In message , at 10:35:43 on Mon, 5 Aug
2019, Martin Brown remarked:

Can the canals not cope with a greater flow of water into them than
was originally intended?

Canals are designed to lose as little water as possible with each lock
movement

True, but...

so they cannot be used to dump water into without seriously damaging
the mechanisms. There is usually a small bypass for any excess.

.... just because they are designed to be as water-efficient as possible
doesn't mean you can't open the paddles at both ends of a lock and quite
safely result in a significant flow. Every now and again a boater does
that by accident, but it's routine to do it to drain a pound for
maintenance, or to bring water through to fill up a drained pound.

--
Roland Perry

In message , at 12:54:36 on Mon, 5 Aug 2019,
NY remarked:

What is the typical number of lock-emptyings per hour that a canal can
handle?

Depends on the size of the paddle-gear. But one lock every five minutes
is about the fastest one would normally achieve.

However, you don't do it like that - the correct method is to open the
paddles both ends, which will at least double the flow compared to a
lock full ever five minutes.
--
Roland Perry

In message , at 15:09:59 on Mon, 5 Aug 2019,
Gareth's was W7 now W10 Downstairs Computer
remarked:
What is the typical number of lock-emptyings per hour that a canal
can handle? I presume there is a peak rate which is a lot higher than
the sustained 24-hours-a-day rate ;-)

When boating, you reckon on 1/4 hour per lock

That includes all the gate closing and opening, as well as the
possibility that the lock has to be prepared first (which doubles the
water-flowing time). And the time taken to manoeuvre the boat in and
out.

(except perhaps on the Tardebigge flight on the Worcs & Brum canal,
about 7 minutes, especially if you've got a crew member lock-wheeling
at the next lock, making sure it is ready for you to go directly in).

Flights are usually quicker for all these reasons.

But to make water (rather than boats) flow, you don't do it a lock at a
time; you simply open all the paddles simultaneously.
--
Roland Perry

In message , at 12:19:41 on Mon, 5 Aug 2019,
Gareth's was W7 now W10 Downstairs Computer
remarked:
On 05/08/2019 10:37, Mike Clarke wrote:
On 05/08/2019 10:18, NY wrote:

I may have missed something in the earlier new reports, but why are
they having to *pump* water out of the reservoir? Is there a problem
with taking water out in the normal way? I think it's a canal feeder
reservoir. Can the canals not cope with a greater flow of water into
them than was originally intended?
Canals weren't designed to carry a significant flow of water.

With the exception of the LLangollen Canal which is a source of
drinking water for Manchester.

There are many canals which are mainly water-feeders. I expect the first
few miles of the canal at Whaley Bridge are (for the Ashton and
Macclesfield canals).
--
Roland Perry

In message , at
04:30:31 on Mon, 5 Aug 2019, Cynic remarked:

Hopefully "lessons will be learned" and dam designs include means of
drainage for maintenance or emergency. A bloody big tap at the bottom?

This dam was last drained in order to maintain that very facility. The
question is: why aren't they using it?

Or perhaps it is being used and the civilians writing in the press
haven't noticed.
--
Roland Perry

In message , at 12:53:39 on Mon, 5
Aug 2019, charles remarked:

How do you remove surplus water from the canal without opening the locks -
which are specifically designed to stop that happening.

Actually, the locks have paddles at both ends which are specifically
designed to promote the flow of water. It's just that normally you don't
open both ends at once.
--
Roland Perry

Tim+ Wrote in message:
Harry Bloomfield, Esq. wrote:
Tim+ expressed precisely :
Nonsense! Have you actually tried it? I?ve syphoned water plenty of times
and never had to keep the outlet underwater.

As have I, it works fine on small pipes, but have you tried it on
larger pipes - I have. Air rushes up above the water from the discharge
pipe and soon breaks the syphon effect.

Only if your inlet is obstructed and the flow is very low. Otherwise the
water velocity is too fast to allow air back up.

If the discharge is kept below
water, then air cannot be sucked in.


Well that?s true, but not necessary in my experience.

Tim


Perhaps it's your experience that's lacking...
--
Jim K


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

"Roland Perry" wrote in message
...
In message , at 12:54:36 on Mon, 5 Aug 2019,
NY remarked:

What is the typical number of lock-emptyings per hour that a canal can
handle?

