The Thames was once a much broader, shallower river than it is today. It has been extensively embanked. The Thames is tidal (the Tideway) up to Teddington Lock, and London is vulnerable to flooding by storm surges. The threat has increased over time due to a slow but continuous rise in high water level, caused by both the slow 'tilting' of Britain (up in the north and down in the south) caused by post-glacial rebound and the gradual rise in sea levels due to climate change. The Thames Barrier was constructed across the Thames at Woolwich in the 1970s to deal with this threat, but in early 2005 it was suggested that a ten mile long barrier further downstream might be required to deal with the flood risk in the future.