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Loch Thom, Aqueduct

Aqueduct (19th Century)

Site Name Loch Thom, Aqueduct

Classification Aqueduct (19th Century)

Alternative Name(s) Greenock Waterworks, Main Aqueduct; Overton; Greenock Cut; Loch Thom - Overton, Water Cut; Shaws Waterworks

Canmore ID 75372

Site Number NS27SW 24

NGR NS 2296 7300

NGR Description NS 2472 7208 to NS 2696 7488

Datum OSGB36 - NGR


Ordnance Survey licence number 100057073. All rights reserved.
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Administrative Areas

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

Archaeology Notes

NS27SW 24.00 2472 7208 to 2696 7488

NS27SW 24.01 NS 23940 72125 Sluice (House)

See also NS27SW 40.00, NS27SE 57.00 and NS27SE 58.00.

For (associated) Loch Thom, Reservoir (NS 26300 72319) and Loch Thom, Compensation Reservoir (NS 25038 72264), see NS27SE 58.00 and NS27SE 58.01 respectively.

For (associated) Overton Reservoirs, see NS27SW 40.00 and NS27SE 57.00, and sub-numbers.

NS 2472 7208 to NS 2696 7488. The main aqueduct made by Robert Thom in 1827 to supply Greenock's mills.

J Ferrier 1966

No longer used for water supply, but preserved by the Lower Clyde Water Board.

J R Hume 1976.

NS27SW 69 2467 7204 to 2664 7481

See also NS27SE 58.00.

Structures related to aqueduct (Inverkip and Greenock parishes)

NS 2467 7204 to NS 2664 7481 A survey was carried out of the upstanding remains along the 8km Greenock Cut, constructed by Robert Thom in 1827 to provide water power to mills at Greenock. The scheme is well-documented historically, but despite being Scheduled many of the physical remains are now in very poor condition.

The features fall into two main types: bridges and sluice buildings. The former are standard rubble-built hump-back bridges spanning the 3m wide lade, c 3.5m wide, with parapets 1m high with distinctive rounded ends. Some bridges incorporate cast-iron sluice runners on their upstream side, with an ashlar course in the bed of the lade below, which allowed temporary damming of the lade for maintenance.

The flow in the lade was controlled by a row of sluices at the head of the cut at NS 2467 7204, but water from various burns contributing to the cut along its length could cause overtopping when in spate. Thus the need for the second main group of features along the cut, the rubble sluice buildings with vaulted roofs. These are located on the downslope side of the cut, with walls 0.6m thick and a square door with the sluice exit vertically below it. Originally each building enclosed an automated overflow mechanism or 'waster' invented by Thom, first used at his Rothesay cotton mills in 1817, but few now remain.

Working downstream, the features are:

NS 2467 7204 Timber sluices at entry to cut from compensation reservoir. Much modern alteration in this area.

NS 2421 7189 Bridge, upstream parapet ruined.

NS 2407 7204 Road bridge over lade with flat deck.

NS 2394 7212 Waster house near Shielhill farm (NS27SW 24.01).

NS 2376 7227 Bridge, upstream parapet ruined.

NS 2356 7243 Rubble bothy, 4.3 x 3.3m, with fireplace, pipe flue and plastered walls. Monopitch steel joist and concrete infill roof.

NS 2352 7245 Bridge, intact; 20m downstream of bridge, lade wall is breached allowing complete loss of water.

NS 2337 7263 Rubble waster house, 3.7 x 3.2m, set into lade bank on edge of gorge. Doorway on downhill side, accessed by steel access platform. Inside house, iron sluice mechanism largely intact, including cast-iron flap valve with lever and chain attached, pulley wheel in roof, and float cylinder.

NS 2331 7270 Bridge, loose parapet masonry.

NS 2309 7285 Bridge, intact.

NS 2297 7305 Bridge, upstream parapet partly ruined.

NS 2309 7328 Bridge, upstream parapet missing.

NS 2313 7337 Ruined roofless rubble waster house, 2.5 x 1.7m, set into lade bank, walls reduced to 1.5m height. Cast-iron flap valve in situ on wall adjacent to lade.

NS 2320 7358 Bridge, upstream parapet ruined.

NS 2339 7373 Bridge, downstream parapet missing.

NS 2366 7387 Bridge, upstream parapet missing.

NS 2383 7378 Roofless ruined rubble bothy, 4 x 3.7m, partly set into lade bank, with fireplace in pitched gable facing door. Walls reduced to 1.6m height.

NS 2382 7382 Timber sluice gate in iron frame, largely intact.

NS 2383 7390 Overflow passing through ashlar-lined culvert under lade path with vaulted concrete deck.

NS 2385 7405 Bridge, keystone of arch missing.

NS 2404 7431 Bridge, intact.

NS 2417 7441 Bridge, intact.

NS 2469 7460 Timber sluice gate in iron frame, largely intact. Overflow passes through ashlar-lined culvert under lade path with cast-iron beam edging concrete deck.

NS 2465 7461 Rubble waster house, back wall missing exposing rubble arch of roof vault. Front wall ruined, partly repaired in brick.

NS 2475 7479 Bridge, parapets partly collapsed.

NS 2501 7486 Bridge, parapets partly collapsed.

NS 2517 7491 Bridge, intact.

NS 2544 7494 Stone banks indicate former bridge site.

NS 2597 7478 Bridge, deck completely collapsed into lade, parapets ruined but still free-spanning across lade.

NS 2601 7469 Rubble waster house, 3.8 x 3.6m, vaulted roof crumbling at rear, interior floor concreted over. Iron frame and ashlar tunnel of former sluice gate under lade path 17m to E. Overflow channel leads to concrete dam (breached) directly downstream.

NS 2647 7484 Stone banks, 3m long, indicate former bridge site.

NS 2664 7481 Overton Bridge; wider than standard bridge to carry road traffic. Cast-iron memorial drinking fountain in upstream parapet marking centenary of opening (1927). Lade then enters Long Dam before commencing descent into Greenock.

Sponsor: Renfrewshire Local History Forum.

S Nisbet 2004.


Publication Account (1984)

Water flowed from the Loch Thom or Great Reservoir on 16th April 1827 to the eastern line of falls. A great technical feat, at the time of opening there were 4 mills on the 19 falls on the eastern line. These were James Walkinshaw's papermill, Tasker, Young and Co.'s sugar refinery, the Associated Baker's grain mill and a powerloom factory (McNab and Co.).

J Shaw 1984

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.

External Reference (2 September 2011)

Scheduled (with NS27SE 54.00 and constituent elements) as 'The monument known as Loch Thom-Overton, water cut... an aqueduct. reservoir, sluices, sluice houses and workmen's bothies, commonly known as "The Greenock Cut". The monument is part of a larger water system built to provide drinking water for Greenock and water power for industry in the town. Water was collected from the moorland to the south of Greenock and conveyed around the aqueduct to the town's mills. The monument was designed by Robert Thom and built between 1825-7 by Shaw's Water Company. The aqueduct became obsolete in 1971 when a tunnel was opened from Loch Thom to the town. The monument is located in rough pasture at 165m above sea level.'

Information from Historic Scotland, scheduling document dated 2 September 2011.


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