Depends on the size of the paddle-gear. But one lock every five minutes is
about the fastest one would normally achieve.

However, you don't do it like that - the correct method is to open the
paddles both ends, which will at least double the flow compared to a lock
full ever five minutes.

Ah yes, I was forgetting about the paddles (I, too, would have called them
sluice gates, but I stand corrected) which would be needed anyway to fill
the pound before the upper gates could be opened.

So if you needed to transfer a lot of water in the shortest time, how long
could you leave the paddles of all the locks open without damaging the
sides/bottom of the canal by scouring? I wonder if that is being done in
parallel with pumping water directly out of the reservoir into non-canal
waterways?

450,000 litres every 5 minutes by the lock paddles is a hell of a lot more
water than 7000 litres every minute by the pumps. But that is making the big
assumption that it is OK to drain a lock's worth of water every five minutes
as a sustained rate over many hours, rather than just a burst rate with gaps
in between.

In article ,
The Natural Philosopher wrote:
On 05/08/2019 22:38, NY wrote:
"The Natural Philosopher" wrote in message
...
On 05/08/2019 12:30, Cynic wrote:
Hopefully "lessons will be learned" and dam designs include means of
drainage for maintenance or emergency. A bloody big tap at the
bottom?

No lessons will be learnt. Virtue signalling is more important than
actually achieving reliable infrastructure.

Hopefully the company that did the annual safety inspection and
pronounced the dam "absolutely fine" is well insured - because all the
work over the past week will have cost a lot.

It probably WAS absolutely fine until the heavy rain


Doubt it. From the photos of the concrete break up, the earth underneath
had been washed away for weeks beforehand.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

On 06/08/2019 05:51, The Natural Philosopher wrote:
On 05/08/2019 22:38, NY wrote:
"The Natural Philosopher" wrote in message
...
On 05/08/2019 12:30, Cynic wrote:
Hopefully "lessons will be learned" and dam designs include means of
drainage for maintenance or emergency. A bloody big tap at the
bottom?

No lessons will be learnt. Virtue signalling is more important than
actually achieving reliable infrastructure.

Hopefully the company that did the annual safety inspection and
pronounced the dam "absolutely fine" is well insured - because all the
work over the past week will have cost a lot.

It probably WAS absolutely fine until the heavy rain

Maybe. Certainly the heavy rain stressed one edge of the spillway to a
point where it failed catastrophically. There may well have been a
latent fault that allowed water to get behind one of the panels.

I bet you the work hasnt cost even one useless wind turbine yet

I dunno. The flying time of the Chinnooks must be mounting up by now.
£24k an hour of flying time according to defence minister Bob Ainsworth:

https://www.pprune.org/archive/index.php/t-302234.html

And that was about a decade ago - Hansard entry:

https://publications.parliament.uk/p...71126w0001.htm

Military aircraft operating costs. Apache is nearly double that!

--
Regards,
Martin Brown

On 05/08/2019 22:25, The Natural Philosopher wrote:
On 05/08/2019 12:19, Gareth's was W7 now W10 Downstairs Computer wrote:
On 05/08/2019 10:37, Mike Clarke wrote:
On 05/08/2019 10:18, NY wrote:

I may have missed something in the earlier new reports, but why are
they having to *pump* water out of the reservoir? Is there a problem
with taking water out in the normal way? I think it's a canal feeder
reservoir. Can the canals not cope with a greater flow of water into
them than was originally intended?

Canals weren't designed to carry a significant flow of water.

With the exception of the LLangollen Canal which is a source of
drinking water for Manchester.

Then technically it is an aqueduct...


The Pontcysyllte Aqueduct is famous on that canal.

On 05/08/2019 15:18, Tim+ wrote:
Harry Bloomfield, Esq. wrote:
Chris Green formulated the question :
Is there a size of pipe above which a syphon won't work because the
water empties out of the down pipe without 'sucking' the water above
down? It works well with small pipe because, I assume, surface
tension helps to prevent the water from 'dropping out'.

Correct!

Air has to be prevented from being sucked up the discharge pipe, by
having the discharge under water, or the syphon will be immediately
lost with a larger pipe.

Nonsense! Have you actually tried it? Ive syphoned water plenty of times
and never had to keep the outlet underwater.

