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Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Watershed Management to Meet Water Quality Standards and Emerging TMDL (Total Maximum Daily Load) Proceedings of the Third Conference 5-9 March 2005 (Atlanta, Georgia USA) Publication Date 5 March 2005  701P0105.(doi:10.13031/2013.18110)
Authors:   K. Wu and Y. Jun Xu
Keywords:   Spatial hydrologic modeling, SWAT, Manning’s roughness coefficient, Coastal watersheds, Louisiana

The Soil & Water Assessment Tool (SWAT) has been widely used for spatial hydrologic analyses at various watershed scales. However, little is known about the models behaviors in coastal watersheds that have gentle topography and high drainage density. In this study we evaluated the SWAT model for its ability to predict hydrologic components in three coastal lowland watersheds in size from 1896 to 4822 km2. The model was calibrated and validated with daily discharge data from 1976 to 1977 and from 1979 to 1999, respectively. Deviation of mean discharge and the Nash-Sutcliffe efficiency were used to evaluate the models performance. The study found that Mannings roughness coefficient for main channel (CH_N(2)), SCS curve number (CN), soil evaporation compensation factor (ESCO), deep aquifer percolation fraction (RCHRG_DP), groundwater delay (GW_DELAY), and maximum canopy storage (CANMX) were the most sensitive model parameters for these coastal watersheds. CH_N(2) showed the greatest effect on the surface runoff response time in hydrograph, indicating its critical role in hydrologic routing processes for the lowland watersheds with a flat topography. The SWAT model showed an excellent performance with a Nash-Sutcliffe model efficiency of 0.935, 0.940 and 0.960 for the calibration period and of 0.851, 0.811 and 0.867 for the validation period for the three watersheds. The estimation errors in annual average runoff were below 5.6%. In addition to discharge, SWAT produced reasonable estimates for other relevant components such as evapotranspiration, soil moisture, and groundwater flow. These results demonstrate that SWAT is capable to simulate hydrologic processes for medium to large scale lowland coastal watersheds.

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