Urban River Overflow Weir Reoxygenation And Water Quality Of The Water

In order to study the shape and the gradient and the material of the overflow dam in the city river, monitor the water current character at the top and the toe of the plane overflow dams, the different stroma dams, the different roughness dams, the different shape dams, the different grade dams, and analysis the water quality at the top and the toe of the overflow dams timely, the result is:(1) The plane overflow dams and the stepped overflow dams can change the water current configuration, and increase the interface area of the hydrosphere. Using the two overflow dams, more oxygen is dissolved in the water body, some organic contaminants are degraded, and the self-purification power of the water body is enhanced. The aeration process play a major role in enhacing the water self-purification capacity when compared with the biochemistry process.(2) In the study, the effect of two dams (plane dam and stepped dam) are compared. Results showed that: when using the plane dam, the water velocity is rapid and the interface of the hydrosphere is small, therefore the reoxygenation extent is low, and the removal effect of the contaminants is not prominent; however, when using the stepped dam, the water velocity is slow and the interface of the hydrosphere is bigger, so the reoxygenation extent is evidently enhanced, and more contaminants is removed;(3) Three different gradient stepped dams(30°, 45°and 60°) were studied. The results indicates that not only the interface of the hydrosphere at the 45°dam is bigger than the other two dams, but also its reoxygenation extent and contaminants removal rate are both better than the other two dams.(4)The stroma and the roughness of the dam can affect the aeration and the contaminants degradation. The function is operated by the accreted biofilm of the dams. The stroma and the roughness of the dams can affect the biofilm growth and the abscission. When water flowing the roughness dams, the more roughness dam accretes more biofilm, which can reduce the biofilm permeability. Therefore, the function of biofilm can't well operate, and due to the old biofilm can't easily fall off the dam, the contaminants it releases would pollute the water again; For the smooth dam, because its slope is so smooth that no biofilm can be accreted, the fuction is only operated by the aeration process. Its efficiency in purifying water is not markedly. After compared the condition of the stroma and the roughness of the overflow dam, only if choosing the material that benefits the water aeration and the old biofilm can easily fall off the dam, the overflow dam can exert the self-purification fuction.When constructing the overflow dam in the city river, the optimum shape of dam is stepped, and the optimum gradient is 45°when flowing the same distance. Additionally, the principle to choose dam material is the material not only should be good for the new biofilm growth but also can accelerates the old biofilm falling off the dam.