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Dam Solution?

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Neil Wyatt03/08/2019 10:34:32
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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

charadam03/08/2019 10:44:32
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Yes, Neil.

But who's going to risk a mouthful of dirty water?

Bazyle03/08/2019 10:49:03
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Maybe not. A syphon can only apply one atmosphere to overcome the friction per 30 ft pipe but a pump can be configured to apply more. I think their bigger problem is where to put the water as the river is full.

idea they should have configured all the loos in the town to be fed from the reservoir. Then if they supplied free beer to all households the natural course of things would reduce the level involving symphonic action.

ega03/08/2019 10:59:32
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Posted by charadam on 03/08/2019 10:44:32:

Yes, Neil.

But who's going to risk a mouthful of dirty water?

Or worse. I once attempted to drain a flooded single story flat roof with a garden hose by this method and the rush of water to the back of my mouth had me (standing on the ground) fighting for breath.

Circlip03/08/2019 11:01:01
982 forum posts

idea they should have configured all the loos in the town to be fed from the reservoir.

Extra water supply pipes to each household? Who wants to be a plumber, Yipeeeeee.

Regards Ian.

SillyOldDuffer03/08/2019 11:21:54
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Posted by Bazyle on 03/08/2019 10:49:03:

Maybe not. A syphon can only apply one atmosphere to overcome the friction per 30 ft pipe...

Or maybe that's wrong too!

I think I'm correct in saying that no-one understands how siphons work. Air-pressure might have some effect, but can't be the main mover because siphons work in a vacuum. Another hypothesis suggests gravity provides the force rather as the weight of a length of chain pulled over a lip might cause the rest to follow. But this requires us to believe that water is strong enough to pull a large mass of water along behind it, and water has almost no tensile strength. Hmmm.

I wonder if the Fire Brigade are siphoning already? The press aren't noted for technical accuracy, and they might assume that a siphon started by a fire engine pump was still being mechanically pumped. Dunno.

Dave

Nigel Graham 203/08/2019 11:36:01
427 forum posts

I wondered about syphons, too, but whichever method's used the water has to be released somewhere, and that seems only to be a river already swollen, and the canal - but the latter may be effective by judicious opening of lock and side-spill hatches down-hill.

We can only watch and hope that the reservoir can be drained as quickly and safely as possible. The first need is to render the area safe enough for everyone to return home.

I would guess proper repairs will take a long time and might necessitate replacing the entire dam face.

++--

As for the town's lavatories....

I recall a former work colleague describing his parental home's arrangements in a "Coronation Street" style, Victorian housing-estate, in Leeds I think.

The necessaria at the ends of the back yards were flushed by rain-water from the roof down-spouts filling flop-jacks below the outhouse floors. Inevitably, in dry weather, down the yard had a certain, umm, ambience; whilst in wet, the place resounded with the constant " whoosh! crash! " of lots of flop-jacks all working away.

The homes including my grandparents' in Nottingham's similar Hyson Green estate also had brick outhouses beyond the tiny back gardens. Plush ones though, due to these new-fangled, high-level, cast-iron syphonic cisterns supplied from the mains water. (T'other grandparents over in Arnold were even better-off: their 1930s home's loo was indoors, off the side of the back porch.)

JA03/08/2019 11:57:00
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Posted by SillyOldDuffer on 03/08/2019 11:21:54:
Posted by Bazyle on 03/08/2019 10:49:03:

Maybe not. A syphon can only apply one atmosphere to overcome the friction per 30 ft pipe...

 

Or maybe that's wrong too!

I think I'm correct in saying that no-one understands how siphons work. Air-pressure might have some effect, but can't be the main mover because siphons work in a vacuum. Another hypothesis suggests gravity provides the force rather as the weight of a length of chain pulled over a lip might cause the rest to follow. But this requires us to believe that water is strong enough to pull a large mass of water along behind it, and water has almost no tensile strength. Hmmm.

I wonder if the Fire Brigade are siphoning already? The press aren't noted for technical accuracy, and they might assume that a siphon started by a fire engine pump was still being mechanically pumped. Dunno.

