London England
Thames Barrier
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Unfortunately for London the southwest corner of England is slowly sinking 30cm (1 ft) per century. Although this change is small it is enough to put London at risk of flooding when there is a high tide and the wind blows from the wrong direction. In 1953, during an exceptional surge tide, 300 people were drowned and a huge area was flooded with salt water including 160,000 acres of farmland. To counter this threat, the Thames barrier was built and completed in 1982 The design, chosen from 41 proposals, minimises interference with the natural flow of the river and does not pose a headroom restriction for shipping. Charles Draper, the engineer got the idea for the radial gates which normally are parked flat below the bed of the river, from the design of a domestic gas-tap. The Thames Barrier, took 8 years to build and was opened by HM The Queen in 1984. It spans 520 metres (a third of a mile) across the Thames at Woolwich Reach (where the river is comparatively straight and the chalk-with-flints strata was suitable for its construction). Half a million tonnes of concrete were used to build the piers and sills on which the gates rest when not being used. When raised, each of the 4 main gates is as high as a 5-storey building and as wide as the opening of Tower Bridge (61 metres). Each gate, with it's controlling arm, weighs 8,700 tonnes. The gates are moved by electrically powered "hydraulic power packs". Since electrical power is crucial for Barrier operation, the barrier has three alternative supplies and there are 3 on-site power generators. Since its completion, the Thames Barrier has been raised more than 25 times as a precaution to protect London from flooding.
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