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Clachan Tunnel [Power Station]

Clachan Power Station, NE of Inveraray, Loch Fyne, Argyllshire.

Tunnel & Subsurface power station (1956-).

"Water is taken from an intake structure adjacent to the Lower Shira dam into the low pressure tunnel, 6 miles long by 11' in diameter, to the junction with the expansion chamber, inclined surge shaft, and surge pond. From there the water falls down a steel-lined high-pressure shaft, inclined at 39º, at the base the shaft becomes level, and turns to lead to the MIV at Clachan power station. Clachan was constructed (just) underground, using the 'cut & cover' method. After passing through the turbines at Clachan, a short tailrace tunnel leads to a long tailrace canal, which discharges the water into the river Fyne close to the point where the river enters the sea at the head of Loch Fyne." [Corestore]

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"The tunnel from Lochan Sron Mor to Clachan power station, on the banks of Loch Fyne, was around 6 miles (9.7 km) long and 11 feet (3.4 m) in diameter. Half of it was completed in the first year. Costings for Clachan power station were similar for a surface building and an underground station, as there was a shortage of steel at the time, and the underground option saved 350 tons of it. This option was therefore adopted, and the cavern was created by cut-and-cover. Once the enormous machine hall had been excavated, a reinforced concrete arch roof was built over it, and rocks were used to return the ground surface to its original profile. This was the first large underground station that the Board built. The machine hall housed a single Francis turbine driving a 40 MW generator, the largest water-powered generator in the United Kingdom at the time. The power station was commissioned in January 1955." [Wikipedia]

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"Water is taken from an intake structure adjacent to the Lower Shira dam into the low pressure tunnel, 6 miles long by 11 feet in diameter, to the junction with the expansion chamber, inclined surge shaft, and surge pond. From there the water falls down a steel-lined high-pressure shaft, inclined at 39°, at the base the shaft becomes level, and turns to lead to the Main Intercept Valve (MIV) at Clachan power station.

The water from the Lower Shira reservoir is supplemented to a considerable degree by two major systems of aqueducts and diversion tunnels; the Kilblaan section leads water into the top of the surge shaft, [&] the Brannie section water flows into the main tunnel where it surfaces briefly to cross the Brannie Burn. A noteworthy feature of the scheme is the way the levels of the intakes and tunnels were so arranged that, when Clachan power station is not running, the water from these diversions flows backwards up the main tunnel, to replenish the Lower Shira reservoir." [A. Wilson]

Alternative Names: None recorded.

Notes: Old photos showing construction of the tunnel indicate that (at least) much of it is through bedrock, with sections of concrete-lining.

Northern extremity of the tunnel is probably a site beside the dam at the S end of Lochan Sron Mor [NN 16341 19293]. A number of intakes are labelled around Allt an t-Sithean on the OS map to the S of this dam.

The Shira Hydro-Electric Scheme is a project initiated by the North of Scotland Hydro-Electric Board to use the waters of the River Shira, the River Fyne and other small streams to generate hydroelectricity.

Given coordinates are for the access tunnel entrance. The tailrace outfall is located further SE at [NN 1925 1329]. See separate entries for the surge shaft and N & S Brannie portals.

Hydrographic Feeds: Lochan Sron Mor / Allt an t-Sithean / Brannie Burn

Hydrographic Resurgences: Loch Fyne