Research On Coupling Mechanism Between Morphology And Development Of Rill's Flow And Erosion And Sediment Yield Under Variable Flow Scouring

The severe soil erosion in the Loess Plateau not only makes the Yellow River become the largest sedimentary river in the world,but also forms a unique geological formation in the region.As one of the main ways of slope erosion,rill erosion is the main source of power for the convergence of erosive rainfall.Therefore,the two main factors,hydrodynamic characteristics and rill soil conditions,are analyzed to reveal the coupling relationship between the rill morphological characteristics and rill erosion and sediment yield during the development of rills and various hydraulic parameters under unsteady flow,which have certain reference significance for further study of rill erosion mechanism.In this dissertation,the Ansai yellow loess soil is taken as the research object,and this research investigated the hydrodynamic characteristics of the rills in the loess area,the erosion mechanism and dynamic characteristics accompanying the morphological evolution of the horizontal and vertical sections,and the mechanism of runoff and sediment production under four types of flow combination types(increased,uniform,concave and peak)and five slopes in the loess area based on artificially simulating the indoor water flushing erosion experiment.The main conclusions are as follows:(1)The average flow rates of uniform,peak and increased types increase with the increase of slope.The average flow velocity of the concave type increase first and then decrease with the increase of slope,and the average flow velocity,flow rate and slope satisfy the power function relationship.Under the same slope,the Reynolds number of the increased,concave and peak types is basically consistent with the flow combination type,and the larger the flow rate,the more the Reynolds number Re fluctuates.The range of Froude number is 1.24~3.49.The rill water flow belongs to the rapid flow,and the number of Froude number increases with the increase of slope,and Fr growth rate of peak type is fastest.The flow resistance coefficient of lambda ? of the increasing type,the concave type and the peak type increase as the slope increases,and the uniform type ? decreases as the slope increases.The cross-sectional width and average flow velocity of each flow combination type satisfy the quadratic function relationship.The average flow velocity corresponding to the maximum width of the increased cross-section of the increased,uniform,concave and peak types is 0.633m/s,0.438m/s,0.570m/s and 0.423m/s.(2)The cross-sectional width-depth ratios of the increased,uniform,concave and peak types are respectively ranged from 2.56 to 4.97,2.29 to 4.29,1.97 to 4.02 and 2.31 to 5.32,and they decrease with the increase of the slope.The rill cross-section shape of the increased and peak types is approximating to the trapezoidal hydraulic best section,and the maximum depth of the rills is satisfied in different slopes: up-slope > down-slope > middle-slope;the maximum depth of uniform and concave types is satisfied in different slopes: up-slope > middle-slope > down-slope.The pit development co-efficient SP of the longitudinal section shape is ranged from 1.014 to 1.100.Under each slope,the SP and energy dissipation rate of the peak type are the largest,and the energy dissipation rate increases with the increase of SP as a parabola.The Manning roughness coefficient of each flow combination type increases linearly with the increase of the pit development co-efficient SP.(3)Under the same slope,the runoff intensity and erosion amount of the concave and increased types are basically consistent with the change of flow combination type,while the peak type of erosion has been increasing.The soil erosion rate under each flow combination type generally increases with the increase of water flow shear force,water flow power and effective water flow power.The dimensionless analysis of each parameter shows that water flow power is the most representative and accurate for the prediction of soil erosion rate,and the runoff shearing force is second,and the water flow velocity is the worst.The soil erosion rate and runoff intensity and energy dissipation rate of the four flow combination types all satisfy the power function,and the correlation is higher.The soil erosion rate of the peak type increases fastest with the runoff intensity,and the soil erosion rate increases with the energy dissipation rate obviously.The soil erosion rate of each flow combination type increases with the increase of pit development co-efficient SP,and decreases with the L/H value figure increases.