Curve numbers and Green-Ampt effective hydraulic conductivities
Nearing, M.A. | Liu, B.Y. | Risse, L.M. | Zhang, X.
The SCS curve number method is an accepted method for estimating surface water runoff caused by rainfall. Several modern process-based hydrologic models, including the Water Erosion Prediction Project (WEPP) model, use the Green-Ampt infiltration equation, but the basis for selecting model parameters is not as comprehensive as for curve number selection. The purpose of this study was to quantitatively relate curve numbers to Green-Ampt effective conductivity parameters, Ke, so that the information available relative to application of curve number technology may be applied to WEPP for predicting runoff from rainfall. Data used to develop relationships included descriptions of 43 soils, CLIGEN-generated weather information for ten geographic locations in the U.S., and eight different types of cropping practices. Values of Ke were derived by optimizing WEPP model output to match that predicted by curve numbers for a 20-year weather sequence. Relationships were developed to describe the optimized Ke values for both fallow and cropped conditions. The relationships were tested on approximately 350 plot years of measured data from 11 runoff and erosion stations in the U.S. and shown to perform as well as or better than the SCS curve number approach for individual storm predictions of run off volumes.
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