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<br />INTRODUCTION <br /> <br />Environmental Setting <br /> <br />legal agreements in 1928 (Carlson and Carlson 1982) separated the <br />Colorado River into upper and lower basins at lee Ferry, Arizona. The upper <br />basin was subsequently sub-divided into three hydrologic sub-basins: Green, <br />Upper Main-Stem, and San Juan-Colorado (Iornes et al. I965). The 1arg2st sub- <br />basin, the Green River, comprises about 116,000 kmZ of the 284,000 km <br />occupied by the upper Colorado River basin (see Preface for English conversion <br />factors). The Green River extends about 800 km to its source, the Wind River <br />Range, in western Wyoming. <br /> <br />The study area included the Green River from its confluence with the <br />Colorado River (km 0) to its confluence with the Yampa River (km 552) in <br />Dinosaur National Monument (DNM; Figure I). The Yampa River was included <br />because the movements and distribution of the target fishes included both <br />rivers, and Yampa River flows affect habitats of fishes in the Green River. <br />The Green River above its confluence with the Yampa River has been influenced <br />by operations of Flaming Gorge Dam since its completion and filling in 1962. <br />Endangered fishes still inhabit the Echo Park area of the Green River and are <br />incidental from Lodore Canyon to Swallow Canyon. However, native fish habitat <br />in the Green River upstream of DNM has been greatly altered by the Dam <br />(Pearson 1967; Vanicek I967) and no longer supports endangered fish <br />populations. <br /> <br />The Yampa and Green rivers contain relatively high-gradient reaches <br />dominated by boulder, cobble, and gravel substrates (e.g., Cross Mountain and <br />Yampa canyons, Yampa River; Whirlpool, Split Mountain, Desolation and Gray <br />canyons, Green River), and low-gradient alluvial reaches of meandering canyon <br />and flat, open terrains dominated by finer substrates. The Yampa River, with <br />an average annual discharge of about 1.5 mi11ion-acre-feet, arises on the <br />western slope of the Rocky Mountains near Steamboat Springs, Colorado, then <br />flows northward and westward, and enters DNM and Yampa Canyon below its <br />confluence with the little Snake River. Upper Yampa Canyon (km 72-32) has a <br />moderate gradient and is characterized by rocky runs, shallow riffles, and <br />rapids. The lower Yampa River deepens, widens, and becomes slower moving as it <br />passes to its confluence with the Green River at Echo Park. The Yampa River <br />flows about 320 km and drops in elevation about 2,256 m (Joseph et al. 1977). <br /> <br />Downstream of its confluence with the Yampa River, the Green River enters <br />upper Whirlpool Canyon, a reach dominated by deep eddies, riffles, sheer <br />cliffs, and boulder-strewn banks. The Green River then meanders through sand <br />and cobble shorelines in Island and Rainbow parks where cottonwood, willow, <br />and saltcedar grow along the river bank. The river passes through Split <br />Mountain Canyon, a moderately high-gradient reach dominated by riffles, runs, <br />and rapids, and enters the Uintah Basin where it again becomes broad and <br />shallow. The Duchesne River, draining the southern slope of the Uintah <br />Mountains, enters the Green River near Ouray, Utah (km 396.48). The White <br />River, with headwaters on the western slope of the Rocky Mountains, enters the <br />Green River just below the mouth of the Duchesne River. Below these large <br /> <br />4 <br />