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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, Colorado, Utah, New Mexico, Nevada, Arizona, California) could develop their respective water entitlements. The dam and reservoir also produce hydropower and provide fish and wildlife benefits. Mean annual discharge in the Green River upstream of the Yampa River has not changed appreciably as a result of dam closure (59 m'/s post-dam versus 56 m'/s pre-dam). However, seasonal flow variability has been considerably reduced. Since Flaming Gorge Dam was closed in 1962, June mean maximum flow of the Green River has been reduced from 381 m'/s to 139 m'/s (Tyus and Karp 1991, Muth et al. 2000). Flows at all other times of the year have increased. In addition, releases for peaking power production were made up to twice per day, resulting in short-term daily fluctuations much greater than historically occurred. Annual volume of sediment transported by the Green River below Flaming Gorge Dam has decreased by 54% as a result of deposition in the upstream reservoir (Andrews 1986). The relatively unregulated Yampa River, a major tributary of the Green River, exhibited greater seasonal variability and more stable daily flows than the Green River below the dam. During the period 1963 to 2004, annual flow maxima in the Yampa River occasionally reached 7