The first flush effect of different urban underlying surfaces through artificial simulated rainfall

Three kinds of underlying surfaces: asphalt road, impervious tiles and grassland at Chang'an University in south second ring road of Xi'an were chosen as testing sites. Self-made device was used to moderate rainfall with different raining conditions: uniform rainfall intensity of 0.3mm/min, 0.5mm/min, 1.0mm/min; front peak type rainfall and back peak type rainfall. The pollutants in the runoff were measured, that included TN, TP, NO₃^--N, NO₂^--N, NH₄⁺-N, PO₄^3--P and PN M(V) curves and MFF₃₀ values were analysed to drew these conclusions: under uniform rainfall intensity of 0.3mm/min, 0.5mm/min, 1.0mm/min, the mean values of MFF₃₀ from asphalt road runoff were 0.47, 0.42, 0.41, the mean values of MFF₃₀ from watertight tiles runoff were 0.40, 0.39, 0.38, the mean values of MFF₃₀ from grassland runoff were 0.33, 0.34, 0.32. The first flush magnitude decreased with the increasing of rainfall intensity on asphalt road and watertight tiles, while the first flush intensity first increased and then decreased with the increasing of rainfall intensity on grassland. The mean values of MFF₃₀ from the front peak type rainfall were larger than that from the back peak type rainfall on both asphalt road and watertight tile. The mean values of MFF₃₀ from the back peak type rainfall were larger than that from the front peak type rainfall on grass. Grassland should be built around asphalt road and watertight tiles to attenuate first flush effect. (paper)