8 May 1984: The Queen opens the Thames Barrier

The Tower of London, the Houses of Parliament, St Paul's Cathedral, pretty much all of London within a stone's throw of the river, would regularly be under water if it wasn't for the Thames Barrier and that's more true now than when it was first built.

It was predicated that a major flood in the capital would cause up to £3bn of damage, as well as kill around 100,000 people. So, in August 1972, the Thames Barrier Act received royal assent, providing for a barrier to be built across the Thames to protect London against flooding. It would be designed by Rendel, Palmer and Tritton and the cost of building the barrier was estimated at £315m in today's money.

Ten years, 18,000 tonnes of steel, and £1.6bn later, the barrier was complete. "Its spectacular overruns on price and delivery date, as majestic in their way as the statistics of its novel and unparalleled technology, could stand as an emblem of the industrial history of the seventies and eighties", noted The Times grumpily.

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It was, however, an impressive achievement. Stretching for 520 metres across the river, the barrier consists of falling radial gates, as well as rising sector gates that allow for the natural flow of water, and for boats to pass, when laid flat on the river bed. But when raised into position, an operation that takes an hour and a half, the gates stand 20 metres tall. Weighing 3,300 tonnes, each gate can hold back over 9,000 tonnes of water.

On 8 May 1984, the Queen set off from Festival Pier on her barge, the Royal Nore, passing under bridges bedecked with bunting.Just after 3.30pm, shearrived at Woolwich Reach, to behold "the glittering new structure, resembling a row of drowned Sydney Opera Houses" (The Times again). After a short speech, the Queen pressed the button, and the gates swung slowly into action.

In 2014, the Thames Barrier was closed a staggering 48 times. That's impressive and more than a little worrying considering the previous record in 2003 was19 times.