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Adaptation option

Storm surge gates / flood barriers (2015)

Storm surge gates / flood barriers are fixed installations that allow water to pass in normal conditions and have gates or bulkheads that can be closed against storm surges or spring tides to prevent flooding. They can close the sea mouth of a river or waterway. These barriers can be major infrastructure systems involving significant costs for construction and are often linked with other flood protection measures, such dikes, seawalls and beach nourishment. Storm surge barriers are normally used to protect urban settlements and infrastructure heavily affected by storm surges and sea flooding. Their number in Europe is therefore rather limited. Due to their expense and potential impacts, storm surge gates / flood barriers are relatively rare. They are built to protect urban areas and infrastructure where storm surges and sea flooding could have major impacts. For this reason, this fact sheet focuses on three of the largest barriers in place or in construction in Europe:

  • The Thames Barrier, London, can close off the Thames River just east of the City of London, at a point where the river is about 520 metres wide.
  • The Maeslantkering gate, on the Nieuwe Waterweg between Rotterdam to the North Sea, closes a shipping canal whose width is 360 meters (the gate itself consists of 2 wings, 210 m wide and 22 m high each).
  • The Venice barriers (also called the ‘Mose’ system) are being built across the three outlets of the Lagoon of Venice to the Adriatic Sea. The total span covered is about 1.6 km. (in construction).

Other examples include the IJssel Barrier as well as other projects in the Netherlands and a storm surge barrier for St. Petersburg.

Additional Details
Reference information

Adaptation Details

Category
Grey

Stakeholder participation

Proposals for storm surge barriers are likely to require stakeholder and public participation, including in SEA and EIA procedures as well as under the UNECE Aarhus Convention (see below).

Success and Limiting Factors

Effectiveness:

  • Existing gates barriers have provided effective against storm surges.
  • The Thames Barrier has been closed over 100 times without problem since it started operation in 1982.
  • Except for routine test closing once a year, Maeslantkering was closed only once (in 2007) for a high water level exceeding the assumed safety threshold.
  • In some cases, storm surge gates / flood barriers could be used to regulate the seawater penetration into freshwater areas and the water level, thus also providing eco-system services.

Limiting factors:

  • One important issue is the time needed to close the barriers: for existing barriers, this takes at least an hour. The existing barriers are linked to effective meteorological forecasting systems that predict storm and tidal surges, so the time required is more than sufficient for protection. For the Thames Barrier, the whole system can be closed in about 1 hour, though closing typically is done more slowly. The Maeslantkering takes about half an hour to close, but four hours are needed prior to closure so harbour activities can be brought to a standstill. As a result, effective systems are needed to predict storm and tidal surges.
  • A second issue is the risk of technical failure (e.g. a barrier not closing properly). This has not been a problem for the existing barriers, which are tested regularly. For the Maeslantkering, 2006 newspaper reports challenged the official estimate of risk of failure (gates not closing properly), which was estimated at 1:1000, claiming on the basis of a confidential report that the actual risk was higher. This issue was investigated and subsequently technical modifications were taken.
  • A third issue is the extent to which barriers will remain viable in the face of future climate change and sea-level rise. In the case of the Thames Barrier, the installation was built with a foreseen lifetime of about 50 years, to 2030. Current sea-level rise is less than the projection used in design and the Barrier is not estimated to be in use to 2070. The Environment Agency has looked at longer term options, including the construction of a larger barrier further seaward. The long-term viability of the system in Venice has been a source of controversy. In 2002, a scientist at the French National Research Council (CNRS) asked in a scientific article whether the MoSE project for Venice was ‘obsolete’ in the face of future climate change. Project scientists and engineers responded, maintaining that the system would be effective in the face of sea-level rise.
  • A fourth issue is their environmental impacts (discussed under costs and benefits).
  • Finally, a key limiting factor is the high cost of these systems. In 1977, the Sigma Plan to protect Belgian areas of the Scheldt Estuary included a barrier; however, cost was a key factor in delaying preparation of this project. In 2005, the Sigma Plan was revised and the proposed storm surge gate / flood barrier was postponed indefinitely: the revised plan focuses instead on strengthening dikes together with the restoration of coastal wetlands, which will attenuate storm surges, as a more cost-effective and affordable approach to flood risk management and adaptation to climate change, as well as one with lower environmental impacts.

Costs and Benefits

Overview of benefits:

  • Storm surge gates / flood barriers provide protection for settlements and infrastructure against seaward storm surges.
  • This type of infrastructure allows continued passage for shipping, fisheries and aquatic species more generally compared to fixed gates, as storm surge gates / flood barriers are only closed when necessary.

Direct Costs:

  • Construction of the Thames Barrier cost GBP 535 million in 1982 (about GBP 1.7 billion or EUR 2.5 billion in 2007), according to the Environment Agency. Operational costs are about GBP 8 million a year (about EUR 9.5 million in 2013 prices).
  • The Maeslantkering cost about EUR 450 million to build (1991-1997; equivalent to approximately EUR 630 million in 2013 prices).
  • Building the Venice system (including three mobile barriers at the three lagoon inlets) will cost EUR 5.49 billion, according to official 2013 estimates.

Other costs:

  • As major infrastructure projects, tidal barriers can affect the ecosystems where they are built. In 1998, a national EIA opinion on the Venice barriers gave a negative opinion, highlighting their impact on the Lagoon’s sediment balance and the risk of accelerated erosion of its salt marshes and other ecosystems. Following a lower court judgement on procedural issues, this technical opinion had no legal standing; three subsequent and separate EIAs were carried out at regional level for each of the three barriers and did not address this question.
  • The construction phase in particular may result in ecosystem damage. Following information provided by local NGOs, the European Commission questioned Italy on the impact of the MoSE on Natura 2000 sites on Venice’s outer barrier islands; in a resulting agreement, compensatory measures, including the reconstruction of lagoon features and habitats, has been put in place.

The EU Floods Directive (2007/60/EC) provides a legal framework for flood actions and defence (the three major systems used as examples here were all designed and put in place before the conception of the Floods Directive). As major infrastructure systems, storm surge gates / flood barriers are likely to be part of a flood protection plan, which undergo a strategic environmental assessment (SEA), as per Directive 2001/42/EC (for example, the Maeslantkering is one part of an extensive network of dikes, dams, sluices and levees that makes up the system of protection against flood in the Rhine Delta). As coastal works, storm surge gates / flood barriers fall into Annex II of the EIA Directive (codified as Directive 2011/92/EU): Member States decide whether projects in Annex II should undergo an EIA procedure, either on a case-by-case basis or in terms of thresholds and criteria. As measures that affect the environment, proposals for storm surge gates / flood barriers are likely to require public information and participation under the UNECE Aarhus Convention.

Implementation Time

More than 15 years.

Life Time

More than 25 years.

Reference information

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

Keywords

Barrier, coast, gates, storm surge

Sectors

Coastal areas, Disaster Risk Reduction

Climate impacts

Flooding, Sea Level Rise, Storms

Governance level

Local (e.g. city or municipal level)
Sub National Regions

Geographic characterisation

Global

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