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Case study

Managed realignment at Medmerry, Sussex

28 September 2015
Managed realignment at Medmerry, Sussex
The managed realignment project at Medmerry is the biggest on the open-coast in Europe (Image: Environment Agency)

Medmerry is a nature reserve on the coast of Sussex, England. This stretch of shoreline is one of the south coast’s most vulnerable areas to flooding from the sea.

The managed realignment project at Medmerry was completed in 2013 at a cost of £28m. It is the largest open-coast scheme in Europe and is one of the most sustainable projects the Environment Agency has ever delivered. It provides 1000 times better flood protection than the previous defence system and has delivered extensive new intertidal and freshwater habitat, compensating for losses elsewhere in the region caused by coastal squeeze.

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 simply 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 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 Medmerry?

Coastal flooding has long been a problem at Medmerry and a serious risk to the nearby towns of Selsey and Pagham. The previously existing defence, a 3km shingle bank, was subject to regular breach, mostly recently in 2008 when over £5m of damage was caused.

Aerial view of Medmerry including labels of key features
View of Medmerry showing the location of Selsey and features in the surrounding area (Image: Environment Agency)

As well as offering a deficient level of protection, the shingle bank’s maintenance – largely done through constant re-profiling throughout the winter, using bulldozers – had become costly and unsustainable. The Environment Agency was spending up to £300,000 each year for its upkeep.

An issue in the wider region of The Solent has been the loss of environmentally important coastal habitat, as a result of coastal squeeze. The impacts of development and flood defence infrastructure around the large, urbanised areas of Southampton and Portsmouth have caused local sea levels to rise and wetland and intertidal habitats to be lost to the sea. The Medmerry scheme is the first site in the region to offer large-scale provision of compensatory habitat.

Community Engagement

As with all managed realignment projects, an important element is to engage with all local stakeholders and involve them in the planning and decision-making processes. The deliberate return of land to the sea as part of a realignment project can understandably elicit fear in local people. This was true at Medmerry where residents doubted the scheme would work and thought that it would damage the local economy.

The project team devised an engagement strategy largely involving the Medmerry Stakeholder Group, with representation from local authorities, parishes, businesses and other local people. The Group was involved in decision-making, agreeing project objectives and messages, as well as designing access routes, viewpoints and car parking facilities, all of which help form the legacy of the project as a nature reserve and visitor attraction.

Other elements of the strategy included workshops, public exhibitions, guided walks and a dedicated public relations officer, all intended to keep the local community fully involved with the project.

Delivery & Construction

The project was led by the Environment Agency in partnership with the RSPB, who now manage the completed nature reserve and its new habitat. The principal contractor was Team Van Oord and Jacobs carried out design. Construction took 62 weeks.

Fundamental to the scheme was the creation of a breach in the existing shingle bank to allow the sea to reclaim an area of land close to the shore. New floodbanks were built around the perimeter of this new flood inundation zone, and while they sit much closer to the surrounding communities than the previous shingle bank, the result is significantly increased flood protection. The inundation zone absorbs the energy and impact of the waves while also offering important new habitat.

The features of the site include:

  • A 110m wide breach of the existing shingle bank, allowing tidal water to flow in and create 183ha of new intertidal habitat area
  • 7km of newly constructed floodbank stretching almost 2km inland. Around 400,000m3 of earth was taken from within the site to build the banks, reducing the environmental footprint of the project (by avoiding lorry transport) and improving delivery time by 2-3 years
  • A number of pits created from the earth excavation, forming features of the new intertidal habitat area
  • A 10km long drainage ditch system, four eel and fish friendly freshwater outfall structures and a number of ponds, all of which provide habitat for aquatic invertebrates and water voles
  • Two rock armour revetments situated at the east and west boundaries of the scheme, integrated with the remaining shingle bank at the seafront
  • A 1.8km diversion channel alleviating flood risk in the nearby Earnley catchment
  • Maintenance and public access tracks, car parking facilities and viewpoints

The project team adopted sustainable and environmentally friendly approaches wherever possible throughout construction, e.g. by using 3D modelling and GPS technology to optimise excavation and use of construction materials. Much of the rock used was delivered directly to the site by sea, reducing impact on local roads, and access tracks were built from recycled materials. Ground nesting birds were protected from construction impacts by using an innovative cropping regime devised by the RSPB and local farmers. The regime was so successful that no construction phases were delayed because of nesting birds.

Heavy rain during the very wet summer of 2012 caused delays when the construction site became waterlogged. The project team used this period to refine design plans and ensure that the remainder of the project was completed as cost effectively as possible.

Timelapse footage of the breach being made in the shingle bank, allowing tidal waters to flow into the site

Completion & Benefits

The scheme was completed in late 2013 and immediately showed its worth by successfully protecting local communities from flooding during storms that winter. A total of 348 properties, plus sewage works, caravan parks and Selsey's main road route are now protected to a standard of 1 in 100 years (previously just 1 in 1 year).

The site contains 300ha of habitat of principle importance under the UK Biodiversity Action Plan, including mudflats, reed beds, saline lagoons and grassland. This includes 183ha of newly created intertidal habitat important to wildlife on an international level, and crucial in compensating for losses due to development around The Solent, allowing the region to meet its European directive targets. Birds and other new wildlife began to appear at the site long before completion.

Around £90m of direct economic benefit is expected from the scheme. Maintenance costs are now far less than for the old shingle bank. The local economy has received a boost from an increase in green tourism and the caravan parks have been able to extend their season, generating income and jobs.

Further Information

Read our case studies on other UK managed realignment schemes:

RSPB’s Adrian Thomas presents a guide to the Medmerry managed realignment scheme
  • Ben McAlinden, manager (international partnerships) at Royal Academy of Engineering