Watershed model sensitivity to bacteria parameters

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Radcliffe, David E.
Matthews, Monte
Cabrera, Miguel L.
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Watershed-scale models can be used to determine the pollutant daily load in TMDL streams, or to test the effect of different scenarios for reducing bacterial load. HSPF (Hydrological Simulation Program – FORTRAN ) is a watershed-scale model distributed as part of the EPA BASINS system. EPA has also developed a Bacterial Indicator Tool for calculating the effect of livestock and septic systems on the bacterial parameters required by HSPF. We used HSPF and the Bacterial Indicator Tool to predict stream flow and FC concentrations in the Little River watershed of the Upper Oconee River basin and test for model sensitivity to bacteria parameters. We calibrated flow and FC concentrations using data from a USGS gaging station at the Highway 16 crossing near Eatonton, GA. The bacteria samples were collected during the period 1990 to 1994. We tested the sensitivity of the model predictions of FC to bacteria parameters by doubling the values of the parameters and calculating the root mean square change in predicted FC concentration. The most sensitive parameters were (in order of decreasing sensitivity): number of beef cattle, number of dairy cattle, time cattle spend in stream, and in-stream first-order decay rate.
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