Pontcysyllte Aqueduct & Canal World Heritage Siteon the Llangollen Canal near Llangollen

Pontcysyllte Aqueduct & Canal World Heritage Site: A Masterpiece of Engineering

A Masterpiece of Engineering Inscribed in 2009 for outstanding universal value, this 11-mile stretch of innovative engineering was built to complement the stunning scenery of the Dee Valley while serving the demands of the Industrial Revolution.

An impressive museum at the Pontcysyllte Aqueduct & Trevor Basin Visitor Centre is very much worth a visit.

The Pontcysyllte Aqueduct, located in Wales, is one of the most remarkable feats of 19th-century engineering, connecting the Llangollen Canal across the River Dee. Opened in 1805, it remains the longest and highest aqueduct in Britain, standing at a towering height of 126 feet and stretching 1,007 feet in length. Today, it is recognised as a UNESCO World Heritage Site, a testament to its historical significance and engineering brilliance.

The Visionary Engineers Behind the Design
The design of the Pontcysyllte Aqueduct was the work of two renowned engineers: Thomas Telford and William Jessop. Telford, often regarded as one of Britain’s greatest civil engineers, led the project, while Jessop provided oversight and guidance due to his extensive experience with canal construction.

Telford's vision was groundbreaking at the time, as the aqueduct was part of the ambitious Ellesmere Canal project, intended to connect Chester with the Severn River. The challenge was to create a navigable waterway that could span the River Dee valley, with both durability and functionality at the core of its design.

Thomas Telford began his planning in 1795. He discarded previous design options changing them dramatically. One plan was for a shorter aqueduct with 5 or 6 locks at either end. Thomas Telford favoured a single aqueduct that followed on from an impressive 1500 foot long embankment. The embankment was built from the excavations taken from the Chirk Tunnel 

Design and Construction of the Pontcysyllte Aqueduct
The Pontcysyllte Aqueduct is a blend of two primary materials: stone and cast iron, each playing a vital role in its structural integrity and aesthetic appeal.

The Stone Piers
The aqueduct is supported by 18 slender, hollow stone piers. These piers rise majestically from the valley floor, each spaced 53 feet apart. They are 20 feet by 12 feet at the base and taper to 13 feet by 7 feet 6 inches at the top. The trough stands 126 feet above the River Dee at the highest point. They are 20 feet by 12 feet at the base and taper to 13 feet by 7 feet 6 inches at the top.

What makes the stone piers remarkable is their hollow construction, a deliberate choice by Telford to reduce weight while maintaining strength. These piers taper as they ascend, giving the structure a graceful appearance, while ensuring the aqueduct could withstand the forces of nature, such as wind and water pressure.

Each pier is composed of local sandstone, quarried from nearby Chirk. The stone was chosen for its durability and availability, ensuring that the aqueduct would have a long lifespan while blending harmoniously with the surrounding landscape.

The Cast Iron Trough and Arches
Perhaps the most innovative feature of the Pontcysyllte Aqueduct is its cast iron trough, where the water and boats travel. At the time of construction, using cast iron for such a large-scale project was relatively new, but Telford's confidence in this material paid off.

The trough is made up of large cast iron plates, bolted together to create a continuous, watertight channel. This trough is 11 feet 10 inches wide and at 5 feet deep, holds roughly 330,000 gallons of water, allowing narrowboats to cross safely. The use of cast iron not only reduced the weight of the structure but also ensured that it could be built more quickly than if traditional masonry had been used.

The towpath sits over 4 feet of the trough width and has water beneath it. This helps tremendously with water displacement from a boat. Without this, water would slosh over the sides of the trough.

Each of the 19 cast iron arches are 40 feet in length, supported by the 18 stone piers. Each arch is a combination of 11 sections bolted together and when complete, stand 7 feet and 6 inches high.  

To further secure the structure, mortar made from lime and ox blood was applied between the joints of the cast iron plates to prevent water leakage—a technique that might sound unusual today but was highly effective in the early 19th century.

Opening Ceremony and Reception
The Pontcysyllte Aqueduct was officially opened on November 26, 1805, with much fanfare and public interest. At the time, it was seen as a monumental achievement in engineering, pushing the boundaries of what was thought possible. The opening ceremony included a procession of boats crossing the aqueduct, showcasing its functionality and grandeur to an excited crowd. Dignitaries, including local officials and engineers, gathered to witness what many hailed as a wonder of the industrial age.

At 2 pm and to great fanfare, a procession of flag bedecked boats set off from the Froncysyllte end and crossed over to Trevor Basin. A brass band on one of the boats playing God Save The King and other patriotic pieces accompanied by cannon fire in the valley below and a crowd of some 8000 or more onlookers. The brass cannons had been captured at the siege of Seringapatam in India. Two cannon fired 8 shots apiece.

Stopping for refreshments in Trevor before turning around and crossing back to Froncysyllte. This time, two highly decorated boats, laden with coal made the crossing as well, becoming the first cargo boats to use the aqueduct.

The aqueduct's successful construction not only revolutionised canal engineering but also cemented Thomas Telford's reputation as a pioneer. It demonstrated how new materials like cast iron could be incorporated into large infrastructure projects, paving the way for future innovations in bridge and aqueduct design.

A six mile feeder, also designed and built by Thomas Telford ran from Horseshoe Falls on the River Dee at Llantysilio. Every day, the feeder provides millions of gallons and is also the reason the Llangollen Canal has the flow that is strong enough to impede passage when navigating towards Llangollen, through the tunnels at Chirk and Whithurst.

Legacy and Continued Use
Over 200 years later, the Pontcysyllte Aqueduct still serves as a fully functioning part of the British canal system, carrying narrowboats across the River Dee as it did when first opened. Its design has stood the test of time, with minimal alterations needed over the centuries. Its historical and architectural importance was further recognised in 2009 when it was designated a UNESCO World Heritage Site.

Today, the aqueduct is a popular attraction for boaters, walkers, and tourists alike. It offers breathtaking views of the Dee Valley and the surrounding countryside, with many visitors marvelling at its scale and beauty. The aqueduct continues to inspire engineers and enthusiasts around the world, standing as a symbol of innovation, craftsmanship, and the sheer determination of those who dared to push the limits of engineering.

Conclusion
The Pontcysyllte Aqueduct is more than just a bridge for boats—it's a testament to the genius of Thomas Telford and the transformative power of engineering. Its blend of stone and cast iron, along with its pioneering construction methods, makes it a truly unique structure. For over two centuries, it has captured the imaginations of engineers, tourists, and canal enthusiasts, and it continues to stand as a monument to human ingenuity.