Scottish Water

Conditions Of Contract
NEC Option C

94 weeks

Contract Value


Loch Thom reservoir was built in 1824 and is located within the Clyde Muirshiel Regional Park in the hills above Greenock, Inverclyde.

Driven by guidance documents that were produced after a number of incidents experienced in England in 2007, the project team’s task was to design and construct a mechanism to lower the water level within the reservoir quickly and over a short period of time, to alleviate potential water pressures against the dam face.


The complex project, which required significant temporary works to excavate through the dam structure, consisted of the installation and commissioning of 3 No 1100mm dia. siphon pipes at the Main Embankment including earthworks to form an access berm on the downstream face of the embankment to provide vehicular access to a new chamber set within the crest of the dam; laying of pipework within the reservoir through the crest chamber and down the downstream face of the embankment to discharge into the existing spillway channel, together with associated control valves and priming pipework.

Works to the existing spillway channel included the raising of the spillway channel walls along its length by constructing a new reinforced concrete invert and walls, generally within the existing channel except for approximately a 60m section of the left hand wall, immediately downstream of the weir, which was broken out and re-built to widen the channel and maintain existing outflow characteristics.

The crest heights of Embankment No. 4 will be raised by 1.30m and Embankment No. 5 by 0.95m to provide sufficient freeboard.

Would you like to know more about this project?
Get in touch with Simon Butler