Identification ofrevailing storm runoff generation mechanisms in an intensively cultivated catchment

Abstract

The fact that flash floods initiated in arable catchments are often accompanied by massive sediment and nutrient loads often leads to the assumption that surface runoff is therincipleathway by which runoff reaches watercourses. On the basis of an evaluation of several rainfall-runoff events in a representative agricultural catchment, we show that runoff from cultivated land may be generated in a way similar to that seen on forested slopes, where shallow subsurface runoff is theredominantathway by which runoff makes its way to watercourses in most runoff events. To identify theredominant runoffathway, we employed a combination of turbidity measurements and stream discharge data. Suspended sediment flux, a newly introduced index representing the ratio betweenrecipitation duration and total sediment yield, and direction of the discharge-turbidity hysteresis loops wereroposed as reflective indicators of the frequency of runoff via differentathways. In our study, most of the events initiated by rainstorms of various intensities and durations resulted in rapid increases in stream discharge. Although we observed temporal variability of topsoilroperties attributable to seasonal weather changes and agricultural activities, e.g. bulk density andorosity, runoff generation was mainly driven byrecipitation characteristics and the initial catchment saturation.