Study On The Total Amount Control And Margin Of Safety For Three Gorges Reservoir Area’s Main Pollutants

Three Gorges Reservoir is a large-scale water conservancy project and has drawngreater attention. The construction and operation of this project have far-reachingimpacts on surrounding areas’ ecological environments. In order to ensure water qualityand safety and improve water environmental quality, not only pollution sources in ThreeGorges Reservoir area should strictly meet discharge standards, but also waterenvironmental capacity should be studied, which could be the basis for Total AmountControl of main pollutants.This thesis was a part of national water project ‘Study on the total amount controland integrated control technologies for water pollution in Three Gorges Reservoir area’,and based on the investigation and analysis of water pollution status the structuralcharacteristics of pollutants in Three Gorges Reservoir area was studied. The majorpollutants in Three Gorges Reservoir area manly derived from non-point sources, and60.59%of COD load,65.45%of NH3-N load and87.43%load were come fromnon-point sources. Based on various hydrology and water quality measured data, fieldsurveys and simulating lab tests, this study divided Three Gorges Reservoir area into106pollution control units according to the characteristics of the major pollutants,including59units in Yangtze River,6units in Jialing River,3units in Wujiang and38units in32tributaries in the mainstream of Yangtze River （Jialing River and Wujiangwere not included）.Then, with the cooperation of Scientific Research Institute of WaterResources Protection in Yangtze River, the water environmental capacity of eachpollution control unit was calculated by two-dimensional steady-state attenuation model.The results showed that generally Three Gorges Reservoir area had surplus waterenvironmental capacity, but in some individual units there was no surplus capacity forhigher water quality requirement and larger land-sourced pollutants load.First order error analysis was applied to analyze the impacts of various keyparameters on the water environment capacity calculation model’s results. The resultsshowed that the order of importance for these parameters was backgroundconcentration（C₀）>the depth of the mixing zone length（x）=depth of water（h）>velocity（u）=diffusion coefficient（E_y）>degradation coefficient（K）;under175m waterlevel condition, the reserved margin of safety for CODCr,NH3-N and TP accounted for11.9%,12.3%and12.4%of water environmental capacity, respectively; under145m level condition, they were15.6%,15.4%and15.8%. According to the results ofcalculated water environment capacity and margin of safety,the economic conditions,environmental conditions, water quality protection goals, as well as demographicfactors, AHP was the used to determine the total amount of pollutants for pollutioncontrol units and corresponding pollutants reduction measures were proposed.This thesis based on field survey data, after consulting domestic and internationalresults in total amount control and combining the actual situation of Three GorgesReservoir area, the total amount control for Three Gorges Reservoir area was studiedwith scientific and rational method. Therefore, this study had important significance forthe pollution prevention and water quality and safety in Three Gorges Reservoir area.