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<br />Draft Fmal Completion Report to UDWR for Contract #93-1070, Amendment 3 <br /> <br />17 <br /> <br />system may vary greatly. Thus, from a geomorphic point of view, annual variability in habitat availability is expected. <br /> <br /> <br />Neither PHABSIM or the methodology of PuchereUi and others (1990) account for the dramatic changes in <br /> <br /> <br />channel morphology that occur from year to year in alluvial rivers, nor the competition and predation pressures (Mathur <br /> <br /> <br />and others, 1985) which are presumed to be significant in the Green River (fyus, 1992). <br /> <br />Complexity Indices <br /> <br /> <br />Complexity indices based on physical habitat parameterS such as depth. water velocity, and substrate size have <br /> <br />been related to habitat complexity in cold water streams (Bovee, 1982). In that light, river ecologists have used a "bank <br /> <br /> <br />coefficient" (Gosse, 1963, as cited in Sedell, 1989) as an indication of river heterogeneity and hence, habitat <br /> <br />heterogeneity or complexity (Sedell, 1989). High values of the bank coefficient indicate the presence of islands and/or <br /> <br />bank irregularities. Consequently, a complexity index such as the bank coefficient should reflect within-chaJmel <br /> <br />morphology. <br /> <br /> <br />The "bank coefficient", the ratio of shoreline length to channel centerline length. quantifies the relative amount <br /> <br /> <br />of shoreline per unit length of river (Gosse, 1963, cited in Sedell, 1989). The presence of islands or emergent bars <br /> <br /> <br />greatly increases this index. In the context of nursery habitat, the convoluted nature of the shoreline may be indicative of <br /> <br /> <br />the area of low or no velocity areas within the channel. The Green River near Ouray includes mid-chaJmel bars and <br /> <br /> <br />some very large vegetated islands. As is shown below, these features greatly increase the length of shoreline, but do not <br /> <br />necessarily contribute to nursery habitat area, and the "bank coefficient" of Gosse (1963) may overestimate habitat <br /> <br /> <br />availability in this reach. Consequently, a complexity index that, to some degree, minimizes the effects of mid-chaJmel <br /> <br />bars and large islands may be more desirable for reaches such as Ouray NWR. <br /> <br />Previous Studies and the Need for New Formulations <br />for Row Recommendations <br /> <br />While sand-bedded rivers and the response of these rivers to flow regulation have been the focus of much study <br /> <br /> <br />over the past 3 decades, many questions remain unanswered. The response of channels to disturbance was studied by <br /> <br />Andrews (1986), Lyons and others (1992), and Yu and Wolman (1987). While the first two studies addressed the <br /> <br /> <br />downstream effects of RaIning Gorge Dam and the latter study the response of channels to flood passage. all of these <br /> <br />studies used channel width, not within-channel distribution of bars as the barometer of channel response, Pucherelli and <br /> <br />" <br />