Quantifying the impact of channelisation on channel behaviour and coarse sediment budgets over a decadal scale: Implications for managing downstream flood risk

Heritage, G and Entwistle, NS ORCID: https://orcid.org/0000-0002-5799-0506 2020, 'Quantifying the impact of channelisation on channel behaviour and coarse sediment budgets over a decadal scale: Implications for managing downstream flood risk' , Water . (In Press)

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Abstract

Although knowledge of sediment transport has improved over the last 25 years, our understanding of bedload transfer and sediment delivery is still based on a limited set of observations or on models that make assumptions on hydraulic and sediment transport processes. This study utilises repeat LiDAR survey data of the River Caldew above the City of Carlisle in the UK to investigate the balance of erosion and deposition associated with channel switching from an engineered and managed single thread channel to a naturalising incipient wandering system. Over the 11-year survey period (4 bankfull flood events) around 271,000 m3 of sediment were delivered to the river and floodplain and 197,000 m3 eroded suggesting that storage rates of around 7000 m3/annum occurred. The balance of erosion and deposition is influenced by channelisation with very restricted overbank sedimentation and only limited local and transient in-channel bar deposition along the engineered reach (8000 m3 eroded). This contrasts with the activity of the naturalising reach downstream where a developing wandering channel system is acting to store coarse sediment in-stream as large bar complexes and associated upstream aggrading plane bed reaches and overbank as splay deposits (87,000 m3 stored). Such behavior suggests that naturalisation of channelised systems upstream of flood vulnerable urban areas can have a significant impact on sediment induced flooding downstream. This conclusion must, however, be moderated in the light of the 28 relatively small volumes of material needed to instigate local aggradation in over-capacity urban channels.

Item Type: Article
Schools: Schools > School of Environment and Life Sciences > Ecosystems and Environment Research Centre
Journal or Publication Title: Water
Publisher: MDPI
ISSN: 2073-4441
Depositing User: USIR Admin
Date Deposited: 06 May 2020 12:57
Last Modified: 06 May 2020 13:00
URI: http://usir.salford.ac.uk/id/eprint/56972

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