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2021 International Year of Caves and Karst: BCRA online seminars

Mark Wright

Member
pwhole said:
DCA did have a plan in place to take folks from Historic England down on a winch last summer, and they said they'd do it, but Covid wrecked that - though I suspect it could have been done quite safely if they'd checked the dig one at a time. Oh well - maybe this summer! There's an online UCF meeting in a month, so it would be well worth having it as a discussion item. You could join in, it would be very useful.

PM sent
 

Benfool

Member
Sounds good in theory, but...

I'm pretty sure that such sensors wouldn't get through either the choke at the end of Whirlpool Rising, or the sandy horrorshow at the bottom of New Leviathan in Main Rising.

Having said that, a live frog managed to get to the bottom of New Leviathan when I visited in 2018, so it is possible (assuming it wasn't a narcosis induced hallucination!).

B
 

pwhole

Well-known member
Isn't the bottom of East Canal also a deep gloop-fest with no obvious exit point? It's funny that it drains so well really, but there must be a lot more sediment going in off the bog than appears to the casual viewer. I have seen the water in the Crabwalk looking brown once, but it usually looks crystal clear - but I bet there's tons a year gets washed in there in reality. I'm amazed a frog can handle that sort of pressure though - isn't it like -70m down there?
 

ChrisJC

Well-known member
MarkS said:
ChrisJC said:
I don't think so. Choice of housing material would play a part, but ultimately, it would just get bigger to ensure buoyancy.

I was thinking of situations where there may be fairly deep sumps where buoyancy could be problematic.

I see what you mean, in the sense that it would bob about on the top, and never make it through the sump?

It is for that reason that I thought that making it only marginally buoyant would be the answer. So it will get swept down by a reasonable flow, but if it snagged a stone or boulder on the floor, it would tend to rise up and get carried forwards eventually.

I guess buoyancy varies with depth, so that would need a bit of thought.

Chris.
 

Benfool

Member
pwhole said:
Isn't the bottom of East Canal also a deep gloop-fest with no obvious exit point? It's funny that it drains so well really, but there must be a lot more sediment going in off the bog than appears to the casual viewer. I have seen the water in the Crabwalk looking brown once, but it usually looks crystal clear - but I bet there's tons a year gets washed in there in reality. I'm amazed a frog can handle that sort of pressure though - isn't it like -70m down there?

-72m. I was rather confused when I found it - so much so that I'm not convinced it was real.
 

ChrisJC

Well-known member
Andy Farrant said:
Similar sensors have been used to investigate subglacial flow under ice sheets. In preliminary tests on the Leverett glacier in West Greenland during August 2009 researchers demonstrated that radio frequency detection methods can be used to locate and retrieve dummy sensor packages: 50% and 20% of the dummy sensor packages introduced to moulins at 1 and 7 km from the ice sheet terminus respectively, emerged in the sub-glacial stream (incidentally I used to share an office with one of the co-authors). Nasa once used rubber ducks but they were never seen again.

See
https://ui.adsabs.harvard.edu/abs/2009AGUFM.C43B0506B/abstract
https://onlinelibrary.wiley.com/doi/full/10.1002/hyp.9451
https://core.ac.uk/download/pdf/227104429.pdf
http://news.bbc.co.uk/1/hi/sci/tech/7780200.stm

Of course, retriving the sensors at resurgences would be much easier than on pro-glacial outwash fans, just use a large net.

If someone were to develop this technique for caves, that would be fantastic, although the risk of sensor packages getting stuck would probably be much higher; many UK sumps would not be suitable. Perhaps trial with a few dummy sensors first, and then try with the real thing. They would need to be cheap enough to lose a significant proportion. The BCRA CSTRF fund would be there if anyone is serious.

The E-Tracer and Cryoegg look very much like what I had in mind. I would ease off a lot on the radio as there's no need for transmit ranges of kilometers!, and increase the sample rate a lot to very few seconds. But the hardware spec, down to battery chemistry is very much appropriate.
And make a simpler housing.

To be honest, I would think that most of the cost is in the housing, as the electronics part will be very cheap.

You would definitely expect to lose a few.

I would certainly send a barrow-load through first that were just empty housings to check that you do at least get some out at the other end!

Seems like a nice MSc project for a technically minded student.

Chris.

 

JoshW

Active member
Mark Wright said:
I know where I can lay my hands on about 5000 ping pong balls if that helps.

Mark

Would think they?d be too flexible if the sumps are down to -20m. 3 atmospheres of pressure would shrink the ball and it would lose any buoyancy. Smarter people may be able to correct me on that
 

alastairgott

Well-known member
Surely the more you have the better.  (y)  Combat pressure with volume  :ras:


Maybe rubber ducks would hold up better, I know a stockport based caving club which is excellently named for the task  ;)
 

pwhole

Well-known member
What about cork balls? If they're solid they should survive, though they may be too buoyant as well. Maybe we could get some chav to chuck a bin-liner of clay pebbles from a grow-op down there - probably the only place they haven't been chucked!

Actually, that could work, if they were spray-painted in fluoro colours. I got some orange from Halfords last year. Not too unfriendly for the environment if they get stuck too ;)
 
Once again, I'm way outside my comfort zone...

Do you want your Nemos to be positively buoyant or to have neutral buoyancy? If they had positive buoyancy, wouldn't they get held up whenever they reached a sump? If they were neutrally buoyant, they'd stand a better chance of following the water, whatever it did. If you incorporated a pressure sensor, you're be able to tell (mostly) when they were submerged or on the surface....

