In message <qibegl$d6f$ snipped-for-privacy@dont-email.me, at 09:41:57 on Tue, 6 Aug 2019, Gareth's was W7 now W10 Downstairs Computer snipped-for-privacy@yahoo.com remarked:
That's a different meaning of the word "Aqueduct", being the waterways version of a viaduct.
It doesn't imply the water itself is part of a wider scheme to supply water over a long distance (although sometimes, by coincidence, the two will co-exist).
In message <qibdu3$att$ snipped-for-privacy@dont-email.me, at 09:31:27 on Tue, 6 Aug 2019, NY snipped-for-privacy@privacy.invalid remarked:
They are a form of sluice gate, so it's not a big issue. Paddles can either be in the gates themselves or in tunnels to the side of the gates (and are then called "ground paddles"). Some busy locks have both.
Indefinitely (well, in the timescale of an incident like this). The bottom paddles (and especially bottom ground paddles) unleash massively turbulent water that can be quite a risk for any boats caught up in it. And have been doing it at every lock for hundreds of years.
That's my question. Is it happening and no-one has reported it, or is there some specific reason it's not being used.
That number's too big. A narrow lock of the kind round there is typically 150,000 litres.
There's also some numbers in there for the capacity of pumps used on some waterways to re-circulate the water.
Note also their estimate of ten minutes per lock cycle includes manoeuvring the boat in and out, as well as the actual filling and emptying.
If a canal has been emptied for maintenance (or because a careless boater has left a paddle open overnight) it's perfectly routine to just open all the paddles fully and wait, possibly hours, for the affected levels to restore.
But, seeing how many sacks were delivered, the erosion under the slabs was massive.
In message snipped-for-privacy@outlook.com, at
11:31:36 >>>> I don't see how you can possibly infer that. It's *possible* but given"Within the last few years new valves have been placed in the dam to expedite rapid drawdown in emergencies: presumably, this is happening now."
Although the question being asked in this thread is "if that's the case, why also use lots of pumps".
Once the slabs lifted there would be massive erosion very quickly. That's why you have spillways: if the water overtops anywhere else the earth embankments fail v v quickly.
From the l "What would appear to have happened is that the dam was originally built with a small spillway on the hillside beside the dam. The design standards for spillways then increased, i.e. it became a requirement for the dam to be able to pass a larger flood flow. To provide that, a large central spillway was constructed on the dam surface using slabs laid on the downstream face of the earth embankment. This has the risk that, if the slabs crack, then high velocity water can get underneath the slabs and erode the underlying earthfill and the slabs then settle, and failure of the slabs takes place. This is what appears to have happened here."'
In message snipped-for-privacy@outlook.com, at
12:14:51 on Tue, 6 Aug 2019, Robin snipped-for-privacy@outlook.com remarked:
But let's not forget that without the additional spillway, the dam would probably have collapsed anyway.
Precisely.
If the pumps are draining into the same waterways that the normal exit valves (which now permit rapid drawdown) flow into, then there is no advantage - unless the rate-limiting step is the rate at which water can flow out of the drawdown valves, rather than the rate at which water can flow away from the area.
If the pumps are draining into other waterways (eg rivers rather than the canal system) then there *is* an advantage in using pumps because it avoids overloading the canal - but the photos this morning
Roland Perry submitted this idea :
No need, they could just open one gate and open the paddle/sluice in the other gate.
In message <qibo9q$va7$ snipped-for-privacy@dont-email.me, at 12:28:57 on Tue, 6 Aug 2019, Harry Bloomfield <?.?@NOSPAM.tiscali.co.uk.invalid> remarked:
That's not normally done because too many gates close themselves when your back is turned. Not least because that's a natural effect of the direction of the water flow. But sometimes it's just because they are warped and rather "springy".
NY explained on 06/08/2019 :
Correct, the more vertical the pipe, the less chance of the syphonic action being disturbed, but its difficult to have a large long pipe vertical for any appreciable distance.
Even an hosepipe size, suffers the syphon action being disturbed.
The water's skin (name?) is the main thing which allows it to work well in the smaller pipes. Add in some soap, disrupt the skin and then you have more issues syphoning with even a small diameter pipe.
Surface tension.
In message <qibobm$vhl$ snipped-for-privacy@dont-email.me, at 12:28:56 on Tue, 6 Aug 2019, NY snipped-for-privacy@privacy.invalid remarked:
I'm wondering if they are using both.
The spillways appear to drain into the River Goyt, while the water that's drawn of for the canal is from a valve at the base of the reservoir.
"Harry Bloomfield"; "Esq." snipped-for-privacy@NOSPAM.tiscali.co.uk> wrote in message news:qibp7t$4ij$ snipped-for-privacy@dont-email.me...
Odd that I've never noticed it. But it's something I'll look out for. I presume in a clear pipe you can see air collecting at the top of the pipe and maybe even bubbling up the outlet pipe.
That sounds like the makings of a "try this at home" experiment: siphon first from a "reservoir" of clean tapwater and then from one with a lot of soap in it, using the same pipe laid out in the same way (*). I wonder if the flow rate is noticeably worse with soapy water? Repeat with the outlet of the pipe under water.
(*) Eg at 45 degrees, discharging into a vessel which a) always keeps the output out of water, and then into a vessel which keeps the output under water.
Ah, I wasn't sure if the River Goyt was connected to the canal, in the same way that the River Cherwell and the Oxford Canal intermingle every so often.
Well yes, but that still doesn?t have to have happened over a long period. Did you watch the video and see how much water was flowing over top?
Tim
In message <qibs6b$jo7$ snipped-for-privacy@dont-email.me, at 13:35:14 on Tue, 6 Aug 2019, NY snipped-for-privacy@privacy.invalid remarked:
It's very likely that the canal has its own spillways and sluices into the River Goyt, which would help spread the load. Given that they are almost side by side all the way to Marple.
Last month I was on the waterways west of Nottingham and the Trent and Mersey canal has a "level crossing" with the river Trent at Alrewas.
But I digress; the canal from there towards Burton on Trent has multiple spillways and sluices to channel excess water back into the Trent.
well I don't claim to have any engineering qualifications but it seems to me a plausible answer is in the public statements:
- the spillway was damaged leading to a risk of catastrophic failure,
- there was a lot of water in the reservoir
- water was still coming in at a high rate (and with the risk of more rain to come)
so it seemed like a good idea to lower the level faster than would be possible without the pumps (with the added benefit of being able to send water to different places and so avoid downstream flooding).
To the best of my recollection and belief, all the above is on the public record.
But then some prefer speculation.
Tim Streater explained on 06/08/2019 :
Ta!
well to state the bleeding obvious having pumps and valves will be quicker.
Its only mud and earth, that's why the rush.
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