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> Drainage Snafu, NTC waste public money on uphill drainage
Simon Kirby
post Aug 1 2011, 08:45 PM
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Newbury Town Council have wasted public money installing field drains with the fall going uphill. Even accepting that NTC's grasp of hydrogeology is famously weak, this does seem to be stupendously poor even by their standards of public waste.

Wash Common allotments can flood badly in the winter. It's typical to have several weeks like this anytime into March.


Wash Common was drained in the 1858 enclosure and the four acre site was created with a ditch and hedge all the way round it feeding into the the main Wash Common ditch #1 on the eastern side of the allotments and thence all the way down to Wash Water.

Through years of neglect and mismanagement most of the south ditch has been lost - enclosure boundaries were by law defined by the outside edge of the ditch with the hedge planted on the spoil which was piled on the inside, with the consequence that cheeky neighbours would fill in neglected ditches and gain an extra four or five feet of land. Without the south ditch and with the north ditch regularly blocked site drainage has become a problem.

So the Town Council decided to lay some lateral land drains which would discharge into the site ditches. Unfortunately they've layed them with a 14" fall away from the ditch they're meant to flow into, so the drain is completely useless and all the time and public money spent on materials is completely wasted.

Here's the start of one drain, and you can see the main ditch in the background by the oak trees. The ground level is about 18" below the height profile here, and the drain another 3" below the surface - so the drain is 21" below the height profile.


This is the drain run near the discharge end. The ground is now about 1" below the same height profile, and the land drain another 6" below the surface - so the drain is now 7" below the height profiel - that's 14" higher then where the drain starts.



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Andy Capp
post Aug 1 2011, 09:02 PM
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I don't understand your geological references, but are you saying they have built the drain-away the wrong way round?
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Dodgys smarter b...
post Aug 1 2011, 09:13 PM
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Pardon my ignorance, but are you saying that the end of the pipe is actually higher above sea level than the begining?

Whereas conventional wisdom has it that water flows downhill....
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NWNREADER
post Aug 1 2011, 09:22 PM
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Do I gather the last two posters have managed to clarify in 1 or 2 lines what dear old Simon needed three pages and a book of photos to completely befuddle me over?
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Simon Kirby
post Aug 1 2011, 09:26 PM
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QUOTE (Andy Capp @ Aug 1 2011, 10:02 PM) *
I don't understand your geological references, but are you saying they have built the drain-away the wrong way round?

It's like this:


And the Town Council have installed the drains as in the top diagram, rather than the bottom one.


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Simon Kirby
post Aug 1 2011, 09:27 PM
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QUOTE (Dodgys smarter brother. @ Aug 1 2011, 10:13 PM) *
Pardon my ignorance, but are you saying that the end of the pipe is actually higher above sea level than the begining?

Whereas conventional wisdom has it that water flows downhill....

Quite so.


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user23
post Aug 1 2011, 09:29 PM
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So when the ditch fills up, the water drains down the pipe?

It seems to work much like a overflow on a cistern or basin.
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Simon Kirby
post Aug 1 2011, 09:29 PM
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QUOTE (NWNREADER @ Aug 1 2011, 10:22 PM) *
Do I gather the last two posters have managed to clarify in 1 or 2 lines what dear old Simon needed three pages and a book of photos to completely befuddle me over?

Ah, but hydrogeology is devilishly difficult to explain. Allegedly.


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Simon Kirby
post Aug 1 2011, 09:33 PM
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QUOTE (user23 @ Aug 1 2011, 10:29 PM) *
So when the ditch fills up, the water drains down the pipe?

Fortunately the drain emerges into the ditch at the top, and the ditch is four feet deep, so that won't happen, but it will drain half a dozen extra plots down into the low plots in the first photo.


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user23
post Aug 1 2011, 09:36 PM
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QUOTE (Simon Kirby @ Aug 1 2011, 10:33 PM) *
Fortunately the drain emerges into the ditch at the top, and the ditch is four feet deep, so that won't happen, but it will drain half a dozen extra plots down into the low plots in the first photo.
Not sure what the issue is here, you wouldn't put the overflow at the bottom of the trench, would you?

