Study On Unbalance Characteristics Of Sediment Transport By Rainfall Runoff Erosion On Slope

The processes of erosion,transport and deposition occur anytime and anywhere in the slope erosion process,which indicates that the rainfall-runoff erosion and sediment transport on the slope is an unbalanced process.However,the existing erosion and sediment transport models can not reflect the unbalanced transport process of runoff erosion and sediment transport by calculating and simulating the average amount of erosion on the slope.Rainfall runoff on slope erosion sediment research the problem of inadequate unbalanced process,according to soil erosion mechanics,mechanics of sediment movement,river sediment engineering,watershed hydrology and other related theories,adopt the method of simulating rainfall experiment,different rainfall intensity and slope length is studied under the condition of unbalanced slope rainfall runoff sediment characteristics,made the following main conclusions:(1)Variation characteristics of hydrodynamic parameters of slope runoff erosion:when the slope is 10°,the flow velocity increases with the increase of rain intensity and slope length,and there is a power function relationship between the flow velocity and rain intensity and slope length.The Reynolds number(Re)is less than 500.According to the criterion of open channel flow,the water flow belongs to laminar flow.However,the Reynolds test shows that the water particles are mixed under rainfall conditions,so the water flow is in a turbulent state under the test conditions.Froude number(Fr)is greater than 1,belonging to the jet stream;During the test,the change of the resistance coefficient is non-constant and its magnitude is related to the position of slope surface and the shape of bed surface.When the slope length is constant,the flow shear force,flow power and unit flow power increase with the increase of rainfall intensity;when the rainfall intensity is constant,the flow shear force fluctuates with the increase of slope length,and the flow power and unit flow power all increase with the increase of slope length.(2)Sediment carrying capacity of overland flow: in the erosion process of rainfall-runoff on slope,the balance state is relative,while the imbalance state is absolute.The sediment carrying capacity of overland flow refers to the sediment carrying capacity of overland flow under the condition of no scour and no silt under the condition of a certain rainfall intensity and bed surface shape.Under the condition of rainfall-runoff erosion,the sediment carrying capacity is proportional to the cubic power of flow velocity and inversely proportional to the product of hydraulic radius and settling velocity.Based on the laboratory test data,the calculation formula of sediment carrying capacity of overland flow under rainfall conditions is obtained,which lays a foundation for the establishment of the unbalanced sediment transport model of rainfall erosion on overland.(3)Characteristics of Unbalanced Sediment Transport by Rainfall-Runoff Erosion on Slope: The rule of sediment production and failure in the test field all showed a sharp increase and change in the first few minutes after runoff production,and then showed an overall fluctuating increasing trend with the passage of rainfall time.The process of runoff production and sediment transport on slope presented an obvious non-constant and non-uniform unbalanced characteristic,indicating a sharp change in slope erosion.The quantitative relationship between the saturated coefficient of water flow and sediment recovery and rainfall intensity under erosion condition was studied.The unbalanced sediment transport model of rain-runoff erosion on slope with a slope of 10°and rainfall intensity of 40-120 mm/h was established and verified.The research results are of great significance to deepen the theoretical understanding of slope erosion and runoff transport.