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Thames Barrier
The Thames Barrier is located downstream of central London. Operational since 1982, its purpose is to prevent the floodplain of all but the easternmost boroughs of Greater London from being flooded by exceptionally high tides and storm surges moving up from the North Sea. When needed, it is closed (raised) during high tide; at low tide it can be opened to restore the river's flow towards the sea. Built approximately due east of the Isle of Dogs, its northern bank is in Silvertown in the London Borough of Newham and its southern bank is in the New Charlton area of the Royal Borough of Greenwich. The report of Sir Hermann Bondi on the North Sea flood of 1953 affecting parts of the Thames Estuary and parts of London〔(1953 floods in Canning Town, Accessed 30 December 2010 ) 〕 was instrumental in the building of the barrier.〔(Oxford Dictionary of National Biography entry for Herman Bondi, accessed 30 December 2010 )〕
==Geography and background==
London is vulnerable to flooding and from heavy tides closing in. A storm surge generated by low pressure in the Atlantic Ocean sometimes tracks eastwards past the north of Scotland and may then be driven into the shallow waters of the North Sea. The surge tide is funnelled down the North Sea which narrows towards the English Channel and the Thames Estuary. If the storm surge coincides with a spring tide, dangerously high water levels can occur in the Thames Estuary.
The threat has increased over time due to the slow but continuous rise in high water levels over the centuries (20 cm (8 inches) per century) and the slow "tilting" of Britain (up in the north and west, and down in the south and east by up to 5 cm (2 inches) per century) caused by post-glacial rebound.
In the 1928 Thames flood, 14 people died. After 300 people died in the UK in the North Sea flood of 1953, the issue gained new prominence. Early proposals for a flood control system were stymied by the need for a large opening in the barrier to allow for vessels from the London docks to pass through. When containerization replaced older forms of shipping and Tilbury was expanded, a smaller barrier became feasible with each of the four main navigation spans being the same width as the opening of Tower Bridge.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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