Determination of the first-flush criteria from railway bridge area

The management of non-point source pollution is necessary, because it may degrade the water quality. The railway facility areas located in South Korea are considered significant non-point source pollution. Therefore, the method of managing non-point source pollution in the railway areas is crucial. This study was conducted to quantify the first flush in the railway bridge area and to suggest the method of reducing the pollution level of the facilities that create non-point source pollution. The first-flush criteria are analyzed using the volume ratio method, the dynamic event mean concentration method, and the mass first-flush ratio method. As a result of an effective rainfall analysis, the first-flush effective rainfall depths were determined to be 8.4 mm in the concrete roadbed area and 16.5 mm in the gravel roadbed area. These first-flush rainfall depths are greater than the sizing criteria (5 mm) of best management practices (BMPs) for capturing first flush in South Korea. Thus, a rigorous rainfall-runoff management is required in the gravel roadbed area. This study implies that BMP must be properly installed upon consideration on the characteristics of the railway facility areas, which have rarely received attention as a significant non-point source as opposed to paved urban areas such as parking lots and roadways.