Ever wondered how London doesn't flood more often given there's a massive great river running right through it (and other, smaller bodies of water).

Your answer is, simply, the Thames Barrier.

If it wasn't for the barrier, based out near Woolwich Arsenal in South East London, areas such as the Houses of Parliament, the Isle of Dogs, the O2 at Greenwich, Tower Bridge, areas of Southwark, and other parts of Central London would all be under water.

And with sea levels continuing to rise, the whole city could be submerged at some point.

The barrier stretches 520m across the river


Yet thanks to the barrier built on the Thames back in 1982, London doesn't have this problem.

The Thames Barrier was built to protect a whopping 48 square miles of London from flooding due to tidal surges.

Essentially, it is closed every time there is a danger of extra water being pushed back up the river by the sea at high tide, therefore causing flooding.

It takes up to 90 minutes for the barrier to fully close

Sometimes it is closed very often in a short space of time, and sometimes a long time passes before it needs to be. The BBC reported that between March 2010 and December 2012, there were no closures at all.

How does it work?

The Thames Barrier is made of 10 steel gates stretching 520m across the river.

When the barrier is open the plates lie on the river floor as if they aren't there at all - so don't go trying to see the barrier unless you know it's closed.

This incredible invention saves 48 square miles of London from flooding

Then when it needs to close to prevent flooding, the plates are rotated upwards.

If predictions are that flooding may occur, the barrier closes just after low tide so an empty reservoir is created for water to flow into.

Interestingly, it takes anywhere between 75 and 90 minutes for the barrier to actually close fully as the gates on the outside move upwards first followed by the middle gates.

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The four main gates weigh an enormous 3,000 tonnes each.

Then the gates stay shut, holding the river water, until the tide turns and the water has reached the same level on both sides, or "equalised", as it is called.

The gates are then opened again for the held water to spill back into the estuary.

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Got a story? Email lucy.skoulding@reachplc.com