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0 0 <br />Objective 1. <br />Three specific reaches have already been identified for study. Concerns were also <br />raised by the Yampa work group that other natural channel conditions may occur that <br />could impede fish passage at low flows due to insufficient depth (limiting reaches). Such <br />a potential channel condition was identified at Lily Park below the confluence of the <br />Little Snake River, and others are suspected. It is proposed to use aerial photographs, <br />published information, and available experience on the existence and location of limiting <br />reaches in the Yampa to identify and possibly include one or more of these reaches for <br />field investigation. <br />Existing information regarding mapping and previously constructed hydraulic <br />models will be reviewed. This information exists at the Juniper and Cross Mountain <br />Canyon sites due to their candidacy as dam sites. Also, previous habitat studies have <br />generated local channel cross - sections and hydraulic models. Based on available <br />information, field activities will be designed to gather additional information necessary <br />to evaluate flow effects in selected reaches. <br />A team of endangered fish biologists, river mechanics engineers and <br />geomorphologists will be used to conduct aerial reconnaissance of the study sites, and <br />conduct topographic surveys of the limiting reaches sufficient to support a local hydraulic <br />modeling effort. This team will also develop criteria for the limiting physical factors <br />affecting migration such as barrier height, hydraulic drop, velocity, riffle /pool <br />sequencing, swimming speeds of Colorado squawfish reported by Bulkley et al. (1982), <br />and body configuration (height- width) data on adult Colorado squawfish in the Yampa <br />River from Nesler (1995). The team will document conditions at the flows experienced <br />during the site visit. <br />Data analyses will include computer modeling of the hydraulics of the study <br />reaches. The interrelationships between habitat composition, velocity, and depth in the <br />immediate areas of passage barriers will be examined over the range of low -flows <br />represented by historic hydrologic records in mid- to late summer. <br />Objective 2. <br />Using the hydrologic computer model of the Yampa River generated during the <br />Yampa Feasibility Studies, an evaluation of: 1) the frequency of critically low flows at <br />current and future consumptive use levels, 2) the need for and frequency and duration <br />of flows which can be provided to enhance fish passage and habitat, and 3) the potential <br />of providing storage releases in varying patterns based on the need to improve flow <br />conditions for fish passage in the study reaches under reasonable operating rules, will be <br />conducted. <br />Collection of Colorado squawfish population data was initiated in 1979, and is <br />available from multiple studies through the present. These data may be suitable for <br />examining potential adverse effects to Colorado squawfish if flow conditions identified <br />as meeting threshold criteria occurred after 1979. These data include relative abundance <br />indices, length frequency distributions, growth and larval production from field sampling <br />of adult fish throughout the river and larval drift sampling in Yampa Canyon; and <br />radiotelemetry and mark - recapture data for movements and migration. Environmental <br />4 <br />