Characteristics analysis of first flush effect on runoff pollutants from different urban underlying surfaces

Surface water quality is negatively influenced by the urbanization process to pollutant loads in stormwater runoff and increases in runoff peaks and volumes. The first flush effect is the main impetus for pollutants transportations. This study compared the characteristics of first flush effect on stormwater runoff from blacktop driveway, concrete roof, and roof with grassland. The first flush effects of chemical oxygen demand (COD), Ammonium-Nitrogen (NH₃-N), Nitrate-Nitrogen (NO₃-N) and Total Phosphorous (TP) were studied through monitoring of rainfall runoff on three different kinds of underlying surface, including bituminous roof, green roof and asphalt road. And four linear relationships for these pollutants were stimulated. The results demonstrated that the first flush effects of these four pollutants on three different kinds of underlying surface presented significantly. Over 80% of pollution load was delivered within the first 40% of the whole runoff period. Thus, retaining the initial runoff could effectively reduce runoff pollution. The linear relationships of four pollutants were presented significantly as well. Most of the correlation coefficients were more than 0.9, which showed that controlling pollution source could significantly diminish pollutants for the similarity of these four pollutants.