Moving Dredged Material Is a Full-Time Job

To maintain navigable waterways, approximately 400 million cubic yards of material are dredged in the United States every year. Of this amount, about 60 million cubic yards are placed in ocean waters at more than 100 Environmental Protection Agency approved sites. The other 340 million cubic yards are dredged in coastal and inland waters and placed in a variety of locations, including uplands, beach sites, wetlands construction sites, and riverine sandbars, to name a few.

Ocean Placement

Typically, in ocean placement, a hopper dredge or towed barge is filled with dredged material, sails to a designated area of the ocean, opens its hull, and allows the sediment to drift to the bottom. Dredged material meeting the evaluation criteria is placed in ocean sites. This material usually comes from inlet, bar, and main approach navigation channels.

Beach Nourishment

Beach nourishment is the placement of the material on or near the beach, usually to renourish an eroding beach. In some cases, suitable material is placed just offshore on an eroding beach, and natural drift processes may carry the material onto the beach over a long period of time. Beach nourishment is typically done with pipeline and hopper dredges. The material usually comes from inlet, bar, and approach navigation channels.

Upland Placement

Upland placement isolates the material from the environment by placing it in diked areas where the material is contained. Upland placement usually occurs by pipeline dredge, but in special circumstances dredged material is pumped or mechanically rehandled directly from barges or hopper dredges. In some cases, this is the most economical method for managing the material. However, urbanization threatens the availability of suitable sites.

Open-Water Placement

Open-water placement refers to dredged material placement in near-coastal and inland waters and might also include capping, which is a specially engineered method to contain contaminated sediments.

The contaminated dredged material is placed on a level bottom or in deep pits or bottom depressions and capped in a precisely engineered manner to ensure that the cap stays in place and the contaminated material remains isolated from the environment.

Within-Banks Placement

The within-banks placement method generally occurs on river systems where the sands are placed on eroded banks or downstream of the shoals along the shoreline. Sometimes these sands are used for construction aggregate or other commercial purposes. Material placed within banks is usually coarse-grained sand that has accreted into rapidly shoaling navigation channels.

Dredging Can Benefit the Environment

About 95 percent of dredged material is not contaminated and is a resource that, placed in proper locations, can be put to productive use. Our search for opportunities to beneficially use dredged material includes wetlands construction, borrow pit reclamation, landfill cover, construction aggregate, beach nourishment, and wildlife and endangered species habitat.

The Corps of Engineers and the Environmental Protection Agency use scientific procedures for identifying and assessing contaminated sediments at dredging projects. These procedures have been published in technical manuals to ensure that dredged material will be managed in an environmentally responsible manner.

When contaminated sediments are identified in material that must be dredged for navigation, proper safeguards are undertaken to isolate the contaminants from the environment.

Where the dredged material is highly contaminated and traditional disposal is not suitable, one of a number of special remediation technologies might be considered. Activities such as physical separation (hydrocycloning or attrition scrubbers) and incineration can be used to remove contaminants from the dredged material. However, these techniques are very expensive, have limited application, and create management problems of their own.

Beneficial Uses

Placing dredged material in areas that benefit the environment is referred to as "beneficial uses." This method offers perhaps the greatest number of possibilities for placement. Suitable dredged material is placed as fill to create recreational areas, airports, or other projects. Constructing wetlands is a beneficial use that has evolved into a scientific process where habitat can be designed for specific plants and animals, including critical habitat for endangered species.

Where clean sand cannot be economically transported to renourish beaches, underwater berms can be constructed just offshore from the beach zone and the sands may be transported by natural forces to the beach. Agriculture and industry have also welcomed the beneficial use concept. Some disposal areas leased to farmers have been successfully converted to crop and pasture lands. Sites in or near cities have been used as industrial sites, parking lots, and airports.

London Convention

The Convention on Prevention of Marine Pollution by the Dumping of Wastes and Other Matter, more commonly referred to as the London Convention, was negotiated in London in November 1972 and came into force in August 1975. Member nations meet annually to debate and resolve legal, policy, and technical issues regarding ocean dumping of all materials. The United States is a signatory member of the London Convention. Thus, regulatory criteria developed by the United States must, at a minimum, be equivalent to and contain all the basic constraints set forth in international regulations.

Dredging is for People

The importance of dredging cannot be underestimated. Our national defense and economic well-being depend on our successful participation in the global marketplace. Our military vessels depend on rapid access to land-based facilities. This participation and access is possible only if state-of-the-art shipping vessels can safely operate in our navigable waters.

Constructing and maintaining our underwater highways keeps these big ships moving.

The men and women of the U.S. Army Corps of Engineers work closely with port authorities and other stakeholders to keep our shipping channels open for the benefit of the people of the United States.