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| This Skyscan photo shows the enormous scale of the barriers protecting the historic city of London. |
Cover story by Alan Symes,
Staff Correspondent,
London Press Service, UK
Recently, the great Thames flood gates were closed for the 200th time, a smooth procedure that underlies its effective design and operation that has performed well since it started operation in 1982.
London has been saved from possible serious flooding on several occasions by the activation of the Thames Barrier that has prevented surge tides from sweeping up-river where they could have caused considerable damage.
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| This Skyscan photo shows the enormous scale of the barriers protecting the historic city of London. |
The cost of a major flood would be enormous, possibly more than $20,000 million, not counting the human suffering and possible loss of life.
The Barrier's series of massive movable gates are activated at regular test intervals but have been raised only 30 times to control threatening tidal flows. More than 50 staff members operate the Barrier that consists of 10 separate movable gates, each pivoting and supported between concrete piers and abutments that house the operating machinery.
The aerial picture shows the gates in action, controlling the flow of water from the sea. When a dangerously high tidal surge threatens, the gates swing up through about 90 degrees from their riverbed position, forming a continuous steel wall facing downriver.
The width of the Barrier from bank to bank is some 520 metres (1,700 ft.) with four main openings each having a clear span of 61 m (200 ft.). Each of the four main gates is 20 m (66 ft.) high, weighs about 3,700 tonnes and is capable of withstanding an overall load of more than 9,000 tonnes. When not in use the gates rest out of sight in curved recesses in concrete sills in the riverbed, allowing free passage of river traffic through the openings between the piers.
Quite apart from its crucial flood protection role, the Thames Barrier has become an established tourist attraction. Many people from other countries were among the 67,000 who visited the project during the past year.
They were able to view the civil engineering landmark while dining at the adjoining Visitors Centre. Here, animated models and audio visual programs explain how the Barrier works and fits into the overall pattern of London's evolution from Roman times to the present day.