When you tell me I'm totally wrong, please use very, very short words and simple sentences

 

PeteHall

Moderator
Speleofish said:
If they had positive buoyancy, wouldn't they get held up whenever they reached a sump?
Depends on the conditions at the sump, I suppose. If it was turbulent enough, I can imagine them getting dragged along with the current. A nice calm sump pool (or air bell en route) would very likely trap anything buoyant.

What you want is a sensor that detects if it hasn't gone anywhere for a while and adjusts the buoyancy up or down depending on the current depth, so that it can return to the main flow  ;)
 

ChrisJC

Well-known member
Speleofish said:
Once again, I'm way outside my comfort zone...

Do you want your Nemos to be positively buoyant or to have neutral buoyancy? If they had positive buoyancy, wouldn't they get held up whenever they reached a sump? If they were neutrally buoyant, they'd stand a better chance of following the water, whatever it did. If you incorporated a pressure sensor, you're be able to tell (mostly) when they were submerged or on the surface....

When you tell me I'm totally wrong, please use very, very short words and simple sentences

I'm no expert!

But you are right. I would have a tiny tiny amount of positive buoyancy, so they would float, but only just. Any sort of downward flow would take them downwards. Whether it's possible to fine-tune that I don't know.

And I agree about the pressure sensor, you would be able to tell whether the passage at that point was vadose or phreatic by the pressure. Positive pressure means underwater. That in itself, plotted against time would be very interesting.

Chris.
 

ChrisJC

Well-known member
pwhole said:
What about cork balls? If they're solid they should survive, though they may be too buoyant as well. Maybe we could get some chav to chuck a bin-liner of clay pebbles from a grow-op down there - probably the only place they haven't been chucked!

Actually, that could work, if they were spray-painted in fluoro colours. I got some orange from Halfords last year. Not too unfriendly for the environment if they get stuck too ;)

My gut feeling is that cork would be too buoyant. But it would be an easy test, to find out if the buoyancy is actually important.

Chris.
 
I like Pete's idea about adjustable buoyancy in theory. However, wouldn't it be a little too complex (and expensive) for a real world experiment?
 

alastairgott

Well-known member
I'm going to be honest, but I think the idea of sending anything through a 70+m deep sump (or the other unknown total depth sump). Is probably a jump from reality into sci-fi.

The rise in water depth between the boulder piles and main rising probably corresponds to a proportion of the drop in the head of the sumps of the swallets. If the rainfall is long in duration, then the increased "head" on the sumps in the swallets probably won't decrease completely till the rainfall has let up. So the system then achieves another "steady state" where it's flowing a foot or two above the boulder piles.

In normal conditions from the graphs the temperature looks fairly steady, and decreases in heavier flow, meaning the usual "warm water at the top" gradient has been disrupted. The speed with which the temperature drops and then rises again will give you an indication of whether you are seeing significant flow from depth for some time.

If the temperature drops and increases rapidly, I would make an assumption that you're seeing a seesaw effect in the level of the sumps, rather than a substantial throughput flow.
When I say substantial, I mean enough to give a neutrally buoyant thing enough lift to get up a wide water filled aven for 70m.  :blink:
 

alastairgott

Well-known member
Ah, I've just compared two different graphs and the temperature differential is different in summer than it is in winter, who would have thought!

(descent 270, oct 2019, pg 28) is summer data.
Whereas speleology 19 (BCRA, Dec 2013, pg 38-39) deals with a winter flooding event.
 

Mark Wright

Member
JoshW said:
Mark Wright said:
I know where I can lay my hands on about 5000 ping pong balls if that helps.

Mark

Would think they?d be too flexible if the sumps are down to -20m. 3 atmospheres of pressure would shrink the ball and it would lose any buoyancy. Smarter people may be able to correct me on that

They would have to be opened up and resealed to install the electronics so they could be stiffened up somehow and given some extra weight?

The 5000 balls I mentioned aren?t actually ping pong balls. They are black plastic balls used to float on the top of a large water tank to stop scum building up on the surface of the water.

In the meantime, I?ll get my crowbar.

Mark
 

PeteHall

Moderator
Speleofish said:
I like Pete's idea about adjustable buoyancy in theory. However, wouldn't it be a little too complex (and expensive) for a real world experiment?

Hmm...  :-\

If that's going to be too expensive, how about training some frogs to survey underwater?

On a more sensible note, I think that something that floats just below the surface is likely to be most successful. It would be easy enough to test somewhere like Swildon's, where there are several easily accessible sumps of varying depths and lengths all are fairly straightforward, so unlikely for things to go missing.

If you were to make a small spherical canister that could be opened up to add weight, you could play with the buoyancy until it passed sump 1, then try it on sump 2 and 3 where the depth starts to increase a bit. With a bit of luck, you'd find an optimum.
 

mikem

Well-known member
But would you want to be down swildons when there was enough flow to carry them through?

Another problem is that buoyancy doesn't only vary with depth, but also with turbulence, so ones that didn't float on surface would likely end up in boulder piles.

& whilst those stuck in smooth airbells could potentially be identified from the data, those in violent eddy currents couldn't, although they may be stuck for just as long.

Also some pulses are the actual water entering the system reaching the end & others are the water arriving & displacing different water from the bottom (which is almost certainly the case with a -70 sump) - you would probably need balls of lots of different buoyancies to find out which got through - it would be different for each set of passages.
 
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