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STUDY AREA The Green River Basin drains mountainous and high desert portions of southern Wyoming, eastern Utah, and northwestern Colorado (Fig. 1) and is the largest tributary of the Colorado River. The study area encompassed the Green and Yampa rivers in and above Dinosaur National Monument and included highly regulated and regulation-attenuated river reaches. The Green River below Flaming Gorge Dam downstream to near Jensen, Utah, was the primary focus of the study. The river below Flaming Gorge Dam flows for 22 km through Red Canyon, enters the 48-km-long low gradient Browns Park valley, and then flows for 32 km through high-gradient Lodore Canyon before entering Echo Park at the Yampa River confluence. From Echo Park, the Green River flows 18 km mostly through Whirlpool Canyon, another 11 km through Island- Rainbow Park, and another 13 km through Split Mountain Canyon before emerging into the alluvial Uintah Basin valley reach near Jensen. Extent of river meandering (river plan form) and habitat types in the major reaches of river are controlled by local geology. In Lodore, Whirlpool, and Split Mountain canyons the Green River is generally confined to a single, relatively narrow channel. Canyon river reaches constricted by debris fans form riffles and rapids with cobble and boulder substrate. These river reaches generally have higher current velocities and deeper runs and pools than lower gradient areas without debris fans. In lower gradient alluvial reaches such as Browns and Island- Rainbow parks, river plan form is characterized by restricted meanders (Grams 1997), and the channel is relatively wide, shallow, and sometimes interspersed with islands. Lower velocity runs with sand and cobble substrate predominate. Flaming Gorge Dam in northeastern Utah impounds the mainstem Green River at the upstream end of the study area. With a storage capacity of 3.74 million acre-ft (4,624 million m'), it is the largest reservoir in the Green River Basin. Upstream Fontenelle Reservoir, the only other mainstem Green River reservoir, does not appreciably affect releases from Flaming Gorge Dam. Flaming Gorge Dam was closed in 1962 as part of the Colorado River Storage Project (CRSP) to store water so that states of the Upper and Lower Colorado River basins (Wyoming, 7