First flush analysis using a rainfall simulator on a micro catchment in an arid climate.

Urban runoff water from simulated rainfall for three different land uses (residential, industrial, commercial) at six different locations of Doha, Qatar was analysed for physico-chemical parameters such as, trace metals, pH, total suspended solids (TSS), total organic carbon (TOC), total phosphorus (TP), total kjeldahl nitrogen (TKN) and polyaromatic hydrocarbons (PAHs). Rainfall events with two different intensities (40 mm/h and 20 mm/h) were simulated in a micro catchment area (4.55 × 4.55 m2) using a specially designed portable rainfall simulator. Out of six sites, runoff samples were collected from five sites with paved surfaces. The study results demonstrated significant concentration of TSS, Cu, Fe, Mn and Zn in the urban runoff exceeding the Qatar Ministry of Municipality and Environment (MME) and Tropical Australian Standards. The first flush effect was also investigated during the experiment which exhibited first flush effect of selected pollutants (TSS, TKN, TP, TOC and heavy metals) at five study sites with impervious surfaces. The magnitude of the first flush varies across the study sites and was found to be affected by the surface texture of the sites. Analysis of variance revealed that, rainfall intensity has limited effect on the first flush in the studied scenarios, however, first flush effects showed relation with the event mean runoff concentration. Furthermore, strong positive correlations were observed between analysed water quality parameters, particularly between TSS, TOC and metals. This study is the first study investigating first flush in Qatar's capital, Doha which will provide a ground for future researcher to design appropriate stormwater treatment devices that will capture and treat the first flush for significant reduction of urban stormwater pollution.