WATERSHEDSS GRASS-AGNPS MODEL TOOL

A modeling tool that utilizes a raster-based geographic information sy stem to build an input file for the spatially distributed pollutant ru noff model, AGNPS, was developed as a component of the WATERSHEDSS dec ision support system. In addition to automatically computing input dat a from basic soils, topography, and land use maps, this modeling tool adds the capability to input point source, channel characteristic, and pesticide application data for user-selected areas in the watershed. The tool was used to simulate runoff and sediment, nitrogen, and phosp horus loads for a small gaged watershed located in North Carolina. Out put from the tool was compared to observed runoff and pollutant loads for II storms. Statistical comparisons between observed and model-simu lated loads at two monitoring stations showed no significant differenc e between observed and predicted runoff volumes and nitrogen, phosphor us, and sediment loads, indicating that the modeling tool provides rea sonable estimates of pollutant loads from storm events.