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bucket dredge

Bucket Dredge

hydraulic dredge

Hydraulic Dredge

Bottom-dump scow

Bottom-Dump Scow

Beach nourishment

Beach Nourishment

Great Lakes Dredged Material Testing & Evaluation Manual

Dredging and Dredged Material Management on the Great Lakes

Each year, approximately 5 million cubic yards of bottom sediments are dredged from the Great Lakes and its tributaries for a variety of purposes, including the maintenance of navigation channels, flood protection, waterfront construction, clearing water supply intakes, placing or repairing utilities that cross under rivers, and environmental remediation.

The Corps of Engineers expends approximately $20 million for maintenance dredging at some 35 of the federal navigation projects on the Great Lakes each year. Over 100 dredging permits are issued annually by the Corps to industries, marinas, and local governments in the Great Lakes. There are a variety of methods for dredging sediments, including mechanical buckets, drag lines, and hydraulic dredges that transport sediment through pipelines or in large hoppers. Individual dredging projects may be as small as 10-100 cubic yards for a pipeline crossing to as large as 500,000 cubic yards from a major commercial harbor.

The options for managing dredged material might be divided into the following categories:

Open water placement involves the discharge of dredged material directly to the lake or river. Hydraulically dredged material may be discharged by pipeline a short distance offshore. Mechanically dredged material may be placed in bottom-dump barges or scows and towed to disposal sites several miles away. Discharged dredged material settles through the water column and deposits on the bottom at the disposal site. The dredged material may remain in a mound at the site or disperse depending on the material's physical properties and the hydrodynamics of the disposal site. Open water placement is used with approximately 32% of Great Lakes dredged material (1993-1996).

Beach/littoral nourishment involves the placement of dredged material directly onto a beach or into the shallow water. Beach nourishment is typically discharged by pipeline from a hydraulic dredge. Suitable dredged material is typically a fine sand, and may only stay on the beach for a limited time before being eroded into the littoral drift. Littoral nourishment involves a discharge to near shore, shallow areas, and is typically done with bottom dump scows when a mechanical dredge is used. Beach and littoral nourishment are used with approximately 12% of Great Lakes dredged material (1993-1996).

diagram of Capping

Capping is the placement of a contaminated dredged material in a subaqueous disposal site and covering the material with a layer of clean material. Level bottom capping is the placement of dredged material onto a level bottom surface, as shown. Confined aquatic disposal (CAD) involves the use of a depression or excavated subaqueous pit for disposal to provide lateral containment, as shown. Cap materials are typically a clean, sandy dredged material. Capping has been used extensively for management of dredged material in the ocean in New York and New England, but has not been used in the Great Lakes.

Open water placement, beach and littoral nourishment, and capping are dredged material management options that are regulated under Section 404 of the Clean Water Act. The Great Lakes Dredged Material Testing and Evaluation Manual is applicable to all of these management options.

A significant amount of research and development have been conducted on  dredging and the management of dredged material.  The Corps of Engineers' Dredging Operations Technical Support (DOTS) program has much of this research information, including computer models available on-line.

The Great Lakes Dredging Team, a partnership of Federal and State resource agencies, has developed a number of informational materials on dredging, dredged material management, and dredged material regulations which are all available on-line.


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