Laboratory Studies on the Influence of Rainfall Pattern on Rill Erosion and Its Runoff and Sediment Characteristics

Rill is a major type of erosion on upland slopes. Continuous rainfall is commonly used in laboratory studies on rill erosion despite the fact the rainfall was often discontinuous in the field; this is particularly true in the Chinese Loess Plateau. This study compares rill erosion under continuous and intermittent rainfalls by using laboratory experiments. The experiments include two rainfall-intensity treatments (90 and 120 mm h-1) and two rainfall-pattern treatments (continuous and intermittent). The results indicate that rill formation had a significant effect on runoff and sediment concentration. For continuous and intermittent rainfall at the rainfall intensity of 90 mm h-1, the mean sediment concentrations were 1.91 and 1.73 times after rill initiation than that before rill initiation, respectively, the rill erosion accounted for 75.5% and 77.7% of runoff duration, respectively. For continuous and intermittent rainfall at the rainfall intensity of 120 mm h-1, the mean sediment concentrations after rill initiation were 1.38 and 1.32 times that before rill initiation, respectively, the rill erosion represented 88.7% and 78.8% of the total runoff duration, respectively. We observed sediment sorting under all treatments, however, the low rainfall intensity boosted but the high rainfall intensity lowered the clay fraction; in contrast, the sorting remained roughly the same between the rainfall-pattern treatments. The runoff velocity also affected the sediment sorting. Our empirical results indicated the important significance of the rainfall intermittence in predicting rill erosion.