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Holding back the tide

Updated Tuesday 7th September 2004

Managing flooding might prove more effective than a losing battle with the tides, explains Paul Brown

Flood protection wall Copyrighted image Icon Copyright: Production team

At last the lesson King Canute tried to teach his subjects, that no man can turn back the tide, has finally sunk in. After 1,000 years of building sea walls and grabbing more and more land from the sea, carefully built sea defences are, in many places, beginning to be deliberately destroyed.

Although, at £400 million a year, more is still being spent on 20,000 miles of flood defences than at any time in history, the Environment Agency and the Government have accepted that all of Britain cannot be protected from the sea. As the East and South of England sink below sea level at increasing speed, the plan is that more and more low lying land will be abandoned. Experiments have shown that a sea wall costs £5,000 a metre to build and maintain.

However, retreating 80 metres inland and allowing a salt marsh to form breaks up the tide and waves, so the new sea wall sheltering behind it costs only £400 a metre to do the same job. The problem for the Environment Agency and the Government is that the sea is rising all the time, and the natural salt marshes are being washed away, leaving more and more sea wall exposed.

The problem is made worse by two factors. The South-East continues to tilt into the sea as a result of the "rebound" of the Scottish mountains from the last Ice Age, and the sea level is rising every year because global warming is both melting glaciers and causing thermal expansion of the oceans.

Sea levels may rise by a metre (about 39 inches) in some places in fifty years. Add to that the effect of higher tides and large areas vulnerable to a storm surge. There is no suggestion that urban areas will be abandoned, but like Canvey Island in the Thames Estuary, "drowned" in the 1953 flood, they may become islands surrounded by sea defences while agricultural land is used as a buffer against floods.

The policy of pushing back the sea began in Roman times, when the first defence banks were built in the Wash. The reversal of this practice is controversial. Farmers used to the Government building and paying for sea defences to protect their land are reluctant to see arable land, farmed for generations, revert to salt marsh.

But the need to save money and concentrate on averting the threat to towns has found support in the scientific community and in the British love of the natural world. Salt marshes and inter-tidal mud flats in estuaries support two million wildfowl and wading birds in winter and are home to rare and specialised plants and animals. Coastal wetlands provide a vital source of food and shelter for commercially exploited fish and shellfish. The mud and plants also digest pesticides, nutrients and other pollutants that would otherwise damage the environment. But they all are fast disappearing.

In Essex one of the first projects to let the sea back onto farmland, at Abbots Hall at Salcott Creek, took three years to gain acceptance. It needed 32 separate planning permissions and licences, as well as the consent of the farmers and the oyster fishermen who feared mud would interfere with their oyster beds.

Elliot Morley, the Minister responsible for sea defences, interviewed on the BBC/Open University TV programme Flooded Britain concedes the issue is so sensitive that he calls the process not coastal retreat but "managed realignment." He believes that the future will see "unsustainable defences being replaced by managed realignment." Farmers will graze cattle on salt marshes and sell premium local beef, rather than grow wheat, and Essex will become a Mecca for tourists looking at the wildlife, he claims.

The Royal Society for the Protection of Birds (RSPB) say these projects will be needed on a large scale if existing salt marshes are to be replaced as the sea drowns existing ones and washes them away. Already there are schemes to replace salt marches, four in Essex, one each in Devon and Somerset and in the Cromarty Firth in Scotland. Six more are planned. But the RSPB and the Environment Agency estimate 10,000 hectares of farmland will have to be abandoned to the sea in the next 15 years to keep pace with the encroaching tide.

This article was originally published in 2003


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