Difference in Level at each end of a Sump

[glyders]

This is just a question coming from some idle ponderings. Does anyone know the largest altitude difference between the two ends of a static sump?
I know that if both are open to the atmosphere they will be at the same altitude.
However I was thinking that if water went into one end following rain and the other end was in a sealed chamber then air pressure could possibly build up and thus the water level at that end not rise as much as the open end. I guess it will become a discussion about when does an airbell become a chamber.
Whilst writing I also wondered about chimney effects, ie. one end has a passage opening high up in strong winds and the other end has a passage opening in the valley. However I would doubt that the difference in air pressure in that case would lead to a measurable difference in water level across a divable sump.

 

[graham]

Not sure about the largest difference, but I think I can answer the one about airbells and chambers.

In the Grotte Cosquer, a Palaeolithic decorated cave now accessed by diving in from the Mediterranean Sea not far from Marseilles, there is a significant difference between the water level inside and out. So, the whole cave after the sump acts as a sealed airbell, although there is significantly more than one chamber.

From a conservation point of view, this is a 'good thing', as it means that the cave cannot be accessed via any sort of dug tunnel in the future as this would change the pressure, change the interior water level and drown some of the art work. From a personal point of view this becomes a 'bad thing' as it means this will be the only major decorated cave of this type that I'll not be able to visit in person.

The access sump is 175 m long & Jean Clottes the foremost French expert on this stuff learnt to cave dive when in his 70s purely to study it. Respect.

 

[glyders]

Thank you. That is very helpful, and interesting on a different note too.

 

[Duncan Price]

The water level in sealed airbells may be at different levels that the open and connected ends of either side of a sump:

Davies, R. E., "Water at a Depth of - 5 ft. Discovered by Diving in Peak Cavern" Nature, Volume 166, Issue 4230, pp. 894-895 (1950).

If the sump has a restriction in it then water can back up a lot - the "static" sump pool of the Gloom Room in Daren Cilau rises to overflow into Psychotronic Stangeways by around 10 m owing to the restrictions downstream of where the water flows out of Duke's Sump.

 

[peterk]

Graham, Re: Grotte Cosquer. There is a you tube video/slideshow at https://www.youtube.com/watch?v=YaHs49wD2c4. I would have thought the sump height difference would be down to water density with a part of a static sump being at "rock" temperature and the remainder at sea temperature or dissolved gases coming out of solution or salinity affecting density.  My french is not up to finding the answer.

 

[graham]

Intrigued, I asked Jean about it.

Firstly, he tells me that the difference in water levels is about 3 feet.

Secondly, I asked about air quality as, if it is sealed then maybe there would be a problem, but he tells me that it is perfect. Not once in 24 dives did he have any problem with it and never has anyone else as far as he knows.

That makes me think that, maybe, the height difference is down to a reason other than simply air pressure. If it was down to salinity, I'd expect the fresh water to pond up on the saline & the level in the cave to be higher, not lower. I cannot see there being a temperature effect unless there was a significant flow.

If he comes back with any more info, I'll post it here.

 

[Pitlamp]

Duncan is right about the Toricellian Chamber in Peak Cavern, the point being that water at a "depth of -5 ft" refers to the water level being 5 ft higher than either end of the sump. Davies explained this in terms of the specific passage morphology causing a vortex to form in flood, which removed some air from the Chamber. I still find it amazing that, at a time just after the war when the priority in sumps was just staying alive, Davies & friends were conducting long term scientific experiments - perhaps the first ever done in sumps. Us modern sump floppers indeed stand on giant's shoulders!

A good example of a water surface in an airbell below each end of a sump is the one 18 m from the upstream end of Ink Sump in Peak Cavern. The upstream sump pool has a big waterfall crashing into it in flood; some of the resulting bubbles are swept into the sump from where they gurgle up into the chamber concerned, lowering the water level (typically by about 1.8 m, from memory).

None of which actually helps the O.P. of course - but gives me the opportunity to offer to lend Graham a pair of tanks so he can go into the Gte Cosquer   

 

[graham]

- but gives me the opportunity to offer to lend Graham a pair of tanks so he can go into the Gte Cosquer   

I'm fairly certain that no-one has been allowed access since Luc Vanrell in about 2003. So, thanks for the offer but I don't think permission will be forthcoming. Such is life. 

