Analysis And Evaluation Of Urban River Water Quality And Improvement Measures

In the urban river regions of water shortage type and high development intensity,where natural runoff is scarce and water bodies have almost no environmental capacity,the rapid development of regional economy has brought excessive pollution load to water bodies in river basins.The water quality of rivers is characterized by low capacity and heavy load.The water quality of rivers is declining and the ecological environment of river basins is deteriorating year by year,which has brought many impacts on the environment,residents’lives and economic sustainable development of urban areas along the river and downstream.The competition between cities in the future is more reflected in the competition in the urban environment,and the improvement of the urban river water environment will definitely bring huge economic returns.In the process of watershed water environment management,it is difficult to predict the effect of meeting water quality standards.It is difficult to objectively measure the contribution of different management measures to the improvement of watershed water quality.This article takes a watershed management project in Guangdong Province as an actual case,through monitoring the water quality of the main rivers and tributaries of the watershed,to grasp the spatial and temporal distribution characteristics of pollution indicators.At the same time,based on the collected information,a water quality model is established,with the premise that the water quality of the main stream cross section meets the standard,the relationship between water resources utilization and tributary remediation and the response of the main stream water quality is studied.Designing the boundary conditions in the governance plan to provide scientific cognition for the comprehensive management of the river basin has significant practical guiding significance in the process of water pollution management.After research and analysis,the following conclusions are mainly obtained:（1）Combine the water quality of the basin itself to collect,sort and summarize the water quality of main and tributaries in all directions.By analyzing the monitoring data of the main tributaries in the river basin,we can see that the changes of the NH₃-N and TP concentrations in the tributaries of the basin are:dry season>average water period>high water period,and the water quality exceeding the standard at the junction of the main stream is mainly affected by the downstream tributaries with poor water quality.The overall water quality of the basin was evaluated based on the single-factor water quality index method.The results showed that the overall water quality of the basin was the worst in March 2019,with a comprehensive water quality index of 5.61 and water quality of category V.（2）According to the collected flow,water level and water quality data,a one-dimensional water quality model is established,its roughness,diffusion coefficient and comprehensive attenuation coefficient of pollutants are calibrated,and the measured and simulated values are compared and verified.The results show that:The model has achieved good results for both NH₃-N and TP simulations.The water quality simulation can effectively complete the water quality data information along the main stream,which lays a foundation for the subsequent analysis of the feasibility of meeting the standard of the water quality of the main stream junction.（3）Aiming at the water quality of the cross section of the main stream reaching the ground surface category IV,simulate and analyze the impact of various factors on the water quality of the cross section to meet the standard,so as to provide a reference for the subsequent operation and management of the wetland water replenishment system.The simulation results show that the effect of artificial wetland water replenishment is mainly affected by the water replenishment quality.The water replenishment quantity is 166,500m³/d,and the water replenishment quality is Class III on the surface,which can achieve the water quality of the cross-section.（4）In the empty window period when water supply is not formally carried out in the constructed wetland,the goal is to reach the surface quality category IV of the cross-section of the main stream.By diversion of clean water from the reservoir in the basin,the diversion volume is 100,000 m³/d and the diversion water quality is the surface In the case of categoryⅡ,the water quality of the cross section of the main stream can reach the surface categoryⅣ.The effect of improving the water quality of the main stream cross section after remediation of the heavily polluted tributaries was analyzed,and the priority of tributary remediation was determined as:TT River>SX River>MQK River>CA River>DZ River.In the case where the TT River and SX River are renovated to reach the surface class IV,the water quality of the cross section of the junction without supplementing the main water flow can also be achieved to the surface class IV.（5）Under the restriction of the water quality of the cross-section to meet the Class III surface water,simulate and analyze the influence degree of the changes of various factors on the water quality of the cross-section,and then verify the rationality of the layout of the water quality standard of the river basin.The results show that it is difficult to rely on the existing designed constructed wetland water replenishment scheme to achieve the water quality of the cross section to reach Class III.It is necessary to increase the treatment of the TT River,SX River,MQK River and CA River on the basis of the wetland water replenishment.