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

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

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