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Last modified
7/14/2009 5:02:34 PM
Creation date
5/20/2009 3:39:59 PM
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UCREFRP
UCREFRP Catalog Number
8251
Author
Rakowski, C. L. and J. C. Schmidt.
Title
The Geomorphic Basis of Colorado Squawfish Nursery Habitat in the Green River Near Ouray, Utah.
USFW Year
1996.
USFW - Doc Type
#93-1070,
Copyright Material
NO
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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 />
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