Dam Solution?

[Michael GilliganParticipant @michaelgilligan61133]

I thought it might be interesting to see what is being done regarding the Canal:

**LINK**

https://www.towpathtalk.co.uk/event/peak-forest-canal-macclesfield-canal/

[quote] In the meantime we have taken the decision to close the Marple flight on the Peak Forest canal and the Bosley flight on the Macclesfield canal whilst we manage the potential risks. The emergency services are taking every precaution including evacuating local properties and closing local roads to maintain public safety. If you are boating in this area please take every precaution. [/quote]

MichaelG.

[struggling to comprehend the meaning of that final sentence]

[ken king, King DesignParticipant @kenkingkingdesign]

Rod Renshaw, regarding that 32 foot lip …… correct up to a point, but …..

1 atmosphere will push water 32 feet, and no more, up a longer vertical pipe sealed at the top, and evacuated of all air. Here's the 'but', if a syphon pipe is constructed, exceeding the 32 foot draw pipe length, but with an even longer discharge pipe, then it will syphon, provided the entire pipe is initially filled with water. 32 feet of the discharge pipe cancels out 32 feet of drawpipe and we have a working syphon. Of course we must remember when talking about pipe lengths, we should really be referring to differences in water level on each side of the syphon. For practical reasons the draw pipe would have to extend some distance below the surface to avoid whirlpools admitting air into the flow (killing the syphon dead0 and similarly the discharge pipe should end underwater to avoid sneaky bubbles creeping upward against the flow (similar effect).

[Swarf, Mostly!Participant @swarfmostly]

Hi there, all,

I recommend this YouTube channel. **LINK**

Juan Brown gave the most objective running account I was able to find throughout the Oroville Dam situation.

Best regards,

Swarf, Mostly!

[ken king, King DesignParticipant @kenkingkingdesign]

To All, and Rod Renshaw in particular … Having thought a little more I'm not sure I can agree with what I wrote just above. My hypothetical syphon pipe starts off closed at each end, and is filled via a port at the top. When the port is closed we have a filled syphon, but, when either end is opened its column of water would fall to a level 32 feet above the adjacent water surface, because that's as much as 1 atmosphere can support, and we would have a vacuum zone, longer on the discharge side than the draw side, and a static situation i.e. no flow and no help to anyone.

This will teach me to do my thinking before I write, and to do it at home and not on the forum. Apologies all round,

(slinks off, stage left)

[Robert Atkinson 2Participant @robertatkinson2]

KKKD Indeed the top of the "hump" in a syphon cannot be higher than the local air pressure can push the fluid for a simple fluid. One other issue is vapour pressure. Not a real issue with water but I once looked at control system for a project that was sucking solvent out of a tank to a higher level (pump at higher level) I said it would not work, they would just boil the solvent, but hey I'm just an electronics engineer so they didn't listen to me. Then the pump supplier came over from North America to discuss details, took one look at what they we doing and said "no we don't do pumps that defy the laws of physics".

Robert G8RPI.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, many people don't understand about pumping water out of a hole or a container of some sort. Where I used to work many years ago, processing water was a main thing and very often pits and clarifiers had to be pumped out before we could do maintenance work on the pipes or equipment within them. One occasion I remember was a new chap (you know the sort, been everywhere, done everything, got the T shirt, but alas knew Jack nothing at all) this particular day he got the job of rigging up a hired Sykes pump like **LINK** in a pit, he had spent about 3 to 4 hours setting it all up and couldn't get it to pump when he came and asked me to advise him what the problem was, so I went along and as soon as I saw the pump on top of the bank, where Sykes had off loaded it, I said to him "you'll never get that to pump in a month of Sundays" to which he asked why and had to explain that it was beyond the vacuum priming at around 45 feet above the water level and he had to move it down much closer to the water, bit of a lazy git he was, because it was a lot more work to do it in the first place and he wasn't all that pleased that he had to redo his work. Of course when he did finally set it up correctly it pumped full bore on the first attempt.

Regards Nick.

Edited By Nicholas Farr on 05/08/2019 13:25:50

[SillyOldDufferModerator @sillyoldduffer]

Posted by Robert Atkinson 2 on 05/08/2019 12:50:55:

KKKD Indeed the top of the "hump" in a syphon cannot be higher than the local air pressure can push the fluid for a simple fluid. One other issue is vapour pressure. Not a real issue with water …

Robert G8RPI.

Nope, it can – read all about it here. I think we've established that air pressure doesn't push the fluid in a siphon. But the appearance of a vacuum at the top of a siphon would break the column so the 32 ft figure isn't too far off for practical purposes. Bubbles and leaks will break it too.

Another interesting factoid at the end of that link is a figure for the tensile strength of water – about 150Mpa, which I think is amazingly high.

