Loch Errochty

Loch Errochty
The eastern end from Beinn a' Chuallaich
Location	Perth and Kinross, Scotland
Coordinates	56°45′40″N 4°8′40″W / 56.76111°N 4.14444°W / 56.76111; -4.14444Coordinates: 56°45′40″N 4°8′40″W / 56.76111°N 4.14444°W / 56.76111; -4.14444
Type	freshwater loch, reservoir
Basin countries	United Kingdom
Max. length	5 km (3.1 mi)
Max. width	1 km (0.62 mi)
Surface area	3.03 km2 (1.17 sq mi)
Surface elevation	330 m (1,080 ft)

Loch Errochty is a man made freshwater loch situated within the Perth and Kinross council area at the edge of the Scottish Highlands near the Highland Boundary Fault where the topography changes to lowland.

The Errochty dam lies at the head of Glen Errochty, two km NW of the hamlet of Trinafour at the approximate grid reference of NN689654. The loch has an area of 303 hectares and is 5 km long and a kilometre across at its widest point. The loch is entirely man made, being created by the damming of the Errochty Water, the river which runs down the glen. The dam was constructed in 1957 by the contractors A. & M. Carmichael Ltd as part of phase two of the Tummel hydro-electric power scheme. The loch stands at 330 metres above sea level. The dam itself is an example of a diamond-headed buttress dam, it is 49 metres high and 354 metres across. The diamond-headed buttresses provide extra strength to deal with possible tremors from the Highland Boundary Fault which runs just to the south of Pitlochry. Water from Loch Errochty is diverted through a 10 km long tunnel to the Errochty hydroelectricity power station at the western end of Loch Tummel. The gatehouse for the tunnel at Loch Errochty is near the southern shore, the actual intake is beneath it at the bottom of the loch. The power station has a maximum output of 75 MW and is the largest power producer of the nine main stations in the Tummel scheme. Water is released from the dam to compensate the flow of the Errochty Water, this compensation water flows down a pipeline for 1.5 km to the very small 500 kW hydro power station at Trinafour before being released into the Errochty Water.

Loch Errochty’s main feeder streams are the Allt Sléibh and the Allt Ruighe nan Saorach which both rise in the high ground to the west of the head of the loch. Other small streams flow directly off the 892 metre high mountain of Beinn a' Chuallaich which stands just to the south. Supplementary water is diverted into the loch from the east by the Errochty catchwater, a system of tunnels and surface pipelines at a height of approximately 380 metres which redirects water from five small tributary streams of the River Garry, and the Garry itself. The catchwater then goes through a tunnel in the hill which separates the Garry and Errochty valleys to join the loch. This method of re-directing water allows it to be used more often to generate electricity. Some of the water within the Tummel scheme passes through five of the power stations and thus generates electricity five times.