Dave

Sorry, siphons are simple. A bit of fluid dynamics -

Looking at the BBC news site the dam is about 45 ft. Let us have a siphon pipe, 1 foot diameter, full of water from and to the bottom of either side of the dam. With the dam full the water pressure difference between the leak surface and bottom of the dam is

                    height of water x density of water = 45 x 62.4 [lb/ft^3] = 2808 [lbf/ft^2] = 19.2 [lbf/in^2]

This drive the flow of water whose velocity can be calculated using Bernoulli's equation (really conservation of energy). The velocity in the pipe is

                   square root of (2 x pressure difference / water density) = (32.2 x 2 x 2808 / 62.4)^0.5 = 54 ft/s

                  [the 32.2 is required because imperial units  gets into a bits of a mess when handling mass and force]

 The water flow rate can then be calculated for the full reservoir

                   water velocity x pipe cross sectional area = 54 x 3.1415/2 x 1^2 = 85 ft^3/s = 530 gallons/s

This flow will reduced as the water falls and as already pointed out will cease when the water pressure at the top of the siphon approaches a vacuum.

I am sure that some one has posted a similar reply during the twenty minutes it has taken me to post this.

Edited By JA on 03/08/2019 12:27:02

Ian Johnson 103/08/2019 12:23:19
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Apparently the reservoir was originally a supply water feed basin for the canal and lock systems. Local news info!

Michael Gilligan03/08/2019 12:47:06
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Posted by Ian Johnson 1 on 03/08/2019 12:23:19:

Apparently the reservoir was originally a supply water feed basin for the canal and lock systems. Local news info!

.

.... and that is what it remains

See my posts [yesterday] on the "What did you do ... ?" thread.

MichaelG.

Michael Gilligan03/08/2019 12:48:21
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Posted by Ian Johnson 1 on 03/08/2019 12:23:19:

Apparently the reservoir was originally a supply water feed basin for the canal and lock systems. Local news info!

.

.... and that is what it remains

See my posts [yesterday] on the "What did you do ... ?" thread.

**LINK**

MichaelG.

Neil Wyatt03/08/2019 13:03:04
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It's also a huge liability for the CRT, which is having to cope with the loss of government funding that helped it move over to the charitable sector. As well as disastrous for the people of Whaley Bridge, it could kybosh their finances.

Neil

Michael Gilligan03/08/2019 13:04:33
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Here is one that I didn't post yesterday: **LINK**

https://www.newcivilengineer.com/latest/engineers-battle-night-save-derbyshire-dam-02-08-2019/

[please note the publication date though]

.

I have just returned from a walk, and can confirm that even more roads in the area are closed, and there is a significant Police presence ensuring compliance !

Rain and thunderstorms are forecast for tomorrow.

MichaelG.

Michael Gilligan03/08/2019 13:20:42
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road_closures.jpg

Martin of Wick03/08/2019 15:08:43
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Siphons are a practical solution for rapid drain down in situations where it is clear there are no valve arrangements to discharge water in quantity.

A company I used to work for employed just such a mechanism to supply the transmission pumps, for circumstances when the usual draw off valve arrangements were not available (usually due to statutory reservoir inspections). Volumes could be maintained at up to 80 million litres per day via an 18 inch diameter siphon - limited by pump capacity and need to maintain reasonable suction conditions to protect the pump impellers.

If the calculation above is correct, 500 gallons/s approximates to 190 million litres per day, factor in a few losses and say 150 Ml/d should be achievable.

Compare that to the current rate of pumping - approx. 96 million litres day according to BBC (not clear whether this was the rate of pumping or the net water removed).

I suppose there are practical issues with sourcing and handling large diameter pipe quickly, but I would have thought the water companies or their contractors would have material available.

After the Rotherham dam incident, we were all told by our political masters to determine the cost of remedials to emplace rapid drain-down arrangements in critical infrastructure that did not have appropriate facilities. When the great and the good saw the cost, they turned white at the gills and ran for the hills.

As I recall we did consider siphons, but these were not put forward on the grounds of aesthetics - serried ranks of blue plastic pipe snaking over the dam was the issue, so they said...

Adam Mara03/08/2019 16:25:23
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The Enviroment Agency have some massive pumps, used locally at the recent flooding in Wainfleet. Pretty sure it was reported they had 6 running, and 6 in reserve, and they were brought in from all around the country. Trouble is it takes a few days get pumps in and running. A search on Google Images for 'Wainfleet Pumps' gives some idea of the size of them!

