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Adaptation option

Raising coastal land (2015)

For centuries, coastal communities have used rocks and soil to raise coastal land as a defence against storms and rising sea levels. Relatively few examples are seen more recently, however (this option does not include landfilling of wetland areas and marine areas below the mean tide level to build new urban or industrial sites, a commonly used technique in modern times with high impacts on coastal ecosystems.)

A historical example of raising coastal land can be seen in the Wadden Sea coast and barrier islands (now Denmark, Germany and Netherlands): here, small settlements were built on small man-made hills, called warften in German and tierpen or wierden in Dutch, to protect against storm surges. The first artificial hills identified date to the Bronze Age and some hills were still used in the 1800s, by which time the construction of dikes had largely replaced this form of coastal protection; many of these mounds remain and some are heritage sites.

In the 1990s, the level of many embankments and streets in Venice (Italy) was raised to strengthen protection against flooding due to high water events and to counter at least partially the effects of sea-level rise and ground subsidence (the latter due in particular to industrial groundwater abstractions, a practice started in the first half of the 20th century and stopped at the end of the 1970s). This work was carried out along with a major programme to maintain and renew drinking water and sewerage conduits and other service infrastructure below the streets, as well as works to dredge sediment accumulated in the city’s canals. Additional sand or other material was laid after the work under the streets, before replacing paving stones. Where possible, embankments and streets were raised up to the designated protection height of 110 cm above the reference sea level (by up to 30cm above the previous pavement level), significantly reducing the number of tides that cover the street. According to Venice Municipality data (updated in 2011) 12% of the city is still located below the safeguard level of 110 cm, including the iconic and low-lying St. Mark’s Square.

A more mundane example is seen in a parking lot exposed to the sea in Penclawdd, Wales (United Kingdom): the lot lies outside the seawall protecting the main settlement, and its level was raised to improve its protection. 

Additional Details
Reference information

Adaptation Details

Category
Grey

Stakeholder participation

If needed, an appropriate assessment under the Habitats Directive (see legal aspects) will require public participation. Moreover, proposals to raise urban land will most likely require public consultation under national and local laws.

Success and Limiting Factors

Success factors:

  • In most cases, low costs relative to other forms of grey infrastructure for coastal defence.

Limiting factors:

  • One risk, seen also in low-lying inland areas, is that bringing in landfill materials can lead to soil compaction and at least partial subsidence (this depends on the local soil conditions, including water content).
  • It can be difficult to ‘raise’ areas with modern urban and industrial areas and infrastructure. This can also be the case for fragile historical areas, such as St. Mark’s Square in Venice: the latter was not included in the street-raising work in Venice; raising the level of the Square, surrounded by heritage buildings, is expected to be far more expensive and difficult.
  • Dikes, seawalls and other coastal protection infrastructure can be built to higher levels and thus offer greater protection.

Costs and Benefits

The costs and benefits depend greatly on the individual location and adaptation needs. In Venice, synergies with other work reduced costs significantly.

Under the EU Habitats Directive (92/43/EEC), an appropriate assessment will be needed if works to raise coastal land affect protected species or natural habitats.

Implementation Time

Variable.

Life Time

Variable.

Reference information

Websites:
Source:
Fact sheet provided by the OURCOAST II Project

Keywords

Coast, grey measure, land, raising

Sectors

Buildings, Coastal areas, Disaster Risk Reduction, Urban

Climate impacts

Flooding, Sea Level Rise, Storms

Governance level

Local (e.g. city or municipal level)

Geographic characterisation

Global

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