Pontcysyllte Aqueduct

Pontcysyllte Aqueduct and Canal*
UNESCO World Heritage Site
State Party	United Kingdom of Great Britain and Northern Ireland
Type	Cultural
Criteria	i, ii, iv
Reference	1303
Region**	Europe and North America
Inscription history
Inscription	2009  (33rd Session)
* Name as inscribed on World Heritage List. ** Region as classified by UNESCO.

The Pontcysyllte Aqueduct (Welsh pronunciation: [ˌpɔntkəˈsəɬtɛ], full name in Welsh: Traphont Ddŵr Pontcysyllte) is a navigable aqueduct that carries the Llangollen Canal over the valley of the River Dee, between the villages of Trevor and Froncysyllte, in Wrexham in north east Wales. Completed in 1805, it is the longest and highest aqueduct in Britain, a Grade I Listed Building^[1] and a World Heritage Site.

The Longdon-on-Tern aqueduct, a similar construction by Telford

History

The aqueduct, built by Thomas Telford and William Jessop, is 1,007 ft (307 m) long, 11 ft (3.4 m) wide and 5.25 ft (1.60 m) deep. It consists of a cast iron trough supported 126 ft (38 m) on iron arched ribs carried above the river by nineteen hollow masonry piers (pillars). Each span is 53 ft (16 m) wide. Many people were sceptical that the construction method would work but Telford was confident: he had built at least one previous cast iron trough aqueduct - the Longdon-on-Tern aqueduct on the Shrewsbury Canal, still visible in the middle of a field, though the canal was abandoned years ago. Part of what was originally called the Ellesmere Canal, it was one of the first major feats of civil engineering undertaken by leading civil engineer Thomas Telford (supervised by the more experienced canal engineer William Jessop). The iron was supplied by William Hazledine from his foundries at Shrewsbury and nearby Cefn Mawr. It was opened on 26 November 1805, having taken around ten years to design and build at a total cost of £47,000.

The mortar used comprised lime, water and ox blood. The iron castings were produced at the nearby Plas Kynaston Foundry, Cefn Mawr, which was built for the purpose. The trough was made from flanged plates of cast iron, bolted together, with the joints caulked with Welsh flannel and a mixture of white lead and iron particles from boring waste.^[2] The plates are not rectangular but shaped to give the impression of traditional stone voussoirs, continuing the line of the arch ribs beneath. The supporting arches, four for each span, are of cast iron ribs, with infill panels to the outside to give the appearance of solid supports. The trough is not fastened to the arches, but lugs cast into the "floor" plates fit over the ribs to prevent movement.^[2] It was left for six months with water inside to check it was watertight.^{[citation needed]}

The River Dee runs beneath the aqueduct

The towpath is cantilevered from the side of the trough. This arrangement allows the trough to be the maximum width and thus the displaced water from ahead of the boat can more easily flow past the boat, ensuring that narrowboats are able to move freely through the water. Walkers are protected by railings on the outside edge of the towpath, but the holes to fit railings on the other side of the aqueduct were never used. As the edge of the trough is only about 6 inches (15 cm) above the water level, and therefore below the deck of a narrowboat, the boat steerer has nothing between them and the sheer drop. The Cosgrove aqueduct has a similar structure, although on a much smaller scale.

Every five years a plug in the centre of the of aqueduct is opened to drain the canal water into the River Dee below for maintenance.^[3][4]

World Heritage Site

The aqueduct and surrounding lands were submitted to the tentative list of properties being considered for UNESCO World Heritage Site status in 1999^[5]. The aqueduct was suggested as a contender in 2005—its 200th anniversary year^[6]—and it was formally announced in 2006 that a larger proposal, covering a section of the canal from the aqueduct to Horseshoe Falls would be the United Kingdom's 2008 nomination.^[7][8]

The length of canal from Rhoswiel (Shropshire) to the Horseshoe Falls including the main Pontcysyllte Aqueduct structure as well as the older Chirk Aqueduct, were visited by assessors from UNESCO during October 2008, to analyse and confirm the site management and authenticity. The aqueduct was inscribed by UNESCO on the World Heritage List on 27 June 2009, alongside previously inscribed sites such as the Taj Mahal, Great Wall of China and Stonehenge.^[9]

Gallery

A canal boat crossing the aqueduct. Note the shape of the iron plates, cast to give the impression of traditional stone voussoirs

A view of the Dee Valley from the aqueduct

See also

UK Waterways portal

• Canals of the United Kingdom
• List of canal aqueducts in Great Britain

References

Further reading

• "Memories of Pontcysyllte" by Amy Douglas and Fiona Collins (2006)
• "Pontcysyllte Aqueduct and Canal Nomination as a World Heritage Site: Nomination Document" (Wrexham County Borough Council and the Royal Commission on the Ancient and Historical Monuments of Wales, 2008)

External links

Wikimedia Commons has media related to: Pontcysyllte Aqueduct

• 360 Degree panoramic view at BBC Shropshire (Java Applet Required)
• Aerial photo at Windows Live Local
• Wrexham on-line tour: Pontcysyllte Aqueduct
• Construction visualisation video
• Articles on the construction of the Pontcysyllte Aqueduct from the Royal Commission on Ancient and Historical Monuments of Wales
• Management plan for the nomination as a World Heritage Site. Includes detailed description on the scope of the World Heritage site which starts at Rhoswiel and goes through to the Horseshoe Falls

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