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<br />-," <br /> <br />000358 <br /> <br />Draft - Do Not Cite <br /> <br />34 <br /> <br />August 2003 <br /> <br />fewest number of days above this threshold would occur in the driest year of the period, 1917. In <br />this year, the Reclamation scenario would only have 38 days in which the wash load criterion <br />would be met. The other scenarios would be above this threshold twice as many days. All <br />scenarios would meet the Millious recommendation for maintaining wash load. <br /> <br />3.4.2.2 Scour Side Channels <br /> <br />Millious (1998) recommended a flow of 7,420 cfs or greater in one of three years to scour <br />side channels. Table 11 presents the number of days the flow threshold for scouring side <br />channels would be exceeded at the Grand Jooction gage for the six scenarios. Historically (gage <br />scenario), exceedances of this threshold ranged from 0 to 76 days, with a maximum occurring in <br />1995. For all scenarios, this threshold would be exceeded a mean of about 20 days/year. <br />Exceedances would have occurred in about 15 of the years evaluated for return periods of about <br />2 years. All scenarios would meet the Milhous recommendation for scouring side channels. <br /> <br />3.4.2.3 Remove Sand and Fines from the River and Riftles <br /> <br />Milhous (1998) recommended a flow of 12,500 cfs in one of two years to remove sand <br />and fmes from the river and a flow of 12,540 cfs in one of three years to remove sands and fines <br />from riffles. Our evaluation focused on the higher flow because if this flow condition is met, the <br />other, slightly lower threshold would also be exceeded. Table 12 presents the number of days the <br />flow threshold for removing sand and fines would be exceeded at the Grand Joocti-on gage for <br />the six scenarios. Historically (gage scenario), the number of days that flow exceeded this <br />threshold ranged from 0 to 49 days, with the maximum number of days occurring in 1984. The <br />mean number of days per year this threshold is exceeded is similar among scenarios and ranges <br />from 5.7 (Reclamation) to 7.0 (Western D). Exceedances would have occurred in 7 to 10 of the <br />26 years evaluated Return periods range from 2.6 (Western C) to 3.5 (gage, Reclamation, and <br />Western A). Western B, C, and D scenarios are the only scenarios evaluated that would achieve <br />this threshold flow at the frequency recommended by Millious for flushing riffle habitat (lout of <br />three years) and none would occur at the recommended frequency for river-wide flushing (1 out <br />of two years). <br />