The performance of grass filter strips in controlling high-concentration suspended sediment from overland flow under rainfallon-rainfall conditions

摘要

There is little information on the performance of vegetative filter strips (VFS) in filtering high-concentration sediment from subcritical overland flow. Flume experiments on simulated grass strips were conducted using combinations of three slope gradients (3°, 9° and 15°), five 1-m-wide slope positions (from upslope to downslope), two flow rates (60 and 20 L min~(-1) m~(-1)) and sediment concentrations of 100-300 kg m~(-3) under simulated rainfall and non-rainfall conditions. The results showed that sediment deposition efficiency increased with VFS width as a power function. Rainfall significantly reduced sediment deposited within VFS. Higher sediment concentration corresponded to a larger sediment deposition load but reduced deposition efficiency. Flow rate had a negative effect on deposition efficiency but no effect on deposition load. Sediments were more easily deposited at the upper slope position than downslope, and the upper slope position had a higher percentage of coarse sediments. The deposited sediment had significantly greater median diameters (D_(50)) than the inflow sediment. A greater proportion of coarse sediments larger than 25 μm in diameter were deposited, and particles smaller than 1 μm and of 10-25 μm had a better deposition performance than particles of 1~(-1)0 μm. Rainfall reduced the deposited sediment D_(50) at a slope gradient of 3° and had no significant influence on it at 9° or 15°. A higher sediment concentration led to a smaller D_(50) of the deposited sediment. Rainfall had no significant effect on overland flow velocity. Both the deposited sediment load and D_(50) decreased with increasing flow velocity, and flow velocity was the most sensitive factor impacting sediment deposition. The results from this study should be useful to control sediment flowing into rivers in areas with serious soil erosion.