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Modeling water quality in the Sandusky watershed, Ohio

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

Citation:  Paper number  032058,  2003 ASAE Annual Meeting . (doi: 10.13031/2013.14940) @2003
Authors:   Sabine Grunwald, Thomas F. A. Bishop
Keywords:   SWAT, water quality, sensitivity, hydrology

The Soil and Water Assessment Tool (SWAT) was used to model water quantity and water quality in the Sandusky river watershed (SRW), Ohio. The specific objectives of this research were to examine the sensitivity of the simulated outputs of SWAT to different levels of spatial discretization as defined by the threshold area (TA) which is minimum drainage area for the origin of a stream to be defined. Five scenarios were created with threshold area values of 450, 1000, 2125, 4250 and 8500 hectares. The simulated outputs for each scenario were compared to measured values for stream flow, total suspended sediments, mineral phosphorus and nitrate. All simulated variables were sensitive to changes in TA. Based on the simulated versus observed results, the optimal TA value was identified to be between 450-2125ha depending on the variable. The 450ha delineation was the best for nitrate and the 2125ha delineation was the best for hydrology. TSS simulations were quite stable in terms of prediction quality while the mineral phosphorus predictions were too poor to make a sensible judgment. The authors recommend that a spatial sensitivity analysis as presented in this paper should be performed prior to a full calibration-validation study.

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