The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

HOW NAVIGATIONAL LOCKS OPERATE ‘These diagrams show how a ship is lowered in a lock—a ship is raised by reversing the operation. No With both UPPER GATES ‘and LOWER GATES closed, UPPER GATES OPEN LOWER GATES CLOSED. and with the EMPTYING VALVE closed and the FILL- Ss The UPPER GATES have been opened allowing the ship to enter the LOCK CHAMBER. Now the ship is in the LOCK UPPER GATES CLOSED. LOWER Gates cLoseo CHAMBER. The UPPER GATES and the FILLING VALVE have beer! closed, and the EMPTYING VALVE hi water to flow from the LOCK CHAMBER to the LOWER ‘The water level in the LOCK CHAMBER has gone down to UPPER GATES CLOSED. LOWER Gates oPEN~ Courtesy U.S. Corp of Engineers Pumps are used after the close of navigation in order to remove the water from the locks. Considerable maintenance work is done during winter, when area waters are frozen over and steamboat whistles are no longer heard on the busy waterway.