Experimental Study on the Impact of Slope and Silt-laden inflow Conditions on Vegetation Sediment Trapping Process

Vegetation-restored hillslope surfaces not only reduce erosion but they also remove sediment from upslope silt-laden inflow. To investigate the sediment trapping effect of grassland, this study conducted a series of crossed sediment trapping experiments that examined various factors, such as slope (5°–20°), sediment concentration (40–160 g L⁻¹), and unit flow rate (7.5–45.0 L min⁻¹ m⁻¹). The duration of each experiment was longer than required to reach the stable state of sediment trapping, so we measured and verified the individual sediment trapping capacity (R_m) by experiments. The results showed that gentler slopes generated higher instantaneous sediment trapping efficiency (ISTE) and greater R_m. As the sediment concentration of the silt-laden inflow increased, the impact of slope on R_m increased. Higher sediment concentration led to lower ISTE but greater R_m. Similar to the effect of sediment concentration, a larger unit flow rate led to lower ISTE and greater R_m. Thus, it is evident that interaction among these factors affects sediment trapping process. The experiments revealed the greatest sediment trapping effect of grass strips was concentrated mainly in the first 2-m width, and that 90% of sediment deposition occurred within half the time needed to reach the stable state. Slope and flow rate were found to have an effect on sediment trapping in each section of grass strips, whereas the effect of sediment concentration was concentrated primarily in the first 5-m width. Standard regression coefficients of a comprehensive regression analysis showed that the intensities of the influencing factors on R_m were as follows: slope (0.736) > grassland width (0.498) > unit flow rate (0.398) > sediment concentration (0.240). It was established that slope is the strongest influencing factor, and that sediment concentration and unit flow rate mainly affect R_m by changing the rate of sediment delivery. These results will help expand the theoretical basis regarding the effects of vegetation restoration on watersheds in soil erosion research.