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Cardiff Water Supply
Taff Fawr Valley, Nant Ddu, Powys, Wales, UK
Cardiff Water Supply
associated engineer
John Avery Brandon Williams
Charles Henry Priestly
date  1884 - 1897, 1909 - 1927
era  Victorian  |  category  Water Supply/Pipes  |  reference  SN987183
ICE reference number  HEW 2632
photo  © Gareth James and licensed for reuse under this Creative Commons Licence
In the late 19th century, Cardiff's water was supplied from a distribution reservoir and two impounding reservoirs in the Taff Fawr Valley, Powys. Another impounding reservoir was constructed in the 20th century. All feature earth embankment dams with clay cores. Located in the centre of the Brecon Beacons National Park and now Grade II listed, they remain in use, and are also important for recreation and fishing.
From 1850, Cardiff water was supplied by a private company from the River Ely and local streams. In 1865, a storage reservoir was constructed at Lisvane (ST189821), to the north of the city, to augment the supply via a treatment plant and distribution pipework. In 1879, Cardiff Corporation bought out the private company with a view to expanding the supply, which was becoming inadequate for the city’s growing population.
In 1881, John Avery Brandon Williams (1835-1925) reported on the necessity of new reservoirs to boost supply. Williams had been appointed Cardiff's Borough Engineer on 14th August 1876, a post he held until becoming Waterworks Engineer to the corporation from 11th June 1883 to 24th June 1895. In June 1882, his 1881 report was endorsed by then president of the Institution of Civil Engineers, John Frederick la Trobe Bateman (1810-89).
The Cardiff Corporation Act (Part 2) gained royal assent on 7th August 1884. It authorised the corporation to collect and impound waters from the Taff Fawr River and its tributaries, over a catchment area of 4,210 hectares. The catchment was divided into an upper area of 1,620 hectares and a lower area of 2,590 hectares, and the Act proposed constructing two storage reservoirs in the upper area and one in the lower. Other works included three balancing reservoirs at Cefn, Blackbrook and Rhiwbina, service reservoirs at Llanishen and Rhiwbina, plus filter beds at Rhiwbina. A conduit connects all these reservoirs with the storage reservoirs at Lisvane and Llanishen.
The project began with construction of the conduit — 51.5km of 737mm and 610mm diameter pipework — in October 1885. In 1886, Llanishen Reservoir (ST187817) was completed next to the smaller original reservoir at Lisvane. It is constructed on flat ground, encircled by an earth embankment dam 1.5km long. The dam's clay core is faced with stone on the water side. Its reservoir has a capacity of 1,440 million litres and an area of 24 hectares.
On 4th May 1886, ground was broken for the construction of the first of the three impounding reservoirs near the head of the Taff Fawr River. Cantref Reservoir has a capacity of 1,401 million litres, with a top water level 327m above sea level. Its water is piped to the storage and distribution reservoir at Llanishen, with a combined output of up to 55 million litres per day.
Cantref Dam (SN996153), at the southern end of the reservoir, is 125m long and 25.6m high. Its earth embankment has a clay core faced with local stone, though the weir and the steps of the spillway channel are of Cornish granite. A segmental arch bridge crosses the spillway at the south west end of the dam and a circular masonry draw-off tower is offset to the east side of the dam.
In December 1887, while construction was progressing at Cantref, work began on the three balancing reservoirs, and the service reservoir and filters at Rhiwbina. The conduit pipework was completed in September 1888, and the balancing reservoirs and Rhubina contract in November 1888.
Cantref Reservoir opened on 14th September 1892. It cost £153,000 to build and had to be completed by direct labour from June 1891, after the failure of two contractors. A water filtration plant (SN999151), added in 1926, is located to the south east of the dam in a two storey masonry building.
In April 1893, direct labour work began on the second impounding reservoir. Temporary workshops and accommodation that had been erected south east of Cantref Dam were moved north to the Beacons Reservoir site for the workforce. As at Cantref, men and materials were brought to site on a temporary standard gauge railway laid along the west bank of Taff Fawr (dismantled 1897).
In 1894, an Act of Parliament increased Beacons Reservoir’s planned capacity from 727 million litres to 1,577 million litres. Its embankment dam was also sited higher up the valley to ensure a watertight rock foundation. Williams, the corporation’s engineer, made the change in design.
Top water level in Beacons Reservoir is 408m above sea level, retained by a masonry faced clay core earth embankment dam (SN988182) with a circular castellated valve tower offset to the east of the dam on a masonry platform projecting from its inner face. The dam is situated at the south end of the reservoir and is 310m long and 18.6m high with a spillway at its east end. A small stone bridge crosses the spillway.
In June 1895, Charles Henry Priestley (1854-1936) took over from Williams as the corporation’s engineer and the project was completed under his supervision. It cost £207,000 and opened on 30th September 1897.
The 1884 Act had also authorised a third impounding reservoir of 3,046 million litres capacity, larger than the other two put together, at Llwyn On to the south of Cantref Reservoir. In 1909, a new Act authorised its capacity to be increased to 5,728 million litres, with a top water level 260m above sea level.
Work commenced in January 1911, under Priestley’s supervision. A temporary supply railway was laid from Cefn Coed to the site. However, work was suspended in 1915 during World War I (1914-8) and did not resume until 1919.
The clay core earthen embankment of Llwyn On Dam (SO010113, pictured above), at the south end of the reservoir, is 400m long and 23.9m high with a spillway at its east end. The dam’s crest carries a single track metalled road, crossing the spillway on a bridge. A circular masonry draw-off tower is offset from the east of the dam.
The reservoir was completed on 23rd June 1926, and fully commissioned in May 1927. It cost £258,000 to construct and its completion enabled Cardiff's water supply scheme to double its capacity to 109 million litres per day. The railway and site accommodation were removed by 1928.
In the mid 20th century, the original water treatment plant downstream of Llanishen at Heath was closed and replaced with a treatment plant and storage reservoir upstream at Rhiwbina. The reservoir at Llanishen is now used as a recreational facility.
All the major elements of the Cardiff water supply project have been Grade II listed — Cantref’s dam and reservoir in June 2002, Beacons’ masonry structures in June 2005, Cantref's water filtration plant in July 2005, and dams and reservoirs of Beacons and Llanishen in July 2009.
Public access to Llanishen Reservoir is restricted and its owner, Western Power Distribution, plans to develop part of the site for housing.
Contractor (1886-9): William Jones of Neath
Contractor (1889-91): John Mackay of Newport
Contractor (1891-7): direct labour
Contractor (1911-15): Louis P. Nott of Llanelly and Bristol
Contractor (1919-26): direct labour
RCAHMW_NPRN 404685, 416347, 404684, 404686
Research: ECPK
reference sources   CEH Wales

Cardiff Water Supply