London building £500M anti-flood barrier; thousands in danger

Press, 31 August 1977, Page 24

London building £500M anti-flood barrier; thousands in danger

By

TONY CRAIG,

“Observer,” London

The threat of London ;eing destroyed by a terrible flood is now so real that — despite astronomically rocketing costs — a unique Thames flood barrier is to be completed as rapidly as possible.

And the Greater London Council’s interim flood warning is to be extended at the end of August to give Londoners four hours notice, as opposed to one hour, of imminent flooding. The need for the barrier, which breaks unexplored ground in pioneering engineering, was spelt out by Peter Black, leader of the Greater London Council’s recreation and community services policy committee, who is himself an engineer. Black made his comments against the background of a disturbing report published by the House of Commons Committee of Public Accounts. It revealed that the projected cost of the barrier — intially estimated at between £B3 million and £92 million — had risen to £441 million. The final cost, taking inflation into account, is likely to be higher still. London is vulnerable to severe flooding when a combination of geographical circumstances induces a storm “surge” tide up the Thames. All Britain is slowly tilting, and London and the South-East is dipping downwards at the rate of a foot every 100 years. At the same time, the capital is sinking on

its bed of clay while high rides are getting higher. As a result, tides at London Bridge are more than two feet higher than they were a century ago. Recalling the floods ot 1928 and 1953 — in which more than 300 people died — Black said: "In a tide of such proportions today, more than 1.25 million people are at risk. Fortyfive square miles might be flooded, and London cut in two by a huge lake.” He said there were more than a quarter of a million homes in the low-lying potential flood areas. More than 50 Underground stations could be under

water, and some 35 hospitals, four major sewage works, 20 fire stations, and seven ambulance stations could be flooded.

Even on the assumption that London’s drainage system was not damaged, the Houses of Parliament,

most government offices, and New Scotland Yard might be under three feet of water for a day. Black said: “At any time God or the Heavens, or whoever does it, could send us the combination of wind, tide, and surge that could take us over the top. The recorded surge tides are continually increasing. In my lifetime we have had the floods of 1928 and 1953, and the next one will be worse than both of these. That is

why we have pushed ahead with the interim raising of the banks, adding an extra 18 inches." That, too, is why, when the Greater London Council meets again after the summer recess. Black’s committee will be considering the possibility of organising a full practice alert, on the new fourhour warning, to give Londoners a taste of what might happen. Major flooding could cause between £2OOOM and £3OOOM of damage, and the seat of government could be forced away from London, perhaps never to return. The chances of the

Thames’s flood defences being broken between now and when the barrier is operational — the present estimate is the winter of

1981 — is put at about once in 50 years. But the danger increases every year.

London was serverely flooded in 1236 and 1663. In the 1928 floods. 14 people were drowned in their basements in Hammersmith and Westminster: and the 1953 disaster cost the lives of more than 300 people in the lower reaches of the Thames. In 1965, water lapped within six inches of the top of the river walls in central London. And in January last year, London faced the threat cf an B|-foot "surge” tide.

Fortunately, it coincided with a low tide. About three-quarters of the cost of the Thameterrier is being met by the Government; London< ratepayers are finding the rest of the money. But. Black said, Britain was also proving its extraordinary engineering expertise in the field: and world experts were "beating a path to our door” to examine the scheme, and consider whether similar structures could be used elsewhere. “This could lead to a huge export market for us.” he said. The barrier has been designed on the "rising sector gate” principle. It will stretch 570 yards from bank to bank across Woolwich Reach, and will consist of a series of enormous steel gates set between huge concrete islands which will also house the hydraulic engines powering the gates. When the barrier is not in use the gates will lie horizontal, recessed in pre-cast concrete sills — each the size of a small football pitch — laid in the river bed. This will allow shipping to navigate the Thames normally. To close the barrier the gates will turn through 90 degrees to a vertical position.

There will be 10 gates in all, and when the barrier is up they will stand more than 52 feet above the river bed. Yet the barrier will take only about 30 minutes to close. —OFNS COPYRIGHT.