Sediment (gravel, sand, and silt) is deposited in a harbor or river channel when a river slows down. Accumulated sediment reduces the channel depth and can make the waterway unsafe for navigation. Mechanical and hydraulic dredges are used to deepen and widen channels filled with sediment and deposit the sediment in an approved location. Mechanical dredges shovel or scoop up bottom materials and place them on a barge or scow. The two hydraulic dredges shown on this poster use pumps to remove a mixture or water and sediment ("slurry') from the channel bottom. The HOPPER DREDGE is an ocean-going vessel used to dredge sediment from the bottom of a deep-water channel or coastal harbor. Dredged material is stored in "hopper bins" inside the ship before disposal in the open sea or other location.
PIPELINE DREDGE: Vessel commonly used to dredge sediment from the bottom of shallow rivers or calm coastal waters. Dredged material is pumped from the river or ocean bottom and flows through a floating pipeline to shore. The dredged material commonly is used to restore eroded beaches.