Coastal erosion United Kingdom
The UK has many eroding coastlines (see Table below), the total length of which has recently been estimated to be over 3000 km (3). The UK vulnerability is indicated by the fact that it has around 2300 km of artificially protected coast, the longest in Europe. Annual damages due to coastal erosion are expected to increase by 3-9 times, costing up to £126 million per year by the 2080s (4). Some 28% of the coast in England and Wales experiences erosion at rates higher than 0.1 m/year (1). In Scotland erosion is less severe than elsewhere due to isostatic uplift and its extensive areas of hard geology (2).
Table. Coastal erosion and protection in the UK. Islands with a surface area < 1km2 and inland shores where the mouth is less than 1 km wide are not included (10).
|Region||Coastal length||Coast length eroding (%)||Length with artificial beaches and defence works (%)|
|Yorkshire and Humber||361||56.2||43.2|
However, on its own, coastal erosion is not a major economic issue. Coastal erosion losses represent only just over 3% of the total risk, although this is based upon an average estimation of property numbers (value £7.7 billion at 2000 prices). Even taking the extreme property number estimates, for which asset values vary between £2.7 and £12.2 billion, this still only represents 2–6% of the total capital value of assets at risk (5). However, in the context of broader coastal zone management issues and also the viability of coastal settlements on eroding coastlines, coastal erosion merits serious attention.
Rising sea levels and potential increased storminess will increase rates of coastal erosion. Protecting coastal assets (or relocating them) may be costly if the effects of climate change are sudden rather than gradual. Increased wave heights and potential storminess may lead to damage to coastal amenities including piers, promenades, beach cafes etc. Flooding caused by storm surges and sea level rise may damage coastal rail lines and roads. The unpredictable coastal dynamics may lead to erosion of some beaches. These problems are likely to be particularly acute in the region due to the fact that the landmass is subsiding. Natural assets in the coastal zone may be lost, such as wetlands, mudflats, salt marshes, beaches and sand dunes. The flora and fauna associated with these will also be affected. Areas of saline intrusion will increase, particularly in low lying coastal areas (6).
Retreating from coastal areas may not be viable and protecting the area at risk may be uneconomical in many places. The resulting costs of maintaining and building new coastal defenses are likely to be significant (6).
The predicted rise in sea level is not large enough to have a significant impact on rocky coasts. On "soft" coasts, fringed by mudflats and salt marshes, where there are no sea defences, the shoreline may move inland. Where there are no protective sea defences, the area of salt marshes could shrink as they are inundated at their seaward edge, and restrained from expanding inland by the defensive barriers. In Scotland, the low lying firths are most vulnerable to this potential loss of salt marsh and mudflats, which support internationally significant numbers of overwintering ducks, geese and wading birds, and are important staging areas during annual migrations (7).
The length of the English coastline, including the islands, is approximately 10,000 km, of which some 44% seems to be protected by some form of structure (14). The proportion of the ‘open’ coast that is protected by structures is much lower, some 15%. The highest proportion of defended coast is found in southern and eastern England, which is relatively low-lying and densely populated (2).
Over the course of the past decade, there has been a move away from the construction of new ‘hard’ defences except in areas where there is a requirement to protect land or infrastructure of high asset value, principally, but not exclusively, in urban and industrial areas. Even in such areas, there has been increasing use of ‘soft’ engineering methods in beach and dune management. In some case, beach nourishment has been undertaken as a standalone method of beach management, but in the majority of cases, it has been used in conjunction with the construction of rock groins and offshore breakwaters (2).
The main areas at risk of erosion are those where the coast is formed by soft cliffs or unconsolidated sediments. Some cliffs in eastern and southern England erode at rates up to 2 m/year (15). At most dune sites, average rates of frontal dune erosion are typically 1 m/year (16).
The coastline of Wales is some 1,200 km, including offshore islands. Tidal range varies from a maximum in the Bristol channel (12 m) to a minimum of around 3 at Cardigan Bay. Coastal erosion occurs along 23% of the Welsh coastline, which is protected by various structures (9). Some 415 km of man-made sea defence structures (breakwaters, seawalls, jetties, revetments, groins) protect assets from coastal erosion and tidal flooding (10). Beach nourishment schemes in Wales have been on a very minor scale; excessive nourishments could cause harbour sedimentation problems (2).
The Scottish coastline is 18,670 km, including the islands. Only about 6% of its coastline are defended, compared with some 44% of those in England and Wales (11). Some 12% of the country’s coastline is subject to erosion (12).
In Scotland 179 km of road, 13 km of rail track, and 3310 dwellings are at risk from coastal erosion. In total this equates to an asset value of approximately £1.8 - £3.7 bn. The number of dwellings equals 0.13% of all dwellings in Scotland (18). For context, approximately 5% of all dwellings are currently at risk from a 1 in 200-year coastal or fluvial flood event (19), equating to approximately 127,000 dwellings. Despite the number of dwellings exposed to coastal erosion being considerably less than from flooding, the value of the dwellings exposed (£524 m at 2017 values) remains considerable.
