8031

• UCREFRP Catalog Number: 8031
• Author: U.S. Department of the Interior.
• Title: Fish and Wildlife Service Final Biological and Conference Opinion on Lower Colorado River Operations and Maintenance - Lake Mead to Southerly International Boundary.
• USFW Year: 1997.
• USFW - Doc Type: \
• Copyright Material: NO

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BIOLOGICAL OPINION

Proposed Action

half of each year. Minimum available flood control space increases from 1.5 maf on August 1 to
5.35 maf on January 1. Required flood storage space can be located within Lake Mead and in
specified upstream projects: Lakes Powell and Navajo, and Blue Mesa, Flaming Gorge and
Fontenelle Reservoirs. Minimum Lake Mead space required for exclusive flood control is 1.5 maf.

Releases from Lake Mead are initially scheduled by taking the scheduled consumptive use
downstream of Hoover Dam, adding any additional volume of water required to meet reservoir
target storage levels for Lake Mohave and Lake Havasu, and subtracting the net volume of gains
and losses for the month for all reaches of the system downstream of Hoover Dam. Releases in
excess of the initial release schedule can be caused by either: 1) Lake Mead exceeding maximum
capacity or target storage levels; 2) excess releases scheduled to avoid spills; or, 3) releases
dictated by flood control requirements. Reclamation is not consulting on COE's existing flood
control regulations for Lake Mead.

The COE is not responsible for the flood control criteria related to Davis Dam and Parker Dam,
although the lake elevations behind these dams are affected by flood control releases from
Hoover Dam. Releases through Davis and Parker Dams for flood control fall within the
Secretary's discretion and are managed by Reclamation. Therefore, Reclamation is consulting on
flood control operations at Parker and Davis Dams. Lake Havasu's elevations corresponding to
Reclamation's discretion over flood control are depicted in Fig. 3. Although not anticipated to
occur within the five-year time frame of this consultation, flood control releases are made if
reservoir elevations exceed those depicted by the dashed line (450.5 ft), labeled "flood control".
At Lake Mohave, the reservoir elevation is adjusted monthly to accommodate potential side-
channel inflow, as shown in Fig. 4. For example, the decreasing target elevation for Lake Mohave
during June to October corresponds to the period of greatest likelihood of side-channel inflow.
Superimposed on these flood-control elevations are the elevations desired for raising and
transplanting razorback suckers, also described under the "Endangered Species Conservation
Activities" section in this document and on pages 61-62 of the BA.

2. Storage and Delivery of Entitlement Waters

a. Equalizing Lakes Powell and Mead

Articles 11(3) and 11(4) of the Criteria for Coordinated Long-Range Operation of Colorado River
Reservoirs (Operating Criteria)(developed pursuant to the Colorado River Basin Project Act of
1968, Public Law 90-537) specify that "If, in the plan of operation, the Upper Basin Storage
Reservoirs' active storage forecast for September 30 of the current water year is greater than the
quantity of 602(a) [of the Act] storage determination for that date, water shall be released annually
from Lake Powell at a rate greater than 8.23 maf per year to the extent necessary. . . to maintain ,
as nearly as practicable, active storage in Lake Mead equal to the active storage in Lake Powell."
Furthermore, the annual release made for equalization purposes". . . will be madeto the extent

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