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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. 1965). The larg~st sub-
<br />basin, the Green River, comprises about 116,000 km2 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 1). 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 1967) 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 million-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
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