Scotland’s coastline is dominated by hard rocky coast and other areas of mixed sediments (superficial consolidated sediments with limited erosion potential) that are largely resilient to coastal erosion, together making up a coastal length of 15,604 km or 78% of the shoreline by length (20). The soft shoreline (beaches and dunes) covers 3812 km or 19% of the shoreline by length, with 590 km of artificial shoreline making up the remaining 3% (20). The distribution of these coastal types varies spatially with the east coast having a larger proportion of soft and artificial coast and the north and west coasts being characterized by a long, rock-dominated and often fjord-like indented coast.
Since much of the east coast is backed by low-lying land, it has experienced extensive urban and industrial development and, together with extensive transport infrastructure, the east coast is asset rich. On the other hand, the north, south and west coasts and their islands are dominated by rocky coastlines with more limited development and infrequent built assets. An exception to this general pattern in the west is the Firth of Clyde where extensive lengths of previously soft coast have been defended to protect asset-rich hinterlands that support infrastructure, industrial and housing development (18).
In many areas, the piecemeal approach to coastal erosion management, which for decades was so typical in Scotland, has led to the installation of unsightly defences. At Skara Brae in the Orkney Islands, Europe’s most complete Neolithic village, which has been accorded UNESCO World Heritage Site status, is under threat from flanking erosion at the ends of the seawall built initially in the 1920s to protect it. At numerous locations around the country, harbour walls and jetties have unintentionally interrupted longshore sediment transport rates. Since the 1980s soft engineering measures (planting eroding dunes, geotextile/jute membranes, limited public access) have become more generally accepted. Beach nourishments are rare in Scotland (2).
Projected sea level rise in 2080, incorporating best estimates of glacio-isostatic adjustment, varies between 0.2 m and over 0.32 m (13).
Projection rock coast cliff retreat rates
Erosion of rock cliffs due to climate change
Rock coasts make up over 50% of global coastlines yet focus on future coastal erosion under sea level rise so far was mainly on soft, erodible coastlines. The presence of rock coast cliffs is a clear sign that coasts are eroding. Sea level rise will likely accelerate the erosion of rock coast cliffs because the energy of waves will reach further inshore to attack the rock cliffs. It is very complicated to project the impact of future wave energy attacks on rock coasts, however, for several reasons. One of them is the fact that rock weathering is an important component that determines the effect of wave energy on cliff retreat (22), and the rate at which the rock weathers varies with type and structure of the rock present at the coast (23). Another important factor is the impact of extreme storm events, which is difficult to include in long-term projections.
The past: a key to the future
If we can quantify rock coast cliff retreat rates in the past, over a time scale of thousands of years, and determine how these rates have changed in response to changes in the rate of sea level rise since the end of the last ice age, we can use this information to make projections for the future. We are, then, using the past as a key to the future. But how do you reconstruct the retreat of coast cliffs that have disappeared? The answer is hidden in the rocks that are left behind as a rocky platform after the rock on top of them – being the rock cliffs at some time in the past – had eroded (21).
In this intertidal shore platform, rare nuclides formed once the rock was exposed to cosmic rays. The concentration of these nuclides in the rock is an indication of the time the rock has been exposed to the air and, thus, of the moment in the past the rock on top of them has eroded. By combining this information from rock samples across the intertidal rock platform with information on the processes of wave erosion and intertidal weathering of the rock, scientists were able to reconstruct rock coast cliff retreat rates for the past 8000 years and make projections for the future (21). This long time series encompasses a time where rates of sea level rise are comparable to projected future rates of accelerated sea level rise. This time, therefore, is the key to understanding the response of current rock cliffs to future climate change. The study was carried out at two sites in the UK.
Future cliff retreat rates
According to historical maps and recent aerial imagery, cliffs have retreated at these two sites over the past 130 years at rates of just 5.8 ± 4.0 cm/year and 5.9 ± 4.3 cm/year, respectively. The scientists conclude that the projected acceleration in the rate of sea level rise will accelerate cliff retreat. By 2100, cliff retreat rates are forecast to accelerate by at least 3–7 times present-day rates and cliff positions are likely to retreat by at least 10–14 m at the one study site, and 13–22 m at the other (21).
These numbers are up to an order of magnitude larger compared to long-term cliff retreat rates for the past 500 years. The scientists also conclude that these findings ‘challenge conventional coastal management policies, in which rock coasts are considered stable environments compared to sandy coastlines.’ According to them, historical rates of rock cliff erosion cannot be used for climate change risk assessments because these coastlines will no longer be as stable in the future as they were in the past (21).
