Discussion On Urban Non-point Source Pollution Simulation And Prevention Measures In Tianhe District Of Guangzhou Under The Background Of Sponge City Construction

With the rapid acceleration of the urbanization process,different functional areas in cities with large populations have suffered from increasingly serious urban non-point source pollution.Heavy rainfall washes the surface of cities and forms runoff carr ying large amounts of pollutants which finally diffuse toreceiving water bodies.In order to solve various urban environmental problems including urban non-point source pollution,our country proposes to build sponge cities with their essence of natural ac cumulation,natural penetration,and natural purification.The non-point source pollution characteristics of different urban functional areas are different to some extent.Therefore,in order to more reasonably develop sponge cities,it is necessary to car ry out researches on non-point source pollution in different functional areas of the city.This research chose Changxing street,Tianhe district,Guangzhou city as the study area.The non-point source characteristics of different functional areas(commercial areas,industrial areas,residential areas,roofs,road and grasslands)are discussed and the sources of pollutants were preliminary analyzed by principal component analysis(PCA)method.SWMM model of water quality is used to simulate the dynamic varia tion of pollutants in different functional areas during rainfall events.Finally,the prevention and control measures of non-point source pollution are proposed based on the situation of non-point source pollution in the study area.The main results of the research are as follows:(1)The characteristics of non-point source pollution of rainfall runoff in different functional areas are as follows:(1)The rainwater in the research area is generally weakly acidic(p H value is around 6.5),and the content pollutants is lower than that of the runoff water.There existed pollution of different degrees in the runoff of commercial areas,industrial areas,residential areas,roofs,highways and grasslands.Except for the roof,COD,TP,TN and SS pollution in all the functional areas was relatively serious.The COD,TP and TN in the commercial area runoff generally exceeded the Class Ⅴ level of the surface water environmental quality standard.The EMC value of the COD even exceed ed 900 mg / L.The pollution of Zn and Cu in the runoff of the industrial zone is the most serious,with the EMC value of Zn exceeded 3mg / L.(2)The concentrations of runoff pollutants generally decreased with rainfall duration,and the peak concentration appeared within the initial 10 minutes of the rainfall event,the concentration of some pollutants peaked at the initial moment;(3)There were multiple sources for the runoff pollutants.The main sources of the runoff pollutants in commercial areas were traffic emissions,domestic sewage and urban garbage,especially,the contribution of traffic emissions was the highest;the main sources of runoff pollutants in industrial areas were industrial activities(including hardware processing activities and auto-repair activities)and traffic emissions;the source of pollutants in residential areas were domestic sewage and atmospheric deposition;the main source of pollutants from rooftop runoff was atmospheric deposition;the sources of pollution in urban green land runoff was the soil itself and atmospheric deposition;(4)Correlation of different degrees were observed between the water quality indicators of rainwater and runoff.COD in rain water showed a significant positive correlation with SS,TP,TN,Fe,Cu,and Zn;in the runoff of commercial areas,there was a close relationship between the non-metallic pollutants and metal pollutants,the correlation coefficients of SS and COD,BOD,TP,TN,Fe,and Cu,and Zn in runoff in residential areas were closely related at the confidence level of p <0.01;in the industrial area,COD showed significantly correlation with all the heavy metal,except for Pb.(2)The SWMM model was used to simulate the current water quality of SS,COD,TP,and TN in the runoff in the study area.The simulation results show ed that: for heavy rain and rainstorm events,the concentrations of surface runoff pollutants in all the different functional areas rapidly decreased within the initial 0.2 h(12 min)period.Then,with the prolonged rainfall time,the pollutant concentrations showed slight variation and remained stable as whole.The simulation results also showed that the runoff water quality of all functional areas,except for the roof of the building,exceeded the class Ⅲ of the surface water standard.(3)Taking the biological retention tank as the representative of typical low impact development(LID)measures,and simulating the variation of runoff water quality in different functional areas under LID measures,the results showed that the reduction rate of pollutants from LID measures covering an area range of 10-30% varied between 17% and 80%,and the greater the proportion of measures,the higher the reduction rate.According to the characteristics of runoff non-point source pollution in the study area,the following control measures are proposed: permeable pavement measures with strong water permeability and anti-skid properties are suitable for sidewalks,single lanes and highways in all functional areas;idle land in industrial areas can be constructed with constructed wetlands;on roof,cedars and pennisetum can be built as green roof measures.In the small areas of residential areas and commercial areas,concave green spaces or biological retention ponds can be used on idle land;narrow concave green spaces and biological retention ponds can be used as green belts on both sides of the highway.