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<br />' 2.3.6 Flow Targets
<br />' As indicated in: (1) a memo from the Service (Maddux, February 2,1999), (2) the RIPRAP action plan
<br />(April 1, 1999), and (3) the Final PBO (U.S. Fish and Wildlife Service, December 20, 1999, pg. 11), the
<br />Service is first and foremost interested in augmenting the peak of the spring runoff hydrograph with
<br />I an additional 20,000 acre-feet of water on average based on the years which the flow triggers at the
<br />Cameo gage are realized. The Service's priority is to increase spring peak flows when the peak runoff
<br />is expected to be in the range of 12,900 to 26,600 cfs at the head of the 15-Mile Reach or
<br />approximately 15,000 to 29,000 cfs at the Cameo USGS gage (Coordinated Reservoir Operations
<br />Group, 1999 and personal communication from George Smith to Leo Eisel and Sue Uppendahl,
<br />January 2000). The upper limit, 26,600 cfs, is based to some extent on downstream flooding
<br />considerations and is not totally habitat based. The Service has the objective of increasing the
<br />frequency of occurrence of flows greater than 12,900 cfs. The Service has identified target flows in the
<br />15-Mile Reach in the range of 12,900 to 26,600 cfs because flows of this magnitude have been shown
<br />1 to mobilize gravel cobble substrate (U.S. Fish and Wildlife Service, December 20,1999). The Service is
<br />not interested in increasing the peak when the actual peak or augmented peak is likely to be less than
<br />12,900 cfs or greater than 26,600 cfs. The Service would like to see as much as possible of the average
<br />20,000 acre-feet made available during the 7 to 10 day period surrounding the peak spring discharge.
<br />' The Service has indicated that the 20,000 acre-feet will be determined as an average volume in those
<br />years when the triggers at the Cameo gage are realized. (Smith and Muth, July 1999). In years when
<br />flows in the Colorado River at the top of the 15-Mile Reach are less than 12,900 cfs or greater than
<br />-2", 00-cfs,-no-wat-er-rill-be provided:-F'er-those-ye-ars when the-flow is between 12,900 and 26,600
<br />cfs, an average of 20,000 acre-feet will be provided, i.e., in some years more than 20,000 acre-feet will
<br />be provided, and in some years less.
<br />With some alternatives it may be possible to carry over unused water to the next year for purposes of
<br />meeting the average 20,000 acre-feet target in that year.
<br />If some portion of the average 20,000 acre-feet remains after augmentation of the spring peak
<br />discharge and this water can not be carried over for use in the succeeding spring, this water may be
<br />used for augmenting low flows during the July 15 through October 31 period. Augmentation of low
<br />flows in late summer and fall is second priority to augmenting the spring peak discharge during the 7
<br />to 10 day spring peak period.
<br />The following characterize the low flow target:
<br />¦ During the July 15 through October 31 period, the goal will be to maintain minimum
<br />' flows at the head of the 15-Mile Reach as specified by the Service (U.S. Fish and
<br />Wildlife Service, May 1995).
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<br />¦ During years of above average precipitation (i.e., precipitation greater than the
<br />50th percentile), efforts would be made to maintain flows at or around 1,630 cfs.
<br />¦ During years of low precipitation (i.e., precipitation less than the 50th percentile),
<br />efforts would be made to maintain flows at or greater than 1,240 cfs.
<br />¦ During drought years (the lowest 20th percentile), efforts would be made to maintain
<br />flows at or greater than 810 cfs.
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