Loch Farraline / Mhor
Loch Farraline and Loch Garth were two separate lochs in Strath Errick until 1896 when the British Aluminium Co raised the level of the larger Loch Garth just sufficiently to merge the two lochs into one much larger loch which they rather imaginatively named Loch Mhor.
BACo used a series of tunnels and pipes to bring the water down to Foyers on Loch Ness. This gave them a workable head of water of around 180mts, enough to run a conventional hydro electric scheme. The electricity generated was used to power the smelter and was the first large scale use of Hydro electric in Britain.
The smelter at Foyers closed in the late 1960s and the North of Scotland Hydro Electric Board took over the scheme. They uprated it to a Pumped Storage Scheme to produce power for the National Grid. They also increased the water catchment area by diverting another river, the Fechlin, into the loch.
Although Foyers can be run as a conventional hydro power station its real value is as an emergency boost to the national grid during peak demand times. It is also an emergency standby which can be used to provide power for a short time if a major power station goes of line without warning. Like Cruachan and Dinorwig the power station at Foyers can go from zero to full power in less than 120 seconds. The water released can then be pumped back up during the night when demand for electricity is low or the loch can just be allowed to refill naturally, probably a bit of both.
When the water is released then briefly Loch Mhor once more becomes two lochs again