Numerical Simulation Of Contaminant Of Prestorage Baisn Based On EFDC

With the rapid development of China's economy,water pollution incidents occur frequently,which not only bring enormous economic losses to the society and economy,but also have a serious impact on the water security of resident and ecological environment.In order to deal with the water pollution incident in the Yangtze River,Zhenjiang Water Supply Company has built a comprehensive water source protection project,integrating water quality monitoring,raw water prestorage,emergency treatment and other functions.It can effectively delay the arrival time of raw water from the Yangtze River,realize the early warning and emergency treatment of water pollution incidents,and improve the safety level of water supply.The project is the first one in China.At present,there is no design criterion for water quality protection project in China.There is no mature technology to directly utilize the diffusion and migration rules of pollutants in the prestorage basin,and ifs difficult to verify by experiments.Therefore,using the numerical simulation method to calculate the duration of pollutants from inlet to outlet of the prestorage basin,and define warning time is an efficient and convenient method,which has important reference value and significance for dealing with water pollution incidents.In this paper,based on raw water prestorage basin of comprehensive water source protection project of Zhenjiang Water Supply Company,established the numerical model of pollutants through the water environment numerical simulation software EFDC.Three flow conditions(4m~3/s,5m~3/s,6m~3/s)and two kinds of pollutants(hydrophilic and hydrophobic)were used to carry out numerical simulation of pollutant diffusion.The Acoustic Doppler Current Profilers was used to detect 9 sections of prestorage basin and verify the reliability of the model.By numerical simulation,the warning time of prestorage basin under various conditions is defined,the diffusion state of pollutants is analyzed,and the emergency treatment measures to deal with water pollution incidents are put forward.The research results are as follows:(l)The contaminated cloud diffuse along the prestorage basin in a conical shape at a steady rate,with the highest concentration in the center and the lowest concentration gradient on the both sides.With time migration,the area of cloud gradually expands and the overall concentration gradually decreases due to diffusion and dilution.(2)The main driving force of pollutant diffusion is water pushing,and the geometric shape,flow rate and pollutant type of prestorage basin are the factors affecting pollutant diffusion.The larger the flow rate is,the faster the movement rate is,and the shorter the warning time of prestorage basin is.When the flow rate is 4m~3/s,the diffusion rate of pollutants is about 83m/h,and the time for pollutants to reach the outlet is about 18h;when the flow rate is 5m~3/s,the diffusion rate of pollutants is about 99m/h,and the time for pollutants to reach the outlet is about 15h;when the flow rate is 6m~3/s,the difftision rate of pollutants is about 120m/h,and the time for pollutants to reach the outlet is about 12.5h.Hydrophilic pollutants are easy to melt with water and have a larger diffusion area;Hydrophobic pollutants are difficult to dissolve in water and have a higher concentration in the center of cloud.(3)The discharge time of pollutants was simulated with the emergency treatment scheme of 5m~3/s flow rate,reverse drainage of pumping station and backup water source after hydrophobic pollutants entered the prestorage basin for 6h.At a rate of about 100 m/h,the contaminated cloud spread farthest in the 7th hour,located in the middle of the first corridor.Then,under the action of reverse drainage of pumping station and reverse pushing of backup water source,the prestorage basin is discharged slowly at a rate of about 60m/h.About 14 hours later,the contaminated cloud was basically discharged from the basin and the water was purified.If a water pollution incidents occurs in the prestorage basin,the emergency treatment plan should be carried out in time.The outlet will not be affected by pollutants,and the polluted water can be discharged quickly and effectively with the normal water supply.The function of the prestorage basin can be effectively played.