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Mississippi River: Lock and Dam 4 Winter Maintenance, Alma, Wisconsin

Published April 16, 2020
Updated: April 16, 2020

Purpose of this project is to assure proper periodic maintenance and subsequent operation of the Lock and Dam 4 system.


Lock and Dam 4 is located in Alma, Wisconsin. The U.S. Army Corps of Engineers completed the facility in 1935 as part of the overall 9-foot channel navigation project, and it began operation in the same year.


Lock and Dam 4 was last dewatered in 1994. The St. Paul District locks have been dewatered approximately every 20 years.

On average, more than 12.6 million tons of cargo and 4,300 recreational craft pass through the dock annually. The difference between upper and lower pools during normal conditions is nine feet. The dam is 6,876 feet long, including 1,367 feet of movable gate sections and 5,500 feet of earth fill dike. The movable gate section consists of six roller gates and 22 Tainter gates.

The lock chamber is dewatered to perform maintenance on the miter gates and bubbler system and repair damaged concrete on the walls. The work is performed during the traffic closure period to avoid impacts to users of the navigation system.

To stop water from flowing into the chamber, bulkheads are placed upstream and downstream of the chamber. Once the water is pumped from the chamber, the miter gates, bubbler system and concrete are inspected. The miter gates are sandblasted and painted, and equipment is replaced as needed. Concrete repairs are made on the walls and floor as needed. The bubbler system is removed and replaced with stainless steel.

The Corps’ maintenance and repair crew performs the work during the dewatering, which includes sandblasting, painting, welding, carpentry and equipment operation. They place the sill beam and bulkheads, dewater the chamber, perform the inspections and repairs on the miter gates, sandblast and paint the miter gates, remove and replace the bubbler system and repair damaged concrete.


Maintenance will start when river traffic closes, which is estimated to be early December 2020 and reopened in March 2021.


The project was authorized as part of the Rivers and Harbors Act approved July 3, 1930.


Project design and construction costs are 100 percent federal.

Estimated Total Cost                                   $3,500,000