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Gartmorn Dam
Sauchie, Alloa, Clackmannanshire, Scotland, UK
associated engineer
George Sorocold
date  rebuilt c.1694, 1710 - 1713
era  Stuart  |  category  Dam/Reservoir  |  reference  NS912938
ICE reference number  HEW 2589
Although the date of its original construction is unclear, Gartmorn is believed to be the oldest dam in Scotland still in use for water supply. It forms part of the Alloa Waterworks system and is associated with Derby hydraulic engineer George Sorocold for the works he carried out after 1710 to increase the reservoir's holding capacity.
Gartmorn Dam and reservoir were likely constructed in the 17th century, and were located on the estate of Sir John Erskine (1675-1732), 6th Earl of Mar, who also owned a number of local collieries. In 1694, Erskine rebuilt the earth dam, as he needed the empounded water in order to run his mines and mills.
Water ingress in the coal mines became a serious issue as time went by, as coal began to be extracted from deeper levels. Pumps were needed. In 1709, Erskine sought Sorocold's advice and, in 1710, commissioned him to report on draining the mines at Sauchie, just west of Gartmorn Dam.
At that time, Gartmornís reservoir was fed by water from Brothie Burn. Sorocold recommended that the reservoir should have its capacity ó and therefore potential power output ó increased by means of substantial additional water diverted from the River Black Devon. He proposed the construction of a feeder stream (lade) that would take water from the river at Forest Mill, about 3km to the east. Erskine agreed.
To set out the alignment of the feeder stream, Sorocold used a surveying instrument described as a "large wooden quadrant set upon a tripod, with brass lights along the upper radius, the index being a plummet suspended by a fine thread". The channel was cut soon afterwards and is around 1.5m wide. Its construction on the north side of the valley required several rock cuts, and was a considerable challenge for the engineering technology of the period.
At Forest Mill, two horsehoe-shaped ashlar masonry weir dams, some 5-6m high and 9m long, were built to divert water into the feeder. These are still standing. The feeder stream meets the reservoir at its eastern end ó the opposite end from the main dam.
Another lade was cut, from Gartmorn to the Sauchie mines. The idea was to supply water to a waterwheel to drive pumps Sorocold built at least one, and possibly two, waterwheels about 5.5m in diameter. However, his advice for improved pumping at the mines seems to have been disregarded as earlier rag pumps and chain and bucket arrangements continued in use. Later, the lade supplied water to power a colliery winding engine.
Sorocold's endeavours enabled Gartmorn's water level to be raised more than 3m, making its surface area some 1.2km long by 500m wide, then the largest man-made body of water in Scotland. His fee for the work was £50 ó which would be £100,000 today.
Downstream, the tailrace continued to the River Forth. It was used by various mills in Alloa and featured in the Earl of Marís pleasure grounds at Alloa Tower (NS888925) north of the river, before being dammed again to provide a scour, via a stone flume, to clear the former harbour of silt.
Half a century later, in around 1760, the hydraulic pumps that Sorocold had proposed were installed at Sauchie. In 1767, engineer John Smeaton (1724-92) was consulted about improving the transport of coal from Sauchie, and also reported on making the River Black Devon navigable south west to the Forth.
In 1785, the Gartmorn earth dam was heightened, extended to 293m long and surfaced with rough-hewn stone. The power it provided helped Alloa's industrial development and, by the 1860s, its water was driving three colliery pit engines and 11 waterwheels at various mills.
From 1820 onwards, the reservoir's water was supplied to Alloa for domestic use through timber pipes. In 1827, the dam was repaired for £300 at the instruction of John Craich (1775-1854) of the Alloa Colliery Company. In 1867, it was improved (or repaired) further.
In 1835, Sorocold's weir at Forest Mill was rebuilt for £248. It consists of a raised platform of slabs around a curve of dressed stone enclosing a basin founded on bedrock. It has been a Category B listed structure since June 1972.
Since 1860, the reservoir has been used solely for water supply. In 1877, filter beds and a water house were built at Jellyholm (NS909938, now dismantled) west of Gartmorn, and water conveyed to Alloa through a 305mm diameter pipeline. The population of Alloa increased rapidly and by the late 19th century water ran out during dry summers. The Alloa Water Act, granted on 28th July 1891, established a continuing public water supply and described the works carried out.
A new compensation weir at Forest Mill ensured a minimum of 9 million litres of water per day were released into the River Black Devon. The feeder from Forest Mill to the reservoir was enlarged, Gartmorn Damís crest level was raised and a 12m wide overflow sluice constructed. New filter beds (NS914937) were added and a pump house (NS913939) was built for a hydraulic pumping engine to transfer water to the filters and into a new service reservoir. The 292mm diameter pump, powered by town gas, delivered 1,270 litres of water per minute at a 10.4m head and was in use until the early 20th century.
In 1894, the dam was given a stone face and its crest was raised by a further 610mm, increasing the water area to 69 hectares. However, with a head of less than 30m the dam generated low water pressure. In 1928, to meet industrial and domestic demand, daytime pressure was boosted by an electric pumping system installed at nearby Carsebridge.
The dam and reservoir are now part of the 150 hectare Gartmorn Country Park, established in February 1980, which enables public access to all surviving features of the system. The 1891 filter beds were transformed into a sunken garden. The pump house was used as the parkís visitor centre during 1980-96.
Scottish Water now owns Gartmorn Dam. In 2013, a £440,000 programme of maintenance was undertaken including constructing a new platform and penstocks in the spillway (NS911940) to allow for emergency drawdown of the reservoir, reducing the risk of flooding, and repairs to the damís stonework.
Research: ECPK
"John Erskine, 6th and 11th Earl of Mar (1675Ė1732): Architecture, Landscape and Industry" by Margaret Stewart, in Architectural Heritage, Vol.23, pp.97-116, November 2012
"Gartmorn Dam Country Park", Clackmannanshire Council, Communications Unit booklet, Greenfield, Alloa, March 2009
"The Gartmorn Lade System" by Murray Dickie, in Forth Naturalist and Historian, Vol.33, pp.13-32, 2010
reference sources   CEH SLBBDCE1

Gartmorn Dam