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Watershed - lakes constitute a complete system, both through the river network system linking watershed runoff to the lakes in the convergence process within the watershed pollutants into the lake body, causing the pollution of the lake. With the rapid economic and social development in the Taihu Lake Basin, Taihu lake facing increasingly severe eutrophication problems, has a great contribution of pollutants from the river basins of the lake eutrophication. The Xitiaoxi River is one of the main basin of Lake Catchments, has an important impact on the watershed of Taihu Lake water and pollutants balance. Research the runoff Xitiaoxi process and pollutant outputs understanding of hydrology, water quality in Taihu Lake change, and to carry out similar basins around the research is of great significance. Distributed hydrological model SWAT (Soil and Water Assessment Tool), In this paper, the United States Department of Agriculture Agricultural Research Service developed on the basis of the survey the collection basin Basic information, combined with GIS and RS technology means of the River Basin Xitiaoxi the runoff process and water balance simulation, and analysis of the impact factor of the regional water balance. First, according to the basin rainfall, hydrological and other data of Xitiaoxi Catchment rainfall runoff trends 1968-2001 consistency analysis and Inspection, precipitation intensity and precipitation affect the runoff coefficient Xitiaoxi main reason for the change. This conclusion is further rainfall runoff model and model rate given the basis for the choice of the period. Second, to collect a the River Basin Xitiaoxi the DEM data, land use, soil classification, basin-wide, and other basic meteorological data maps and data, and modify the database of maps in ArcView platform, its database structure conforms to simulate data requirements, in order to establish the the SWAT model space and attribute database. Form a database based on the use of AVSWAT module carried by the watershed hook painted basin is divided into 47 sub-watersheds and 180 hydrological response unit (HRU). SWAT model divided the HRUs and input of the attribute database of 14 years Xitiaoxi month, day runoff simulation. The model rate regular monthly, daily runoff simulation and measured values ??of the linear regression coefficient R 2 0.848,0.8321 its the Nash-Suttclife coefficient the Ens respectively 0.84,0.908 model validation period of months , daily runoff simulation and measured values ??of R 2 , respectively 0.8945,0.8109, Ens were 0.88,0.856. The results show that the measured flow and simulation flow linear regression coefficient and Nash-Sutcliffe simulation efficiency coefficient to meet the requirements, and show that the model can be applied to the area. Then, the application of SWAT model of the river basin 1988-2001 water balance sub analog calibration and validation results meet water balance requirements. Parameter sensitivity analysis methods using single factor, the three most sensitive parameters in the SWAT model ESCO (soil evaporation compensation coefficient), CN 2 (semi-humid conditions runoff curve number) and AWC (soil layer, the effective use of water) sensitivity analysis obtained: ESCO, CN 2 proportional to runoff, the greater the parameter value, the greater the runoff AWC runoff inversely, the smaller the parameter values the greater the runoff. Model CN ?? 2 value of maximum sensitivity. In this study, the use of distributed hydrological model SWAT model of the basin Xitiaoxi runoff process simulation, simulation results verify the applicability of the model in the basin, rich data, and laid the foundation for the next step simulation of pollutant transport .
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