Lock Entrance:

Wet docks have lock entrances to overcome the high fluctuations in water level in the sea. Figure 7 gives a layout of a lock entrance. It consists of a lock chamber which has one gate at its entrance from the open sea, and another on the dock side. The first gate is opened and the lock chamber is flooded with water from the open sea. The ship then enters the lock chamber. The entrance gate is closed and the water level in the chamber is adjusted to the water level in the docks by pumping. The dock side gate is opened and the ship enters the docks.

Figure: Plan of Lock Entrance