Clapper bridges are something I’d previously associated exclusively with Dartmoor; there is a famous large one at Postbridge but there many more examples spanning watercourses on the moor. A recent tweet from Forestry Commission Scotland alerted me to the fact that they can be found in Scotland and, with my antennae tuned, I spotted a couple of examples on the hilltrack that links Cashel Dhu with the public road to the north.
Clapper bridge construction relies on building up piers of rock, using dry-stone techniques, then spanning the gaps with longer, flat stones. This is the weakness of the approach, as the stones can be flipped off the piers during flood events. You can see where this has happened in the photo below.
The requirement for certain types of stone that will yield suitable blocks is a classic example of geology determining a construction method.
This style of bridging is much more geographically widespread in the upland areas of Great Britain than I had first appreciated, with examples in Snowdonia, Anglesey, Yorkshire and Lancashire. Tarr Steps is routinely billed as the ‘oldest bridge in Britain’, with an accompanying myth about the Devil having dibs on sunbathing rights there, although there is no dating evidence for the claims of the structure being 3000 years old. Nonetheless, this bridge has 17 spans and is very unusual. The techniques were still being used in the early 20th century in some places, as a record of a clapper bridge at Shawbost demonstrates and I reckon there are probably more recent rough and ready examples out there used on walking routes. When I did footpath work we never built anything quite like this but it has potential and is an attractive style of work. Anyone got any examples of such work? If you want to build your own model, you can use the material in the Forestry Commission Scotland tweet.