Effects Of Heavy Rainfall On The Stability Of Soil Reservoir Bank And Sand Content In The Reservoir Area

Gravitational erosion is an important source of soil loss in the Loess Plateau region,and vegetation is a necessary measure for the ecological construction of the area.However,the influence of vegetation on the stability of gully slopes is complex and multifaceted.The scientific evaluation of the role of vegetation on gravity erosion and the erosion of avalanches and slides is an important issue in the study of the evolution of the soil and water environment in the region and the techniques of regulation and control.This paper quantitatively analyzes the effects of heavy rainfall and water level changes on the sand content in the reservoir area by using self-developed miniature test plots,catch basins and self-developed down-spray rainfall devices for plant root model tests under rainfall conditions,and self-developed multi-point samplers with the test chamber previously built by the group for reservoir bank collapse model tests.The paper mainly accomplishes the following.(1)The plant root system model test was designed,with miniature test plots and catch basins of 1 m,1 m and 0.4 m in length,width and height respectively,with representative tree and shrub plants,The rainfall simulation was also carried out by means of an independently improved rainfall device.A total of two sets of rainfall devices were required,connected by hoses for easy movement,with a single rainfall device 5.5m high and an effective rainfall coverage area of 25m~2,thus exploring the effect of vegetation roots on the shear strength and hardness of loess under heavy rainfall conditions.Water samples were taken simultaneously at four depths in the reservoir area by means of a self-made multi-point sampler,and then the density bottle method was used to calculate the sand content of the reservoir area.The rainfall apparatus previously made by the group and the test terrain were used to study the changes in the sand content of the reservoir area under the combined effect of heavy rainfall and water level changes.(2)The difference in the effect of water level change on the sand content of the reservoir area under heavy rainfall conditions is revealed.In the second rainfall,when the water level in the reservoir area on the left side rises,the average value of sand content shows a trend of fluctuating and decreasing with the increase of the distance between the measurement point and the bottom of the slope,and then a trend of significant increase with the increase of the depth of the reservoir area.On the right bank where the water level does not change,the mean sand content shows an overall fluctuating decreasing trend as the distance between the measurement point and the bottom of the slope increases;and a significant increasing trend as the depth of the reservoir area increases.It also reveals that the sampling method has an opposite effect on the sand content of the reservoir area with and without rainfall under changing water level conditions.(3)The differences in the effect of shear strength and hardness of soil next to Pinus tabuliformis and Amorpha fruticosa with increasing soil depth under heavy rainfall conditions were compared.In shallower soils(20 cm),soil shear strength and soil hardness were 23%and 52%lower next to Pinus tabuliformis than in the same soil at greater depths(40 cm).In shallower soils,soil shear strength and soil hardness were 16%and 44%lower next to Amorpha fruticosa than in the same soils in deeper layers.The soil and water conservation effects of Pinus tabuliformis and Amorpha fruticosa were also analysed under the conditions of this test.The shear strength of the soil next to Pinus tabuliformis was generally slightly higher than that of the soil next to Amorpha fruticosa in the shallower soils,and the hardness of the soil next to Pinus tabuliformis was slightly higher than that of Amorpha fruticosa in the shallower soils,while the opposite was true in the deeper soils.This study suggests that trees are more effective in soil conservation on the Loess Plateau from the perspective of soil consolidation,and this study recommends planting trees as a planting measure to control soil erosion on the gently sloping sections of the Loess Plateau.