The Thames Barrier with its iconic steel hoods.

The large, stainless steel ‘hoods’ on each pier of the Thames barrier are what make this London landmark so instantly recognizable to both tourists and locals alike. But while people may find it easy to recognize they might not understand how it works.

With this in mind, Humans Invent went on a guided tour with Operations Manager, Steve East, to find out exactly how the Thames Barrier keeps Londoners dry.

Designing flood defence

First of all, however, a quick history lesson is needed to explain its origins. Over the centuries London has been subject to serious flooding. In 1928, 14 people died and thousands were made homeless when a tidal surge poured over the Thames embankment. It wasn’t until 1953 however, after the North Sea Flood killed 307 people in the UK, that plans were made to defend London from future floods.

520 meters of steel effectively stops the incoming tide

Lengthy debates ensued about how to create a barrier that could both defend against tidal surges and let ships pass through. The breakthrough came in 1966 when Sir Hermann Bondi was commissioned by the Government to write a report on flood defence; he concluded that a moveable barrier was the best solution.

The Thames Barrier Act was passed in 1972 with construction beginning in 1974 – it was officially opened by the Queen in 1984. Since then it has only been used on 124 occasions for defence purposes.

The bad weather over Christmas and the New Year saw the barrier close five times in one month. But while there maybe periods when the barrier is closed frequently, there are also long stretches of time when it remains open. East says, “Before the recent closures it hadn’t closed in anger since March 2012.”

One of the gates in closed position.

When it comes to understanding how it works, East says the concept is simple: “It puts a wall of steel right across the river – 520 meters of steel effectively stops the incoming tide from going into central London.”

London’s steel wall

With hard hats on, we walk onto the barrier from the south bank to get a closer look at what, on the surface, is a simple idea but in detail is an ingenious concept. The four main gates are 61 meters long and weigh 3,3000 tonnes, which is the same weight as 6 fully loaded Jumbo Jets. These are flanked by two 31m gates either side. The floodgates are circular segments in cross section that are turned by enormous, hydraulic rocker beams.

What is clever about the design is that the floodgates can be raised to allow some water to flow underneath so that the upstream and downstream equilibrium can be maintained as much as possible.

Every single system is backed up and there is usually a backup to the backup.

From the first pier we climb down a metal staircase right to the bottom where a huge tunnel burrows along under the riverbed. As we walk along this tunnel, East tells me that when ships pass through you can hear their propellers.

We climb out onto the middle pier where East points towards the navigation lights that tell vessels if the gates are open or closed. He jokes, “We have a highly sophisticated navigation light system, you either get a big red cross or a big green arrow.”

The UK’s biggest ships are able to pass through the main four barriers. East says, “The largest vessel we’ve got in the navy at the moment is HMS Ocean that came up to be a military platform during the Olympics and that got through. You probably wouldn’t be able to get the American aircraft carriers through though.”

One of the pistons used to open and close the gates.

Reliable and resilient

As we walk back to dry land East tells me that the whole system, which is controlled electronically, is backed up in case something goes wrong. He says, “The whole concept of the barrier is reliability and resilience. If we get a problem of a technical nature when we are trying to use the barrier, we don’t stop and fix it, we move onto the next system. Every single system is backed up and there is usually a backup to the backup.

East adds, “It would be fairly career limiting if the Prime Minister was standing in the House of Commons in his wellies because we let through a tide we shouldn’t have and we said, ‘sorry Prime Minister we’ll get it right next tide.’”

After this brief tour of the Thames Barrier it is clear to see that London is safe from flooding. Let’s just hope the city doesn’t need the assistance of the U.S. Navy anytime soon.

For more information go to: Environment Agency

Photo credit: ThamesBarrier-1 and -2 by the Environment Agency.


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