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Coastlines are evolving as sea level rises; but what’s our strategy?

Written by Dr Sophie Ward and Dr Martin Austin, Bangor University, UK


This seastory is adapted from an article originally written by the authors for The Conversation


The village of Fairbourne, built on low-lying land in Cardigan Bay, Wales
The village of Fairbourne, built on low-lying land in Cardigan Bay, Wales © David Roberts

The impact of sea-level rise on the coastline can be profound. A natural shoreline may have the chance to respond to rising seas and coastal erosion; given enough time, its flora and fauna may even have a chance to adapt. However, a coastal area that has been heavily developed will respond differently to sea-level rise – sometimes with catastrophic impacts on nearby homes, businesses, and communities.


In the UK, coastal defence planning and management is orchestrated through Shoreline Management Plans [1]. These plans provide a framework to assess potential risks and outline the range of options for coastal defence management. Approaches range from the construction of new defences in the ‘Advance the Line’ method, maintaining the coastline with ‘Hold the Line’, permitting some natural erosion processes in ‘Managed Realignment’, and adopting a hands-off approach known as ‘No Active Intervention’, where natural processes are allowed to shape the coastline. The management option selected for a specific stretch of coastline will reflect the available evidence and will consider key factors spanning from climate change and coastal processes to flood risk, social dynamics, and economic assessment.


The canary in the coal mine?


Nestled along the west coast of Wales, the village of Fairbourne found itself in the spotlight owing to being one of the first villages assigned the ‘No Active Intervention’ policy. This led the British Media to dub the inhabitants of this stretch of coastline in Cardigan Bay “the UK’s first climate change refugees”. The fate of the village hangs in the balance with an initial phase of Managed Realignment planned from 2025 to 2055, but with the potential for Fairbourne to be decommissioned by 2054 [2]. This is a contentious issue with the local community who are fighting for increased support from local governing bodies – be it for financial compensation, for a change in the policy and level of coastal defence, or for support for alternative coastal defence schemes to trial [3].


Undoubtedly, the situation at Fairbourne is devastating for many. While some might say the media coverage has been unfair, arguably the issue of coastal inundation due to climate change-related sea-level rise must be widely spoken about and acknowledged. What is happening in Fairbourne is going to happen to other coastal areas of the UK too.


What is happening in Fairbourne?


At the turn of the 20th Century, Fairbourne was but a cluster of a few houses but over the past 100 years, the village has expanded to over 400 properties, with around 800 residents, plus a significant summer tourist population.


The village is built on a low-lying floodplain and reclaimed saltmarsh and is backed by cliffs and fronted by a natural gravel barrier which supports an existing coastal defence, a sea wall. The village and surrounding land are at risk from coastal flooding as well as riverine and groundwater flooding during periods of high rainfalls. As sea-levels rise, high tide flooding events are likely to become more frequent, in particular when higher sea-levels are combined with high tide, waves, and storm surges. The situation is not unique to Fairbourne and threatens other coastal communities in Wales and further afield.


Why global sea-level is rising (and it’s rising fast)


Two main factors drive global mean sea-level rise: the addition of freshwater to the oceans from melting glaciers and ice sheets and the expansion of ocean water as it warms up as a consequence of increasing global temperatures. Global mean sea-level rose higher in the 20th Century than in any other century during the last three thousand years [4] and in 2021 the rate of global mean sea-level rise was the highest ever recorded [5]. Although uncertainty remains in the projections of future sea-level rise (in particular around the response of the major ice shelves/sheets to climate change), the latest estimate [4] is that a global mean sea-level rise of up to 1 m by 2100 is possible.


It is worth noting that global sea-level rise is not uniform. The worst hit places are low-lying areas where the regional sea-level rise is greater than the global average - the Pacific Island nations are a prime example.


Around the UK, the rate of sea-level rise is slightly lower than the global mean. This can be mainly attributed to vertical land movement as a response to melting ice sheets thousands of years ago. Nevertheless, our coastal waters are on the rise.


No time, and nowhere to go


The response of a natural gravel barrier coastline, akin to the coast of Fairbourne, to sea-level rise, is principally controlled by the balance between the sediment supply and the rate at which sea level is rising.


Steep gravel barrier coastline at Fairbourne with seawall along the crest. The village sits below the level of the barrier crest on historically reclaimed land.
Steep gravel barrier coastline at Fairbourne with seawall along the crest. The village sits below the level of the barrier crest on historically reclaimed land. © David Roberts

In Fairbourne, these dynamic coastal processes combine to increase the coastal flood risk to the village and community. Sediment supply to the barrier is limited with only minor inputs from the adjacent cliffs to the south. The sediment supply from offshore is negligible since the sediments are mostly too large to be transported onshore by the waves. Furthermore, as sea-level rises, the water becomes deeper, which leads to a reduction in the wave energy at the seabed necessary for pushing sediments onshore. The migration potential of Fairbourne’s seaward gravel barrier is limited by a lack of accommodation space; it is trapped between the hard rock geology of the cliffs to the southeast and the mouth of the river Mawddach.


What’s more, the existing man-made seawall fixes the barrier crest in place preventing roll-over, promoting over-steepening and increasing its vulnerability to storm over-wash. Groundwater flooding is also of significant concern at Fairbourne due to its location and the highly permeable reclaimed floodplain and saltmarsh soils upon which it is built. Squeezed between the marine environment and the Mawddach estuary, groundwater levels can rise substantially during periods of high rainfall, and when combined with high tides can potentially inundate the village from within. Meanwhile, sea level continues to rise.


Climate migration from coastal areas


Physical and environmental processes aside, sea-level rise is a complex socio-economic problem which plays out on a global scale. Regardless of the financial cost, building defences is not always the best method for adapting to climate change related sea-level rise. A strategic approach to coastal management and defence that integrates the dynamics of the natural physical processes with the latest projections for future sea-level rise and the socio-economics of the specific region is essential. The UK’s Shoreline Management Plans are just that. Of course, the last resort of ‘No Active Intervention’ requires careful and collective consideration. Retreating from the coastline, disbanding established communities, abandoning homes, and decommissioning villages is the ultimate adaptation option. Given that around 10% of the world’s population lives in coastal areas less than 10 m above sea level [7], coastal management will become an increasingly debated issue of the 21st Century.


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