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Cutterhead Dredges

Mechanical dredging is when a crane and barge are used to remove sediment off the river floor. It's used when the area being dredged is too small and too costly for the more common hydraulic dredging, which is the kind performed with the Dredge Thompson. On the Thompson, there's a cutter with teeth that churns up the material. The sediment and water is suctioned up a long tube.

The Dredge Thompson is a USACE vessel under mission to conduct dredging operations along the upper part of the Mississippi River. Of the Corps' Mississippi fleet, only the Thompson (St. Paul District) is a cutterhead dredge, better suited to the river's upper reaches. The Dredge "Willam A. Thompson" is named after William A. Thompson who worked for the Army Corps of Engineers from 1878-1925. It was built by Dravo Corporation out of Pittsburgh, PA. Christened by William Thompson's granddaughter in March 1937, it arrived in Fountain City, WI on May 22, 1937.

The Government Dredge THOMPSON is used primarily for hydraulic dredging, and contract dredges are used for mechanical dredging. Dredged material placement is extensively planned for the long term and is actively managed to maximize beneficial use of the material. The St. Paul District is responsible for maintaining 284 miles of the Upper Mississippi River (UMR) 9-foot channel navigation system. The area of responsibility is from the head of navigation at Minneapolis, Minnesota, to Guttenberg, Iowa. Channel control structures are maintained to minimize dredging quantities without affecting natural resources. Dredging Operations are conducted with a 20 inch cutterhead, pipeline hydraulic dredge. Approximately 2 million cubic yards each year. Can dredge 1,000 cubic yards per hour. Maintains 850 miles of the Upper Mississippi River. Dredges in St. Paul, Rock Island and St. Louis Districts. Works 24 miles on the St. Croix River & 335 miles on the Illinois River. With Booster Barge "Mullen" and additional pipeline, they can now reach over 10,000 feet from dredge site to disposal site. Season from April until December.

The biggest single piece of equipment used by the St. Paul District, Thompson weighs approximately 1200 tons and is 267 feet long, 48 feet wide and 52-foot, 9-inch minimum bridge clearance. With a 22-inch intake and 20-inch discharge, Thompson can dredge to a 23 1/2-foot depth and 350 feet wide from one mooring.

More than 75 people visited the Dredge William A. Thompson on 21-22 June 2000 when it was in St. Paul for channel maintenance. The Thompson dredged 116,000 cubic yards in the Upper Mississippi River near the St. Paul downtown airport and excavated a channel cut of 2,450 feet at mile 838.

The cutter suction dredge Pontchartrain, owned by Great Lakes Dredge and Dock Company, performs maintenance dredging on the Mississippi and Missouri Rivers under contract to the Corps of Engineers. Pontchartrain is especially suited for this type of work owing to her shallow draft. The dredge's cutter and pump power suit her for the range of materials. The contract cutterhead dredge Pontchartrain works at a rate of $30,000 a day.

On May 23, 2001 Great Lakes Dredge & Dock Co., Oak Brook, Ill., was awarded a $6,000 increment as part of a $5,547,100 firm-fixed-price, multi-year contract to lease the Cutterhead Hydraulic Pipeline Dredge "Pontchartrain," fully operated with attendant plant, Mississippi River and harbors. The dredge was to be used principally for harbor work at Hickman, Ky.; New Madrid, Mo.; Carruthersville, Mo.; Osceola, Ark.; Memphis, Tenn.; and Helena, Ark. It was anticipated that the dredge would be used for 30-45 days performing channel realignment work in the Mississippi River in the vicinity of Mile 771. The dredge may be used on the Mississippi River at any point between Wickliff, Ky., and Greenville, Miss. Work was expected to be completed by Dec. 31, 2001.

On June 20, 2002 Great Lakes Dredge and Dock Co., Oak Brook, Ill., was awarded a $5,658,790 increment as part of a $5,658,790 firm-fixed-price contract for lease of one Cutterhead Hydraulic Pipeline Dredge, "Pontchartrain", Fully-Operated with Attendant Plant. Work will be performed at any point on the Mississippi River between Wickliff, Ky., and Greenville, Miss., and was expected to be completed by Dec. 31, 2002.

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