Simulation Study On Water Pollution Control And Flood Control In Typical Urban Rivers In Northern Anhui Plain

With the acceleration of urbanization in China,the relative lag of urban infrastructure construction leads to the disharmony of urban green development.The northern part of Anhui province is located in the plain area with flat terrain.The urban river network has many disadvantages,such as heavy pollution load,insufficient hydrodynamics,unsteady flow direction of water in the area,etc.It is difficult to renew the inland river water body in time and effective,and the rainwater runoff is not smooth,which makes the water environment pollution and urban flood control problems prominent.Taking a city in northern Anhui province as an example,the hydrodynamic model,water quality model and rainfall and runoff model of typical river network in northern Anhui plain area are established in this paper.Based on the model,the pollution diffusion law of the typical river network in northern Anhui province was analyzed,and the water environmental capacity of the river network was calculated with the zero-dimensional model,and the technical scheme of water environment optimization of the river network was put forward.Based on the study of water body movement law in the study area,the influence range of insufficient hydrodynamic force and unsteady flow direction in the area are analyzed in detail,and several flood control schemes under different rainfall conditions are put forward.The research contents and main conclusions are as follows:（1）According to the established rainfall-runoff model and hydrodynamic model,the water depth and flow of the river network in the study area in 2021 were simulated,and the model coupling calculation results were carried out through the measured data of Honghe Pumping Station and Gegou Pumping Station in the west boundary.Calibration,the calibration process makes the model meet the research needs by adjusting parameters such as the channel Manning coefficient,the initial conditions of the river network,and the maximum water content of the surface aquifer.The calibration results show that the R~2 and Ens of the water level of the Honghe section in the western boundary are 78.35%and 0.689,respectively;the R~2 and Ens of the flow of the Gegou section are 85.54%and 0.807,respectively.（2）Combined with rainfall-runoff model,hydrodynamic model and water quality model,by adjusting the attenuation coefficient and diffusion coefficient of river pollutants,the model coupling results are calibrated according to the measured data of COD,ammonia nitrogen and total phosphorus in honghe section,Wuchuhe section and Gegou section of the Western boundary.The results of calibration show that Ens of COD,ammonia nitrogen and total phosphorus are 0.72,0.94 and 0.72,respectively.Ens of COD,ammonia nitrogen and total phosphorus in Wuchuhe section are 0.69,0.84 and 0.79,respectively.Ens of COD,ammonia nitrogen and total phosphorus in Gegou section are 0.72,0.88 and 0078,respectively.（3）The MIKE 11 joint zero-dimensional model proposed in the study calculates the dynamic water environment capacity of the study area,and adopts the traditional one-dimensional steady-state model method to calculate the steady-state water environment capacity of the study area,and compares and analyzes the environmental capacity under two different methods.The comparative analysis results show that the water environment capacity calculated based on the MIKE 11 software combined with the zero-dimensional model is fluctuating because the software can continuously simulate various hydrological and biochemical reactions in the river,which can reflect the water environment capacity under different temporal and spatial conditions.dynamic changes,and the calculation accuracy is significantly improved.（4）The effect of pollution control in the study area was predicted through the water quality hydrodynamic model.The simulation results show that the measures to improve the urban water environment by diversion have little effect,and the improvement effect of COD,ammonia nitrogen and total phosphorus in the river only increases by 1.5%,3%and 2.5%when the diversion flow increases by 1 m~3/s.Pollution reduction is the key to improve the urban water environment.After the implementation of source emission reduction measures,the content of COD,ammonia nitrogen and total phosphorus in water decreased by more than 50%,so as to meet the requirements of surfaceⅳwater.（5）Through the rainfall-runoff model and the hydrodynamic model,the combination scheme of the river hydraulic structures under different heavy rainfall is set up,and the flood control of the river network in the study area is studied and analyzed.The simulation results show that through reasonable configuration and scheduling of hydraulic structures,the flood discharge of the river network can be effectively prevented under the condition of heavy rainfall once in 20 years.and the right bank embankment at 662-2700 m of Gegou.