Hydrology and Earth System Sciences www.hydrol-earth-syst-sci.net 1027-5606 1607-7938 13 5 2009 10.5194/hess-13-605-2009 http://www.hydrol-earth-syst-sci.net/13/605/2009/ http://www.hydrol-earth-syst-sci.net/13/605/2009/hess-13-605-2009.html http://www.hydrol-earth-syst-sci.net/13/605/2009/hess-13-605-2009.pdf 605 615 2009-05-15 Investigation of the direct runoff generation mechanism for the analysis of the SCS-CN method applicability to a partial area experimental watershed K. X. Soulis soco@aua.gr J. D. Valiantzas N. Dercas P. A. Londra Agricultural University of Athens, Department of Natural Resources Management and Agricultural Engineering, Lab. of Agricultural Hydraulics, Athens, Greece The Soil Conservation Service Curve Number (SCS-CN) method is widely used for predicting direct runoff volume for a given rainfall event. The applicability of the SCS-CN method and the direct runoff generation mechanism were thoroughly analysed in a Mediterranean experimental watershed in Greece. The region is characterized by a Mediterranean semi-arid climate. A detailed land cover and soil survey using remote sensing and GIS techniques, showed that the watershed is dominated by coarse soils with high hydraulic conductivities, whereas a smaller part is covered with medium textured soils and impervious surfaces. The analysis indicated that the SCS-CN method fails to predict runoff for the storm events studied, and that there is a strong correlation between the CN values obtained from measured runoff and the rainfall depth. The hypothesis that this correlation could be attributed to the existence of an impermeable part in a very permeable watershed was examined in depth, by developing a numerical simulation water flow model for predicting surface runoff generated from each of the three soil types of the watershed. Numerical runs were performed using the HYDRUS-1D code. 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