Navajo Reservoir Operations Vol. II

• File Number: 8220.105.I
• Description: Colorado River-Water Projects-Navajo-Environmental Studies
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 9/1/2002
• Author: BOR
• Title: Navajo Dam EIS-Draft EIS-Navajo Reservoir Operations-Volume II
• Water Supply Pro - Doc Type: EIS

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e. Category:

Duration:

Frequency:

Purpose:

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Category:

Duration:

Frequency:

Purpose:

E. Category:

Timing:

SJRIP Biology Committee
May 1999

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Flow> 5,000 cfs during runoff period.

A minimum of 21 days between March 1 and July 31.

Flows> 5,000 cfs for 21 days 01' more need to occur in 50% of the years
on average for the period of record 1929-1993. Maximum number of
consecutive years without meeting at least a flow of 4,850 cfs (97% of 5,000
cfs) within the 65-year period of record is 4 years.

Flows of 5.000 cfs or greater for 21 days are necessary to clean backwaters
and maintain low-velocity habitat in secondary channels in Reach 3. thereby
maximizing nursery habitat for the system. The required frequency of these
flows is dependent upon perturbating stonn events in the previous period.
requiring flushing in about 50% of the years on average. Backwaters in the
upper portion of the nursery habitat range clean with less flow but may be too
close to spawning sites for full utilization. Maintenance of Reach 3 is
deemed critical at this time because of its location relative to the Colorado
pikeminnow spawning area (RM 132) and its backwater habitat abundance.

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Flow >2.500 cfs during runoff period.

A minimum of 10 days between March 1 and July 31.

Flows> 2,500 cfs for 10 days 01' more need to occur in 80% of the years
on average for the period of record 1929-1993. Maximum number of
consecutive years without meeting at least a flow of 2,425 cfs (97% of 2,500
cfs) within the 65-year period of record is 2 years.

Flows above 2,500 cfs cause cobble movement in higher gradient areas on
spawning bars. Flows above 2,500 cfs for 10 days provide sufficient
movement to produce clean cobble for spawning. These conditions also
provide sufficient peak flow to trigger spawning in Colorado pikeminnow.
The frequency specified represents a need for frequent spawning conditions
but recognizes that it is better to provide water for larger flow events than to
force a release" of this magnitude each year. The specified frequency
represents these tradeoffs.

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Timing of the peak flows noted in A through D above must be similar to
historical conditions, and the variability in timing of the peak flows that
occurred historically must also be mimicked.

Mean date of peak flow in the habitat range (RM 180 and below) for any
future level of development when modeled for the period of 1929 to 1993

5-7

Executive Summary
Flow Report