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Nevis Tunnel [Outfall]

Fort William, Lochaber, Inverness-shire.

Hydro electric scheme tunnel (constructed 1926-30).

Outfall point for the extensive Nevis Tunnel where the portal is covered by a valve or pump house from where penstock tunnels transport waters to a powerhouse below.

"The most remarkable feature of the [Lochaber Hydro] scheme was the construction of a pressure tunnel 15 miles long beneath Ben Nevis, from Loch Treig to the entry with steel pipes situated 600 ft above the power station at Fort William.

In driving the tunnel, four vertical access shafts were sunk and seven horizontal adits driven to allow 22 separate working faces, all in solid rock. The tunnel has a roughly horseshoe cross-section with an equivalent diameter of 15 ft. Eleven streams on Ben Nevis were dammed and their flows taken into the tunnel through three construction shafts adapted for the purpose.

The tunnel drive began in 1926 and was completed in 1930. The work required the construction of a temporary hydro-station to power construction equipment, an extensive network of 3 ft narrow gauge railway to transport men and materials, and a reinforced-concrete pier 200 ft long on Loch Linnhe which later became permanent. At the height of the work 3000 men were employed. The consulting engineer was William Halcrow and the main contractor, Balfour Beatty & Co. Ltd." [Lochaber Detecting Group]

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"The main challenge was the pressure tunnel from Loch Treig under the Ben Nevis massif, which commenced in summer 1926. The tunnel was dug by hand through the solid rock, with compressed air drills used to bore holes for the explosive charges. Initially liquid oxygen based explosives were used, but despite being safer their use was complicated, so gelignite was used instead. The final stage of construction, was to connect the tunnel to Loch Treig, having dug to a point about 20 feet (6 m) from the bottom of the loch and 100 feet (30 m) below the surface. On 3 January 1930, a charge of 1.5 tons of specially prepared gelignite was detonated to blast out the remaining section of rock.

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." [Wiki]

Alternative Names: Lochaber Tunnel

Notes: Given coordinates are for resurgence (drained by large dual penstock pipes down hillside).

Given length / VR approx.

Hydrographic Feeds: Loch Treig / various streams