Does anybody know where slate was worked at the deepest depth below its lowest drainage level and how far below below? Both for surface and underground quarrying.

UK?

In North Wales, probably Oakeley, but Foty/Bowydd might run it close?

"Natural" drainage in Oakaley is G (Lefel Dwr) (726' AOD), workings went down to R (131' AOD) (Figures courtesy of GrahamI).

Thus, 595'.

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Votty bottom floor was M at 368ft asl, lowest Adit/drainage level was floor C at 859 ft asl (entrance) gives 491 ft difference.

Depends where you actually measure, however.

Whatever, On this basis Oakeley still has it.

Cheers

Grahami

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Votty bottom floor was M at 368ft asl, lowest Adit/drainage level was floor C at 859 ft asl (entrance) gives 491 ft difference.

Depends where you actually measure, however.

Whatever, On this basis Oakeley still has it.

Cheers

Grahami

What would have been the lowest entrance to the outside world at Oakeley?

G floor, somewhere around Ch.6?

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Lefal Dwr on G was always the lowest point - had to be to drain. From there to the west was "uphill" and from there to the east was "uphill." Water from the Vertical Balance sump ran "downhill" roughly south into the sinc, and round to the entrance to Lefal Dwr, thence straight along it to PenyBont.

The main entrance to G was therefore in the sinc at the area between B6 and B1 (nomenclature here is very confusing and changed over time) - obviously when the open sinc was at its deepest, and most of the falls etc. had been removed, you could get into G in the open at around wall 6 as shown on the closure plans. Sadly by the late 1970's when I finally got to the bottom of the sinc, F and G had been largely filled up with waste from the Ffestiniog Slate CO's operations and I never did get to measure up the gravity incline from F down to G floor which had replaced the old water balance from F up to DE! 😢

Cheers

Grahami

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Thanks chaps.
Have tried to match Grahami's comments to the various plans available on this site but have unfortunately learned little more than that I can't understand plans of slate mines even half as well as I can plans of metal mines.
Think a trip down in the new year beckons to at least try and gain a very basic knowledge of the place.

You may struggle to understand the lower reaches of Oakeley unless you're *very* adept at holding your breath! :lol:

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Well SRL seems very keen on his wet trips so thought we might be able to pursuade him to bring his wetsuit out...

What I actually meant though was to try and figure out how the plans relate to the presently accessible workings so I can get a better idea of how the whole thing fits together as presently I don't have the first idea.

Out of interest, has anyone ever done any diving there? Sounds like there could be a lot to see.

In the Oakeley side, the flooding takes care of virtually everything below G (ie the height of the Lefal Dwr drainage adit).

(Pumping was dewatering the workings to somewhere below H to allow untopping works in the sinc (pit), but this has presumably now been stopped since the quarry was closed.)

If you're trying to match plans to reality, Cwmorthin is a good place to start - Graham's various plans are very comprehensive.

Diving in mines is not quite as illuminating as it might seem - there tends to be massive problems with silt, which gets suspended and wrecks visibility. As a result, most (sensible) divers will retreat pretty sharpish!

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Apologies - my reply was probably a bit more obscure than I intended. I'll extract part of one of my big Oakeley plans and post it here. That will show the bit I was talking about - though, of course most of it's not there anymore 😉 apart from the watery depths.....

Cheers

Grahami

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Apologies - my reply was probably a bit more obscure than I intended. I'll extract part of one of my big Oakeley plans and post it here. That will show the bit I was talking about - though, of course most of it's not there anymore 😉 apart from the watery depths.....

Made perfect sense to me!

I would imagine the Arches level would have been the main access on G? That said, there seem to have been a couple more openings from the sinc at G and I'd imagine that there may have been some breakthrough into H at some point when the sinc was drained.

The levels/drainage issue is well worth remembering as there can be some pretty significant disparities across distances and it can have some slightly odd effects - I'd cite chamber Z44 on Floor G (Oakeley) being directly under Cwmorthin E, yet at the Oakeley end, there's a lot of F between what's by then DE and G.

"Back of a fag packet sketch" for illustrative purposes:

🔗Personal-Album-2-Image-56877[linkphoto]Personal-Album-2-Image-56877[/linkphoto][/link]

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Yes...but....

Don't forget that Cwmorthin and Oakeley although eventually connected, were developed separately and that the "slope" of the floors for drainage purposes were also different. Floors driven by Oakelely drained to the east while those driven by Cwmorthin drained to the west - at least as far as the Back Vein and Old Vein Inclines, west of there of course they sloped the other way.