Pete Rimmer03/08/2019 17:27:55
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Posted by SillyOldDuffer on 03/08/2019 11:21:54:
Posted by Bazyle on 03/08/2019 10:49:03:

Maybe not. A syphon can only apply one atmosphere to overcome the friction per 30 ft pipe...

Or maybe that's wrong too!

I think I'm correct in saying that no-one understands how siphons work. Air-pressure might have some effect, but can't be the main mover because siphons work in a vacuum. Another hypothesis suggests gravity provides the force rather as the weight of a length of chain pulled over a lip might cause the rest to follow. But this requires us to believe that water is strong enough to pull a large mass of water along behind it, and water has almost no tensile strength. Hmmm.

'Tensile strength' doesn't come into it because the water in a syphon is being pushed by atmosphere, not pulled by vacuum.

Newton's Law, " an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force ". The external force is pressure. You can't be pulled by a vacuum since a vacuum is just the absence of anything. You can't pull against nothing and 'nothing' can't exert a force on 'something'.

Nick Clarke 303/08/2019 17:32:15
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Posted by Nigel Graham 2 on 03/08/2019 11:36:01:

The homes including my grandparents' in Nottingham's similar Hyson Green estate also had brick outhouses beyond the tiny back gardens. Plush ones though, due to these new-fangled, high-level, cast-iron syphonic cisterns supplied from the mains water. (T'other grandparents over in Arnold were even better-off: their 1930s home's loo was indoors, off the side of the back porch.)

When my dad had a house built in Sherwood, Nottingham in the early 1960s there was a problem - My mum, having grown up in a house with an earth closet outside, had got used to a downstairs loo just outside the back door at our previous Edwardian house at the junction of Arnold and Hucknall roads in Old Basford.

The solution - the architect was asked to include the same in the new bungalow, so I suspect it might be the last outside loo included in a house anywhere in the country! (Although we did have one in the bathroom as well!)

Rod Renshaw03/08/2019 17:53:46
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I am rather taken with SOD's explanation for how siphons work using the analogy of a chain being dragged over an edge by gravity. ( I am sure JAs explanation using maths will be correct but I don't have the maths to follow it)

If we assume SODs explanation is a good analogy then I don't see any problem about water having nearly no tensile strength- which may well be true in general but in this case the water is in a pipe. The water has to stay in an unbroken length within the pipe because any break would cause a vacuum in any gap that formed. and air pressure on the water at both ends of the pipe would not allow that to happen- so the water behaves as if it does have tensile strength.

There is a limit though. It is well known that a siphon will not work over a "lip" of over 30 feet or so because the atmospheric pressure will not support the water column, and this may limit the use of siphons in large civil engineering situations. I am not clear how, or indeed if, siphons work in a vacuum.

Rod

Neil Wyatt03/08/2019 18:09:23
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Posted by Pete Rimmer on 03/08/2019 17:27:55:
Posted by SillyOldDuffer on 03/08/2019 11:21:54:
Posted by Bazyle on 03/08/2019 10:49:03:

Maybe not. A syphon can only apply one atmosphere to overcome the friction per 30 ft pipe...

Or maybe that's wrong too!

I think I'm correct in saying that no-one understands how siphons work. Air-pressure might have some effect, but can't be the main mover because siphons work in a vacuum. Another hypothesis suggests gravity provides the force rather as the weight of a length of chain pulled over a lip might cause the rest to follow. But this requires us to believe that water is strong enough to pull a large mass of water along behind it, and water has almost no tensile strength. Hmmm.

'Tensile strength' doesn't come into it because the water in a syphon is being pushed by atmosphere, not pulled by vacuum.

Newton's Law, " an object will remain at rest or in uniform motion in a straight line unless acted upon by an external force ". The external force is pressure. You can't be pulled by a vacuum since a vacuum is just the absence of anything. You can't pull against nothing and 'nothing' can't exert a force on 'something'.

It seems that siphons are very complex and no-one really understands how they work.

You can do experiments to prove they don't need cohesion (yes water does have tensile strength but you can siphon a broken stream of water.. ) or atmospheric pressure (you can siphon in a vacuum). It seems that there are multiple mechanisms that mean on takes over if another isn't sufficient.

en.wikipedia.org/wiki/Siphon

Neil

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