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Application of Soil and Water Assessment Tool (SWAT) to Landscapes with Tiles and Potholes. Part II. Validation of New Procedures. Case of Walnut Creek Watershed (Iowa)

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

Citation:  Paper number  032164,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.13791) @2003
Authors:   B. Du, A. Saleh, J.G. Arnold, D.B. Jaynes
Keywords:   Water quality, modeling, tile drains, pothole, watershed, SWAT

The SWAT model with modified tile drain and pothole components (SWAT-M) was evaluated at a watershed scale using 9 years of measured flow and nitrate nitrogen (NO3-N) data sets in Walnut Creek watershed (WCW). The model was calibrated during the period of 1992 to 1995 and validated during the period of 1996 to 1999. In addition, comparisons between the modified version and 2000 version (SWAT2000) of SWAT models were conducted. In assessing overall performance of SWAT models, the center location (site 310) and outlet (site 330) of WCW were selected. Nash-Sutcliffe E values of the simulated monthly flows and NO3-N loads were 0.69 to 0.78 and 0.52 to 0.79, respectively, indicating that SWAT-M reasonably well estimated the monthly flows and NO3-N loads in the large flat landscape of WCW with tile drains and potholes. SWAT-M was capable of simulating daily flow and NO3-N loads but with smaller E values (0.31 to 0.50 and 0.20 to 0.46, respectively), compared to the monthly results. By investigating site 210, which was exclusively selected for the evaluation of subsurface tile drain, it was concluded that the simulated monthly subsurface flows and NO3-N loads( E values ranging from 0.71 to 0.79 and 0.72 to 0.78, respectively) were reasonably well matched to the measured values. Nevertheless, SWAT-Ms simulations of daily subsurface flows (E values of 0.09 to 0.18) and NO3-N loads (E values of 0.37 to 0.43) were less accurate than monthly results. SWAT-M estimated daily and monthly flows, NO3-N loads, subsurface tile drains and subsurface tile NO3-N loads better than SWAT2000.

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