Fwd: Somerset levels - monks that dug them knew undredged rivers do not drain
chapter7 at tlio.org.uk
Sat Feb 1 17:32:55 GMT 2014
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
> 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.
> On 01/02/2014 01:20, Simon Fairlie wrote:
>> No its still coming through to me as gobbledegook. Try sending it
>> in another format.
>> On 31 Jan 2014, at 22:21, ReedMace wrote:
>>> Has my re-submission made it through? I sent it several hours ago
>>> but haven't seen it posted.
>>> On 31/01/2014 17:20, Simon Fairlie wrote:
>>>> Thanks. Some of this came across as gobbledegook, could you send
>>>> it again?
>>>> On 31 Jan 2014, at 16:12, <reedmace at ymail.com> wrote:
>>>>> Speaking as a professional hydrologist there are merits on all
>>>>> sides of the argument. But 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
>>>>> 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
>>>>> because of a gradient in the river bed, but a gradient in the
>>>>> water level. This is how pumping works - it artificially lowers
>>>>> the water level at one location creating a
>>>>> 24mIzM5O3QgaGVscCBlaXRoZXIg YmVjYX VzZSB0a GV5IHd
>>>>> ��A 533;r vRA
>>>>> �bFW6W'Bf���G2���'#&# 65533;& #65533;'#A 533;A
>>>>> GJlaW5nIGJyb2tlbiBvbiBhIGZhaXJseSByZWd1bGFy IGJhc2 lzIG92Z
>>>>> GUg 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 25
>>>>> years ago.
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