This Swiss paper describes an approach for assessing the risks caused by urban wet-weather discharges to the sediment compartment, based on total suspended solids (TSS), and is validated with field measurements.
Sediment represents an important compartment in surface waters. It constitutes a habitat or spawning site for many organisms, and is an essential trophic resource for higher level organisms.
Sediment can be impacted by anthropogenic activities, in particular through urban wet-weather discharges like stormwater and combined sewer overflows.
Here Swiss researchers report on an approach for assessing the risks caused by urban wet-weather discharges to the sediment compartment, based on total suspended solids (TSS).
TSS is routinely measured in field surveys, and can be considered as a tracer for urban wet-weather contamination. Three assessment endpoints linked with TSS were proposed: siltation of the riverbed, oxygen demand due to organic matter degradation, and accumulation of ecotoxic contaminants on the riverbed (heavy metals, polyaromatic hydrocarbons).
These criteria were translated in terms of the maximal TSS accumulation load and exposure time (percentage of time exceeding the accumulation criteria), to account for sediment accumulation dynamics and re-suspension in streams impacted by urban wet-weather discharges.
These assessment endpoints were implemented in a stochastic model that calculates TSS behaviour in receiving waters, and therefore allows an assessment of potential impacts.
The approach was applied to three Swiss case studies. In each case good agreement was found between risk predictions and field measurements, confirming the reliability of the approach.
