The Scottish Highlands contain the United Kingdoms highest hills and ground, the largest and deepest inland lochs, the most extensive of its moorlands.
The Tummel Valley catchment area and hydro power developments cover about 1800km2 of the Grampian mountains.
The terrain was formed during the last ice age, when glaciers moved through the region, carving deep, steep-sided valleys. Loch Tummel, Loch Rannoch and Loch Ericht now fill the valley bottoms. Higher up in the hills of this region sit two smaller lochs - Loch Garry and Loch Errochty. The high ground between these valleys receive very heavy rainfall, keeping water levels in all the Lochs consistently high.
The heavy rainfall and the difference in height between the water masses in the lochs are the natural features that have been used in the development of the hydro electricity generation this century.
The locations of the main hydro facilities in Scotland are shown on the map below. The Tummel Valley catchment area is shown in purple.
Water is diverted from the Loch to Errochty power station through an underground tunnel. The tunnel is 10km long and the flow of water is sufficient to produce a maximum of 75MW - Errochty power station is the largest of the Tummel Valley stations. Water from its turbines discharges into the west end of Loch Tummel.
Errochty power station is a high-head development; water drops 186m between Loch Errochty and the turbine inlets. The turbines are designed to exploit the large water pressures but relatively low water flow rates compared to the dam at Pitlochry described below.
At the east end of Loch Tummel, 11km from Errochty power station, Clunie dam was constructed to control the flow of water out of the Loch. This raised the level of the whole of Loch Tummel by 5m. Water flows from Loch Tummel through a tunnel to supply the 61.2 MW Clunie power station. After passing through one of the turbines at the power station, water discharges into Loch Fascally.
The Southern Hydro Group control centre is at Clunie power station. All the major installations in the Tummel Valley are controlled from the centre by remote control.
All the water from the Tummel Valley Hydro electric scheme passes through Pitlochry dam. The varying water flow from Clunie power station and the River Garry upstream of the dam can be absorbed because of the volume of water that Loch Faskally now holds, so that a controlled and fairly constant flow of water can be maintained at Pitlochry power station.
Pitlochry power station is a low - head system. There is a 15m difference between the turbine inlet and the normal water level in Loch Faskally. When operating at full capacity, the power station generates 15MW. Though the generated power is five times less than that produced at Errochty power station, it is generated from a head of water twelve times less. The power station at Pitlochry has a different turbine arrangement, designed to exploit the greater water flowrates available at the dam.