Knowledge base

First Flush Stormwater Pollutants from Carparks in Different Urban Settings

Carparks make up a large portion of impervious urban areas. Stormwater runoff from these areas is therefore considered a significant source of pollutants to receiving urban waterways, particularly of total suspended solids (TSS) and heavy metals such as zinc (Zn), copper (Cu) and lead (Pb). Pollutant concentrations can be substantially high during the initial period of the runoff hydrograph commonly known as first flush (FF). In Christchurch, the influence of land use around urban carparks on the water quality of the first flush is poorly understood. This research thus focuses on quantifying FF TSS and metals from carparks within different urban land use settings. To achieve this objective, grab samplers (1 L HDPE) were deployed in a hospital carpark, a university carpark, and an industrial carpark in Christchurch. Concentrations of TSS, Zn, Cu, and Pb were quantified for each of seven rain events. TSS and total metal concentrations were higher in the FF from the industrial carpark due to its unique land use activities as compared to the other two sites studied. Furthermore, dissolved Zn and Cu were found to be above recommended guidelines for all carparks. It is concluded that characterizing the FF for individual carpark types is important for the design of effective stormwater treatment systems such as filters.