3.1. PROTECTION OF LAND AND INFRASTRUCTURE BY PREVENTION OR REDUCTION OF COASTAL EROSION

(Moschella & Hawkins, MBA)

Sea level rise, due to global warming, subsidence processes, increased storminess and tidal surges, expose several European coastlines to serious erosion and flooding events. In highly developed coastal areas, erosion and flooding cause conspicuous socio-economic losses in terms of damages to houses, infrastructures such as roads and railways, industries and farmland. The coastal protection provided by LCSs has positive effects on coastal economies.

These are:

Coastal defences including LCSs must be constructed with due regard to sustainable management of habitats, species and ecosystems and their living natural resource (including goods and services) observing European Directives on habitats, birds, and water plus comply to any national or regional environmental legislation.

An example comes from the Elmer Defence scheme (West Sussex, England), built to protect a low-lying residential area from flooding as a result of severe storms associated with spring tides. Since the construction of the breakwaters in 1993, no flooding events were recorded in that area, causing a significant increase in the property values and a decrease in home insurance premium.

3.2. IMPROVEMENT OF RECREATIONAL CONDITIONS

(Moschella, MBA; Airoldi, FF; Thompson & Hawkins, MBA)

LCSs can stabilize beaches or create wider beaches, improve conditions for swimming as well as beach quality with respect to amenity-friendly beach material such as fine sand. Such development should also observe relevant environmental legislation, guidance and emerging best practice in order to ensure sustainable usage of the coastal zone.

LCSs have significant influence on the recreational conditions for beach users. Some influences are regarded as positive, while others are considered as negative. The influence is either direct due to the physical presence of the structure in the nearshore zone, or indirect due to the consequent effects on the local hydro-morphodynamics (eg. rip currents).

Sea conditions behind LCSs are generally calmer than on open beaches and this can improve bathing conditions, especially for children. The improved safety of bathing and swimming in a calm sheltered zone (probably excluding for boat traffic) is a very positive effect since this is the most common recreational activity taking place in the nearshore area.

However the possible formation of strong rip currents at gaps and/or ends of the LCS shore protection system during rough seas may endanger the safety of bathing.

The presence of organisms that grow on the structures or colonise the sheltered habitats behind LCSs can be a nuisance for beach tourism, leading to expensive beach cleaning or removal of the organisms. Examples of these negative effects on the recreational value of the beach come from the Italian shores of the North Adriatic Sea, where the ephemeral green algae that extensively colonise LCSs (also favoured by local eutrophic conditions) are torn off the structures and washed up the shore, where they decay. In the UK, large amounts of drift algae are trapped on the landward side of the structures and eventually decompose leading to unpleasant smells due to formation of anoxic conditions and increase in number of flies. Further, periods with calm weather conditions may lead to stagnant water and degradation of bathing water quality.

Boating with various craft and surfing may be negatively affected by the presence of the LCS if the crest elevation is not clearly visible, due to the risk of collision. Even more dangerous could be diving into the sea from a boat and hitting on the hard structure.

Conversely, activities like snorkelling or sport fishing can be positively enhanced if the structure provides a new attractive habitat for marine life. If the structure is emergent it favours access for fishermen.

3.3. PROTECT AND MINIMISE IMPACTS ON CULTURAL AND NATURAL HERITAGE OF THE COASTLINE

(Moschella, MBA; Airoldi, FF; Gacia, CSIC; Thompson & Hawkins, MBA)

Coastal erosion and flooding also threaten coastal areas of high ecological value such as intertidal and mud flats, shingle ridges, sand dunes, wetlands, salt marshes, coastal lagoons, maritime cliff grasslands and soft cliffs. These natural habitats are subject to Community interest and many are designated as Special Areas of Conservation (Habitat Directive 92/43/ EEC). One of the objectives of the Habitat Directive and the Water Framework Directive is to promote and maintain diversity of natural habitats and their ecosystems and where necessary human intervention can be required to achieve these objectives. Low crested structures can therefore contribute to the protection and maintenance of these coastal habitats providing the following effects:

In addition, special features of natural heritage importance (e.g., saline lagoons, saltmarshes, vegetated shingle banks and sand dunes) or special sectors of interest (bird reserves) may be threatened by coastal erosion. Therefore circumstances may occur where a coastal defence structure is proposed to expressly protect endangered habitats or species. For example, in the coastal area between Happisburgh and Winterton-on-sea in Norfolk (East Anglia, UK), a system of LCS and a seawall were built to protect The Broads wetlands.

In Tuscany sea defence structures were built to protect the maritime pine tree forest in the national park of San Rossore endangered by coastal erosion. Sometimes habitats or species protected by conservation legislation such as the vegetated shingles (habitat listed on Annex 1 of the EC Habitats Directive) can indirectly benefit from coastal defence schemes that were built with the only purpose of protecting properties. For example, the Elmer defence schemes in West Sussex (South of England) also protects the vegetated shingle ridge which host species of special national conservation interest such as little robin Geranium purpureum, a rare plant in West Sussex, the toadflax brocade moth Calophasia lunula, a Biodiversity Action Plan species and many birds which nest in this zone. Elmer defence scheme has been designated as an SSSI (Site of Special Scientific Interest). In Poole Bay (south of England), the recently built rock groyne system not only protects residential properties and the beach from erosion but also helps restoration of native vegetated sand dunes. If protected, these will in turn provide additional natural protection against erosion.

LCSs can be used to protect areas of cultural heritage value such as archaeological and historic sites, monuments, churches and buildings threatened by coastal erosion. Non-visible LCSs are probably preferable; if necessary combined with a revetment or a seawall to strengthen the shore. For example, on the Adriatic coast, along the promontory of Conero, a system consisting of LCS and rocks were deployed to protect historic buildings from erosion.

3.4. ENHANCEMENT OF NATURAL LIVING RESOURCES FOR FOOD AND RECREATION

(Moschella, MBA; Airoldi & Bulleri, FF; Thompson & Hawkins, MBA)

Whilst the primary objectives of LCS are to modify hydrodynamic and sedimentary regimes to protect sensitive areas or improve recreational conditions, any LCS that is put in the sea will also become colonised by marine organisms. Such colonisation must be recognised as an important change to the identity and/or abundance of habitats and hence species in coastal areas, and cannot be avoided. It is, however, possible, within the limits set by the primary necessity of engineering performance of LCS, to modify selected design features to enhance growth of selected organisms. Thus features of LCS design can sometimes be used to maximise desired secondary management end points (where perception of desirability or undesirability are intended as value judgement related to societal goals and expectations). Examples of such secondary management end points include: