Experimental Evidence on Runoff Generation Mechanisms

The present investigation aims to better understand the runoff generation mechanisms in an experimental basin of 32 km2 in Southern Italy. Particular attention was paid to the influence of the soil moisture content, measured on a hillslope of a small subcatchment of 0.65 km2, on runoff activation mechanisms, evaluated at the two spatial scales. We found that, the threshold value, responsible of runoff activation, is almost equal to field capacity. In fact, we observed a rapid change in the subcatchment response when the mean soil moisture reaches a value close to the observed range of variability of the evaluated field capacity. In the small subcatchment, the runoff coefficient is almost zero for each of the events recorded during dry periods. During wet periods, however, it is rather variable and depends almost only on the total rainfall. Changing from the small scale up to the medium scale) the threshold mechanism in runoff production is less detectable because masked by the increased spatial heterogeneity of the vegetation cover and soil texture.