Non-point Sources Pollution Modeling in Watershed Scale:Case Study of Xili Reservoir(Shenzhen) with HSPF.

Assessments of environmental impacts of non-point source(NPS)pollutants at watershed scale are necessary as a basis for water resources management effectively,simulation techniques are necessary to develop management strategies for abating the NPS pollution.In this study,the basic structure of a model called HSPF(Hydrologic Simulate Program-FORTRAN)developed by United States Environmental Protection Agency was introduced,which was employed to simulate water quantity and water quality of Xili Reservoir Watershed in Shenzhen,Guangdong Province.The model was calibrated using the water year 2000,and validated using the data from July 2004 to June 2005.Watershed was delineated and segmented using GIS technique,with field surveillance supplying water quality data.The model was calibrated and validated by comparing various simulated and monitored scenarios,included stream flow and concentration of pollutants in the river outlets,finally total loadings of SS,TN and TP in each sub-basin were calculated.According to the good-of-fit statistical analysis,the coefficients of determination and Nash-Sutcliffe coefficients for daily surface runoff,sediment,TN and TP were calculated;the simulation was acceptable on the whole.The consequence revealed that NPS had been the primary causes triggering water quality devastation,and fertilizers use in orchards is the first contributor for nitrogen and phosphors pollution,minimizing fertilizer utilization can reduce non-point sources loadings at a large scale.