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point in the cluster. Cross sections upstream of the control were positioned in the lower, <br />middle and upper parts of the run, and through a pool, if present. Also in each cluster at <br />least one cross - section was positioned across the shallowest part of the riffle upstream of <br />the control. Because of extraordinarily high base flows in 1997, priority was give to <br />sampling riffles. In 1997, in some clusters only the riffles were surveyed. Some <br />contained up to three profiles and a few stand -alone cross sections were also taken. <br />This study on the Yampa River performed cross sectional analysis for three <br />purposes. The first was to describe certain channel and habitat characteristics of the <br />river. i.e., stream width, percent wetted perimeter, average depth, rise in stage, <br />width/depth ratio, and average velocity. The second was to determine habitat availability <br />as a function of flow and the third was to address fish passage issues. To understand how <br />channel morphology influences habitat characteristics, the values for each of the six <br />variables were plotted for a range of flows between 1 to 500 cfs. The resulting curve, the <br />relationship between the y variable and flow, is a function of channel geomorphology and <br />the inflection point of that curve indicates a regulating property of the channel. Inflection <br />points were identified for all six variables at all cross sections by determining the slope of <br />the line between each paired sets of x and y coordinates. Along the curve there may be <br />several significant changes in slope. Since our concern is with how habitat declines with <br />declining flows, we defined inflection point as the first large slope change in a declining <br />direction along the x axis. Therefore inflection point is not the maximum curvature of the <br />relationship as it is usually considered. Cross sections were arranged by the habitat type <br />it represented, either riffle, run, or pool. The average inflection point for each variable <br />was used to indicate the flow at which the slope of a variable, e.g. percent wetted <br />perimeter, was steeper at lower flows compared to higher flows. Two methods were used <br />6 <br />