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<br />Grams and Schmidt 19 <br /> <br />5). This supports the designation of the selected reaches on criteria of bedrock geology as <br />well as physiography. <br />The ratio of alluvial valley width to bankfull-channel width differs between canyon <br />and meandering reaches. These ratios are higher for the meandering reaches than the <br />canyon reaches (Table 5). The inverse relation between bedrock resistance and alluvial <br />valley width is shown in Figure 14. Note that the coefficients of variation are higher in <br />the meandering reaches (except Echo Park) than in the canyons. This is a result of the <br />large variation in proximity of bedrock to the active channel in most meander reaches. <br />6.5 Spatial Distribution of Rapids <br />The rapids on the Green River through the eastern Uinta Mountains are formed <br />where streamflow is constricted by coarse material impinging on the channel from one or <br />both banks. We inventoried 95 rapids and riffles from aerial photographs, 45 percent <br />more than Graf (1979) identified in the same reach using published river guides (Evans <br />and Belknap, 1973; Hayes and Simmons, 1973). Of the 95 rapids identified, 76 percent <br />(Table 6) are constricted by tributary fans, and 24 percent are constricted only by the <br />expansion gravel bars just downstream from debris fans. The percentage of rapids <br />constricted by debris fans includes some rapids that are impinged on the opposite bank by <br />a gravel bar. Rockfall or a bedrock wall are frequently found on one bank at a rapid or <br />rune, but never on both banks; a debris fan or gravel bar is present at all constrictions. A <br />majority of debris fans create rapids or riffles. Of 110 debris fans tallied on aerial <br />photographs in the study area, 73 percent are colocated with rapids. Thus while all rapids <br />are caused by debris fans or downstream gravel bars, not all debris fans cause a rapid. <br />7. DISCUSSION <br />The steep gradient and low channel width-depth ratio of the debris-fan dominated <br />canyons of the eastern Uinta Mountains are correlated with both lithologic resistance and <br />debris fan frequency. The fact that the river does not flow directly over bedrock and that <br />less than 50 percent of the b~ is composed of bedrock or talus suggests that bedrock <br />