Nature-based solutions (NBS) are increasingly popular infrastructure protection options, particularly in coastal engineering. These systems have shown the ability to provide similar coastal protection services to traditional hard schemes while providing other ecological and economic benefits, and a capacity to adapt to changing contexts. One prominent example of coastal NBS are saltmarshes: fields of flexible or semi-flexible vegetation, which have been found to significantly reduce damage to local communities under daily and storm conditions. Scientific study of these complex, multi-faceted structures is growing in volume, but there remain many knowledge gaps in the field.
Numerical modelling is a powerful tool for investigating both large- and small-scale behaviours of saltmarshes. Numerical models provide a controlled, repeatable, and easily variable method for testing how a marsh impacts local hydrodynamic climates and how incident flow or wave conditions affect the behaviour of their constitutive vegetation. Small-scale plant behaviour is the focus of this thesis. Literature on the subject has been chiefly limited to greatly simplified vegetation modelling, reducing plants' behaviour to that of straightforward rigid cylinders. While this can be effective, it requires significant calibration to measured data and may not provide an accurate picture of the intricate flow dynamics surrounding an individual plant, let alone a full marsh system. Recently, numerical models capable of modelling flexible structures have been developed and used by researchers. However, studies applying these tools have focussed on replicating the more significant hydrodynamic effects of marshes, such as mixing or wave attenuation. By doing so, the calibration requirements of the rigid-type models remain, and the way the plants themselves are modelled loses physical meaning beyond their hydrodynamic impacts.
The work presented in this thesis aims to expand on current flexible plant modelling research by evaluating a new numerical modelling tool in the open-source software REEF3D for replicating in situ saltmarsh plant behaviour in terms of drag force and motion response to hydrodynamic forcing. Three experimental programs were designed and conducted in order to thoroughly evaluate both aspects of the model. The first, based on a flume study performed by Paul et al. (2016), tested the drag force response to regular wave action. The second, based on the work of Tschisgale & Fröhlich (2020), further investigated the drag force response using closed- and open-channel flow, as well as solitary waves. The third, based on a flume study performed with live vegetation by Markov et al. (2023), evaluated the accuracy of the motion response to irregular waves. Consistent through all three programs was an overestimation of the examined behaviour and, in the third case, persistent model breakdown. These results demonstrate that, as tested, the evaluated tool is unsuitable for this purpose. It is suggested that this is due to the foundational assumptions of the model, namely that the material of the flexible structure is of a linearly viscoelastic type, whereas a nonlinear elastic material would be more appropriate for this application. These results highlight the difficulty of numerically modelling these systems and the need for further research developing and applying practical modelling tools for marshes.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/44933 |
| Date | 15 May 2023 |
| Creators | Henteleff, Ross |
| Contributors | Nistor, Ioan, Stolle, Jacob |
| Publisher | Université d'Ottawa / University of Ottawa |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Attribution-NoDerivatives 4.0 International, http://creativecommons.org/licenses/by-nd/4.0/ |
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