The link pic is (allegedly) a well. Whilst it was originally a normal vertical well, at some point in the late 19th Century it was decided to make it into a spring to serve a growing small village. It's (allegedly) something like 300 metres in length.
https://www.aditnow.co.uk/Photo/Cwm-Well-Adit_62926/ 

Here's the inside of it :
https://www.aditnow.co.uk/Photo/Inside-Adit-For-Well-Spring-At-Cwm-Dyserth_62927/ 

The amount of work people were prepared to carry out to drain a mine/vein, or to get a supply of water to where it was needed, is continually surprising. The Halkyn deep level drainage tunnel (I posted the pic link of the portal yesterday) was 3 or 4 miles in length.
The Milwr tunnel - again, principally a drainage tunnel - is about 11 miles in length.
I'm currently trying to locate another drainage tunnel in Flintshire, allegedly 1.5 miles in length. The map references are not correct though, and fieldwork hasn't got me anywhere as yet.

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The link pic is (allegedly) a well. Whilst it was originally a normal vertical well, at some point in the late 19th Century it was decided to make it into a spring to serve a growing small village. It's (allegedly) something like 300 metres in length.
https://www.aditnow.co.uk/Photo/Cwm-Well-Adit_62926/ 

Here's the inside of it :
https://www.aditnow.co.uk/Photo/Inside-Adit-For-Well-Spring-At-Cwm-Dyserth_62927/ 

The amount of work people were prepared to carry out to drain a mine/vein, or to get a supply of water to where it was needed, is continually surprising. The Halkyn deep level drainage tunnel (I posted the pic link of the portal yesterday) was 3 or 4 miles in length.
The Milwr tunnel - again, principally a drainage tunnel - is about 11 miles in length.
I'm currently trying to locate another drainage tunnel in Flintshire, allegedly 1.5 miles in length. The map references are not correct though, and fieldwork hasn't got me anywhere as yet.

That's all staggering stats. Our entrance looks exactly the same construction as the Halkyn tunnel though there's not nearly enough spoil around for a very long tunnel. That said the beam of my 4-cell Maglite torch couldn't see the end of it.

I'm so glad I posted my question. It's opened up a whole new, interesting world, although I still have no desire to go subterranean!

That's all staggering stats. Our entrance looks exactly the same construction as the Halkyn tunnel though there's not nearly enough spoil around for a very long tunnel. That said the beam of my 4-cell Maglite torch couldn't see the end of it.

I'm so glad I posted my question. It's opened up a whole new, interesting world, although I still have no desire to go subterranean!

Spoil doesn't really mean anything. The Halkyn tunnel, for example; in spite of being 3 or 4 miles in length, has no spoil at all in the area. It's in a lovely wooded valley, and you could be 50 yards from it and have no idea it even existed.
It wasn't only a drainage level either. When they dug it, it also intersected a few veins, so they dug those out too !

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Exception though rather than the rule?

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Exception though rather than the rule?

Oh, agreed. I'm just saying not to assume that you need a substantial amount of spoil to indicate how large a tunnel or system is. There must have been huge quantities of material that came out of Halkyn Deep Level (even if it was just 8ft * 5ft * 3 miles, you'd be looking at 40-50,000 tonnes, even in low density rock) and yet there is nothing to indicate where all that material has gone to.
If you've got weak areas of rock, if the passage is bigger, if it is closer to the 4 miles than 3, patches of granite, etc, then you could easily be getting up to 100,000 tonnes of material that came out of there.
And yet, it all looks completely natural - unless you're walking up the stream in the woods, and then you come to a fork. The right branch is natural, the other is walled and dead straight, going 100 yards straight into the portal.
So the absence of a spoil heap doesn't really mean much.

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Hi,
Halkyn adit...3-4 miles long. Milwr...11 miles !
Some Cornish adits are as long as Halkyn, but Milwr?
The Cornish 'County Adit' was supposedly some 30 miles long, but in fact referred to a surface drainage system that collected adit outlets on the way, (some miles long).
The Harz siver mines also drain a huge surface area, but more to feed underground waterwheel pumps than anything else....
All these adit diggers must have had considerable topographical skill for the time!
D.Send.

I fell into my own trap years ago.
The spoil from Camdwrbach indicated just a trial, actually much of it was trammed down to Brynyrafr for tipping. Misleading.

The now flooded stope has been plumbed at over 100 feet, something to think about if you stand on the false floor.

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Sorry not been on here for a while, there are plans of the mines in Mylor and Carclew areas Wheal lemon and an iron mine with associated shafts. lots of shafts and at least one adit course recorded some tin and antimony mining locally too.

Just an additional observation. The image of the portal shows very clear water with no mineral staining in the stream bed.

Forget all my drivel and speculative maps as I think I've been looking at the WRONG creek!:-[