COMPARISON OF GREEN-AMPT AND CURVE NUMBER METHODS ON GOODWIN CREEK WATERSHED USING SWAT

Abstract

Two methods of simulating excess rainfall were compared on a large basin with multiple rain gages. The SCSdaily curve number method (CN) was compared with the Green-Ampt Mein-Larson (GAML) method on the Goodwin CreekWatershed (GCW). GCW is 21.3 km2 in area and has 32 rain gages located within and surrounding the watershed. Themodel used was the Soil and Water Assessment Tool (SWAT). SWAT is a comprehensive watershed scale model developed tosimulate management impacts on water, sediment, and chemical yields for ungaged basins. SWAT was modified to acceptbreakpoint rainfall data and route streamflow on a sub-daily time-step. Eight years of measured climatic data were used inthe study. Simulated and measured streamflow at the watershed outlet were evaluated. Results were not calibrated. Monthlymodel efficiencies were 0.84 for CN and 0.69 for GAML. The use of a sub-daily routing technique allowed for very goodcorrelation between measured and simulated hydrographs. Generally, CN undersimulated surface runoff while GAML hadno pattern associated with events. Results suggest that no significant advantage was gained by using breakpoint rainfalland sub-daily time-steps when simulating the large basin used in this study.