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The Thames Barrier is one of the largest movable flood barriers in the world. The Environment Agency runs and maintains the Thames Barrier as well as the capital’s other flood defences.

The barrier spans 520 metres across the River Thames near Woolwich, and it protects 125 square kilometres of central London from flooding caused by tidal surges.

It became operational in 1982 and has 10 steel gates that can be raised into position across the River Thames. When raised, the main gates stand as high as a five-storey building and as wide as the opening of Tower Bridge. Each main gate weighs 3,300 tonnes.
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The River Thames rises at Thames Head in Gloucestershire ST9899 on the slopes of the Cotswolds and flows generally eastward to its mouth near Southend in Essex. At 215 miles long it is the second longest river in Britain after the Severn, and the longest entirely within England. Link

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