He is basically right at least when the pipe size becomes large enough
that the water in free fall near the middle allows bubbles of air to get
back up the top side where friction slows the water to a crawl.

Talking large diameter pipes here not thin hose pipes. It doesn't take
much to prevent air going back up the outlet but it does require a bit
of care or bubbles of air will rise up the top side of the pipe and
accumulate at the top of the syphon.

--
Regards,
Martin Brown

On 06/08/2019 09:32, charles wrote:
Doubt it. From the photos of the concrete break up, the earth underneath
had been washed away for weeks beforehand.


Actually, that was an interpretation that I had not considered.

"Martin Brown" wrote in message
...
On 05/08/2019 15:18, Tim+ wrote:
Harry Bloomfield, Esq. wrote:
Chris Green formulated the question :
Is there a size of pipe above which a syphon won't work because the
water empties out of the down pipe without 'sucking' the water above
down? It works well with small pipe because, I assume, surface
tension helps to prevent the water from 'dropping out'.

Correct!

Air has to be prevented from being sucked up the discharge pipe, by
having the discharge under water, or the syphon will be immediately
lost with a larger pipe.

Nonsense! Have you actually tried it? Ive syphoned water plenty of times
and never had to keep the outlet underwater.

He is basically right at least when the pipe size becomes large enough
that the water in free fall near the middle allows bubbles of air to get
back up the top side where friction slows the water to a crawl.

Talking large diameter pipes here not thin hose pipes. It doesn't take
much to prevent air going back up the outlet but it does require a bit of
care or bubbles of air will rise up the top side of the pipe and
accumulate at the top of the syphon.

I presume if the outlet pipe is kept vertical, there is less chance of air
bubbles getting in at the bottom and rising to the top of the loop, breaking
the siphon.

I imagine few of us have ever used a very fat pipe for siphoning - normally
it is something about the diameter of a hosepipe.

Is it purely the diameter that causes air to bubble back up, or is it the
ratio of the diameter to the length? In other words, is a short fat pipe
more likely to do it than a longer pipe of the same diameter?

charles wrote:
In article ,
The Natural Philosopher wrote:
On 05/08/2019 22:38, NY wrote:
"The Natural Philosopher" wrote in message
...
On 05/08/2019 12:30, Cynic wrote:
Hopefully "lessons will be learned" and dam designs include means of
drainage for maintenance or emergency. A bloody big tap at the
bottom?

No lessons will be learnt. Virtue signalling is more important than
actually achieving reliable infrastructure.

Hopefully the company that did the annual safety inspection and
pronounced the dam "absolutely fine" is well insured - because all the
work over the past week will have cost a lot.

It probably WAS absolutely fine until the heavy rain


Doubt it. From the photos of the concrete break up, the earth underneath
had been washed away for weeks beforehand.

I dont see how you can possibly infer that. Its *possible* but given the
speed with which fast moving water can erode riverbanks etc, it seems
equally likely that this was an €œacute€� event.

Tim

--
Please don't feed the trolls

"Tim+" wrote in message
...
Doubt it. From the photos of the concrete break up, the earth underneath
had been washed away for weeks beforehand.

I dont see how you can possibly infer that. Its *possible* but given the
speed with which fast moving water can erode riverbanks etc, it seems
equally likely that this was an €œacute€� event.

The BBC article about the dam yesterday or the day before had comments by
various dam experts who were alarmed by the amount of vegetation that had
been growing in the cracks between the concrete slabs in the weeks/months
before. They said that this suggested that water had been getting through
the spillway concrete into the earth fill below. So it's possible that the
problem had been going on for a while. I presume it's a lot worse when the
spillway is actually carrying water than when the only water is rainwater
falling on the slabs.

In article
, Tim+
wrote:
charles wrote:
In article , The Natural Philosopher
wrote:
On 05/08/2019 22:38, NY wrote:
"The Natural Philosopher" wrote in message
...
On 05/08/2019 12:30, Cynic wrote:
Hopefully "lessons will be learned" and dam designs include means
of drainage for maintenance or emergency. A bloody big tap at the
bottom?

No lessons will be learnt. Virtue signalling is more important than
actually achieving reliable infrastructure.

Hopefully the company that did the annual safety inspection and
pronounced the dam "absolutely fine" is well insured - because all
the work over the past week will have cost a lot.

