On the hydrodynamics of flexible vegetation canopies

Houseago, Robert

Abstract

Aquatic vegetation canopies, including seagrasses, provide a host of ecosystem services within coastal environments. The environmental, social, and economic benefits are primarily controlled by the detailed interactions between hydrodynamics and canopy properties, which governs energy cascades and long-term coastal morphodynamics. This research focuses on the evaluation of the common seagrass species, Zostera marina, which is present along coastlines globally. Although previous research has recognised canopy properties as key drivers in the modulation of flow and turbulence processes, the quantified influence of canopy flexural rigidity remains limited. This thesis addresses how the variation in flexural rigidity results in feedbacks on local hydrodynamics. A series of laboratory-based experiments systematically investigate the influence of varying canopy blade flexural rigidity on flow and turbulence processes. High spatio-temporal resolution velocity datasets are acquired through the implementation of novel methodological approaches, including refractive-index-matching techniques allowing non-intrusive laser-based techniques to obtain detailed measurements within canopy for the first time. Coupled with the bespoke design of geometrically and dynamically scaled flexible surrogate seagrass vegetation, these measurements allow for a range of novel quantifications of the fluid-structure interactions. Including evaluation and visualisation of coherent vortices within the canopy and the canopy mixing layer, in unprecedented detail. The influence of varying canopy flexibility is evaluated in both unidirectional and oscillatory flows driven by propagating surface waves. Overall, this allows enhanced quantification of mean currents and turbulence processes within and above flexible canopies, energy cascades, wave attenuation capacity, and canopy bulk drag. The results detail how the influence of canopy reconfiguration and canopy motion results in distinct hydrodynamics, and is recognised as a primary underlying component in the modulation of flexible canopy turbulence in both steady and wave driven flows. The results enhance our knowledge on flexible canopy hydrodynamics and this new understanding is contextualised in terms of biological, sedimentological, and socio-environmental implications.

Citation

Houseago, R. (2021). On the hydrodynamics of flexible vegetation canopies. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4200892

• Thesis Type: Thesis
• Deposit Date: Feb 15, 2023
• Publicly Available Date: Feb 15, 2023
• Keywords: Geography, Geology and Environment
• Public URL: https://hull-repository.worktribe.com/output/4200892
• Award Date: 2021-01