PEAK FLOW ESTIMATES FOR COASTAL PLAIN WATERSHEDS

Abstract

An empirical equation based on storm data from the midwestern U.S. has been used in a number of water resourceand water quality models for estimating peak flows for storm events on ungaged watersheds. Limited testing of the equationhas shown a tendency to overpredict storm peaks in regions of low topographic relief. The objective of this study was to testthe Smith and Williams equation and develop improved methods for estimating peak flows from ungaged watersheds in thesoutheastern U.S. Coastal Plain, a region characterized by lowgradient drainage networks and extensive riparian storage.The equation was evaluated on 58 storm events from seven experimental watersheds. Results indicate that the Smith andWilliams equation significantly overpredicts peak flows in the Coastal Plain region, with an average error in peak estimationof over 250%. Regional peak flow equations were developed using stepwise linear regression analyses of logtransformedstorm peak flows and watershed and storm event characteristics. These equations, which relate storm peaks to drainage area,runoff amount, and a drainage network parameter, explained up to 94% of the variability in measured peaks from CoastalPlain watersheds. The Coastal Plain peak flow equations provide improved algorithms for estimating storm peaks fromungaged watersheds in the region.