The Bridge of Oich
The Old Bridge Is Swept Away
In 1849 floods swept through the Great Glen, breaching the Caledonian Canal behind you and destroying the stone bridge over the River Oich. It took five years before its replacement, this bridge, was open to traffic.
An Engineer Spans the Gap
Illustration of the structure of the Bridge of Oich.
With a double cantilever bridge like this each half of the bridge can support its own weight. At the end of each cantilever (the middle of the bridge) there is little weight to support, so Dredge tapered the chains to almost nothing thus cutting the overall weight of the bridge.
With a normal suspension bridge the supporting chain must be the same size throughout, producing a heavier, less rigid structure.
A New Bridge Is Designed
James Dredge, a brewer turned engineer from Bath in Somerset, England, designed this new iron bridge using his patented "taper principle. The river crossing needed a single wide span to avoid the dangers of more floods so a stone bridge was out of the question. Dredge's sophisticated design differs from a normal suspension bridge in two ways; it is lighter since the chains get gradually thinner towards the centre and it is more stable in that if you break the
bridge in the middle it will stay up, in theory at least.
The Bridge Helps Support
The Highland Economy
Roads came late to the Highlands where goods were traditionally transported by pack animal over poor tracks. By the 1830's the building of roads and the Caledonian Canal by Thomas Telford had transformed communications in the area. There was now a stage coach service along this road 3 times a week. The bridge would have been used by local traffic, by wool and horse traders, as well as the first tourists and the huge cattle droves heading south every autumn. Larger cargoes, and ships avoiding the journey round the north of Scotland, would have used the Canal. In 1932 the bridge and the swing bridge over the Canal (whose base can still be seen) fell into disuse as the increase in traffic required larger bridges.
( photo captions )
- The road network in the Highlands in the mid-19th Century.
- Illustration of the structure of a typical suspension bridge.
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