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<br />Grams and Schmidt <br /> <br />16 <br /> <br />the thalweg of the channel is dominated by coarse material in the canyons, fine-grained <br />material occurs at 60 percent of the cross sections. <br />6.2.4 Fan-Eddy Complexes <br />In the canyon reaches, fan-eddy complexes are common and are the dominant <br />storage location of fine- and coarse-grained alluvium. For example, the constriction in the <br />fan-eddy complex shown in Figure 4 is created by a debris fan formed at the mouth of a <br />tributary entering from the south side of the canyon. Channel-margin deposits occur on <br />both sides of the channel in the backwater above the constriction. A large eddy bar, 150 m <br />long, mantles the downstream edge of the debris fan and extends the full length of the <br />eddy at bankfull flow. The gravel bar is located downstream from the eddy where <br />downstream flow occurs across the full width of the channel during bankfull flow. <br />Although there is variation in the size and characteristics of individual debris fans, eddy <br />bars, and gravel bars each of these elements is present in most fan-eddy complexes. <br />Another fan-eddy complex at Rkm 558.3 in Lodore Canyon is shown in an aerial <br />photograph (Fig. 9). This debris fan constricts the channel and forms a small rapid. The <br />eddy bar mantles the downstream edge of the fan and is a typical separation bar. The large <br />downstream expansion gravel bar is attached to the left bank and is covered by a veneer of <br />sand. While most of our data and discussion focuses on the plan-view characteristics and <br />distribution of the fan-eddy complex, these complexes are in fact three-dimensional forms. <br />Pools are present above and below the constriction, increasing depth by a factor of 2 to 3 <br />(Fig. 10). At the constriction, depth is reduced by a similar magnitude. Gravel bars are <br />located below the lower pool and thalweg depth decreases. <br />There are a total of 96 fan-eddy complexes in the mapped area. Not all debris fans <br />create a fan-eddy complex; 79 percent of all fans in the mapped reach create ~ constriction <br />that forms a fan-eddy complex. However, there are nearly twice as many debris fans as <br />fan-eddy complexes because some fan-eddy complexes are formed by a debris fan on each <br />bank; this often occurs wher~.!l structural control, such as a fault. crosses the river. The <br />