Dave

[duncan webster 1Participant @duncanwebster1]

Firstly, this paper refers to fully degassed water, not a lot of that in Todbrook reservoir. In real life as opposed to some artificial laboratory situation 32 feet is about your lot

Secondly, the definition of tensile strength used by most sensible people refers to a steady uniaxial stress. Not too sure how you apply a uniaxial stress to water as pressure (stress) in a liquid acts in all directions. If they are talking about the stress necessary to rip molecules away from each other the I'll believe them but that bears little relationship to what most people would call strength. Metals fail due to crack propagation, which happens very quickly indeed, but not all bonds broken instantaneously.

[pgk pgkParticipant @pgkpgk17461]

Some fascinating links in this thread.. thanks folks, I enjoyed it so far: siphoning gasses, breaking the 32 foot water head and siphoning in a vacuum. I note the degassed water was tap water so still colligative properties from dissolved minerals – makes me wonder whether the column could be higher still with really pure water +/- what effects one might get with different adhesion/friction values between water and tube.

I recall some talk of using high molecular weight polmers to reduce friction on the boundary layer of boats (back in the 60's) to reduce drag.

pgk

[JAParticipant @ja]

Posted by pgk pgk on 05/08/2019 16:40:30:

I recall some talk of using high molecular weight polmers to reduce friction on the boundary layer of boats (back in the 60's) to reduce drag.

pgk

Just don't get me on that one. They are used in fuel pipe lines in the States and cause havoc. They block filters and can do other horrible things.

JA

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 03/08/2019 10:34:32:

I see the fire service are using pumps to drop the dam at Wahley Bridge.

I'm sure a syphon could have been prefabricated in place with a bore of about 0.5 metres and suitable cocks for priming and control that would shift a lot of water a lot faster.

Easiy and cheaply scaled as well, to match the rate of water loss to the capacity of teh river below.

Neil

.

Just returning to Neil's opening post, for a 'sanity check'

Does anyone actually believe that a "syphon […] with a bore of about 0.5 metres […] would shift a lot of water a lot faster." than the pumps ?

Can any of you clever chaps give a realistic estimate of the flow-rate provided by a 0.5m syphon ?

Thanks

MichaelG.

.

No offence intended; I'm just an interested neihbour

[Alan VosParticipant @alanvos39612]

Posted by SillyOldDuffer on 05/08/2019 13:20:50:

Another interesting factoid at the end of that link is a figure for the tensile strength of water – about 150Mpa, which I think is amazingly high.

Dave

Here is an example of what I suggest is water in tension, in free space. The front of the raft has just bounced up off a rock. The water is being pulled up, not falling down. For those who like to see the numbers: Canon EOS 30D, f/4.5, 1/1600 sec, ISO-400, focal length 200mm

.

[peak4Participant @peak4]

Back to the original story about the dam for a moment.

A friend has just shown me this youtube link via his Facebook page. I thought it worth 11 minutes of my time.

Also as of 05/08/19 this has just popped up on one of my local Facebook groups

"Update: 5:50pm. Staff levels at the dam have dropped by 70% . The army and fire services have left and maybe no more than 40 personnel are on site.
We've had vast amounts of food delivered to Whaley Hall & the sailing club today and no doubt as much at Chapel school n the sports club in Whaley.
Plans for dispersal of non perishable goods are in place for a gesture towards people being repatriated to their homes when the crisis is over. "

[JAParticipant @ja]

Posted by Michael Gilligan on 05/08/2019 18:00:45:

Posted by Neil Wyatt on 03/08/2019 10:34:32:

I see the fire service are using pumps to drop the dam at Wahley Bridge.

I'm sure a syphon could have been prefabricated in place with a bore of about 0.5 metres and suitable cocks for priming and control that would shift a lot of water a lot faster.

Easiy and cheaply scaled as well, to match the rate of water loss to the capacity of teh river below.

Neil

.

Just returning to Neil's opening post, for a 'sanity check'

Does anyone actually believe that a "syphon […] with a bore of about 0.5 metres […] would shift a lot of water a lot faster." than the pumps ?

Can any of you clever chaps give a realistic estimate of the flow-rate provided by a 0.5m syphon ?

Thanks

MichaelG.

.

No offence intended; I'm just an interested neihbour

From my earlier calculations, with the water level at the top of the dam a 0.5m syphon will give a flow of 1480 gal/s (24 million litres/hr). Once the water level has dropped by 10 feet this flow will fall to 1300 gal/s.

I have tried to find the capacity of the pumps being used without success. 24 million litres/hr sounds like an awful lot. However if the bore of the pipe was 1" the flow would be 3.7 gal/s which seems sensible.

JA

[peak4Participant @peak4]

Posted by JA on 05/08/2019 19:10:53:

I have tried to find the capacity of the pumps being used without success. 24 million litres/hr sounds like an awful lot. However if the bore of the pipe was 1" the flow would be 3.7 gal/s which seems sensible.

