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<br />.,...-"..., <br /> <br />INTRODUCTION <br /> <br />Habitat loss is one of the single greatest causes of declines in populations of native <br /> <br />fishes in North America (Williams et al. 1989), The need to preserve minimum stream flows <br /> <br />,-c.-~ <br />t ! <br /> <br />was recognized by the state of Colorado by the passage of Senate Bill 97 in 1973. Espegren <br /> <br />, .. <br />s .1 <br /> <br />(1998) states that most in stream flow water right filings in Colorado have been for protecting <br /> <br />minimum flow for cold water (headwater) habitats. The most common methodologies used in <br /> <br />L I <br /> <br />Colorado is the R2Cross method (Nehring 1979) and Instream Flow Incremental <br /> <br />n <br />LJ <br /> <br />Methodology (IFIM) (Bovee 1982). IFIM estimates the amount of usable habitat for fish as a <br /> <br />function of discharge by combining habitat suitability curves with the hydraulic model. The <br /> <br />o <br /> <br />habitat component of the model has received much criticism because of assumptions implicit <br /> <br />r"'l <br /> <br />with using suitability curves and assumptions of positive relationships between habitat <br /> <br />, '.1 <br />i '; <br />t j <br /> <br />~. <br />availability and fish abundance. Validation of these assumptions have been obstacles for <br /> <br />successfully using IFIM to model minimum flow impacts on large warm water rivers of the <br /> <br />, , <br />!. 1 <br />11 <br />L~J <br /> <br />west slope (Rose and Hahn 1989). <br /> <br />[.'...............~..}. <br />m <br /> <br />Currently there is no standardized approach to establish minimum flow needs on warm <br /> <br />water river sections, and the use of sophisticated models appear to be required in high profile <br /> <br />situations (Espegren 1998). Warm water fish assemblages appear to require a more intensive <br /> <br />t........~.l.. <br />.. J <br />I <br />.;::.1 <br /> <br />approach to instream flow modeling compared to cold water fish communities. Warm water <br /> <br />river reaches tend to be lower gradient and have higher channel complexity and sediment <br /> <br />r1 <br />tj <br />bJ <br /> <br />loads. Warm water fish populations tend to have higher species diversity. Also habitat <br /> <br />suitabilitycurves derived from microhabitat observations do not adequately describe habitat <br /> <br />use for many warm water species. A broader community-level perspective, as opposed to an <br /> <br />f 1 <br />tJ <br /> <br />indicator species approach, may be required to protect all habitats of a functioning warm <br /> <br />r"::,:] <br />r .'.1 <br />,:,.;1 <br /> <br />water stream ecosystem. <br /> <br />1 <br />