Loch Vaich, Dam

Vaich Dam gathers water from a separate catchment to Loch Glascarnoch (see separate item) providing storage capacity in the scheme. Water leaves the dam through a tunnel before existing into Loch Glascarnoch via a small later turbine. The dam wall is composed of rubble with a vegetated turf top. As a consequence the dam cannot spill as this would excessively erode the dam wall. In place of a spillway two large spill towers sit out in the loch which drain water through a pipe, existing downstream of the dam wall. This dam is of an unusual type for Scotland with a rubble and earth downstream face abutting a waterproof concrete up-stand. The large spillway towers are an unusual technical response to the problem of erosion which would caused by conventional spilling in this case with an earth downstream face. 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; E Wood, 2002, 30; J Miller, 2002, 92:88918; 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.