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A combined field, laboratory and numerical study of the forces applied to, and the potential for removal of, bar top vegetation in a braided river

Bankhead, Natasha L.; Thomas, Robert E.; Simon, Andrew


Natasha L. Bankhead

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Dr Robert Thomas
Senior Research Fellow in Geomorphology and Flood Risk

Andrew Simon


Vegetation can have an important role in controlling channel planform, through its effects on channel roughness, and root-reinforcement of bank and bar materials. Along the Platte River in central Nebraska, USA, The Platte River Recovery Implementation Program (PRRIP) has been tasked with managing the planform of the river to benefit endangered species. To investigate the potential use of planned Short Duration High Flow events (SDHFs) to manage bar vegetation, this study combined several approaches to determine whether flows of up to 227 m3s-1 through the central Platte River, could remove cottonwood, Phragmites and reed canarygrass stands of various ages and densities from in-channel bars. First, fieldwork was carried out to measure the uprooting resistance, and resistance to bending for each species. Second, a set of flume experiments was carried out to measure the forces exerted on the three species of interest under different flow conditions. Finally, a numerical study compared drag forces (driving) measured in the flume study, with uprooting forces (resisting) measured in the field, was carried out for each species to determine the likelihood of plant removal by SDHFs. Results showed that plants with more than a year of root growth, likely cannot be removed through drag and local scour alone, even at the 100-year recurrence interval discharge. At most, a few cottonwood seedlings could be removed from bars through drag, scour and undercutting, where rooting depths are still small. The results presented here help us further understand the positive feedbacks that lead to the creation of permanent, vegetated bars rather than mobile braided channels. As such, the findings could help inform management decisions for other braided rivers, and the combined field, flume and modelling techniques used in this study could be applied to other fluvial systems where vegetation and planform dynamics are of interest.


Bankhead, N. L., Thomas, R. E., & Simon, A. (2017). A combined field, laboratory and numerical study of the forces applied to, and the potential for removal of, bar top vegetation in a braided river. Earth surface processes and landforms : the journal of the British Geomorphological Research Group, 42(3), 439-459.

Journal Article Type Article
Acceptance Date Jun 14, 2016
Online Publication Date Jul 18, 2016
Publication Date Mar 15, 2017
Deposit Date Oct 29, 2018
Journal Earth Surface Processes and Landforms
Print ISSN 0197-9337
Electronic ISSN 1096-9837
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 42
Issue 3
Pages 439-459
Keywords Vegetation management; Braided planform; Drag coefficients; Modelling; Numerical study
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