Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2010
Publication Date: 10/1/2010
Citation: Bosch, D.D., Arnold, J.G., Volk, M., Allen, P.M. 2010. Simulation of a Low-Gradient Coastal Plain Watershed Using the SWAT Landscape Model. Transactions of the ASABE. 53(5):1445-1456. Interpretive Summary: Watershed scale natural resource models are being used to quantitatively evaluate the benefits agricultural conservation programs supported by the U.S. Government. While watershed scale natural resource models have made considerable advances in recent years, one shortcoming of these models is their inability to accurately represent water flow and transport from higher positions in the landscape to lower positions. The Soil Water Assessment Tool, SWAT, has been revised to represent the runoff, run-on, and infiltration processes that typically occur in different parts of the landscape. The revised watershed model was tested for a hillslope in a small Georgia watershed. The model simulates important changes in the hydrologic water balance as the water moves from the field area at the top of the hillslope, through grass and wooded buffers, and eventually into the stream. Model results indicate surface runoff was dominant in the upland divide while groundwater flow was dominant in the hillslope and the floodplain. While additional testing is necessary, the revised model holds considerable promise as a tool for watershed management.
Technical Abstract: Accurate representation of landscape processes in natural resource models requires distributed representation of basin hydrology and transport processes. To better represent these processes, a landscape version of the SWAT model has been developed. The model has been modified to represent the runoff, run-on, and infiltration processes that typically occur in different parts of the landscape. The SWAT landscape model consists of a three component system, hill-top, upland, and near stream sections. The model addresses flow and transport across hydrologic response units prior to concentration in streams, and is capable of simulating flow and transport from higher landscape positions to lower positions within a single river basin. The SWAT landscape model was tested using data collected from a heavily vegetated riparian buffer system in the Atlantic Coastal Plain near Tifton, Georgia, USA. Simulations of surface runoff, lateral subsurface runoff, and groundwater flow for the upland divide, hillslope, and a sub-divided floodplain were generated. Model results indicate surface runoff was dominant in the upland divide while groundwater flow was dominant in the hillslope and the floodplain. These results agree well with general observations from the hillslope. The annual total water yield at the bottom landscape unit averaged 284 mm or 26% of the annual precipitation while the estimate of the observed water yield was equal to 29% of the annual precipitation. Surface runoff predictions at the edge of the upland field closely approximated observed data. However, estimates of lateral subsurface flow and groundwater flow at the same position were low. The Nash-Sutcliffe Efficiency for annual estimates of surface runoff at the outlet of the pine forest buffer was 0.97. A comparison of the results from the SWAT landscape model to those obtained from the SWAT 2005 model indicated a more accurate representation of the surface and subsurface hydrology by the landscape model. While additional calibration and testing are necessary, the results are encouraging. The results demonstrate the ability of the model to simulate filtering of surface runoff, enhanced infiltration, and water quality buffering typically associated with riparian buffer systems.