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000906 PHABSIM field data becomes available in the future, the procedures used to assess it would follow the same rationale presented here. In their report, "Relationship between flow and fish habitat using the Instream Flow Incremental Methodology (IFIM) in the Platte River System", Chadwick and Associates (1989) present the results of their analysis in numerous Weighted Usable Area (WUA) versus discharge graphs for each segment within the central Platte River and for each species modeled. The basic relationship between available habitat and discharge, given as WUA in square feet per 1000 feet of stream, was derived from the HABTAT model of the Physical Habitat simulation (PHABSIM) (Milhous et al. 1989). The principal objective of the Chadwick & Associates report was not to determine a "target flow" but to analyze potential impacts of project operations. However, to assist in developing a "target flow" for the central Platte River, the WUA versus discharge curves developed by Chadwick and Associates for each study segment were weighted by the length of the segment and summed to develop a total WUA versus discharge curve for the entire river reach for each of the four species. This was done by totaling the WUA among the separate segments in a study reach following the procedures described in Bovee (1982). The individual species curves where normalized as an individual percent deviation (IPO) from the maximum predicted WUA. By normalizing each species curve to a standard number, each species is weighted equally and can be combined to develop a composite curve for the entire central Platte River. The composite curve in Figure B1 represents the percent of optimum habitat as a function of discharge for 4 species of fish. This approach is consistent with the guilding approach previously recommended to the Joint study, and was based on both the velocity and depth variables being used to partition the Platte River habitat into four guilds (Biology Workgroup 1990). The four guilds were: a) a slow/shallow guild; b) a fast/shallow guild; c) a slDw/deep guild, and; d) a fast/deep guild. This technique was suggested by Leonard and Orth (1988). Four separate species were recommended to represent the above guilds. The channel catfish adult was selected as the characteristic species of the slow/deep guild; the speckled chub as the characteristic species of the fast/shallow guild; and the plains killifish as the characteristic species for the slow/shallow guild. The fast/deep guild had no members but the goldeye was a strong candidate species if additional information became available. The sand shiner was also listed as an acceptable additional characteristic species of the slow/shallow guild. 9