Orrin Dam

The construction of Orrin dam marked the last phase in the development of the Conon scheme and brought in a further catchment on the Orrin River. The dam is of a mass gravity type and is some 300 meters long. Water from the outlet is transferred by a 5km lined tunnel and steel pipeway through to Orrin power station (see separate item). The dam includes a particularly unusual fish pass housed in the central buttressed section of the dam. The pass is composed of four adjacent Borland lift type passes which all exit into the dam at different levels. This is to accommodate the large fluctuations in water level which characterise this dam. A small subsidiary dam is located to the East of the main section, separated by a small hill and is rubble fill with a turfed downstream face. This is a large-scale dam which occupies a dominant position at the top of a large valley in an upland area. The prominent walkway spans the fixed spillway on large concrete piers. The large central buttress flanked by concrete gate control towers is a dramatic feature and houses an unusual four level fish pass. National Archives of Scotland (NAS), Ref: NSE North of Scotland Hydro Electric Board Collection (1943 -1990); NAS, Ref: NSE1 North of Scotland Hydro Electric Board Minutes (1943-1990); NAS, Ref NSE2 North of Scotland Hydro Electric Board Annual Reports (1943-1990); PL Payne, 1988; J Miller, 2002, 92; Scottish Hydro Electric, 2000, 10.

The Conon scheme

This project involves three separate stages: the Fannich scheme, the Glascarnoch-Luichart-Torr Achilty scheme and the Orrin scheme. The first of these involved tunnels and aqueducts to increase the flow into Loch Fannich, and a tunnel from the bed of Loch Fannich to the Grudie Bridge power station at the west end of Loch Luichart. This involved a severe problem at the Loch Fannich end. Work began in 1946 and a dam was built later, completing the section in 1951.

Work began on the second stage in 1951., producing two artificial lochs Vaich and Glascarnoch by damming the respective rivers, using the earth and rockfill method. Tunnels were excavated between these lochs and from Loch Glascarnoch to Mossford power station on Loch Luichart. A dam at the east end of Loch Achanalt allows loch to supply the Achsanalt power station near Grudie Bridge. Two artificial lochs Meig and Achonachie were produced by dams on the rivers Meig and Conon to supply power stations at Luichart and Torr Achilty respectively. Work on this section was completed in 1957.

The Orrin scheme was started in 1955 and involved the building of a mass gravity dam 1000 feet long and an earth embankment also 1000 feet in length to seal off a branch valley, thus forming the Orrin Reservoir. The outflow is through a concrete -lined tunnel to a steel pipeline supplying the Orrin power station at Loch Achonachie. Four Borland fish lifts had been installed at Luichart, Meig, Achanalt and Torr Achilty. The scheme was completed in 1961, the six power stations producing an output well over 100,000 kW.

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