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METHODS Two general approaches were used to address the status and quality of PHABSIM study site related data. One included an evaluation of the PHABSIM associated data sets following procedures outlined in Milhous et al. (1984) and (Milhous, 1984a and b). The other was an evaluation of PHABSIM study site data for conformance to representative and critical reach selection criteria as contained in Bovee (1982) and Bovee et al. (1978). PHABSIM Data Set Evaluation Twenty-two existing PHABSIM study sites distributed throughout the UCRB were the focus of this evaluation. Data sets associated with these sites were evaluated by Bruce Wahle and other personnel of the Instream Flow and Aquatic Systems Group (IF & ASG), Western Energy and Land Use Team (WELUT), U.S. Fish and Wildlife Service, Fort Collins, Colorado. Generally, the evaluation included an assessment of: 1) the original field notes supplemented by discussions with the original surveyors; 2) surveying and field measurement errors; 3) ranges of flow extrapolations for simulation; 4) error messages from evaluating "input versus outputs" of the model; 5) existing documentation describing any manipulations on the data; and 6) calibration results of both methods, water surface profile and IFG4, using associated evaluation criteria. More detailed discussions regarding specific methods and procedures followed are provided in the "Results" section. For some of the above evaluations .standard procedures have been published as noted above. Other evaluations performed on these data sets were more subjective in nature. However, given the experience of the IF & ASG in this area, we consider them the experts. Evaluation of PHABSIM Study Sites for Conformance to Reach Selection Criteria Prior to evaluating the value of existing PHABSIM study sites for .use in this study, the rivers included within the project boundaries were evaluated for conformance to segment boundary criteria contained in Bovee (1984) and Bovee et al. (1978). These rivers and associated river mile (R.M.) designations included: Colorado River (R.M. -16 to 185), Green River (R.M. 0-364), Yampa River (R.M. 0-140), White River (R.M. 0-40) and the Gunnison River (R.M. 0-40) (Figure 1). Accordingly, these geographic boundaries define the current distribution of Colorado squawfish and humpback chub based on Colorado River Fishery Project (CRFP) fish capture efforts and represent river reaches to be included in the habitat analysis. Detailed discussion of the segment boundary selection criteria and their use can be found on pages 38-58 (Bovee 1984) and pages 44-52 (Bovee et al. 1978). Generally, segment boundaries include major tributaries and other locations 2