8th May: The Thames Barrier

On this date in 1984 the Thames Barrier, built to stop flooding in London, was opened by the Queen. 10 things you may not know about the Thames Barrier:

1. The idea of a flood defence across the Thames dates back to at least 1953, when there was a serious flood which killed 300 people. However, any barrier had to be able to let ships through. This engineering problem is why it was the 1980s before the barrier was finished.
2. The idea for the rotating gates was devised by (Reginald) Charles Draper in 1969. He got the idea from the design of the taps on his gas cooker.
3. The Thames Barrier is the world's second-largest movable flood barrier, after the Oosterscheldekering in the Netherlands.
4. It spans 520 metres across the Thames at Woolwich Reach. Its northern bank is in Silvertown in the London Borough of Newham and its southern bank is in the New Charlton area of the Royal Borough of Greenwich.
5. When the Thames barrier is raised the main gate stands as high as a 5 storey building. The four large central gates are 20.1 metres (66 ft) high and weigh 3,700 tonnes.
6. The barrier cost £534 million to build, and at the same time £100 million was spent on boosting the banks of the river for 50 miles to prevent flooding elsewhere - because all the water has to go somewhere if the gate is closed. It costs about £16,000 to close the Thames Barrier on each occasion.
7. Up to February 2016, there have been 176 flood defence closures. It is also raised monthly for testing, with a full test closure over high tide once a year. In 2012, this annual test was scheduled to coincide with the Queen's Jubilee, so the boats taking part in the river pageant could enjoy more stable tides that day.
8. The Thames Barrier flood defence closes when a combination of high tides forecast in the North Sea and high river flows at the tidal limit at Teddington weir indicate that water levels would exceed 4.87 metres (16.0 ft) in central London. On 20 August 1989, hours after the Marchioness disaster, the barrier was closed against a spring tide for 16 hours "to assist the diving and salvage operations"
9. When it was built, the barrier was expected to be used 2–3 times per year. It is now being used 6–7 times per year. The threat of flooding in London has increased due to the slow but continuous rise in high water levels over the centuries (20 cm (8 inches) per century) but also because Britain is tilting up in the north and west, and down in the south and east by up to 5 cm (2 inches) per century due to post-glacial rebound, ie land masses that were weighed down by ice in the ice age springing back up.
10. The barrier has survived 15 boat collisions without serious damage, but boats crashing into it could have very serious consequences. On 27 October 1997, the dredger MV Sand Kite, operating in thick fog, hit one of the Thames Barrier's piers. As the ship sank she dumped her 3,300 tonne load, finally sinking by the bow on top of one of the barrier's gates where she lay for several days. This incident meant the gate couldn't close until the mess was cleared up. If there had been a flood at this time it could have caused £13 billion in flood damage, not to mention potential loss of life.