Project Location: The U.S. Army Corps of Engineers (USACE), Rock Island District (District) proposed project, dredge material placement, is located on the Upper Mississippi River between river miles (RM) 300 and 614 within the states of Missouri (MO), Illinois (IL), Iowa (IA), and Wisconsin (WI). Dredging and material placement is required at numerous locations in this reach of the river.
Background:
A. The Project extends approximately 314 river miles (RM) from just downstream of Lock and Dam (L&D) No. 10 at Guttenburg, IA, to just downstream of L&D No. 22 near Saverton, MO). The
present navigation system was initiated when Congress passed the Rivers and Harbors Act of July 3, 1930, which authorized funds for its development, operation, and maintenance. This and subsequent legislation provided for the construction of a series of locks and dams and dredging to create and maintain a reliable navigation channel of at least 9 feet deep and 300 feet wide and wider in bends. A Final Environmental Impact Statement (EIS) was prepared in 1974 for operation and maintenance of the Upper Mississippi River 9-Foot Channel Navigation Project, pools 11 through 22 (USACE,1974). The Statement of Findings (now referred to as the Record of Decision) was signed by the Director of Civil Works on October 30, 1974.
B. The UMR 9-Foot Channel Navigation Project within the U.S. Army Corps of Engineers (USACE), Rock Island District (District), is comprised of 12 pools (Pools 11 through 22) created by a
series of locks and dams. Channel training structures, such as wing dams, closing dams, and revetment works are also an integral part of the project. Aside from routine maintenance on these structures, annual dredging is required at various locations in the navigation channel.
C. Dredged material is removed from the navigation channel by either hydraulic or mechanical methods. Hydraulic dredging is typically performed by a cutter-suction dredge which transports material in a slurry to the placement site through a pipeline for final placement. Mechanical dredging is typically performed by a clamshell dredge or backhoe, which loads material onto barges for transport to approved placement sites. In rare situations, the District may use a hydraulic dustpan dredge which side casts material into approved placement sites.
D. The dredging method will vary by event and location. Common determining factors for the dredging method include the volume of material requiring removal, the distance to the placement sites, availability of equipment, and material type. The dredging depth is typically 11 feet below low operating pool elevation, but width can vary based on location. Straight areas of the channel are typically dredged to 300 feet wide. Bends width requirements are calculated based on curve radius and can be from 300 feet to several hundred feet wider.
E. Annual maintenance dredging of the Project is normally performed at 15 to 20 sites. Over the last 20 years, the annual volume of dredged material ranged from approximately 95,000 cubic yards (CY) to 1,300,000 CY. Due to the large sediment load carried by the waterway and continually changing flows, specific dredging locations and quantities to be dredged vary from year to year and cannot be determined sufficiently in advance to perform individual Clean Water Act (CWA) 404(b)(1) Evaluations. The District uses long-term (10-year) 404(b)(1) evaluations to provide flexibility to rapidly respond to dredging needs while complying with Section 404 of the CWA. Long-term 404(b)(1) evaluations allow for the use of historic (previously used) placement sites so long as those sites are compliant with applicable Federal laws. Newly identified placement needs, and potential locations are evaluated through the District’s Dredged Material Management Program and corresponding National Environmental Policy Act (NEPA) reviews, including site specific 404(b)(1) evaluations completed for any new placement sites.
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