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<br />EXECUTIVE SUMMARY <br /> <br />Purpose and Approach <br /> <br />The goal of this study is to define the base flow needs of endangered fish populations in the Yampa River. <br />The approach taken was to simulate habitat availability associated with several low flow scenarios and <br />relate changes in habitat availability to habitat use by endangered fishes. Specific objectives identified to <br />accomplish this goal include: <br /> <br />1) Determine the composition, dimensions and characteristics of the riverine habitat at randomly <br />selected sites in the Yampa River during the baseflow period (August - O~tober) 1996 and 1997. <br />2) Determine the relationship between channel morphology characteristics and flow in the Yampa River, <br />and relate them to passage criteria for endangered fishes. <br />3) Monitor movements of Colorado pikeminnow, humpback chub, channel catfish, and northern pike in <br />the Yampa River during low flows to determine the range of movement and habitats occupied during <br />the baseflow period. <br />4) Determine the relationship of riffle characteristics at various flows to passage requirements of <br />endangered fishes <br />5) Using the data collected above and from previous studies in the Yampa River, determine whether a <br />low flow management plan for the Yampa River Basin is necessary. <br /> <br />Our approach to defining flow needs was to identify the relationship of habitat availability to discharge <br />and relate availability to habitat use by endangered fishes. Initially the study area of the Yampa River <br />was stratified into the lower gradient reach above Yampa Canyon and the higher gradient reach in Yampa <br />Canyon. River channel variables were used to identify similarities and differences between reaches. <br />Three approaches were used to identify flows that will maintain habitat for endangered fishes: 1) <br />identifying of the greatest rate of change in stream morphology as flows decline, Le., curve break <br />analysis, 2) estimating of available habitat based on suitability curves, and 3) defining barriers to fish <br />passage. The first approach is a general, holistic approach that defined the flow at which the greatest rate <br />of decline in major features of the channel, as well as potential for instream productivity (wetted <br />perimeter) using hydraulic simulation (RHABSIM). The second approach was based on the Instream <br />Flow Incremental Methodology (IFIM) RHABSIM that integrated suitability curves of depth, velocity <br />and substrate from fish capture or telemetry observations with hydraulic simulation to generate a set of <br />weighted useable area estimates for simulated flows. The lowest flow required for fish passage over <br />riffles was determined by estimating riffle depth at various flows using RHABSIM. The rate of habitat <br /> <br />8 <br />