Site Records

Glenmoriston: Tailrace

Glenmoriston has an unconventional tailrace arrangement - putting the power station vertically below the dam, and using a long tailrace is not common. The drawing below makes the arrangement clear, and shows just how long the tailrace is:

The tailrace at Glenmoriston is a pressure tunnel; it's permanently filled to the roof with water, no airspace. So it's not possible to access the tunnel. So here is one from the Duncan Logan archives - the tailrace under construction. It was unusual in that it was the first Scottish hydro tunnel to be constructed using the 'Swedish technique', the traditional temporary narrow-gauge railway used for removing spoil and moving equipment being replaced with all rubber-tyred equipment.

The tunnel itself is 21,800ft long, and 20ft 9in diameter - big enough to drive a double-decker bus down! Two headings were driven from an adit, itself 1,300ft long, which was made about a mile downstream from the dam. The tunnel is unlined.

Photo: Glenmoriston: Tailrace
Photo by: Scanned by Mike Ross, from Duncan Logan archival material

The tailrace discharges into the bank of the River Moriston, at the point where the river itself discharges into Loch Ness. A track leads down from the A82 to the outfall works. Note the steel gate (with yellow sign) on the left - this is at the head of a ramp; when the tunnel is dewatered it's possible to drive down that ramp and into the tunnel!

The bridge structure on the right in the above photo contains the screens (to prevent fish entering the tunnel) and stoplog grooves (to allow a temporary barrier to be erected, holding the river water back when the tunnel is dewatered for maintenance). Walking onto the bridge and looking left, the tunnel outlet is below water level:

From almost the same viewpoint, but half a century ago. The outfall under construction.

Looking out from above the tunnel outfall - the screen/stoplog bridge under construction, and beyond it the temporary cofferdam holding back the river:

Words and images © 2005 Michael J. Ross