The canal technology Leonardo da Vinci helped develop by using hinged gates to control water levels was a canal lock.
Leonardo worked on canal and hydraulic projects in northern Italy, where locks allowed boats to move between stretches of water at different elevations. A lock chamber is enclosed by gates: a boat enters, the water level is changed, and the boat leaves at the new height. This avoids requiring a canal to remain at one uniform level.
Leonardo is associated especially with improvements to mitre gates, whose angled faces press tightly together when water pushes against them. Such gates made lock chambers more practical and resistant to leakage. The broad principle of canal locks predates Leonardo, so he should be credited with improvements and applications rather than with inventing the entire technology.
His hydraulic studies also covered canals, pumps, water flow, and river engineering. These projects show that Leonardo’s inventions were not limited to flying machines or weapons; water control was a major part of Renaissance engineering.