When a canal or other waterway passes over rough terrain with steep inclines, a lock or series of locks is built to enable ships to travel safely.
A lock is a watertight enclosure equipped with gates at both its upstream and downstream ends. Its size depends on the size of the ships using the waterway. Small locks, 72 feet long and 7 feet wide, are found on canals in England; the Mississippi and Ohio rivers contain massive 1,200 by 110 foot locks.
If a ship is traveling upstream, the water level within the lock must at first be the same as that on the downstream side of the lock, in order for the ship to enter.
Once the ship is inside, the gates swing shut, and the water level in the lock is raised by pumping in water through conduits that open into the bottom or sides. When a water level equal to that on the upstream side is reached, the gates at that end open, and the ship proceeds. This procedure may be repeated through as many locks as are necessary to lift the vessel to the water level of its destination.
Locks have distinct disadvantages, however. The process is extremely slow and requires huge amounts of water.
Alternate methods include inclined planes, which enable substantial differences in water level to be overcome within relatively short distances. Ships are removed from the water and transported on trucks up or down planes to the desired level of the canal. An inclined plane at the Big Chute of the Trent Waterway in Canada spans 58 feet, and one at Krasnoyarsk, Russia, can accommodate a 1,500 ton vessel.
Lift locking, in which the lock itself is raised or lowered mechanically, is common in Europe. Vertical lifts operate by means of high pressure hydraulic rams, or by a system of counterbalances and ropes, with electrically driven gearing.
The Anderton Lift in England and Les Fontinettes in France are among those that enable ships to move uphill without undue delays.
