Tow of 'Northern' entering Cannelton Locks downbound, showing emergency gate structures, Ohio River mile 721, May 1988.
In case of miter gate failure and uncontrolled water flow through the lock, emergency gates can be raised from wells below the lock floor, stopping the flow.
They can also be raised when doing maintenance on the miter gates.
The older of the two 1200-foot locks at McAlpine Locks and Dam has the same structures. I seem to recall reading that the Corps of Engineers once tested the system, and it proved to work as designed.
Towboat 'Northern' entering Cannelton Locks downbound, Ohio River mile 721, May 1988
Northern (doc. # 512466)
Twin screw towboat, b. 1968 by Dravo Corp., Neville Island, Pa. 168 x 40. GM 16-645E5B diesels, 5000 hp. Falk red. 3.759:1. Kort nozzles.
Owned by Union Barge Line until transferred April 1973 to Union Mechling Corp., Pittsburgh.
Transferred Dec. 1980 to Dravo Mechling Corp., New Orleans.
Sold Feb. 1988 to National Marine, Inc., New Orleans.
Leased 1986 to Western Kentucky Navigation, Inc., Paducah.
Sold June 1998 to American Commercial Barge Line, Jeffersonville, Ind.
present whereabouts unknown to me