JA

These from Hereford and Worcester are 7000 litres / Minute apparently

i.e. 420,000 l/hr and there were at least 23 of them working at one time so about 9.6 million l/hr

Bill

Edited By peak4 on 05/08/2019 19:27:11

[duncan webster 1Participant @duncanwebster1]

Ah but, if you just have a syphon, once it empties the dam down to the level of the intake it will suck air and stop working, so you either need an air pump to re-prime the system, or a valve to stop the flow before it gets too low.

Also, the dam is 24m deep (to the water level, never mind the extra height of the wall), so you can't empty it with a syphon anyway

To go off on another tangent (who me?) if the pump design was sufficiently clever and the outlet is well below the inlet, once it is running you could use the pump as a water turbine and use the motor as a generator

[JAParticipant @ja]

I am not sure if I am right or wrong!

Sorry, I am getting old.

JA

Edited By JA on 05/08/2019 20:33:02

[S.D.L.Participant @s-d-l]

Posted by peak4 on 05/08/2019 19:26:08:

Posted by JA on 05/08/2019 19:10:53:

I have tried to find the capacity of the pumps being used without success. 24 million litres/hr sounds like an awful lot. However if the bore of the pipe was 1" the flow would be 3.7 gal/s which seems sensible.

JA

These from Hereford and Worcester are 7000 litres / Minute apparently

i.e. 420,000 l/hr and there were at least 23 of them working at one time so about 9.6 million l/hr

Bill

Edited By peak4 on 05/08/2019 19:27:11

At 7000l/s the velocity in the 150mm / 6" pipe the pump sets have, would be about 1.13m/sec. ie in the normal range of 1 to 3m/s pipe velocity.

for the syphon at 1480 gps is 88800GPM so allowing 18" pipe (500mm as suggested the velocity would be 35m/s

So two questions

how thick does the pipe have to be to resist erosion?

How do you stop it working as a water jet cutter at the discharge?

And in the time we have been speculating on this they have mobalised the pumps and drained 50% or the water

Steve

[old martParticipant @oldmart]

I noticed in the Wikipedia entry for the dam that a proportion of the water feeding the dam is diverted into the stream alongside. I assume that steps have been taken to divert all the incoming water into the stream and that it can handle the increase.

[SillyOldDufferModerator @sillyoldduffer]

Posted by old mart on 06/08/2019 17:41:29:

I noticed in the Wikipedia entry for the dam that a proportion of the water feeding the dam is diverted into the stream alongside. I assume that steps have been taken to divert all the incoming water into the stream and that it can handle the increase.

That I think is another aspect of the problem.

There were already flood warnings in place in the area due to heavy rain making this a bad time to add another million tons of water to the outflow. Emptying the dam would have to be managed to avoid bursting banks downstream. There's nowhere else for the water to go apart from into the valley.

Dave

[old martParticipant @oldmart]

If there is increased rainfall in the area, it will go downstream whether or not the dam exists. Normally the dam would be full and overflowing. They may have to stop pumping if the rain starts in earnest, but there will now be a period of respite before the level rises back to danger levels. That bypass channel on the north side of the dam is of vital importance now.

[Alan VosParticipant @alanvos39612]

Posted by SillyOldDuffer on 06/08/2019 18:06:49:

Emptying the dam would have to be managed to avoid bursting banks downstream. There's nowhere else for the water to go apart from into the valley.

From what I have seen (but can't now find to link to), the only outflow is into the canal system, not the river. Canals are not built to handle high flows. The only way to get a large volume out in a hurry was to take it over the top of the dam, which does take it into the river.

[S.D.L.Participant @s-d-l]

Posted by old mart on 06/08/2019 17:41:29:

I noticed in the Wikipedia entry for the dam that a proportion of the water feeding the dam is diverted into the stream alongside. I assume that steps have been taken to divert all the incoming water into the stream and that it can handle the increase.

The first Chinnok loads before they started on the slipway were to dam the infeed.

Steve

[Michael GilliganParticipant @michaelgilligan61133]

Posted by duncan webster on 05/08/2019 19:53:41:

Ah but, if you just have a syphon, once it empties the dam down to the level of the intake it will suck air and stop working, so you either need an air pump to re-prime the system, or a valve to stop the flow before it gets too low.

Also, the dam is 24m deep (to the water level, never mind the extra height of the wall), so you can't empty it with a syphon anyway

.

I'm not suggesting it would be a practical idea, Duncan … but I'm struggling to understand your assertion.

Please look at the elevation profile that I linked on the 'What did you do today …' thread when it all started.

[quote]

See the Google Earth & Elevation composite on this BBC page:

**LINK**

[/quote]

MichaelG.

.

Edit: or check the contours on the OS Map 

Edited By Michael Gilligan on 06/08/2019 21:57:02

[julian atkinsParticipant @julianatkins58923]

What is this reservoir for?

The canal.

The Marple locks were closed earlier this year for repairs, so the level in the reservoir built up, unlike last year.

I would suggest that had the Marple locks not been closed this year, none of this would have occurred.

I don't know why the canal system hasn't been used to drain the reservoir.

A simple online search indicates the reservoir has been causing problems for many decades.

Cheers,

Julian

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