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<br />adult pikeminnow and humpback chub. In this respect, IFIM analysis was included as supplementary <br />information to the curve break analysis. <br /> <br />The objective of this chapter is to describe the characteristics of the channel morphology with changes in <br />flow within the designated critical habitat of the Yampa River and quantify habitat/flow relationships for <br />adult Colorado pikeminnow and humpback chub. <br /> <br />Methods <br /> <br />Cross Section Profiles <br />Channel cross section profile methodology is frequently used to determine minimum flows needed to <br />maintain habitats for the aquatic community (Allan 1995). These methods use a stage-discharge <br />relationship to simulate depths and velocities for a desired range of flows. Because of its greater slope, <br />riffle habitat is influenced more by reduced flows than other mesohabitats such as tuns and pools. <br />Therefore, riffles were the focus of our low flow analysis. <br /> <br />This study was designed to determine habitat availability during the baseflow period (August 1 to October <br />31), when flows typically range below 300 cfs (approximately 50% exceedance during baseflow period). <br />All measurements were taken at flows between 300 and 800 cfs during the baseflow period in August and <br />September 1996 and in September and October 1997. During this period flows ranged from less than 100 <br />cfs to as much as 6,770 cfs (Figure 3.1). Sample sites, called habitat clusters, were identified and <br />numbered sequentially along the Yampa River in the study area. Habitat clusters were long enough to <br />contain at least two representative riffle-pool-run-riffle habitat sequences. The length of a habitat cluster <br />was ten times the average river channel width (Leopold et al. 1964). The average channel width of the <br />Yampa River was estimated to be 102 ft in Yampa Canyon and 250 ft above Cross Mountain Canyon <br />based on aerial photographs taken on 18 September 1990 when baseflows were 74 cfs at the USGS gage <br />at Maybell, Colorado. The number of habitat clusters per stratum was determined by dividing the stratum <br />length by the cluster length. For example, Stratum 1 had approximately 104 habitat sample clusters and <br />was based on the following equation: <br /> <br />Number of Habitat Clusters = <br /> <br />20 miles *(5280 feet) <br />1 mile <br />(10 * 102 feet) <br /> <br />=104 <br /> <br />40 <br />