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Invergarry Tunnel [Adit]

Invergarry, Loch Oich, Great Glen, Inverness-shire.

Tunnel, Hydro electric scheme (1956-).

"From the dam, water is led to the power station by a low-pressure tunnel, 14,000ft long, and horseshoe in section, with an equivalent diameter of 16' 6". There is one sidestream intake on the way - the Aldernaig burn is captured and the water brought into the low-pressure tunnel via an intake tunnel 500ft long, and sloping down at 1 in 3.

The low-pressure tunnel terminates at the base of the surge chamber, which is of the differential type, and is 112ft high by 60ft in diameter. From the base of the surge chamber, the water falls down a vertical high-pressure shaft, 90ft deep by 16ft in diameter. From the base of the shaft, the short remaining distance to the power station is covered by a high-pressure tunnel 340ft long, followed by a steel penstock tunnel 460ft long, to the main inlet valve." [Corestore]

Alternative Names: None recorded.

Notes: Adit marked on OS map.

Cross-section from Water Power (1959) states lengths of 14,033ft [4277m] for Invergarry Tunnel (low-pressure), & 809ft [246.5m] for the high-pressure tunnel section (collectively 4523.5m).

"Completed in 1956, [Invergarry is] a relatively small station with a single 20MW generator, and a gross head of 174ft. It is an interesting example of a semi-underground construction - it has walls and a roof, but the walls are very low on three sides of the structure, and the fourth side is reached by a short curving 'cutting' through the rock, which descends steeply and provides road access. Everything inside the station, from the top of the generator on down, is below ground level." [Corestore]

The dam is located at the E extremity of Loch Garry at [NH 2761 0202], and tailrace adit is at the mouth of the River Garry at [NH 31938 01255].

Given alt. is for the adit mouth. The 62m depth relates to the surge shaft that opens onto the hillside at an elevation of 99m.

Hydrographic Feeds: Loch Garry / Aldernaig Burn

Hydrographic Resurgences: River Garry