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When the barrier is closed, a solid steel wall sealing the upper part of the river from the sea is created, stopping water from flowing upstream towards the capital. The gates can also be part closed in the underspill position, allowing a controlled amount of water to pass under the gate and up the river. Individual gates can be closed in ten minutes but the whole barrier takes around one hour and a half to close completely. The barrier is only reopened once the water level upstream of the barrier matches the water level downstream.
When not in use, the gates rest out of sight in curved recessed concrete cills in the riverbed, which allows river traffic to pass through. Before the barrier was built, the solution to flooding was to build higher and stronger river walls and embankments — a solution that became popular following the Thames Flood Act of and remained an accepted measure until midway through into the 20th century.
Following a report in by Sir Herman Bondi, it was decided that the best solution was bank raising and a flood barrier with movable gates built across the Thames. The Thames Barrier and Flood Protection Act gave powers to carry out this solution and led to the construction of the barrier. The barrier was originally designed to protect London from a very large flood 1 in years up to As climate change and rising sea levels are creating a higher risk of flooding in London, improvements to the Thames Barrier and its flood management are needed to keep on protecting London from flooding.
In the Thames Estuary project headed by Dave Wardle was set 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. Staff wait for the water on both sides to "equalise" - reach the same level - and then the gate is opened and the river water can rush out into the estuary. There is no danger that the water will overwhelm the barrier.
Storm surge from the North Sea, high tides and exceptional fluvial river flow are the three factors that make it necessary. At the moment the major factor is the amount of water flowing down the Thames. That impact is felt up the Thames as far as Molesey - about 12 miles from central London.
That is where the effect of the tide runs out. The closest any flood has come to topping the barrier is 2 meters. So far, so good! On to the final challenge. The gates need constant maintenance to fight rust and water damage. How do you get that done without shutting down? By designing the whole thing for high and dry repairs! The gates come with an extra hydraulic piston to rotate them up and out of the water so workers can repair damage and touch up the paint job.
The barrier has averaged about 5 closures per year since it opened, but if forecasters are right, there could be as many as 30 per year in the coming decades, and that's quite simply because water levels have been rising steadily. Only time will tell how long this astounding work of engineering will hold up.
Skip to main content. Video: How does the Thames Barrier work? Thames Flood Barrier Click for a transcript of the How does the Thames Barrier work? Thames Flood Barrier video. Figure
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