Dredging: Digging Out Harbors So the Biggest Ships Can Reach Port

Rivers are always moving the land. Sand and silt wash downstream and settle in channels and harbors, slowly filling them in. Left alone, a harbor would eventually become too shallow for the ships that depend on it. Dredging — removing sediment and debris from the bottom of lakes, rivers, harbors and other waters — is the routine work that keeps them open around the world.

As sand and silt wash downstream, sediment gradually fills channels and harbors, and it must be removed periodically by dredging. Credit: U.S. Environmental Protection Agency.

Keeping ships afloat

Much dredging maintains or deepens navigation channels, anchorages and berths so boats and ships can pass safely. A vessel needs a certain depth of water to float without touching bottom, and that depth keeps increasing as ever larger ships come into service. Because massive ships carry the bulk of the goods the country imports, dredging plays a vital role in the nation's economy.

Cleaning up contamination

Dredging is also used to protect fish, wildlife and people from contaminants, and to stop contamination spreading through a body of water. This environmental dredging is often needed because sediments near cities and industrial areas are frequently polluted. Pollutants reach waterways from point sources — sewer overflows, municipal and industrial discharges, spills — and from nonpoint sources such as surface runoff and deposition from the air. NOAA's Office of Response and Restoration plays a major role in protecting and restoring marine resources when environmental damage occurs.

Who handles the dredged material

Federal, state and local governments and private organizations such as port authorities manage and carry out the disposal of what is dredged up. Two federal agencies oversee it:

Sources

Based on "What is dredging?" from NOAA's National Ocean Service, a work of the United States government in the public domain.