Temporal-spatial distribution and first flush effect of urban stormwater runoff pollution in Shanghai City

Increased stormwater flow and the companying runoff pollution are a direct result of urbanization and the consequent increase in the proportion of land area under impervious surface.Runoff from urban areas is often presumed to be a significant contributor to nonpoint source(NPS) water pollution and has been identified as one of the major causes of the deterioration of the quality of receiving waters.The objectives of this study were to investigate the characteristics of pollutants in storm events,and the relationships between pollutant load and flow-runoff patterns,and to analyze EMCs loadings of pollutants,and then reveal Flush of road runoff in different functions in Shanghai City. Stormwater quality and quantity were investigated in urbanized catchments in the central Shanghai city in order to characterize temporal-spatial distribution and First Flush Effect of stormwater runoff pollution.Sampling locations selected can be grouped into four sites with different land use categories(traffic,industrial,commercial and residential areas).Results of the sampling program indicate that concentrations of total suspended solids,TP,chemical oxygen demand(COD_(Cr)),ammonia(NH_(3)-N),nitrate(NO~-_(3)-N) and NO~-_(2)-N present in the runoff from these areas. The result indicates that the concentration of contaminants decreases with the increasing of flow time.And the pollutions variations in traffic area are more complex.Event mean concentrations(EMC) is defined as the total pollution load divided by total runeff volume.The results indicated that the main contaminants of road runoff are TSS and COD_(Cr).The highest EMCs are found in traffic area,then industrial and commercial areas.Residential areas have the lowest pollution level.The relative magnitude of EMC in June is higher than in March rainfall event,especially for the constituents of TSS and COD_(Cr). The first flush phenomenon may be defined as the initial period of stormwater runoff during which the concentration of pollutants is substantially higher than during later stages.The result indicates that the magnitude of the first flush phenomenon was found to be greater for high intensity rainfall events(June 2004) and less for low-intensity ones(March 2004),and also greater for some pollutants(e.g.suspended solids and chemical oxygen demand) and less for others.Accordingly,the magnitude of the first flush phenomenon is characterized in the order of commercial areas residential watershed industrial watershed traffic areas.