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<br />Draft~DoNoi:Cite <br /> <br />OilJ3r-) <br />~... <br /> <br />28 <br /> <br />August 2003 <br /> <br />sensitivity of suspended load models to discharge.. Because the sediment loads predicted with the <br />, - <br /> <br />Pitlick et al. model are less than those predicted with the Van Steeter and Pitlick model, the <br />Pitlick et al. model should produce conservative estimates of the effects of varying flow <br />conditions (i.e., higher flows would be required to trailsport the same quantity of sediment). <br /> <br />Yearly sediment loads at the Grand Junction gage for 1975 to 2000 as calculated with the <br />Pitlick et al. model are shown in Table 6. For dIy and average years, the predicted suspended <br />sediment loads are very similar among scenarios. In very wet years (e.g., 1984), the gage flows <br />resulted in the largest sediment load; the next largest load is that for the Reclamation scenano <br />(4.33 million metric tons and 4.14 million metric tons, respectively). The difference in predicted <br />loads is about 4%. The loads predicted for the Western scenarios are about 0.6 million metric <br />tons less than the gage value for this year (approximately 15% less). Calculated sediment loads <br />for the four Western scenarios are fairly similar. For the 26 years evaluated, about 30 million <br />. metric tons of sediment are predicted to pass the Grand Junction gage. The total load predicted <br />with the Reclamation scenario exceeds the total gage load by about 3.6% (31.9 million metric <br />tons versus 30.8 million metric tons). !he largest predicted Western total load is less than the <br />total load for the gage by about 0.6% (30.6 million metric tons versUs 30.8 million metric tons). <br />- ~ <br /> <br />The Van Steeter and Pitlick model predicts slightly higher total sediment loads (about <br />34 million metric tons/year or more; Table 7). Overall,. the sediment loads predicted for gage <br />flows by the Van Steeter and Pitlick model would be about 10% greater than that predicted with <br />the Pitlick et al. model. Sediment loads for the Western scenarios calculated with the Van Steeter <br />and Pitlick model are higher (between 4% and 8%) than either gage flows or the Reclamation <br />scenario (Table 7). The Reclamation scenario would produce total sediment loads that are <br />virtually identical to those produced by gage flows. <br /> <br />~ost sediment transport models have considerable uncertainty r and the differel!.~ <br />between the two ~ndp.ls are not unusual. The differe~model results make comparison of the <br />- <br /> <br />~cenari~as..ed strictly oasew-m~ttransport calculations problema~. 2nthe basis of the above <br />comparisons and differences among model results, it can be concluded that the scenarios <br />evaluated would transnort relativelv similar amounts of suspended sediment <br />