The Corps of Engineers has a number of programs and authorities related to the management of sediments in the Great Lakes region. This page will briefly describe these programs, and direct you to other pages containing more detailed information about specific programs.
What are sediments?
Sediments are soils that are eroded from land surfaces, washed off streets and carried into streams and rivers where they eventually settle to the bottom. Sediments are a naturally occurring environmental media. However, the erosion of soils from land surfaces can be greatly increased by some farming and forestry practices. Construction, mining and other physical disturbances contribute to the sediment loading to rivers, streams and lakes. Dust, soot and solids washed off streets, parking lots and other impervious surfaces can make urban runoff a significant source of sediments as well.
What impacts can sediments have?
The civil works projects that the Corps constructs and maintains for flood protection and navigation are directly impacted by sediments. The deposition of sediments in reservoirs and navigation channels diminishes the performance of these projects and increases the overall project costs. The "design life" of a flood control reservoir can be significantly reduced by the accumulation of sediments which take up valuable flood storage space. Navigation channels must have sediments dredged periodically to maintain safe depths. Maintenance dredging of sediments at Federal navigation channels in the Great Lakes costs over $20 million annually. The costs and controversy for managing dredged material can be even more substantial.
Excessive sediment loadings and contaminated sediments can create significant environmental problems. Excessive sediment loadings can destroy critical aquatic habitats, bury spawning areas, and degrade water quality. Contaminated sediments have been linked to a number of use impairments, including fish flesh tainting, fish tumors and abnormalities, and restrictions on fish and wildlife consumption. Contaminated sediments are a major obstacle to the restoration of beneficial uses are Great Lakes Areas of Concern.
What are the options for managing sediments at the source?
Whether for navigation or environmental restoration, dredging is a reactive solution to sediments. Source control is a proactive solution, but is not easily implemented. Source control of sediment and sediment contamination include soil conservation and stormwater management practices, as well as point and non-point source contaminant controls. The Natural Resource Conservation Service recently completed a demonstration study of techniques for promoting soil conservation practices, such as no-till farming, in the Maumee River watershed in order to reduce the load of sediments which deposit in the Federal navigation channel. An economic study by the Ohio State University indicated that the costs of promoting soil conservation could be more than offset by the savings to dredging and dredged material disposal.
It was with this thought in mind that Congress, in 1996, authorized the Corps of Engineers to develop sediment transport models for Great Lakes tributaries. These computer models simulate the erosion, transport and deposition of sediments within a watershed, and can be used to evaluate the effectiveness of soil conservation and other source control measures on the loadings of sediments and sediment contaminants to Great Lakes harbors and navigation channels. Visit the homepage of this Sediment Management program for more information about the models and copies of the studies mentioned above.
Sediment transport models are a tool for prioritizing areas within a watershed that are contributing a large portion of the sediment load, and for comparing the efficiency of conservation and source control options. Implementing conservation measures and non-point source control is not easy, especially when the sources of the sediments are in areas of the watershed that are far removed from the portion of the waterway that is feeling the impact of excessive sediments or sediment contamination.
What are the mechanisms for implementing sediment source controls?
The USEPA and Department of Agriculture (Natural Resource Conservation Service) are the lead Federal agencies in implementing sediment source controls. The Corps does have limited authorities to support sediment source control, in addition to the sediment transport modeling program mentioned above. These other authorities include:
What are the options for the remediation of in-place contaminated sediments?
There are four basic approaches to addressing in-place contaminated sediments:
- Containment in-place
- Treatment in-place
- Removal and confinement
- Removal and treatment
Of these options, removal and confinement has been applied at the vast majority of sediment remediation projects at Great Lakes sites. This is not to say that the other options are inferior, but the costs of treatment is significantly greater than containment, treatment in-place has not been tested widely, and the merits of containment in-place need to be assessed on a case-by-case basis. For more information about contaminated sediment remediation alternatives, check out USEPA's Assessment and Remediation of Contaminated Sediments (ARCS) web site.
The Corps of Engineers is assisting state and local agencies in the remediation of contaminated sediments under the following authorities:
- Great Lakes Remedial Action Plans and Sediment Remediation The Corps has developed feasibility studies of remedial alternatives for contaminated sediments at five Areas of Concern with this authority, which can also be used for demonstrations of promising technologies.
- Environmental Dredging Full scale removal of contaminated sediments can be performed at areas outside Federal navigation channels.