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8 <br />In-channel geomorphic features were mapped on these photos (Fig. 4). Sand <br />deposits, coarse gravel, and debris-flow deposits were easily distinguished; areas of <br />moderately gray tone for which substrate characteristics were uncertain were mapped <br />as "sand and gravel". Sand, gravel, or sand-and-gravel deposits were subdivided into <br />submerged, wet, and dry phases. Dry sand is white, while wet sand is darker in hue; wet <br />areas may be covered by a veneer of mud. The typical annual flood snowmelt cycle leads <br />to deposition of uniformly white sand bars by the annual peak flow when well-sorted <br />fine- to medium-grained sand bars aggrade, and finer deposits are washed downstream. <br />Summer monsoon rainstorms in desert watersheds deliver high concentrations of silt <br />and clay that cover low-elevation parts of these same bars later in the season. Thus, the <br />late season character of Green River sand bars includes high-elevation platforms of <br />clean white sand surrounded by low-elevation areas of silty, wet sand. <br />The longitudinal distribution of shoreline complexity at different discharges was <br />estimated by assuming that the contacts of the three phases of the map units -- <br />submerged, wet, and dry -- represent pseudo-topographic contour lines (Fig. 5). <br />Shoreline complexity has been shown to be an adequate measure of habitat complexity in <br />large rivers (Gosse, 1963, as reported by Sedell et al., 1989). The line length of the <br />perimeter boundary of each pseudo-topographic level was measured, and reported as the <br />perimeter length per unit channel length as measured down the channel centerline. The <br />minimum possible value of this parameter is 2 because both banks were measured. In <br />order to calculate the shoreline complexity of the wet phase, all polygons that were <br />mapped as water, submerged deposits, or wet deposits were combined, and the perimeter <br />length of the entire aggregated area was calculated. Similarly, the perimeter of the dry <br />phase was calculated after aggregating dry, wet, submerged, and river map units.