Curve Number Estimation of Ungauged Catchments considering Characteristics of Rainfall and Catchment

Abstract

The Soil Conservation Service Curve Number (CN) method is widely used to calculate the flood runoff in ungauged catchments. However, the existing CN calculation method has a disadvantage in that it cannot calculate the CNs considering the spatiotemporal variability of rainfall in the ungauged catchments. In this study, the authors used a distributed rainfall-runoff model and a simple runoff generation method to generate the hourly runoffs of the ungauged catchments considering the spatiotemporal variability of rainfall, and estimate the CNs of the ungauged catchments using the generated runoff and the CN back calculation method. As a result of calculating the CNs of the ungauged catchments for past 20 rainfall events, the CNs had a large variability even in the same catchment. In addition, the mean CNs for the 20 rainfall events of independent ungauged catchments differed even if the ungauged catchments were close to each other. The method of estimating the CNs of the ungauged catchments presented in this study properly reflects the characteristics of actual rainfall and catchment, and thus can be usefully used to estimate valid CN.