| Unbalanced sediment transport is the basic attribute of slope rainfall runoff erosion sediment transport.The balanced sediment transport of slope runoff in nature is relative and the unbalanced sediment transport is absolute.The study of the unbalanced law of slope erosion transport has important theoretical and practical significance.However,the study of unbalanced sediment transport in the process of slope rainfall runoff erosion and transport is still less involved,aiming at the problem of insufficient research on the unbalanced sediment transport process of rainfall runoff erosion on slope,based on the relevant theories of soil erosion mechanics,sediment movement mechanics and river sediment engineering,taking Yan’an Huangmian soil in Shaanxi Province as the research object,the indoor artificial rainfall simulation test method is adopted,under the control of 5 slopes(3,6,9,12,15°)and 8 slope lengths(1,2,3,4,5,6,7,8 m),the variation law of unbalanced sediment transport and sediment carrying capacity of rainfall runoff erosion on loess slope was studied.The main conclusions are as follows:(1)Under the test conditions,the velocity,water depth and Reynolds number of overland flow increase as a power function with the increase of slope length,the shear force increases linearly with the slope length,and Froude number and resistance coefficient fluctuate with the slope length.On the whole,the sediment concentration of runoff increases in a power function with the increase of slope length under different slopes,and the increasing rate decreases with the increase of slope length.The greater the slope,the shorter the slope length required for the sediment concentration of runoff to be stable.When the slope is 3～15 and the slope length is 1～8 m,the initial runoff time decreases with the increase of the slope length,the law of runoff yield and sediment transport of slope runoff shows that it increases greatly in the first six minutes after runoff yield,with the backward extension of rainfall duration,there is an overall fluctuation trend,and the larger the slope and slope length,the greater the fluctuation change.(2)The velocity,Reynolds number and Froude number of slope flow increase with the increase of slope,runoff shear increases logarithmically with the increase of slope,the flow resistance coefficient of slope increases at first and then decreases with the increase of slope,reaching the maximum when the slope is nine,the maximum resistance coefficient is0.258.When the slope length is the same,the sediment concentration of slope runoff increases with the increase of slope,when the slope increases from 3 to 15 and the slope length is 1～8m,the increase of sediment concentration is the largest at 5m,increasing by2.34 times,and the increase of sediment concentration in runoff is different when the slope is equal.Under the same slope length,the rainfall runoff and sediment transport rate per unit width on the slope increased at first and then decreased with the increase of slope,reaching the peak when the slope was 12.The average sediment transport rate per unit width is exponentially related to slope and discharge,and the effect of discharge on the average sediment transport rate per unit width is greater than that of slope.(3)Under the condition of rainfall runoff erosion,the sediment carrying capacity of water flow is directly proportional to hydraulic gradient and velocity,and inversely proportional to water depth.Furthermore,the formula of sediment carrying capacity of water flow under experimental conditions is given,found that the sediment-carrying capacity of slope flow has a power function relationship with the ratio of turbulent diffusion and gravity((1~3/2)?),compared with open channel flow,the ratio of turbulent diffusion and gravity is larger.It shows that the turbulent action of raindrops on slope flow is obvious,and the slope flow is"Thin layer flow with two turbulent sources".(4)Sediment concentration in runoff is proportional to the 1/2 power of hydraulic slope and the 4/5 power of slope length.Based on the formula of sediment carrying capacity and unbalanced sediment transport equation,the formula between the saturation coefficient of sediment recovery and hydraulic gradient is given,the unbalanced sediment transport model of slope rainfall-runoff erosion under the condition of rainfall intensity of100mm/h and slope of 3～15 was simulated,and verify the equation with the measured data.The research results provide a reference for in-depth analysis of slope runoff erosion and transport mechanism and prediction of slope runoff erosion and sediment transport changes along the way. |
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