Research On Water Environment Simulation And Water Quality Improvement Of Small Urban Rivers Based On MIKE21

In urban river waters with high development intensity,natural runoff is scarce and water bodies have almost no environmental capacity.Urbanization process and rapid economic development bring heavy pollution load to water bodies.The water quality of the river decreases and the ecological environment of the basin deteriorates year by year,which brings a lot of impacts on the environment of the urban area along the river and downstream,residents’ life and the sustainable development of economy.It is difficult to predict the effect of water quality improvement in the process of watershed water environment management,and it is difficult to objectively measure the contribution of different management measures.In this thesis,H River in Chongqing Main City Development Zone is taken as an example.By carrying out water quality monitoring work in the basin,the spatial and temporal distribution characteristics of pollution indicators are mastered,and the two-dimensional hydrodynamic and water quality coupling model established based on MIKE21 software is verified and calibrated.By simulating the change of pollutant concentration in the study area under different treatment measures,This thesis evaluates the water dynamics and water quality improvement of rivers,and puts forward a scientific plan based on the water quality objectives of urban rivers,so as to ensure the stability and sustainability of river ecosystems,effectively improve the water mobility,and solve the black and odourous situation of water bodies,providing a valuable theoretical basis for the subsequent improvement of river water quality in the old urban areas.The main research achievements of this thesis are as follows:(1)Monthly water quality monitoring was carried out on the river.During the monitoring period,the overall law of pollutant pollution in River H followed: dry period >normal period > wet period;moreover,due to the serious pollution from point source and non-point source,the self-purification capacity of water body was weakened,and pollutant concentration in the downstream was higher than that in the upstream.Under the influence of high temperature and drought,the hydrodynamic conditions deteriorated and the pollutant concentration increased significantly.The water quality was evaluated by single factor evaluation method,comprehensive pollution index evaluation method and Nemerow comprehensive pollution index evaluation method.The water quality in normal season and wet season was at the level of severe pollution,while the water quality in dry season was at the level of serious pollution.The main pollutants exceeding the standard in rivers are COD and TN,among which point source pollution caused by sewage discharge is the main reason for exceeding the standard of N element pollution,and high organic matter content in upstream inflow is the main reason for exceeding the standard of COD.(2)Based on the measured hydrology and water quality data as well as the basic data of the research area,the coupling model of hydrodynamic and water quality was constructed using MIKE21 software,and the model was adjusted and calibrated according to the measured data to establish the basin hydrodynamic and water quality model conforming to the research object.Model simulation results show that the reduction of pollutants in the river is not significant,and the source control and pollution interception measures will be the most beneficial to the reduction of pollution.All measures have the best effect on the improvement of N and P elements,followed by COD.The downstream point source pollution causes more serious N and P element pollution,and COD pollution mainly comes from the high concentration of upstream inflow.(3)After comprehensive treatment with source control and ecological water replenishment measures,the pollution situation of the river can be improved.The reduction rates of comprehensive pollution index in normal season,wet season and dry season can reach 28%,27% and 48% respectively,and the reduction rates of Nemerow comprehensive pollution index can reach 33%,28% and 37% respectively.The pollutant concentration before and after treatment in dry season can be reduced the most.According to the above simulation results,the improvement of H river water environment should give priority to point source pollution control,further realize rain and pollution diversion,and combine with non-point source pollution control,internal pollution control and river ecological restoration to reduce the external input pollution load of water,enhance water hydrodynamic conditions,and improve water self-purification capacity.