Runoff Pollution Characteristics And Spatial Differences In Typical Northern Cities

Urbanization has been developing rapidly for a long term,with urban areas and populations daily expanding and becoming dense.The social functions and forms of human activities are becoming more complex and the pollutants accumulated on the urban face are becoming more serious.When rainfall events occur,a large amount of pollutants are carried by runoff and enter the received water through the pipes or remain in the urban water environment,all causing serious damage.Therefore,in order to protect the urban environment and surrounding received water better,it is essential to study the general characteristics and spatial differences of urban runoff pollution,which can provide some theoretical guidance for planning design and implementation to reduce the damage of urban pollution.This study focused on the typical northern urban of China,represented by Xi’an,which analyzed the variation characteristics of pollutants event mean concentration（EMC）and instantaneous concentration of runoff in the typical transport area,commercial area and campus area of urban space.Which were shown by the results of four monitoring rainfall events,the EMCs of organic pollutants（COD,NH₃-N,TP）and heavy metals（Cu,Pb,Zn）from Yanta North Road,the typical transport area were 393.7,12.63,2.54mg/L and 0.02502,0.02413,0.07864mg/L;the EMCs of Xingshansi East Street,the typical commercial area,were 186.36,2.33,2.54mg/L and 0.01092,0.00145,0.03355mg/L;as for Chang’an university of Yanta District,the campus area,the EMCs of organic pollutants were 12.56,0.83 and 0.91mg/L.The degree of runoff pollution in a typical transport area was obviously more serious than in other areas,and the typical campus area has shown the lowest pollution degree.For the variation characteristics of runoff instantaneous pollution,fewer variations were shown in organic indexes in the different urban spaces,and shown more steady release processes.However,the higher differences in instantaneous concentrations among rainfall events existed in heavy metals,which were deeply affected by rainfall characteristics and underlying surface conditions.Then,this study analyzed the transportation rules of runoff pollutants in different urban areas,and qualitatively and quantitatively analyzed the first flush phenomenon of runoff pollutants in certain areas.In the four rainfall events researched,the first flush phenomenon obviously occurred in all typical transportation areas and commercial areas,but slightly in the typical campus areas.Meanwhile,the strength of the first flush was Yanta North Road>Xingshansi East Road>Chang’an University based on the quantitative analysis.And there were also distinctions observed in different pollutants for their first flush phenomenons in different areas,especially for the heavy metals,which showed an obviously unsteady characteristic.Subsequently,the high～concentration runoff of organic and heavy metals pollutants usually existed in the first 20%and 35～40%of the whole runoff volume respectively under the study of pollutants concentration characteristics varied with the runoff volume.Lastly,our study investigated the situation of road runoff pollution and its control measures in Xi’an,a traditional city,and Xixian New District,the Sponge City,and analyzed the driving factors which affected the spatial distributions of runoff pollutants.As the results showed,there are serious damages caused by runoff pollutants in the city environment and green constructures,and the current control measures cannot effectively reduce the pollution degree wherever in the Xi’an or the Xixian New District.At the same time,the factors（the previous sunny days）related to the pollutant accumulations contribute more to runoff pollution degree variations than the factors affecting the release of the pollutants based on the study of the correlations of rainfall parameters with runoff pollutants in different areas.However,this research showed that the traffic flow and vehicle density are still the main factors influencing road runoff pollution degree among the regional factors,the runoff pollution control measures should be designed under the background of different traffic flows in certain areas.