Stormwater pollutant process analysis with long-term online monitoring data at micro scale sites

Stormwater runoff quality was measured with on-line turbidity sensors at four common types of small urban subcatchments: (i) a flat roof, (ii) a parking lot, (iii) a residential catchment and (iv) a high traffic street. Samples were taken to estimate site specific correlations between TSS and turbidity. Continuous TSS time series were calculated and used to estimate event loads and event mean concentrations. Rainfall-runoff event characteristics were subjected to correlation analysis to TSS loads. Significant correlations were found for rainfall intensities at sites with high imperviousness and decrease with increasing catchment size. Antecedent dry weather periods are only correlated at site parking lot. Intra-event TSS load distributions were studied with M(V)-curves. M(V)-curves are grouped at runoff quantiles and statistically described with boxplots. All sites show in general a more pronounced first-flush effect. While wash-off of the flat roof tend to be source-limited, the sites parking lot and high traffic street show a more transport-limited behaviour. Wash-off process of the residential catchment appears to be influenced by a composition of different subcatchments.