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Loch Thom, Compensation Reservoir

Reservoir (19th Century)

Site Name Loch Thom, Compensation Reservoir

Classification Reservoir (19th Century)

Alternative Name(s) Greenock Waterworks; Shaws Waterworks; Kip Water; Shielhill Glen

Canmore ID 202205

Site Number NS27SE 58.01

NGR NS 25038 72264

Datum OSGB36 - NGR

Permalink http://canmore.org.uk/site/202205

Ordnance Survey licence number 100057073. All rights reserved.
Canmore Disclaimer. © Copyright and database right 2020.

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Digital Images

Administrative Areas

  • Council Inverclyde
  • Parish Inverkip
  • Former Region Strathclyde
  • Former District Inverclyde
  • Former County Renfrewshire

Archaeology Notes

NS27SE 58.01 25038 72264

For dam and sluice at the SW end of this reservoir, see NS27SW 72.

Formerly entered as NS27SE 112: location cited as Centred NS 25038 72264.

Formerly entered in error as within Greenock parish.

Extends onto map sheet NS27SW.

Compensation Reservoir [NAT]

OS 1:10,000 map [NS27SE], 1980.

Activities

Publication Account (2007)

Greenock Water Works – Loch Thom and ‘Cut’

Following an Act in 1773, James Watt planned and supervised the provision of an improved water supply from two small reservoirs built on the lower slopes of Whinhill, from which water was conducted in wooden pipes to a cistern at the Wellpark. Although augmented, by the 1820s the supply had become inadequate and the town embarked on an innovative ‘green’ project designed and directed by Robert Thom, owner of Rothesay Cotton Mills, Bute, and a leading hydraulic civil engineer at Rothesay Mills, where he had a ‘green’ power scheme operational by 1820.

The Shaws Water Company, as Thom’s Greenock scheme was known, involved creating behind the town from 1825–27 the ‘Great Reservoir’, later renamed ‘Loch Thom’ by means of an earth dam about 48 ft high. It had a capacity of about 1800 million gallons. From a ‘Compensation Reservoir’ to the west, water was fed into an almost level (1 in 600) open five and a half mile ‘Cut’, as it still isknown, along the hillside to the contour Town Head service reservoir at Overtown (‘N’ on above figure) about 512 ft above the Clyde (see plan). The estimated cost of the scheme in 1824, including numerous smaller reservoirs and channels, was £16 000. The Cut, which falls about 50 ft over its length, intercepted intervening burns, is about 5 ft wide and whenoperational contained up to about 2 ft of water, is rubblemasonry lined and has a downside bank and inner clay puddle wall. At intervals there are stone waster sluice houses and 22 hump-backed bridges.

The work was done by contractors responding to local advertisements. A William Kirkwood was paid £6 10s for building a bridge.The project abounded with novel self-acting machinery of which an example, although not now working, of one of his more simple mechanisms has survived at a waster (NS 9076 4437). When maximum water level in the Cut was reached, water passed via a pipe into a suspended cylindrical bucket with small holes at its base. As thebucket increased in weight it descended and operated a mechanism which opened the waster valve. Being no longer fed, the water in the bucket ran out through the holes causing it to rise and thus close the valve. From sluices at the service reservoir, Greenock was supplied with water for domestic and industrial consumption and, via a lade with two branches down to the Clyde, power at ‘mill-seats’ or falls en-route for waterwheels at mills, factories, and other industrial concerns.

The first phase of the scheme was completed in 1827. The Company guaranteed a specified supply of up to 1200 cu. ft of water per minute, 12 hours a day, 310 days a year, to its subscribers. As late as 1900 there were still 25 falls let on the lade. They varied in the power produced from 21 hp at Scott’s sugar refinery to 578-hp in the six falls at the mills

of Fleming, Reid & Co. The Shaws Water Cotton Spinning Company harnessed its falls of 64 ft to a remarkable iron water wheel of 70 ft 2 in. diameter, 12 ft wide, weighing 117 tons; one of the world’s largest and most powerful, designed and made by the engineer James Smith at his Deanston works, Doune, in the 1830s. The wheel produced about 192 hp net, assuming 75% efficiency, and operated 25 760 mule and throstle spindles. It was replaced in use by a turbine in 1881 and dismantled in 1918. Thom’s success led him in 1829 to propose a supply and power scheme for Edinburgh from a reservoir at Harperrig to a cistern at Craiglockhart 227 ft above Haymarket, and several schemes in and around Glasgow from 1835–41. Only one, at Paisley, seems to have been executed, although an almost identical Harperrig scheme was

executed under Leslie’s direction for Edinburgh water supply in 1859 as compensation water, mainly for mills. Of three Glasgow schemes his most ambitious was for a 30 ft wide canal 30 miles long from the Clyde above Stonebyres Falls, via Airdrie, to a ten acre night storage reservoir at Glasgow, 220 ft above the Clyde. He envisaged producing 3850 hp and an annual income from water power alone of £92 750 for an outlay of £318 560. There were drawbacks and neither this nor his other proposals for Glasgow in 1836–37 were adopted.

The Cut, disused and deteriorating since it was bypassed in 1971 by Loch Thom Tunnel (consulting engineers Babtie, Shaw & Morton), is now part of Clyde–Muirsheil Park. There is local interest in its retention as an outstanding landmark and in 1995 consulting engineers Scott, Wilson, Kirkpatrick were commissioned and reported fully on the feasilibility of restoration.

R Paxton and J Shipway 2007

Reproduced from 'Civil Engineering heritage: Scotland - Lowlands and Borders' with kind permission of Thomas Telford Publishers.

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