One result of all this is the Cwmorthin E floor is slightly below Oakeley DE. and while Oakeley F floor was not driven below Cwmorthin, the inter floor gap for it was left, so that Oakeley G in Z44 has no intervening floor between it and Cwmorthin E is true, but the depth is still there. Unfortunately Oakeley G was never driven fully west to meet up with Cwmorthin G, other wise the bottom incline in Cwmorthin, G and E would be dry today (relatively).

Back soon.

Grahami

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Indeed, on reflection I realised that Lefal Ffrench must have been driven (slightly) uphill, otherwise they would have been working underwater by the end!

I'm not 100% convinced that there's space for an F floor above Chamber Z44 though - iirc there's a shortish manway immediately above a stumpy chamber.

Only photo I can find in a hurry is this one of Simon's:

🔗Cwmorthin-Slate-Mine-19-02-2006-Image-013[linkphoto]Cwmorthin-Slate-Mine-19-02-2006-Image-013[/linkphoto][/link]

If it comes to it, I'm sure we could measure it!

Updated sketch:

🔗Personal-Album-2-Image-56887[linkphoto]Personal-Album-2-Image-56887[/linkphoto][/link]

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What about Penrhyn ? Although it is opencast there is the old drainage level coming from lower down the Ogwen. The workings went a long way below adit level.

I'll come back on Penrhyn in a bit when I can find my notes on the depths.

Regarding F below Cwmorthin, F was only a "half floor" depth below DE, so as Cwmorthin E was already slightly below DE, there was probably little point in having F floor as the amount of rock between F and Cwmorthin E was hardly worth the expense and time of driving the levels, opening, widening etc. It was probably thought easier to just drive forward on G and have a slightly higher than normal chamber.

Cheers

Grahami

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Ah, indeed, only 39' of difference in height between DE and F at Ch.38, strangely small.

Looking at the figures, the bottom of the BV incline at Cwmorthin E Floor is 812' AOD.

The water drains into the top of Z44, from Cwmorthin 4 East - given a water level of about 3' at the bottom of the incline, that puts the floor of 4E at about 815' AOD.

Cwmorthin E Floor rises to 826' AOD (ie 11' more) at Ch.12, around the point it meets Lefel French.

Oakeley G Floor is quoted at 754' AOD at Chamber 38, then has a slightly wandering route eventually to Z44 - these chambers correlate to Cwmorthin E Floor Ch.12 and Ch.4 albeit the route is not as direct.

Allowing for the same sort of height difference as found on Cwmorthin DE (albeit the other way round), that would put floor level at Ch. Z44 as being around 764' AOD, ie about 10' higher than Ch.38 (and indeed, the water does drain down from Ch.Z44).

Thus, the difference in height from Z44 up to Ch.4E directly above is going to be 815' - 764' = 51'. This seems slightly more than my memory of it, but the length of the manway is hard to judge.

Essentially, as you travel from Ch.12/Ch.38 to Ch.4E on Cwmorthin E, you lose 11' in height.

However, as you travel on Oakeley G Floor, one level below, from Ch.38 to Ch.Z44 (below Ch.4E), you gain about 10', thus the difference in height between E and G is reduced by about 20' over the length.

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Regarding Penrhyn. Floor separations were standardised at 20yds, and taking measuirements below the main mills floor known as Red Lion we have:

Ponc Sling 20yds
Sinc Bach 40yds
Douglas/Fitzroy 60yds
Sebastopol/George 80 yds (Drainage Adit Level)
Lord/Rushout 100yds
Lady/Edward 120yds
Princess May/Alice 140yds
Pennant 160yds

That gives 80yds between Pennant and Sebastopol - i.e. 240ft.

Now surprisingly I can't put my finger on the actual height of Red Lion floor above OS Datum! So I can't give the actual depth. The drainage adit exit downstream looks about 430ft aod, but I'll stand to be corrected on this.

That would make Pennant about 190ft aod at a guess.

Cheers

Grahami

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OK

Extract from map adapted top explain my original description:
http://www.aditnow.co.uk/documents/Oakeley-Slate-Mine/Plan-Showing-Part-of-the-Oakeley-Slate-Quarries-Old-Vein-ca.pdf 

Enjoy.

Grahami

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OK

Extract from map adapted top explain my original description:
http://www.aditnow.co.uk/documents/Oakeley-Slate-Mine/Plan-Showing-Part-of-the-Oakeley-Slate-Quarries-Old-Vein-ca.pdf 

Enjoy.

Grahami

Excellent, thank you! :thumbup:

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