Leonardo da Vinci’s movable canal gate for controlling water levels was a miter lock.
A miter lock uses two gates that meet at an angle pointing upstream. Water pressure pushes the gates together, helping them seal the passage when the water level differs between the two sides. Opening and closing the gates allows boats to pass between canal sections at different elevations. Leonardo studied and improved canal-lock arrangements while working on hydraulic engineering in northern Italy.
Leonardo did not invent the entire idea of canal locks. Earlier forms existed in Europe, and pound locks had been used before his work. His importance lies in his detailed observation, design refinement, and application of hydraulic principles to canals around Milan.
A miter lock is not simply a sluice gate. A sluice usually regulates flow through an opening, while a lock chamber lets vessels change elevation. Leonardo’s canal studies also included water diversion, excavation, irrigation, and navigation, making them part of a much wider engineering program.