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• The bottomlands will act as depressions after levee removal. The lowest- elevations in the bottomlands range from 3.5' to 9' lower than the proposed flooding elevations. Therefore, as the bottomlands drain, water will be retained in the bottomlands. It is assumed that at most sites, with the exception of Above Brennan, seepage connections will completely dry the bottomlands, or will not allow the bottomlands to retain sufficient water to overwinter fishes after runoff season. After the hydrologic connection is lost, fish will be trapped in the bottomland. This function will allow the Fish and Wildlife Service to potentially manage non- native fish species. It is hoped that native fish species, which have evolved and adapted to this type of bottomland habitat, will instinctively return to the river before the connection is lost. Site by Site Levee Removal Strategy Each site has a unique levee removal strategy. This next section will provide an overview of the design parameters and methodology at each site. Summary sheets for each site can be found in Appendix E. These sheets give the following information: • Schematic showing breach dimensions • Brief description of the proposed cut • Location of the breach relative to the river cross sections • Cut and fill quantities • Spoils quantities and proposed placement location • Vegetation descriptions at the site • Inundation area at 13,000 cfs • Access information • Proposed bank cut and flooding inlet elevations • Approximate base of bottomland and 100-yr floodplain elevations In addition to the summary sheets, 1"= 200' topographic maps on 11" x 17" sheets of the BLM sites showing the bottomland and proposed breach locations are also included in Appendix B. For the ONWR sites, 1" = 400' maps of each bottomland site are included on 11" x 17" sheets. -The aerial photos which are included in Chapter I also provide an excellent reference to identify flooding locations. The aerial photos can be used with the topographic maps to develop a better understanding of existing flooding conditions relative to the proposed levee removal locations. It should be noted that for the ONWR sites, the displayed contours are based on 1962 topographic data. For the proposed levee removal analysis, supplemental topographic data was taken and used to verify levee heights and locations. However, the current information is not shown on the mapping. More detailed mapping of the ONWR bottomlands has been proposed as part of a different project and will be available for future analyses. Bureau of Land Management Sites Bonanza Bridge Bottomland - At the Bonanza Bridge site a 350' wide section of the bank will be lowered, located at an existing low spot (see sheet B-1 in Appendix B) where a surface connection was actually made during the 1996 runoff season. Due to a lack of larger, old cottonwoods along the back at this location, a longer opening was a possibility. A wider opening may provide an opportunity for larval fish to drift into the bottomland area. The adjacent area between the bank cut location and bottomland area will have to be cleared and grubbed and graded down to an elevation which will allow flow to enter and recede from the bottomland. The controlling inlet elevation of 4705.1, should be set 50' back from the bank cut location which has a proposed elevation of 4703.5. The inlet elevation location should be armored with any available cottonwoods roots, logs, or other materials extending across the flow path. Vegetation will need to be disturbed along the flow path and this material will need to be buried with spoils pile. The BLM personnel had a concern with aesthetics of the site in regard to the spoils pile. The proposed spoils pile location was chosen to be placed up in the draw adjacent to the site, somewhat out of public view. The spoils piles should be • revegetated with native vegetation which will reduce erosion and provide better aesthetics in the future. The approximate cost of restoration at the Bonanza Bridge was $20,000.00. 55