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Adaptation option

Restoration and management of coastal wetlands (2015)

Coastal wetlands (or tidal marshes) are saltwater and brackish water wetlands located in coastal areas. They provide natural defence against coastal flooding and storm surges by wave energy dissipation and erosion reduction, helping to stabilise shore sediments. In some locations (such as the Schedlt Estuary), coastal wetlands can be used to absorb storm surge waters, attenuating flooding. Coastal wetlands also are important habitats, for example providing a nursery function for fish and shellfish and a variety of services to birdlife and can contribute to water purification. The restoration of coastal wetlands and managed realignment are increasingly considered as measures for adaptation:

  • Restoration of coastal wetlands: wetland restoration aims at re-establishing natural functions of wetlands that have been degraded by natural and human activities. One method is to add sediment to raise land above the water level and allow wetland plants to colonise, or to modify erosion processes that are degrading wetland areas. Alternatively, rewetting of drained coastal wetlands by blocking drains and reducing groundwater extraction is an effective restoration technique for brackish wetlands. A more resource intensive technique is the transplantation of vegetation from healthy marshes or specialised nurseries (e.g. LIFE Barene project).
  • Managed realignment and ‘depolderisation’: setting back the line of hard flood defences to a new line, further inland and/or on rising ground to recreate intertidal habitats between the old and the new defence. The wetland will serve as a buffer zone where storm surges will be attenuated. Depolderisation refers to returning reclaimed land (a “polder” in Dutch) to the sea. Managed realignment can involve deliberate breaching or complete removal of a coastal defence such as a dike, or the relocation of defences further inland. For example, in the Hedwige-Prosperpolder project in the Scheldt Estuary (Belgium and Netherlands), outer dikes are being removed to turn reclaimed land into wetlands, while inland dikes are being strengthened.
Additional Details
Reference information

Adaptation Details

Category
Green

Stakeholder participation

If a project creates significant impacts for a Natura 2000 site, the required ‘appropriate assessment’ may include a public participation process. The restoration of coastal wetlands may be part of the management plan for a Natura 2000 site. Member States may provide for public information and participation processes on these plans. Managed realignment is likely to require consultation with residents living in or near the area to be flooded. Where reclaimed land is returned to wetlands through management realignment, this will affect any residents and economic activities on the site and could lead to opposition (for example, the Hedwige-Prosperpolder project on the Belgium-Netherlands border saw protests by farmers and local residents).

Success and Limiting Factors

Wetland restoration and managed realignment have many advantages compared to other techniques in terms of adaptation to climate change and preservation of coastal ecosystems:

  • Managed realignment and wetland restoration reduce the need for hard coastal defences. Even in combination, these approaches can reduce the need to heighten and broaden dikes, leading to a positive impact on the landscape.
  • A healthy wetland can also able to cope with sea level rise as long as sufficient sediment is available and sea level rise does not exceed local accumulation rates.
  • Managed realignment recreates important intertidal habitats, potentially including those playing a valuable role (nursery, spawning or feeding area) for species of commercial interest. In addition to preserving biodiversity, these new areas can be used for recreation and ecotourism.
  • The restoration and preservation of wetlands marshes reduces eutrophication and can help maintaining freshwater quality also by reducing saltwater intrusion.

The main difficulty in implementing managed realignment involves changing land use: it can result in the relocation of buildings and activities, possibly at high costs (including expropriation), or in the loss of land used for recreation and agriculture. Managed realignment should be carefully planned to minimise the costs of relocation of activities. However, significant realignment projects are carried out on agricultural land as it does not require relocation of infrastructure.

Costs and Benefits

Costs:

  • Managed realignment can significantly reduce the cost of coastal defence and erosion protection measures, notably as less further works on coastal defences such as heightening or broadening will be required. As coastal wetlands reduce the impact of waves against coastal defences, it is also likely that maintenance costs will be lower. However, the relocation of infrastructures or activities that might be required can (partly) offset these benefits.
  • Purchasing the land to be flooded is usually the main cost for managed realignment.
  • Total costs for an integrated project can nonetheless be high. For example, the Kruibeke project in the Scheldt estuary (BE) included modification of outer dikes, the construction of an inner set of dikes, consolidation of land and other activities: total costs have been about 100€ million for the 600 ha. site.
  • For wetland restoration, indirect costs are generally lower, as purchasing land is not necessary. However, restoration is cost-effective only if required sediments are easily available.

Benefits can include: protection against storm surges and erosion, improvements in water quality and increase of biodiversity and habitats.

TEEB has evaluated the monetary value of services of wetlands, notably the services provided by mangroves and tidal marshes (The Economics of Ecosystems and Biodiversity, TEEB, 2013). Although Europe does not have mangroves, these figures are relevant for tidal marshes, which are numerous in Europe. They estimate the value of service provided (water supply, raw materials, food, genetic, medical and ornamental resources) between US$ 44 and 8289 (33 – 6200€)/ha/year, the value of services regulated (air quality, climate, waterflow regulation, erosion prevention, nutrient cycle, water purification etc) to US$ 1914 to 135,361 (1430-101,200€)/ha/year. In particular, the moderation of extreme events is estimated between US$ 4 and US$ 9729 (3-7272€)/ha/year and erosion prevention between US$ 97 and 755 (72-565€)/ha/year. Both are counted among the most important services regulated by tidal marshes. Habitat services are estimated between US$ 27 to 68,795 (20-51400€)/ha/year and cultural services between US$ 10 and 2904/ha/year (2007 values). According to TEEB, coastal wetlands in the USA are estimated to currently provide US$23.2 billion per year in storm protection services alone.

In some cases, it may be possible to recover a share of the costs of interventions by selling land that becomes available when old coastal defences are removed.

Coastal wetland habitats, such as different types of salt marshes, are considered habitats of EU interest under Annex 1 of the EU Habitats Directive, and some of these are priority habitats. The restoration of coastal wetlands may be part of the management plan for a Natura 2000 site, or may create a new Natura 2000 site. However, wetland restoration can raise legal issues under the Habitats and Birds Directives if it changes the type of habitat in a protected area. If a project could have a significant impact on a Natura 2000 area, it should undergo an ‘appropriate assessment of its implications for the site’ to determine whether it will adversely affect the integrity of the site. Restoration actions can also be required under Natura 2000 as compensation for other interventions. The restoration of coastal wetlands may be supported by habitat compensation requirements under the EU Habitats Directive: for example, in the Scheldt Estuary (Belgium), habitats destroyed by port expansion were compensated via the restoration of wetlands that provided storm surge protection.

Implementation Time

Implementation time will vary greatly based on the extent of the site and the specific conditions. Implementation time can involve both works as well as also related communication and legal actions, for example expropriating land.

Life Time

The lifetime of coastal wetlands will depend on local conditions, in particular erosion and sedimentation processes. Regular maintenance may be required to maintain wetland conditions.

Reference information

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

Keywords

Green measure, management, realignment, restoration, wetlands

Sectors

Biodiversity, Coastal areas, Disaster Risk Reduction

Climate impacts

Droughts, Flooding, Sea Level Rise, Storms

Governance level

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

Geographic characterisation

Global

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