Canal & River Locks
Page 8: Alternative Locks
As well as the 'static' approaches mentioned earlier (various types of contouring, excavating, and spanning), there were many ingenious dynamic solutions, mostly variations on the boat lift or the inclined plane. These tend to be more expensive to install and operate, but offer faster transit and waste less water.
An inclined plane consists of a cradle (to hold a barge) or caisson (a box full of water in which a barge can float) which moves on rails sideways up a slope from one waterway to the other. There may be two caissons balancing each other's weight via a connecting cable. The motive power may be steam or hydraulic, or may come from overbalancing the top caisson with extra water from the upper waterway. There are no working waterway inclined planes in the UK at the moment, but the remains of a famous one can be seen at Foxton in Leicestershire on the Leicester arm of the Grand Union Canal. The plane was replaced by a flight of locks, but there are plans to restore it.
Here are three examples of boat lifts (the last two are currently in operation)
Somerset and Camden
Around 1800 the use of Caisson locks (actually a type of boat lift) was proposed by Robert Weldon for the Somerset Coal Canal in England. In this underwater lift, the chamber was 80 ft long and 60 ft deep and contained a completely enclosed wooden box big enough to take a barge. This box moved up and down in the 60 ft (18.2 m) deep pool of water. Apart from inevitable leakage, the water never left the chamber, and using the lock wasted no water. Instead, the boat entered the box and was sealed in by the door closing behind it, and the box itself was moved up or down through the water. When the box was at the bottom of the chamber, it was under almost 60 feet of water—at a pressure of three atmospheres, in total. One of these "locks" was built and demonstrated to the Prince Regent (later George IV), but it had various engineering problems and the design was not put into use on the Coal Canal. However, in about 1817 the Regents Canal Company built one of these locks at the site of the present-day Camden Lock, north London. Here the motivation was, again, water supply problems. Even though the change in level is much lower than that would have been the case in Somerset, the system was soon replaced by conventional locks. No commercially successful example has ever been built.
The Victorian Anderton Boat Lift, the world's first vertical boat lift, linking the Trent and Mersey Canal and the River Weaver in Cheshire has recently been restored.
The Falkirk Wheel, the world's first rotating boat lift, acts as the centrepiece of the restoration of the Forth and Clyde and Union Canals. The spectacular "Wheel" presents the 21st century's solution to replacing a flight of locks which formerly connected the canals and which were filled in 1930. The Falkirk Wheel was the winning design in a competition to design a new lock. Visitors can now take a boat trip on the Wheel and be lifted over 100 feet in a few minutes compared to the time it took when the original lock staircase operated.
A combined system - the Three Gorges Dam
At the Three Gorges Dam on the Yangtze River (Chang Jiang) in China there are two stair-steps of five large ship locks. In addition to this there is a ship lift (a large elevator) capable of moving a three thousand ton ship vertically in one motion.
Page 1 - Introduction & use of locks...Go
Page 2 - Basic construction and operation...Go
Page 3 - Details & Terminology...Go
Page 4 - Variations...Go
Page 5 - Illustrations...Go
Page 6 - History & Development...Go
Page 7 - Use of water...Go
Page 8 - Alternatives...(Current page)