The importance of accurately representing submerged vegetation morphology in the numerical prediction of complex river flow

Boothroyd, R.J.; Hardy, R.J.; Warburton, J.; Marjoribanks, T.I.

Abstract

This paper reports a novel method for the incorporation of complex plant morphologies into a computational fluid dynamics (CFD) model, allowing the numerical prediction of flows around individual plants. The morphological complexity, which comprises the vertical and lateral distribution of individual branches and leaves is captured through terrestrial laser scanning (TLS) and is maintained in the numerical prediction of flow fields. This is achieved where the post-processed, voxelised plant representation is incorporated into a CFD scheme through a mass flux scaling algorithm (MFSA). Flow around Prunus laurocerasus has been modelled under foliated and defoliated states following the removal of leaves. The complex plant morphologies are shown to produce spatially heterogeneous downstream velocity fields, with velocity profiles that deviate significantly from the idealised inflected shape. Rapid transition between the high velocity free stream zone and the zone of reduced velocity in the plant wake indicate shearing of flow, with the point of reattachment extending up to seven plant lengths downstream. The presence of leaves significantly modifies the flow field response, with development of a second, more pronounced wake structure around the dense foliage. This approach provides a full flow numerical description of the pressure field, enabling the vegetative drag force to be quantified. For the example given here, drag force is an order of magnitude greater for the foliated state. The methodology outlined here demonstrates the importance of accurately representing complex plant morphology in hydraulic models, and allows drag forces and coefficients to be calculated for specific plant species. This article is protected by copyright. All rights reserved.

Citation

Boothroyd, R., Hardy, R., Warburton, J., & Marjoribanks, T. (2016). The importance of accurately representing submerged vegetation morphology in the numerical prediction of complex river flow. Earth Surface Processes and Landforms, 41(4), 567-576. https://doi.org/10.1002/esp.3871

• Journal Article Type: Article
• Acceptance Date: Nov 17, 2015
• Online Publication Date: Jan 5, 2016
• Publication Date: Mar 30, 2016
• Deposit Date: Nov 17, 2015
• Publicly Available Date: Jan 5, 2017
• Journal: Earth Surface Processes and Landforms
• Print ISSN: 0197-9337
• Electronic ISSN: 1096-9837
• Publisher: British Society for Geomorphology
• Peer Reviewed: Peer Reviewed
• Volume: 41
• Issue: 4
• Pages: 567-576
• DOI: https://doi.org/10.1002/esp.3871
• Keywords: CFD, Channel vegetation, Terrestrial laser scanning, Drag coefficient.
• Public URL: https://durham-repository.worktribe.com/output/1398003