Postcard from Dredging in the Duluth Harbor Paul Lundgren 3 years ago Keeping Duluth’s shipping channels open requires occasional dredging. This undated postcard offers a look at the process in the early 20th century. Recommended Links:Postcard from the Grain Elevators on the Duluth-Superior HarborPostcard from a Section of the Duluth Harbor and Railroad YardsPostcard from Tugboats Record and SinclairPostcard from Skyline of Business District from Harbor