Study On The Evolution Of Rill Cross Section Morphology

Soil erosion is one of the important reasons of land degradation and deterioration of ecological environment. Loess Plateau is one of the most serious soil erosion area of our country. Rill erosion is an important way and the origin of loess plateau slope erosion, and it is also an important object of domestic research on soil erosion. The rill cross section morphology is created by the interaction of rill flow and soil, it has a direct bearing on the flow discharge, velocity of flow, sediment and soil erosion resistance,at the same time, the rill cross section morphology restricted the erosion intensity by influencing the rill hydraulic characteristics and sediment transport. In this paper, several quantitative indices of rill cross section morphology were evaluated, then the rill hydraulic characteristics were analysed by the scouring experiment. The focus of the study were how the slope, flow discharge, slope length, soil texture and other factors affected the rill cross section morphology and the relationship between rill cross section morphology and rill sediment transport. The main results are as follows:1. Several indices which can describe the rill cross section morphology were discussed. The rill width and depth has good maneuverability, the rill cross section morphology index η and rill cross section morphology coefficient C are more comprehensive. The rill width,depth and width/depth ratio can describe the size of the rill betterly, the rill cross section morphology coefficient C can describe the rill transverse profile twists or smooth degree betterly, the rill cross section morphology index η can easily describe the cross section likes a triangle or a rectangle.2. The rill hydraulic characteristics and sediment concentration were analyzed. With the slope increas, the flow velocity, Reynolds number, Froude number, resistance coefficient, shear stress and sediment concentration all increased; With the flow discharge increases, the flow velocity, Reynolds number, shear stress and sediment concentration all increased, the Froude number increased first and then decreased, the resistance coefficient has no obvious change; As the slope length extends, the flow velocity, Froude number and sediment concentration increased, the resistance coefficient decreased, the Reynolds number and shear stress have no obvious change; In the whole process of the rill development, with the passage of time, the Reynolds number decreased, the shear stress and sediment concentration have no obvious change. In the beginning stages, the flow velocity and Froude number decreases, the resistance coefficient increase, in the subsequent process, they remain unchanged.3、The evolution of rill cross section morphology were explored. As the slope increases, the rill width and depth developed faster, the width/depth ratio decreased and then gradually stabilized at 1.5~2.0; As the slope length extends, the rill changes from wide and deep to narrow and shallow, the width/depth ratio increased; As the flow discharge increases, the rill width and depth developed faster, the width/depth ratio first increased and then decreased; The rill on the slope of medium silt loam developed faster than that on the slope of heavy silt loam; the rill cross section morphology index η on the slope of heavy silt loam mainly concentrated in 0.70~0.85, but on the slope of medium silt loam, it concentrated in 0.40~0.75. In the whole process of the rill development, with the passage of time,the rill developed slower and slower, the width/depth ratio gradually reduced,on the slope of heavy silt loam, the rill cross section morphology index η and the rill cross section morphology coefficient C gradually increased, but on the slope of medium silt loam, they first increased then decreased.4. The relationship between rill cross section morphology and potential sediment transport capacity was revealed. The rill flow potential sediment transport capacity increased with the slope increased, but the flow discharge had less impacts on it. There was a negative correlation between the rill flow potential sediment transport capacity and the rill cross section morphology index η.