Effect of Soil Data Resolution on Hydrologic Modeling in a Southern Piedmont Watershed.

Soil data is an integral part of watershed scale hydrologic models. Soil properties such as bulk density and hydraulic conductivity affect processes such as infiltration and surface transport of water and pollutants. The Soil and Water Assessment Tool (SWAT) tool, a widely used physically based watershed scale model for water and pollutants uses the State Soil and Geographic (STATSGO) database as the default dataset for soil information. We compared the performance of this 1:250,000 scale resolution database with the Soil Survey Geographic (SSURGO) database having 1:24,000 scale resolution in a calibrated SWAT model for the Broad River watershed in Georgia. The SSURGO soil database was incorporated into the SWAT database after preprocessing the original data using the preprocessing tool. Spatial Modeling was performed using digital elevation model (DEM), land use layer, soil layer and daily rainfall data. The model was simulated for the period from 2005 January to 2007 December using daily time steps. Our preliminary results indicate that the model predicted higher flow during storm events with SSURGO database. However, STATSGO predicted more sediment during storm events. These results could be due to the effect of differences in spatial representation of hydraulic conductivity values in the two soil databases.