Characteristics Of Rainwater Runoff Pollution In Tianjin City And Its Influence On Water Quality Of Inflow Rivers

In recent years,the scale of China’s modern cities has continued to expand,and the amount of domestic sewage and industrial wastewater has also increased,which has caused serious damage to the water environment.Solving the problem of urban water environment has become the focus of sustainable development.At present,the water environment problem caused by non-point source pollution is very serious.For the sake of increasing the utilization of urban rainwater resources,it is imperative to analysis the characteristics of rainwater runoff pollution and explore the process of runoff pollution affecting the river channel.This is of great significance for the conduction of urban water pollution prevention and control,and scientific urban water environment planning.In this thesis,and river water samples,the water quality indicators such as NH⁴⁺-N,NO³-N,TP,TSS and COD_cr were monitored by collecting different functional areas,including residential areas,campus areas,commercial areas,traffic roads,park areas.Also,the characteristics and process of pollutants for different intensity rainfall conditions were analyzed.Among them,the rainwater runoff pollution in the campus area and the commercial area is relatively serious,reflected in the TSS,TP,and NH⁴⁺-N indicators exceeding the standard.While the COD_cr indicator of the rainwater runoff collected from traffic roads is far beyond the standard.The runoff water quality in the residential area and the park area is relatively good.By monitoring the changes in river water quality after rainfall,it was found that the water quality of the river changed from the Grade IV water quality standard to the inferior V water quality standard,and the NH⁴⁺-N exceeded the standard remarkably.After one week of a heavy rain,the water quality of the river was still inferior to the V water quality.So it is drawn out that the flow of rainwater runoff has brought a huge impact on the water quality of urban rivers.According to the topography and catchment characteristics in the study areas,SWMM software was used to establish the non-point source pollution model and explore the process of rainwater runoff pollution under different rainfall conditions.The given recurrence period is five years,one year,two years,five years,and ten years respectively.By comparing the difference between different return periods and the rainwater runoff at different locations,the drainage interception suggestions are proposed from the change of the discharge pollutants at the outlet.The SWMM software calculation results are input into the river water quality model,and the HEC-RAS software is used to calculate the change of the water body after the river channel is fed with rainwater runoff pollution.The water quality indicators in the river channel rise rapidly,and when the final water quality is stable,the concentration of pollutants in the river water body far exceeds the V water standard.Finally,based on the experimental results and the analysis of water quality simulation results,the effects of runoff pollution on urban rivers are alleviated by improving the hydrodynamic conditions of the rivers and increasing the LID facilities in the old urban areas to control runoff pollution from the source.Through the river water quality model simulation analysis,when the river flow is increased to 1m3/s after one day of rainfall,the river water quality in the study area can be effectively improved within 20 hours,and the river water quality is restored to superior to the V water quality standard.On the other hand,the most effective LID facilities are selected by analyzing the characteristics of rainwater runoff pollutants in different functional areas,and the localized transformation method is adopted to reduce the pollutant content carried in the runoff at the source,thereby reducing the impact on the river channel.