| With the rapid development of economy, the deterioration of the environmental quality is threatening the human survival and development in the world. Now soil erosion and non-point source pollution are becoming the attentive topic among the people. Rainfall-runoff simulation is the very important technique for soil erosion, non-point source pollution, surface water balance calculation and some other study fields. Water is always the main factor not only during the course of soil eroding but also during the process of non-point source pollution moving. So hydrological process of watershed is the central problem in the study of soil erosion and non-point source pollution with watershed in scale.With the development of computer technology and some cross knowledge, the study method of watershed hydrological simulation has changed ultimately. The outstanding trends are that computer technology, spatial technology and remote sensing technology are applied in hydrological model and distributed physical hydrological model is brought about widely. In the hydrological simulation, RS and GIS technology bring innovation for the traditional study methods. Digital elevation model (DEM) technology provides stable foundation for the development of digital hydrology and the naissance of the digital hydrological model in particular. DEM has abundant information about terrain, and we can extract the watershed basic characters, which include land surface characters, drainage network et al based on GIS, and also can make certain the watershed boundary and set off sub watersheds from DEM, which provide the flat roof for digital hydrological simulation.Taken Yanjia river watershed as an example, this study extracted watershed digital characters from DEM, and simulated rainfall-runoff with the rainfall-runoff model based on GIS and WMS. The main contents and results include:(1) The building of the spatial database of watershed. Windows 2000 Professional was used here for operating system, and Arc/Info 8 from ESRI Company was used for the work flat floor. This study builds the spatial database of Yanjia river watershed, which includes digital elevation model, watershed drainage network, soil, land use et al. In the Yanjia river watershed, paddy field and dry land are the main types in land use, which are 68.05% of the whole watershed. And woodland is 27.47% of the whole watershed. The primary soil in the watershed include sand land, yellow land, which is 57.59% of the whole watershed. And sand land is 41.47% of the whole watershed, which mainly distributes in the middle of the study area. There are many areas that slope is < 3° and slope is between 7° and 25°, which is 41.58% and 34.5% of the whole watershed respectively. While in the study area there are 13.59 Km2 that slope is >25°, which is 18.74% of the whole watershed.(2) The construction of the digital watershed. This study extracted watershed drainage network, set off sub-watersheds and made certain watershed boundary. And this study also extracted some parameters about hydrology and terrain based on DEM. This study set off six sub-watersheds from the Yanjia river watershed, and calculated the areas of each sub-watershed. The areas from the first to the sixth watershed are 19.72 km2, 7.31 km2, 9.03 km2, 18.55 km2, 10.04 km2, 7.91 km2 respectively, and the percentage of each sub-watershed from the first to the sixth is 27.18%, 10.07%, 12.44%, 25.57%, 13.84%, 10.90% respectively. Among the six sub-watersheds, the forth is the biggest about watershed length, which is 8.18 km, the second sub-watershed is the highest in average elevation, which is 588.76m, the forth sub-watershed is the longest about drainage network length, which is 11.5 km, the second is the biggest about drainage network slope, which is 0.0814.(3) The rainfall-runoff simulation applying rainfall-runoff model. Firstly, this study set up rainfall-runoff model in each sub-watershed, and then set up conflux model using Muskingum method. In each sub-watershed from DEM, we used SCS runoff curve...
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