Tuesday, February 11, 2014

Watch those Cumec flow

More on Thames flow and flooding.

The post yesterday showed how the Thames Barrier is being raised to allow as much water as possible to flow down river to ease the floods in the Thames valley.

The figure above shows the Thames flow at Teddington, which is where the river goes from non-tidal to tidal, taken again from this great web site.

The yellow lines show the mean and the {10, 50, 70 ,95) % of time exceeded flow rates, with the 10% of time exceeded flow rate 161 cumecs, a lovely little word that is short for cubic metres per second.

For the last couple of days the actual rate has been pretty constant at 300 cumecs, almost twice the level which is only exceeded for 10% of time. It's so constant that it looks like its being controlled, limited to that rate.

However you have to look at the video of the Thames valley to get a sense of the scale of the flooding: this not just worse than its been in years but decades if not centuries. It will take some time for these waters to subside.

One big debate is on which locations should be protected against floods with the usual complaints about London getting the resources.

However we only have to look at the damage that Sandy did to New York to see the extreme cost of letting down your guard.

Take the underground network as described in this article: consider how London would grind to a halt without its tube and how many billions that would cost. Other measures are possible - such as floodgates within the network itself - but these are no longer functioning because of the Thames Barrier.

The Thames Barrier might have cost a lot but it means that central London assumes that it will be taken care of and hence would actually be vulnerable to flooding without the constant protection of the barrier.

However expensive the flooding is in the Thames valley it would be dwarfed by the cost should central London flood.

Though maybe we should all be thinking more carefully about the cost of global warming.


Tillerman said...

Sounds like my old stomping grounds in the Tames Valley - Slough - Maidenhead - Cookham - Marlow are getting it bad.

I was also sorry to hear about that kayaker lost on the River Usk near Crickhowell. I did go whitewater kayaking on that stretch once and capsized multiple times. I was a total beginner tempted to go along with a local club. I didn't drown, obviously, but that was probably the closest I have ever come to it.

JP said...

Yup, looks pretty bad up there.

Even those playing fields of Eton are underwater.