| With the rapid development of our society and the rapid development of engineering technology,large-scale water diversion project has become the main way to solve the unreasonable distribution of water resources,the shortage of water supply,and the contradiction between supply and demand in water shortage areas.The construction of water diversion project can promote the coordinated development of urban economy,society,population,resources and environmen.However,large-scale water diversion project is a dual transfer of water resources and water environment capacity,which has a very complex impact on the water environment of the basin.It is of great significance to study and analyze the water environment of the downstream channel of the diversion project,which can provide reference for the design and construction of the project,reduce the impact of the project construction on the water environment,and give full play to the maximum benefits of the project.Based on the water quality analysis of the lower reaches of Oujiang River in Wenzhou City,this paper analyzes and studies the influence of Oujiang River Diversion Project on the water quality of the lower reaches of Oujiang River.Firstly,based on the measured hydrological data and water quality data,the dynamic characteristics and water quality status of Oujiang River Basin are studied.Secondly,a two-dimensional tidal current and water quality mathematical model of Oujiang River estuary is established,and the reliability of the model is verified by comparing with the measured data.On this basis,the effects of different water diversion schemes on the concentrations of COD(chemical oxygen demand),NH3-N(ammonia salt)and TP(total phosphorus)in Oujiang Estuary were studied,and the impact of water diversion on the water environment of downstream river was evaluated.The main research results are as follows:Oujiang River Estuary belongs to strong tidal current area,the upstream flood peak rises and falls sharply,the tidal wave is mainly standing wave,the maximum velocity can reach more than 2m / s,the pollutant discharge is mainly concentrated in two tributaries of Guxi River and Nanxi River,the overall water quality is good,mainly for class II.The verification of the two-dimensional tidal current water quality mathematical model in Oujiang Estuary shows that the model can simulate the tide,tidal current process,tidal level,velocity and flow direction of large,medium and small tides in Oujiang Estuary in terms of hydrodynamic characteristics,and reflects the movement law of water flow and main pollutants(COD,NH3-N and TP)in Oujiang Estuary in terms of water quality.It is proved that the model is effective in simulating the water quality of Oujiang River Basin.The simulation results show that the Oujiang water diversion project has an impact on the water quality of the two water diversion outlets in the water source area.In different typical years and different periods of water diversion conditions,COD,NH3-N,TP water quality indicators in the new ferry head intake increase within 3%,with little impact;The maximum concentration of COD,TP and NH3-N increased by 7.4 ～ 10.3%,22.6 ～ 26.9% and 24.9 ～29.7% respectively in dry year,dry season and normal year,respectively.Therefore,it is feasible and practical for the design and site selection of Oujiang River Diversion Project to build a new ferry head intake as the main water source area,but it is necessary to strengthen the water quality monitoring of the diversion outlet.After the implementation of the Oujiang River Diversion Project,the water quality simulation of three typical sections in the lower reaches of Oujiang River,Xiaodan,Yangfushan and Longwan,shows that the maximum COD concentration decreases by 14.5 ～ 16.9% at Longwan section in dry year and wet season;The maximum concentration of NH3-N increased by 9.4 ～ 32.6% in Xiaodan section in dry year and dry season;The maximum concentration of TP increased by 6.1 ～ 24.2% at Xiaodan section in dry year and dry season.And the variation range of water quality index of each section increases with the increase of water diversion.Therefore,the water diversion project has a great impact on the water quality of the three sections in dry years.The above results show that in the actual water diversion process of Oujiang River diversion project construction,the water quality of the water source area and each typical monitoring section can be basically guaranteed,but it is necessary to pay attention to the water quality changes near the diversion mouth and the typical monitoring section in the dry season of the normal year,the wet season of the dry year and the dry season of the dry year. |
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