The Thames Barrier was designed to protect the capital from flooding until at least the year 2030. Based on the estimates of rising sea levels at the time it was designed, there is no current reason to doubt that the Barrier will serve its full intended term. The high water level at London Bridge has risen by about 75 cm each century, due to a combination of melting Polar ice caps, the tilting of the British Isles towards Europe (the south of England is sinking at a rate of 30 cm per century), and the activities of man. Currently, due to global warming some authorities now suggest that sea levels are estimated to start rising globally at about a meter per century. However, the major flood threat to central London, which the Barrier was designed to prevent, is from surge tides. These are 'humps' of water, crossing the Atlantic and which usually pass north of Britain but, if driven by northerly winds (usually in winter), may descend into the North Sea and cause flooding on the surrounding coasts and along the banks of the tidal Thames.
London was often subjected to flooding in the past and there are reports of this happening in the Middle Ages and during Tudor times. However, it was not until the 1953 floods, during which over 300 people were drowned and 160,000 acres of farmland were flooded with salt water, that the Government appointed a committee to develop anti-flooding measures. Several schemes were proposed and rejected and it was only in 1965 that government consent was given to build a barrier. The design by Charles Draper was chosen from 41 proposals because it was compact, attractive, practical and environmentally sensitive. The Thames Barrier, cost over £1 billion and took 8 years to build. The Barrier was inaugurated by The Queen in 1984 and spans 520 meters across the Thames at Woolwich Reach. Half a million tons of concrete were used in the coffer dams inside which the piers were built and in the sills on which the gates rest on the river bed when not in service. 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 and, with the two gate arms, weighs 3,700 tonnes. The hydraulic power packs (sheltered by the stainless steel shells) are electrically driven; using 3 alternative supplies, routed via each of the riverbanks and, should these options become unavailable, from 3 on-site power generators. Since its completion in 1982, the Thames Barrier has been raised more than 20 times, largely as a precaution, to protect London from flooding.
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