Site Records

Invergarry Power Station

OS Grid Ref: NH 31916 013025
Date opened: 1957
Date closed : Operational

The surge shaft at Invergarry is hidden away in the trees on the slope immediately above the power station. It's accessible by a forestry road:

The design is unique in Scotland: a differential shaft with a central riser:

This drawing makes the arrangement clear. The differential riser extends the vertical HP shaft upwards. In a surge condition, water can rise up the riser and overflow into the surge chamber. The restrictor orifices at the base of the riser damp the surge between the chamber and the HP shaft.

The access bridge to the riser. Not used for anything very much, obviously. And I don't like the look of that rope 'handrail' at the end of it; it's sheer drop of 230ft down the riser and HP shaft!

On the day I visited the refurbishment was in full swing, and the shaft was dewatered for maintenance. On the full-size image you can just make out the orifices at the bottom of the riser shaft. The shaft is 60' in diameter and around 100' deep:

Just downslope from the surge shaft is the construction adit, on the left below, with a drain outlet for seepage water below it:

This original construction drawing shows how the adit is built, and how it intersects with the LP tunnel just upstream from the surge shaft:

Words and images © 2006 Michael J. Ross