A DETAILED MODEL FOR SIMULATION OF CATCHMENT SCALE SUBSURFACE HYDROLOGIC PROCESSES

A catchment scale numerical model is developed based on the three-dime nsional transient Richards equation describing fluid flow in variably saturated porous media. The model is designed to take advantage of dig ital elevation data bases and of information extracted from these data bases by topographic analysis. The practical application of the model is demonstrated in simulations of a small subcatchment of the Konza P rairie reserve near Manhattan, Kansas. In a preliminary investigation of computational issues related to model resolution, we obtain satisfa ctory numerical results using large aspect ratios, suggesting that hor izontal grid dimensions may not be unreasonably constrained by the typ ically much smaller vertical length scale of a catchment and by vertic al discretization requirements. Additional tests are needed to examine the effects of numerical constraints and parameter heterogeneity in d etermining acceptable grid aspect ratios. In other simulations we atte mpt to match the observed streamflow response of the catchment, and we point out the small contribution of the streamflow component to the o verall water balance of the catchment.