WSP03308

• File Number: 8220.105.I
• Description: Colorado River-Water Projects-Navajo-Environmental Studies
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/26/2004
• Title: Navajo Dam EIS-Draft Bio Opinion-US Fish and Wildlife Service New Mexico Ecological Services Field Office
• Water Supply Pro - Doc Type: Report/Study

Area Manager
DRAFT

.

.

,r

,

7

Maintaining Authorized Navajo Unit Purposes
As indicated previously, in addition to meeting Flow Recommendations, the proposed plan is
intended to maintain the authorized purposes of the Navajo Unit. The Unit, along with other
major storage units, was authorized by the Colorado River Storage Project (Act of April II,
1956, ch. 203, 70 Stat. 105). The storage units were authorized to:

o Regulate the flow of the Colorado River,
o Store water for beneficial consumptive use, making it possible for the States of the Upper
Basin to utilize the apportionments made to and among them in the Colorado River
compacts,
o Provide for irrigation,
o Provide for flood control,
o Provide for the generation of hydroelectric power, and
o Provide for recreation and facilities to mitigate or enhance fish and wildlife.

According to Reclamation, both the Flow Recommendations and the Unit's authorized purposes
can be met under the proposed action.

Flow Recommendations
The basis of the Flow Recommendations for the San Juan River is to mimic the natural
hydrograph. The recommendations provide flow variability considered necessary to create and
maintain habitat for pikeminnow and razorback sucker. The recommendations integrate
hydrology, geomorphology, habitat, and biology to define flow magnitude, duration, and
frequency for the spring runoff period and base flows for the non-runoff periods.

The proposed action follows the recommended operating rules (Holden 1999) and meets or
exceeds flow criteria according to model results (Reclamation 2003). This model uses long-term
historic flow data, which encompass a variety of wet and dry conditions; however, there is
always a level of uncertainty in future climatic conditions which could have a positive or
negative effect on the amount of water available to meet the Flow Recommendations.

Flow recommendations are targeted for the 180 miles of the San Juan River between the Animas
River confluence and Lake Powell.

A summary of flow recommendation criteria follows:

A. Category:
Duration:
Frequency:
B. Category:
Duration:
Frequency:
C. Category:
Duration:
Frequency:

Flows greater than 10,000 cfs during runoff
A minimum of 5 days between March I and July 31
20 percent of years, with a maximwn number of 10 years between events.
Flow greater than 8,000 cfs during runoff
A minimwn of 10 days between March I and July 31
33 percent of years, with a maximum number of 6 years between events.
Flows greater than 5,000 cfs during runoff
A minimum of21 days between March I and July 31
50 percent of years, with maximum number of 4 years between events.