Walking close to London Bridge office, alongside the Thames, we noticed that the river was looking rather high.

On Tuesday (June 18), we were strolling opposite the Shard, and noticed the river water in the Thames was splashing up against the banks and getting pretty close to the pavement.

Seeing as 27-hours of storms is on the horizon, it got us thinking, why do the water levels in London's river rise and fall so irregularly?

And how and who decides when to close the Thames Barrier in Woolwich to prevent the city flooding?

The water is close to splashing over the path

While it seems like there's no rhyme or reason as to when waters are high or low in The Thames, there is in fact an explanation.

It's all to do with the tide.

A whole bunch of things affect tides, meaning that high tides never occur exactly 12 hours apart. They are influenced by the Earth's rotation, the Moon's rotation around the Earth and the rotation of both of these around the sun. Science!

It didn't seem to put the boats off

With the Thames, high tide on each day happens an hour, or sometimes more, later than it did the previous day.

It is ridiculously confusing but basically high tide is at different times each day and this means water levels in the river go up and down very irregularly.

Look how close that is to the path!

So if you're looking at the water levels right now and also thinking about the fact floods are predicted, you might be feeling a bit concerned.

This is where the Thames Barrier comes in.

Run and maintained by The Environment Agency, the Thames Barrier is one of the largest movable flood barriers in the world, which aims to prevent London from flooding.

It spans 520 metres across the river near to Woolwich and protects the 125 square kilometres that is central London from flooding caused by tidal surges.

This happens on the same day London has been issued with flood warnings

It will usually close when a storm hits and sometimes when there is high flow over Teddington Weir, the latter of which would prevent parts of west London flooding.

As of March 2019, the Thames Barrier had been closed 184 times since it started operating in 1982.

So we trust that the Thames Barrier will close if the predicted storm gets bad overnight. We don't fancy wet feet while traveling to work, thank you.

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