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Abbotts Hall in Essex is the site of a pioneering managed realignment scheme developed in 2002, and shows how farming and nature conservation can work side by side at the coast.
Abbotts Hall is an area of farmland in Essex, south of Colchester. Located at the centre of a 25km section of coastline between the Blackwater Estuary and the Colne Estuary, it is the site of a pioneering managed realignment scheme developed in 2002.
Owned by the Essex Wildlife Trust, the land at Abbotts Hall is an area of international wildlife importance. The scheme has shown how farming and nature conservation can work side by side at the coast – as well as delivering the important additional benefit of protection from flooding.
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.
Essex's saltmarsh land has been in decline for many decades, long before delivery of the scheme in 2002, but losses accelerated in more recent years due the impacts of coastal squeeze. This created major problems for coastal wildlife that depend on this important habitat. Conservation and restoration of habitat was therefore a primary driver for delivering managed realignment at Abbotts Hall.
The site's existing flood defences were being put under greater strain due to the rising sea levels as a result of climate change and coastal squeeze. A 3.5km sea wall built 300-400 years ago was in place along the southern edge of the land at Abbotts Hall, but its maintenance was becoming prohibitively expensive. A cost-benefit analysis showed that the preferred option was not to maintain the defence any longer.
Of the sites around this part of the Essex coast, Abbotts Hall was chosen partly because of the relief of the shore. The natural gradient of the rising land would open up an optimal area of inter-tidal flood zone to allow regeneration of habitat. Another factor was that funding was available to implement the scheme – from the Essex Wildlife Trust, the World Wildlife Fund (UK) and the English Heritage Lottery Fund.
Stakeholder engagement focused primarily on those most at risk of impact from the scheme, as well as local residents and businesses, and key statutory bodies. The local planning department was engaged throughout development and well in advance of formal planning submissions, at a time when it was not commonplace to do so. This led to a smoother progression through the planning process.
Two stakeholders in particular were concerned about hydrodynamic impacts. The West Mersea fishermen had significant oyster fisheries downstream of the site, which would be depleted if there were any significant changes to the hydrodynamic and sediment flow regime. The RSPB were concerned about erosion and flood risk impacts to their site on the opposite side of the water. Their questions and concerns were addressed through numerical modelling which demonstrated that there would be negligible impact only.
The local community and surrounding parishes were engaged through public meetings and open days, which were also targeted at local landowners who were encouraged to consider managed realignment as an option for the future. The project acts as an excellent showcase demonstrating how managed realignment can take place alongside farming activity without requiring wholesale change.
The Essex Wildlife Trust purchased the site and undertook the scheme in partnership with the Environment Agency and Natural England. Following detailed surveying and modelling carried out in 2000, a plan was established to allow breaches of the existing sea wall – four of them 10m wide and one 100m wide.
In preparation for breaching the sea wall, a number of new features were constructed. Feeder creeks were dug behind the wall to help distribute the incoming tidal seawater and promote formation of new saltmarsh habitat. New spur walls were built at each end of the site to protect neighbouring land, though much of the rest of the site's frontage has no sea defence and the sea is allowed to rise to its natural level.
A new freshwater pond was created to compensate for losses of other freshwater areas that would become saline, providing habitat for protected species such as the great crested newt. Three viewing hides were also built to provide visitor facilities.
The sea wall was breached in four of the strategic locations in 2002, opening up 80 hectares of land as the new flood inundation zone. This previously arable farmland quickly developed into saltmarsh, mudflat and coastal grassland, providing important habitat for several bird species including Brent geese, redshanks, lapwings and the short-eared owl. The restored marshland and the constructed creeks also encourage populations of fish and marine invertebrates, for which the wading birds forage.
The new intertidal inundation zone also forms a natural, sustainable solution to coastal defence, and helps reduce coastal squeeze around the region.
The scheme has proved to be a cost effective and sustainable solution for the needs of the site. It acts as an internationally important demonstration of what can be achieved by thorough planning and execution of coastal defence and managed realignment.
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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