Vol. 2 - August - No. 42
St. Anthony Falls Lower LockA navigation lock works like an elevator. The water surface in the lock chamber is the floor of the elevator while the lock gates are the elevator doors.
The lock takes a boat safely and quickly from one water level to another, past natural rapids, falls or man-made dam. Such a lock is a long, narrow, concrete chamber with steel gates at either end. Two of this type of locks, the St. Anthony Falls Lower and Upper locks are located in Minneapolis.
The St. Anthony Falls Lower Lock (above) raises upward bound river traffic from the lower pool level to the upper pool, a vertical lift of 25 feet, and lowers downward bound traffic the same distance. The St. Anthony Falls Upper Lock operates the same as the Lower, but lifts traffic 50 feet and over the Falls, the highest lift of any lock on the Mississippi River.
The water in the lock is separated from the lower pool by a pair of miter gates at the downstream end, and from the upper pool by a tainter gate at the upstream end. The miter gates are like double swinging doors hinged at the lock walls, while the tainter gate resembles the blade of a huge bulldozer - with the tainter gate raised, the lock is closed and when lowered the lock is open, permitting boats to travel between the upper pool and the chamber.
The useful length of the lock chamber is 400 feet and its width is 56 feet. About 6 million gallons of water are required to fill the chamber for each lockage. By comparison, the average output of the water supply system for the city of Minneapolis is about 74 million gallons a day. The lock will accommodate two standard barges, each 195 feet long by 35 feet wide, and a tug boat, 65 feet long by 18 feet wide, moored alongside. Loaded to a draft of 9 feet the gross weight of two such barges would be about 3800 tons.
Except for the vertical life, dimensions and operations of the Upper Lock are the same as the Lower Lock.
The procedure for an upward bound lockage is illustrated by sketches (1), (2), and (3). The water surface in the lock is at the level of the lower pool when the miter gates are opened and the vessel enters the lock (1). The vessel is then tied to mooring bitts on either lock wall to keep it steady, and the lower lock gates are closed.A valve is opened and water flows from the upper pool into the lock through a tunnel in the wall and openings in the floor. This operation raises the water level in the lock (2), and, with it, the vessel until they reach the level of the upper pool. At this point, the upper gate is opened and the vessel starts upstream (3).
In reverse manner, a downward bound vessel enters the lock and is fastened to the mooring bits. The Upper Lock gate is then closed and the emptying valve is opened to drain the water through the floor openings into the downstream pool. When the water level and vessel in the lock drop to the lower pool elevation, the lower miter gates are opened and the boat moves on downstream. The entire lockage operation in either direction, from the time a vessel enters one gate and leaves the other, takes about 20 minutes; filling or emptying operation alone requires about 8 minutes.
The St. Anthony Falls Upper Harbor Project is open to commercial and pleasure craft users. These locks, as are all other inland waterway structures, may be used free of charge by commercial and pleasure boats.
learn more about this fascinating subject:
Engineering the Falls: The Corps Role at St. Anthony Falls
A History of Minneapolis: River Transport
Archaeology of the Minneapolis Riverfront
Pool, Tailwater, and NSP Elevations
