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

deemed critical at this time because of its location relative to the Colorado
squawfish spawning area (R.1'v1132) and its backwater habitat abundance.

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D.

Category: Flow >2,500 cfs during runoff period.

Duration: 10 days minimum.

Frequency: 80% on average. Maximum period without meeting at least 97% of the
specified conditions is 2 years.

Purpose: 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 squawfish. 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.

E.

Category:

Peak timing similar to historical conditions, including variability.

Timing: Mean peak with reoperation to be within 5 days:!: of historical period mean.

Variability: Standard deviation of date of peak to be 14 to 25 days.

Purpose: Maintaining similar peak timing will provide ascending and descending
hydro graph limbs similar to the historical conditions that are suspected
important for spawning the endangered fish.

F. Category:

Level:

Purpose:

Target Base Flow (mean weekly nonspring runoff flow).

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500 cfs from Farmington to Lake Powell, with 250 cfs minimum from
Navajo Dam.

Maintaining low, stable base flows enhances nursery habitat conditions.
Flows between 500 and 1,000 cfs optimize backwater habitat. Selecting
flows at the low end of the range increase the availability of water for
development and spring releases. It also provides capacity for storm flows
to increase flows and still maintain optimum backwater area. This level of
flow balances provision of near-maximum low velocity habitat and near-
optimum flows in secondary channels, while allowing water availability to
maintain the required frequency, magnitude, and duration of peak flows
important for Colorado squawfish reproductive success.

SJRIP Biology Committee
, 6 September 1998

8-7

Executive Summary
Draft Aow Report

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