Laggan Dam

Laggan Dam

A curved-plan gravity dam constructed in 1934 under the supervision of engineers C S Meik and William Halcrow, with Balfour Beatty as general engineers. Later additions were made to the structure.

The dam features a continuous arcade of arches interrupted only by a central valve house, which supports a roadway and control towers above. The downstream face to the west is constructed of concrete with coursed bullfaced rubble forming the arched arcade and parapet. A broad central bay breaks through the parapet, incorporating a tall narrow round-arched opening with paired rectangular openings above.

At the centre of the dam stands a single-storey control tower of square plan and single bay, constructed in coursed rubble with a round-headed doorway on the west side and multi-pane glazed windows. A similar but two-storey control tower is situated at the south end of the dam, both structures housing control valves and gates.

The architectural design combines plain classical elements with striking modernist forms, particularly evident in the sweeping line of the flared dam wall. The dynamic use of concrete exemplifies the modernity and progress associated with hydroelectric development during this period.

The dam incorporates innovative self-regulating automatic siphon valves on the upstream face. These siphons contain float-operated air valves that prime and break the siphon action at preset reservoir levels, allowing the water level to regulate without human intervention.

Laggan Dam forms part of the Lochaber water power scheme, one of the most significant civil engineering achievements of twentieth-century Britain. Water stored in the dam is passed through a tunnel into Loch Treig and then conveyed to the Lochaber powerhouse via a further tunnel running beneath Ben Nevis. The powerhouse supplied electricity for an associated aluminium smelter. The pressure tunnel bored through solid bedrock under Ben Nevis was a major technological achievement, completed in 1929. The scheme was designed with exceptional efficiency, capturing every available water supply.

The Lochaber scheme predates the 1943 Hydroelectric (Scotland) Act, which formalised hydroelectric development in Scotland. Unlike later schemes developed under national policy, Lochaber was developed by individual companies responding to specific market and topographic conditions. The achievement is exceptional for its technical excellence and the consistency of high-quality aesthetic and engineering design.

William Halcrow was one of the foremost engineers of the twentieth century, experienced in hydroelectric development through his apprenticeship with Thomas Meik and Sons, who were responsible for both the Kinlochleven and Lochaber schemes on behalf of the British Aluminium Company. His experience is evident in the highly efficient and pioneering nature of the work. After 1943, Halcrow went on to work for the North of Scotland Hydro-Electric Board on projects including Glen Affric and Glen Morriston schemes, and completed commissions elsewhere in the UK and overseas.

The dam is located in a prominent position adjacent to the A86 road, set against a picturesque backdrop of mountains formed by the Grey Corries.