Simulation of the effects of forest cover, and its removal, on subsurface water

A distributed, physically based mathematical model was developed to simulate the effects of forestry operations on both soil water and streamflow. It combines Galerkin's finite‐element method with an implicit backward finite‐difference scheme to solve the Darcy‐Richards equation of porous media flow, and uses sink concepts to simulate water use by trees. The validity of the model was checked by simulation of one‐dimensional vertical infiltration into a soil column. Five forest configurations, imposed on a hillslope, were simulated: fully treed, upper slope clear‐cut, lower slope clear‐cut, patch‐cut, and entire slope clear‐cut. The results, displayed as total potential and soil water fields, were qualitatively compatible with accepted hydrological concepts. A field study was simulated and the results compared with field measurements. Explanations are offered for discrepancies between the simulation results and the field measurements. The model's primary usefulness rests in its capability to simulate soil water movement and redistribution, on a distributed basis, in response to the processes of infiltration, evaporation, and transpiration.