A novel approach in assessing the first flush effect in urban stormwater runoff
城市暴雨径流初期冲刷现象识别模式

Assessment methods in identifying the first flush effect(FFE) in urban stormwater runoff have been disputed so far. Based on the analysis of the limitations of current methods, an optimal segmentation mode (OSM) was presented in this paper to detect the FFE. The results from two case studies(2009-8-3 and 2010-7-31) showed that through using the OSM, the initial runoff volume from concrete road with no slope can be controlled within 6mm, while FFE can't be recognized by traditional method based on the 83/30(80% of pollutant mass is transported in the first 30% of runoff volume) standard, but 5mm can be controlled by 50/25 standard. For a large-scale urban watershed with an average slope of 2.3%, the initial controlled volume can be ascertained as 2.7mm, while the actual metaphase flush effect can't be recognized by using the traditional method. The analysis of the influential factors indicated that the results could be affected by both subsection amount and the selected pollutants. Limitations existing in traditional method could be overcome by the OSM, such as the difference among estimation standards, inability to capture initial volume needing to be controlled directly, and failure in detecting the flush effect if middle or end pollutant concentrations were high, and so on. As a preliminary study, the results provided a new reference for more scientific assessment of FFE.