Green-Ampt Curve-Number mixed procedure as an empirical tool for rainfall-runoff modelling in small and ungauged basins.

The Soil Conservation Service - Curve Number (SCS-CN) method is a popular rainfall-runoff model that is widely used to estimate direct runoff from small and ungauged basins. The SCS-CN is a simple and valuable approach to quantify the total stream-flow volume generated by storm rainfall, but its use is not appropriate for estimating the sub-daily incremental rainfall excess. To overcome this drawback, we propose to include the Green-Ampt (GA) infiltration model into a mixed procedure, which is referred to as CN4GA (Curve Number for Green-Ampt), aiming to distribute in time the information provided by the SCS-CN method. For a given storm, the computed SCS-CN total net rainfall amount is employed to calibrate the soil hydraulic conductivity parameter of the Green-Ampt model. The proposed procedure is evaluated by analysing 100 rainfall-runoff events that were observed in four small catchments of varying size. CN4GA appears to provide encouraging results for predicting the net rainfall peak and duration values and has shown, at least for the test cases considered in this study, better agreement with the observed hydrographs than the classic SCS-CN method.