The significance of basin slope for curve number estimation and the impact on flood prediction in arid basins

Abstract

The Natural Resources Conservation Service (NRCS) method was developed in agricultural basins with slopes less than or equal to 5%. Extension of the method to arid regions and at higher slopes is needed. This research aims to investigate the relationship between the basin slope and runoff depth in arid basins by using the Natural Resources Conservation Service Curve Number (NRCS-CN). The results show that there is a clear effect of the proposed curve number equation with slope (the slope adjusted CN, CNIIα ) on the runoff depth in the studied basins, and this is consistent with the literature. However, large basin areas with a high percentage of alluvium area, vegetation, and high infiltration rates countereffects the slope of the basin, and consequently, the basin slope will not have a significant effect on runoff. The correlation coefficient of various developed equations varies between (0.89-0.93) and the root mean square error of runoff depth varies between 11 mm for λ=0.2 and 5.2 mm for λ=0.01.