It probably WAS absolutely fine until the heavy rain


Doubt it. From the photos of the concrete break up, the earth
underneath had been washed away for weeks beforehand.

I don‘t see how you can possibly infer that. It‘s *possible* but given
the speed with which fast moving water can erode riverbanks etc, it seems
equally likely that this was an ”acute• event.

If the water had been going over the slipway, then I'd agree with your
suggestion. But it wasn't.

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

"charles" wrote in message
...
I don't see how you can possibly infer that. It's *possible* but given
the speed with which fast moving water can erode riverbanks etc, it seems
equally likely that this was an "acute. event.

If the water had been going over the slipway, then I'd agree with your
suggestion. But it wasn't.

I thought on the day that the news first broke about Whaley Bridge there was
a video which showed a lot of water cascading over the full width of the
spillway. I got the impression that this was a recent video dating from a
day or so earlier, with the implication that it was after this that they
slabs were found to be cracking.


Interesting that https://www.bbc.co.uk/news/uk-englan...shire-49247226
shows them taking the outlet of the pumps over the lower part of the
spillway on the opposite side to the collapse. I'd have thought they'd want
to avoid any more water flowing over the spillway in case of undermining of
the earth fill beneath the concrete.

charles wrote:
In article
, Tim+
wrote:
charles wrote:
In article , The Natural Philosopher
wrote:
On 05/08/2019 22:38, NY wrote:
"The Natural Philosopher" wrote in message
...
On 05/08/2019 12:30, Cynic wrote:
Hopefully "lessons will be learned" and dam designs include means
of drainage for maintenance or emergency. A bloody big tap at the
bottom?

No lessons will be learnt. Virtue signalling is more important than
actually achieving reliable infrastructure.

Hopefully the company that did the annual safety inspection and
pronounced the dam "absolutely fine" is well insured - because all
the work over the past week will have cost a lot.

It probably WAS absolutely fine until the heavy rain


Doubt it. From the photos of the concrete break up, the earth
underneath had been washed away for weeks beforehand.

I don‘t see how you can possibly infer that. It‘s *possible* but given
the speed with which fast moving water can erode riverbanks etc, it seems
equally likely that this was an ”acute• event.

If the water had been going over the slipway, then I'd agree with your
suggestion. But it wasn't.


It had been going over the spillway though.
https://www.bbc.co.uk/news/uk-englan...shire-49189955

It only needed the grouting to fail between the slabs for erosion of the
soil beneath to begin.

Tim
--
Please don't feed the trolls

On 06/08/2019 11:09, NY wrote:
"charles" wrote in message
...
I don't see how you can possibly infer that. It's *possible* but given
the speed with which fast moving water can erode riverbanks etc, it
seems
equally likely that this was an "acute. event.

If the water had been going over the slipway, then I'd agree with your
suggestion.Â* But it wasn't.

I thought on the day that the news first broke about Whaley Bridge there
was a video which showed a lot of water cascading over the full width of
the spillway. I got the impression that this was a recent video dating
from a day or so earlier, with the implication that it was after this
that they slabs were found to be cracking.


Interesting that
https://www.bbc.co.uk/news/uk-englan...shire-49247226 shows them
taking the outlet of the pumps over the lower part of the spillway on
the opposite side to the collapse. I'd have thought they'd want to avoid
any more water flowing over the spillway in case of undermining of the
earth fill beneath the concrete.

Indeed. The spillway was being asked to do its job. But ISTM as yet
unclear if the problem was lack of maintenance, poor design, or more
water than it was designed to handle.

Some rather more than averagely informed comments are at
https://www.sciencemediacentre.org/expert-reaction-to-news-that-the-whaley-bridge-dam-has-been-damaged/


--
Robin
reply-to address is (intended to be) valid

In message , at 09:41:57 on Tue, 6 Aug 2019,
Gareth's was W7 now W10 Downstairs Computer
remarked:

Canals weren't designed to carry a significant flow of water.

With the exception of the LLangollen Canal which is a source of
drinking water for Manchester.

Then technically it is an aqueduct...

The Pontcysyllte Aqueduct is famous on that canal.

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).
--
Roland Perry

In message , at 09:31:27 on Tue, 6 Aug 2019,
NY remarked:
"Roland Perry" wrote in message news:h7aW3xpsdSSdF
...
In message , at 12:54:36 on Mon, 5 Aug
2019, NY remarked:

What is the typical number of lock-emptyings per hour that a canal
can handle?

