OMAHA, Neb. -- A draft supplemental environmental assessment for additional repairs to the Fawn Island Chute in Harrison County, Iowa is currently available for public review.
The SEA evaluates the environmental impact of repairing areas of the chute damaged in the 2011 flood and subsequent high flow events in 2018 and 2019; these repairs are needed to restore the intended habitat function of the Fawn Island Chute and prevent it from degrading further.
In 2010, the Fawn Island Chute was constructed near river mile 673.6 as a flow-through chute to function as shallow water habitat intended to benefit the federally endangered pallid sturgeon and other native fish and wildlife species. The unprecedented flood of 2011 eroded the east bank of the chute beyond the designed construction footprint, and the chute became deeper and flowed faster than desired. As a result, Phase I chute repairs were conducted in 2015.
Phase I repairs consisted of the construction of a revetment built to an elevation of 1019.3 feet mean sea level (msl), which is 4.1 feet above the construction reference plane (CRP). Sixteen dikes were constructed to direct flows and reduce energy within the SWH site. The constructed dike crown elevations were 1018.5 feet msl, or 3.3 feet above CRP. Approximately 24,260 tons of new quarried rock riprap was placed riverward of the ordinary high-water mark. The ordinary high-water mark defines the area in which the Corps has the authority to work within the river channel through Navigational Servitude.
Following the completion of the Phase I construction activities conducted under Navigational Servitude, the chute was evaluated to determine if it could be re-opened. It was determined that Phase I provides significant bank protection and risk reduction for future high flow events, however; it was noted that due to the relatively low top of rock elevation, there is some remaining risk for further chute development that could continue to impact the riverbank.
The proposed Phase II project includes further stabilization to minimize bank erosion and minimize or prevent lateral migration to the extent possible. Proposed construction activities include the extension of three existing dikes, and the construction of four new dikes to fortify the toe of the existing revetment. In areas where no bank protection currently exists, a total of approximately 1,100 linear feet of new revetment would be installed in various locations to stabilize the banks. Revetment construction would involve minor grading of the rock placement areas. All rock structures would be constructed up to the elevation of the ordinary highwater mark. The proposed construction would require approximately 21,000 tons of rock rip rap acquired from a commercial quarry. Access and construction would take place entirely from river with river-based equipment. If aggradation within the backwater inhibits access from the river, the contractor may find it necessary to displace the accumulated sediment to the side to facilitate access to the proposed work areas. No real-estate certification or involvement would occur since the project will remain at or below the OHWM and within the Corps’ Navigational Servitude authority.
Repairs are being made under USACE’s Missouri River Recovery Program, which helps to fulfill the requirements of the U.S. Fish and Wildlife Service’s 2018 Biological Opinion on the Operation of the Missouri River Main Stem Reservoir System, the Operation and Maintenance of the Missouri River Bank Stabilization and Navigation Project, the Operation of the Kansas River Reservoir System, and the Implementation of the Missouri River Recovery Management Plan.
The public is encouraged to provide comments on the draft supplemental EA which is available for viewing at https://usace.contentdm.oclc.org/digital/collection/p16021coll7/id/18576. Comments can be mailed to: U.S. Army Corps of Engineers, Omaha District; CENWO-PMA-C; ATTN: Fawn Island Phase II Supplemental EA; 1616 Capitol Avenue; Omaha, NE 68102-4901. Comments can also be emailed to: cenwo-planning@usace.army.mil. Comments must be postmarked or received no later than July 30, 2021.
This draft supplemental EA is consistent with the National Environmental Policy Act of 1969 (NEPA), as amended, the Council on Environmental Quality’s (CEQ) regulations for implementing NEPA (40 CFR 1500-1508), the Corps’ regulations for implementing NEPA (33 CFR325 and Engineering Regulation 200-2-2) and other applicable environmental laws and regulations.
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