Leonardo da Vinci improved the canal mechanism known as a mitre lock by using hinged gates to control water levels.
A navigation lock lets a boat move between stretches of water at different elevations. The chamber is sealed with gates, then filled or emptied until the water level matches the section of canal the boat must enter. Mitre gates meet at an angle, allowing water pressure to help press them shut.
Leonardo worked on canal engineering in northern Italy and is associated with refinements to this system, including improved lock-gate arrangements. His studies addressed practical problems such as controlling flow and moving boats through changing levels.
Leonardo did not invent the entire concept of canal locks. Earlier water-control systems existed, and the precise history of the first mitre gates involves several engineers and locations. The specific term here is mitre lock, not simply sluice gate, because a lock raises or lowers vessels between water levels.