The London Marathon, Dedicated To The Olympic Games In 2012

Since the Victorian era the Thames has been extensively embanked, and many of its London tributaries now flow underground. The Thames is a tidal river, and London is vulnerable to flooding. The threat has increased over time due to a slow but continuous rise in high water level by the slow 'tilting' of Britain (up in the north and down in the south) caused by post-glacial rebound.
In 1974, a decade of work began on the construction of the Thames Barrier across the Thames at Woolwich to deal with this threat. While the barrier is expected to function as designed until roughly 2070, concepts for its future enlargement or redesign are already being discussed.