These forecasts are consistently higher than the results of previous studies that forecast an increase in cliff retreat rates for 1 m sea level rise at 2100 between 1.2 and 2.3 times the rates of historical observations (24). According to the authors of the new study, this is due to simplifications in previous studies, for instance not including the impact of tidal range on wave attack on the rock cliffs. In fact, the authors consider their updated cliff retreat rate projections ‘conservative estimates’ since these estimates do not include a possible increase of storm frequency and intensity (25), which would ‘increase the speed of cliff retreat rates beyond their estimates in the future.’
In the UK, Shoreline Management Plans, first introduced in England and Wales in 1993, serve to provide a strategic framework for decision making along the coast, especially with respect to defence, taking account of the natural coastal processes, human and other environmental influences and needs. Today the whole length of the English and Welch coast is covered by such plans; for Scotland only a part of the coast is covered by these plans. In Wales, the extent of enhanced erosion due to climate change affecting sea levels and waves is uncertain and the current view is not to build higher defences, but to utilize risk management approaches and work with nature wherever possible (2).
The approach to coastal protection in the United Kingdom focuses now on ‘sedimentary cells’ to reflect the adaptation needs of a regionally-varying coastline in terms of landscape, sedimentology and coastal dynamics. There are four Strategic Coastal Defence Options (17):
- do nothing
- maintain the existing protection line (while possibly adjusting the protection standard)
- advance the existing protection line
- retreat the existing protection line (subsequently referred to as ‘managed realignment’)
The intention is that the Shoreline Management Plans provide a ‘route map’ for local authorities and other decision makers to identify the most sustainable approaches to managing risks to the coast in the short term (0 - 20 years), medium term (20 - 50 years) and long term (50 - 100 years), recognising that changes to the present protection structures may need to be carried out as a staged process (17).
"Managed re-alignment" is a possible response to the potential loss of coastal mudflats and salt marshes, resulting in the creation of new habitat by allowing inundation of low-lying coastal land, sometimes requiring the breaching of sea defences to allow inland movement of water. Experience in several parts of the UK suggests that inundated areas of coastal grassland are colonised rapidly by salt marsh. In Scotland, where coastal landowners are responsible for the upkeep of sea defences, this may be a cheaper option than upgrading them to cope with rising sea level, as well as ensuring the continued availability of wildlife habitat. Agri-environment payments are available to farmers to encourage the conversion of agricultural land to salt marsh (7).
An example of an area where “managed retreat”, or in fact large-scale abandonment of a prime agricultural area, would seem likely, is the Fens. In this area the interaction of sea-level rise, increased river floods and subsidence could lead to severe flood impacts (8). In East Anglia, sea-level rise appears to threaten existing salt marshes. In some areasover half the existing stock of salt marsh could be lost by the 2050s (8). These losses will exacerbate the increase in coastal flood risk already described. Taking account of both managed realignment, and/or possible coastal abandonment of low value areas that are flooded frequently, the net effect on the stock of salt marsh habitats is likely to be stability or even a gain in area. Salt marsh gains come largely at the expense of the loss of coastal grazing marsh, which is expected, to decline in area under all climate change scenarios. Adaptation options are limited, as there are limited opportunities to create replacement habitat within the coastal zone (8).
The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for the United Kingdom.
- Burgess et al. (2004); Evans et al. (2004), both in: Blott et al. (2013)
- Blott et al. (2013)
- Eurosion (2004), in: Hall et al. (2006)
- Foresight (2004)
- Halcrow (2001), in: Hall et al. (2006)
- C-CLIF and GEMRU (2003)
- Kerr et al. (1999)
- Holman et al. (2002)
- EA (2010), in: Blott et al. (2013)
- Masselink and Russell (2008), in: Blott et al. (2013)
- DEFRA (2001), in: Blott et al. (2013)
- Baxter et al. (2008), in: Blott et al. (2013)
- Ball et al. (2008), in: Blott et al. (2013)
- DEFRA (2010), in: Blott et al. (2013)
- Valentin (1971), in: Blott et al. (2013)
- Pye et al. (2007), in: Blott et al. (2013)
- Niemeyer et al. (2016)
- Fitton et al. (2018)
- SEPA (2009)
- Hansom et al. (2017)
- Shadrick et al. (2022)
- Trenhaile (2008); Coombes (2014); Matsumoto et al. (2018), all in: Shadrick et al. (2022)
- Rosser et al. (2013); Sunamura (2015); Prémaillon (2018); Buchanan (2020), all in: Shadrick et al. (2022)
- Dickson et al. (2007); Castedo et al. (2012); Hackney et al. (2013); Limber et al. (2018); Walkden et al. (2019), all in: Shadrick et al. (2022)
- Trenhaile (2014), in: Shadrick et al. (2022)