Breadalbane Hydro-Electric Scheme

Breadalbane hydro-electric scheme
River Tay River Lyon Loch Tay River Almond Lednock power station River Earn Dalchonzie power station St Fillans power station Loch Breaclaich Lochan na Lairige dam Finlarig power station River Lochay Loch Earn Lochay power station Cashlie power stations Stronuich Reservoir Loch an Daimh Lubreoch power station Loch Lyon dam River Lochay River Dochart

The Killin section consists of three power stations, Cashlie, Lubreoch and Lochay, with two major dams and a third smaller one. Furthest west, Lubreoch dam was constructed at the eastern end of Loch Lyon by James Miller and Partners. It was 1,740 feet (530 m) long and 129 feet (39 m) high from the foundations to the crest. It was of the massive butress type and was completed in 1958. The catchment area was increased by building a network of tunnels and aqueducts to the south of the dam, picking up the headwaters of a number of tributaries of both the River Lochay and the River Dochart. Lubreoch power station is located below the dam, and was commissioned in 1958. It has a gross head of 98 feet (30 m) and can generate 4 MW. To the north of the power station is Loch an Daimh, which is dammed at its eastern end by Giorra dam. The structure was built by Edmund Nuttall and is 1,518 feet (463 m) long, with a maximum height of 114 feet (35 m). It is also of the massive butress type, and was completed in 1959. Its catchment has been increased by tunnels and aqueducts to the south and east, picking up tributaries of the River Lyon. A tunnel runs from the dam to Cashlie power station, which discharges into Stronuich Reservoir. It has a gross head of 466 feet (142 m), can generate 11 MW, and was commissioned in 1959.[16]

Stronuich Reservoir is formed by the Stronuich dam, a long low structure that dams the River Lyon. It stores water from the tailraces of Lubreoch and Cashlie power stations. Compensation water to maintain the flow in the River Lyon passes through a generator set below the dam. An intake gatehouse tower is located at the southern end of the dam, and controls the flow of water to Lochay power station.[17] A long tunnel from the reservoir supplies water to Lochay power station, which discharges into the River Lochay a short distance before it joins the River Dochart and enters Loch Tay. It has a gross head of 591 feet (180 m), can generate 47 MW, and was commissioned in 1958.[14]

The St Fillans section consists of another three power stations, Lednock, St Fillans and Dalchonzie, with two major dams, Breaclaich and Lednock. Lochan Breaclaich dam prevents water flowing into the Loch Tay catchment. It is a rockfill dam, with a concrete panels on the upstream side and coursed rubble on the downstream side. A gatehouse controls the inlet to a tunnel and pipeline which feeds Lednock power station.[18] A tunnel collects headwaters from streams flowing into Loch Tay to the south-west of the reservoir, while another tunnel conveys water to Lednock power station.[14] This contains a single 4 MW turbine, which is protected by a surge tower to the north-west of the station. The water discharges into Loch Lednock.[19] The power station has a gross head of 299 feet (91 m) and was commissioned in 1961.[14]

Loch Lednock is contained by a diamond-headed butress dam at its eastern end. The dam was constructed by Taylor Woodrow, is 950 feet (290 m) long and 133 feet (41 m) high. It was completed in 1957. The catchment of Loch Lednock is supplemented by a tunnel collecting the headwaters of the River Almond.[14] There is only one other diamond-headed butress dam in Scotland, at Errochty. Because it is close to the Highland Boundary Fault, it was designed to cope with earthquakes. A dispersal valve discharges compensation water through the dam to maintain the flow in the River Lednock. There is an intake gatehouse around half way along the loch, which controls the flow of water to St Fillans power station.[20] This was the first of the additional power stations to be commissioned when it was completed in 1957. It has a gross head of 830 feet (250 m) and can generate 21 MW. The power station is constructed underground, whereas all of the others have buildings on the surface. It discharges into Loch Earn, which in turn supplies the River Earn.[14] A small weir just below the outlet from the loch diverts some of the flow into a tunnel to provide power for Dalchonzie power station. It contains a single 4 MW turbine,[21] and discharges back into the Earn. Its gross head is 95 feet (29 m) and it was commissioned in 1958.[14]

Dalhonzie power station and tailrace

The North of Scotland Hydro-Electric Board were always looking for ways to improve their processes, and there is evidence of this at Breadalbane. The rock fill dam at Breaclaich was built to reduce the amount of cement used, and this technique had previously been used at Quoich. Fly ash was used to replace some of the cement used in the construction of the dams at Lednock, Lubreoch and Giorra. This causes the concrete to harden more slowly, but is less permeable once it has cured.[12] Although several of the dams are similar, they are different in detail, as new methods were used to reduce the amount of concrete and shuttering that was required. The massive butress dam proved to be considerably cheaper to build than a solid gravity dam, by about 30 percent.[22]

There were advances in tunnelling techniques too. The main tunnels connected the reservoirs to the power stations, but there were also lots of tunnels used to divert water from other catchments. In total, the scheme involved some 60 miles (97 km) of tunnels, and the Board worked hard to train tunnellers and improve drilling techniques. The tunnel from Stronuich to Lochay is 13 feet 5 inches (4.09 m) in diameter, and some 4.73 miles (7.61 km) long. While a world record was claimed in October 1955 when a collecting tunnel in the St Fillans section advanced by 557 feet (170 m) in seven days,[23] the Lochay tunnellers hit a water-bearing fault which resulted in 50,000 imperial gallons (230 m³) per hour flowing into the workings, and flooding 5,000 feet (1,500 m) of the tunnel. The potential disaster was dealt with relatively easily, by pumping out the tunnel and using cast iron segments to line a diversion. All of the tunnelling on the Killin section was completed nine months ahead of schedule. Most of the scheme was completed by late 1959, with only the Lednock station held up by issues with the Breaclaich section, resulting in it not being commissioned until March 1961.[24]