The Port of Portland explains dredging in Portside Magazine:

  “A pipeline dredge is little more than a barge with a house built on it; it has no propulsion capability and cannot move great distances under its own power. For this reason, a dredging plant is accompanied by assisting vessels that can double as towboats and crew shuttles operating betweeen the dredge and the shore.

   The dredge is stationed in the channel at a position determined by earlier survey work and is able to move forward slightly by turning on two spuds (poles attached to the stern of the dredge that are dropped alternately into the river bottom and function as pivots). At the bow of the dredge is an extended metal framework called a ladder, with a cutter head on the end and pipeline running through it. . . spoil is sucked through the pipeline pumped to shore, witht eh aid of a booster pump if the pipeline is particularly long.

   At the shore site, a fill superintendent oversees a crew operating heavy equipment and moving the spoil to maintain a level fill. Spoil generally is about 85 percent water, and a drainage system with a spillway is constructed by the shore crew to allow the water easy return to the river.”