Over and under

Your guide to remarkable bridges on our waterways

 

It’s hard not to marvel at the craftsmanship and sheer ingenuity of engineering exhibited along our waterways –particularly when it comes to the bridges. From simple stone structures hundreds of years old to moving platforms that allow taller boats to pass through, a stroll along the towpath will take you past an assortment of different types. Each one was designed for a set purpose: to meet the needs of the industry of that time or to work harmoniously with the contours and constraints of the canal. The context is often as compelling as the design. As you walk, imagine a time when heavy horses would have pulled cargo-laden barges along the canal and when carriages passed over the bridges, headed for nearby markets and towns.

Bascule lift bridges

Derived from the French word for ‘see-saw’, bascule bridges were common on canals at the start of the 18th century. The simplest examples had a counterbalanced beam (or arm) on the other side of the pivot point, allowing the bridges to be opened by leaning on the beam. A lengthsman would have adjusted the weight of the beam to allow for the increased weight caused by rain in the winter months. Travelling along the southern parts of the Oxford Canal, you can still see many of these original black and white bridges in action.

A more complicated design uses an overhead beam, pivoted in the middle, with chains attached to the bridge deck on one side and a counterbalanced weight on the other. Many of the original bridges have been replaced by steel structures and are hydraulically powered, but along some stretches of the Llangollen Canal you can still find original wooden designs.

A lengthsman was a term coined in the 1700s to describe someone employed to keep an length of canal (road or railway) neat and tidy.

Swing bridges

The Gloucester & Sharpness Canal was originally intended to take high-masted sailing ships, making traditional stone and brick bridge designs unsuitable. Instead, 16 swing bridges were constructed along the length of the 16.5 mile waterway, many designed by famous civil engineer Thomas Telford who was also responsible for the Ellesmere, Shrewsbury and Caledonian canals.

As the name suggests, these bridges swing or swivel around a central pivot, with a symmetrical double leaf design being used to span wider distances. They became commonplace in the 19th century; the advent of cast iron made the design far more functional, as wood had a tendency to warp and affect the movement of the bridge. The bridges were operated by a keeper, who usually lived in a small cottage next to the bridge.

Roving bridges

You might notice that the towpath sometimes switches to the opposite side of the canal. This may have originally come down to a landowner who refused to allow the canal path to run through their land, but it was also to ensure that the pull on the horse’s shoulder was balanced. To avoid the time consuming and awkward task of unhitching the horse, roving or turnover bridges were invented. Different regions adopted their own unique approach… 

  1. Snake bridges

The Macclesfield Canal is known for its beautiful stone bridges; some of its finest are six turnover bridges, locally known as ‘snake’ bridges. A ramp on one side leads up onto the overpass, which then spirals back under the bridge on the opposite bank, allowing the horse to ascend, cross and descend, without obstructing the tow rope. The smooth, stone form prevented the line from snagging, although if you look closely you may see the stonework worn away in places. This is evidence of decades of ropes running over the stone’s surface.

Snake bidge

  1. Split bridges

Cast iron allowed for the construction of a simple, double cantilevered bridge and some of these appealing feats of engineering can still be seen in the southern pasts of the Stratford Canal. A thin gap left in the centre allowed the rope to be threaded through without unhitching the horse and was especially useful when the towpath did not pass under the bridge. Stop for a closer look and you might spot a series of furrows or grooves in the iron stanchions, caused by countless ropes rubbing against the metal while the horses were going over the bridge.

Split bridge

Cast iron bridges

It’s fair to say that the introduction of cast iron to bridge building in the 1770s changed the canal landscape. The iron could be ‘cast’ in moulds, replicating a wooden pattern and allowing bridge construction to be standardised. The Birmingham Canal Navigations system was at the centre of this new industry and the Horsley Iron Works foundry based itself on a branch of the canal to it could meet the demand. The foundry’s characteristic design made it a forerunner at the time, with many of its bridges still identifiable today – look out for the cast iron plaques for the foundry’s signature and date of construction.

Cast iron bridge

Curling bridge

One of the newest and most innovative canal bridges, The Rolling Bridge, was the brainchild of designer Thomas Heatherwick. Spanning the Grand Union Canal, it is made of eight triangular sections that, when closed, form a curious octagon shape sitting unobtrusively on the bank. Using hydraulics, over ten minutes it slowly unfurls to its full length of 12 metres, allowing pedestrian access to the other side. It only unrolls once a week, however, so be sure to arrive promptly at midday on a Friday to witness the spectacle.

Curling bridge

Illustration: Joe Rampley