Stormwater Runoff Pollutant Loading Distributions and Their Correlation with Rainfall and Catchment Characteristics in a Rapidly Industrialized City

<div><p>Fast urbanization and industrialization in developing countries result in significant stormwater runoff pollution, due to drastic changes in land-use, from rural to urban. A three-year study on the stormwater runoff pollutant loading distributions of industrial, parking lot and mixed commercial and residential catchments was conducted in the Tongsha reservoir watershed of Dongguan city, a typical, rapidly industrialized urban area in China. This study presents the changes in concentration during rainfall events, event mean concentrations (<i>EMCs</i>) and event pollution loads per unit area (<i>EPLs</i>). The first flush criterion, namely the mass first flush ratio (<i>MFFn</i>), was used to identify the first flush effects. The impacts of rainfall and catchment characterization on <i>EMCs</i> and pollutant loads percentage transported by the first 40% of runoff volume (<i>FF₄₀</i>) were evaluated. The results indicated that the pollutant wash-off process of runoff during the rainfall events has significant temporal and spatial variations. The mean rainfall intensity (<i>I</i>), the impervious rate (<i>IMR</i>) and max 5-min intensity (<i>I_max5</i>) are the critical parameters of <i>EMCs</i>, while <i>I_max5,</i> antecedent dry days (<i>ADD</i>) and rainfall depth (<i>R_D</i>) are the critical parameters of <i>FF₄₀</i>. Intercepting the first 40% of runoff volume can remove 55% of <i>TSS</i> load, 53% of <i>COD</i> load, 58% of <i>TN</i> load, and 61% of <i>TP</i> load, respectively, according to all the storm events. These results may be helpful in mitigating stormwater runoff pollution for many other urban areas in developing countries.</p>