In 1930 the 9-foot draft channel was legislated by Congress to increase commerce on the river. The U.S. Army Corps of Engineers began construction of the series of 29 locks and dams between St. Louis and Minneapolis, creating a stairway of water for river traffic. Since the river is constantly shifting its load of sand and sediment and tributaries along the way contribute more it is necessary to remove the material from the bottom of the channel to prevent a closure to navigation. This process of underwater excavation is called dredging.
The St. Paul District operated three hydraulic dredges in the 1920s and 1930s. The Vesuvius, Peelee and Cahaba were responsible originally for the majority of the dredging done to maintain the channel. Other dredges used in the early days were the Dundee, Taal, and St. Croix. Many million cubic yards of sand and silt had to be dredged to establish the 9-foot channel and the old steam dredges were slow with the capability to move only 500,000 cubic yards of material during a season. A new dredge with a far larger capability and modern equipment was needed to meet the challenge on the rivers.
Plans and specifications for a new more efficient hydraulic dredge were begun in 1935. It was to be named after William A. Thompson (b. Dec. 16, 1854), who graduated from the University of Vermont with a degree in civil engineering in 1878 and entered federal service that same year with the Corps of Engineers. In 1896, he was appointed to the position of Assistant Engineer responsible for the improvements on the Upper Mississippi River.
Built by Dravo Corporation in Pittsburgh Pennsylvania, the dredge William A. Thompson was christened there in March 1937. A granddaughter of William Thompson broke the traditional bottle on the hull. Construction cost was $846.130. The new vessel arrived at the Corps Fountain City, Wisconsin, Service Base in 14 days arriving on May 22, 1937.
The hydraulic dredge Thompson may be likened to a gigantic vacuum cleaner as its pipeline cutterhead sucked up the sand from the river bottom. It was capable of extracting 1,800 cubic yards per hour. The hydraulic pump was driven by a 1,800 horsepower diesel engine; two 850 horsepower diesel engines generate electrical power to run the two 500 horsepower motors used for propelling the vessel.
The Thompson was the biggest single piece of equipment used by the St. Paul District. It is 267 feet long from the tip of the cutterhead to its stern. It was 48 feet wide and had a minimum bridge-clearing elevation of 52 feet, 9 inches. It had a 22-inch intake and 20-inch discharge. The vessel could dredge to a depth of 26 feet and cut a channel 350 feet wide from one mooring.
In order to maintain a three-shift operation the 1,370-ton dredge can carry up to 66 persons for a four-crew complement to work 24 hours a day, seven days a week. The Thompson normally dredged 1.5 to 2 million cubic yards each year. During the Dredge Thompson’s first 50 years of service 102,951,300 cubic yards of material passed through its pump. This quantity would create a pyramid one square mile approximately 300 feet high.
The Dredge Thompson was replaced by the Dredge William L. Goetz, which was christened on June 24, 2005, at the Winona Levee Park, in Winona, Minnesota. The Thompson continued to serve as a quarters boat until 2008. In 2012, the Thompson was sold to Community Development Alternatives in Prairie Du Chien, Wisconsin. It departed on its last voyage on June, 12, 2012, arriving at its new home the following day. CDA is working to preserve the Thompson and its rich history of service on the Upper Mississippi River. CDA is currently developing plans to convert the Dredge Thompson into a Museum of River Transportation.
Dredge William A. Thompson in Prairie Du Chien, Wis.