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Pontcysyllte Aqueduct and Canal*
UNESCO World Heritage Site

The aqueduct
State Party Flag of the United Kingdom.svg 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.
Pontcysyllte Aqueduct
Carries Llangollen Canal
Crosses River Dee
Location Trevor
OS grid reference SJ270420
Maintained by British Waterways
Designer Thomas Telford
Trough construction Cast iron
Pier construction Brick
Number of spans Eighteen
Piers in water Four
Total length 1,007 ft (307 m)
Width 11 ft (3.4 m)
Height 126 ft (38 m)
Boats can pass? No
Towpath(s) East side
Opening date 1805
Heritage status Grade 1
Coordinates 52°58′14″N 3°05′16″W / 52.97053°N 3.08783°W / 52.97053; -3.08783Coordinates: 52°58′14″N 3°05′16″W / 52.97053°N 3.08783°W / 52.97053; -3.08783

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 name is in the Welsh Language and means junction or link bridge. For most of its existence it was known as 'Pont y Cysyllte' - 'Bridge of the Junction'.

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

Contents

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) above the river on iron arched ribs carried on nineteen hollow masonry piers (pillars). Each span is 53 ft (16 m) wide. Despite considerable public scepticism, Telford was confident the construction method would work: he had previously built at least one 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 (£2,930,000 as of 2010),[2].

Structure

The lime 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 bedded with Welsh flannel and a mixture of white lead and iron particles from boring waste.[3] The plates are not rectangular but shaped as voussoirs, similar to those of a stone arch. This is because cast iron and stone share the property of relative strength in compression and weakness where tensile stress is applied. The supporting arches, four for each span, are in the form of cast iron ribs, each cast as three voussoirs with external arches cast with an un-pierced web to give greater strength at the cost of extra weight. They also give an impression of greater solidity than would be the case were the webs pierced. This impression is enhanced by the arrangement of strips of thicker stiffening incorporated into the castings, arranged in the manner of joints between voussoirs. Cast plates are laid transversely to form the bed of the canal trough. The trough is not fastened to the arches, but lugs are cast into the plates to fit over the rib arches to prevent movement.[3] It was left for six months with water inside to check it was watertight.[citation needed] A feature of a canal aqueduct, in contrast with a road or railway viaduct, is that the vertical loading stresses are virtually constant. According to Archimedes' principle, the mass (weight) of a boat and its cargo on the bridge, pushes an equal mass of water off the bridge.

The River Dee runs beneath the aqueduct

The towpath is mounted above the water in the trough. This arrangement allows the water displaced by the passage of a narrow boat to flow easily around it, enabling relatively free passage. Pedestrians and horses once used for towing, are protected from falling from the aqueduct by railings on the outside edge of the towpath, but the holes in the top flange of the other side of the trough, capable of mounting railings were never used. The trough sides rise only about 6 inches (15 cm) above the water level, less that the freeboard of an empty narrow boat, so the helmsman of the boat has no visual protection from the impression of being at the edge of an abyss. The trough of the Cosgrove aqueduct has a similar structure, although it rests on trestles rather than iron arches. It is also less impressively high.

Every five years the ends of the aqueduct are closed and a plug in one of the highest spans is opened to drain the canal water into the River Dee below, for inspection and maintenance of the trough.[4][5]

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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[6]. The aqueduct was suggested as a contender in 2005—its 200th anniversary year[7]—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.[8][9]

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.[10]

Gallery

See also

References

  1. ^ "Listed Buildings: Pontcysyllte Aqueduct, Trevor", Wrexham County Borough Council, viewed on 2007-05-25
  2. ^ UK CPI inflation numbers based on data available from Measuring Worth: UK CPI.
  3. ^ a b Staff writers (February 2009). "The Pontcysyllte Aqueduct". The Royal Commission on the Ancient and Historical Monuments of Wales. http://www.rcahmw.gov.uk/HI/ENG/Heritage+of+Wales/World+Heritage+Wales/The+Aqueducts/. Retrieved 2009-06-05. 
  4. ^ "Plug pulled on historic aqueduct". BBC News Online. 1998-01-20. http://news.bbc.co.uk/1/hi/uk/49078.stm. Retrieved 2008-11-25. "At midday on Tuesday, they pulled the plug and 1.5 million litres of water, enough to fill 8,000 baths, cascaded to the River Dee below." 
  5. ^ "Birthday clean for aqueduct". BBC News Online. 2003-11-16. http://news.bbc.co.uk/1/hi/wales/north_east/3271665.stm. Retrieved 2008-11-25. "next Monday and Tuesday all 12,000 cubic metres - around 12,000 bath tubs - of water will be completely drained away." 
  6. ^ "Pont-Cysyllte Aqueduct". Tentative Lists Database. UNESCO. 1999-06-29. http://whc.unesco.org/en/tentativelists/1326/. Retrieved 2008-11-25. "Pont-Cysyllte Aqueduct; Date of Submission: 21/06/1999; Criteria: (i)(ii)(iv); Category: Cultural" 
  7. ^ "Aqueduct's big bicentenary party". BBC News Online. 2005-11-27. http://news.bbc.co.uk/2/hi/uk_news/wales/north_east/4470534.stm. 
  8. ^ "Aqueduct set for heritage status". BBC News Online. 2006-10-10. http://news.bbc.co.uk/1/hi/wales/north_east/6037203.stm. 
  9. ^ "Pontcysyllte Aqueduct And Canal - 'Magnificent Masterpiece Of The Canal Age' - To Be UK's Next Bid For World Heritage Status". Department for Culture, Media and Sport. 2008-01-11. http://www.culture.gov.uk/reference_library/media_releases/2143.aspx. Retrieved 2008-11-25. "It consists of 11 miles (18 kilometres) of continuous waterway, from Horseshoe Falls near Llangollen to Gledrid Bridge near Rhoswiel" 
  10. ^ "Aqueduct crowned 'world wonder'". BBC News Online. 2009-06-27. http://news.bbc.co.uk/1/hi/wales/north_east/8115190.stm. 

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


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