Managed realignment at Steart, Somerset

The £21m Steart Coastal Management Project is one of the UK’s largest coastal management schemes. It is an example of taking a “working with nature” approach to addressing the challenge of flood risk from rising sea levels and increased frequency of storms.

The scheme involves returning land on the peninsula to the sea, reducing flood risk and creating important new habitat
The scheme involves returning land on the peninsula to the sea, reducing flood risk and creating important new habitat

The Steart Peninsula is an exposed section of coast in Somerset, south-west England, next to the Severn Estuary. It is home to a number of residents and businesses and a designated conservation area at national and international level, providing valuable habitat to birds, fish and other marine wildlife. The peninsula is vulnerable to flooding from the River Parratt at the point where it meets the sea.

The £21m Steart Coastal Management Project is one of the UK's largest coastal management schemes. It established a new wetland nature reserve through opening up 400ha of land to deliberate flooding. The scheme is an example of taking a "working with nature" approach to addressing the challenge of flood risk from rising sea levels and increased frequency of storms.

What is managed realignment?

Managed realignment is an environmental management approach that involves altering the location of the line of defence, working to provide a more sustainable position from which to manage flood and erosion risks. It can involve advancement (moving forward), set back, or breach of the existing defence line. Most commonly, it involves establishing a new set back line of defence on the coast or within an estuary.

The need for managed realignment is driven by a number of factors, including historic and proposed development, climate change and increasing costs of maintaining fixed linear coastal defences in the dynamic coastal environment. In the UK, much of the coastline is internationally designated for its conservation value. However, as coastlines naturally evolve and as sea levels rise through climate change impacts, coastal habitat is being lost where there is a sea defence in place – a process known as "coastal squeeze".

This creates a driver for managed realignment sites to provide replacement coastal habitat to compensate for losses at locations where the existing defence line must be maintained (or even advanced seawards), such as at ports, urban areas and other high value sites. Managed realignment at low priority coastal frontages can also alleviate the pressure of coastal forces on adjacent/nearby sites of higher value, which reduces the costs associated with maintaining essential coastal defences.

Typically, managed realignment involves breaching or removing the existing coastal defence – this can range from halting current management practices and allowing failure and breach of the defence line to active removal of a defence in whole or in part. New defences are often constructed behind the original line to continue to protect key assets, and because they are usually then less exposed to waves, and in estuaries the water level is also reduced, they can be lower in height and are not as expensive.

In some cases it is possible to make use of existing high ground as the new line of defence; the land between the new and old defence is then opened up to the sea, with the resulting habitat created depending on the level of the ground relative to the tidal sea. The creation of coastal habitat such as saltmarsh also helps to absorb wave energy as it approaches the new line of defence. The result is an effective, sustainable solution to flood and erosion risk at the coast.

Why managed realignment at Steart?

The village of Steart sits on an isolated part of the peninsula, joined to other communities in the south by a single road. The peninsula sits just at the point where the River Parratt flows into the Severn Estuary, putting it at risk of flooding from one of the strongest tidal forces in the world. The threat of flooding has grown in recent years due to rising sea levels and increased frequency of severe storms, as caused by climate change. Maintenance of the existing flood defences on the peninsula was becoming costly and unsustainable, so there was a clear need for a new and sustainable approach to flood protection.

National and European directives dictate that the Environment Agency must offset intertidal habitat losses, as caused by coastal squeeze. Development across the Severn Estuary has caused considerable habitat loss across the region. Proposals for projects such as The Bristol Port Company's development of its Avonmouth container identified Steart as an ideal location for compensatory habitat. The site at Steart is in fact large enough to compensate for 40% of the total losses in the region.

Managed realignment involves taking a working with nature approach to create important new habitat and achieve a sustainable and environmentally beneficial solution to flood risk, so was identified as an ideal solution.

Community Engagement

From the outset, the project team engaged with local stakeholders to involve them in decision-making and alleviate their concerns about the scheme. Consultation exercises with local people as far back as 2002 identified managed realignment as the preferred course of action to alleviate flood risk on the peninsula. When the required funding and the pressing need for habitat creation emerged a few years later, allowing the project to proceed, the local community remained close to the decision making process through further consultation exercises and stakeholder engagement.

Inherent in the design and planning stages was the shaping of a "community vision" for peninsula's marshland through engagement with community groups, technical groups and specialist volunteers. The Wildfowl & Wetland Trust were a key partner from early on in the project and their input helped influence design of the marshland habitats to deliver a community minded wetland nature reserve.

Throughout delivery, the project team offered regular updates to local people. Because of the size of the site, access risks were communicated directly to residents and visitors rather than constructing a perimeter fence. Monthly progress meetings took place to ensure concerns and questions could be addressed.

Delivery & construction

The Environment Agency purchased the land in early 2012. Detailed modelling, assessment and design by CH2M Hill then took place before works began in May 2012. Construction was carried out by Team Van Oord, a joint venture partnership between Van Oord, Kier Group, Mackley Construction and Royal Haskoning DHV.

Construction works included:

  • Excavating a channel and a system of creeks to divert water into and across the new flood inundation zone
  • Creating tidal lagoons as new habitat environment
  • Building flood defence embankments around the perimeter of the inundation zone to protect surrounding land
  • Building extensive paths and walkways for maintenance and visiting
Managed realignment at Steart
Managed realignment at Steart

The final stage was to create the breach in the existing flood defences to allow waters to flow into excavated channel and creeks. This stage was aligned with tide patterns to allow time to remove the existing defence and connect to the main excavated channel.

The project team used environmentally friendly approaches wherever possible during construction. Clearing of the existing habitat took place before works began, for example relocating protected species such as great crested newts to new receptor ponds, and badgers into new man-made setts.

The new flood defences were built using material excavated from the site to minimise requirements for transporting goods and waste. Areas of vegetation were left in place to act as foundations, rather than being stripped away and disposed of.

Completion & Benefits

The scheme was completed in September 2014 when the breach was opened to allow waters to flood into the site.

Although land on the peninsula is effectively returned to the sea, the overall result is reduced risk of flooding to the surrounding community and its transport and energy infrastructure. The newly created marshland within the flood inundation zone absorbs the impacts of tidal floodwater while new flood defence banks around the perimeter provide additional protection.

The project has delivered a range of valuable new wetland habitat including:

  • 183ha of saltmarsh
  • 40ha of intertidal mudflat
  • 69ha of transitional brackish habitat
  • 79ha of coastal grazing marsh
  • 32ha of brackish and saline lagoons
  • 26ha of freshwater lagoon
  • Numerous ponds and ditches

The creation of this habitat delivers significant compensation for losses elsewhere in the Severn Estuary, providing diverse environments for wading birds, plants, amphibians, fish and other marine wildlife. The wetland has particular value as habitat for birdlife, important on an international scale.

The Wildfowl & Wetland Trust now manages the site as a nature reserve and farmland. With visiting facilities and walkway access it also has value as an educational facility.

The finished project has delivered a much sought after legacy for local communities on the peninsula that combines protection from flooding, valuable intertidal habitat for wildlife and a space for public use.

Further Information

Read our case studies on other UK managed realignment schemes:

Read our discussion paper The Role of Coastal Engineers in delivering No Net Loss through Biodiversity Offsetting for further information on offsetting policies and their application to civil engineering in coastal and estuarine areas.

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