London Fights Off Disaster

A giant bulwark rises in the Thames as a flood barrier

Driven by high winds and tides, the great surge of water spills over the embankments of the Thames River and sweeps across dozens of square miles of London, endangering countless thousands of people. More than a quarter of a million homes, offices and factories in such low-lying areas as Westminster, Hammersmith, Lambeth and Southwark are inundated. In the streets, thousands of cars are left stranded. In central London, the underground is paralyzed, bridges and tunnels are closed. Hospitals struggle valiantly to maintain services, their task made all the more difficult by power blackouts, loss of telephone service, contamination of the water supply and the difficulty of mobilizing rescue teams. The Houses of Parliament and New Scotland Yard stand in several feet of water. Total damages from the great Thames flood: more than $6 billion.

This scenario is not the product of an avid Hollywood scriptwriter. It is a grim projection by British experts who know only too well that the apparently placid Thames can turn with little warning into a terrifying torrent. To forestall the disaster that a "worst case" Thames flood would produce, British engineers are rushing to complete by the end of 1982 an extraordinary project: a giant, movable steel and concrete flood barrier that in normal circumstances will allow the passage of large ships but rise up during flood threats to block the menacing waters.

Lying upriver about 96 km (60 miles) from the North Sea, London has through history been swamped by the rampages of the Thames. During a flood in 1236, reports one chronicle, "in the great palace of Westminster men did row with wherries [small skiffs] in the midst of the hall." In his diary entry for Dec. 7, 1663, Samuel Pepys wrote: "There was last night the greatest tide that ever was remembered in England to have been in this river: all Whitehall having been drowned." As recently as 1978, the Thames came within 30 cm (12 in.) of topping flood walls.

For centuries, London and other communities along the lower Thames have been raising their embankments. After a sudden flood in January 1928 killed 14 people, including four youngsters asleep in a Westminster basement, the walls along the Thames were elevated to more than 5 meters (17 ft.) above the mean water level. More recently, the height has been increased to nearly 6 meters (19 ft.). But even these towering embankments could not cope with an extreme combination of circumstances. While Thames tides normally do not exceed 4.6 meters (15 ft.), the level can be pushed far higher by sudden onslaughts of water. In 1976, a 2.4-meter (8 ft.) surge was recorded on a low tide. If such a surge came atop one of the highest tides, it could raise the river to 1.2 meters (4 ft.) above the Thames' embankments and cause, in the words of the Greater London Council, "a catastrophe for the capital on the scale of the Great Fire of London or the Black Death."

Surges result from a coincidence of meteorological conditions. One is a trough of low atmospheric pressure over the North Atlantic, causing the water to rise in a kind of hump. When this low moves southward into the North Sea powered by northerly gales, the hump is funneled into the Thames estuary. If the tide is rising as well, the result can be a huge mass of water growing ever higher as the river narrows near London.

To make matters worse, Britain is slowly tilting, apparently an aftereffect of the last great Ice Age, with the northwest of the country rising and the southeast sinking at about a foot a century. London, built on a foundation of clay, is settling even faster; and normal tides are becoming higher and higher.

Because continuing to raise the walls along the Thames would cut off London's view of the river and ruin the historic waterfront, government officials years ago began looking for another answer to the flood peril. In 1972, after weighing dozens of schemes, they settled on a novel system of floodgates proposed by Engineer Charles Draper, 47. The entire barrier, a 521-meter (1,710 ft.) structure, will span the Thames 14 km (8.5 miles) downstream from London Bridge. It has ten openings, six of which are large enough to accommodate the more than 5,000 seagoing ships that are expected to pass through each year.

The gates in these larger openings are actually sections of cylinders, rounded on one side, flat on the other, with a disc at either end. Under ordinary circumstances, they will lie flat-face up in rounded troughs planted in the riverbed. But if there is a threat of flooding, each of the gates will be rotated 90DEG by hydraulic rocker arms, housed at either end inside well-designed piers (which resemble the futuristic opera house in Sydney, Australia). The rotation raises the gates to a vertical position, turning them into five-story-high barricades against the rising waters. Though the gates weigh 3,200 tons each, they can be raised in only 30 minutes.

Now nearly two-thirds completed, the project is expected to cost more than $800 million. Additional flood defenses along the banks downstream (to contain the water blocked by the barricade) are expected to put the total tab of taming the Thames at more than $1.5 billion. Meanwhile, the Greater London Council is taking precautions against any flooding that might occur before the great Thames barrier is in place. With the onset of winter gales, the council is stepping up distribution of instructions about what to do in case the waters begin to rise. Says one poster: "If you live, work or travel through the Flood Risk Area, you should learn the Thames Flood Drill now. Cut it out and keep it handy. We hope you'll never need it. There's a 1 in 50 chance you will."

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