Effects of Infiltration Conditions and Rainfall Characteristics on Simulated Curve Numbers

AbstractThe curve number (CN) method is the most widely used method to estimate the depth of runoff resulting from a given depth of rainfall. However, there are still doubts about the effect of rainfall characteristics and soil moisture conditions on the method’s parameters (CN, and the standard initial abstraction ratio, λ). In this study, design rainfall distributions were used along with Hortonian infiltration characteristics to calculate CN and λ values for a highly clayey soil (>80%). Prerainfall infiltration conditions were characterized by the measured initial soil moisture content, and Hortonian infiltration model was obtained from experimental infiltration test measurements. The main results show that there is no influence of initial infiltration rates on CN values, and rainfall duration generates substantial influence on CN. The CN is inversely related to rainfall depth, and λ is dependent on the initial soil moisture. Further, neither tabulated CN nor standard λ corresponds to the simulated values obtained in this case. Therefore, these findings suggest that the method’s parameters should be specifically adapted to local hydrological conditions.