Our coastlines may appear as fi rm lines on a map but they are constantly changing. A European Commission report in 2004 stated that over 17% of the UK and nearly 20% of the RoI coastline is eroding, challenging the very existence of some ports and harbours, associated industries, heritage sites and wildlife havens. Several communities are facing a stark and cruel choice: is it worth defending homes and livelihoods or should expensive defences be abandoned and the crumbling land be evacuated?

Erosion and accretion

Coastal erosion can be promoted through human activity but it is ultimately caused by the action of water: rain, frost and, most of all, wave and tide. By defi nition, just 1m3 of water has a mass of 1 tonne so the forces involved are huge. Destructive waves erode by:

• pounding – the sheer force of hitting the rock

• pneumatic action – compressing the air in cracks in the rock

• abrasion – hurling rock fragments that scrape away at the rock

• attrition – smashing fragments together, wearing down to sand and silt

• scour – breaking and swirling around at the base of a structure, removing loose material

• solution or corrosion – salt water dissolving chemicals in the rock.

The naturally sculpted caves, arches and stacks at Flamborough, Yorkshire, provide spectacular examples of erosion. However, the material lost in one location may build up elsewhere, forming beaches, bars, dunes or spits. South of Flamborough is Spurn Point, a crooked fi nger of land stretching 3 miles into the Humber estuary and a prime example of such accretion.

Around 3% of the material eroded from the intervening Holderness coast is deposited at Spurn, but this home to Humber lifeboat station is itself far from stable. There have been occasional partial breaches of the spit but a complete breach could force the station to be moved, losing a 20–25- minute advantage in response times. Meanwhile, the RNLI has invested in power generators, water storage and contingencies to retain access.

rock and resistance

Different rocks offer hugely varying resistance to erosion. Rates of loss can be less than 1mm a year with igneous rock to more than 4m a year with sand. It is usually only where coastlines are comprised of mud, sand, shingle or glacial deposits that erosion progresses suffi ciently rapidly to be of concern. Erosion is greater where the ...

• rock – is poorly resistant

• wave – is steep; has a long fetch, gaining energy from the wind; hits at its point of collapse; hits a cliff at its base

• beach – is steeply shelving, which creates steeper waves; is narrow, which focuses the wave energy; provides abrasive material to be carried in the waves

• weather – includes ground frost, which expands in cracks in the rock

• marine environment – includes bioeroders, which are organisms that ‘eat’ rock

• humans allow inappropriate – drainage, access by pedestrians and vehicles, grazing and ‘protective’ works.

However, at the same time, our islands are literally on the rebound from the weight of the ice sheets that once almost covered them. The effect is uneven so east England is sinking into the sea while north Scotland is rising.

The Holderness coast is one of Europe’s fastest eroding, shrinking by around 2m each year. Yet Dumfries and Galloway, Shetland and the Western Isles have suffered from erosion too. An astounding 20m of Western Highlands coastline was washed away in 2005 and stretches of Fife, Aberdeen and Kirkcaldy are now of concern.

Huge stretches of the Welsh coast are also threatened, from the Gower peninsula in the south to Porthdinllaen on the Llyn peninsula, and the north west coast of the Isle of Man has seen the sandy shore retreat. In Ireland, most erosion is along the east and south east coasts, with the largest ongoing coastal protection scheme at Rosslare Port, but the far western Aran Islands are not immune.