A Modified SCS-CN Method: Characterization and Testing
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The Soil Conservation Service Curve Number (SCS-CN) method (SCS, 1956) is modified by accounting for the static portion of infiltration and the antecedent moisture. A volumetric analysis shows that the ratio of the potential maximum retention (S) to the precipitation amount versus the runoff factor relation is equivalent to the average suction pressure-moisture content relation for a unit rainfall amount and a given soil porosity. A simple spreadsheet procedure is suggested for determining S with use of a 5-day antecedent precipitation amount. The modified method is found to perform well on the same data sets as used in the National Engineering Handbook (SCS, 1971).