| The Wudinghe watershed is located the south margin of Mu Us desert in the north of the loess plateau, and the Wudinghe River is a main branch in the Hekouzhen-Longmen Reach of the loess plateau. In the Wudinghe watershed, Heavy Rainstorm centralized, soil texture loosed, natural vegetation scarce and the natural corrosion is intense. Under the long-term influence of unreasonable human activities, such as the reclamation of steep slope, over-grazing and the destruction of natural vegetation, the human activities accelerated corrosion extremely and caused serious soil erosion. The soil erosion area reaches 26,500 km~2, 87.7% part of the total basined area.The material indicated that, from 1956 to 1969 the Wudinghe River transports sand 218 million tons per year, approximately 21% quantity of the sand come to the Hekouzhen-Longmen Reach at the same time.The Hekouzhen-Longmen Reach in the middle reaches of Yellow River not only is the main source area for the water of the Yellow River, but also is the main source area for the thick silt of the Yellow River.The soil erosion is a important ecological problem in the western region of our country。similarly, the soil erosion causes the land to degenerate, the soil fertility weakens, the river, lake and storehouse silts up in the basin, brings the significant influence to the life of local people and the people living in the middle and lower reaches Yellow River.The forest vegetation which has huge hydrology function such as restrainting headwaters, regulating flows, improving water quality, protecting soil and water environment, therefore the reasonable forest vegetation ecological construction is the critical path to resolving the problem of water resources and water environment.The significance of this thesis lies in improving the ecological environment in the west, reducing soil erosion, especially cognizing the effect of the forest vegetation environment, thus provides the important scientific basis for the ecological environment construction and the sustainable development in the western area.This thesis chooses The Hekouzhen-Longmen Reach, a branch of the Yellow River, as the example research object, imitating and studying the runoff, sediment yield situation in the research area with the application of distributed hydrological model SWAT(the Soil and Water Assessment Tool), and stressing on the influence of rainfall and land use / evolution of forest vegetation structure to erosion and sediment yield responds.This thesis analyses and studies the research object synthetically with the application of geographic information system (GIS), remote sensing (RS) technology. First we obtained 3 period of land utilization type chart separated 10 years and used the shift matrix analytic method to analyze the evolution and the driving-force of the land utilization pattern in the research area. Next, the Wudinghe Basin spatial databases (including digital elevation model (DEM), land use maps, soil type maps, etc.) and attributive databases (including rainfall, temperature, wind speed, relative humidity, etc.) were established. With the support of SWAT model, the 15 sub-basins have been delineated by the DEM and the river system distribution map. And the model parameter sensitivity has been analyzed and the parameter has been calibrated and validated with the real data collected from the study area in the years from 1980 to 2000. In calibration period, the relative error is within 11.57%, relative coefficient and Nash-Suttcliffe coefficient are 0.887 and 0.886, in validation period relative error is within 9.89%, relative coefficient and Nash-Suttcliffe coefficient are 0.851 and 0.829 respectively. The results indicate that the linearity regression coefficient of the actual current capacity and the simulation current capacity satisfy the request of the model simulation, as well as the model coefficient of efficiency. This model is suitable for the research basin, has realized the hydrology response simulative study of the distributional hydrology model to the runoff, sediment yield situation in the west arid area.According to the simulation result of SWAT model, applying the GIS spatial analysis function, the thesis analyze the characteristic of spacial distribution of runoff, sediment and nutrient loss in different period of time in 1980,1990 and 2000 and the influence of sediment yield situation by different kinds of landuse. The result shows that the rainfall and landuse both have a great impact on the runoff, sediment and water quality. The more rainfall in a month, the more runoff and sediment; contrarily is the opposite. The land utilization change mainly represented that the reduction of the unused land and the cultivated area, and the increase of the forest land, the lawn. The corresponding hydrology change is the reduction of runoff, sediment.The application and establishment of distributed hydrological model SWAT in Wudinghe watershed, fully reflect the spacial difference of rainfall factor and underlying surfaces. Realistically simulate runoff and sediment process in basin, not only helps to deeply understand the process of the runoff and sediment production, but also use to simulate the response of sediment and runoff under different land uses, and provide an effective way to study the response of runoff and sediment to land use.
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