Documentation of Existing Conditions in the Central Platte Valley

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SECTIOHTWO Environmental Setting 2.1 DESCRIPTION OF THE CENTRAL PLATTE STUDY AREA The Central Platte Valley study area extends along the Platte River from near Lexington, Nebraska east to near Chapman, a distance of approximately 110 miles. This section of the 'Q Platte provides habitat for three of the four target species - whooping crane, least tern, and piping plover - and is designated critical habitat for the whooping crane. It includes portions of nine central Nebraska Counties - Dawson, Gosper, Phelps, Buffalo, Kearney, Hall, Adams, Hamilton, and Merrick: The major cities and towns include Grand Island near the eastern end, Kearney in the middle, and Lexington near the western end. The elevation of the Platte River ranges from about 1,750 feet on the east to 2,300 feet on the west. The study area is divided into 12 bridge segments, including the 11 bridge segments used by Currier et al. (1985), and a twelfth segment on the western end from Overton to Lexington. The bridge segments are identified in Table 2 -1 and shown in Figure 2 -1. These bridge segments are used in the presentation of biological data in the subsequent report sections, where this level of detail is available. The width of the study area is about 7 miles (3.5 miles on either side of the Platte River). This width is consistent with the analysis by Currier et al. (1985) and provides a buffer area of upland habitat on either side of the 1- to 2 -mile -wide floodplain. Table 2 -2 summarizes some basic features of each bridge segment, including river and floodplain characteristics, presence of developments, and conservation areas. 2.2 VEGETATION AND LAND COVER TYPES Vegetation and land cover types present in the Central Platte Valley were mapped in the early 1980s, and are currently being re- mapped by the Bureau of Reclamation (BOR) based on aerial photography flown in August 1998. The results of the BOR study will be added to this document when it is available. Table 2 -3 will provide a summary of the acres and percent of each land cover type within each bridge segment based on the 1998 aerial photography. Table 2-4 will provide a comparison of changes in the areas of riverine habitats from 1982 to 1998. Currier et al. (1985) provides the results of the first study, which used a GIS database developed by the Platte River Whooping Crane Maintenance Trust, Inc. (Trust) through a contract with the FWS Western Energy and Land Use Team (WELUT). The database consists of the river channel in each segment and an area extending for 3.5 miles on both sides of the channel. The number of river miles covered by the database is greater than the 11 bridge segments because a buffer of 3.5 miles of river channel was included at the ends of Segments 1 and 11. The database was based on aerial photography from September 1982, which represents a period of low flow for the Platte River (about 260 cubic feet per second (cfs) at Grand Island). Twenty -four surface cover types were identified and used in the analysis, including six riverine, four agricultural, ten development, and four other types. Riverine surface cover types were designated in those areas inside the historical floodplain boundary. For a few surface cover types such as alfalfa, open water, emergents, and cropland, land areas were designated both inside and outside the floodplain boundary. l�S' Wa►�raid 68FOD9728600 /rl.dw 6/2/1999(9:52AM)/URSC'=FS/2 2-1