Lochan Shira, Lower Dam

Completed.

The Glen Shira Hydro-Electric project was designed to harness the Shira and Fyne and adjacent streams between Loch Fyne and Loch Awe. The Shira Dam is the centrepiece of the scheme.The project generates 45MW.

The geography of the catchment area led to the construction of a smaller concrete and earth filled dam, 58 ft high, below the main dam to fully utilise the storage potential. This lower reservoir is also used for pumped storage to top up the upper reservoir as required. The high-pressure tunnel to the main dam’s power station is unusual in that it is a partly sloping shaft. It was driven almost entirely from the bottom, because the slope allowed most of the spoil to be removed with very little mechanical assistance.

The original scheme was conceived by James Williamson. The consulting engineers for the works as built were Babtie, Shaw & Morton and the main contractor was A. M. Carmichael of Edinburgh. The scheme was completed in 1956.

R Paxton and Jim Shipway 2007b

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

Lower Shira Dam is a combination of curved section gravity dam and earth embankment dam spanning either side of a natural rock outcrop. The dam contains the outflow from Sron Mor (see separate item) power station and creates storage and flow regulation for Clachan power station (see separate item). The gravity section of the dam incorporates a fixed spillway with oversailing walkway and a tunnel intake gatehouse with twin roller gates to allow for the isolation of the tunnel through to Clachan. Lower Shira Dam is a good example of the use of the adaptation of engineering to suit local circumstances with the use of both mass gravity and earth sections. Although the combination of technologies is unusual, individually each is of predominantly standard design as an individual item. P L Payne, 1988, 5; E Wood, 2002, 38; J Miller, 2002.

The Shira scheme

Dams were built at Lochan Shira, Lochan Sron Mor and the reservoir supplying Allt na Lairige power station via a tunnel. Sron Mor power station is fed by an aqueduct from Lochan Shira. Aqueducts and a long tunnel supply Clachan underground power station at the top of Loch Fyne at a head of 965 feet. Sron Mor was supplied with pumping facilities in effect to give Clachan the advantage of pumped storage. The installed capacity of the scheme is 51MW. Construction took place between 1951 and 1959.

Information from NRHE item catalogue number WP007424, compiled by George Walker, 2005.