30 October 2015

"River, Railway and Ravine: Foot Suspension Bridges for Empire" by Douglas Harper

Here is a lovely work of special-interest history. River, Railway and Ravine (The History Press, 2015, 164pp) [amazon.co.uk] documents the suspension bridges of John and Louis Harper, Aberdeenshire fence-makers turned bridge-builders.

Between 1870 and 1910, the Harpers designed and built over 40 suspension footbridges, mostly in the UK, but also as far afield as India, Nepal, Estonia, South Africa and the West Indies. Few survive now, and I've only visited one, at Newquay, although there are bridges built by the Aberdeen firm of James Abernethy in which Louis Harper may have had a hand, such as those at Aberlour and Cambus O'May.

Descendant of the Harper family, Douglas Harper, has been researching his family's engineering history for some time, with much of it documented on the Harper Bridges website. Now, this excellent book offers far more detail on the family firm's achievements, and I'd recommend it to anyone with an interest in historical suspension bridges.

The Harpers were innovators in their field: early users of steel wire rope; developers of a specialist wire-tensioning device; and users of pre-tensioned cables at deck level to greatly increase the stiffness of their designs.

The book gives a good history of the family, and their work both in fencing and then bridge-making, and puts this in context with a chapter exploring other suspension bridge developments in the 19th century.

The main part of the book offers detailed discussions of every bridge built by John Harper, and his son Louis. These are accompanied by numerous well-reproduced photographs and drawings, both present-day and archival. The level of research presented is remarkable.

What makes the book a particularly enjoyable read is the personal touch, as the author has attempted to visit as many of the bridges sites as he could, even where long-since demolished. In particular, the tale of his trip to Nepal turns the book from a simple historical record into a narrative which brings the past very much to life.

13 October 2015

Welsh Bridges: 5. Barmouth Bridge

This is described as the longest estuarial bridge in Wales, and it's certainly the longest timber bridge in Britain, being a total of 731m long. It has carried the Cambrian coast railway across the mouth of the Mawddach Estuary, between Barmouth and Fairbourne, since 1867. There are 113 timber spans, comprising braced wooden trestles, and five metal truss spans at the northern end.

Originally, an opening span was included of so-called "cock-and-draw" construction, which reportedly took some 37 minutes for two men to open. This was replaced by Cleveland Bridge in 1900 with the present arrangement. The timber trestles have been entirely replaced at least once in their history, and were most recently refurbished by Network Rail the early 1980s.

The metal spans are an interesting arrangement. There are two bowstring trusses, which at first glance appear identical. However, one is a simply-supported span, and the other is a swing bridge supported from its centre on a pivot pier. Closer examination reveals that the swing span has vertical members above its pier which are not present on the other span, as you would expect, and I expect the detailed build-up of steel sections is also different.

The bridge has clearly not opened for some time (there's a photo of it open here). The opening mechanisms are in a state of considerable disrepair, and the rails across the bridge are now continuous across the span joints.

Only a single rail track passes over the bridge. The bulkhead rails are supported from longitudinal baulk timbers, which are held at the correct spacing by a series of metal struts and ties. Metal cleats hold the timbers in position on the main timber decking. On the metal spans, short lengths of longitudinal timber sit within "bath-tubs" in the metal bridge deck.

A timber footway passes along the eastern edge of the viaduct. This is a very pleasant walk, with fine views of the Mawddach estuary, but also a vital link between Fairbourne and Barmouth. There is an occasional passenger ferry between the two towns, but after the rail viaduct, the next crossing upstream is the toll bridge at Penmaenpool, which is only open during the daytime, and beyond that, the road bridge near Dolgellau.

A toll was levied on the footway since the early twentieth century, but this has recently been abolished.

At the south end, the footway slopes steeply up to the nearby highway, and Barmouth residents have established a campaign for a better footway connection.

The timber parts of the bridge are in fair condition, although there are a number of holes in the trackside decking which have been covered over with metal or GRP plates. From below, isolated areas of rotted or damaged timber can be seen, and metal fixings are severely rusted, as is only to be expected in a tidal estuary.

The condition of the metal spans is of greater concern, being extremely poor with little or no worthwhile protective treatment, and extensive corrosion. Network Rail have plans for a full refurbishment of the metal elements, which appears to be long overdue. This is not a busy railway line, and it must be difficult to justify the expense that properly maintaining this type of bridge should entail.

Walking over the bridge, it's hard not to speculate about the possibility of building a highway bridge nearby. When the Penmaenpool toll bridge is closed, the highway journey between Barmouth and Fairbourne takes about 17 miles, and even when its open it's still 14 miles. As the crow flies, the actual distance is only 2 miles, so a highway bridge would be of considerable benefit both to local residents, and to others passing north and south along the coastline. It would be an expensive endeavour, due to the need for lengthy highway improvements approaching from the south, and potential conflict with Barmouth harbour at the north end.

Meanwhile, the local council, which essentially "rents" the walkway from Network Rail for £30,000 per year, is under severe pressure to reduce costs and is considering closing the footpath. It's hard to argue that it should be more of a priority than many other hard-pressed council services, but unsurprisingly there is a great deal of opposition to closure, including an online petition with over 40,000 signatures.

I think this is a lovely bridge, of great engineering, historic and social value, and it would be a shame to see it closed or not maintained. It's not far from the site of Pont Briwet, another timber viaduct which, despite its Listed status, was recently demolished and replaced with a new concrete bridge. It would be a terrible shame for Barmouth Bridge to ever follow suit.

Further information:

03 October 2015

Welsh Bridges: 4. Penmaenpool Bridge






Further information