Lochaber hydroelectric scheme

The hydro scheme has a catchment area of , including the headwaters of the River Spey, the River Spean and River Treig, and the northern flanks of the Grey Corries and Ben Nevis. There are two principle reservoirs, Loch Treig and Loch Laggan (which was extended as Laggan Reservoir), both with a top water level of about above sea level. These reservoirs are linked by a 2¾ mile (4.4 km) long, diameter low pressure tunnel, Floodwaters of the Spey are captured by Spey Dam and diverted via an open cut to Loch Crunachdan then through a tunnel to Loch Laggan. In addition, the River Mashie (a tributary of the Spey) is diverted via an aqueduct and tunnel into the River Pattack, which flows into Loch Laggan. ==Construction==

The scheme was initially designed by engineer Charles Meik but after his death in 1923, the scheme's realisation was left to William Halcrow, by then a partner in the firm founded by Meik's father Thomas Meik. The project was finally sanctioned by Parliament in 1921, but construction did not start until 1924. Given the scale of construction, it was undertaken in three main phases: • The works to the west of Loch Treig, including the pressure tunnel, intake, powerhouse, and smelter. • The Treig and Laggan dams, plus connecting tunnel and intakes. • The Spey dam, Crunachdan cut and tunnel, plus the River Mashie diversion and Strathmashie tunnel. Over 3,000 men were employed during the peak of construction. A narrow-gauge railway was used in construction and subsequent maintenance of phases 1 and 2, see Lochaber Narrow Gauge Railway for details. Stage 1 – downstream of Loch Treig The first stage of construction took five years, from 1924 to 1930, and cost around £3m. To facilitate construction, work progressed in both directions from 11 intermediate points: four vertical shafts and seven horizontal adits, giving a total of 23 working faces including the western portal above Fort William. These intermediate points were located close to watercourses, which were later captured by a series of dams and contributed around 16% of the total water for the scheme. The power station and smelter were completed by the end of 1929, initially equipped with five 6,800 kW generators, connected to Pelton turbines. The turbines sat in a deep rock excavation, as close to sea level as possible to maximise the head of the scheme. powered only by the waters from the side streams. Three years later, following a period of slack demand for aluminium, the power station was upgraded. Three additional pipes were installed on the hillside above the power station. These were in diameter, delivered in long sections, and welded together in-situ. Five additional Pelton turbines and generators were installed, each rated at 7,000 kW. Treig Dam A dam was built approximately 1/4 mile (400 m) downstream of Loch Treig, raising the top water level by to OD. This significantly increased the storage available, with 7,838 million cubic feet (221.9 million m3) available above the lowest draw-down level of OD. The dam also increased the head of the hydro scheme, providing more power. The dam is rock-filled with a central concrete core-wall keyed into the bedrock. The exposed part of the dam is high and wide, while the core wall has a crest length of and maximum depth of . Both upstream and downstream faces have a slope of 3:1, with the spillway protected by reinforced concrete, cast in-situ. In plan, the dam has a slight curve with a radius of , although it does not function as an arched dam. The dam has a plain spillway along its length, together with six siphons to increase the flood flow capacity. Many of these Canadian soldiers were ex-miners from Kirkland Lake. Water impounded by the dam flows westwards through a cut into Loch Crunachdan, against the natural flow of water. It then passes through a tunnel approximately long which discharges into the eastern end of Loch Laggan. The maximum abstraction from the Spey is , although the average for 2020–2022 was just 14 m3/s. The tunnel was constructed in 1941, completed at the end of December. This was to replace the original twelve turbines, which were horizontal-axis twin-jet Pelton wheel machines driving two DC generators with a total capacity of 72 MW. Five new horizontal-axis Francis turbines driving AC generators were installed by 2012, each rated at 17.3 MW giving a 20% increase in power output. ==Present operation==

Fort William Smelter Following the closure of Rio Tinto/Alcan's other UK smelters at Invergordon (1981), Kinlochleven (2000), Anglesey (2009) and Lynemouth (2012) the hydro-electric scheme and smelter at Fort William was operated by Rio Tinto Alcan. Under threat of closure the smelter was put up for sale in 2016. GFG Alliance, which incorporates SIMEC and the Liberty House Group, as the successful bidder, bought the Lochaber Smelter for £330 million. It announced plans to expand the factory and produce car parts such as alloy wheels. This was later dropped, replaced by plans for an aluminium recycling facility announced in November 2020. The Alcan Estate On 3 April 2021, it came to light that the Jahama Highland Estates (formerly the "Alcan Estate") had been purchased in 2016 as part of the Rio Tinto Mines deal for the Lochaber aluminium plant, because the furnace requires so much power that the smelter is located near a hydroelectric plant, which drains the basin of the 114,000 acre Estate. Alcan designed all their smelters that way. The Estate includes the north face of Ben Nevis. According to reports, the Scottish Government mandated that the Estate never be split from the hydro plant and aluminium smelter, but Gupta ignored them and placed ownership of the Estate in a company that is domiciled on the Isle of Man. The 2016 deal was worth £330 million and was guaranteed by the UK Chancellor of the Exchequer. Conservative finance spokesperson Murdo Fraser was critical about the alleged breach of the Scottish Government agreement and urged the Scottish Government to "take whatever steps are necessary to protect public funds". == See also ==