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Site Records

Subterranea Scotia

Ceannacroc Power Station

Ceannacroc Power Station sign

OS Grid Ref: NH 22393 10846 (access tunnel portal)
Date opened: 1959
Date closed : Operational





There are a couple of construction adits leading to the low-pressure tunnel at Ceannacroc. Here's Adit 1, not too far downstream from the dam:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

And here's Adit 2, below the surge chamber, on the hill above the power station. Adit 2 is MUCH more fun:

Ceannacroc Adit

Illustration: Ceannacroc Adit
Illustration by: Scanned by Mike Ross, from Proceedings of the Institution of Civil Engineers, Sept. 1958

Adit 2 was much more fun because, thanks to a very nice chap who was working in it during the refurbishment, I got inside and got the full guided tour! Inside the adit, looking back out to a small circle of daylight - the railing is to stop you falling in the 'ditch' which carries seepage water from the tunnel:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

Turning round 180 degrees from the above picture, we see the end of the adit: a solid concrete plug, with a very heavy bolted cover - don't forget, 99.9% of the time the tunnel beyond this point is flooded with 150ft head of water:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

A little bird told me it was worth my while coming back the next day... so I did, and sure as hell the cover was off the end plug of the adit, and work was going on in the dewatered tunnel inside. Here you can see the pipes draining seepage water from the tunnel, and discharging it into the 'ditch' to the right of the railings:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

Here follows a couple of drawings of the adit which I photographed (badly)... in plan:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

...and in elevation.You can see it's not quite 'as built' - this shows the entire adit as lined, whilst there is in fact an unlined section:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

A closer view of the end plug - you can see the pipe running through the thick concrete plug:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

Stooping through the steel pipe and the rest of the concrete tube, entering the terminal section of the adit, turning round and looking back. Beyond the plug, the adit is unlined. All this section is normally totally flooded to the roof of course. Looking back through the plug, we can see the circular section of the steel pipe, the white davit for lifting off the end plug, the railings in the adit, and, in the far distance, a circle of daylight:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

Moving a little further down the unlined section, still looking back - you can see the circle of the pipe through the plug, the bare rock walls... and my Trusty Native Guide. Apologies for the poor quality of the shots; I was handheld, I only had a digital point & shoot with a tiny flash, and the walls absolutely soaked up what little light there was. If I had the equipment and experience of underground photography I have now, things would have been much better. Crying shame, it'll probably be another 50 years before they do a refurbishment like this again:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

Turning round 180 degrees from the above shot... the adit ends in a concrete wall. This is the lining of low-pressure tunnel itself; the small square hole on the left where the light is gives access to the tunnel:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

Passing through the hole (clearly visible in the photo below), we're now in the tunnel itself. The dim light from the lamp illuminates the sandbags which mark the safe route around a sump in the floor of the tunnel. From this sump the seepage water leaking into the empty tunnel drains into the adit, and thence outside:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

Moving a few feet downstream, and then looking back upstream. The tunnel is fully lined of course, horseshoe in section, 12ft equivalent diameter and 14,000ft long. You can just make out the square hole from which we emerged on the left hand side of the tunnel, and the figures of my Trusty Guides. Used the (almost useless) camera flash on this shot, and got a lot of backscatter from the moisture in the air:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

Turning round 180 degrees from the above shot, and looking downstream. The walls of the tunnel are somewhat clearer, and a short distance downstream things get a lot brighter. That's the bottom of the surge shaft; the tunnel transitions to a rectangular section, to accomodate the control gate at the bottom of the surge shaft, and the prominent metal screen you can see protects the top of the vertical high-pressure shaft which takes the water the final drop to the power station below:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross

Heading dowstream. You can clearly see the daylight flooding down the surge shaft, illuminating the screen protecting the top of the HP shaft, and the staples in the right wall for climbing into the surge shaft itself. The scaffolding is there as there was refurbishment work going on with the control gate, which allows the flow from the LP tunnel into the surge shaft to be shut off. From here I went on to explore the surge shaft, and you can too, by clicking HERE:

Ceannacroc Adit

Photo: Ceannacroc Adit
Photo by: Mike Ross


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Last updated 6th May 2006
Style 1998-2001 Subterranea Britannica

Words and images 2006 Michael J. Ross.