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In previous studies supported by the Recovery Program, Pitlick et al. (1999), and Pitlick <br />and Cress (2000), provided flow recommendations for different reaches of the Colorado River, <br />including the 15-mile and 18-mile reaches. These recommendations focused on discharges that <br />would exceed thresholds for (i) initial mobilization, and (ii) complete mobilization of the bed <br />sediment of the Colorado River, under the assumption that these flows are important for <br />maintaining habitats used by the native fishes and other aquatic organisms. Table 3 lists the <br />threshold discharges, the recommended durations of these discharges (days per year), and the <br />number of days that those discharges were observed during the period 1998-2004. The results <br />provide an indication of the ability of the Recovery Program to meet the flow recommendations <br />given in previous studies and reports. The data listed in Table 3 indicate that the target flows for <br />initial motion (-1/2 the bankfull discharge) were exceeded very infrequently- only about 1/3 of <br />the recommended frequency- and the target flows for complete mobilization of the bed (bankfull <br />discharge) did not occur at all. <br />Table 3. Comparison between recommended and observed frequencies of sediment- <br />transporting flows in the 15 mile and 18 mile reaches, 1998-2004. Threshold discharges <br />and recommended frequencies are based on results presented in Pidick and Cress (2000). <br />15 Mile Reach 18 Mile Reach <br />Threshold flows: Qc = 278 m3/s Qb = 608 m3/s Q, = 548 m3/s Qb = 979 m3/s <br />Recommended 30 <br />Observed (days/yr) <br />1998 <br />1999 <br />2000 <br />2001 <br />2002 <br />2003 <br />2004 <br />Total <br />5 <br />30 <br />5 <br />24 0 13 0 <br />31 0 0 0 <br />10 0 0 0 <br />0 0 0 0 <br />0 0 0 0 <br />13 0 6 0 <br />0 0 0 0 <br />78 0 19 0 <br />26