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Another odd one - I'm going through a few older reports at the moment (not mine) and have twice come across reference to concerns that a waterway is "too deep" to be useful. The two projects are completely independent, one in northern England and one in Wales, one involves a lake and one an old shipping dock. They have nothing in common other than I happen to know of them both - one of them I've never even worked on 

 

Why would a water body be "too deep" for a narrow boat? I can see that a large expanse of water might make some users anxious, and in some conditions be difficult, e.g. a strong wind picking up waves, but too deep? 

 

Thoughts anyone?

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Parts of the Cannock Extension got too deep to be safe, ( from a civil engineer's perspective, not from a boating viewpoint)  because the ground underneath was subsiding at a great rate and the banks were being raised to keep the water in.

 

Other parts of the BCN, the T&M and the L&L  suffered similarly from subsidence, but a programme of filling in the base of the canal to keep the water depth down was successful in maintaining a safe canal ( though a part of the T&M was eventually diverted through a new line IIRC).

 

N

 

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8 minutes ago, BEngo said:

Parts of the Cannock Extension got too deep to be safe, ( from a civil engineer's perspective, not from a boating viewpoint)  because the ground underneath was subsiding at a great rate and the banks were being raised to keep the water in.

 

Other parts of the BCN, the T&M and the L&L  suffered similarly from subsidence, but a programme of filling in the base of the canal to keep the water depth down was successful in maintaining a safe canal ( though a part of the T&M was eventually diverted through a new line IIRC).

 

N

 

 

Interesting - could you explain? Presumably it's the integrity of the canal that is a problem rather than the use of a boat on it? 

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A friend of my brother-in-law drowned pre-2000 in one of the midlands canals suffering from subsidence, too deep for the usual "stand up" solution to work and they couldn't find him in the muddy water. Not sure of the exact circumstances (BIL is now in Canada), drink may have been involved, but on a normal depth canal he'd probably have survived.

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16 minutes ago, magpie patrick said:

 

Interesting - could you explain? Presumably it's the integrity of the canal that is a problem rather than the use of a boat on it? 

  Yes it is structural integrity of the lower sides of the waterway.

 

If you have a canal in flat ground the pressure of the water acts on the bottom and the sides which are substantial enough to resist it.   Now lower the ground, but leave the canal water surface  where it is.  The canal has become deeper and so the water pressure at the base rises:  Rho Gee aitch and all that.  You need an embankment to hold  the water.  Lower the ground some more and you need to raise  both the top of the bank and reinforce the sides ( widen the foot ) of the embankment to sustain even more water pressure.  If you don't strengthen the embankment you can fill the canal in and reduce the depth.  There are still embankment integrity considerations, because of the added infill, but they are not as pressing.

 

On the Cannock Extension the ground was subsiding as much as a foot a week.  BW could just about keep up with raising the top of the banks, by adding course after course to the brick banks but widening the base of the embankments was simply not practicable.  Money was not the problem , as the NCB were paying for the work, it was construction capacity either to widen or to backfill when things like the 360 degree hydraulic digger did not exist.

 

There are some pictures of  Churchbridge top lock,  Rumer Hill Junction and of the bank raising works,  by Philip Weaver,  that show the scale of the problem. 

 

N

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At Armitage on the T and M the canal was affected by subsidence from the nearby pit, hence the raised concrete banks. The powers-that-be decided the canal was too deep so tipped in material - trouble is they rather overdid it.....

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If you cruise on the Northern BCN you can easily see evidence of the raised banks with the courses of bricks, or concrete, disappearing at an angle into the water.

And not just the banks but bridge decks also had to be raised. You can see on some flat deck bridges, the abutments have cutouts to enable jack's to be inserted to raise the deck then the height of the abutments rsised.

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1 hour ago, magpie patrick said:

Another odd one - I'm going through a few older reports at the moment (not mine) and have twice come across reference to concerns that a waterway is "too deep" to be useful. The two projects are completely independent, one in northern England and one in Wales, one involves a lake and one an old shipping dock. They have nothing in common other than I happen to know of them both - one of them I've never even worked on 

 

Why would a water body be "too deep" for a narrow boat? I can see that a large expanse of water might make some users anxious, and in some conditions be difficult, e.g. a strong wind picking up waves, but too deep? 

 

Thoughts anyone?

Could it be the consequences of a breach?

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51 minutes ago, BEngo said:

  Yes it is structural integrity of the lower sides of the waterway.

 

If you have a canal in flat ground the pressure of the water acts on the bottom and the sides which are substantial enough to resist it.   Now lower the ground, but leave the canal water surface  where it is.  The canal has become deeper and so the water pressure at the base rises:  Rho Gee aitch and all that.  You need an embankment to hold  the water.  Lower the ground some more and you need to raise  both the top of the bank and reinforce the sides ( widen the foot ) of the embankment to sustain even more water pressure.  If you don't strengthen the embankment you can fill the canal in and reduce the depth.  There are still embankment integrity considerations, because of the added infill, but they are not as pressing.

 

 

Part of the Bridgewater canal was "in filled" if that's the correct term, to reduce the depth of water during the seventies for just this reason.  A mate of mine who had been for years a volunteer restoring canals worked on it, and thought it rather ironic being paid during the week to fill one canal in and paying at the weekend to dig another out.

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19 minutes ago, MoominPapa said:

I can't see a problem with depth for powered boats. The Gloucester and Sharpness is pretty deep and no one raises any objections. 

Good point - I'd forgotten about the G&S, which is a bit remiss of me given I had a boat based on it at one time!

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