Lock

A lock is a chamber with gates at each end that raises or lowers vessels between stretches of water at different levels, on a canal, a river, or at the entrance to an impounded dock. The vessel enters the chamber, the gates close, and water is admitted or released through culverts or sluices to equalize the chamber level with the onward reach, then the far gates open. Gate types include mitre gates (a self-supporting V pointing upstream), sector or vertical-lift gates, and caisson gates. Lock size sets the maximum beam and length of ship the waterway can pass, the controlling dimension behind Panamax and the New Panamax locks. Each cycle consumes a lockful of water from the upper reach.