Influence of rainfall characteristics towards first flush behaviour

Urban stormwater runoff has been recognised as one of the main contributor in degradation of water quality as it wash-off varies pollutants on impervious surface to receiving water. One important characteristic of urban stormwater runoff is that pollutant discharge in the early phase of runoff is significantly higher than that in later phase of the runoff and this process is identified as first flush phenomenon. The understanding of first flush is important to provide information on pollutant control and water quality management. This research investigates the influence of rainfall characteristics toward first flush behaviour. This study involved field work, sampling of stormwater runoff, laboratory testing and data analysis. A total of 115 stormwater runoff samples were collected from 11 rainfall events in the study area, located at School of Civil Engineering, Universiti Teknologi Malaysia, Johor. Rainfall characteristics and runoff data were collected from May 2017 to April 2018. Stormwater quality parameters analysed were total suspended solid (TSS), total dissolved solids (TDS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), and zinc (Zn). In order to analyse first flush occurrence, two methods were employed; concentration-based First Flush (CBFF) method (using data from pollutant’s concentration and hydrograph) and mass-based First Flush (MBFF) method (distribution of M(V) curves). CBFF confirmed that rainfall events with peak pollutant concentration which occurred before peak flow-discharge indicated the occurrence of first flush phenomenon. In contrast, first flush was absent when peak concentration occurred after peak flow-discharge. It was found from the distribution of M(V) curves that the percentage of first flush occurrence is different for each pollutant. Based on the mean value of M(V) curve for each pollutant, the relative strength of the first flush was COD>TSS>Zn>BOD>TDS. Detail analysis on the influence of rainfall characteristics on first flush behaviour was carried out by PROMETHEE and GAIA software. Result of rainfall characteristics showed that rainfall duration and intensity were significant in controlling the wash-off of pollutants while antecedent dry period (ADP) is important for understanding the build-up process of pollutants. In addition, high rainfall depth and intensity have influenced the behaviour of first flush for TSS, TDS and BOD. For COD, longer rainfall duration and ADP play a significant role in influencing the first flush behaviour. Meanwhile, Zn was influenced by longer duration of rainfall. Therefore, it is concluded that the behaviour of first flush varied due to variations in the characteristics of rainfall events

Influence of rainfall characteristics on first flush behaviour

Urban stormwater with impervious surface often produces runoff with a variety of contaminants. This paper discusses an investigation into the influence of rainfall characteristics toward the first flush behaviour. This study involved field investigations, sampling of urban stormwater runoff, laboratory testing and data analysis. 15 stormwater samples were collected and executed manually in a small catchment, which represents the higher institution area in Skudai, Johor. Data collections were carried out on 9 November 2017. Correlation of pollutants such as total suspended solids (TSS), total dissolved solids (TDS), biological oxygen demand (BOD), chemical oxygen demand (COD) and zinc with runoff were derived within the evaluation of hyetograph, hydrographs and pollutographs. The concentration varied at different stages of the same rainfall event. The higher strength of first flush was seen in case of TSS, BOD and zinc compared to TDS and COD. The finding shows that high rainfall intensity in the beginning of the event had contributed to the high wash off of some pollutants such as TSS, BOD and zinc. The concept of the first flush cannot be used alone to establish a reliable methodology to design treatment facilities. Additional knowledge and information are necessary

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

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