Leonardo da Vinci designed a miter lock for canals to manage changing water levels.
A miter lock has two gates that meet at an angle, typically forming a V whose point faces the higher water. Water pressure pushes the gates together, helping them seal. Leonardo used this principle in canal-engineering designs associated with Milan and the Naviglio system.
The lock allowed boats to move between sections of canal at different elevations. Instead of draining an entire canal, operators could close the gates, adjust the water level in the chamber, and then open the gates at the new level. Leonardo improved practical details such as gate operation and water control.
The general canal lock predates Leonardo, so he was not the inventor of the lock itself. His importance lies in studying and refining hydraulic engineering for transport, irrigation, and urban water management.