Bridge of Oich

After flooding destroyed the old stone bridge over the River Oich in 1849, a new bridge was needed. It needed a single wide span to avoid further flooding, so a stone bridge was out of the question.

English brewer-turned-engineer James Dredge used an innovative double-cantilever design for the new bridge. It differed from a normal suspension bridge in two ways:

• it was lighter, since the chains got thinner towards the centre

• it was more stable - if the bridge broke in the middle, the two separate cantilevered sections would, in theory, stay standing

The Bridge of Oich was completed in 1854. It comprises three parts:

• arched granite pylons set on granite piers with earthen embankments

• a wrought-iron structure which took support over the pylons and was anchored into the embankments behind

• a timber deck

The main chains supporting the bridge were formed of wrought-iron links about a metre long. At each junction of the links, the two outermost cast-iron bars were taken down as wires to support the deck, reducing the number of separate bars in the link by one.

The result is a remarkably elegant and pleasing piece of engineering.

Bridges designed by Dredge were built in Jamaica and India, though none now survive there. The Bridge of Oich is one of seven to survive out of 30 built in the British Isles.