Carlisle Flood Defences: the one chart I’d like to see

Carlisle flood

Carlisle, in the north of England, has been hit, again, by severe floods. I feel huge sympathy for those whose homes, again, have been damaged by floodwater. The £38 million spent on flood defences by the Environment Agency since the last major floods in 2005 is being described as ineffective. “How could all that money not have protected the houses?” they are being asked.

First of all, the EA never said the defences would protects against all future flooding.

What I’d like to see is a chart like the one above, but with real rain data. All the labelled years were genuine flooding years, but I do not know the actual rain values (apart from the 34.1cm-in-one-hour being reported for 2015). For the purposes of this, I’m using that value of 34 as the index value for 2015.

When setting a flood defence, an agency has to balance cost against the predicted maximum future level of flooding. If the EA predicted in 2005 that there would never be a 34cm deluge, then they wouldn’t waste public money building flood defences that high.

With real data in the above chart, we’d be able to see:

  1. How unprecedented is 2015? (in my chart, it’s 5cm higher than 2005)
  2. What level of rainfall are the flood defences set to protect against? (in my chart it’s higher than 2005 and 1822 flood events)
  3. What predictions do they have for future precipitation levels and how regularly will they be higher than the flood defence level?

If 2015 truly is unprecedented and wholly exceptional, then blame shouldn’t be put on the flood defences.

This post was inspired by memories of the Fukushima disaster. Then, the tsunami which hit the power station was higher than the station’s sea wall.

What do you think? Would this chart help asses the success of the Environment Agencies flood defences? What chart would help you answer the question?

NOTE: don’t forget, the data in the chart is not real. It’s for illustrative purposes only.

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