Study On Numerical Simulation Of Water Environment And Water Quality Evaluation In Dongzhuang Reservoir

With the rapid development of China’s economy,the development of hydropower is an important energy strategic measure to promote sustainable development.Dongzhuang water conservancy project is mainly used to alleviate the contradiction between supply and demand of water resources in Jing River and Wei river basins,and to slow down the sedimentation of Jing River and Wei River.However,while the economic benefits are brought by the water conservancy project,the impact on the environment can not be ignored,such as the adjustment of hydrological situation such as the dam blocking the fish return,the ecological water demand of the river and the change of water environment in the reservoir area.Based on Dongzhuang reservoir basin,this study simulates the hydrodynamic changes in different hydrological years after the operation of Dongzhuang reservoir,analyzes the water environment characteristics in the inundated area、the convective-diffusion trend of pollutants and spatial and temporal distribution of important water quality index(COD_Mn,Do,TN,TP,NH₃-N,Chla),analyze the pollution source and judge whether the water quality level is up to standard.The specific conclusions are as follows:（1）After the reservoir water storage,the water level in the front section of the dam changes greatly,and the water level rises obviously.From the perspective of spatial distribution,due to the change of topography from dam site to reservoir tail,the range of water level change gradually decreases.When the reservoir is at high water level,the horizontal inundation affects the place 80km away from the dam site,and the water depth and water surface width change greatly in this area.From 80km away from the dam site to the area at the end of the reservoir,the water level is mainly affected by‘tail raising’,while the reservoir has little influence on the water depth and the width of the water surface in this area.From the perspective of time distribution,with the change of the operation level of the hub and the flow condition of the natural river course in a typical year,the change amplitude of the water level fluctuates to a certain extent,which changes the water form of the original natural river course.Due to the influence of the reservoir’s own regulation and the north line water supply,the annual flow process at the dam site is generally smaller than that of the natural river course.（2）In the aspect of water environment,the main pollution factors generally show a decreasing trend from the end of the reservoir to the front of the dam.There are many pollution sources in the reservoir area along the line of the reservoir.The water volume of the pollution source is small,but in a certain period of time,the local area of the reservoir area still causes the phenomenon of the pollutant concentration rising in a short time.（3）The source of pollution in Xunyi county and Binzhou City,which has a great impact on the reservoir area,causes obvious pollution in the shallow water area at the end of the reservoir.Chunhua County,Yongshou county and Liquan county are located in the reservoir and in front of the dam,which has a significant impact on the water quality in front of the dam.The pollutant concentration in the reservoir area（especially in front of the dam）is higher than that in the normal and low water periods after the flood season.During the flood season（July and August）,the inflow flow and the discharge flow at the dam site increase rapidly,and the flow speed of the water body in the reservoir area accelerates.The pollutant concentration in the water body in front of the dam increases after the flood.（4）Based on the BP neural network,the non mechanism water quality evaluation research is explored.The analysis shows that the water quality results in extremely low water year include class I water quality,class II water quality,class III water quality and class IV water quality.The water quality of the reservoir is mainly class II from January to March,class IV from April,class III from May to July,and class I from August to December through self-purification.The water quality of Dongzhuang reservoir is basically in the state of moderate eutrophication after impoundment.