Locks on the Rhone River
entering the lock
A lock is a device for raising and lowering boats between stretches of water of different levels on river and canal waterways. 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 take a reasonably direct line across land that is not level.
Guillotine gates are also used on the downstream side of larger locks such as the 23m Bollène lock on the River Rhône.
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