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    The publication date for issue 289 is the 10th of December, meaning subscribers should receive their copies during the week leading up to that date. It is also available from caving suppliers such as Inglesport and Starless River, or from our new website

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mikem

Well-known member
By bottom I meant downstream end rather than depth

& The frog may well have come through a different (too small for a caver) route, rather than the sump - especially as it's capable of hopping upstream from wherever it entered.

I wonder how much of the pulsing is just caused by variance in rainfall intensity (& because it lands on one part of the catchment before getting to other bits) & how much by the different lengths of flooded passage in-between? A regulated flow of water into the top end will take some time to overcome the friction of a long flat stretch & reach the bottom end, the water coming in behind it will get there quicker, as it rides on the back of what is already moving, but then the outlet will overspill faster than the flow entering & it may return to a steady state that has to be overcome again...
 

pwhole

Well-known member
I saw this featured on the news this morning - a capsule camera they're using to check for bowel cancer that travels through the whole body. Seems to be along similar lines to what we're discussing, though cost wasn't mentioned. Also recovery of these is more or less guaranteed! International coke smugglers probably have the advantage in that regard. Incidentally, having had a colonoscopy, I don't know what they're all moaning about - it was fine, and fascinating. They had the most hi-res monitor I've ever seen and a fisheye lens that's about 160? - I did the Fantastic Journey up my own arse ;)

https://www.theguardian.com/society/2021/mar/11/bowel-cancer-screening-capsules-the-latest-in-at-home-care-trend
 
The capsules you swallow are single use and end up in the sewage network (very few people would be prepared to swallow a second-hand one...). They take pictures frequently and transmit them to a receiver that you wear for several hours. Therefore, the difficulties would include (1) having a decent camera and sufficiently powerful light source to capture images of the cave walls - hopefully metres away (2) transmitting the pictures to a distant receiver (3) enough funds to put several into the sump that interests you as some would get held up/trapped/lost.

I suspect the most difficult bit would be retrieving the images. If that were doable, everything else should be possible, if expensive.

However, could you not do something with a very small, powered device trailing a wire that would allow you to power it from 'shore' and also transmit the images back along it? You might even be able to retrieve the device afterwards (I'm sure I've heard of something like this already, so I don't think it's an original idea).
 

mikem

Well-known member
They work well in sumps, but not turbulent streamways - especially as free flowing flood stage water behaves more to the rules of ballistics, than it does laminar flow. We're also talking distances that are too long (friction / snagging of cable).
 

aardgoose

Member
Talking of powered devices trailing a line there is this project: the original version was untethered, the latest version has 10 Gb fibreoptic tether so probably a bit too pricey and big for the Peak. Its predecessor was the thing trialed in Ecton.

https://unexup.eu/
 

pwhole

Well-known member
It seems to me the problem of finding the outlet from East Canal, and guaranteeing that whatever tracer object we use actually goes down it, is probably as difficult as choosing the device. Sadly I don't have the extract from the sump index for East Canal, but I assume it's just gloop, with no obvious floor or flow-direction?
 

ChrisJC

Well-known member
pwhole said:
What about these as a purely visual test object? It says solid rubber, so they should handle the pressure, but there's no clue as to their relative buoyancy. And they glow in the dark. Imagine seeing them coming up Main Rising - beats frogs ;)

https://www.amazon.co.uk/Pieces-Assorted-Colour-Bouncing-Balls/dp/B07CBJQKV4

I think as a starter, that would tell a lot. If some did come out the other end, then it would at least confirm that a fully featured Nemo would have some chance of doing the same.

If you lobbed 85 balls in, and none came out, then one would indeed have to revert to the somewhat stone age approach of hitting lumps of rock with a hammer until the hole was bigger... And I'd pack my bags!

Does one need permission to pour bright plastic balls into a watercourse?

Chris.
 

JoshW

Active member
ChrisJC said:
Does one need permission to pour bright plastic balls into a watercourse?
not entirely sure it's environmentally the best thing to be doing, with already far too many micro-plastics in the rivers/seas.
 

pwhole

Well-known member
It says they're 'rubber'? I'm guessing that means some sort of synthi-rubber, at that price.
 

ChrisJC

Well-known member
JoshW said:
ChrisJC said:
Does one need permission to pour bright plastic balls into a watercourse?
not entirely sure it's environmentally the best thing to be doing, with already far too many micro-plastics in the rivers/seas.

It does concern me a bit. With electronics, you will always have some dodgy substances in there, although in small quantities. It might turn out that the biggest obstacle is not technical, but bureaucratic! You would have to find a way to get a 100% retrieval rate, otherwise it's not allowed...

Chris.
 

JoshW

Active member
I've also just clocked one of the key sensors you wanted in there was pressure (as a digital depth gauge presumably), yet to maintain a constant buoyancy at any depth you'd need to Captain Nemo to be rigid - which would then negate any changes in pressure inside the ball.
 

ChrisJC

Well-known member
The reference from Andy Farrant had a solution to that - there was a hole in the casing to permit the sensor to access the outside. Of course it would need sealing very well!

And yes, the pressure sensor was to measure sump depth, and differentiate between vadose and phreatic conduit.

Chris.
 

mikem

Well-known member
You would only want a constant buoyancy in a vadose system, for phreatic you would want it to be stay in the flow rather than rise to the roof.

pwhole said:
It says they're 'rubber'? I'm guessing that means some sort of synthi-rubber, at that price.
At one point it does say they are synthetic (which still covers a multitude of possible sins).
 

JoshW

Active member
mikem said:
You would only want a constant buoyancy in a vadose system, for phreatic you would want it to be stay in the flow rather than rise to the roof.

by constant buoyancy I mean constant neutral buoyancy i.e. neither positively or negatively buoyant, but just hovers in place in still water, but follows the flows/currents
 

ChrisJC

Well-known member
JoshW said:
by constant buoyancy I mean constant neutral buoyancy i.e. neither positively or negatively buoyant, but just hovers in place in still water, but follows the flows/currents

Agreed. A smidge of positive buoyancy would be required I think to prevent it getting stuck at the bottom.

I think that because water is not compressible, then the density of water must be constant irrespective of depth, therefore a rigid object would have constant buoyancy regardless of depth. This means we could determine the buoyancy in a bucket of water and be confident that it would remain like that throughout the system.

Chris.
 

mikem

Well-known member
You have approx 1 atmosphere more in pressure for every 10m deeper you go, so there is a slight increase, plus any flow creates turbulence, which will be particularly effective if it's dragging air down from the surface (that will reduce buoyancy). However, temperature has a much greater effect on the density than pressure.
 

JoW

Member
An interesting thread of conversation! For those that missed John's talk there will be another showing of it at some future date, but this hasn't been scheduled yet - watch this space along with our Facebook page and website for more details.

And a reminder that our next talk in the series is on Monday (12th April) at 7pm. This time we will be hearing Andy Farrant talk about chalk caves :)

 

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