Orrin Portal Valve

This valve house contains the large butterfly valve which allows for the isolation of the penstock carrying water out of the tunnel from Orrin Dam and down to Orrin Power Station. This valve house echoes the functional style of the powerhouses on the Conon scheme and exhibits a similarly restrained use of architectural detailing, predominantly limited to some plain detailing to the door surround. In line with the wishes of James Shearer the buildings is constructed from local stone some of which may have been reclaimed from the excavation of the tunnel through to Orrin Dam as was the case with other underground structures such as Deanie and Cuilligran Power Stations (see separate items on Affric scheme). PL Payne, 1988, 5; E Wood, 2002, 38; J Miller, 2002.

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.