Canal lock diagram
Canal lock diagram.
The three diagrams shows how a boat travels through a canal lock which controls water level.
The diagrams indicate that when a boat is near the upper gates, they open and allow a boat to sail in a canal on an upper water level while the lower gates are closed. After that, first gates are shut down and when a boat reaches the second gates, which control lower water level, the paddles are opened and letting water from the upper level to float in.