Some years it hasn't been used at all. When it shut in December , it was reported to be the first closure since March The barrier, made up of 10 steel gates, reaches m 1,ft across the river. When open, the gates lie flat on the river floor and close by being rotated upwards until they block the river. The four main gates span The barrier is closed just after low tide to create an empty "reservoir" for the river flow to fill up. It takes minutes to close it, starting with the gates on the outside until the middle gates are shut.
With no barrier, at high tide, the sea would normally flow up the estuary and into London, pushing the river water back. With all the extra rainfall, this could worsen the flooding. The barrier prevents this from happening. The gates are left shut and the river water is held until the tide turns. Trolleymusic Click here to view Wikimedia source. The Thames Barrier from the north bank of the river at Silvertown, in normal open operation.
Further readings:. Related links:. Print page to PDF. About the author. Alexander Hall is a historian interested in the intersection of science, policy, and the environment, and is currently a visiting scholar at the Institute for Science and Technology Studies at York University, Toronto.
Further articles by this author: The North Sea Flood of Themes Disasters Infrastructure Landscape Transformation. Keywords dams floods rivers storm surge. Explore on map. Javascript is required to view this map. Because the river is tidal from Teddington weir all the way through London, this is only a problem at high tide , which prevents the floodwater from escaping out to sea.
From Teddington the river is opening out into its estuary , and at low tide it can take much greater flow rates the further one goes downstream. When the river is in flood upstream, if the gates are closed shortly after low tide, a huge empty volume holds behind the barrier which can act as a reservoir to hold the floodwater coming over Teddington weir.
Most river floods will not fill this volume in the few high tide hours when the barrier needs to be closed. If the barrier was not there, the high tide would fill up this volume instead, and the floodwater could then spill over the river banks in London. About a third of the closures up to were to prevent flooding caused by heavy rain to the west of London.
In the s there were four closures, 35 closures in the s, and 75 closures in the first decade of this century. The rate of closures is above that predicted, and is increasing rapidly. An incident that was potentially catastrophic for London occurred on 27 October As the ship started to sink she dumped her 3, tonne load of aggregate, finally sinking by the bow on top of one of the barrier's gates where she lay for several days.
Initially the gate could not be closed as it was covered in a thick layer of gravel. During periods of heavy rain there is a danger during high tide that the extra water in the Thames will be pushed back up river by the sea, causing flooding in the capital. The gates normally lie flat on the floor of the Thames but can be rotated upwards until they block the river. The danger of widespread flooding is very real and not just to property which, if it were to occur would no doubt run into billions of pounds worth of damage.
The barrier has been fully closed for flood defence reasons times from the day it opened until October
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