Laggan Dam is a

dam A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use ...

located on the

River Spean The River Spean flows from Loch Laggan in a westerly direction to join the River Lochy at Gairlochy in the Great Glen in the West Highlands of Scotland. Major tributaries of the Spean include the left-bank Abhainn Ghuilbinn and River Treig, th ...

south west of

Loch Laggan Loch Laggan is a freshwater loch situated approximately west of Dalwhinnie in the Scottish Highlands. The loch has an irregular shape, runs nearly northeast to southwest and is approximately in length. It has an average depth of and is at its ...

in the

Scottish Highlands The Highlands ( sco, the Hielands; gd, a’ Ghàidhealtachd , 'the place of the Gaels') is a historical region of Scotland. Culturally, the Highlands and the Lowlands diverged from the Late Middle Ages into the modern period, when Lowland S ...

History

The structure was built as part of the Lochaber hydroelectric scheme by

Balfour Beatty Balfour Beatty plc () is an international infrastructure group based in the United Kingdom with capabilities in construction services, support services and infrastructure investments. A constituent of the FTSE 250 Index, Balfour Beatty works acr ...

for the

British Aluminium Company British Aluminium was an aluminium production company. It was originally formed as the British Aluminium Company Ltd on 7 May 1894 and was subsequently known as British Alcan Aluminium plc (1982-1996). History In the late 1880s and early 1890s, ...

and construction was finished in 1934. The supervising engineers were the firm of C S Meik and William Halcrow, now known as the

Halcrow Group Halcrow Group Limited was a multinational engineering consultancy company, based in the United Kingdom Halcrow was one of the UK's largest consultancies, with origins stretching back to 1868. The UK-based consultancy specialised in the provision ...

. The dam was designated a Category B

listed building In the United Kingdom, a listed building or listed structure is one that has been placed on one of the four statutory lists maintained by Historic England in England, Historic Environment Scotland in Scotland, in Wales, and the Northern Irel ...

in 1985. It was upgraded to Category A listing in 2011, following a review as part of Hydroelectric Power Thematic Survey 2010.

Design

The dam is about long, and high between the level of the foundations and the crest of the spillway. It is curved upstream like an

arch dam An arch dam is a concrete dam that is curved upstream in plan. The arch dam is designed so that the force of the water against it, known as hydrostatic pressure, presses against the arch, causing the arch to straighten slightly and strengthe ...

with a

radius of curvature In differential geometry, the radius of curvature, , is the reciprocal of the curvature. For a curve, it equals the radius of the circular arc which best approximates the curve at that point. For surfaces, the radius of curvature is the radius o ...

of , but works purely on the principle of a gravity dam. The whole crest of the dam, except for a section in the middle that houses equipment, is a

spillway A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure th ...

broken into 29 bays by piers that support a roadway across the dam. As well as the spillway, there are six pipes embedded into the centre of the dam, controlled automatically by system of air valves. The foundations are built on

granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...

, and the dam was built in seven sections, with copper strip and hot poured asphalt water stops in the joints. The dam contains a reservoir which has a capacity of . Water from the dam is conveyed to Loch Treig through of tunnel. From there, the waters travel through a further of tunnel in diameter, before descending the hillside to a power house at Fort William through five steel pipes. The dam can be found next to the

A86 road The A86 is a major road in Scotland. It runs from the Great Glen at Spean Bridge to Kingussie and the Cairngorms National Park via Loch Laggan. It is a primary route for its entire length. The road was built as a parliamentary road by Thomas Tel ...

from Fort William. The catchment area of the dam was increased by an aqueduct which can be seen at the side of the road in Strath Mashie.

References

External links

{{Commons category
Magazine cover showing the dam under construction
Dams in Scotland Dams completed in 1934 Energy infrastructure completed in 1934 Category A listed buildings in Highland (council area) 1934 establishments in Scotland