Thames Flood Barrier, Woolwich, Greater London
This aerial view shows the construction of the Thames flood barrier. Work started in 1974 and the barrier officially opened in 1984. The Thames Barrier is one of the largest movable flood barriers in the world. The barrier spans 520 metres across the River Thames near Woolwich. It protects 125 square kilometres of central London from flooding caused by tidal surges. It 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.