Logjams with a lower gap: Backwater rise and flow distribution beneath and through logjam predicted by two-box momentum balance

Follett, E. ORCID: https://orcid.org/0000-0001-9993-5313, Schalko, I. and Nepf, H. 2021. Logjams with a lower gap: Backwater rise and flow distribution beneath and through logjam predicted by two-box momentum balance. Geophysical Research Letters 48 (16) , e2021GL094279. 10.1029/2021GL094279

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Abstract

Logjams with a gap at the bed form naturally in small channels and are used in engineering practice to maintain river connectivity at base flow. Limited understanding of a jam's effect on backwater rise and flow velocity limits assessment of geomorphic and ecological impacts of natural logjams, design of river restoration interventions, and representation in flood models. The distribution of flow through and beneath the jam satisfies a two-box, momentum-based model constrained by drag generated in the jam, momentum loss in flow through the lower gap, and net pressure force. The model was validated with 68 flume experiments. Backwater rise is predicted from discharge beneath the jam following established models for solid sluice gates. As a result, backwater rise increases with jam resistance, which forces a greater discharge beneath the jam. Below-jam velocity and Shields parameter increased with ratio of friction coefficient to slope and decreasing gap height.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Engineering
Publisher:	Wiley
ISSN:	0094-8276
Funders:	Royal Academy of Engineering, European Regional Development Fund through Welsh Government Sêr Cymru Programme
Date of Acceptance:	25 July 2021
Last Modified:	09 Nov 2022 11:29
URI:	https://orca.cardiff.ac.uk/id/eprint/143530

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