Urban Sediment Transport through an Established Vegetated Swale: Long Term Treatment Efficiencies and Deposition

Abstract

Vegetated swales are an accepted and commonly implemented sustainable urban drainage system in the built urban environment. Laboratory and field research has defined the effectiveness of a vegetated swale in sediment detention during a single rainfall-runoff event. Event mean concentrations of suspended and bed load sediment have been calculated using current best analytical practice, providing single runoff event specific sediment conveyance volumes through the swale. However, mass and volume of sediment build up within a swale over time is not yet well defined. This paper presents an effective field sediment tracing methodology and analysis that determines the quantity of sediment deposited within a swale during initial and successive runoff events. The use of the first order decay rate constant, k, as an effective pollutant treatment parameter is considered in detail. Through monitoring tagged sediment deposition within the swale, the quantity of sediment that is re-suspended, conveyed, re-deposited or transported out of the swale as a result of multiple runoff events is illustrated. Sediment is found to continue moving through the vegetated swale after initial deposition, with ongoing discharge resulting from resuspension and conveyance during subsequent runoff events. The majority of sediment initially deposited within a swale is not detained long term or throughout its design life of the swale.

Modelling the Role of SuDS Management Trains in Minimising Flood Risk, Using MicroDrainage

“…Winston et al [46] suggest that swales effectiveness for moderate scale events can be greatly improved by integrating check dams to further limit runoff and increase storage of stormwater. Additionally, their effectiveness is limited by the infiltration rate of a site, which corresponds with the modelled results for the higher intensity events [47,48]. The reduction in runoff for the two lowest intensity rainfall events (360 and 720 min) was negligible, ranging from a maximum of 1.3 L/s to 0.1 L/s.…”

On the Role of Spatial, Temporal, and Climatic Forces on Stream Sediment Loading from Rural and Urban Ecosystems

“…Much of the rural stream network was also straightened and dredged to accommodate farming both of which likely increased the peak flows from the rural areas in Paradise Creek. In urban areas, controlling erosion during construction projects and managing sediment use on road systems is critical ( e.g ., Allen et al ., ). In Paradise Creek, we identified a critical threshold of peak discharge (7.5 m 3 /s at the urban station and 4.8 m 3 /s at the rural station) that typically results in individual event sediment loads exceeding the annual TMDL target (236 t/year).…”

The short-term influence of cumulative, sequential rainfall-runoff flows on sediment retention and transport in selected SuDS devices

“…Each SuDS device was considered in isolation. A fine sediment tracer methodology using rare earth oxides (REO) (described in Allen et al 2015, Allen 2017) was employed at selected established SuDS device field sites to allow the natural movement of urban sediment to be recorded in conjunction with rainfall, flow characteristics and mass deposition within monitored SuDS.…”