Quantifying the combined effects of multiple extreme floods on river channel geometry and on flood hazards

Guan, M., Carrivick, J.L., Wright, N.G. ORCID: 0000-0002-1289-2830, Sleigh, P.A. and Staines, K.E.H., 2016. Quantifying the combined effects of multiple extreme floods on river channel geometry and on flood hazards. Journal of Hydrology, 538, pp. 256-268. ISSN 0022-1694

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Effects of flood-induced bed elevation and channel geometry changes on flood hazards are largely unexplored, especially in the case of multiple floods from the same site. This study quantified the evolution of river channel and floodplain geometry during a repeated series of hypothetical extreme floods using a 2D full hydro-morphodynamic model (LHMM). These experiments were designed to examine the consequences of channel geometry changes on channel conveyance capacity and subsequent flood dynamics. Our results revealed that extreme floods play an important role in adjusting a river channel to become more efficient for subsequent propagation of floods, and that in-channel scour and sediment re-distribution can greatly improve the conveyance capacity of a channel for subsequent floods. In our hypothetical sequence of floods the response of bed elevation was of net degradation, and sediment transport successively weakened even with floods of the same magnitude. Changes in river channel geometry led to significant impact on flood hydraulics and thereby flood hazards. We found that flood-induced in-channel erosion can disconnect the channel from its floodplain resulting in a reduction of floodwater storage. Thus, the frequency and extent of subsequent overbank flows and floodplain inundation decreased, which reduced downstream flood attenuation and increased downstream flood hazard. In combination and in summary, these results suggest that changes in channel capacity due to extreme floods may drive changes in flood hazard. The assumption of unchanging of river morphology during inundation modelling should therefore be open to question for flood risk management.

Item Type: Journal article
Publication Title: Journal of Hydrology
Creators: Guan, M., Carrivick, J.L., Wright, N.G., Sleigh, P.A. and Staines, K.E.H.
Publisher: Elsevier
Date: July 2016
Volume: 538
ISSN: 0022-1694
S0022169416301858Publisher Item Identifier
Rights: © 2016 Elsevier B.V. All rights reserved.
Divisions: Professional Services > The Directorate
Record created by: Linda Sullivan
Date Added: 29 Oct 2018 10:12
Last Modified: 29 Oct 2018 10:12
URI: https://irep.ntu.ac.uk/id/eprint/34776

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