Three thousand men, working with picks and dynamite and a narrow-gauge railway, drove eighteen miles of tunnel through solid rock under the Grey Corries and Ben Nevis between 1924 and 1943. The reason was aluminium. Aluminium smelting requires enormous amounts of cheap electricity, and in the wet Western Highlands the cheapest electricity comes from gravity. So the British Aluminium Company built dams at Loch Treig and Loch Laggan, captured the headwaters of the Spey and the Spean, and ran the water westward through hidden tunnels until it reached penstocks above Fort William. There it dropped hundreds of metres into Pelton wheels and made power. The smelter started pouring aluminium in 1929 and is still pouring it today, almost a century later, the last operating aluminium smelter in Britain.
Water naturally flows downhill, and in the central Highlands most of it flows east into the Spey or south into the Spean. The engineers of the Lochaber scheme decided water should flow west instead, toward Fort William and Loch Linnhe, because that was where the smelter needed it. The catchment they captured spans 303 square miles, including the headwaters of the Spey, the entire Spean basin, the River Treig, and the northern flanks of the Grey Corries and Ben Nevis. Spey Dam diverts floodwaters into Loch Crunachdan and then through a tunnel into Loch Laggan. A 2.75-mile low-pressure tunnel links Loch Laggan to Loch Treig. From Loch Treig, the main pressure tunnel runs 15 miles westward through the mountain, emerging at the powerhouse above Fort William, where the water falls and the turbines spin.
The first stage of construction ran from 1924 to 1930 and cost three million pounds. To move quickly, the engineers attacked the long pressure tunnel from multiple directions at once: four vertical shafts and seven horizontal adits, giving twenty-three working faces, were driven into the hillside between Loch Treig and Fort William. Each adit ran out to a small burn, which was later dammed to add its water to the system. Roughly sixteen percent of the total flow now comes from these side-stream captures. The narrow-gauge Lochaber Railway hauled out the spoil. The men slept in temporary camps. The power station was completed by the end of 1929, originally fitted with five Pelton turbines rated at 6,800 kilowatts each. The turbines sat in a deep rock excavation, dropped as close to sea level as possible to maximise the head.
The Treig Dam stands a quarter-mile downstream of the natural loch outlet, a rock-filled structure with a central concrete core. It is 40 feet high above the original ground and 380 feet wide, though the buried core wall goes down 122 feet to bedrock. Raising the water level by 35 feet expanded storage to over 7.8 billion cubic feet and increased the head available to the turbines below. The second-stage tunnel from the Spey was completed in December 1941, in the middle of the Second World War. Many of the men driving it were Canadian soldiers, ex-miners from Kirkland Lake, Ontario, sent to Scotland to do what they knew how to do. In 2012 the original Pelton machines and DC generators were finally replaced with five Francis turbines and AC generators, each rated at 17.3 megawatts, raising the scheme's output by twenty percent to roughly 86 megawatts.
The British Aluminium Company built and ran the scheme until 1982, when Canadian-based Alcan bought it. Alcan in turn was bought by Rio Tinto in 2007. When Rio Tinto put the Fort William smelter up for sale in 2016, the buyer was GFG Alliance, the conglomerate then controlled by the metals trader Sanjeev Gupta. Their price was 330 million pounds, guaranteed by the UK Treasury. GFG announced plans to expand the plant, build a wheel factory, then a recycling facility. The deal also bundled in the 114,000-acre Jahama Highland Estate, including the north face of Ben Nevis itself. In 2021 it emerged that ownership of the estate had been moved to an Isle of Man company, reportedly against an undertaking given to the Scottish Government. The smelter, the dams, the tunnels and the estate remain entangled, just as the original engineers made them: bound by water, and by power, and by money.
The Lochaber hydroelectric scheme spans a catchment of 303 square miles across central Lochaber. The Fort William smelter and powerhouse sit at 56.829 degrees North, 5.073 degrees West, on the northeast edge of Fort William. The reservoirs lie roughly 15 to 30 miles east-northeast: Loch Treig at the foot of the Grey Corries, Loch Laggan further east. Spey Dam is near Laggan village at the eastern end. The nearest airport is Oban (EGEO) about 40 nautical miles south. Glasgow (EGPF) is the main commercial gateway 90 nautical miles south, Inverness (EGPE) 55 nautical miles northeast. Best viewed at 4,000 to 6,000 feet AGL to capture the full west-east sweep of the catchment from Fort William to Loch Laggan. The penstocks descending the hillside above the smelter are visible from miles away.