Water quality characteristics of stormwater runoff and the first flush effect in urban regions

Urbanization has been a dominant trend of social development all around the world over the last half century. This has led to increases in paved areas and changes in hydrological regimes, including increased volumes of storm water runoff with higher peak flow rates and floodwater levels. In order to understand the characteristics of urban stormwater runoff and the first flush effect, Panxi River Basin and Huxi Basin in Chongqing University were selected as study areas to monitor six rainfall events. Samples were collected at specified intervals during the rainfall seasons. Specifically, one sample was collected every 5 minutes during the first 30 minutes after the runoff started, every 10 minutes during the period of 30-60 minutes, and thereafter every 30 minutes until the runoff disappeared or became gradually stable. The rainfall was recorded automatically with an automatic rain gauge (JDZ-1, China) placed near the monitoring points. The results of water quality analysis showed that pollutant concentrations appeared in a parabolic distribution in the urban watershed runoff during rainfall seasons. The averages of ρ(TSS), ρ(CODCr), ρ(TN) and ρ(TP) were 2000, 420, 13.0 and 5.7 mg/L in the Panxi River Basin, while the means of ρ(TSS), ρ(CODCr), ρ(TN), ρ(NH3-N), ρ(NO3--N), ρ(TP), ρ(Fe), ρ(Zn), ρ(Pb) and ρ(Cd) were 33, 38, 2.6, 0.7, 1.1, 0.1, 2.1, 0.2, 0.6 and 0.06 mg/L in the Huxi Basin, respectively. Particle organic phosphorus (PON) consisted of most of the total phosphorus concentrations in the two studied watersheds (56% and 87%), and the total nitrogen concentration was mainly composed of inorganic nitrogen (72% and 82%). Analysis of the first flush effect indicated that no first flush effect was found in Panxi River watershed, and 50%-80% of the total pollution loads were carried by 40% of the initial runoff volume in Huxi Basin. Runoff volume analysis showed that peak runoff flow was determined and followed by peak rainfall intensity in unimodal rainfall events, and multimodal rainfall could also lead to multiple peak flow rates. Our study results provide reference for the management of urban runoff. ©, 2015, Editorial department of Molecular Catalysis. All right reserved.