The ebb and flow of ruling the waves

Next month, 21 hectares of Essex farmland will be flooded as part of a plan to save England's coast. Malcolm Smith explains

Our literature hasn't helped. From the biblical episode to the writings of Shakespeare, Tennyson, Wordsworth and others, floods have been associated with destruction and death. Reality - take Lynmouth and Tywyn - has borne out their ogreish musings.

It may seem unseasonal in high summer to worry about there being too much water, but the fact is that the flood tide is winning. In the south and east of England, where sea levels are rising relative to coastal land, the Government has acknowledged that it is economically impossible everywhere to hold back the sea with man-made defences. Provided communities remain protected, reflooding farmland - much of it producing an excess of corn or feeding livestock - to create saltmarsh and mudflats and to reduce the substantial costs of continually raising sea walls is de rigeur. The process is called "managed retreat".

According to Dr Geoff Radley, of English Nature, which, with the Ministry of Agriculture, Fisheries and Food and the National Rivers Authority is involved in managed retreat trials, England is losing around 100 hectares of saltmarsh and 500 hectares of mudflat each year. Most disappear as a result of so-called "coastal squeeze", where rising sea levels raise the low water mark while the high water mark is fixed by sea walls or banks. "In Essex, south Suffolk and north Kent alone," says Dr Radley, "a fifth of the saltmarsh area present in 1973 had been lost by 1988."

At Tollesbury Fleet, on the north side of Essex's Blackwater estuary, a full-scale trial is in progress. The idea is to flood 21 hectares of arable land that English Nature bought especially. Some saltwater is already inundating parts of it, controlled by sluices. Come August, the sea wall will be breached to flood the lot. The trial will allow scientists to study the best ways of establishing saltmarsh on this type of farmland.

To encourage private landowners to accept a bit of coastal flooding, the Government has written a "saltmarsh option" into its set-aside programme, the European Union measure to take a proportion of farmland out of production. In exchange for allowing their land to become intertidal again, farmers receive pounds 190 per hectare per year for grassland and pounds 500 for arable land. The payments are guaranteed for 20 years. British government (and EU) money is saved on crop subsidies because sea defences do not have to be maintained.

The wildlife gain is also substantial. Saltmarshes and mudflats - bleak though they might appear - are home to an array of plants and animals, especially invertebrates, which attract vast numbers of wading birds, especially during winter when most remain ice free.

Tollesbury Fleet is a testbed. So far, most of what is known about creating saltmarshes where they never previously existed, or where they have not done so since sea defences were erected long ago, has been gleaned indirectly. Fiona Burd, of the University of Hull's Institute of Estuarine and Coastal Studies, contracted by English Nature, has studied natural breaches of sea defences in Essex and Suffolk to see what lessons could be learnt. Her report, "Managed Retreat: A Practical Guide", was published last month and advocates a strategic approach to selecting suitable bits of coast, as breaching a sea wall to flood land in one place may have an impact on other nearby stretches of coast. When assessing suitability for managed retreat, several factors have to be assessed, she says.

Was saltmarsh present there historically, so that the soil structure and chemistry are suitable? If not, the place probably isn't convertible in the short term. Is the land slope such that mudflats can develop nearer the sea, and saltmarsh farther away, inundated by fewer tides? If not, it may be possible to dredge material to raise the land surface at the new landward edge. Because it has been drained, much coastal farmland has sunk to a level lower than that on the seaward side of existing defences.

Information on the tidal hydraulics of the coast in question, on tidal heights, the width of breach to be considered and many other facts have to be assessed before the floodwaters are allowed in. More practice and experience is essential before parts of England's coast again take on a more natural appearance. Even biblical quotes such as that from St Matthew: "The rain descended and the floods came" could take on a positive spin for the first time.

'Managed Retreat: A Practical Guide' is available free from English Nature, Northminster House, Peterborough PE1 1UA.