Tummel hydro-electric power scheme

The Tummel hydro-electric power scheme is an interconnected network of dams, power stations, aqueducts and electric power transmission in the Grampian Mountains of Scotland. Roughly bounded by Dalwhinnie in the north, Rannoch Moor in the west and Pitlochry in the east it comprises a water catchment area of around and primary water storage at Loch Ericht, Loch Errochty, Loch Rannoch and Loch Tummel, in Perth and Kinross. Water, depending on where it originates and the path it takes, may pass through as many as five of the schemes nine power stations as it progresses from north-west to south-east. The scheme was constructed in the 1940s and 50s incorporating some earlier sites. It is currently managed by SSE plc.

Early Development

With a growing need for electricity in the central belt of Scotland individual power stations at Rannoch and Tummel Bridge plus associated dams and infrastructure were constructed in the 1930s for the privately owned Grampian Electric Supply Company. These were notable for being the first storage high-head stations, where water is held in a reservoir above the power station, rather than simply relying on water passing as part of the run of the river as had previously been done in Scotland.

Water started in the catchment of Loch Ericht, where a dam was built to raise the natural level by which, along with a deepened section of loch, resulted in approximately 78,050 acre feet (96,277,000m³⁾ of water storage. Water would then pass through tunnels and increasingly narrow pipes, reducing from 12 ft 4 in to 7 ft 10.5 in (3.7 m to 2.4 m), as it dropped the to Rannoch power station on the northern bank of Loch Rannoch. At that time Rannoch was fitted with two 22,000 hp (16,500 kW) water turbines with provision for a third. Steel towers, some high, carried 132 kVA power lines east along the bank of the Loch.

Loch Rannoch formed the main storage for the next station in line at Tummel, about downstream to the east. A weir was built at Kinloch Rannoch to regulate the depth at the exit of Loch Rannoch to , this being an increase of about 4 feet, with water passing down the River Tummel for to a narrow point where Dunalastair dam was constructed creating an artificial loch known as Dunalastair Water. From here an open aqueduct carried the water the remaining 3 miles (5 km) to Tummel where a head of was provided for two 24,000 hp (18,000 kW) horizontal generators with the electricity generated connected into the same transmission line as Rannoch. The discharge water then rejoined the river Tummel for 2 km before entering Loch Tummel.

The various works were designed and built by Balfour Beatty with consultant engineer William Halcrow.

Main Scheme

Background

In the early 1940s various schemes were proposed for electricity development across Scotland and the nationalised North of Scotland Hydro-Electric Board was established in 1943 to undertake some of them. The schemes, including the then named Tummel-Garry Scheme, were not universally welcomed. Objections were varied but centred around the loss of landscape, the likely use of a transient workforce and the economic advantages being 'exported' to England where the demand for electricity was higher as, when the Tummel-Garry scheme was introduced, only 1 in 6 farms and 1 in 200 crofts in Perthshire had electric power. The various campaigns resulted in the resignation of the first chair of the board Lord Airlie and Tom Johnston was appointed to run the board in 1946. His tenure lasted until 1959 and successfully completed many projects by pushing an agenda of social change through development.

Edinburgh based architect Harold Tarbolton of Tarbolton & Ochterlony was part of the NoSHEB architectural panel, along with Reginald Fairlie and James Shearer. The panel was responsible for much of the design of the later scheme's structures several of which are now listed. Listings include Pitlochry which is Category A (defined as "Buildings of special architectural or historical interest which are outstanding examples of a particular period, style or building type.") and is described by Historic Environment Scotland as "an outstanding example...a bold modernist design by Harold Tarbolton." The earlier Tummel and Rannoch power stations are also listed as Category A, being designed in "a simple classical style and with a bold outline."

Sir Edward MacColl was the board's engineer having previously been responsible for other hydro schemes. The contracting engineers were Sir Alexander Gibb and Partners and around 12,000 workers were employed at the peak of construction with workers including German and Italian former prisoners of war as well as a cohort of Donegal Tunnel Tigers, Irish tunnelling specialists who moved from job to job.

The scheme was expected to generate 635 Gigawatt-hours a year, by 1986 it had achieved an average of 663 GWh a year.

Water route

The 'green energy trail' map shows the completed scheme as offering four main water paths all of which ultimately arrive into Loch Tummel to feed the Clunie and Pitlochry stations. From the north the highest storage point in the scheme is at Loch an t Seilich (427 m above sea level). Water passes through a tunnel to Loch Cuaich at 397m to feed the Cuaich station discharging in to the north-east end of Loch Ericht at 359 m.

Alternatively water from Loch Garry at 415m feeds west through a tunnel to Ericht power station to also join Loch Erich. The combined water, along with Ericht's own catchment, then feeds to Rannoch and onto Tummel as per the 1930s scheme.

From the west water from Rannoch Moor is impounded at Loch Eigheach on the River Gaur to feed Gaur power station before discharging along the river and into Loch Rannoch to join the Ericht feed as well as Loch Rannoch's catchment.

In the centre of the system water from the River Bruar and River Garry is fed to storage at Loch Errochty at 329 m. Here it feeds directly to Errochty power station discharging into the mouth of the River Tummel. Some bypass water, used to maintain a small river known as the Errochty Water, is used to generate power at Trinafour.

Regardless of path the water arrives at Loch Tummel where it is impounded by the Clunie Dam located in a narrow valley at the eastern end of the loch. The construction of this dam raised the water level by to create a reservoir with a capacity of 36,400,000 cubic metres. Water then passes through Clunie station to Loch Faskally which feeds the Pitlochry station.

The scheme power stations are generally, though not exclusively, named for their physical location as opposed to their feedstock. For example; Loch Ericht station is fed from Loch Garry but is adjacent to, and discharges into, Loch Ericht. A notable exception is Errochty power station, which discharges into Loch Tummel. It is also known as Tummel Bridge to disambiguate from the nearby, pre-existing Tummel station.

Ecological Impact

The scheme made many changes to the natural water courses across the region. Many of the schemes rivers and lochs are categorised as Heavily Modified Water Bodies (defined as a body of surface water which, as a result of physical alterations by human activity, is substantially changed in character.) Near the highest point in the scheme the upper River Garry was completely dry for a distance of 20 kilometres from the 1950s until a project in 2017 returned some water, around 1 cubic meter a second, to the section. Other associated changes included the removal of a weir at Struan to allow fish to pass up the river.

The scheme has nine named dams and one weir. The 1930 dam at Ericht (for Rannoch) appears to have been extended as part of the later scheme.

Listed by SSE as main dams are: Gaur, Errochty, Clunie and Pitlochry. Other dams are at Ericht, Dalwhinne, Dunalastair, Cuaich, and Tromie (Lochan-t-Seilich). A significant weir at Kinloch Rannoch is also part of the scheme.

References

Department of Trade and Industry statistics

External links

Tummel hydro-electric scheme informationMap of the scheme on page 19

Buildings and structures in Perth and Kinross
Hydroelectric power stations in Scotland

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