Why Dredge? There are 136 Federal harbors within the Great Lakes Basin, with 745 miles of navigation channels. A "Federal" channel or harbor is one that has been authorized by Congress. Most of these navigation authorizations date from the early 19th century. These harbors and channels were constructed to serve commercial navigation, recreational navigation, or both.
Channels and harbors are maintained for safe navigation. The depths of channels vary with the types of traffic. The navigation channels on the Mississippi and Ohio Rivers are maintained at authorized depths of 9 feet, which is sufficient for the barges and cargo they carry on these rivers. In contrast, the Connecting Channels between the Great Lakes are maintained at depths of 30 feet for the ocean-going ships which carry ore, coal, and other cargos between domestic and international ports. The channels at a particular harbor may have depths up to 30 feet at the entrance with progressively shallower depths as one moves upstream. This is especially common at harbors where commercial navigation is concentrated near the river mouth while recreation traffic extends a distance upstream.
In order to maintain channels and harbors at safe depths, periodic dredging is required. Great Lakes harbors and channels are maintained by the Corps' districts in:
- Buffalo (harbors in New York, Pennsylvania and Ohio)
- Chicago (harbors in Indiana and Illinois)
- Detroit (harbors in Michigan, Wisconsin and Minnesota)
How Much is Dredged? Dredging and the management of dredged material are an important function of Corps districts. Typically, about 4 million cubic yards of sediments are dredged by the Corps of Engineers each year from Great Lakes harbors and channels. This is equivalent to 400,000 truck loads of soil. This may seem large, but is actually only a small piece of the 300-350 million cubic yards dredged by the Corps nationwide annually. On average, the Corps of Engineers spends about $20 million dollars annually for dredging and dredged material management in the Great Lakes Basin.
What is Dredged Material? Dredged material is a term used to describe the material excavated from a river, harbor or lake by a dredge. In the case of maintenance dredging, the material is sediment that has accumulated in the channel bottom since the last time it was dredged. In rivers, these sediments are soils that have been eroded from farmlands, forests, and gardens or washed off city street and carried by the water before depositing in a deepened channel. In the harbors and entrance channels that extend out into the lakes, the sediments are sand and silts that have been carried along the lake shoreline by littoral currents and deposited in the deepened channel. Over 90% of the dredged material is a clean soil that is physically and chemically the same as the soil on a field or in the park. The other ten percent may have contaminants that came from a number of possible sources including urban runoff and sewer overflows. For more information about sediments..
Where Do Dredged Materials Go? Sediments dredged from Great Lakes harbors may be managed in a number of different ways:
- open water placement
- beneficial use (beach/littoral nourishment)
- beneficial use (upland)
- confined disposal
The Corps is required to use the disposal alternative that is least costly and complies with applicable environmental laws and regulations. Guidance developed jointly by the USEPA and Corps is used to determine which disposal methods are environmentally acceptable.
The Technical Framework is a national guidance manual developed by the Corps and USEPA that outlines the process for evaluating all possible management options for dredged material.
The Great Lakes Dredged Material Testing & Evaluation Manual is a regional guidance manual used for determining if a dredged material is suitable for placement in the Great Lakes. Developed by the USEPA and Corps, the manual is for use by ports, marinas, governmental agencies, consultants, and laboratories in evaluations conducted under Section 404(b)(1) of the Clean Water Act.
How Can Sediments and Sediment Contamination be Reduced? The Corps' has authority to remove sediments that accumulate in navigation channels, but has limited authority to control the sources of sediments or sediment contamination. The Corps has worked in partnership with state agencies in the Great Lakes region to develop plans for the remediation of contaminated sediments through the Great Lakes Remedial Action Plan program. The Corps is also working with state and local agencies to perform environmental dredging of contaminated sediments from areas outside Federal navigation channels under the Environmental Dredging authority. In 1996, Congress provided the Corps with a proactive authority for sediment management. This authority enabled the Corps to developed sediment transport models of Great Lakes tributaries which would highlight areas where soil conservation and non-point source control measures by state and local interests might be most effective in reducing the loadings of sediments to downstream navigation channels.
Where Can I Get More Information?
Extensive research on dredging technologies, dredged material management, and their environmental impacts has been conducted by the Corps of Engineers since the early 1970's. The Engineering Researc and Development Center, Environmental Lab conduct research in ecosystem science and technology, environmental resiliency, environmental sensing, ecological modeling and forecasting, risk and decision science, environmentally sustainable material, systems biology, climate change, and environmental security.
The Great Lakes Dredging Team is a Federal/State partnership established to be an advocate for timely, cost-efficient and environmentally responsible dredging on the Great Lakes. Their web site contains a white paper on the dredged material management decision making process, fact sheets on confined disposal facilities, and public outreach tools.
The USEPA Great Lakes National Program Office conducted a five-year study and demonstration program called the Assessment & Remediation of Contaminated Sediments (ARCS). This program produced numerous guidance documents on sediment assessment and remediation that are all available on-line.