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Realignment of the coastline at Abereiddy was identified as the best approach to addressing the failing sea wall and its impacts on the beach. The underlying thinking of the project was “to accept a move away from an ever increasing need for management”.
Abereiddy is a small village in Pembrokeshire, on the west coast of Wales. It has a number of cottages situated behind a small pocket beach, which is a busy tourist and recreation spot in summer months.
Sea defences were built at the beach in the 1960s, but deteriorated significantly over the following decades. Studies showed that they were also having an adverse impact on the beach in front. Pembrokeshire County Council’s Shoreline Management Plan identified that the best approach would be to allow natural realignment of the coast.
The works involved progressive removal of the existing defences, allowing nature to take its course. As a realignment project, Abereiddy is very different to many other examples, with the underlying thinking being “to accept a move away from an ever increasing need for management”.
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.
Abereiddy beach is located within a steep sided and infilled glacial outwash valley. It is composed of hard metamorphic Ordovician slate gravel and rests on a gently sloping lower beach of finer material. A car park – important for local tourism – separates the beach from the cottages, which sit on slightly raised ground beyond the southern section of the site.
During the 1960s there was concern over the continuing erosion of the upper beach and the car park. The solution then was to construct a relatively low cost defence over the whole frontage, using old railway sleepers and bullhead rails. Over time, rocks were placed behind the structure for added reinforcement.
The performance of the structures was measured by Pembrokeshire County Council’s defence monitoring programme. Findings showed that the defences were having an increasingly deleterious impact on the beach in front, which was in turn causing increased pressure on the defence.
Following through on the recommendations of the Shoreline Management Plan, it was recognised that the time had come to allow natural realignment of the coast. This was brought to a head as the old defence deteriorated and became a safety hazard.
Historically, the area was used as part of the depot associated with quarrying of slate from the now impressive Blue Lagoon; now an important tourism feature of the Pembrokeshire coast. During its industrial past, significant quantities of quarry waste were placed on the beach, advancing its position.
Analysis of historic maps and analysis of other similar beaches nearby, coupled with a conservation of beach volume approach, demonstrated how the beach might readjust if the defences were removed. This gave confidence that realignment would not substantially increase the risk to properties in the area. There would be significant impact on the car parking area but, balancing this, it would also provide a far more natural beach and improve access between the hinterland and the sea.
Throughout the development and delivery of the project, there have been concerns and areas of uncertainty. Fundamentally, it is very difficult to model exactly how an area of coastline will respond and change. Examples were draw form similar beaches in the area to demonstrate how Abereiddy beach might develop.
The local authority understood the need to engage local residents and regulators and involve them in decision-making. Accepting the uncertainty has been crucial in securing the backing of all local stakeholders. The process was helped by the fact that people can see how the beach could in fact be allowed to change and that the change would be in a manner very similar to that predicted by the studies.
Various options were considered, including ideas for the reuse of the rock to assist in reshaping the beach plan shape. While the examination of such ideas allowed and encouraged discussion of how the bay would develop, in the final analysis it was agreed that realignment would be allowed to develop purely by progressive removal of the existing defence.
Abereiddy is a very different form of realignment compared to many more obvious examples – in scale, simplicity and in some ways in purpose – “to accept a move away from an ever increasing need for management”.
Read our case studies on other UK managed realignment schemes:
Read our paper The Role of Coastal Engineers in delivering No Net Loss through Biodiversity Offsetting for further information on offsetting policies and their application to coastal and estuarine areas.
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