Abstract
Understanding the amount of pollutants contributed by impermeable urban surfaces during rain events is necessary for developing effective stormwater management. A process-based pollutant load model, named Modelled Estimates of Discharges for Urban Stormwater Assessments (MEDUSA), was further developed (MEDUSA2.0; Christchurch, New Zealand) to include simulations of dissolved metal loadings and improve total suspended solids (TSS) loading estimations. The model uses antecedent dry days, rainfall pH, average event intensity and duration to predict sediment and heavy metal loads generated by individual surfaces. The MEDUSA2.0 improvements provided a moderate to strong degree of fit to observed sediment, copper, and zinc loads for each modelled road and roof surface type. The individual surface-scale modelling performed by MEDUSA2.0 allows for identification of specific source areas of high pollution for targeted surface management within urban catchments.
Highlights
The accumulation, or build-up, of pollutants on an impermeable surface during dry periods is the result of interactions between several processes, including atmospheric deposition, wind erosion, surface material breakdown due to weathering, and direct deposition of particles from vehicle wear [1,2,3]
Of the four sampled surfaces, the optimized MEDUSA2.0 model was most effective at predicting road runoff pollutant loads (NSEs of 0.66–0.74)
The highest zinc loads were from the galvanized roof, and MEDUSA2.0 was effective at predicting TZn and DZn from this roof type (NSEs of 0.66 and 0.68, respectively)
Summary
The accumulation, or build-up, of pollutants on an impermeable surface during dry periods is the result of interactions between several processes, including atmospheric deposition, wind erosion, surface material breakdown due to weathering, and direct deposition of particles from vehicle wear [1,2,3]. Additional pollutants may enter the runoff from wet deposition, where the raindrops scavenge particles from the air as they fall [4], or via dissolution of the surface material due to acidity of the rainfall [5,6]. Rainfall characteristics, such as rainfall pH, rainfall intensity (average event intensity (INTavg) and peak intensity (INTpeak)), duration (Dur), depth, and the length of the dry period between rain events (antecedent dry days: ADD), influence the amount of pollutants that build up and are washed off urban surfaces. Several studies have found correlations between pollutant build-up and wash-off and rainfall characteristics for both total suspended solids (TSS) and heavy metals (Table 1), and these relationships vary with both pollutant and surface type.
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