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Predicting the Deposition of Highway-Derived Sediments in a Receiving River Reach

Author(s): Ian Guymer; Virginia Stovin; Paul Gaskell; Lorraine Maltby; Jonathan Pearson

Linked Author(s): Ian Guymer

Keywords: Sediment; Pollutant; Highway; Runoff; Tracers; Receiving water; River; Travel time; Deposition

Abstract: Previous research has shown that highway runoff contains contaminated particles which, if deposited within the receiving water, may negatively impact on the ecology. A preliminary investigation into the potential benefit of field sediment tracing studies has been performed as a component of an integrated research programme, commissioned by the UK Highways Agency and the Environment Agency, on the impact of contaminated sediment. The sediment tracing study utilised two sediment sizes, with both magnetic and fluorescent properties, which were introduced into a simulated runoff event. Visual evidence showed deposition of the coarse sediment adjacent to the outfall bank within the first 5 m downstream from the outfall. Photographs taken during the introduction of the sediment show a plume of predominantly fine particles emerging from the outfall pipe and being conveyed through the reach. This provided an envelope of extremes of expected sediment behaviours. Limited success of the experimental work, including several practical difficulties of sediment recovery, prompted the consideration of alternative methods for predicting sediment behaviour based on locallyderived characteristics of the highway runoff sediment load combined with measured receiving water hydraulic characteristics. Importantly the method proposed recognizes the need to consider spatial variations in the cross-sectional velocity distribution in open channel flows and a reach travel time distribution is employed in preference to a single reach mean velocity. The results are coupled with knowledge of sediment characteristics to provide a method for estimating likely sediment deposition, and predictions are consistent with the field observations.


Year: 2010

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