Study On Numerical Simulation Of Water Quality In Xiang Jiang River Based On EFDC Model

Xiangjiang River,as the largest river in Hunan province,is the province’s economic and social development and the important support of people’s production and life.As an important water source and sewage body,the water quality of Xiangjiang River has always been the focus of attention from all walks of life,especially the influence of Changsha comprehensive hub operation on the water quality of Xiangjiang River,is an important topic of academic research.Based on the conventional water quality monitoring data of Chang-Zhu-Tan water quality monitoring section of Xiangjiang River from 2011 to 2015,the water quality status of Changsha-Zhuzhou-Xiangtan section of Xiangjiang River before and after the operation of Changsha comprehensive hub was evaluated by using single index method and Nemerow index method.The evaluation results of single index method show that the BOD5 and petroleum water quality indexes have exceeded the standard in different degrees before and after the construction and operation of the hub.Nemerow index evaluation results show that the river water bodies are clean level before and after the operation of the hub,but Nemerow index after operation shows an upward trend,the main reason may be that the water level in the river after the operation of the hub rises,water flow slows down,water self-purification and sewage capacity is reduced.The environmental hydrodynamics model EFDC is applied to the study of water environment of Xiangjiang River for the first time.a two-dimensional hydrodynamic-water quality model of Changsha-Zhuzhou-Xiangtan river is established to study the hydrodynamic characteristics of Changsha-Zhuzhou-Xiangtan river before and after the construction and operation of Changsha hub.The simulation results show that the construction and operation of the hub can significantly reduce the water surface slope,raise the water level in Chang-Zhu-Tan and increase the water depth.At the same time,the operation of the hub can slow down the flow velocity in the river,especially the average flow velocity in the lower Changsha section is only 0.18 m/s in the dry season,which will affect the water exchange and self-purification capacity in the river and the water quality in the lower reaches.A water quality model was established to study the migration and transformation of pollutants in the case of sudden heavy metal pollution accidents before and after the operation of Changsha comprehensive hub.The simulation results show that the operation of the hub slows down the migration of pollutants downstream,reduces the pollution range,and accelerates the attenuation of pollutant peak concentration and the time to reach the downstream hub.At the same time,the flow rate is an important factor affecting the migration of pollutants in water.Aiming at the sudden heavy metal water pollution accident,three emergency measures were set up to study the removal effect of pollutants.the results showed that:Increasing the larger discharge flow will enable the fastest removal of pollutants in the river course,and the greater the basic flow,the better the removal effect.