CHARACTERIZATION OF FIRST FLUSH IN THE LIBRARY LESE-NUST URBAN AREA OF RAWALPINDI

Abstract

Storm water runoff is one of the major sources of pollution in urban streams and reservoirs. Urbanization has generated a huge impervious area which leads to an enormous storm water flow. This large quantity of storm water washes away all the pollutants built up at the exposed urbanized structures, of which roads are the mujor coinponent. For an appropriate management of this large volutne of water, a proper understanding of first flush quantity and quality is required. The investigation of the initial storm water runoff having high pollutant concentrations is the main objective of this study. The investigation of the first flush quantity and quality in terms of pH, COD, conductivity, turbidity, sulphate (S04), chloride (CIO, total organic carbon (TOC), total phosphorous (TP), total nitrogen (TN), heavy metals (Pb, Fe, Cu, Cr, and Zn), total suspended solids (TSS) and total dissolved solids (TDS) is the main objective of this study. The data were collected for six months for nine storm events from three road seglnents and a roof top in Rawalpindi. The event mean concentrations (EMCs) for all the storm events were calculated to analyze the spatial difference in the pollutant build up. Mass vs. volume [M curves were used to investigate the first flush behavior at all the selected sites. The pollutant loads at 25% (FF25) and (FF30) initial flow volutne was calculated fronl these M (V) curves. The correlation anlong the quality parameters during the storin event was also deternlined to check the inter-dependence of the pollutant concentrations and to highlight the Inajor influential paralneter, among a list of pollutants. The first flush analysis revealed that it was an unavoidable component of storin water Inanagelnent as it carried the pollutant load. At road Siles avelage FF25 and

FF.3() transported 40% and 45% of the pollutants respectively, whereas at roof top the wash OIT in FF25 and FF30 was 45% and 55% respectively. Total suspended solids were found to be the most influential pararneter which affected the quality of the Inost of the pollutants washed off. Total suspended solids (TSS) and chemical oxygen deniand (COD) were the other major pollutants studied in this research. The antecedent dry weather period (AD WT) was not substantially influential to the pollutant add up. The surrounding land use and the characteristics of the drainage area were also not found to be the major contributors of the pollutant load. 'l'hese factors, however, collectively participated in a high level of pollutant wash off. This study is expected to provide a base line for a comprehensive catchment-wise investigation and an efficient storm water management model development.