Abstract
Urban stormwater with large impervious (paved) areas often produces runoff with a variety of contaminants. Although southern California is among the most urbanized coastal areas in the United States, the effect of rainfall variations on washoff efficiency of contaminants from pervious and impervious surfaces is largely unknown. The goal of this study was to investigate the effect of varying rainfall intensities and duration on runoff composition from highly impervious parking lots. In order to control the tremendous natural variability in precipitation of the arid climate in southern California, rainfall simulators were used to generate and quantify pollutant washoff at changing intensities and durations. Washoff of suspended solids, total and dissolved trace metals, and polycyclic aromatic hydrocarbons was strongly inversely correlated with rainfall duration. Rainfall intensity only affected washoff at the smallest measured duration; higher intensities produced decreased concentrations. The effect of rainfall duration was a reflection of the first flush observed in pollutographs for every duration and intensity sampled. Peak concentrations, up to an order of magnitude higher than concentrations later in the event, occurred during the first 10 min after the onset of rainfall. Longer simulated storms effectively diluted the first flush.
Highlights
Urban stormwater runoff mobilizes a variety of contaminants to coastal oceans and inland waterways, affecting their water quality [1,2,3]
The goal of this paper was to answer the question: do concentrations of pollutants in stormwater runoff change with varying rainfall intensities and durations in an arid environment? We explored these rainfall-runoff quality relationships using parking lots, which are critical source areas with almost
The magnitude of the first-flush effect varied between intensities, ranging from 112 mg/L in the 25 mm/h rainfall intensity to 140 mg/L in the 6 mm/h rainfall intensity
Summary
Urban stormwater runoff mobilizes a variety of contaminants to coastal oceans and inland waterways, affecting their water quality [1,2,3]. These contaminants come from different residential, commercial, and industrial land uses within a watershed [4,5]. As development increases and land use activities change and intensify, the concentrations and types of contaminants increase [6]. All land uses can affect water quality, natural processes in undeveloped areas can lessen the impact of contaminants or even remove contaminants from runoff through infiltration [7]. Impervious areas (paved surfaces) reduce the opportunity for natural processes to treat stormwater. Bannerman et al [8]
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