The Great Western Canal Caissons
More detail can be gleaned from the web site :https://en.wikipedia.org/wiki/Grand_Western_Canal But briefly: In 1831 James Green (an engineer of good repute from Exeter) was employed as engineer and proposed 7 caissons/boat lifts and an inclined plane (lifting smaller 'tub-boats- up and down 81 feet). In 1836, when the canal was almost finished, it was realised that the caissons were not properly aligned in the pounds. Green had to put this right at his own expense. He did this by adding a lock at the bottom of the 6th caisson and re-aligning the 7th. He was then sacked! WA Provis was then employed to examine Green's work and found that the inclined plane did not work properly as the mass of the caissons, even when filled with water, was insufficient to counterbalance the tub-boats moving up and down. Steam power was thus later introduced. 1864 The GWR was given the lease for the canal and promplty shut the 'difficult' section between Taunton and and the start of the Tiverton Branch. The best preserved caisson site is at Nynehead (with a drop of 24 feet).
and... http://www.nynehead.org/index.php/canal/grand-western-canal-lifts (excellent!)