Intertidal structures: coastal engineering for sustainability and biodiversity

Abstract

Coastal defence structures (CDS) are propagating globally. Growing environmental concerns are driving modifications to traditional coastal engineering methods through environmentally-enhancing designs which promote biodiversity and socio-economic benefits. Despite a number of tested ecologically-sensitive designs, there is still a gap between research concepts and practical implementations to coastal engineering designs. I investigated design methods for CDS to improve their role as surrogate habitats for coastal assemblages, thus creating more sustainable coastal protection for engineering and maintaining biodiversity. I focused on four key knowledge gaps to identify novel, sustainable and, more importantly, practical methods of designing ecologically sensitive coastal protection: (1) the extent of biological and topographic dissimilarity between natural and artificial shores at different scale levels; (2) the use of porous CDS as multifunctional designs for coastal engineering; (3) the use of 3D printing in coastal engineering to design complexity into defence structures; and finally, (4) the impacts of intertidal and subtidal species and their role as natural coastal protection methods. To address the first knowledge gap, I surveyed seven natural and artificial shores on the South coast, UK, comparing the biological communities and topographic complexity on each shore at three different scale levels. I found that species characteristic of natural and artificial shores differ, and natural shores tend to be characterised by species such as fucoids and some foliose red algae, while artificial shores are largely characterised by invertebrate species. For the second knowledge gap, I surveyed a porous CDS during a groyne reduction process, and compared the coastal assemblages colonising the internal and external habitats of the structure. The results showed significant differences in species richness and diversity on internal habitats to external. For the third knowledge gap, I explored the use of 3D printing to design-in complex habitat features to enhance biodiversity on artificial structures. This study showed colonisation of some coastal species, but more importantly identified key limitations when using this novel material in coastal engineering, which are fundamental at this preliminary stage. Finally, to address the last knowledge gap, I investigated the impact of eight intertidal and subtidal mimic species on wave velocity. The results showed significant reductions in wave velocity due to the presence of all mimics, particularly longer and more flexible species. Additionally, I compared the impact of five different designed tile units on wave velocity. I found significant differences in wave velocity reduction among all tile designs, particularly between units of varying orientations. To conclude my thesis, I summarise the key findings and evaluate these outcomes in the context of their application to sustainable coastal engineering. I then outline challenges and practical methods for designing sustainable and multifunctional coastal defence schemes.

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ORCID for Patrick Osborne: orcid.org/0000-0001-8919-5710

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