The Slope Soil Erosion Process In The Rocky Mountain Area Of North China Under Different Rainfall Patterns

In order to research the impact of rainfall patterns on slope erosion in the rocky mountain area of North China,the loess cinnamon and the calcic cinnamon from this area were selected and indoor experiments were conducted.The experiment treatment included 3 rainfall patterns with the same total rainfall and mean intensity(uniform type,rising type and falling type,the corresponding combination of rainfall intensity was 60,30?60?90,90?60?30 mm/h)and 2 slope gradient(6°,12°).This paper studied the influence of rainfall patterns on the runoff and sediment production of slopes in the rocky mountain area of North China,analyzed the hydrodynamic characteristics of runoff and micro-topography changes of slopes,and clarified the response relationship between slopes erosion and micro-topography.The main conclusions were as follows:(1)The initial runoff time of different rainfall patterns was negatively correlated with the rainfall intensity at the initial stage.The initial runoff generation time of the rising type slope was extended by98.4%and 314.9%than that of the uniform and falling types,the time of the calcic cinnamon was62.8%longer than that of the loess cinnamon.The order of the total runoff was falling type>rising type>uniform type.The total runoff of falling and rising type was 1.01 to 1.12 times of the uniform type.The runoff and contribution rate of the same rainfall intensity at the initial stage was smaller than that at the end stage,and the smaller the rainfall intensity and slope,the more obvious the timing effect.(2)The order of total erosion was falling type>rising type>uniform type.The total erosion of falling type and rising type was 1.78 times and 1.47 times of the uniform type.The highest total erosion of the loess cinnamon was 2.43 times of the calcic cinnamon.The order of morphological characteristics of rills density,maximum rills length and maximum rills width were falling type>rising type>uniform type.Except for the 6°calcic cinnamon slope,the erosion volume and contribution rate of other rainfall intensity at the initial stage were greater than those at the end stage.(3)Compared with the uniform type,the velocity,Reynolds number,Froude number,runoff shear stress and runoff power of falling type increase by 17.5%?35.5%,27.7%?86.8%,0.7%?29.1%,9.8%?51.0%and 29.0%?86.8%,the corresponding parameters of rising type increase by 6.1%?20.4%,2.6%?50.7%,-11.1%?12.5%,2.4%?42.1%and 12.3%?50.7%.Except for the turbulence flow of 12°the calcic cinnamon slope,the surface flow was transitional flow,and Froude number was all less than1,indicated that surface flow was subcritical flow.The sediment yield on the slope had a significant positive correlation with the mean flow velocity,Reynolds number,and Froude number,and a significant negative correlation with the drag coefficient.The sediment yield rate had a very significant power function relationship with runoff shear force and runoff power with the determining coefficient of R~2(runoff power)>R~2(runoff shear stress).So runoff power was the better hydrodynamic parameters to describe the soil erosion process under this test condition.(4)With the increase of rainfall time,the average of micro-slope and surface roughness gradually increased at each stage.The order of micro-slope and surface roughness was falling type>rising type>uniform type,the micro-slope and surface roughness of the loess cinnamon were greater than those of the calcic cinnamon.The total runoff,total erosion,mean flow velocity,Reynolds number,runoff shear stress and runoff power were significantly linearly correlated with surface roughness.