Modeling the hydrochemistry of the Choptank River Basin using GWLF and Arc/Info: 1. Model calibration and validation

We modeled nutrient export in the ChoptankRiver Basin on the coastal plain of the Chesapeakedrainage, using a modified version of alumped-parameter, hydrochemical model (GWLF).Calibration was performed using long-term (WY1980–WY1990)hydrochemistry data from a gauged site. Thecalibrated model reproduced water yields, TN, and TPexport with cumulative errors of <1% over the11-year calibration period and with annual RMS errorsof 10–50%. Model validation was done withindependent measurements at the same gauged site(WY1991 to WY1996) and at another nearby independentlygauged site (WY1991 to WY1995). Local adjustment ofthe groundwater recession coefficient and thedissolved N concentration in agricultural stormflowwas essential for successful application at the secondsite. GWLF appears to be a useful model for estimationof fluxes of water, N and P from ungauged areas withaccuracies of 10–50% at annual time scales.

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