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Computational Modelling of the Coastal Protection Function of Salt Marshes with Flexible Vegetation Cover / THOMAS VEELEN
Swansea University Author: THOMAS VEELEN
PDF | E-Thesis – open access
Copyright: The author, Thomas J. van Veelen, 2020.Download (82.67MB)
DOI (Published version): 10.23889/SUthesis.59834
Salt marshes are intertidal coastal wetlands that are typically found in sheltered locations such as estuaries. They exhibit a diverse vegetation cover with ﬂexible grasses and rigid shrubs. This vegetation provides coastal protection by attenuat-ing currents and waves. Unlike traditional hard defen...
|Supervisor:||Karunarathna, Harshinie ; Reeve, Dominic E.|
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Salt marshes are intertidal coastal wetlands that are typically found in sheltered locations such as estuaries. They exhibit a diverse vegetation cover with ﬂexible grasses and rigid shrubs. This vegetation provides coastal protection by attenuat-ing currents and waves. Unlike traditional hard defences, they oﬀer co-beneﬁts by stabilising shorelines and enhancing natural habitats. However, it has remained unclear how salt marshes with a ﬂexible vegetation cover contribute to coastal protection under storms with surge and wave components.In this thesis, I have developed a new coupled current-wave-vegetation model which includes the eﬀect of vegetation ﬂexibility on wave attenuation. The wave-vegetation model builds on novel laboratory experiments using artiﬁcial vegeta-tion in the Swansea University Wave Flume, where wave damping, water velocity ﬁelds, and plant motion were measured simultaneously for the ﬁrst time. A new work factor is introduced to explicitly account for vegetation ﬂexibility in compu-tational models. Furthermore, a momentum sink term parameterisation is found to best resemble current-vegetation interactions. The advanced coupled model is successfully applied to simulate ﬂood risk in the Taf Estuary under six contrast-ing vegetation scenarios.My results highlight how the vegetation cover aﬀects the coastal protection pro-vided by salt marshes. All modelled vegetation species constrain ﬂood currents to the main estuary channel and damp incoming waves. Although ﬂexible grasses are 50% less eﬀective in wave damping than rigid shrubs in the Taf Estuary. The wave conditions, wind conditions and local topography further aﬀect the protec-tion provided. Additionally, rigid species can amplify orbital velocities above the canopy by inducing wave-averaged currents, but ﬂexible species do not.It is recommended that the biomechanical properties of vegetation, including the ﬂexibility, are included when modelling the coastal protection by salt marshes. My new computational modelling framework provides evidence to support the continuing uptake of salt marshes as sustainable coastal defences.
ORCiD identifier: https://orcid.org/0000-0002-7061-8012
Salt Marshes, Computational Modelling, Coastal Vegetation, Flood Risk, Laboratory Experiments
Faculty of Science and Engineering