Research On Water Quality Prediction In Nuozhadu Reservoir In Yunnan

NuoZhaDu hydropower project in YunNan is the biggest in the step exploitation of LanCangJiang River middle-down stream. The completion of reservoir will change hydrological situation and hydro-environ conditions in the reservoir area, further exerting an important effect upon ecology, farmland irrigation and living water use .ect. For this reason, water quality prediction is an important part of environmental impact assessment before the construction of hydropower station. Prediction of water quality in the reservoir before its construction, is of great significance of environ protection and construction, operation for the project.According to the characters of NuoZhaDu reservoir, A longitudinal one-D dynamic heavy metals model is built in this paper, and the model is simplified by using synthetic sink coefficient. After the simplification, the number of parameter in the model is lesser, it can be solved easier, and the wanted data are lesser. The model is validated by the measured data of water quality in the river, and the relative error is minor. In this paper, the longitudinal change and vertical distribution of organic pollutant is predicted in the reservoir after its completion, which by establishing vertical false two-D water quality model, some problems existing vertical two-D model such as the difficult solve and disposal are overcame. In the case of without similar reservoir data, the predecessor research outcomes are used for reference, then determine oxygen exhaustion coefficient, oxygen recover coefficient and vertical turbulent diffusion coefficient in the paper.According to existing water quality at present, the serious polluted water quality indexes: heavy metals (Zinc, Arsenic), organic pollutant (BOD5, DO) are chosen as prediction objects. When three typical years, every month the water quality in the reservoir is predicted by utilizing the two models which are built above.The prediction results indicate: (1) the completion of reservoir will increase hydraulic detention time, which will be advantage of heavy metal sink. (2) In the three typical years, water quality in low flow year will be the worst, the difference of water quality in high flow year and moderate flow year will be minor. (3) In one year, water quality in rainy period will be the worst, as the upstream reservoir pondage action, water quality in low flow period and moderate flow period will has little difference. (4) BOD5 and Zinc concentration will belong to the range of Group I water in the three typical years; Arsenic concentration will be high in some times and segments when low flow year, but it will belong to the range of Group I water in rainy year and normal year. (5) DO in reservoir surface will meet the range of Group I water, DO in station water outlet will belong to the range of Group I ~ II for water quality standards, because water depth in the reservoir is very big, the reservoir will become stable stratified reservoir, DO in reservoir bottom will be Group IV - V water. (6) The tributary right XiaoHeiJiang River is the main pollutant source, so pollution control and harness in the river basin should be strengthened.