Depends on the size of the paddle-gear. But one lock every five
minutes is about the fastest one would normally achieve.

However, you don't do it like that - the correct method is to open
the paddles both ends, which will at least double the flow compared
to a lock full ever five minutes.

Ah yes, I was forgetting about the paddles (I, too, would have called
them sluice gates, but I stand corrected)

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.

which would be needed anyway to fill the pound before the upper gates
could be opened.

So if you needed to transfer a lot of water in the shortest time, how
long could you leave the paddles of all the locks open without damaging
the sides/bottom of the canal by scouring?

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.

I wonder if that is being done in parallel with pumping water directly
out of the reservoir into non-canal waterways?

That's my question. Is it happening and no-one has reported it, or is
there some specific reason it's not being used.

450,000 litres

That number's too big. A narrow lock of the kind round there is
typically 150,000 litres.

https://www.whatdotheyknow.com/reque...4783/attach/17
/Water%20Management%20FAQ%20s%20parts%201%20and%202 .pdf

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.

every 5 minutes by the lock paddles is a hell of a lot more water than
7000 litres every minute by the pumps. But that is making the big
assumption that it is OK to drain a lock's worth of water every five
minutes as a sustained rate over many hours, rather than just a burst
rate with gaps in between.

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.
--
Roland Perry

In article
,
Tim+ wrote:
charles wrote:
In article
, Tim+
wrote:
charles wrote:
In article , The Natural Philosopher
wrote:
On 05/08/2019 22:38, NY wrote:
"The Natural Philosopher" wrote in message
...
On 05/08/2019 12:30, Cynic wrote:
Hopefully "lessons will be learned" and dam designs include means
of drainage for maintenance or emergency. A bloody big tap at the
bottom?

No lessons will be learnt. Virtue signalling is more important than
actually achieving reliable infrastructure.

Hopefully the company that did the annual safety inspection and
pronounced the dam "absolutely fine" is well insured - because all
the work over the past week will have cost a lot.

It probably WAS absolutely fine until the heavy rain


Doubt it. From the photos of the concrete break up, the earth
underneath had been washed away for weeks beforehand.

I don‘t see how you can possibly infer that. It‘s *possible* but given
the speed with which fast moving water can erode riverbanks etc, it
seems equally likely that this was an ”acute• event.

If the water had been going over the slipway, then I'd agree with your
suggestion. But it wasn't.


It had been going over the spillway though.
https://www.bbc.co.uk/news/uk-englan...shire-49189955

It only needed the grouting to fail between the slabs for erosion of the
soil beneath to begin.

But, seeing how many sacks were delivered, the erosion under the slabs was
massive.
--

--
from KT24 in Surrey, England
"I'd rather die of exhaustion than die of boredom" Thomas Carlyle

In message , at
11:31:36 on Tue, 6 Aug 2019, Robin remarked:
On 06/08/2019 11:09, NY wrote:
"charles" wrote in message
...
I don't see how you can possibly infer that. It's *possible* but given
the speed with which fast moving water can erode riverbanks etc, it
seems
equally likely that this was an "acute. event.

If the water had been going over the slipway, then I'd agree with your
suggestion.* But it wasn't.
I thought on the day that the news first broke about Whaley Bridge
there was a video which showed a lot of water cascading over the full
width of the spillway. I got the impression that this was a recent
video dating from a day or so earlier, with the implication that it
was after this that they slabs were found to be cracking.
Interesting that
https://www.bbc.co.uk/news/uk-englan...shire-49247226 shows them
taking the outlet of the pumps over the lower part of the spillway on
the opposite side to the collapse. I'd have thought they'd want to
avoid any more water flowing over the spillway in case of undermining
of the earth fill beneath the concrete.

Indeed. The spillway was being asked to do its job. But ISTM as yet
unclear if the problem was lack of maintenance, poor design, or more
water than it was designed to handle.

Some rather more than averagely informed comments are at
https://www.sciencemediacentre.org/e...s-that-the-wha
ley-bridge-dam-has-been-damaged/

"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".
--
Roland Perry

On 06/08/2019 11:58, charles wrote:
In article
,
Tim+ wrote:
charles wrote:
In article
, Tim+
wrote:
charles wrote:
In article , The Natural Philosopher
wrote:
On 05/08/2019 22:38, NY wrote:
"The Natural Philosopher" wrote in message
...
On 05/08/2019 12:30, Cynic wrote:
Hopefully "lessons will be learned" and dam designs include means
of drainage for maintenance or emergency. A bloody big tap at the
bottom?

