EXTENDING THE APPLICATION OF SCS CURVE NUMBER METHOD TO BE USED WITH ANNUAL RAINFALL TO ESTIMATE ANNUAL DIRECT RUNOFF IN ARID REGIONS

Abstract

The SCS-CN runoff curve number method is one of the most popular rainfall-runoff transformation method. However, it is considered an event-based method, which creates a problem when the daily rainfall records are not available, and the annual rainfall values are the only available rainfall information. In this respect, this study aimed to propose an approach to provide reasonable estimates of annual direct runoff when daily rainfall records are unavailable. This would be done by developing relationships to relate the total annual rainfall to the runoff depths, using the same SCS-CN methodology and parameters, provided that the difference with the event-based method is tolerable. Study area was divided to 13 regions with their associated rainfall stations, SCS-CN method was applied to calculate the runoff depths using daily and annual rainfall records, then correlation and regression analysis (Simple linear and nonlinear) were used to develop the relationships between the total annual rainfall to the runoff depths at different CN values for each region. Finally, the performance of the developed relationships was evaluated by checking regression coefficients and applying other statistical validation tests on