Study On Non-point Source Pollution Simulation Of Representative Small Watershed In The Three Gorges Resevoir Area

Located at the south of Daba mountain and north of Yun Gui highland edges,Three Gorges Reservoir Area is at the cross-section of three structure units -(which are )fracture fold belt of Daba mountain, fold belt of Sichuan province, and fold belt of SiChuan, HuBei, HuNan, GuiZhou province. The regional water and soil environment have been paid more attention because of the establishment of Three Gorges Reservoir. Since its special geographical position and agricultural structure, non-point source pollution in reservoir area becomes more and more serious. So, in this thesis, the situation of the rainfall, runoff and non-point source pollution had been studied based on the simulation by L-THIA model. The relationship between non-point source pollution and the change of regional land use had been thoroughly analyzed, in order to discover the current situation of non-point source pollution and its response to the change of regional land use in Wangjiaqiao watershed. The study will provide reference for management of watershed in future. The results are as follows:(1) Ia/S value of SCS-CN method was determined as 0.05 by studying observed rainfall-runoff data. This Ia/S-adjusted SCSCN method appeared to be better appropriate for runoff prediction in the TGA of China. After modification, that was relatively satisfied result for the regional simulation by the model, with the coefficient of determination of 0.804, the linear regression slope of 0.834, and model efficiency coefficient (E) of 0.768.(2) The annual average runoff in the watershed was predicted based on the six years'observed rainfall data, land use data in 1995, and hydrologic soil group data The relative error between the prodicted and the observed was 8.2%, which indicted that the model was feasible for this watershed.(3) annual average runoff in the watershed was predicted respectively based on the land use data in 1995, 1999 and 2005. The predicted values were 465.89mm, 458.96mm and 441.81mm respectively, which shows a descending trend, because of the change of land use these years.(4) Non-point source pollution load was predicted by the non-point source pollution module of L-THIA GIS model. It could be seen from the results that land use types being sensitive to total N and total P were paddy field, agricultural, orchard, and rural residential, while land use types being sensitive to sediment were agricultural, orchard, and rural residential.(5) Through investigation, it was discovered that the transformation from paddy field, agricultural to orchard had been suspended by 2005 in the watershed, and its influence to rainfall, runoff and non-point source pollution had been stable. With the development of the watershed in the future, the change of rural residential and forest would become the main factors influening runoff and non-point source pollution in the watershed. In this study,we have optimized the landuse structure in wjq watershed, and there were several suggestions being brought forward for the future management of Wangjiaqiao watershed in the end.