No lessons will be learnt. Virtue signalling is more important than
actually achieving reliable infrastructure.

Hopefully the company that did the annual safety inspection and
pronounced the dam "absolutely fine" is well insured - because all
the work over the past week will have cost a lot.

It probably WAS absolutely fine until the heavy rain


Doubt it. From the photos of the concrete break up, the earth
underneath had been washed away for weeks beforehand.

I don€˜t see how you can possibly infer that. It€˜s *possible* but given
the speed with which fast moving water can erode riverbanks etc, it
seems equally likely that this was an €�acute€¢ event.

If the water had been going over the slipway, then I'd agree with your
suggestion. But it wasn't.


It had been going over the spillway though.
https://www.bbc.co.uk/news/uk-englan...shire-49189955

It only needed the grouting to fail between the slabs for erosion of the
soil beneath to begin.

But, seeing how many sacks were delivered, the erosion under the slabs was
massive.
--

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 link I posted earlier:

'Chris Binnie, Visiting Professor, University of Exeter, Water Engineer
specialising in dams and water resources development and Fellow of the
Academy of Engineering, said:

"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."'



--
Robin
reply-to address is (intended to be) valid

In message , at
12:14:51 on Tue, 6 Aug 2019, Robin remarked:

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 link I posted earlier:

'Chris Binnie, Visiting Professor, University of Exeter, Water Engineer
specialising in dams and water resources development and Fellow of the
Academy of Engineering, said:

"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."'

But let's not forget that without the additional spillway, the dam would
probably have collapsed anyway.
--
Roland Perry

"Roland Perry" wrote in message
...
"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".

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
https://www.bbc.co.uk/news/uk-englan...shire-49247226 show the pumps
discharging onto the emergency spillway half way down on the opposite side
to the collapse, so into the same place that the spillways and the normal
drawdown valves go, which is presumably the canal.

Roland Perry submitted this idea :
However, you don't do it like that - the correct method is to open the
paddles both ends, which will at least double the flow compared to a lock
full ever five minutes.

No need, they could just open one gate and open the paddle/sluice in
the other gate.

In message , at 12:28:57 on Tue, 6 Aug 2019,
Harry Bloomfield remarked:
Roland Perry submitted this idea :
However, you don't do it like that - the correct method is to open
the paddles both ends, which will at least double the flow compared
to a lock full ever five minutes.

No need, they could just open one gate and open the paddle/sluice in
the other gate.

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".
--
Roland Perry

NY explained on 06/08/2019 :
I presume if the outlet pipe is kept vertical, there is less chance of air
bubbles getting in at the bottom and rising to the top of the loop, breaking
the siphon.

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.

I imagine few of us have ever used a very fat pipe for siphoning - normally
it is something about the diameter of a hosepipe.

Even an hosepipe size, suffers the syphon action being disturbed.


Is it purely the diameter that causes air to bubble back up, or is it the
ratio of the diameter to the length? In other words, is a short fat pipe more
likely to do it than a longer pipe of the same diameter?

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.

In message , at 12:28:56 on Tue, 6 Aug 2019,
NY remarked:
"Roland Perry" wrote in message
...
"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".

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

I'm wondering if they are using both.

- but the photos this morning
https://www.bbc.co.uk/news/uk-englan...shire-49247226 show the
pumps discharging onto the emergency spillway half way down on the
opposite side to the collapse, so into the same place that the
spillways and the normal drawdown valves go, which is presumably the
canal.

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.
--
Roland Perry

"Harry Bloomfield"; "Esq." wrote in
message ...
NY explained on 06/08/2019 :
I imagine few of us have ever used a very fat pipe for siphoning -
normally it is something about the diameter of a hosepipe.

Even an hosepipe size, suffers the syphon action being disturbed.

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.

Is it purely the diameter that causes air to bubble back up, or is it the
ratio of the diameter to the length? In other words, is a short fat pipe
more likely to do it than a longer pipe of the same diameter?

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.

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.

