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NONPOINT SOURCE NEEDS ASSESSMENT FOR IOWA PART I: CONFIGURATION, CALIBRATION AND VALIDATION OF SWAT

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

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:10.13031/2013.18113)
Authors:   M. Jha, P.W. Gassman, S. Secchi, and J.G. Arnold
Keywords:   SWAT, modeling, calibration, validation, , sediment, nutrients, stream flow

Calibration and validation of the SWAT model was performed to support an economic and environmental modeling study of mitigating cropland nonpoint source pollution losses in Iowa for the Iowa Department of Natural Resources (IDNR). SWAT was initially tested for the Raccoon River Watershed, which is a major subwatershed of the Des Moines River Watershed (one of the 13 watersheds included in the study). Simulated stream flow, sediment, and nitrate values compared favorably with measured values for the Raccoon. Stream flow R2 and Nash- Suttcliffe modeling efficiency (E) values ranged between 0.77 and 0.96 for annual and monthly comparisons during the Raccoon calibration and validation periods. Strong results were also found for the simulated annual sediment loads, for which the R2 and E statistics generally exceeded 0.83. The R2 and E values computed for the comparison between simulated and measured annual sediment losses were greater than 0.90 in the calibration period, but the monthly statistics for the same period were only 0.45. However, all of the comparison statistics computed for the sediment loss comparisons in the validation period were between 0.83 and 0.96. The statistical evaluation for the nitrate predictions yielded a strong correlation as indicated by R2 and E values of greater than 0.70 for both the annual and monthly results during the calibration and validation periods. The majority of R2 and E values computed for annual comparisons between simulated and measured stream flows for the 13 study watersheds exceeded 0.85; the corresponding monthly statistics were usually greater than 0.75.

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