Why Are There Locks on Some Canals and Rivers?
Locks are watertight
chambers which enable boats to ascend or descend to different levels in a canal
or river. The lock is usually rectangular in shape with gates at either end. If
a boat has to go to a higher level it enters through the bottom or downstream
gates of the lock, which are then closed.
The water level in the lock is raised to that of the higher part of the canal by filling from the upper level and the upstream gates are opened to let the boat out. The opposite procedure takes place when a boat needs to descend. Locks used to be made of timber, brick or stone, but now concrete and steel piling are more usual. Originally the chamber was filled or emptied by sluices in the gates.
The distinguishing feature of a lock is a fixed chamber in which the water level can be varied; whereas in a caisson lock, a boat lift, or on a canal inclined plane, it is the chamber itself (usually then called a caisson) that rises and falls. Locks are used to make a river more easily navigable, or to allow a canal to cross land that is not level. Later canals used more and larger locks to allow a more direct route to be taken.
Nowadays, as locks become bigger, these are often replaced by conduits or pipes running the whole length of the structure, with offshoot pipes running into the lock to give an even discharge of water. Old locks may be manually operated but new ones are worked by hydraulic power. Locks vary tremendously in size from about 126 by 17 feet (38 by 5 meters) on small canals to the giant locks on the Mississippi River in America, which are 1,200 by 110 feet (366 by 33.5 meters). Since 2016, the largest lock worldwide is the Kieldrecht Lock in the Port of Antwerp, Belgium.