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

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
>
> 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
>
>
>
>
>
>
> On 01/02/2014 01:20, Simon Fairlie wrote:
>> No its still coming through to me as gobbledegook. Try sending it  
>> in another format.
>> Simon
>> On 31 Jan 2014, at 22:21, ReedMace wrote:
>>
>>> Simon,
>>>
>>> Has my re-submission made it through? I sent it several hours ago  
>>> but haven't seen it posted.
>>>
>>> Rob
>>> On 31/01/2014 17:20, Simon Fairlie wrote:
>>>> Thanks. Some of this came across as gobbledegook, could you send  
>>>> it again?
>>>>
>>>> Simon
>>>>
>>>>
>>>>
>>>>
>>>> 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  
>>>>> 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  
>>>>> 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  
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>>>>> 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.
>>>>>
>>>>> Rob
>>>>
>>>
>>
>

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