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Glenlee Tunnel [Outfall]

Blackbank Wood, Glenlee, SW of St John's Town of Dalry, Kirkcudbrightshire.

Tunnel, Hydro-electric Scheme.

A tunnel links a causeway intake at Clattershaw Loch with an outfall at the given coordinates where a pump house transfers water into headrace pipes which feed Glenlee Power Station below. A surge shaft is located at [NX 6012 8013], and an adit entrance branch (c.100m long) opens onto the hillside at [NX 59492 79454].

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"Glenlee Tunnel connects Clatteringshaws reservoir to Glenlee Power Station. Water is not drawn off from the reservoir at the dam, but at the eastern side north of it. The tunnel has a total length of 3.6 miles and a flattened circular cross-section of 11 ft equivalent diameter. It is concrete lined throughout and over the greater part of its length is constructed on a gradient of 1 in 350, the last 3600 ft being on a gradient of 1 in 100. At about its midpoint the tunnel passes under the Craigshinnie Burn, which is intercepted and its water led into the tunnel through one of the vertical driving shafts adapted for the purpose. There is a surge shaft on the tunnel close to the downstream portal at Glenlee. The main contractor for the tunnel construction was A. M. Carmichael and for the steel pipeline, Sir Wm. Arrol & Co. Ltd." [Grace's Guide]

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"The water from the reservoir is taken down to Glenlee Power Station in the Ken Valley through a tunnel of horseshoe section 19,050 feet long. The intake to the tunnel is not near the dam itself, but some one and a half miles away on the eastern bank of the reservoir. The water from the reservoir is diverted to the intake tower of the tunnel through a canal 44 feet wide and 2,300 feet long... The intake tower is a reinforced concrete structure with a total height of 98 ft 9-in. It is a circular shaft with an external diameter of 17 feet above ground level, and below ground level the walls are concreted solid against the excavated rock. The base of the tower is connected to the tunnel through a bell-mouth opening with vertical sides lined with reinforced concrete. The transition from the elongated mouth to the normal tunnel takes place in a length of 22 feet.

The tunnel was excavated to full diameter in free air and without a heading, except at one point. The internal diameter of the upper section of the tunnel is 11 ft 6-in. The internal diameter of the invert is 30 feet. Excavation was undertaken from either end of the tunnel simultaneously, and the maximum rate of progress was about 100 feet a week. The rock surface was roughly dressed and a smooth concrete lining was applied.

About half-way along the course of the tunnel a further supply of water enters the tunnel through a shaft from Craigshinnie Burn. Across this stream a weir was built a short distance from the line of the tunnel. Above the weir excavations were made to form a small basin or forebay, from which the water was led through an inverted mushroom siphon into the shaft...

The surge shaft of the Glenlee tunnel was built 700 feet from the Glenlee end. It has a diameter of 24 feet, and was sunk from the hillside to meet the tunnel at a depth of 142 feet. At the surface the shaft has a concrete lip 5 feet high, in which openings have been cut. In the event of a surge the water will overflow through these openings into an artificially formed reservoir... Near the bottom of the surge shaft a large chamber, 105 feet long and about 24 feet high, was driven horizontally. This chamber accommodates sufficient water to keep the tunnel fully charged if the full load were suddenly to be switched on at the power station." [Wonders of World Engineering]

Alternative Names: None recorded.

Hydrographic Feeds: Clatteringshaws Loch