Particle Settlement Property and Size Distribution of Urban Trunk Road Runoff

Urban road runoff caused by 16 storm events were collected proportionally to the total volume and completely through the rainfall time at urban trunk road in Xi'an City using self-made volume proportional collecting device from March to November in 2009. The cumulative curve method was employed in the study of settlement property and size distribution of particles carried by runoff. Influence of precipitation characteristics on particle size distribution was explored as well. Results showed that particles can be removed effectively by settlement and removal efficiency for 60 minutes' setting can be 78.4% and 86.3% for 2 hours' respectively. In order to achieve removal rates of 45%, 60% and 80%, surface loads of sediment tank were 1.1-9.3 cm/min, 0.6-5.9 cm/min and 0.1-2.7 cm/min respectively and the surface load reduced 1.3-3 times with settlement removal rate increasing 10%. Particle size distribution in runoff varied widely and d(10), d(50) and d(90) were 3-23 mu m, 17-56 mu m and 40-65 mu m respectively, which showed that particles within runoff were mainly finely. Maximum rain intensity had most significant impact on particle size distribution, while other precipitation factors had few relationships with it, which showed that maximum rain intensity was the most important factors deciding particle size distribution in runoff.