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13 <br />a <br />still over 30 percent lower than pre-impoundment levels. In recent <br />years (1970-1978) mean annual suspended sediment loading has exceeded <br />2.9 million tons.at Jensen, Utah, 150 KBD (USGS records). <br />Prior to June of 1978, all water releases from the dam were <br />hypolimnetic and near 40C year round. The completion of modified in- <br />take ports on the dam's penstocks now allows a variable depth (and <br />temperature) release, and temperatures are currently maintained at <br />near 130C from May to October. <br />Predominant streamside vegetation in more open areas is big sage- <br />brush (Artemisia tridentata), rabbitbrushes (Chrysothamnus spp.), <br />narrowleaf cottonwood (Populus angustifolia), sedges, rushes, and <br />grasses. In the canyons, Utah juniper, Douglas fir (Pseudotsuga <br />menziesii), boxelder, and tamarisk become more abundant (Holmgren <br />0 1962b). <br />Site Selection <br />0 Sites were located on each river as nearly equidistant from each <br />other as possible to enhance data analysis from the perspective of a <br />stream continuum. Selection was based on the presence of suitable <br />0 sampling habitat, gross similarity of physical attributes of the sites, <br />and accessibility. <br />Suitable habitat was defined as rapid/riffle areas which afforded <br />sampling of substrates from 30-50 cm depths where water velocities <br />were of 0.3-0.6 m/sec. McConnell (1958) found most periphytic growth <br />to occur on rocks 12 cm diameter and larger, and sites were character- <br />0 ized as possessing an adequate amount of substrate in this size range. <br />0