Drochaid a' Bhanna
|Location Map ( geo)|
|Ross-shire • Sutherland|
|1812, 1892, 1973|
The current Bridge at Bonar Bridge is the third to stand on this site, the first having been built by Thomas Telford. The Bridge stands at the head of the Dornoch Firth, where the land closes in, leaving just the narrow channel of the Kyle of Sutherland to be crossed. This made it an ideal location to build a bridge, and certainly the furthest downstream that a suitable location could be found with the technologies available in the early 19th Century. For many years, it carried the A9 north, but since the Dornoch Firth Bridge opened, that has carried the A9 traffic, leaving Bonar Bridge to carry the meandering A836. At the northern end of the bridge, the A836 TOTSOs with the A949, showing the old priority to the A9 traffic.
The original bridge was built in 1811-12 by Thomas Telford, as part of his commission on Highland Roads and Bridges. It was an Iron Bridge, and whilst not as tall or square as Ironbridge in Shropshire, it was clearly a descendant in those early years of using Iron for Bridges. The main span was indeed very flat, forming an elliptical arch with the road arching over the top. There were also two subisdary arches to the south, both of stone and less than half the span of the main arch which begs the question of why two large Iron Arches weren't used. Doubtless stone was cheaper, and building two stone arches would have cost less than a second Iron one!
Soon after completion, floods swept down the Kyle, and everyone concerned was waiting to see how this relatively untried structure would fare, especially when the water carried away quantities of timber from the west. The bridge survived that first flood, and others that followed, but unfortunately, in January 1892, the bridge was swept away in a flood, having served the community that it helped create for just short of 80 years. Although Bonar Bridge was already a settlement, simply called Bonar, when the bridge was built, it was the bridge that turned it into a thriving village on the main high road north.
This original bridge is considered to be the prototype for Telfords later Craigellachie Bridge, which is of a similar design, but refined as the stress and loading qualities of the iron were better understood.
Sir William Arrol's Bridge
After the original bridge was destroyed, it became essential to replace it as soon as possible, to maintain traffic on the road, which temporarily had to revert to using the Meikle Ferry further east. As the bridge crossed from Ross & Cromarty to Sutherland, both county councils contributed to the cost, with Crouch & Hogg as the engineers and William Arrol as contractor. The replacement bridge again had three spans, with the northern one again the longest. Intriguingly, the southern one appears to be shorter than the middle span. This may have been to avoid the piers previously used and damaged when the old bridge fell, and so find some more secure footings for the new structure. Between the stone piers, metal arched trusses carried the loads of the deck over all three spans.
The bridge remained in use by traffic until the 1970s, by which time it was showing the early signs of potential failure, and so a new bridge was constructed alongside. The old bridge was subsequently removed to prevent it becoming dangerous.
The Bonar Bridge
The current bridge, built in 1972/3 was funded by the Scottish Development Department, and again saw Crouch and Hogg as the engineers. The current structure consists of a single span with the deck suspended from an arched steel truss. Although open at either end to let traffic cross, the upper part of the truss is connected by cross-crossing steel beams between the two main curved sections. The horizontal beams across the road openings are both of a heavier section. In comparison, the suspension rods are very slender, with two hanging from the arch beams between each junction of the truss. The road deck carries a wide S2 with pavements, and is supported by steel beams below. These rest on stone abutments which, in part at least, are the abutments of the previous spans. However, as the new bridge was built alongside the old, the main structure rests on new work.
This is the largest span of all of the bridges that have crossed the Kyle here, but an embankment at the southern end has taken the place of some of the original lesser spans.
On the south side of the bridge, a car park and picnic site offer a good view of the structure, while on the north side the 'Three Bridges Monument' is a triangular cairn carrying the original stones detailing the three bridges that have stood here.