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here. It is not possible to rule out (i) without making similar measurements at other sites; however <br />there is nothing in the modeling results to indicate that these sites are unusual, e.g. the modeled <br />water-surface slopes are similar to the measured reach-average slopes. Likewise, it is difficult to <br />evaluate (ii) and (iii) without additional field measurements. However, we have several reasons for <br />believing that either (ii) or (iii) are true. First, we know from talking to USGS personnel who have <br />made sediment measurements at the Cisco gauge that large sand dunes can be present on the bed at <br />certain flows (D. Topping, personal communication). Furthermore, we know that the sand forming <br />the channel below Moab, UT, must come from somewhere, and a very large percentage of it must <br />pass through the reach between Cisco and Moab. Thus, we suspect that much of the bed is covered <br />with sand, however, we rarely see it because it is resting in the runs and pools where we cannot <br />sample. If this were the case, then the true size of the bed material might be over-estimated from a <br />surface sample of particles exposed on a bar. <br />a) <br />0.05 <br />RKM 150 <br />0.04- <br />0.03 <br />T <br />0.02 <br />0.01 <br />0.00 <br />b) <br />0.04 <br />0.03 <br />T <br />0.02 <br />0.01 <br />o <br />0 <br />8 <br />0 <br />8 <br />0 <br />o Y = 0.00027'0 0.35 <br />0 <br />2.0 <br />1.5 <br />T/T <br />c <br />1.0 <br />0.5 <br />0.0 <br />0 200 400 600 800 1000 1200 1400 <br />Discharge (m3/s) <br />0.00 <br />0 <br />2.0 <br />1.5 <br />T/T <br />c <br />1.0 <br />0.5 <br />0.0 <br />2000 <br />Figure 25. Relations between discharge and shear stress at (a) RKM 150 and (b) RKM 106 <br />36 <br />Discharge (m3/s) --