Monday, 10 March 2008

Coastal Defences

The coastal zone is a dynamic area of natural change and of increasing human use. It occupies less than 15% of the earth's land surface; yet accommodates more than 50% of the worlds population (it is estimated that 3.1 billion people live within 200 kilometres from the sea). Coastal zones contain rich resources to produce goods and services and are home to most commercial and industrial activities.
In the European Union, almost half of the population now lives within 50 kilometres of the sea and coastal zone resources produce much of the Union’s economic wealth. The fishing, shipping and tourism industries all compete for vital space along Europe’s estimated 89 000 kilometres of coastline, and coastal zones contain some of Europe’s most fragile and valuable natural habitats.

Coastal protection is already extremely important where there are extensive low-lying areas that require protection (e.g.Venice, New Orleans, and the Netherlands).

Protection against the sea level rise in the 21st century will be especially important, as it is currently accelerating. This will be a challenge to coastal management, since seawalls and breakwaters are generally expensive to construct, and the costs to build protection in the face of sea-level rise would be enormous.

Strategies for coastal defense

1. Do nothing, adding no protection and leading to eventual abandonment.
2. Managed retreat or realignment, which plans for retreat and adopts engineering solutions that recognise natural processes of adjustment, and identifying a new line of defence.
3. Hold the line with shoreline protection, whereby sea defences are constructed around the coastlines.
4. Move seawards, by constructing new defenses to seaward of the original ones.
5. Limited intervention by which adjustments are made to be able to cope with inundation such as creating salt marsh areas, raising coastal land and building vertically.

The decision to choose a strategy is site-specific, depending on pattern of relative sea-level change, geomorphological setting, sediment availability and erosion, as well a series of social, economic and political factors.

Alternatively, integrated coastal zone management approaches may be used to prevent development in erosion- or flood-prone areas to begin with. Growth management can be a challenge for coastal local authorities who often struggle to provide the infrastructure required by new residents

Groynes, seawalls, revetments, rock armour, gabions, offshore breakwaters, cliff stabilisation, river entrance training walls and floodgates are all examples of hard coastal defences. Soft defences include beach nourishment, sand dune stabilisation and beach drainage schemes.

The Centre for Coastal Processes, Engineering and Management (part of the University of Southampton) states that "a full 15 000 km of UK coastline is presently under threat from erosion; a further 10 000 hectares of land is at risk from flooding and 13 000 hectares is predicted to disappear in the next 20 years. The responsible, informed protection and management of our coastline is vital: 50% of the world's ecosystems are found in the coastal zone. Despite the need for protection and good husbandry, virtually all UK exports/imports pass through ports on estuaries, contributing a massive £50 billion per year to the economy (5% of the entire UK GDP). The way we treat the coastline is therefore of fundamental importance to the future of the UK."

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