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Subterranea Scotia

Ceannacroc Power Station

Ceannacroc Power Station sign

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





The tailrace at Ceannacroc discharges into the river Moriston a little distance from the power station. The road bridge in the foreground carries an estate road over the tailrace channel, and doubles as the support structure for the stoplog gates, used to hold the river water out of the tailrace when it's dewatered for maintenance:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

This drawing shows how the tailrace fits into the scheme of things:

Ceannacroc Tailrace

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

The tailrace tunnel is free-flowing; there's always airspace above the water. It's a substantial tunnel. Just how substantial is only revealed...:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

...when it's dewatered for maintenance:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Another view at a different stage of maintenance. The ladders and scaffolding for repointing the stonework give an idea of scale - it's horseshoe section, 19ft equivalent diameter, 1,700ft long. Descending the scaffold tower on the right, into the tailrace, and looking back, we see...:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

...the road bridge/stoplog gantry, with the stoplog gates in place - the other side of those gates is the River Moriston:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Moving now to the other end of the tailrace, inside the power station. Since there is always airspace above the water in the tailrace, it was possible to drive an adit from the main chamber of the power station into the tailrace tunnel, for ventilation. Here's we're looking through the doorway, concealed behind some equipment rack on the main floor of the power station, which leads to the adit. Ahead, there's a concrete wall with climbing steps in it - this was put in to protect the station from flooding through this tunnel, in the case that a machine trip, surge and backsurge in the tailrace, occured at the same time as an enormous flood in the river outside:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

View from the top of the wall - a short, poorly lit, unlined adit runs forward:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Looking back from the wall into the power station:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Moving forward from the wall, after a short distance the adit turns sharp right:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Turning right, the adit ends after just a few feet, in a concrete plug with a 'window', and a hole in the floor:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Quite a forbidding hole, with a very loud roar of surging water coming up from it:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Ahhh... peering cautiously into the hole, it's revealed to be a 'window' in the roof of the tailrace, immediately above the exit of the draft tube from the 4MW machine. Water boils up from the draft tube and surges right-to-left down the tailrace tunnel:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Leaning over still more cautiously, just a few feet downstream the right wall ends, and the much larger discharge from the draft tubes of the main 22MW set is boiling up and surging away down the tailrace tunnel (the pipe is the station dewatering pipe - seepage/leakage water collects in a sump at the lowest level of the station, from where it is pumped 'overboard' into the tailrace):

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

I returned to the same spot during refurbishment. Tailrace dry, cables and hoses lying in the tunnel where the water is surging in the previous picture:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Looking straight down from the 'window'. The normal water level is visible as a 'tide mark' on the wall, but with no water there you can see the outlet of the draft tube from the 4MW unit:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Descending the climbing staples gets us into the tailrace and allows us to look back up at the 'window' from below:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Looking straight ahead from the above shot, the upwards-curving outlet of the draft tube for the 4MW set:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Looking straight up at the 'window' to the adit from which we've just descended:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
Photo by: Mike Ross

Finally, stepping back a few feet into the (very humid) tailrace proper, we see the 4MW set tailrace and the 'window' on the left, and (through the mist) the outlet from the 22MW draft tubes into the tailrace on the right. The sharp edge of the 'splitter wall' which divides the two tailrace channels is very clear. Directly behind me in this shot, the tailrace tunnel runs straight for 1,700ft to the outfall:

Ceannacroc Tailrace

Photo: Ceannacroc Tailrace
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.