Somerset Coal Canal: stop lock at Dundas Aqueduct

At the southern end of Dundas Aqueduct, a branch runs from the Kennet & Avon Canal, through a curious narrow stop-lock.  Nowadays the branch ends abruptly after less than half a mile, at Brassknocker Wharf, where there is an excellent modern restaurant called the Angelfish [http://www.foodanddrinkguides.co.uk/bath/angelfish-restaurant/restaurant/2742].

This is all that remains navigable of the Somerset Coal Canal, a long-forgotten and fascinating piece of canal and railway archaeology.  It was devised by John Rennie (1761-1821), the engineer of the Kennet & Avon Canal, and surveyed by William Jessop (1745-1814) and William ‘Strata’ Smith (1769-1839), whose work is celebrated at the Rotunda Museum, Scarborough.

The original canal was built westwards to Paulton, to tap the potential traffic of the Somerset coalfield.  The first coal was brought out in 1798, though the canal itself fully opened only in 1805.

Bringing barges from the summit level 135 feet higher than the Kennet & Avon required 22 locks.  To reduce the drain on limited supplies of water, the engineer Robert Weldon proposed instead building a caisson lift at Coombe Hay, in a single operation [See http://www.coalcanal.org/history/Rowley/tLev1.htm].

This involved building a series of three 60-foot-deep cisterns, into which each barge would be floated in an airtight container – the caisson – and sunk, emerging at the foot of each lift with no loss of water at all.  [See http://www.coalcanal.org/features/Caisson/Caisson.htm and http://rtjhomepages.users.btopenworld.com/caisson-telegrap.html (which first appeared in The Daily Telegraph)].

An experimental model of this system appeared to work, but the full-sized version was unsuccessful, apparently because of geological rather than mechanical problems.

It was replaced, first by an inclined plane, and eventually – in 1805 – by a flight of locks, from which a steam pump returned water to the summit pound.

A canal branch from Radstock as far as Twinhoe was never completed:  to avoid the expense of a further flight of locks the line was built as a tramway by 1815.  This was superseded in 1875 by the Somerset & Dorset Railway line to Bath.

There was no shortage of coal traffic, but the Somerset Coal Canal was an early victim of railway competition.

Later, the bulk of the main canal between Limpley Stoke and Camerton was converted by the Great Western Railway to a standard-gauge branch-line in 1910.  This was not a commercial success, but after it closed it became the location for the celebrated Ealing comedy The Titfield Thunderbolt (1953).

Much of the route of the Somerset Coal Canal is traceable, including the former aqueduct at Dunkerton, for seriously determined explorers to seek out.  The Somerset Coal Canal Society exists to foster interest in the route:  http://www.coalcanal.org.

Of the caisson lift hardly anything remains.  The masonry was used to build the replacement locks, and archaeological digs have revealed very little.

I wonder if there’s a working model somewhere?

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