Project Location: The Illinois Waterway (IWW) Channel Navigation Project (Project) is located between river miles (RM) 78.9 and 290.7, located entirely within the State of Illinois (IL). Dredging is required at numerous, and often unpredictable locations in this reach.
Background:
A. To maintain the 9-foot navigation channel, maintenance dredging will be performed on the IWW within the U.S. Army Corps of Engineers (USACE), Rock Island District (District). The District’s portion of the IWW extends approximately 212 RMs beginning just downstream of the Lockport Lock and Dam (L&D), Lockport, IL, to the LaGrange L&D, located approximately 9 RMs downstream from Beardstown, IL. The USACE’s operation and maintenance of the present navigation system was initiated when Congress passed the Rivers and Harbors Act of 1927. Congress has appropriated funds for District operation and maintenance work of this segment of the waterway ever since. A Final Environmental Impact Statement was prepared in 1975 for Operation and Maintenance of the Project. The Statement of Findings (now referred to as the Record of Decision) was signed by the Director of Civil Works on November 18, 1975.
B. The Project consists of six locks and dams, from RMs 78.9 to 290.7. Upstream of each dam extending to the next dam is a slackwater navigation pool. Wing dams, closing dams, and revetment works are other physical structures that are normally integral parts of an inland waterway navigation project. These types of structures are not prevalent on the IWW but when present, they require routine physical maintenance. 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 performed by a cutterhead dredge, which discharges material to the placement site via a floating pipeline or onto barges for final placement. Mechanical dredging is performed by a clamshell dredge or excavator, 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. 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. Sediment grain size analyses indicates most sediments in the river navigation channel are primarily sand with intermittent stretches of fine-grained material. Dredging depth is typically 11 feet below low operating pool elevation.
D. Annual maintenance dredging of the Project is normally performed at 10 to 15 sites. Over the last 20 years, the annual volume of dredged material ranged from approximately 76,000 cubic yards (CY) to 705,000 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 utilizes long-term (10-year) 404 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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