An experimental study of rill sediment delivery in purple soil, using the volume-replacement method

Experimental studies provide a basis for understanding the mechanisms of rill erosion and can provide estimates for parameter values in physical models simulating the erosion process. In this study, we investigated sediment delivery during rill erosion in purple soil. We used the volume-replacement method to measure the volume of eroded soil and hence estimate the mass of eroded soil. A 12 m artificial rill was divided into the following sections: 0-0.5 m, 0.5-1 m, 1-2 m, 2-3 m, 3-4 m, 4-5 m, 5-6 m, 6-7 m, 7-8 m, 8-10 m, and 10-12 m. Erosion trials were conducted with three flow rates (2 L/min, 4 L/min, and 8 L/min) and five slope gradients (5°, 10°, 15°, 20°, and 25°). The eroded rill sections were refilled with water to measure the eroded volume in each section and subsequently calculate the eroded sediment mass. The cumulative sediment mass was used to compute the sediment concentration along the length of the rill. The results show that purple soil sediment concentration increases with rill length before eventually reaching a maximal value; that is, the rate of increase in sediment concentration is greatest at the rill inlet and then gradually slows. Steeper slopes and higher flow rates result in sediment concentration increasing more rapidly along the rill length and the maximum sediment concentration being reached at an earlier location in the rill. Slope gradient and flow rate both result in an increase in maximal sediment concentration and accumulated eroded amount. However, slope gradient has a greater influence on rill erosion than flow rate. The results and experimental method in this study may provide a reference for future rill-erosion experiments.