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<br />Approach <br /> <br />The goal of this study is to define the baseflow needs of endangered fish populations in the Yampa River <br />to insure their recovery. The approach taken was to simulate habitat availability associated with several <br />low flow scenarios and relate changes in habitat availability to the use of these habitats by endangered <br />fishes. The specific objectives identified to 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 - October) 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 as a function <br />of discharge and relate availability to habitat needed by endangered fishes. Initially the study area of the <br />Yampa River was stratified into the lower gradient reach above Yampa Canyon and the higher gradient <br />reach in Yampa Canyon. River channel variables were used to identify similarities and differences <br />between reaches. Three approaches were used to identify flows that will provide habitat for recovery of <br />endangered fishes; 1) identifying the greatest rate of change (i.e., curve break) in the stream morphology <br />as flows decline, 2) estimating available habitat based on suitability curves, and 3) defining barriers to <br />fish passage. The first approach is a general, holistic approach that defined the flow at which the greatest <br />rate of change in major features of the channel, as well as potential for instream productivity (wetted <br />perimeter) by estimating river channel variables at various flows using hydraulic simulation (RHABSIM). <br />The second approach was an based on the Instream Flow Incremental Methodology (IFIM) RHABSIM <br />that integrated suitability curves of depth, velocity and substrate from fish capture or telemetry <br />observations together with hydraulic simulation to generate a set of weighted useable area estimates for <br />simulated flows. Estimates of the flow needs for fish passage over riffles was determined using an <br />element of the RHABSIM. The rate of habitat loss or habitat isolation due to flow reductions <br /> <br />17 <br />