Moving boulders in flash floods and estimating flow conditions using boulders in ancient deposits

Alexander, Jan ORCID: and Cooker, Mark (2016) Moving boulders in flash floods and estimating flow conditions using boulders in ancient deposits. Sedimentology, 63 (6). 1582–1595. ISSN 0037-0746

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Boulders moving in flash floods cause considerable damage and casualties. More and bigger boulders move in flash floods than predicted from published theory. The interpretation of flow conditions from the size of large particles within flash flood deposits has, until now, generally assumed that the velocity (or discharge) is unchanging in time (i.e. flow is steady), or changes instantaneously between periods of constant conditions. Standard practice is to apply theories developed for steady flow conditions to flash floods, which are however inherently very unsteady flows. This is likely to lead to overestimates of peak flow velocity (or discharge). Flash floods are characterised by extremely rapid variations in flow that generate significant transient forces in addition to the mean-flow drag. These transient forces, generated by rapid velocity changes, are generally ignored in published theories, but they are briefly so large that they could initiate the motion of boulders. This paper develops a theory for the initiation of boulder movement due to the additional impulsive force generated by unsteady flow, and discusses the implications.

Item Type: Article
Additional Information: This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made.
Uncontrolled Keywords: boulders,flash floods,palaeohydrology,flood front,hydrodynamic impact
Faculty \ School: Faculty of Science > School of Environmental Sciences
Faculty of Science > School of Mathematics
UEA Research Groups: Faculty of Science > Research Groups > Geosciences
Faculty of Science > Research Groups > Geosciences and Natural Hazards (former - to 2017)
Faculty of Science > Research Groups > Fluid and Solid Mechanics
Depositing User: Pure Connector
Date Deposited: 22 Mar 2016 09:29
Last Modified: 22 Oct 2022 00:51
DOI: 10.1111/sed.12274

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