| Many works have been done on soil erosion mechanism of sloping surface by research scientists in China. But there have no physical erosion prediction model that may be practically applied now. The target of model establishment is to predict the occurrence and development of soil erosion and provide scientific decision-making gist for erosion control. So research on erosion model has promoted research on erosion mechanism. At present, research of erosion mechanism and model on Suining group purple soil, which is the weakest erosion-resisting characteristic one of all purple soil, has been rarely found. Such a situation results in the lack of theories and practices basis which guides soil erosion control. The Water Erosion Prediction Project (WEPP) soil erosion model is being developed by an interagency group of scientists including the USDA's Forest Service, Agricultural Research Service, and Soil Conservation Service, and the Dept. of Interior's Bureau of Land Management and US Geological Survey. Scientists from these agencies throughout the United States have been working since 1985 to develop an erosion prediction model to replace the Universal Soil Loss Equation (USLE). The WEPP model is a complex computer program so far and with remarkable superiority compared with the other erosion predication models, which describes the processes that lead to erosion. These processes include infiltration and runoff; soil detachment, transport, and deposition; and plant growth, senescence, and residue decomposition. The model daily calculates the soil water content in multiple layers and plant growth, decomposition. The effects of tillage processes and soil consolidation are also modeled. Research on the application of WEPP model on the Suining group purple soil is very beneficial to the extensive comprehension of purple soil erosion mechanism and providing the scientific theoryfoundation for soil erosion control on the basis of the simulation of soil erosion process and regulating the controllable factors and quantitative assessment the efficiency of different water and soil conservation measures.In this dissertation, the contents are divided into three parts. In the first part, through the datum collected from the observation and experimental analysis of the runoff plot, the model parameters that needed during the erosion prediction are gained by consulting the processing mechanism of WEPP. The results shows that the test parameters are choose rationally. As climate file of the WEPP were created on the basis of the approximately 30 years continuous climate file, and the climate file in these experiment has only 4 years, so, we applied an approximation value for the subordination basal data in this model, which lead to some warp on reflecting the erosion mechanism of purple soil, therefore part of the parameter values need to be further verified and revised in abundant field plot experiments. In the second part, through the observation of the fallowland (15 degrees) in the runoff experiment station in the rainy season from 1999 to 2002, 28 times erosion process caused by rainfall are observed. With the WEPP model to predict the single runoff erosion of the fallow plot, the runoff yield and sediment yield of the runoff plot are obtained respectively, and the results of calculation are compared with the measured values. The result shows that the forecast values is close to the measured values in certain degree, but it may not predict the sediment yield on field grade surface totally and accurately. Using the WEPP prediction model can reflect the process of the actual runoff development and distributed status of the soil erosion yields accurately. Meanwhile, the result shows that the rainfall and the maximum rainfall intensity have great influence on sediment yield. From the contribute coefficient matrix, we can find that the direct effect generated by the rainfall on the runoff yields and indirect effect generated by the maximum rainfall intensity on the runoff yields are 0.7508 and 0.2245,. while the direct effect gen... |
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