Pipelines and Portals
The scheme harnesses the headwaters of the Rivers Treig and Spean and the flood waters of the River Spey (plus a further eleven burns along the way). The Laggan Dam (213 m long and 55 m high) contained the flow of the Spean in a reservoir (Loch Laggan). A 4 km tunnel then linked this body of water with another reservoir (Loch Treig) contained by the Treig dam. From here, the main tunnel, until 1970 the longest water-carrying tunnel in the world, an enormous 24km long and 5m in diameter, was driven around the Ben Nevis massif. From the western mountainside, down five massive steel pipes, the water rushes towards the turbines in the power house at the smelting plant.
Since 1929 Loch Treig has been a reservoir, retained behind the Treig Dam, forming part of the Lochaber hydro-electric scheme, which required diversion of the West Highland Railway. The increase in water level following the construction of the dam submerged the small communities of Kinlochtreig and Creaguaineach at the loch’s southern end, which had historically hosted locally important markets and had been the end point of a cattle drovers’ road.