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Latitude: 56.8895 / 56°53'22"N
Longitude: -4.673 / 4°40'22"W
OS Eastings: 237254
OS Northings: 780749
OS Grid: NN372807
Mapcode National: GBR GBVH.S8K
Mapcode Global: WH2GX.6309
Plus Code: 9C8QV8QG+QQ
Entry Name: Laggan Dam
Listing Name: Lochaber Hydroelectric Scheme and Aluminium Smelter, Loch Laggan Dam
Listing Date: 29 May 1985
Category: A
Source: Historic Scotland
Source ID: 338548
Historic Scotland Designation Reference: LB6835
Building Class: Cultural
ID on this website: 200338548
Location: Kilmonivaig
County: Highland
Electoral Ward: Caol and Mallaig
Parish: Kilmonivaig
Traditional County: Inverness-shire
Tagged with: Dam
C S Meik and William Halcrow supervising engineers; Balfour Beatty general engineers, 1934; some later additions. Curved plan gravity dam with continuous arcade of arches (interrupted by valve house to centre) bearing roadway and control towers. Concrete downstream face (W) with coursed bullfaced rubble to arched arcade and parapet. Broad central bay breaking parapet with tall narrow round arched opening and paired rectangular openings above. Central square plan, single storey, single bay coursed rubble control tower to parapet with round headed doorway in west side and multi-pane glazing to windows. Similar, but 2-storey, control tower at south end of dam both housing control valves and gates.
This dam is located in a very prominent location, adjacent to the A86 road with picturesque backdrop of mountains formed by the Grey Corries. The dam design includes innovative self regulating siphons which manage the water level in the dam without the need for human intervention. The dam also forms part of the Lochaber water power scheme and aluminium smelter, one of the most significant civil engineering schemes of the 20th century in Britain. The dam provides storage capacity for the hydroelectric powerhouse at Lochaber with the water passed through a tunnel (the tower to the S end of the dam contains a control gate for the tunnel) into Loch Treig and then on to the powerhouse via a further tunnel running under Ben Nevis.
The architectural treatment of the dam is a fusion of both plain classical design with a striking modernist form characterised by the sweeping line of the flared dam wall. The striking use of concrete to create dynamic forms clearly illustrates the idea of modernity and progress which characterised the development of hydroelectricity in this period.
The design of the dam includes automatic siphon valves to the upstream face which allow water level to self regulate. The siphons contain a float operated air valves that prime and subsequently break the siphon action at preset reservoir levels.
The Lochaber powerhouse and smelter were part of one of the most significant British engineering achievements of the 20th century. The creation of a pressure tunnel bored through solid bedrock under the flanks of Ben Nevis to connect the powerhouse with the Laggan and Treig reservoirs was a major technological achievement in 1929. The scheme was designed to a very high degree of detail, capturing every available water supply available and was highly efficient.
The development of the Lochaber scheme predates the 1943 Hydroelectric (Scotland) Act which formalised the development of Hydroelectricity in Scotland and led to the founding of the North of Scotland Hydroelectric Board. Those developments which predated the 1943 act were developed by individual companies as a response to particular market and topographic conditions. The completion of a number of schemes (including Galloway, Grampian and those associated with Alcan - see separate listings) without a national strategic policy framework is exceptional as is the consistency of high quality aesthetic and engineering design across all of the schemes.
Sir William Halcrow was one of the foremost engineers of the 20th century, and was highly experienced in the development of hydroelectricity having served his apprenticeship with Thomas Meik and Sons who were responsible for both Kinlochleven and Lochaber water power schemes on behalf of the British Aluminium Company (see separate listings). His work on the Grampian scheme came in between the Kinlochleven and Lochaber developments, and his experience in developing the Kinlochleven scheme can clearly be seen in the highly efficient pioneering nature of the Tummel Garry development. Halcrow's association with hydropower and water engineering was longstanding and after 1943 he went on to work on a number of projects for the North of Scotland Hydro-Electric Board including the Glen Affric and Glen Morriston schemes. The company also completed work elsewhere in the UK and overseas.
(Upgraded B to A as part of Hydroelectric Power Thematic Survey 2010)
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