Drochaid a' Bhanna
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. 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 Highland Roads. 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!
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 when the bridge was built, it was the bridge that turned it into a thriving village on the main high road north.
Sir William Arrol's Bridge
After the original bridge was destroyed, it became essential to replace it as soon as possible. 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 also appears to be shorter than the middle span! Between the stone piers, arched trusses carried the loads of the deck.
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. This is the largest span of all of the bridges, but an embankment at the southern end has taken the place of some of the original lesser spans.