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Forestmill, Gartmorn Lade
Lade (18th Century), Sluice(S) (18th Century), Weir (18th Century)
Site Name Forestmill, Gartmorn Lade
Classification Lade (18th Century), Sluice(S) (18th Century), Weir (18th Century)
Canmore ID 238905
Site Number NS99SE 16
NGR NS 95394 93866
NGR Description Lade/feeder from NS 9539 9386 - NS 9281 9412
Datum OSGB36 - NGR
Permalink http://canmore.org.uk/site/238905
- Council Clackmannan
- Parish Clackmannan
- Former Region Central
- Former District Clackmannan
- Former County Clackmannanshire
Rare, striking horse-shoe plan weir of early design, created to direct water from River Black Devon (flowing E to W) through sluice into Forestmill Lade (see Notes) and return floodwater back over top of weir into river.
Built as part of John Erskine, Earl of Mar's water management system commencing at Forest Mill and incorporating sluices controlling water flow to 2.5km lade leading to Gartmorn Dam, the oldest reservoir in Scotland.
FURTHER DESCRIPTION: ashlar weir formed from raised platform of large slabs set around curve of squared stonework encompassing deep basin apparently set on bedrock. Weir sides at W slope down to approximately 4' in height.
The fine weir at Forest Mill is part of a hugely ambitious water management system visualized by Sir John Erksine in the closing years of the 17th century. Sir John had inherited the family estates in 1689 and needed an efficient and reliable water supply to operate new hydraulic machinery in his collieries at Alloa and Sauchie, as well as ensuring reliable drainage. The system demanded expertise beyond the scope of local engineers and Derbyshire based engineer George Sorocold, who was recognised by two of his contemporaries, Hatton and Thoresby, as the 'Great English Engineer' was commissioned to solve the problem. The resultant hydraulic scheme extends from the weir and sluices at Forestmill, together with a nearby smaller weir which has fallen into disrepair, along a lade a little under 2 miles in length which joins Gartmorn Dam to the west. Gartmorn Dam was created in 1713, and is the oldest reservoir in Scotland. It was substantially strengthened by Sorocold's scheme, and the lade which feeds it and which significantly raised the water level, by some 10' to 16' (accounts vary), runs alongside the River Black Devon which falls into a deep gorge just west of Forestmill.
The weir and lade, referred to as a dam-head and aqueduct, are described in the New Statistical Account: "nearly 140 years ago, the celebrated John, Earl of Mar, ... caused a strong dam-head to be thrown across the Black Devon, at Forest-Mill, ... by which he raised the bed of this river, 16 feet higher. From the top of this dam-head, he carried an aqueduct westward, about four miles, which carried the water into Gartmorn dam" (p8). The distance of four miles is inaccurate as the actual distance is less than two miles. In 1835 the Forestmill weir was rebuilt at a cost of £248, the account was raised by Alloa Colliery (NAS GD 124/17/594).
There are still three sluices near the weir, one is modern, but two significantly earlier examples are of timber and ironwork construction. (Historic Scotland)
Publication Account (2007)
In 1710 George Sorocold, a hydraulic and mining engineer from Derby, was commissioned by the 6th Earl of Mar to advise on the drainage of his coal mines at Sauchie north of Alloa. Sorocold recommended that the reservoir with its earth embankment which had been rebuilt by the Earl as early as 1694, now known as Gartmorn Dam (NS99SW 90.03), and which was fed with water from a small burn, should have its power capacity increased by means of a substantial additional feeder from Forest Mill on the River Black Devon about two miles to the east.
At Forest Mill, water from the river was diverted for the mill and feeder to Gartmorn Dam at a horseshoe shaped masonry weir some 10 ft high. Construction of the feeder along the north flank of the river valley, and requiring several rock cuts, was a considerable challenge in 1710. Sorocold set it out using a large wooden quadrant with a plummet set on a tripod. The feeder was cut soon afterwards (NS99SE 16, from NS9539 9386 to NS9291 9412).
His advice for improved pumping at the mines seems to have been disregarded as an earlier chain and bucket arrangement continued in use. In 1767 Smeaton was consulted about improving the transport of coal from Sauchie and reported on making the Devon navigable to the Forth.
In 1785 the dam (NS99SW 90.03) was heightened and surfaced with rough hewn stone, and in 1827 was repaired for £300. The weir at Forest Mill (NS99SE 16) was rebuilt in 1835 for £248 (see Paxton and Shipway, 2007, 340). From 1820 onwards some of the water was led to Alloa for domestic use through wooden pipes and since 1860 the system has been used solely for this purpose. In 1894 the dam (NS99SW 90.03) was given a stone face and its crest was raised by a further 2 ft increasing the water area to about 160 acres. A pump house was also built which is now the Visitor Centre (NS99SW 90.06).
The dam itself is believed to be the oldest in Scotland still in use for water supply. It is now located in a country park giving public access to all surviving features of the system.
R Paxton and J Shipway 2007
Reproduced from 'Civil Engineering heritage: Scotland - Lowlands and Borders' with kind permission from Thomas Telford Publishers.
Publication Account (2007)
At Forest Mill, water from the river was diverted for the mill and feeder to Gartmorn Dam at a horseshoe shaped
masonry weir (NS99SE 16) some 10 ft high. Construction of the feeder along the north flank of the river valley, and requiring several rock cuts, was a considerable challenge in 1710. Sorocold set [the weir] out using a large wooden quadrant with a plummet set on a tripod. The feeder was cut soon afterwards.
R Paxton and J Shipway 2007
Reproduced from 'Civil Engineering heritage: Scotland - Lowlands and Borders' with kind permission from Thomas Telford Publishers.
Note (26 August 2010)
This sluice is depicted and named on the 1st edition Ordnance Survey 6-inch map (Clackmannanshie, 1868, sheet CXL) and forms part of the Gartmorn Feeder for the Gartmore Dam constructed in the early 18th century.
R Paxton and J Shipway, 2007.
Information from RCAHMS (MMD) 26 August 2010.
Aerial Photography (11 January 2024)
Oblique aerial images of Forestmill Lade.
