Study On The Water Environment Changes In The Middle And Lower Han River Under The Strong Influence Of Human Activities

Based onthe change trend of pollutants in the water body of the middle and lower reaches of the Han River under the influence of strong human activities such as sewage discharge from chemical companies along the middle and lower reaches of the Han River,as well as the changes in influencing factors such as hydrological variation.Enterprise sewage simulation research on the evolution of river water quality.Based on the pollutant accounting,we can grasp the pollutant inflow into the river basin.The model is based on the boundary conditions of the 1996-2017 period,and simulates the evolution of water quality under the influence of human activities such as pollutant discharge from chemical enterprises along the middle and lower reaches of the Hanjiang River,water conservancy hub scheduling,and the mid-line water transfer from South to North Water Transfer,Revealing the influence law of hydrology and water environment in the middle and lower reaches of Han River.The research results and main conclusions are as follows:（1）Establishinga one-dimensional hydrodynamic water quality model for the middle and lower reaches of the Han River.The model simulated the water level of the middle and lower reaches of the Han River and industrial point source discharges along the coast of the chemical plant,phosphate fertilizer plant,and paper mill from2006 to 2007.The calibration and verification of water quality are carried out by comparing the measured data of Huangjiagang,Huangzhuang,Xiantao and Hanchuan hydrological stations in the reach.The diffusion coefficient and the attenuation coefficient of pollutants of the water quality model are used for the calibration and verification.The measured data of NH₄-N,TP,and BOD₅of Shiji,Xingou,Zongguan section were compared.The overall relative error of the hydrodynamic water quality simulation results is small,and the correlation coefficient is good,indicating that the hydrodynamic water quality model has reliable accuracy and can reflect the true river water quality.（2）Verification of the model proves that the model has a relatively high accuracy.On this basis,a series of hydrological 1996-2017 simulation calculations are carried out to analyze the hydrodynamics and water environment of the middle and lower reaches of the Han River after the operation of major water conservancy hubs.In the model,Cuijiaying,Xinji,Yakou,Nianpanshan,Xinglong and other water conservancy hub dispatches are considered,and the Yangtze River to Hanjiang River Water Diversion Project has been built to alleviate the reduction of midstream and downstream flow to implement water supply dispatch for the downstream.The model considers many engineering schedules,and uses Mann-Kendall test analysis method to analyze the simulation calculation results of Huangjiagang,Huangzhuang,Xiantao,and Hanchuan stations in the middle and lower reaches of the Han River.After 2003,the water level and flow showed an upward trend.The main reason was that during this time series,the flow from the upper reaches of the Han River increased,which caused the water levels of the stations in the middle and lower reaches to rise and increase the flow.In the South-to-North Water Diversion Project,the volume of pumped water originally reduced the amount of water in the middle and lower reaches.The flow rate in the middle and lower reaches of the Han River did not show a significant downward trend.（3）Analysis of calculated water quality results through single factor indicators and Mann-Kendall analysis.The concentration of various water environment indicators in the middle and lower reaches of the Han River showed an upward trend during 1996-2017.During the three periods（1996-2003,2003-2014,2014-2017）of the year,the monthly average concentration and comprehensive pollution index of the indicators at the monitoring station showed an upward trend.The main change trend of the water environment capacity in the middle and lower reaches of the Han River was from upstream to downstream,and the water environment capacity gradually decreased;During1996-2003,there is still a certain water environmental capacity.From 2003 to 2014,the water environmental capacity of each indicator has decreased to a certain extent,but there is still a certain amount of pollutant holding capacity.During 2014-2017,the water environmental capacity of each indicator has decreased significantly,especially it is near the estuary that the capacity to contain phosphorus pollutants is basically lost.（4）There are many paper mills,phosphate fertilizer plants,and chemical plant sewage outlets along the middle and lower reaches of the Hanjiang River.Under the rectification of the relevant departments,the number of sewage outlets has been reduced,but as the industry continues to develop,the sewage discharge from the factory to the river is still correct.The river water environment has an impact.In addition,the water diversion projects and cascade water transfers,as well as the water withdrawal from cities and enterprise factories along the route,reduce the water volume in the interval.Therefore,it is recommended to jointly dispatch the water quality and water volume in the middle and lower reaches of the Hanjiang River.Sewage treatment process to reduce the concentration of pollutants into the river and control the total amount of pollutants into the river trend.