Effect Of The Three Gorges Project Impounding On The Water Quality Of Reservoir Area

After the electricity generation, the benefits that the Three Gorges Project takes to people is obvious, for example: controlling the upstream flood effectively, enhancing the flood prevention ability of downriver, adjusting the current capacity of middle reaches in lowfiow perid, simultaneously using the hydro-energy electricity generation substitution burning mineral substance electricity generation, reducing the waste gas pollution, improving the route and so on. However the adverse effect that the Three Gorges Project brings to the society also cannot be avoided, and it has widespread long-term and lag influence to the environment.In view of the importance of the Three Gorges Project in governing and developing Yangtze River, the water quality change of reservoir water impoundment was concerned widespread by the domestic and foreign experts. Although in the forecast period , the domestic and foreign experts have carried detailed investigation, analysis and research on questions which the Three Gorges Project caused to the environment, obtained massive valuable research results, because of many kinds of complex factors influence, until now, the influence that the Three Gorges Project brings to water quality in the future still have not extremely explicit and quantitative conclusion, thus questions on the water quality in the future still is a hot topic in current research.Three years ago, 135 Project had been realized successively. During the three years, what does the first step of the project brings to the water quality? If the first impoundment regards as the preview of the second impoundment and the third impoundment, then studies on this question can provide a model for the later work.The aim of this thesis focused on the change tendency of the water quality parameter, the relations between silt and the water quality parameter,the change of the water quality and the influence of impoundment to the Chongqing down branch water quality during 135 project which based on the monitor data provided by the Changjiang Water Resources Commission. The results are summaried as follows. From 1996 to 2006, the overall water quality of the Chongqing section changes bad and the water quality monitored after 135 Project is better than monitored before 135 Project in the short-term, especially the density of the excrement intestine bacteria colony, the total phosphorus and the lead reduces obviously; After 135 Project, about half of the silt subsidence; there are good relevance between the silt density and the total phosphorus, the suspension, the lead, the copper density, and the correlation amounts to above 0.95. While confirmed that the adsorption capacity of the big size silt is smaller than thin size silt, it is also proved that the silt has strong adsorptive capacity to several kind of pollutant demonstrated above and the silt has not obvious adsorptive capacity to the total nitrogen. Because of density of the excrement large intestine bacteria colony and the total nitrogen exceed the allowed figure for a long time, the water quality level of Chongqing section keeps between V and the poor V kind. After 135 Project, the water quality level changes better because the density of the excrement intestine bacteria colony has reduced; But because the density of the total nitrogen changes not obviously, the water quality level still keeps between IV kind to V kind for its density exceeds the allowed figure; If the excrement large intestine bacteria colony and the total nitrogen does do not participate in the appraisal, the total phosphorus and COD_Mn become the main pollution, the density of this two Project has not surpassed IV kind of water standard, and because of the influence of silt's adsorption, the density of this two kinds Material obviously reduced, so the water quality category maintains below III kind of water standard; Based on the data monitored during 135 Project, after water stored, the tendency of the chlorophyll content in main current rise and in the branch reduce. In one word, after 135 Project, the water quality level changes better because the silt has strong adsorptive capacity to several kind of pollutant, but in the long-term,the impoundment of the Three Gorges Project can accelerate the eutrophication in the branch;influenced by the content of chlorophyll, the main current have the tendency of eutrophication.