 

[Chocolate fireguard]

Wikipedia has a diagram. http://upload.wikimedia.org/wikipedia/commons/8/80/Cosquerova_jeskyne.png
I hope that works!!

As Graham points out if the water in the entrance passage was fresh the level in the cave would be higher than sea level.
In fact if the whole of that passage was full of perfectly fresh water, and using the mean density of sea water as 1025kg/cubic metre (from Wiki) and depth of the entrance as 37m, the level inside the cave would be 3ft higher rather than 3ft lower.
It doesn`t seem likely that the water in the passage could have a density of 1050kg/cubic metre, needed to account for the 3ft lower level.

So presumably its due to the air pressure inside being about 100millibar greater than that outside.
The first divers would perhaps have noticed this as their gauges would have told them that they were still 3ft below the surface when they were wallking around in the chamber.

A good example of a water surface in an airbell below each end of a sump is the one 18 m from the upstream end of Ink Sump in Peak Cavern. The upstream sump pool has a big waterfall crashing into it in flood; some of the resulting bubbles are swept into the sump from where they gurgle up into the chamber concerned, lowering the water level (typically by about 1.8 m, from memory).

The diagram of Gte Cosguer shows the long entrance passage sloping upwards into the chambers. Any air given up by the water and forming bubbles would inevitably finish up in the chamber.

 

[martinm]

Hiya. What r u classifying as 'sumps'? What about WKMC to Keld Head. Don't know about that one much. JC would do.

Most of the underground system between Darfar Pot terminal sump (42m below river bed) and Ilam (4 miles away) is 'sumped'. (The height difference I work out is 9m over about 4 miles distance...)

Else if you counted the top end of the sump when the cave was flooded, it would be about 51m! (Around 160ft.)

Both ends are open to surface. All depends on Geology, constrictions, water flow into the top end, etc...

Regards, Mel.

 

[graham]

Mel

When you say that most of it is 'sumped' that would mean that some isn't.  So the 9m would be lost in the open bits.

A similar thing happened at Little Neath. It was assumed that the start of sump 6b (sump 7) was the same height as the rising until Neath 8 was discovered and found to have a small cascade. I had to go back through the survey and adjust all the figures by a metre or two.

Also, 4 miles is enough to have a noticeable effect from the curvature of the Earth, though I'm posting this from my bed on my birthday so can't be bothered to calculate it.

 

[graham]

Having just looked up the Bedford Level experiment I would guess that over a four-mile distance the curvature effect could be something in the region of just over a metre.

I am quite sure that none of our survey programs take this into account. I am also sure that we do not, routinely, have the equipment to fix the end points of a traverse to the required degree of accuracy.

 

[Hughie]

Mel

When you say that most of it is 'sumped' that would mean that some isn't.  So the 9m would be lost in the open bits.

A similar thing happened at Little Neath. It was assumed that the start of sump 6b (sump 7) was the same height as the rising until Neath 8 was discovered and found to have a small cascade. I had to go back through the survey and adjust all the figures by a metre or two.

Also, 4 miles is enough to have a noticeable effect from the curvature of the Earth, though I'm posting this from my bed on my birthday so can't be bothered to calculate it.

Happy birthday, Graham! 

 

[Fulk]

On a slightly different, but related topic, I believe that there is a small island somewhere off Greece that has seawater going underground on one side of the island and travelling through to the other side, where it resurge slightly above sea level. This is on account of the seawater mixing with fresh water that sinks underground on the island, thus the resurgence water is brackish and less dense.

 

[graham]

Mel

When you say that most of it is 'sumped' that would mean that some isn't.  So the 9m would be lost in the open bits.

A similar thing happened at Little Neath. It was assumed that the start of sump 6b (sump 7) was the same height as the rising until Neath 8 was discovered and found to have a small cascade. I had to go back through the survey and adjust all the figures by a metre or two.

Also, 4 miles is enough to have a noticeable effect from the curvature of the Earth, though I'm posting this from my bed on my birthday so can't be bothered to calculate it.

Happy birthday, Graham! 

Cheers mate. 

 

[mulucaver]

Hiya. What r u classifying as 'sumps'? What about WKMC to Keld Head. Don't know about that one much. JC would do.

Most of the underground system between Darfar Pot terminal sump (42m below river bed) and Ilam (4 miles away) is 'sumped'. (The height difference I work out is 9m over about 4 miles distance...)

Else if you counted the top end of the sump when the cave was flooded, it would be about 51m! (Around 160ft.)