"Roland Perry" wrote in message
...
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.

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.

charles wrote:
In article
,
Tim+ wrote:
charles wrote:
In article
, Tim+
wrote:
charles wrote:
In article , The Natural Philosopher
wrote:
On 05/08/2019 22:38, NY wrote:
"The Natural Philosopher" wrote in message
...
On 05/08/2019 12:30, Cynic wrote:
Hopefully "lessons will be learned" and dam designs include means
of drainage for maintenance or emergency. A bloody big tap at the
bottom?

No lessons will be learnt. Virtue signalling is more important than
actually achieving reliable infrastructure.

Hopefully the company that did the annual safety inspection and
pronounced the dam "absolutely fine" is well insured - because all
the work over the past week will have cost a lot.

It probably WAS absolutely fine until the heavy rain


Doubt it. From the photos of the concrete break up, the earth
underneath had been washed away for weeks beforehand.

I don‘t see how you can possibly infer that. It‘s *possible* but given
the speed with which fast moving water can erode riverbanks etc, it
seems equally likely that this was an ”acute• event.

If the water had been going over the slipway, then I'd agree with your
suggestion. But it wasn't.


It had been going over the spillway though.
https://www.bbc.co.uk/news/uk-englan...shire-49189955

It only needed the grouting to fail between the slabs for erosion of the
soil beneath to begin.

But, seeing how many sacks were delivered, the erosion under the slabs was
massive.

Well yes, but that still doesnt have to have happened over a long period.
Did you watch the video and see how much water was flowing over top?

Tim


--
Please don't feed the trolls

In message , at 13:35:14 on Tue, 6 Aug 2019,
NY remarked:
"Roland Perry" wrote in message
...
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.

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.

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.

https://www.openstreetmap.org/#map=16/52.7336/-1.7441

A month earlier that crossing was closed because the Trent was flooded a
good 4ft above what's normal for the time of year. That's an awful lot
of sideways flowing water.

But I digress; the canal from there towards Burton on Trent has multiple
spillways and sluices to channel excess water back into the Trent.
--
Roland Perry

On 06/08/2019 12:03, Roland Perry wrote:
In message , at
11:31:36 on Tue, 6 Aug 2019, Robin remarked:
On 06/08/2019 11:09, NY wrote:
"charles" wrote in message
...
I don't see how you can possibly infer that. It's *possible* but given
the speed with which fast moving water can erode riverbanks etc, it
seems
equally likely that this was an "acute. event.

If the water had been going over the slipway, then I'd agree with your
suggestion.Â* But it wasn't.
Â*I thought on the day that the news first broke about Whaley Bridge
thereÂ* was a video which showed a lot of water cascading over the
full width ofÂ* the spillway. I got the impression that this was a
recent video datingÂ* from a day or so earlier, with the implication
that it was after thisÂ* that they slabs were found to be cracking.
Â* Interesting that
https://www.bbc.co.uk/news/uk-englan...shire-49247226 shows them
taking the outlet of the pumps over the lower part of the spillway on
the opposite side to the collapse. I'd have thought they'd want to
avoidÂ* any more water flowing over the spillway in case of
undermining of theÂ* earth fill beneath the concrete.

Indeed.Â* The spillway was being asked to do its job. But ISTM as yet
unclear if the problem was lack of maintenance, poor design, or more
water than it was designed to handle.

Some rather more than averagely informed comments are at
https://www.sciencemediacentre.org/e...s-that-the-wha
ley-bridge-dam-has-been-damaged/

"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".

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.


--
Robin
reply-to address is (intended to be) valid

Tim Streater explained on 06/08/2019 :
Surface tension.

Ta!

On 06/08/2019 12:28, NY wrote:
"Roland Perry" wrote in message
...
"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".

Precisely.

well to state the bleeding obvious having pumps and valves will be quicker.

On 06/08/2019 11:58, charles wrote:

But, seeing how many sacks were delivered, the erosion under the slabs was
massive.

Its only mud and earth, that's why the rush.

"Robin" wrote in message
...
Although the question being asked in this thread is "if that's the case,
why also use lots of pumps".

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.

The one thing I've not seen mentioned anywhere is whether they have been
emptying the reservoir by the normal route (valves draining into canal
system) in addition to the much-publicised pumping operation. I presume they
have, but it's not (that I've seen) been mentioned.