BOARD02098

• Board Meeting Date: 11/23/1998
• Description: WSP Section - Colorado River Basin Issues - San Juan Recovery Program - Status Report
• Board Meetings - Doc Type: Memo

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B.

Category:

by the increase in the number of islands following high flow conditions.
Channel complexity is important to both Colorado squawfish and razorback
sucker.

Flow> 8,000 cfs during runoff period.

Duration: 10 days minimum.

Frequency: 33% on average. Maximum period without meeting at least 97% of the
specified conditions is 6 years.

Purpose:

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C.

Category:

Bankfull discharge is generally between 7,000 and 10.500 cfs in the San Juan
River below Farmington, New Mexico, with 8,000 cfs being representative
of the bulk of the river. Bankfull discharge approximately I year in 3 on ,
average is necessary to maintain chanrJel cross-section. Flows at this level
provide sufficient stream energy to move cobble and build cobble bars {..
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necessary for spawning Colorado squawfish. Duration of 8 days at this \.
frequency is adequate for channel and spawning bar maintenance. However, .1
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research shows a positive response of abundance of b1uehead sucker and
speckled dace with increasing duration of flows above 8,000 cfs from 0 to 19 .:'
days. Therefore, the minimum duration was increased from 8 to 10 days to'
account for this measured response. Flows above 8,000 cfs may be important :'
for providing habitat for larval razorback sucker, if flooded vegetation and'
, other habitats formed during peak and receding flows are used by the species..:
This flow level also maintains mimicry of the natural hydrograph during .1
higher flow years, an important fearure for successful Colorado squawfish.'
reproductive success. .

Flow> 5,000 cfs during runoff period.

Duration: 21 days minimum.

Frequency: 50% on average. Maximum period without meeting at least 97% of the
specified conditions is 4 years.

Purpose:

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 storm 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 . r

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SJRIP Biology Committee
16 September 1998

8-6

Executive Summary
Draft Row Report

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