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Content archived on 2024-05-21

Environmental design of low crested coastal defence structures (DELOS)


The aim of DELOS is to identify engineering options in the design of coastal defence structures that are functionally and economically feasible and socially and ecologically acceptable. DELOS offers the possibility to achieve this aim through integrated collaboration among engineers who design coastal defence systems, coastal oceanographers, marine ecologists, economists and political institutions who are operationally responsible for coastal protection works. DELOS covers major research in engineering, ecology and socio-economy. It involves 17 partners from 7 European countries. The major anticipated deliverable are validated guidelines for the design of low crested coastal defence structures to be provided to civil engineers and local authorities planning shore defence measures
Project results are summarised in the following. Ecology Ecological effects of LCSs are site-specific reflecting the complexity and variability of natural systems. LCSs always produce an increase in biodiversity and generate inshore sedimentation that negatively affects the landward soft bottom habitat. LCSs design criteria must be addressed to:
- promote the development of salubrious areas in the protected zone by increasing the water flow through the structures;
- reduce to the minimum LCSs length to avoid large-scale effects of habitat loss, fragmentation and community changes;
- increase structure stability, minimise maintenance works and manage human usage, to facilitate settlement/persistence of algae and marine invertebrates and reduce ephemeral green algae;
- avoid situation and scouring that are felt as disturbances for abundance and composition of epibiotic assemblages, for instance by increasing berm width;
- increase armour geometry complexity and heterogeneity that promote settlement of organisms and enhance diversity;
- assure structure submergence in low-tide to avoid consequent exsiccation of colonising organisms.

Defence Value The construction of LCSs for beach protection is ‘justified’ from an economic point of view by the CVM surveys carried out within DELOS. The value of enjoyment of a beach visit is in average 25 € per person per day. Beach erosion produces a loss of value of about 50%; moreover, the 20% of interviewed declared that would have never visited the beach after the foreseen erosion. LCS design criteria shall account for the preferences that people expressed:
- submerged structures for aesthetic reasons;
- groynes for water quality and recreational activities.
A Benefit Transfer Function was prepared with coefficients that should be calibrated on the site under analysis. The engineering results can be summarised by methodology.
- Site-monitoring improved the knowledge of morpho-dynamic evolution in presence of different intervention type. Periodic bathymetry surveys were carried out in selected study sites. Currents at gaps appear to have a strong influence on local scour, LCS stability and swimming safety.
- Laboratory experiments allowed covering the lack of information on wave and current interaction with LCS both in 2D and 3D conditions. Stability, overtopping, filtration, transmission were examined and parameterised after having identified the most relevant process parameters.
- Numerical modelling produced new validated 2D and 3D tools and calibrated existent models. Models are able to accurately predict most important processes as overtopping and transmission. The representation of morpho-dynamic effects at local scale is still uncertain because of scale-effects.

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Participants (22)