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Modeling complex flow structures and drag around a submerged plant of varied posture

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posted on 28.04.2017 by Richard J. Boothroyd, Richard J. Hardy, Jeff Warburton, Tim Marjoribanks
Although vegetation is present in many rivers, the bulk of past work concerned with modeling the influence of vegetation on flow has considered vegetation to be morphologically simple and has generally neglected the complexity of natural plants. Here we report on a combined flume and numerical model experiment which incorporates time-averaged plant posture, collected through terrestrial laser scanning, into a computational fluid dynamics model to predict flow around a submerged riparian plant. For three depth-limited flow conditions (Reynolds number = 65,000–110,000), plant dynamics were recorded through high-definition video imagery, and the numerical model was validated against flow velocities collected with an acoustic Doppler velocimeter. The plant morphology shows an 18% reduction in plant height and a 14% increase in plant length, compressing and reducing the volumetric canopy morphology as the Reynolds number increases. Plant shear layer turbulence is dominated by Kelvin-Helmholtz type vortices generated through shear instability, the frequency of which is estimated to be between 0.20 and 0.30 Hz, increasing with Reynolds number. These results demonstrate the significant effect that the complex morphology of natural plants has on in-stream drag, and allow a physically determined, species-dependent drag coefficient to be calculated. Given the importance of vegetation in river corridor management, the approach developed here demonstrates the necessity to account for plant motion when calculating vegetative resistance.

Funding

Richard J. Boothroyd was funded under Natural Environmental Research Council (NERC) PhD Studentship 1313876. The flume experiments were funded through NERC grant NE/F010060/1.

History

School

  • Architecture, Building and Civil Engineering

Published in

Water Resources Research

Volume

53

Issue

4

Pages

2877–2901

Citation

BOOTHROYD, R.J., 2017. Modeling complex flow structures and drag around a submerged plant of varied posture. Water Resources Research, 53 (4), pp. 2877–2901.

Publisher

American Geophysical Union © The Authors

Version

VoR (Version of Record)

Publisher statement

This work is made available according to the conditions of the Creative Commons Attribution 4.0 International (CC BY 4.0) licence. Full details of this licence are available at: http://creativecommons.org/licenses/ by/4.0/

Acceptance date

10/03/2017

Publication date

2017-03-17

Copyright date

2017

Notes

This is an Open Access Article. It is published by the American Geophysical Union under the Creative Commons Attribution 4.0 International Licence (CC BY). Full details of this licence are available at: http://creativecommons.org/licenses/by/4.0/

ISSN

0043-1397

eISSN

1944-7973

Language

en

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