Thames Barrier, London
These are two photos of the Thames barrier, a flood control structure on the River Thames, constructed between 1974 and 1984 at Woolwich Reach, and first used defensively in 1983. It has been used over 100 times defensively, the last of which was on March 19, 2007. It is the world's second largest movable flood barrier (the largest is the Maeslantkering in The Netherlands). Located downstream of central London, the barrier's purpose is to prevent London being flooded by an exceptionally high tide moving up from the sea, exacerbated by a storm surge. Built across a 523 metre wide stretch of the river, the barrier divides the river into four 61m and two 31m navigable spans and four smaller non-navigable channels between nine concrete piers and two abutments .
In 2005, a suggestion was made public that it might become necessary to supersede the Thames Barrier with a much more ambitious 16 km long barrier across the Thames Estuary.