First flush analysis of urban stormwater runoff from an urban catchment in Johor, Malaysia

An increase of pollutants that are present in the initial stage of stormwater runoff hydrograph compared to a later stage of runoff is defined as a first flush phenomenon. This study aims to investigate the occurrence of first flush from samples of urban stormwater runoff obtained from the grounds of a University in Skudai, Johor, Malaysia. In order to achieve the study’s objective; field investigations, manual sampling of urban stormwater runoff, laboratory testing and data analysis were carried out and the evaluation of the first flush phenomenon was calculated using concentration-based first flush (CBFF) and mass-based first flush (MBFF. A total of 90 stormwater samples were collected from six (6) rainfall events and were tested for total suspended solids (TSS). For each rainfall event, the pollutographs and the dimensionless curves of the cumulative pollutant mass versus the cumulative discharged volume were plotted. The first flush coefficient was also determined in order to evaluate the occurrence of first flush. The results indicated that the storm events demonstrated a weak presence of first flush.