SOIL DETACHMENT RATES FOR SEDIMENT LOADED FLOW IN RILLS

Abstract

Rill erosion accounts for approximately 70% of the erosion on upland areas. Net soil detachment from rill beds decreases with an increase in sediment concentration in the flow. The objective of this study was to quantify the effect of sediment concentration in water flow on soil detachment. The effects of slope (5³, 10³, 15³, 20³, and 25³), flow rate (2, 4, and 8 L/min), and rill length (0.5, 1, 2, 3, 4, 5, 6, 7, and 8 m) on soil detachment were studied. A flume of 1 m U 8 m was subdivided into strips of 0.1 m U 8 m to imitate rills. A typical silty loess soil from the Loess Plateau of China was packed into the flume to a depth of 20 cm. Soil was saturated from above with tap water and allowed to set for a day prior to each experimental run in order to facilitate consistent pre–wetted conditions. Flow–rate–regulated tap water was introduced into the rills from the upper end of each segment of rill at the different lengths. The change in sediment concentration with rill length was determined, and a method was suggested to compute soil detachment rate from the experimental data. The results indicate that detachment rate decreased linearly with sediment concentration and exponentially with rill length. The results support the validity of the detachment function used in the Water Erosion Prediction Project model.