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HOW NAVIGATIONAL LOCKS OPERATE These diagrams show how a ship is lowered in a lock—a ship is raised by reversing the operation. No i level. With both UPPER GATES ‘and LOWER GATES closed, UPPER GATES OPEN: LOWER Gates cLoseo and with the EMPTYING VALVE closed and the FILL- ING VALVE open, the LOCK CHAMBER has been filled to the UPPER ae The UPPER GATES opened eine the ship to enter the LOCK CHAMBER Now the ship is in the LOCK UPPER GATES CLOSED Lower cares cLoseo: CHAMBER. The UPPER eats and the FILLING VALVE have beer closed, and ia EMPTYING VALVE has been of to allow water to flow from the LOCK CHAMBER to the LOWER LEVEL. ter level in the LOCK CHAMBER has gone down to UPPER GATES CLOSEOW Lowen Gares Oren the LOWER LEVEL, the LOWER a have been ‘opened, and the ship is leav- ing the Tock CHAMBER. this, the lock is ready i ‘an upbound ship to come and be lifted, or may be filles (as show) to lower another downbound ship. 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.