[Diggers350] Fwd: Somerset levels - monks that dug them knew undredged rivers do not drain

[david bangs]

I think George M, Simon F, and Rob's contributions have been good and convincing. 

Just to say...a very large proportion of the Somerset Levels (the southern moors like West Sedgemoor, Kings Sedgemoor, Wet Moor etc; the middle moors, like Westhay and Tealham Moors etc) are SSSIs, and some sites are National Nature Reserves.

I'm a long way away, but I don't hear enough defending this statutory national interest compared to wot I hear from reactionary MPs, Owen Paterson, and farmers.  

There's a good article on the attempts to staunch the steep decline of breeding waders on the Levels in the latest 'British Wildlife' (ironically titled 'Farewell to the Silver Meadows ?' Vol 25, Dec 2013, pages 77 - 84), in which it's made clear that much of the critical wildlife interest has shrunk back to the conservation-owned nature reserves, DESPITE the statutory protection of so much of the wider Levels.

Many folk will remember the appalling farmer-conservationist clashes of thirty plus years ago over drainage in the Levels, after which which some amelioration of the worst farmer / drainage board practices was made.

It's not just changes in upstream farming that need to take place (as all three above have suggested). 

I, for one, can't take the prescriptions of angry Levels farmers seriously (dredge and dredge) when its impossible to separate their contributions from the feeling that their own farming practices are damaging and anti-social,

Dave Bangs


  ----- Original Message ----- 
  From: Simon Fairlie 
  To: diggers350 at yahoogroups.com 
  Sent: Saturday, February 01, 2014 5:32 PM
  Subject: [Diggers350] Fwd: Somerset levels - monks that dug them knew undredged rivers do not drain


    



  Begin forwarded message:


    From: ReedMace <reedmace at ymail.com>
    Date: 1 February 2014 15:30:30 GMT
    To: Simon Fairlie <chapter7 at tlio.org.uk>
    Subject: Re: Somerset levels - monks that dug them knew undredged rivers do not drain


    Simon,

    Perhaps you can post it on my behalf. 


    Speaking as a professional hydrologist there are merits on all sides of the argument. Clearly it is an emotive subject, particularly for those experiencing the flooding at the moment. However, I'm not sure emotive language and insults help anyone.

    The main issues are of scale and importance. Although I don't know the Somerset Levels well, I do know the Fens - a similarly engineered expanse of very flat drains.

    The Levels are man-made and therefore cannot be directly compared to natural catchments whereby water flows through the soil structure towards the lowest point, as they do in the upper catchments. Likewise the channels have been artificially created/widened. But because the area is flat, flow occurs, not due to the gradient in the river bed, but the gradient in the water level. This is how pumping works - it artificially lowers the water level at one location creating a surface (or energy) gradient that allows water to move towards it. A head (difference in water levels) is therefore required in order for flow to take place between two points.

    In this type of situation, dredging will help a little, but only by increasing storage - it does not increase the energy gradient. This is George Monbiot's point. The better solutions by far are to do with changes in upstream land use, retaining soil on the land and improving soil structure, as both George and Simon say. Undertaken over reasonably large areas these activities will retain water longer in the upper catchment, while it is still widely distributed, rather than trying to deal with it once it is all concentrated in the water course. Note that any tree planting undertaken in this regard must not be done by ploughing perpendicular to the contours (as is Forestry Commision practice). This will result in the opposite effect, creating hundreds of additional drainage conduits straight downhill in the upper catchment that wil significantly increase the rate of catchment response to rainfall, exacerbating the situation downstream.

    More drains won't help either because they won't increase the discharge capacity of the system - only the available storage - which, as George points out, is minuscule compared to the volume of flood water. The monks built the drains, not to cope with flooding from the upper catchment, but to drain the local soils so they could grow wool and food. It's a bit like saying we need a few extra minis to evacuate a city. Of course there is always the option of building vast concrete trapezoidal channels for the water, which is what has been done in the Fens (and in places like Jeddah and Kuwait City to cope with the sudden and enormous volumes of desert floods).

    However, the fact that twice the average monthly rainfall has fallen in the wettest January on record actually also plays a small part in this. That is a LOT of water. To say the flooding is entirely a man-made disaster is, I hope, hyperbole (notwithstanding the rather banal comment that there's been 'no cloudburst or crazy storm'). But the solutions advocated in the farmer's article, I suggest, really wouldn't make much difference to the situation at all - the land is flat (that is, neither uphill nor downhill - no disrespect to Mr Temperley) and dredging 15 miles won't change that.

    As for the claim that last year saw a once-in-a-lifetime flood, so we shouldn't have another one the next year, well that's often the way climate works and statistics don't. And it's no secret that climate statistics have been being broken on a fairly regular basis over the last 20 years. Are we experiencing a shift in the climate's underlying statistical distribution? I am just slightly surprised no-one has mentioned climate change - warmer, wetter winters are exactly what have been predicted since I first started working on climate-change impacts over 25 years ago.

    Rob











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