Canal Lock

A canal lock is a device for raising and lowering boats between stretches of water at different levels along a river or canal, using a fixed chamber with gates at each end whose water level can be adjusted to match the water on either side. Engineers working for the Egyptian ruler Ptolemy II are credited with inventing the lock around 274 to 273 BCE to keep saltwater from contaminating the Nile, and during China's Song dynasty the administrator Qiao Weiyue built the first pound lock in 984, using two closely spaced gates to form an intermediate chamber, a major improvement over the earlier flash lock. Medieval Europe's first pound lock was built at Vreeswijk in the Netherlands in 1385, followed by the first pound lock of the fully modern design at Damme in Belgium in 1396, and a lock still works on the same basic principle today: a boat enters through one set of gates, the chamber is filled or drained until the water level matches the next stretch of waterway, and the boat exits through the opposite gates, a passage that typically takes ten to twenty minutes.