Modeling Watershed Hydrologic Water Balance Using the Soil and Water Assessment Tool (SWAT), Lower Coastal Plain, South Carolina USA

Understanding the hydrology at the watershed scale can be complex due to the variability of land use, soil type, climate, and vegetative cover. Hydrological models are valuable tools to fill the gaps in not only understanding the processes, but also assessing the impact of anthropogenic and natural disturbances on water quantity and quality. The objective of this study is to test a spatially-distributed hydrologic model, SWAT, for a third-order, low- gradient forested watershed using spatial watershed characteristics and 2.5-years of continuous stream flow and climate data. SWAT is a public domain model, actively supported by the USDA-Agricultural Research Service; it couples a Geographic Information System (GIS) with a distributed parameter hydrological model in order to predict runoff, water quality and other hydrologic parameters. The model has been developed to evaluate the impact of land management practices on the hydrology and water quality in large, complex watersheds. The watershed investigated in this study, Turkey Creek, is located approximately 60 km northwest of Charleston, South Carolina on the lower Atlantic Coastal Plain of the Southeast U.S. Turkey Creek's approximately 7200- hectare drainage basin is comprised of mostly pine and pine-hardwood mixed forest of varying stand ages on predominantly poorly drained soils. The elevations in this low gradient watershed vary from 3 to 14 meters above mean sea level. This model is currently being tested to calculate the water budget for the watershed and to predict hydrological responses such as stream outflow including surface and subsurface flows and evapotranspiration to storm events. Calibrated and validated to the field measured data, the model can be further applied to predict the long- term hydrologic and water quality impacts of land use change, climate variability, and natural disturbances on this watershed. The results from this model will be used to evaluate the utility of the SWAT model for application in the low gradient watersheds that make up the Atlantic Coastal Plain region of the Southeast U.S.