Lithologic and Structural Controls on Green River Channel Morphologies and the Magnitude of Response to the Closure of Flaming Gorge Dam, Utah and Colorado

Andrew L. Nichols

Variations in large-scale (~1 to 10 mi) channel planform geometries along the Green River from Flaming Gorge Dam to the Split Mountain boat ramp are strongly correlated with the longitudinal distribution of river-level bedrock exposures, reflecting first-order bedrock lithologic and structural controls over channel morphologies. Additionally, regional bedrock lithologies and deformation structures provide secondary controls on sediment delivery processes, thus influencing local scale (~0.1 to 1 mi) alluvial depositional environments. The closure of Flaming Gorge Dam (1962) and resultant hydrogeomorphic process alterations have forced in-channel morphological adjustments downstream from the dam site (Andrews 1986, Grams and Schmidt 2002, 2005). The direction and magnitude of these form adjustments varies at both the reach and segment scales, reflecting the influences of regional geologic structures and lithologies, and inherited channel planform morphologies.