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Corpach Sea Lock, Caledonian Canal
Corpach, Highland, Scotland, UK
Corpach Sea Lock, Caledonian Canal
associated engineer
Thomas Telford
William Jessop
date  1807 - 1812
era  Georgian  |  category  Locks  |  reference  NN095766
ICE reference number  HEW 84/08
photo  © and licensed for reuse under this
Corpach Sea Lock lies at the western end of Telford and Jessop's Caledonian Canal, at the foot of Ben Nevis. At the this point, the canal runs into Loch Eil, Loch Linnhe and the Irish Sea. The lock is tidal and founded on submerged rock. Its construction required an extensive cofferdam. The lock remains in use, though is has been enlarged.
The Caledonian Canal, which opened in 1822, links the Irish Sea with the North Sea via Scotland's Great Glen. Thomas Telford (1757-1834) was its principal engineer and William Jessop (1745-1814) consulting engineer.
The construction of Corpach Sea Lock required exceptional engineering skill, and provides a classic foundation case study. It had to be founded on rock at a point where the lock sill would be covered by 6.4m of water at neap-tide high water, some 90m seaward of the usual high water mark.
Watertight twin mounds faced with rubble stone were built out from the shore to beyond the end of the lock pit site. A timber cofferdam, with a 4.3m thick clay puddle wall, was constructed between them in the spring and summer of 1807. The gravel, sand and mud inside the cofferdam was then excavated. In August that year, the placing of the framing piles for the dock began. Work halted for the winter at the end of October and recommenced in March 1808. Steam-powered pumping was used to dewater the excavation — an early instance of such practice on a large scale.
The piling operation was difficult. The framing piles were dowelled into the rock though some 2.5m of silt and gravel, by means of an iron-hooped timber cylinder (internal diameter 560mm) with an iron shoe, driven by a piling engine equipped with a 457kg ram. Each iron dowel is 51mm square and driven 500mm into the rock. After each dowel was inserted, its iron-bound timber pile was driven onto it, then the whole operation was repeated at the next location. The pile heads are bolted to the leading frame.
The masonry lock walls are constructed in schist from a quarry on the shore of Loch Eil, set in hydraulic lime mortar. The original two pairs of oak lock gates with cast iron framing were designed by Thomas Rhodes (1789-1868), as was the machinery to operate the lock. These gates were replaced by pones of oak framed in steel in 1890-1906.
The sea lock was mechanised in the 1960s. In 1964-5 it was enlarged to accommodate vessels of up to 1,016 tonnes, which served the wood pulp mill (NN085765) constructed beside Loch Eil. Corpach Pulp Mill opened in 1964 and closed in 1981, and was demolished in 2008.
The canal is open in daylight hours and the sea lock is available whenever the tide is more than 1m high. Freight vessels take precedence over leisure craft in the basin.
Resident engineer (1807): John Telford
Resident engineer (1807-12): Alexander Easton
Contractor: John Wilson, John Simpson
Lock gates and machinery: Thomas Rhodes
Ironwork: William Hazeldine, Plas Kynaston
Research: ECPK
"The Caledonian Canal" by Thomas Telford, in Life of Telford, Vol.1, pp.49-67, ICE virtual library, London, January 1838
"Skipper’s Guide: Caledonian Canal” by Scottish Canals,
British Waterways Scotland, Glasgow, 2008
reference sources   CEH SHIBDCE1

Corpach Sea Lock, Caledonian Canal