Both ends are open to surface. All depends on Geology, constrictions, water flow into the top end, etc...

Regards, Mel.

If there is flow then it's not a static sump, it's a dynamic sump and level differences are accounted for by the friction in the summed passage.

 

[mulucaver]

On a slightly different, but related topic, I believe that there is a small island somewhere off Greece that has seawater going underground on one side of the island and travelling through to the other side, where it resurge slightly above sea level. This is on account of the seawater mixing with fresh water that sinks underground on the island, thus the resurgence water is brackish and less dense.

Keflonia, went there in 1983 with Chris Rhodes.

 

[Leclused]

On a slightly different, but related topic, I believe that there is a small island somewhere off Greece that has seawater going underground on one side of the island and travelling through to the other side, where it resurge slightly above sea level. This is on account of the seawater mixing with fresh water that sinks underground on the island, thus the resurgence water is brackish and less dense.

That would be the Island of Argostoli where seawater diasappears underground and travels under the Island. There it is mixed with fresh water what makes it brackish end less dense allowing it to resurface higher then where it went underground. The water even powered a mill

Dagobert (SC Avalon)

 

[martinm]

Mel

When you say that most of it is 'sumped' that would mean that some isn't.  So the 9m would be lost in the open bits.

A similar thing happened at Little Neath. It was assumed that the start of sump 6b (sump 7) was the same height as the rising until Neath 8 was discovered and found to have a small cascade. I had to go back through the survey and adjust all the figures by a metre or two.

Also, 4 miles is enough to have a noticeable effect from the curvature of the Earth, though I'm posting this from my bed on my birthday so can't be bothered to calculate it.

Complicated isn't it Graham. That is why I'm doing water tracing tests to find out exactly where the water goes on its way to Ilam. I did a test a week or two ago and am sure there was a green tinge to the water coming out in the Ladyside Wood Sinks/Resurgences, about half way down the valley, but I need to put more dye in next time. There are some big passages down there so the dye gets massively diluted.

As mulucaver said. Yep there is a big river flowing through the 4 mile long 'sump', (at least at times),  but if my dye testing works out then I will find out whether it is sumped all the way or intersects other cave passage as I suspect it does. It's a jigsaw puzzle I am trying to sort out, lol.

Oh, and happy birthday Graham! Oh, and I'll send you a copy of the map I've just worked on which shows results so far, I'm sure you'll find it interesting. I've got your email address. Don't distribute though, it's for publication in Descent and/or the DCA N/L. (As soon as I get permission from the NT.)

And another thing, sigh. At one time the far end of the main rising of the Manifold (under Ilam Hall) was the deepest dived sump in the Peak, diver was Martin Wright. (Until JNC started diving main rising in Speedwell, that is!)

 

[Leclused]

Complicated isn't it Graham. That is why I'm doing water tracing tests to find out exactly where the water goes on its way to Ilam. I did a test a week or two ago and am sure there was a green tinge to the water coming out in the Ladyside Wood Sinks/Resurgences, about half way down the valley, but I need to put more dye in next time. There are some big passages down there so the dye gets massively diluted.

Why should you put in more dye? Just hang a tiny tea bag with some active charcoal in it. The passing dye will be captured in the charcoal. After you removed the tea bag with the active charcoal you can make the dye again visible with some chemicals. (But I Always forget the name of the chemicals ;-))

when you repeat the proces with several bags (fe every 2 hours) you can even determine the timeframe when the dye passes.

Sample picture of such a test can be seen in the following tekst.
http://scavalon.blogspot.be/2009/08/anialarra-expeditie-nieuwsflash-2.html

Here we did a test between the "Partages" system and "Anialarra" system to determine which stream in the Anialarra system comes from the Partages system.
In each stream there were bags with charcoal after retrieval one of them colored green

BR
Ps did a quick search and came - up with following document (search keywords : fluorescence active charcoal)

http://link.springer.com/article/10.1007/s00254-001-0517-4#page-1

or
http://books.google.be/books?id=bstLXB2SinUC&pg=PT119&lpg=PT119&dq=fluorescence+active+charcoal&source=bl&ots=epF8amli3X&sig=ucHBKUruNSAw45QTBed_IBUf0yQ&hl=en&sa=X&ei=taNXU76XN4a0POOfgTA&ved=0CCkQ6AEwADgK#v=onepage&q=fluorescence%20active%20charcoal&f=false



Dagobert