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

Deonie Allen,Heather Haynes,Valerie Olive,Scott Arthur

doi:10.3390/w7031046

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.

Highlights

Sustainable urban drainage systems (SuDS) are designed to control and treat surface water flow and pollution from the increasing impervious development of urban environs [1]
1, 2, and 3 and demonstrates that the presented Rare earth oxides (REO) trace methodology is effective in illustrating sediment transport through an urban vegetated swale under ephemeral conditions
The two REO tagged sediment material show concentrations that follow a similar trend when analysed at part per million concentrations by an inductively coupled plasma mass spectrometer (ICPMS)

Summary

Introduction

Sustainable urban drainage systems (SuDS) are designed to control and treat surface water flow and pollution from the increasing impervious development of urban environs [1]. Up to 85% of nutrients and heavy metal pollutants are conveyed from urban surfaces adsorbed to fine sediment, ranging from 1 μm to 2 cm [2]. The efficiency of SuDS, including vegetated swales, has been investigated by leading SuDS researchers within the laboratory and in the field under single runoff event conditions. Both simulated and naturally occurring runoff events have been monitored during research completed by Sabourin and Wilson (2008) [3], and single runoff event specific pollutant removal efficiencies have been defined through analysis of this work. Methodological limitations associated with long term source-pathway-sink monitoring of sediment movement through SuDS assets has resulted in limited extended case study research and analysis

Methods

Results

Conclusion