Abstract
Curve number method is a simple method to calculate direct runoff height from daily rainfall and curve number which is determined by soil conditions at the rainfall event. Simple modification methods are proposed by U.S. Department of Agriculture and researchers, as estimation accuracy is not good in some application conditions. Following methods adaptability for CN to an existing dugout in Northern region, Ghana are examined; a) a method to a use standard CN, b) a method to use the average CN, c) a method to consider an antecedent rainfall, d) a method to change an initial abstraction ratio. As a result, the reproducibility of direct runoff height of those methods is found out to be not good. Thus, CN value estimation models developed by multiple regression analysis using rainfall related data which can be easily obtained in Africa are examined. As a result, NSE (Nash-Sutcliffe efficiency) becomes 0.74 in case to use daily rainfall converted to natural logarithm, dry period and rainfall intensity as explanatory variables and the model is highly satisfactory.
