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Title: Upper Mississippi River System Environmental Management Program Definite Project Report/Environmental Assessment (SP-1) : Lake Onalaska Dredge Cut & Island Creation Habitat Rehabilitation and Enhancement Project, Pool 7, Upper Mississippi River, LaCrosse County, Wisconsin
Authors: United States. Army. Corps of Engineers. St. Paul District.
Keywords: Restoration ecology
Environmental protection
Environmental management
Mississippi River
Publisher: United States. Army. Corps of Engineers. St. Paul District.
Abstract: A significant water quality problem and associated fishery degradation has been identified in Lake Onalaska near Rosebud Island. Wave action in Lake Onalaska also reduces water clarity. The Wisconsin Department of Natural Resources, the U.S. Fish and Wildlife Service, and others have done extensive sampling and monitoring of the area since the late 1970's because of the importance of the 7,700-acre area to fish and migrating waterfowl. Sedimentation has occurred in the area near Rosebud Island and the natural islands in Lake Onalaska have been eroding and disappearing. The project objectives are to provide oxygenated water to the valuable fishery area, create additional deep-water fishery habitat; improve water clarity in the lake, and provide additional predator-free waterfowl nesting areas. It is proposed to accomplish these objectives by providing flows to the fishery area; deepening selected areas of the lake; and creating additional islands in the lake. The alternatives considered to accomplish the objectives included various channel layouts and depths, island designs and locations, and construction techniques. Channel design alternatives included bottom widths from 100 to 350 feet, depths from 8 to 40 feet, and short stubs or branches off a central channel for additional "edge" effect. Island designs included side slopes from 1 vertical on 2 horizontal to 1 on 12 and slope protection from vegetative techniques to rock riprap. The island locations were varied to make the best use of existing resources and bathymetry. Construction techniques that were considered included mechanical and hydraulic dredging, deep-dredging, and placement alternatives. The construction alternatives and project boundaries were re-analyzed when it was found that the Wisconsin Department of Transportation was interested in obtaining highway fill from the habitat project area. The selected plan for the habitat project includes dredging an 8,000-foot-long channel between Rosebud Island and the Wisconsin shoreline to a depth of 10 feet with 1 vertical on 3 horizontal side slopes. The channel bottom width would be 200 feet except for 100-foot widths at a location where the- channel splits and at the lower end where the channel would branch into two. A spur channel about 500 feet long and 400 feet wide near the upper end of the central channel would carry flows from Halfway Creek and also serve as a sediment basin. Approximately 600,000 cubic yards would be excavated from the project area. All of the sand (about 220,000 cubic yards) from the channel cut would be used to construct three islands at existing shallow areas or where islands previously existed in Lake Onalaska. The top width of the islands would be a minimum of 25 feet and 6.5 feet above normal pool. Side slopes would be 1 vertical on 3.5 horizontal with rock riprap placed on the north side to minimize erosion and topsoil on the rest of the island. The remainder of the material from the channel cut (fine sediments not suitable for island construction) would be placed in a containment facility constructed on Rosebud Island or at some other upland site in Wisconsin. During the planning of the project, the Wisconsin DOT indicated a need for about 1 million cubic yards of material for a 7-mile-long highway project located a couple of miles from the channel cut. Therefore, it was agreed that material not needed for island construction and dredging of additional material from the project area could be used for highway fill. The additional material would be obtained by dredging up to 35 feet deep and 400 feet wide from a designated borrow area in the area of the channel cut near Halfway Creek. This deeper borrow area would then be backfilled to a depth of about 10 feet with material from the habitat project limits that is unsuitable for island or highway fill. Since the Wisconsin DOT requirement for fill material is much greater than the quantity estimated to be dredged within the habitat project limits, it is proposed that the DOT implement and manage the construction contract to accomplish both the habitat and highway projects concurrently. The Corps would design the habitat project, have review and approval authority of final plans and construction activities, and provide appropriate reimbursement to the DOT for the habitat project via a Section 215 agreement. Using one contract to construct both projects would result in cost savings to both agencies, with additional environmental and intangible benefits. Total direct cost of the selected habitat project is $2,780,000. By combining the habitat project with the Wisconsin DOT highway project, the total direct cost of the habitat project is estimated to be $2,040,000, based on a cost sharing apportionment of 50/50 for material used as highway fill. Indirect costs bring the total habitat project cost to $2,460,000. $80,000 of the total project cost has been expended for the general design phase of the project. Average annual operation and maintenance costs of the project are estimated to be $3,000 (joint project) and would be the responsibility of the U.S. Fish and Wildlife Service. The habitat project would restore some of the habitat diversity in the 7,700-acre Lake Onalaska by creating about 90 acres of deepwater fishery habitat and restoring 10 acres of island habitat. The channel cut would provide good winter habitat for bluegills and largemouth bass by maintaining higher dissolved oxygen levels year-round. The islands would initially create about 12 acres of "shadow zones" south of the islands to encourage the development of emergent and submerged vegetation. This could expand as the aquatic vegetation becomes established. The islands would also improve and maintain water clarity, provide loafing and resting habitat for migratory waterfowl, and provide "edge effect" for a variety of other fish and wildlife.
Description: Definite Project Report with Integrated Environmental Assessment
Rights: Approved for Public Release; Distribution is Unlimited
Appears in Collections:Environmental Documents

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