Crumbling defences against the great flood: In 1953 a wall of water swept over Britain's east coast killing more than 300 people and thousands of sheep and cattle. Could it happen again? Nicholas Schoon reports

FORTY years ago this weekend more than 300 people were killed by the great flood of 1953. A storm surge combined with a spring tide swept a wall of water over the sea walls of the east coast in one of Britain's worst peace-time disasters.

From the Humber to the Thames estuary, thousands of sheep and cattle drowned and tracts of farmland were left infertile. Nearly 25,000 homes were damaged, some entirely swept away. In the Netherlands the disaster was even more severe - 1,400 people died. The sea level was pushed more than 8ft (2.4m) above the usual highest tide.

Twice since that Sunday night of 31 January, a similar combination of spring tide and storm surge has raised the North Sea as high or even higher: in January 1978 and January 1983, according to the Meteorological Office's storm tide warning service.

Twice already in 1993 the Thames barrier has been raised to deal with lesser storm surges and high tides. There has also been minor sea flooding around Colchester in Essex and Wells in Norfolk this year.

But there has been no repeat of the 1953 tragedy because a major programme of rebuilding and heightening of east coast flood walls began soon after the disaster and the strengthened defences have taken the strain.

Now many miles of those sea walls are eroded and in need of major maintenance. It is not only storm surges they have to contend with. The south-east of Britain is tilting down as fast as 5mm a year as Scotland and the North-west rises. The land mass is still responding to the removal of billions of tonnes of ice at the end of the last Ice Age.

Sea levels are also expected to rise by an extra 6.5mm a year in the next century due to man-made global warming; this increase may have already begun.

The Anglian region of the National Rivers Authority, the area most threatened by sea flooding, has increased spending on its 1,000 miles of sea walls by 30 per cent in recent years to pounds 33m a year. The rise is mainly because many of the post-1953 defences now need repair or rebuilding. The aim is to renew or replace about 30 miles a year.

But coastal engineers recognise that old-fashioned sea walls and groynes can stop the flow of sediments along coasts, worsening erosion elsewhere. They are now working with nature, replenishing beaches by dumping sand and shingle and building low offshore breakwaters.

The disaster 40 years ago began with a deep depression over the North Atlantic. The low air pressure sucked up the sea level by an extra foot over a huge area of ocean, moving westwards at about 50mph. Once the depression and its trailing hump of water reached the confined and shallower North Sea waters, the level climbed much higher.

Northerly gales driving the sea south added still more to the surge, and as the level reached the top of the defences, storm waves helped to smash the sea over them. Many of the embankments were dilapidated because of neglect during the war years and the austerity afterwards.

From Grimsby and Cleethorpes in the north to Canvey Island in the south, via towns like Skegness, King's Lynn, Lowestoft and Harwich, the sea raced through streets and houses. The victims, many of them elderly or bungalow dwellers, drowned or collapsed as they tried to flee. At Hunstanton in Norfolk a train collided with a house being swept along the track. The worst incident was on Canvey Island in Essex, where 58 people died.

As well as higher sea walls, residents in threatened areas will now get much more advance notice. The storm tide warning service prides itself on giving at least 12 hours' notice of extra high sea levels for the east coast.

The Proudman Oceanographic Laboratory in Birkenhead on Merseyside develops computer simulations of storm surges to help the warning service, which is funded by the Ministry of Agriculture.

It is now working on an improved model which will take into account the battering effect of waves on sea defences as well as spring tides and storm surges.

(Photographs omitted)