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ABSTRACT <br />Available shoreline habitat along the Green River in Desolation and Gray Canyons <br />is strongly influenced by geology and discharge although the relationship between the three <br />has not been readily apparent. To better associate the two, we established four geomorphic <br />study reaches within the canyons. Within each reach, a series of cross sections was <br />measured at different discharges. Surficial geology of the river corridor was mapped, and <br />historic oblique photos were matched to establish the geomorphic organization of the <br />canyon and assess changes that have occurred over the past century. Maps were also made <br />of the distribution of eddies, low-velocity zones, and the distribution of shoreline habitat. <br />These maps were repeated at several discharges including base flow and bank full <br />discharge. <br />Preliminary results show that low-velocity zones occur predominantly in the lee of <br />obstructions caused by debris fans. Debris fans in Desolation Canyon are predominantly <br />expansive and of low gradient. Only the small portion of the fan that is active delivers <br />sediment that restricts flow and causes rapids and eddies, while the main fan is so large that <br />it acts more as a meander bend as the river flows around the fan. As discharge increases <br />the total area of eddies increases, however, at bankfull discharge many of the relatively <br />small active portions of the fans are overtopped, and eddy frequency decreases. Although <br />very large debris fans dominate the river corridor, fine-grained alluvium is the most <br />abundant bank material at low discharge, and vegetated fine-grained alluvium dominates at <br />higher flows. <br />INTRODUCTION <br />Viable populations of humpback chub (Gila cypha) exist in Desolation and Gray <br />Canyons of the Green River, as well in other debris-fan affected canyons of the upper <br />Colorado River basin. The most comprehensive studies of habitat for these fish at various <br />life stages have been conducted on the Colorado River and the Little Colorado River in <br />Grand Canyon. The Colorado River's discharge, sediment transport, and temperature are <br />2