Abstract
AbstractNatural Flood Management (NFM) techniques aim to reduce downstream flooding by storing and slowing the flow of stormwater to river channels. These techniques include a range of measures, including setback stormwater outfalls and the physical restoration of channels and floodplains, to improve the natural functioning of catchments. An additional benefit of NFM measures is the potential reduction in sediment and pollutant delivery to the channel. Urban development releases a variety of heavy metal and nutrient pollutants that enter rivers through stormwater outfalls with adverse effects on the aquatic ecosystem. In this study, the influence of channel modification and quality of the river habitat on the sediment quality surrounding stormwater outfalls was assessed. Sediment samples were taken at several outfalls within the Johnson Creek catchment, Oregon, USA, and analysed for a variety of urban pollutants. The level of river habitat quality and modification at each site were assessed using a semi‐quantitative scoring methodology. Significant increases in pollutant levels were observed at outfalls, with a greater and more variable increase at direct compared to setback outfalls. Removal efficiency of certain pollutants was found to be significantly correlated to the level of habitat quality or modification (for Fe, Ba, Sn, Mg, P, K) indicating that more natural reaches had greater potential for pollutant removal. The findings highlight the multiple benefits associated with NFM and river restoration approaches in relation to sediment quality and pollutant content. © 2016 The Authors River Research and Applications Published by John Wiley & Sons, Ltd.
Highlights
Natural Flood Management (NFM) is becoming increasingly popular as a means of complementing existing traditional flood management schemes
This study aims to assess the impacts of setback outfalls and channel restoration approaches, as part of natural flood risk management, on the levels of sediment contamination at and downstream of stormwater outfalls
The impact of setback outfalls and river restoration on these pollutants are twofold: (i) the increased deposition of sediment-bound contaminants; and (ii) the increased uptake of dissolved contaminants by aquatic organisms. Both of these mechanisms are likely operating in setback outfalls and within the channel, but, because of the difficulty in monitoring sediment and contaminant flux in stormwater systems, the effectiveness of pollutant removal overall by the schemes is inferred from changes in sediment contamination in this study
Summary
Natural Flood Management (NFM) is becoming increasingly popular as a means of complementing existing traditional flood management schemes. Governmental policies and guidelines, such as the EU Floods Directive (2007), the USA’s Interagency Floodplain management review/Galloway Report (1994), and the UK Flood and Water Management Act (2010), recognize the linkages between catchment-scale land use and flood risk. These guidelines encourage restoration of natural hydrological and geomorphological processes and highlight the potential flood risk and water quality benefits of restored riparian areas and wetlands. NFM aims to work with catchment-scale processes to delay and attenuate flood peaks by altering floodwater pathways through the catchment.
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