SCS Curve Number and Green-Ampt Infiltration Models

Abstract

Soil Conservation Service curve number (SCS-CN) and Green-Ampt (GA) infiltration models are probably the most applied equations in practical hydrology to compute the amount of direct runoff from rainfall. Both models are very simple, require few parameters, and present drawbacks and advantages. The empirical CN model concentrates the infiltration effect in the curve number and in the so-called soil hydrological groups, which have been widely characterized for different soil types, land cover, and antecedent soil moisture conditions (ASMCs), although the latter was considered ambiguous, whereas soil hydrological characteristics, including ASMC, are taken into account for the simplified physically based GA model. The main advantage of the GA model is the temporal variation of the rainfall excess intensity, which is not considered in the CN model. In this paper, CN and GA models are jointly used in order to analytically establish relationships linking each other, so that the positive features of both models together can be taken into account for applications. It is shown that the suggested procedure makes it possible to move from one model to the other and vice versa, according to the derived equations linking the relative parameters. Constant rainfall intensity was assumed; therefore, the procedure is better aimed to its design purpose at the small basin scale, rather than to reproducing rainfall-runoff events. A comparison between the results obtained by applying the suggested analytical procedure with those numerically derived by other researchers for SCS temporal storm distribution is performed and discussed.