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Vyrnwy Aqueduct (1892)
Lake Vyrnwy, Powys, Wales ... to Prescott, Liverpool, UK
associated engineer
George Frederick Deacon
Thomas Hawksley
Joseph Parry
date  July 1881 - May 1891, opened 14th July 1892, 1902 - 1905, 1926 - 1938
UK era  Victorian  |  category  Aqueduct  |  reference  SJ011201
ICE reference number  HEW 1147
The 110km Vyrnwy Aqueduct takes a water supply from manmade Lake Vyrnwy in north Wales north-eastwards to the city of Liverpool. When completed, it was the longest aqueduct in the world. Over the years, it has been refurbished and additional pipework has been laid but it remains in continual use. It is operated by United Utilities.
Liverpool grew rapidly in the 19th century and by the 1860s its demand for water was outstripping supply. In the 1870s, the city’s borough engineer George Frederick Deacon (1843-1909) reported on the creation of a supply reservoir in the glacial valley of the Afon Vyrnwy in Powys.
The scheme found favour and Deacon joined with leading British water engineer Thomas Hawksley (1807-93) to work on the parliamentary plans. On 6th August 1880, royal assent was granted for the Liverpool Corporation Waterworks Act encompassing a large reservoir, a dam and an aqueduct from Wales to Liverpool. The corporation also purchased 9,713 hectares of land surrounding the dam site to ensure the purity of water from its catchment.
During the project, Deacon held the post of corporation water engineer 1880-90 while Hawksley was engineer-in-chief 1881-5. In 1881, work began on the Vyrnwy Dam (SJ018192), the first high masonry gravity dam in Britain. In November 1888, with the dam substantially complete, impounding water to fill the new Lake Vyrnwy (Llyn Efyrnwy) commenced. Northwest of the dam, a masonry straining tower was constructed as the water outlet to the aqueduct.
Meanwhile, work on the aqueduct started in 1881. Its curving north easterly route follows the watershed of the rivers Dee and Severn, maintaining high ground through Hirnant, Oswestry, Malpas and Cotebrook. It then crosses the basins of the rivers Weaver and Mersey to finish at Prescot service reservoirs, east of Liverpool, for onward distribution. The construction entailed tunnels, balancing reservoirs, valve houses, and river and railway crossings.
Initially the aqueduct consisted of a single pipeline, constructed generally of 1.07m diameter cast iron tubes (cast iron had been used for mains since around 1810). However, where the route crosses the River Mersey the pipeline is of 813mm diameter riveted steel to facilitate maintenance, and marks an early use of steel in trunk water mains.
The steel pipe runs under the river through a 2.74m diameter cast iron tunnel constructed in a compressed air environment, then a pioneering technique, to prevent the structure from collapsing under pressure. The tunnel was completed successfully at the third attempt.
The underground tunnels at Hirnant in Powys, and Cynynion and Llanforda in Shropshire, are alike, with brick and concrete linings to protect against leakage. The Hirnant Tunnel was later duplicated by the nearby Aber Tunnel to enable maintenance to be carried out.
At Oswestry Reservoir (SJ270296), a 457m earth dam impounds some 236 million litres. Water from this storage reservoir passes through 23 slow sand filter beds (SJ278292) at Llanfordda before continuing through the aqueduct. The treated water flows under gravity from Oswestry to Prescot.
The balancing reservoirs are lined in mass concrete faced with brickwork, or mass brickwork set in cement mortar, depending upon local conditions. The open reservoirs at Parc Uchaf (SJ147264) in Powys and the closed ones at Cotebrook (SJ569644) in Cheshire were intended originally to have three tanks of 9.1 million litres, but two tanks in each location were found to be sufficient.
Water storage was provided at Norton (SJ553816) near Runcorn, where a tank of 3 million litres is housed within the top portion of a monumental cylindrical tower of red sandstone some 33.5m tall.
The aqueduct terminates at the service reservoirs (SJ472938) north east of Prescot in Merseyside. It delivered the first water from Lake Vyrnwy to Liverpool in May 1891, using a temporary pipeline over the bed of the River Mersey while the tunnel beneath it was being completed.
On 14th July 1892, the Vyrnwy scheme was opened officially and water flowed through the full length of the permanent aqueduct, including the line through the tunnel beneath the Mersey, into the Prescot Reservoirs. The single pipeline was capable of supplying up to 81.8 million litres of water per day. The whole scheme from Lake Vyrnwy and its dam all the way to Prescot cost around £2.1m to construct.
Joseph Parry (1843-c.1933) was the corporation’s water engineer 1892-1914. In January 1899, he was instructed to prepare designs and estimates for adding a second main to the Vyrnwy Aqueduct. In January 1902, the work was authorized at an estimated cost of £785,000 and the contract was let in March the same year.
The new pipeline opened 16th October 1905. The aqueduct was then capable of supplying about 181.1 million litres per day through its unlined mains. A balancing reservoir at Malpas (SJ487481) in Cheshire was completed in 1913, and its tank has a capacity of 20.5 million litres.
in 1926-1938, a third main was added to the aqueduct. The newest pipeline is of steel with a bituminous lining, with diameters varying from 991mm to 1.067m. Its composition signifies the beginning of more general use of bitumen-coated steel pipes — rather than cast iron — for trunk water mains. As part of the work, a new tunnel more than 400m long was constructed beneath the Mersey and the Manchester Ship Canal using techniques very similar to those employed for the original tunnel.
On 26th September 1938, the third line of pipes on the aqueduct was opened by Walter Elliot (1888-1958), the Minister of Health, at Prescot Reservoirs. The success of the work inspired confidence that the corrosion problems associated with steel could be overcome.
After 1946, a fourth pipeline was laid upstream (south) of Oswestry to increase water supply capability to up to a maximum 227 million litres per day. The capacity increase was met downstream of Oswestry by providing booster pumping stations at Oswestry, Bickerton, Norton and Cuerdley.
In 1978-81, the pipeline crossings beneath the Mersey and the Manchester Ship Canal were re-organised and refurbished. In 1991, the two booster pumps at Oswestry were refurbished. The Vyrnwy Aqueduct system now carries up to 210 million litres of water every day, supplying some 900,000 people in Cheshire and Merseyside.
in 2010, a phased programme of aqueduct renovation began and is anticipated to be completed by 2020. The whole length of all three mains is being scraped clean of accumulated deposits of iron and manganese. The 52km of pipelines between Oswestry water treatment works and Malpas balancing tank are being lined with close-fitting polyethylene tubing.
Contractor: direct labour
Research: ECPK
"Deacon, George Frederick (1843-1909)" by W.F. Spear, rev. Anita McConnell, in Oxford Dictionary of National Biography, Oxford University Press, 2004
"Hawksley, Thomas (1807-1893)" by T.H. Beare, rev. Mike Chrimes, in Oxford Dictionary of National Biography, Oxford University Press, 2004
"Liverpool Water Supply", in The Engineer, p.714, London, 26th June 1914
"Lake Vyrnwy and the Vyrnwy Water Supply to Liverpool", supplement to The Engineer, London, 15th July 1892
reference sources   CEH Wales

Vyrnwy Aqueduct (1892)