An Experimental Research On Sediment Transport Capacity Of Rill Flow On Loess Hillslope

The erosion in Loess Plateau is the most serious in the world. Severe soil erosion has resulted in great impacts on local ecological environment and sustainable development, and is the threat to the security on sides of the lower reach of Yellow River. Rill erosion is one of the main erosion processes and the source of sediment yield on hillslope of loess region, being important research object in China and abroad. Rill flow transport capacity is a key parameter of rill erosion processes. So clarifying the rill flow sediment transport capacity could not only promote process-based model of rill erosion effectively, but also provide an important scientfic basis for taking soil and water conservation measures and controlling soil and water loss on loess hillslope.By runoff scouring with non-erosion bed of experiments under different slopes and flow discharges, the process of rill flow sediment transport process on loess hillslope was studied. The study focused on hydraulic characteristics, sediment transport capacity of rill flow and coupling relationships between them. The main results are as follows:1. The hydraulic characteristics of rill flow on hillslopes was studied. The variation between rill flow velocity, water depth, resistance coefficient, Reynolds number and slope and flow discharge could be described by binary power functions, while the variation between flow discharge and flow velocity, water depth, Reynolds number, Froude number, shear stress and unit flow energy could be described by binary linea functions. Flow discharge has greater impacts on rill flow velocity, water depth, Reynolds number, Froude number, shear stress and uni flow energy than slope, but has less impacts on resistance coefficient than slope. The range of Reynolds number is 461.3 to 800.5 and mostly greater than 500, which showing that water flow regime under experimental conditions is water flow regime. The range of Froude number is 3.56 to 5.06, showing that the flow pattern under experimental conditions is rapid flow. Reynolds number increased with the resistance coefficient decreased.2. The variation of sediment transport capacity of rill flow was analyzed. Under different slopes, rill flow sediment transport capacity increased smoothly with flow discharge and it could be described by power functions. Under different flow discharges, rill flow sediment transport capacity increased with slope and it could be decreased exponential functions. Rill flow sediment transport capacity varies with flow discharge and slopes and it could be described by a dual binary power function. Flow discharge had greater influence on rill sediment transport capacity than slope.3. The coupling relationship between sediment transport capacity and rill flow hydrodynamic parameters was revealed. Under different flow discharges, the response of the flow sediment transport capacity to velocity could be described by power function, while the response to others could be described by exponential functions, including flow shear stress, unit stream power, stream power and unit flow energy. Under different slopes, the response relationship of rill flow sediment transport capacity with velocity and flow shear stress could be described by power functions. The response relationship of rill flow sediment transport capacity with unit stream power and stream power could be described by linear equations, and response relationship with unit flow energy could be described by exponential functions. Under different flow discharges and slopes, the response relationship between rill sediment transport capacity with shear stress could be described by power function, and relationship with unit flow energy could be described by exponential function, and relationship with unit stream power and stream power could be described by linear function.4. Rill flow sediment transport capacity dynamics mechanism was clarified. The order of coefficient of determination was: stream power (R~2=0.7851)>unit stream power (R~2=0.5890)> shear flow stress (R~2=0.5590). Under experimental conditions, the stream power is the best hydraulic parameter to describe rill flow sediment transport capacity .and the source of rill flow sediment transport.5. Established a significance dynamic model of rill flow sediment transport capacity. An equation was established: Tc = 0.1216(ω-0.5452), considering characteristics of flow hydrology,rationality of relationships of rill flow sediment transport and flow parameters and the coefficency and the choice of indicator, with significance relationship.