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

must be within 5 days :!: of historical mean date of May 31 for the same
period.

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Variability: Standard deviation of date of peak to be 12 to 25 days from the mean date of
May 31.

Purpose: Maintaining similar peak timing will provide ascending and descending
hydrograph limbs timed similarly to the historical conditions that are
suspected important for spawning of the endangered fishes.

F.

Category:

Level:

.

Purpose:

G.

Category:

Control:

.

Purpose:

Target Base Flow (mean weekly nonspring runoff flow).

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 increases 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 pikeminnow reproductive success.

Flood Control Releases (incorporated in operating rule).

Handle flood control releases as a spike (high magnitude, short duration) and
release when flood control rules require, except that the release shall not
occur earlier than September I. If an earlier release is required, extend the
duration of the peak of the release hydrograph. A ramp up and ramp down
of 1,000 cfs per day should be used to a maximum release of 5,000 cfs. If the
volume of water to release is less than that required to reach 5,000 cfs, adjust
the magnitude of the peak accordingly, maintaining the ramp rates. Multiple
releases may be made each year. These spike releases shall be used in place
of adjustments to base flow.

Historically, flood control releases were made by increasing fall and winter
base flows. This elevates flows above the optimum range for nursery habitat.
Periodic clean-water spike flows improve low-velocity habitat quality by
flushing sediment and may suppress red shiner and fathead minnow
abundance.

SJRIP Biology Committee
May 1999

8-8

Executive Summary
Flow Report

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