LAND-USE IMPACT ON WATERSHED RESPONSE - THE INTEGRATION OF 2-DIMENSIONAL HYDROLOGICAL MODELING AND GEOGRAPHICAL INFORMATION-SYSTEMS

The integration of a two-dimensional, raster-based rainfall-runoff mod el, CASC2D, with a raster geographical information system (GIS), GRASS , offers enhanced capabilities for analysing the hydrological impact u nder a variety of land management scenarios. The spatially varied comp onents of the watershed, such as slope, soil texture, surface roughnes s and land-use disturbance, were characterized in GRASS at a user-spec ified grid cell resolution for input into the CASC2D model. CASC2D is a raster-based, single-event rainfall-runoff model that divides the wa tershed into grid cell elements and simulates the hydrological process es of infiltration, overland how and channel flow in response to distr ibuted rainfall precipitation. The five-step integration of CASC2D and GRASS demonstrates the potential for analysing spatially and temporal ly varied hydrological processes within a 50 square mile semiarid wate rshed. By defining possible land-use disturbance scenarios for the wat ershed, a variety of rainfall-runoff events were simulated to determin e the changes in watershed response under varying disturbance and rain fall conditions. Additionally, spatially distributed infiltration outp uts derived from the simulations were analysed in GRASS to determine t he variability of hydrological change within the watershed. Grid cell computational capabilities in GRASS allow the user to combine the scen ario simulation outputs with other distributed watershed parameters to develop complex maps depicting potential areas of hydrological sensit ivity. This GIS-hydrological model integration provides valuable spati al information to researchers and managers concerned with the study an d effects of land-use on hydrological response.