Thames Barrier

In 1951, the east coast of England was hit with a flood; 300  lost their lives. If the water reached all the way into central London, the death toll could have been a lot worse. The 1951 flood and the prospect of further damage triggered the British Government to restructure the city’s flood defenses. In 1966, Sir Herman Bondi did an investigation and reported that raising the bank together with a flood barrier with movable gates would fulfill London’s needs. Parliament passed the legislation in the Thames Barrier Flood Prevention Act of 1971. A year later the banks were raised and in 1982 the construction of the barrier was complete. To this day, there have been no floods in London.

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The Barrier was designed by Charles Draper who got the idea of ‘rising sector gates’ from the shape of a gas tap. Building such a complicated structure required a lot of very technical engineering. One method they used to build a foundation into the riverbed is called a ‘Cofferdam.’ A Cofferdam is a watertight steel box, formed using steel pipes sunk into the river bed. ‘Tremie’ pipes were used to feed the concrete into an excavated space under the river. Concrete sets underwater forming a water-tight seal, then the water is pumped out. The Romans used the same method.

Seventy-five percent of the project was financed by the central government funding while the rest was provided by the local government. It cost 535 million pounds in 1980. The cost to build it today would be on the order of 1.7 billion pounds. The upkeep of it costs 8 million pounds, then there is the need for capital improvements which cost another 10 million pounds a year.

An individual gate can be closed in 10 to 15 minutes but closing the whole barrier for takes up to 90 minutes. The gates need to  be opened from the bottom so that the water level is even upstream and downstream of the Barrier.

The river front where the Barrier is has a rich history. In 1512 Henry VIII established his Royal Dockyards near there, where his flagship Henry Grace-a-Dieu was built. It was a massive ship for its time and was commonly called Great Harry. HMS Beagle on which Charles Darwin conducted his scientific studies was built there in 1820.

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