First Flush Analysis in the Auckland Region

This paper is concerned with examining the available Auckland stormwater quality data for evidence of contaminant first flush and its characteristics. The first flush refers to the situation of having a very high delivery of either concentration or mass of a pollutant during the early part of the storm runoff event. The data from sixteen sites in the Auckland region and ten water quality parameters were used in the analysis. The data contains water quality samples from eight urban network sites, four urban stream sites, a pond site, a rain garden site, a treatment train site and a permeable pavement site. In this study, the analysis for evidence of first flush is conducted using the mass-based framework which aims at developing a functional relationship between cumulative pollutant mass and volumes when expressed as dimensionless quantities. The analysis reported in this paper identifies the existence of first flush in the Auckland region.