BOARD01565

• Board Meeting Date: 5/22/2000
• Description: WSP Section - Colorado River Basin Issues - Aspinall Operations/Flow Recommendations
• Board Meetings - Doc Type: Memo

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Table 4.2. Continued.

Hydrologic Magnitude
Category (cfs) Discussion/Anticipated Effect
Spring Peak, (Continued)
Wet; Significant motion is reached in 85% of the river, creating and
0-10% ,22,500 maintaining important habitats for Colorado pikeminnow and
exceedence razorback sucker in large areas of the river. Braided channels are
maintained, creating complex areas with a variety of habitats. Gravel is
flushed from pools, creating critical wintering habitat for both species.
Floodplains are extensive (about 320 ac at Escalante SW A at 22,000
cfs); river flows should exceed 12,500 cfs (providing 180 ac of
bottomland habitat) for at least 4 weeks to provide floodplain habitat
for growth and survival oflarval razorback sucker.
Base Flow
Dry; ,1,050, Jun- Flows should gradually decline from peak runoff, but a minimum of
90.100% Aug; 1,050 cfs should be provided during the adult migration and larval drift
exceedence ,750, Sep. periods. This flow provides access to and from the fish passage at
Feb Redlands Diversion and provides pool and slow-run habitats through
out the Gunnison River. River flows may decrease to 750 cfs by late
sununer - early fall (after spawning migrations and larval drift are
completed) and remain there through winter. Flows downstream from
Redlands Diversion should decline by no more than 50 cfs/day during
Moderately Dry; ,1,050, Jun the transition between 1,050 - 750 cfs. Movement to and from the
70-90% -Oct; Redlands Diversion Dam will be significantly restricted, and pool and
exceedence ,750, Nov- slow run habitats will be limited below the dam. However, endangered
Feb fish restrict movements in fall and winter, and adequate pool and slow
run habitat (preferred winter habitat for Colorado pikeminnow and
razorback sucker) is available in other reaches. Gradually reducing
flows will allow endangered fish to leave the 2.5-mi reach and prevent
stranding.
Average, Dry; Flows should gradually decline from peak runoff to the target flows by
50- 70% the dates indicated for the different hydrologic categories. Access to
exceedence >1,050 - fish passage at Redlands Diversion Dam is provided year-round.
2,000, Jul- Further, adequate flows are available to provide year-round habitat in
A verage, Wet; Feb the 2.5 mi of the Gunnison River downstream from the Dam. A wide
30-50% range of habitats are available in the entire Gunnison River when flows
exceedence fall within the target ranges. Stable flows provide warm, quiet-water
Moderately Wet; habitats and backwaters along the shorelines of the river.
10-30%
exceedence 1,500 -
Wet; 2,500, Aug-
Feb
0-10%
exceedence

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Draft Final Repon
January 27, 2000

4-13

Chapter 4