Consequently, it is often necessary to close a series of basins by means of sluices and thus maintain a constant water level in the closed port section. In tidal ports, depths are almost always calculated with the lowest low water line as zero line.

• 因此有必要使用泄水闸来封闭一些港区，以保持封闭港区中的水位。在潮汐式港口，将最低水位计作零水位。