Study On The Effects Of Grass Buffer Strip Under Streams On Soil Slope

Water erosion has a significant effect on soil slope. Grass buffer strip as one of vegetation protection measures on slope has been increasingly applied to practice. In the study, based on the study of scour trail diffusion process by overland flow and its hydraulic characteristics, field point-source scour experiment was conducted using yellow brown soil to evaluate the effect of different percentage of vegetation buffer strips on runoff from upslope by point-source concentrated flow. It revealed the interception effect of soil slope under different percentage of grass strips on runoff and sediment yield. The principles of soil erosion under the vegetation protection were analyzed from the perspective of soil and water conservation. It lain a foundation for designing optimal percentage of grass strips on soil slope and exerting the interception effect of vegetatation buffer strips on runoff and sediment. The experiment results demonstrated:(1)The grass buffer strips had changed the runoff diffusion trail on slope and dispersed the water flow. The diffusion area and trail width of overland flow increased under vegetation cover. The effect of grass strips was more significant under larger flow discharge. The analysis of SAS showed that the percentage of grass buffer strips on slope had a remarkable impact on maximum diffusion width on slopeland and bareland, outflow width of overland flow, the width at the border of grass strip and bareland and diffusion area on bareland under water flow through grass buffer strips.(2)Vegetation cover had a hindering effect on water movement and changed the flow direction. It not only dispersed the water trail constinuously thus increased the flow diffusion area, but also delayed the overland flow, which led to a sufficient infiltration to soil. The infiltration rate with grass buffer strips cover was more than twice as much as that on bareland. Besides, the velocity of overland flow was greatly decreased.(3)Grass buffer strips had changed the water flow regime and flow type. When the flow discharge was 0.75L/s, water flow on bareland was supercritical and the flow on grass strip was subcritical based on the category of laminar flow; when the flow discharge was 1L/s, overland flow on bareland was supercritical according to the category of turbulent flow and water flow on grass strip was subcritical based on the category of laminar flow; when the flow discharge was 1.25L/s, overland flow on bareland was supercritical according to the category of turbulent flow and water flow on grass strip was supercritical based on the category of transitional flow.(4)Compared with bareland, grass cover strip had a significant effect on decreasing runoff and sediment yield. The grass strip could delay overland flow as well as decrease runoff and sediment yield in water flow. Grass buffer strip had a different influence on decreasing runoff and sediment yield with different flow discharge on the same slope. Three levels of flow discharge were applied in point-source scour experiment to study the decreasing effect of different percentage of grass strips on runoff and sediment. The results showed that when the flow discharge was within the range of 0.75L/s to 1.25L/s and one third of soil slope was covered by grass buffer strip, it could play a significant role in soil and water conservation.