This numerical dissipation can be compensated adopting hydraulic conductivity greater than physically meaningful values. The conductivity parameter can take on field measured values if a space-step is used which is smaller than 10 m. For greater grid scales, the conductivity parameter needs to be recalibrated and it must be chosen empirically with increasing values as the grid size increases.