Monday, February 10, 2014

Dam the Thames to relieve the flood

The answer to yesterday's Thames River Flow Puzzle is that the unusual behaviour was due to the Thames Barrier being raised.

As blogged earlier, there's been enough rain in the last few weeks to give modern day Noahs incentive to finally get building that big boat project, and the Thames valley has gone beyond soggy.

Indeed if you type "River Thames" into the Environment Agencies web site you find there are currently 76 warnings including 14 which are "Severe", meaning there is danger to life.

The map above comes from the BBC web site and shows the most at risk locations.

There is one clear direction the water can flow that would ease the flood risk - down river. But uncontrolled increased river flows could combine with a high tide to drown central London, causing catastrophic damage.

So the Thames Barrier has been raised, to stop the incoming tide and allow as much water as possible to drain out of the Thames valley.

This can be seen in the image below from this brilliant web site (as blogged earlier) grabbed last night:

You can see the levels towards Teddington significantly above predicted as increased flows are released with the barrier closed to hold back the tide.

This is unlike the expected requirement for the Thames Barrier, which was to protect the capital from storm surges coming up the estuary, as happened at Canvey Island in 1953.

So you can indeed relieve a flood by damming a river - by using the Thames Barrier.

But it still looks pretty bad - good luck to all those in the at risk locations.


Tillerman said...

Interesting stuff!

JP said...

There's clearly a lot of engineering and thinking gone into this and yet the river still floods. I think no one planned for such extreme rain rates.