Thames Flood Barrier

Thames Flood Barrier, movable barrier on the Thames at Woolwich, London, designed to protect central London from floods from tidal surges caused by North Sea gales, and from a general rise in sea level until at least 2030. Construction of the barrier began in 1972 and it was officially opened in May 1984 by the Queen, although it had been operational since October 1982. The 523-m (1,716-ft) span across the river is divided by nine reinforced concrete piers, which are founded on solid chalk, 15 m (50 ft) below the level of the river. The vast structure, which is the world’s largest movable flood barrier, consists of 51,000 tonnes of steel, including 36,000 tonnes of structural steel and 10,000 tonnes of steel reinforcement, and 210,000 cu m (280,000 cu yds) of concrete. Each of the gates weighs 3,000 tonnes and when raised, each of the four main gates is as high as a five-storey building. Over 4,000 people were engaged in the building work, which cost nearly £500 million.

In 1965 government plans were made to build a barrier following many flooding incidents in London’s history, the most recent and significant having been in 1953, when over 300 people were drowned and 65,000 hectares (160,000 acres) of farmland were flooded with salt water. As of mid-2005, the barrier had been raised more than 80 times, largely as a precautionary measure, to protect London from flooding. The gates are raised monthly for a test period lasting over two hours at low tide, and annually for a full day to test the effects of a full tide. The closure dates are set a few months in advance. The barrier can also be closed within minutes should the need arise. Although the major flood threat to central London is from surge tides occurring during or immediately after severe weather conditions, other environmental factors may cause concern over the long term. The high water level at London Bridge has risen by about 75 cm (2y ft) each century, and global warming and the melting of the polar ice caps are believed to be causing global sea levels to rise at about 1 metre (just over 3 ft) per century.

See alsoFlood Control.