9581

• UCREFRP Catalog Number: 9581
• Author: U.S. Bureau of Reclamation.
• Title: Final Environmental Impact Statement - Navajo Reservoir Operations Volume II Technical Appendices.
• USFW Year: 2006.
• USFW - Doc Type: Grand Junction - Durango, CO.
• Copyright Material: NO

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Table S.1.

Flow requirements needed to produce important biological responses and
habitats in the San Juan River.

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B.OLOGICALRESPONSE/..i ....... ~ ........ ).FLOWCHARACTER.STIC 0
HABITAT REQUIREMENT > ...>). .................. ,.'"
....... .. ..... ..... .... . ........ ... .
Reproductive success of Colorado pikeminnow lower in Mimicry of a natural hydrograph, especially during
years with low spring runoff peaks, and higher in years relatively high runoff years.
with high and broad runoff peaks.
Decline in flannelmouth sucker abundance, increase in Mimicry of natural hydrograph with higher spring flows
bluehead sucker abundance, and increased condition and lower base flows.
factor in both species.
Bluehead sucker reproductive success. Increased number of days of spring runoff >5,000 and
8,000 cfs correlated with increased success.
Speckled dace reproductive success. Increased number of days of spring runoff >5,000 and
8,000 cfs correlated with increased success.
Success of stocking YOY Colorado pikeminnow and Mimicry of natural hydrograph has provided suitable
subadult razorback sucker. habitat for these size-classes.
Eddies, pools, edge pools, other low-velocity habitats Mimicry of natural hydrograph has lowered base flows
year round for adult Colorado pikeminnow and to provide more low-velocity habitats. Flows >10,000
razorback sucker. cfs provide more channel complexity which provides for
more habitat complexity.
Flows to cue razorback sucker and Colorado Mimicry of natural hydrograph with higher spring flows.
pikeminnow for migration and/or spawning.
Adult Colorado pikeminnow and razorback sucker use Flows >10,000 cfs provide more channel complexity
complex river areas. which provides for more habitat complexity, lower base
flows add to amount of low-velocity habitats.
Clean cobble bars for spawning of all native species, Flows >8,000 cfs for 8 days to construct cobble bars,
especially Colorado pikeminnow. and >2,500 cfs for 10 days to clean cobble bars, during
spring runoff.
Backwaters and other low-velocity habitats are High spring flows create conditions for backwater
important nursery habitats for Colorado pikeminnow formation, low base flows allow them to appear in late
and other native fishes. summer and fall, flows >5,000 cfs for 3 weeks create
and clean backwaters.
Flooded bottom lands appear to be important nursery Overbank flows (> 8,000 cfs) increase flooded
areas for razorback sucker, but other habitats may be vegetation, and backwaters formed in association with
used in the San Juan River. edge features maximize on receding flows of 8,000 to
4,000 cfs.
Temperatures of 10 to 14 DC at peak runoff for Proposed releases from Navajo Dam are too cool to
razorback sucker spawning and near 18 to 20 DC at replicate pre-dam temperature timing, but
bottom of descending limb for Colorado pikeminnow temperatures are above spawning threshold for
spawning. Colorado pikeminnow during the correct period.
Reduction of nonnative fish abundance. Most nonnative fishes did not decrease during
research period, summer flow spikes reduce numbers
ofred shiner in secondary channels in the short term.

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Note: cfs = cubic feet per second, YOY = young-of-Ihe-year.

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SJRIP Biology Committee
May 1999

8-4

Executive Summary
Flow Report

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