Low-crested coastal defence structures as artificial habitats for marine life: Using ecological criteria in design

Hard structures for protection against erosion of shores are some of the most common human-made constructions in coastal areas. Nevertheless, little is known as to how marine organisms respond to their presence. The composition and distribution of intertidal epibiota at different positions around different types of defence structures (groynes and breakwaters) at three stations along the Emilia Romagna coast (Italy) were analysed. Sampling covered a range of scales: meters (distance among replicate plots), hundreds of meters (distance among replicate areas) and tens of kilometres (distance among stations). The colonisation and dynamics of conspicuous species over 1 year, following maintenance works on two structures, were also quantified. Assemblages on defence structures were characterised by a notably low richness of species, by strong spatial dominance of mussels and green ephemeral algae, and by high rates of colonisation. Abundance of mussels, Enteromorpha intestinalis and filamentous algae differed significantly among nearby areas within stations. Mussels were significantly less abundant along the landward side of breakwaters compared with all other positions on both groynes and breakwaters. Overall, however, fewer differences, than expected, were observed in the distribution of species at different positions around groynes and breakwaters, probably as a consequence of the low complexity of the colonising assemblages. Possible factors explaining the patterns of distribution observed are discussed, including the roles of harvesting of mussels and frequent maintenance works on the structures. The implications of the low richness of species observed in terms of management of defence structures and other human-made constructions are discussed.

http://www.ecology.unibo.it/page/Bacchiocchi%20%26%20Airoldi2003.pdf

Distribution and dynamics of epibiota on hard structures for coastal protection

https://vbn.aau.dk/files/5425961/European_Experience_of_Low_Crested_Structures_for_Coastal_Management

European experience of low crested structures for coastal management

The use of grain size trend analysis in macrotidal areas with breakwaters : Implications of settling velocity and spatial sampling density

The linearized theory of water waves is used to examine the diffraction of an incident wave by a permeable breakwater that consists of a number of distinct elements. Under the assumption that the wavelength is much greater than the thickness, each element is replaced by a thin structure and the permeability is modeled by a suitable boundary condition applied on its surface. The diffracted wave field is obtained by the solution of an integral equation and results are presented to illustrate the effects of permeability and of the characteristics of the incident wave.

/pdf/diffraction-of-water-waves-by-a-segmented-permeable-2a6vkg1n9i.pdf

Diffraction of Water Waves by a Segmented Permeable Breakwater

The use of offshore breakwaters in the UK is relatively uncommon with only 6 schemes constructed to date (early 1998). The use of this technology in the UK is examined via a case study of the S-unit Elmer Beach offshorebreakwater scheme which fronts a shingle beach. Profile line surveying and aerial survey data are used to show the development of the planform during the first 38 months and the development is compared to empirical design guidelines. Also an intensive fieldwork program investigated shingle transport inshore of the breakwaters using sediment tracing techniques. The results show that the scheme exhibited rapid changes to planform during the first 6 months, with shingle salients and sand tombolos developing in the lee of the breakwaters. Changes to planform after this time were less marked, although areas of continued erosion/accretion were identified. The sediment transport experiments identified sediment pathways and rates of transport in the lee of the breakwaters. It is suggested that the breakwaters have reduced shingle transport by a factor of at least 2 compared to similar open beaches.

/pdf/application-of-offshore-breakwaters-to-the-uk-a-case-study-3cfo9vcugd.pdf

N. J. Cooper

Papers

Application of Offshore Breakwaters to the UK: A Case Study at Elmer Beach