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Used the new generation model——WEPP(Water Erosion Prediction Project) which developed by United States Department of Agriculture, based on Remote Sensing and Geographic Information System, the simulate research on the soil erosion in Xiheidai watershed of loess hilly and gully region was carried out, meanwhile, according to the regional character of Xiheidai watershed, studied the relationship between soil erosion and sediment yield.Based on 22 years meteorological data of Xiheidai watershed, combined with DEM map, land-use map and soil type figure, by the use of WEPP model, the soil erosion and sediment yield process of Xiheidai watershed has been simulated. This paper has taken manual fixed method, calibrated the important parameters of the model, when the model simulated soil erosion and sediment yield of the watershed, the error was less than 15%, the correlation coefficient between simulation value and measured value was 0.998, a level of significance, the nash bargaining model efficiencie was 0.952, it showed the model has a preferable applicability in Xiheidai watershed.WEPP model could simulate soil erosion and sediment yield of different precipitation conditions, this paper combined with precipitation data of 22 years from 1988 to 2009 of Xiheidai watershed, simulated the soil erosion and sediment yield of three typical small watersheds: Fusanbeigou, Manliangou and Yangjiagou of Xiheidai watershed in normal year, dry year and wet year respectively, then analyzed the influence of precipitation on soil erosion and sediment yield changes. The results showed that: for each watershed, the erosion modulus in dry year is high, the erosion modulus in normal year took second place, the erosion modulus in wet year is the lowest, the reason might related to the process of the precipitation.In order to study the soil erosion and sediment yield of different land use types, three land use scenes was designed: whole forestland, with a coverage of 50%; whole grassland, with a coverage of 50%; whole farmland. Then simulated soil erosion and sediment yield of the three scenes of different precipitation level years by WEPP model respectively, the results showed that: for different precipitation level years, the modulus of soil erosion and sediment yield of forestland and grassland were low, most of the slopes erosion modulus were lower than the premise of soil loss tolerance(1000t/(km2·a)), which showed a good soil and water conservation function, at the mean time, it also showed that the effect of soil and water conservation of forestland was better, but the modulus of soil erosion and sediment yield of farmland was high, and the soil erosion modulus was higher than the premise of soil loss tolerance.According to the land use pattern status of the study area and the result of the simulation, optimized the land use pattern of the study area of different precipitation level years, the results showed that: under the request of the erosion modulus were lower than the premise of soil loss tolerance, for common precipitation year, the measures of land use optimization were: converting slop farmland to forestland and grassland, no change for forestland, increasing the coverage rate of grassland to 50%; for low precipitation year, the measures of land use optimization were: converting slop farmland to forestland and grassland, increasing the coverage rate of forestland to 50%; increasing the coverage rate of grassland to 80%, and improving the surface of forestland and grassland; for high precipitation year, the measures of land use optimization were: converting slop farmland to forestland and grassland, no change for forestland, increasing the coverage rate of grassland to 25%. By adjusting the internal structure of forestland and grassland, and converting slop farmland to forestland and grassland, reduced the soil erosion and sediment yield intensity, the erosion modulu was lower than the premise of soil loss tolerance. The result could provide basis for the land use optimization of the study area.
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