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Chirk Aqueduct
River Ceiriog, south west of Chirk, Wrexham/Shropshire border, UK
Chirk Aqueduct
associated engineer
Thomas Telford
William Jessop
date  17th June 1796 - 1801
UK era  Georgian  |  category  Aqueduct  |  reference  SJ286373
ICE reference number  HEW 111
photo  donation
Telford's Chirk Aqueduct carries the Llangollen Canal over the River Ceiriog. It sit next to a later railway viaduct. The Grade II* listed aqueduct’s masonry piers and arches hide its cast iron canal bed, the use of which allowed the height of masonry above the spans to be reduced. It is well maintained and is included in the UNESCO World Heritage Site that also encompasses Pontcysyllte Aqueduct.
Thomas Telford (1757-1834) was deputy to the Ellesmere Canal Company’s engineer William Jessop (1745-1814) for the Llangollen Canal, but he was responsible for the design of Chirk Aqueduct. He was assisted by John Duncombe (d.1810), who carried out surveys, and then by his inspector of works Matthew Davidson (1755-1819). The first plans were produced in 1794, and the foundation stone was laid two years later on 17th June 1796.
From ground level, the structure appears to be a conventional masonry canal aqueduct. This was an interesting choice considering that Telford's other aqueduct on the canal is the Pontcysyllte Aqueduct — a pioneering design that uses an exposed cast iron trough supported on masonry piers. It's possible that Chirk was given a more conventional appearance so as not to upset the local landowner. It was certainly quicker and cheaper to construct than Pontcysyllte, It opened in 1801 having cost £20,898, while Pontcysyllte took 10 years to build and cost £38,500.
Chirk Aqueduct carries the canal 21.3m above the river and measures some 216m in length. The clear spans of its 10 arches measure 12.2m, and the arch spandrels are hollow.
The rectangular water trough is 1.5m deep and its cast iron bed plates are flanged at their edges and secured by bolts. The flanges are built into the masonry on either side. The channel sides were waterproofed using ashlar masonry and hard burnt bricks set in Parker’s cement, rather than the puddle clay lining more commonly used for the purpose at that time.
The combination of hollow spandrels, using cast iron for the channel bed and no puddle clay meant that less masonry was needed above the piers, and that enabled the structure to be relative light. It also meant time savings in the construction programme, which helped the canal company begin transporting iron and lime from Chirk on the canal network sooner. This section of the Llangollen Canal became important as it linked the coal, granite and slate industries of the Ceiriog Valley.
Iron side plates were added to the canal trough in around 1870.
In his autobiography, Telford described Chirk Aqueduct as follows: "The spandrills of the stone arches were constructed with longitudinal walls instead of being filled with earth, and across these the canal bottom was formed by cast iron plates, at each side infixed in square masonry. Those bottom plates had flanges on their edges and were secured by nuts and screws at every juncture". (Life of Thomas Telford, Civil Engineer, written by himself, 1838)
The aqueduct was Grade II* listed in April 1966. On 27th June 2009, as part of the western end of the Llangollen Canal, it was inscribed a UNESCO World Heritage Site.
The adjacent rail viaduct (SJ286372) was constructed for the Shrewsbury & Chester Railway in 1848. Originally it had approach arches of laminated timber but in 1859 these were rebuilt in brick and masonry to match the rest of the structure. It was designed by Henry Robertson (1816-88) and the contractors were Brassey, Mackenzie & Stephenson.
Main contractors: John Simpson, William Davies
Ironwork: William Hazledine
Research: ECPK
reference sources   CEH WalesBDCE1

Chirk Aqueduct