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How does a navigation lock raise or lower a boat?

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View of Utrecht's Oude Gracht canal lined with historic brick buildings, arched doorways at water level, and boats moored along the canal edge in the Netherlands. — canals and inland waterways The *Oudegracht* (Old Canal), Utrecht, Netherlands.

A navigation lock is a chamber with movable gates at each end that allows vessels to move between different water levels. The process relies on filling or emptying the chamber using sluices—openings located in the gates, sidewalls, or floor.12

To raise or lower a boat, the following steps occur:

Filling: When a vessel enters from a lower level, the downstream gates are closed. Water is then admitted into the chamber through sluices until the water level inside matches the higher upstream pound. Once equalized, the upstream gates are opened to allow the vessel to exit.12
Emptying: To lower a vessel, it enters the lock from the higher level. After the upstream gates are closed, water is drawn out of the chamber through the sluices until the internal level matches the lower pound. The downstream gates are then opened for the vessel to proceed.12

The design of these sluices and culverts is critical to ensure the chamber fills or empties quickly while minimizing water turbulence, which helps keep vessels steady during the transition.12