Monday, December 28, 2015

After the Deluge

As I discussed in my piece, Turned Out Wet (Again), we need a new approach to flood management.  We've only had about 1°C of average global surface temperature warming so far, the Paris COP21 agreement promises a 50% chance of limiting warming to 2°, INDCs are heading us to 3° and actual actions are currently on track to push us through 4°.  Whatever the outcome of our endeavours, we should be planning for extreme weather events far more serious than the record rainfall in northern England of December 2015.

So first step is to get government to take climate change seriously and to act accordingly. It's a difficult first step.

And then we need a simple prescriptive framework to apply across river basins and adapt to site specific situations.  Here are some principles:

  1. Slow down the rate at which water enters rivers.
  2. Divert water out of rivers on to land where flooding causes relatively little damage.
  3. Prevent water reaching homes and businesses.
  4. Get water into the sea.

Top of the list, if water doesn't get into the river, the river won't flood!  The whole landscape needs to be looked at in terms of water retention.  The hills of northern England offer great potential.  Their natural vegetation is deciduous woodland and vast swathes of upland Britain should be re-afforested.  The grouse shooters would lose out. Tough on them. We need beavers not game-birds.  A new priority for farmers must be a smarter approach to drainage, allowing the appropriate soil water management for cultivations and pasture but restricting the rate of outflow from the farm overall, with ponds and swales an d wetlands so that heavy rain does not reach rivers in minutes and hours but is retained for days.

At number two, rivers should be engineered to not pass water on downstream quickly.  The dredging lobby have it exactly wrong. Except at the river's mouth, moving water faster downstream just shifts the problem. Rivers need to flood onto their floodplains as soon as possible so we need spillways to land where large volumes can be stored safely and then released slowly.  As with the upland farms, appropriate engineering and management incentives must be provided for farmers on floodplains.  The land has to be made available for flooding, not for housing estates!

Thirdly, flood defences for urban areas need to be improved, raised, strengthened and managed effectively.  That's a continuation of policy already under way, but the point to note is that the cost will be lower and the effectiveness greater if the previous two upstream principles have been dealt with seriously.  Without that, urban defences will sooner or later end in tears.

Finally, the rivers need to discharge to sea as speedily as possible.  It is only here, downstream from vulnerable infrastructure, that there may be local conditions that warrant dredging.  As sea level rises over the coming decades, as it surely will no matter what global warming mitigation measures are adopted, the importance of the three earlier areas for action increases. Discharge to sea is the last resort.


This picture has produced wry smiles around cyberspace.  (If you are the copyright owner do let me know.)  I gather it comes from near Clitheroe where the local planning authority is Ribble Valley Borough Council.  Party political point scorers may like to note that this council comprises 33 Tories, 6 LibDems and an Independent.

As I said, the first step is to get government to take climate change seriously and to act accordingly.

3 Comments:

Blogger Matthew M said...

yup, the image is from the A59 between Billington and Whalley. https://goo.gl/maps/vffCJB29t7H2

1:29 pm  
Blogger Joe Public said...

" ..... rivers should be engineered to not pass water on downstream quickly."

Fine if you're in a downstream village or town; not-so-fine for those in inundated upstream villages & towns.

Who decides the upstream/downstream delineation?

2:41 pm  
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