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Tongland Dam and Tunnel
River Dee, Dumfries & Galloway, Scotland, UK
associated engineer
Sir Alexander Gibb & Partners
date  1931 - 1934
UK era  Modern  |  category  Dam/Reservoir  |  reference  NX701544
ICE reference number  HEW 1457/02
Tongland Dam provides daily water storage for Tongland Power Station, the principal control station of the Galloway Hydro-Electric Scheme. Water is delivered from the reservoir through more than a kilometer of rock-drilled and concrete aqueduct tunnels to the power station, which lies to the south, near Kirkudbright.
The Tongland complex is the most southerly end of Galloway scheme and it generates electricity using water from the entire catchment. The spent water is discharged into the River Dee, which is tidal at this point, and thence to the Solway Firth.
The dam is a 298m-long combined concrete arch and concrete gravity structure, similar in design to the dams at Kendoon, Carsfad and Earlstoun. It impounds 8.8 million cu m of water in a long narrow reservoir to the north, which has a top water level 36.6m above sea level.
The concrete arched section is built on a 44.5m radius out from the west bank of the River Dee, which has a steep cliff more than 30m high at this point. This section is 21.3m high and 88.4m long. The batter on the downstream face has a 4 in 1 gradient. The mass concrete gravity section lies to the east of the arch and seals what is believed to be the former channel of the River Dee.
To the east of this are two free-roller flood gates and the spillway channel. The flood gates are each 7.6m wide and 9.5m high. Either can be lifted clear of the water using the 4.5kW 400V three-phase motor. Water issuing from the gates falls onto a concrete apron and joins water from the 91.5m spillway channel, returning to the river downstream of the dam.
A long, winding fish ladder south of the dam enables migratory fish to travel upstream into the reservoir. It has 29 steps (water-filled chambers) arranged in five flights, each with a rise of a little more than 600mm, and four resting pools. In May 1998 the top five steps were modified with diagonal walls and bigger openings to reduce turbulence, enabling larger fish to pass more easily.
Water from the reservoir is sent to the power station through an intake located on the west bank near the dam. The intake is 33.5m wide and leads into a 146m tunnel excavated through bedrock and lined in concrete. This tunnel connects to a 1km reinforced concrete aqueduct tunnel, which is a flattened circle in cross section, with axes of 6.7m wide and 5.5m high. These proportions produce an approximately uniform circumferential stress in the steel reinforcement not exceeding 82,740kN per sq m under varying internal pressures.
At the end of the aqueduct sits a 30.5m diameter steel surge tower supported on a concrete arched base. Here the water enters a trifurcating steel pipeline. Each of the three 3.5m diameter emerging pipelines conveys water to the adjacent valve house and thence the final 24m run downhill to the turbines inside the power station.
The power station can operate with a net head of water of 29m-34.75m. Power is generated at 11.5kV and then stepped up to 132kV for transmission to the National Grid. The station's three turbines were the largest of their type on installation.
The Tongland dam complex was completed in 1934, and the power station was commissioned in May 1935. It was the first power station to be controlled remotely by a telephonic operating system, and is now activated from a control centre at Glenlee Power Station.
Scottish Power’s Galloway Hydros Visitor Centre is located at Tongland, providing information about the whole scheme.
Contractor: John Howard & Co Ltd
Contractor (power station): Payler & Son, Glasgow
Contractor (surge tower): William Taylor & Son (Glasgow) Ltd
Research: ECPK
"Modifications to a Fish Pass at Tongland Dam" by A. Ervine, B. Couvel, J. Stuart and C. Carnie, Scottish Power and University of Glasgow, 1998
"Galloway Hydro-Electric Scheme" information leaflet
available at www.scottishpower.com
"Galloway Hydros" series of factsheets available at www.spenergywholesale.com
reference sources   CEH SLB

Tongland Dam and Tunnel