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<br />I <br />I <br />I <br />I <br />I I <br />I <br />I I <br />I <br />I <br />I <br />I <br /> <br />I ' <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />generate 268,000 yards and excavating the 50-foot wide channel would generate 397,000 yards <br />of material. The wider pilot channels would speed development of the ultimate channel, however, <br />this advantage would be offset by the greater costs of excavating and disposal of the additional <br />material. The total construction costs of Alternative A are estimated at $2,843,995 to $3,540,892, <br />depending on the width of the pilot channel that is excavated. Average annual operation and <br />maintenance (O&M) costs are estimated at $25,320 per year. The detailed O&M cost estimates <br />can be found in Appendix C. <br /> <br />While Alternative A does not provide as much acreage of aquatic habitat as Alternative B, <br />it is Alternative A which best meets the project goal of providing a diversity of large-river <br />fisheries habitat of the type that existed along the Missouri River prior to channelization and main <br />stern darn construction. <br /> <br />b. Alternative B - BackwaterlWetland Complex: This alternative would result in <br />the creation of 100 acres of backwater wetlands while preserving the 15.3 acres of existing <br />wetlands. Approximately 1,900,000 cubic yards of material would be required to be excavated <br />to create this Alternative. While the flow-through chute (Alternative A) should be self <br />maintaining, there is no reset mechanism for Alternative B and therefore its useful project life <br />cannot be determined accurately. It is possible that even a single large scale flooding event could <br />result in the deposition of a significant amount of material in the wetlands. As sediments <br />accumulate in the backwater wetland, the usefulness of the area for large river fish will decrease, <br />particularly at low river stages. Areas which fill with sediments, to the degree that they are <br />inundated with water only periodically, will revert to vegetated wetlands, Monitoring would <br />verify changes to the created backwater wetland, particularly with respect to water depths, species <br />composition, diversity of the macro invertebrates and fish communities. <br /> <br />The backwater/wetland complex alternative was evaluated to determine its impact on the <br />IOO-year floodplain/floodway. Hydraulic modeling efforts determined that this alternative would <br />have a negative impact on the floodplain/floodway, causing a maximum water surface increase <br />of about 0.6 feet. Details regarding the floodplain analysis can be found in Appendix B. <br /> <br />Water quality in the backwater/wetland complex would not be as high as in the chute <br />channel, (Alternative A), because the flushing action of water would be greater in the chute than <br />in the backwater wetland. In addition, the diversity of aquatic rnacroinvertebrates, and their <br />ability to serve as a food source for other species, would be greater in Alternative A than <br />Alternative B. <br /> <br />The total construction costs of Alternative B are estimated at $6,276,284, while average <br />annual operation and maintenance (O&M) costs are estimated at $29,480 per year. The detailed <br />O&M cost estimates can be found in Appendix C. <br /> <br />While Alternative B would initially create more acres of wetlands than Alternative A, the <br />contribution of the backwater acreage in meeting the project goals is not as great as the chute acres <br /> <br />33 <br />