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Laggan Dam

Dam (20th Century)

Site Name Laggan Dam

Classification Dam (20th Century)

Alternative Name(s) Lochaber Hydroelectricity Scheme; Lochaber Dam

Canmore ID 108350

Site Number NN38SE 7

NGR NN 37241 80786

Datum OSGB36 - NGR


Ordnance Survey licence number AC0000807262. All rights reserved.
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Administrative Areas

  • Council Highland
  • Parish Kilmonivaig
  • Former Region Highland
  • Former District Lochaber
  • Former County Inverness-shire

Recording Your Heritage Online

Laggan Dam, C. S. Meik & Halcrow, 1934 Constructed as part of the British Aluminium Co's damming operations in Lochaber to provide water for the hydroelectric plant in Fort William, this confident monument to engineering marks the eastern boundary of Lochaber. An impressive sight against the billowing grandeur of the Great Corries, it combines the colossal curve of a concrete and stone retaining wall with an arcade of 24 segmental arches. This supports the roadway linking two control pavilions that sit athwart the centre and south end of the dam, allowing water to flow through and lending the structure its considerable architectural vigour.

Taken from "Western Seaboard: An Illustrated Architectural Guide", by Mary Miers, 2008. Published by the Rutland Press

Archaeology Notes

NN38SE 7 37241 80786

Laggan Dam [NAT]

OS 1:10,000 1988.

For (associated) Fort William, Aluminium Smelter (centred NN 12556 75030), see NN17NW 16.00.

For associated reservoir (Loch Laggan), see also NN48NE 9.

Location formerly entered as NN 37254 80749.

Formerly also entered as NN38SE 8 at cited location NN 3723 8079.

Laggan Dam, 10km E [of Roy Bridge]. By C S Meik & Halcrow. Built as one of a chain of dams to provide water power for the Fort William [Foyers] aluminium works [NH42SE 4.00], opened in 1934. Huge stone-faced curve, the water channelled through segmental arches. The machinery is housed in two towers.

J Gifford 1992.

This dam has been constructed to dam the headwaters of the River Spean, in upper Glen Spean.

The location assigned to this record identifies the approximate midpoint of the structure. The available map evidence indicates that it extends from NN c. 37200 80867 to NN 37236 80803 (slight bend) to NN c. 37274 80684.

Information from RCAHMS (RJCM), 8 June 2006.


Build (1934)

Completed along with Loch Trieg Dam.

Publication Account (2007)

Loch Laggan Dam (Institute Civil Engineers Historic Engineering Works no. HEW 1433)

Work on the second stage of the Lochaber scheme included building dams to increase the water storage capacity of both Loch Treig and Loch Laggan.

The Laggan Dam is easily seen from the A86 road as it descends to Spean Bridge from Moy Lodge. The dam, a massive concrete gravity structure 700 ft long and 130 ft high, was built across the River Spean 412 miles below the then outlet to Loch Laggan and increased the length and

storage capacity of the loch without raising its water level. This obviated the need to divert roads and to inundate valuable property.

About 1000 men were employed on the construction of the dams. Those working on the Laggan Dam had accommodation at Roughburn camp adjacent to the site whilst those working at Loch Treig (NN37NW ) were housed at Fersit halfway between the dam sites. Work on both dams was

completed in 1934. The consulting engineer was William Halcrow, and the main contractor was Balfour Beatty &Co. Ltd.

R Paxton and J Shipway, 2007.

Reproduced from 'Civil Engineering heritage: Scotland - Highlands and Islands' with kind permission from Thomas Telford Publishers.

Field Visit (2010)

Laggan Dam is a large concrete gravity dam some 700 feet long and over 130 feet high. The dam increased the length of the loch without adding to its height. It provides storage for the Lochaber scheme, and feeds into Loch Treig (see separate record) via a tunnel at the south end of the dam. The dam contains innovative self regulating siphon valves which use a ball-cock and air filled chamber to automatically start the siphon when the water level reaches a certain height. This is a major dam in the Lochaber scheme, with a significant degree of design interest in the arched arcade which carries the roadway across the top. The landscape contribution of the dam is also significant, set at the top of a steep glen and directly adjacent to a busy A road. The dam also exhibits technical interest with automatic regulation provided by the siphon valves which start the siphons when the water level reaches a predefined height. J R Hume, 1977; P L Payne,1988; E Wood, 2002; Concrete and Constructional Engineering IV (1909); Alcan, ; The British Aluminium Co. Ltd, 1930; Paxton and Shipway, 2007.


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