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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 remarkable engineering enterprise known as the Lochaber Hydro-Electric Power Undertaking, the first and main portion of which was brought to a successful completion early in the present year, embodies a number of novel and interesting features which justify a more extended notice than could be given in the brief paragraph in NATURE of Aug. 9, p. 213, describing the visit of H.R.H. the Duke of York to the works of the Lochaber Water Power Company. The scheme, which is one of the most remarkable of its kind and certainly unique in importance in Great Britain, was promoted by the British Aluminium Co., Ltd., under the direction of Mr. Murray Morrison, director and general manager, who, with the late Mr. C. S. Meik, realised the latent possibilities of water power contained in Loch Treig and Loch Laggan, and devised a plan for their exploitation for the production of aluminium in a factory at Fort William. The work has been executed to the designs and under the supervision of Messrs. Meik and Halcrow, civil engineers, of Westminster." [Nature, 1930]

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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]

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The Lochaber Narrow Gauge Railway was built for the construction and maintenance of the 15-mile-long (24-kilometre) tunnel from Loch Treig to Fort William in Scotland. A 3 ft (914 mm) narrow-gauge industrial railway, it came to be known as the 'Old Puggy Line'. The first stage of the project took five years to build, starting in the mid-1920s, and cost £3 million. Messrs Meik and Halcrow were the consulting engineers, with Balfour Beatty acting as main contractors. The Lochaber Reduction Works, subsequently known as the Fort William factory, were built by Colin Macandrew. Turbines and generators for the power station were supplied by English Electric and Boving. In order to power the drills, pumps, tunnel lighting and other machinery used in the construction, a temporary power station was built at Monessie Gorge, near Roy Bridge.

A 1,400-foot (430 m) unlined tunnel was constructed, which fed water into a 475-foot (145 m) pipeline, providing 100 feet (30 m) of head to the three three-phase generators. Each was rated at 1,500 kW, and around 25 miles (40 km) of overhead 11,000 Volt transmission lines distributed the power around the construction site, to be transformed down to 440 Volts where the power was needed. Some 1.5 miles (2.4 km) of narrow gauge railway were constructed to link the Monessie work sites together. It crossed the River Spean by a pontoon bridge, consisting of 12 pontoons moored in the river. The railway was probably of 2 ft (610 mm) gauge rather than the 3 ft (914 mm) gauge used for the later railway. Materials were delivered by stopping a train on the West Highland Railway main line after passenger services had ended for the day, and transferring them to the adjacent narrow gauge line, which was worked by a small steam locomotive. The tracks were probably removed once the power station had been built.

A temporary jetty was constructed at the mouth of the River Lochy, where materials were delivered by boat, until a more permanent concrete pier was constructed. Work on the pier began in 1924, and was finished by the end of 1926. It was about 0.5 miles (0.8 km) long, and a 3 ft (914 mm) gauge railway linked it to the site of the aluminium factory, known as 'base camp' in the early stages of the project. Meik and Halcrow had specified that a railway would be required to link all of the working sites along the 17-mile (27 km) construction site, and the contract included a bonus payable if the railway and the temporary power station were completed in the first nine months. Good progress was made, and Balfour Beatty received the bonus. The railway linked the base camp to three intermediate shafts, seven adits and the valve shafts close to Loch Treig. Including the tunnel portal near to the factory, this provided 23 faces from which tunnelling was carried out. The railway enabled men and materials to be moved to the work sites, as there was no road access. The railway from the factory eastwards to Loch Treig was known as the Upper Works Railway.

Constructing a railway to serve the tunnel access points was challenging. Base Camp was at an altitude of 35 feet (11 m), and Adit 10, the first stopping point, 2.5 miles (4.0 km) from Fort William was at 640 feet (200 m). This would have required an average gradient of 1 in 22, impossible for an adhesion railway. Instead, the railway was laid at an average gradient of 1 in 35 to a point 3.25 miles (5.2 km) from Base Camp, where a junction served a branch running back along the hillside to the adit. There were several lengths of 1 in 30 within the first 4.25 miles (6.8 km), and some stretches of 1 in 25.[5] Further along, the railway crossed some peat bogs, and the track was laid on fascines made of brushwood, which led to the track being quite flexible. Three teams of men were employed on the construction, one working upwards from Base Camp, a second working from Central in both directions, and the third working from Fersit in both directions. The teams consisted of six to ten men, working with pickaxes and shovels, and they were able to level 30 to 100 yards (27 to 91 m) of the formation each day. [Wikipedia]

The Pier Railway was intended as a permanent feature, and was laid with heavy duty rails. However, its route ran through land intended for the workers village of Inverlochy. The railway therefore was reconstructed along a new route, slightly longer than the original, at 2 miles (3.2 km), and crossed the West Highland Railway and the A82 road from Fort WIlliam to Inverness on plate girder bridges. The earlier railway crossed the A82 road at a level crossing. The Upper Works Railway was laid with lighter rails as it was intended to be a temporary feature. Large teams of men were employed to build trestle bridges using local timber over the many streams which crossed the path of the railway. Two locations were unsuitable for such bridges, and Bridge 15 over the Allt Leachdach between Central and Adit 5 consisted of a 54-foot (16 m) steel span, supported by concrete pillars at either side of the ravine. Bridge 27 near Adit 6 was of similar construction, with a 40-foot (12 m) steel span over the Allt Choimhlidh. Both had timber trestles to link the centre span to the banks.

There was also a 2 ft (610 mm) gauge railway, which was built inside the tunnel to allow spoil to be removed, and later to carry materials for lining the tunnel. It was mostly single track, but emerged into the open air at adits and the portals, where sidings were built to allow shunting of full and empty spoil wagons. At shafts 1, 2 and 7, spoil was removed from the tunnel by hoists. The tunnel railway crossed the Upper Works Railway on the level near Adit 5, and there were 2 ft gauge inclines from the mouths of Adits 3, 4 and 6 up to the level of the Upper Works Railway. Once the tunnel was completed, the railway was removed, but at one time it was about 20 miles (32 km) long.

After tunnelling was complete, a decision was made to retain the 'temporary' Upper Works Railway for the delivery and despatch of materials and to assist with the maintenance of the tunnel.

In October 1971, heavy rainfall caused part of the Upper Works Railway to be washed away, leaving a gap of around 70 ft (20 m) in the track. Following this event, the future of the railway had to be considered. At that time, the Forestry Commission was constructing many access roads in the area. It was therefore decided that further roads should be built, rather than repair the track. However, due to the length of time it took to achieve this, the railway continued to operate for a number of years. Two locomotives and two speeders had been stranded on the far side of the breach from the factory. The railway finally closed in 1977. [Wikipedia]

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

Hydrographic Resurgences: Loch Linnhe