Surely you'd want it at the top as it appears to be, so the trench can fill right up before being drained away.
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Andy Capp
post Aug 1 2011, 09:43 PM
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QUOTE (Simon Kirby @ Aug 1 2011, 10:26 PM) *
And the Town Council have installed the drains as in the top diagram, rather than the bottom one.

Interesting, but how do you know it is as you describe; without the appropriate gradient?
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Simon Kirby
post Aug 1 2011, 09:44 PM
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QUOTE (user23 @ Aug 1 2011, 10:36 PM) *
Not sure what the issue is here, you wouldn't put the overflow at the bottom of the trench, would you?

Yes, you might well have the outfall at the bottom of the ditch, but the crucial point is that the drain must fall towards the ditch it empties into. The issue is that this 100' run of drain falls 14" uphill, and water doesn't run uphill, so the drain is completely useless and the time and public money spent on the material is completely wasted


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Simon Kirby
post Aug 1 2011, 09:47 PM
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QUOTE (Andy Capp @ Aug 1 2011, 10:43 PM) *
Interesting, but how do you know it is as you describe; without the appropriate gradient?

I pegged out the drain run with height profiles and measured the invert (you can see the profiles in the picture) - it's what you'd do if you were digging a drain (or it was 30 years ago, I guess it's done with GPS now).


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user23
post Aug 1 2011, 09:47 PM
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QUOTE (Simon Kirby @ Aug 1 2011, 10:44 PM) *
Yes, you might well have the outfall at the bottom of the ditch, but the crucial point is that the drain must fall towards the ditch it empties into. The issue is that this 100' run of drain falls 14" uphill, and water doesn't run uphill, so the drain is completely useless and the time and public money spent on the material is completely wasted
Surely an overflow needs flow downhill and this it what it appears to do in your picture.


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Andy Capp
post Aug 1 2011, 09:52 PM
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QUOTE (Simon Kirby @ Aug 1 2011, 10:44 PM) *
Yes, you might well have the outfall at the bottom of the ditch, but the crucial point is that the drain must fall towards the ditch it empties into. The issue is that this 100' run of drain falls 14" uphill, and water doesn't run uphill, so the drain is completely useless and the time and public money spent on the material is completely wasted

Perhaps they will dig another ditch at the low point?
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Simon Kirby
post Aug 1 2011, 09:52 PM
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QUOTE (user23 @ Aug 1 2011, 10:47 PM) *
Surely an overflow needs flow downhill and this it what it appears to do in your picture.

It's not an overflow - the black pipe labeled "Drain" is a land drain, its job is to collect ground water from the surrounding land (it's perferated so the water can get in) and carry the water to the ditch. If the outlet is higher than the surrounding groundwater the groundwater will never flow down the drain and escape into the ditch.


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Simon Kirby
post Aug 1 2011, 09:54 PM
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QUOTE (Andy Capp @ Aug 1 2011, 10:52 PM) *
Perhaps they will dig another ditch at the low point?

That's a bit like the Porridge problem of how to hide the spoil from an escape tunnel - you dig another tunnel to put it in!


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Andy Capp
post Aug 1 2011, 09:58 PM
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QUOTE (Simon Kirby @ Aug 1 2011, 10:54 PM) *
That's a bit like the Porridge problem of how to hide the spoil from an escape tunnel - you dig another tunnel to put it in!

Fair enough...at least they tried and it looks like they did something, eh? tongue.gif
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NWNREADER
post Aug 1 2011, 10:00 PM
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I feel another 'allotment management' serial starting...

Surely the thing to do is to write a simple letter to NTC - as a tenant (which I assume you still are) - and ask a simple "It looks to me like the drain runs uphill...." question?
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Strafin
post Aug 1 2011, 10:14 PM
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Good grief here we go again.....

Why don't you just give up your allotment if it's so bad, honeslty you're like a petulant teenager who thinks he knows better than everyone else all the time. I'm starting to agree with Panda, I think you should get a window box or a garden and be done with it.
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