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<br />Grams and Schmidt 22 <br /> <br />grained sediment with respect to the current streamflow regime. This is consistent with <br />the observation made by Schmidt and Rubin (1995) that, prior to the closure of Glen <br />Canyon Dam, many eddies in Grand Canyon were filled with sand, and separation and <br />reattachment bars were merged. <br />The spacing of rapids is not regular, but is controlled by debris fans in both canyon <br />systems. Other major channel elements such as gravel bars, sand bars, and pools are <br />located in association with debris fans. Tributary basin geology and hydrology, which <br />determine debris fan size and location, strongly influence mainstem channel morphology. <br />Deposits such as sand and gravel bars found in each specific fan-eddy complex creaate a <br />quasi-adjustable, self-formed alluvial channel inset within the bedrock/talus canyon. <br />8. CONCLUSIONS <br />The basic geomorphic characteristics of streams in canyons with debris fans are <br />determined by the tributary sediment delivery processes. :Longitudinal prof1le, channel <br />geometry, and the occurrence of rapids in the canyons of the eastern Uinta Mountains are <br />each strongly influenced by tributary-fan frequency. Bankfull channel width-to-depth <br />ratio is smaller and gradient is steepest in the reaches with highest fan frequency; and all <br />rapids are caused by debris fans or the gravel bars below debris fans composed of <br />reworked debris-fan material. <br />Expansion gravel bars are the other element of coarse-grained alluvial deposits in <br />debris-fan dominated canyons. These bars are located in the expansion downstream from <br />debris-fan-created eddies where uniform downstream flow resumes. The lithology of <br />gravels in these bars indicates that their source is the debris fan immediately upstream and <br />its associated tributary basin. This is an indication that the process of local sorting <br />outweighs downstream sorting in these canyons. Estimates of average boundary shear <br />stress during floods and critical shear stress of gravel bars shows that the channel gradient <br />and bar-material size are in approximate adjustment with pre-dam flood conditions in both <br />the canyon and meandering r~~ches of the study reach. Although the river flows <br />