Many stretches of Britain's coast are threatened by erosion. and how a Sussex lighthouse may be saved from the sea
Earlier this month, a 60m by 15m slice of cliff broke away from Beachy Head in Sussex and crashed to the shore 550ft below. It was as sudden as it was spectacular, and was a further reminder of the fragility of Britain's coastline.
Coastal erosion has been an integral feature of our national heritage ever since Britain first broke away from mainland Europe in 6500 BC. Indeed, erosion creates landmarks; the only reason the south coast cliffs remain white is because they are constantly being worn away.
It's not just cliffs that are under threat; many mudflats and estuaries are at risk, and the gently sloping shoreline of East Anglia is disappearing rapidly.
The tilt effect
The main reason that Britain has been subject to erosion over such a prolonged period is that the country is gradually tilting due to earth movements associated with the last Ice Age. The net effect of this is that Scotland is rising and the south of England is falling. This means that the relative sea levels around Britain's coast are constantly changing.
Global warming In recent years the rate at which Britain's coastline has eroded appears to have accelerated significantly. Scientists believe that this is due to global warming. The Hadley Centre, part of the Meteorological Office at Bracknell, forecasts that sea levels will rise an average of 24cm over the next 50 years, due to the thermal expansion of the oceans and to melting glaciers. If the tilt effect is taken into account, then sea levels around Scotland will rise by about 16cm and those in southern England by about 31cm. The overall situation is likely to be even worse if other factors commonly associated with global warming, such as storms, increased rainfall and high winds, occur.
Levels of erosion
Not all parts of Britain's coastline are eroding at the same time. Areas around the south coast are disappearing at the rate of one metre per year, while areas of the east coast are being lost at the rate of between 18 to 20 metres every 10 years. However, while gently shelving coastline erodes at a relatively constant rate, many cliffs can remain apparently stable for many years and then lose tens of metres in one landfall. Cliff erosion is due to the action of the waves on the cliff face, but not all cliffs erode at the same rate. The south coast cliffs were formed up to 100 million years ago in the Cretaceous period and are made of chalk. They are much harder than the clay cliffs of the east coast which were formed 15 to 30,000 years ago, and take longer to erode.
Vulnerable areas
Three parts of Britain's coastline have been identified as immediately at risk of collapse. These are a section of the Holderness coast in Yorkshire, a small strip near Lyme Regis in Dorset and a 190m section of cliff at Freshwater in the Isle of Wight.
Coastal defences
Significant areas of East Anglia, Somerset, South Yorkshire and elsewhere depend on drainage and flood defence systems, some of which have been in place for hundreds of years. In addition, there are a number of coastal towns built on unstable geological formations without such protection. However, there are limits to what can be achieved through defence systems, such as building sea and river walls and tidal barriers, refilling beaches with sand or shingle, or providing pumping stations for drainage. But the Government has committed itself only to coastal investments that can be sustained in the long term. This means that places which would require an ever higher sea wall to protect them may have to be abandoned.
The bulk of the £69 million that has been earmarked for flood defence over the next financial year will go on schemes to ensure the protection of lives. However, the UK also has a duty to conserve some wildlife habitats which are threatened by flooding, and the Government has recently committed itself to any extra expenditure that may be involved.