Simulation And Research On The Water Quality Improvement Schemes For A Complex River Network

The fast pace of the industrialization and urbanization has brought the sharp increase of the pollutant in the coastal area,which impacts the local environmental bearing capacity and results in serious water contanmination.In response to the severe water contanmination situation,China has formulated the Action Plan for Water Pollution Prevention and Control and the Water Ecology Civilization Construction,Zhejiang has implemented the Five Water Governance and Six Goals of Zhejiang.Jinqing Basin,as the typical coastal complex river network,is located on the shoutheast coast of Zhejiang Province.In recent years,plenty of pollution control work has been carried out,and some results have been achieved in Wenling.However,due to historical debt and unreasonable treatment plan,the serious water contanmination problems still exists.Improving the water quality of Jinqing Basin has become the focus of improving the water environment and realizing the harmony between human and water of Wenling City,which has important social significance.The complex river structure,various flow direction,slow flow velocity,various pollution sources and advection-dispersion processes and the lack of water pollution data are the main challenges of the water quality improvement.To solve these challenges,relationships of water utilization and sewage discharge were analyzed.pollution load of the multi-region and multi-source was calculated,a coupled hydrodynamic and water quality model was developed,pollution control and water diversion schemes were proposed and evaluated,exploring feasiable schemes for water quality improvement.The main researches are as follows:1.According to the method of watershed partition-pollution source allocation-pollution load calculation,pollution load of ammonia nitrogen from various pollution sources and watershed partition was calculated,which helps to analysis the topological relationship between the sewage outlet location and the cross section of water function zone and precisely reflects spacial quantity and quality distribution of the pollutant.2.Based on the analysis and calculation of the pollution sources,a coupled Mikel1 hydrodynamic and water quality model of the first and second level rivers of the Jinqimg Basin was developed and calibrated.3.Pollution control and water diversion schemes considering the practicality were proposed,these schemes were evaluated by the coupled model.Implementing the pollution control scheme improves water quality of all the cross sections significantly,especially the Zeguo,Songmen,Xinhe cross sections.Implementing the water diversion scheme improves water quality limitedly.Different flow rate and water diversion location results in different impact on the water quality.4.Suggested schemes that help to archieve the water quality targets were recommended.?Adopting the pollution control scheme of reducing the pollution load of ammonia nitrogen to 1023t,with the water diversion scheme of 20m3/s discharge into the Nanguan river,the water quality target of the control sections of class V could be generally reached.Otherwise,adopting the pollution control scheme of reducing the pollution load of ammonia nitrogen to 1023t,with the water diversion scheme of 10m3/s discharge into the Nanguan river,the water contamination of the Macheqiao and Songmen cross section should be treated additionally to reach the class V target.?Adopting the pollution control scheme of reducing the pollution load of ammonia nitrogen to 728t,with the water diversion scheme of 20m3/s discharge into the Nanguan river,the water quality target of class IV could be generally reached.The research provides a grasp for the refined and precise water quality management of various pollution sources in Jinqing Basin,which may provide reference for water quality improvement in similar areas.