In message <[EMAIL PROTECTED]>
, Adrian Stott <[EMAIL PROTECTED]> writes
>"Graham Speechley"
><[EMAIL PROTECTED]> wrote:
>
>>re all the suggestions to get through the tunnel at Froghall. IMO the
>>only sensible way would be to construct a lock with a 6" drop after
>>the last run off ( the method used to reduce the level of the lower
>>pound was to remove the 2.5" wooden batton on top of this run off).
>
>That gets us back to the previous question of how deep the pound (and
>the tunnel in particular) is.
It appears to be deep enough at the moment that 3ft draft boats
can get through without problems.
My understanding is that the reasons the water level wasn't
lowered any further during the recent works were mainly:
(1) the runoff weir would need to be rebuilt (rather than just the
planks removed)
(2) there is a culvert under the canal which has been patched in
concrete, and would need to be rebuilt to maintain depth.
Neither of these is insuperable; however they were beyond the
budget that could reasonably be expected to be raised from the
available sources in the timescale of the largely volunteer-run
Destination Froghall project.
But I'm not sure how much further the water level of the canal in
general along this pound could be lowered without giving
problems for deep draft boats. I suspect not very much.
>It won't help to have boats not hitting
>the top if they hit the bottom instead.
>
If there's only (say) 8ft 6in height available between the invert and
the crown (over a typical boat width), then nothing short of
rebuilding the tunnel would get a 3ft draft 6ft headroom boat
through it anyway. (thinks: except perhaps if you tip it on its side?)
But the caisson idea might just get a 6ft high 2ft 6in deep boat
through, while still allowing a 5ft 6in high 3ft deep boat to continue
to use it.
I'm almost starting to believe that this particular whacky idea might
be a goer!
[these measurements are purely illustrative, by the way]
--
Martin Ludgate
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