WSP05236

• File Number: 8220.106
• Description: Animas-La Plata
• State: CO
• Basin: San Juan/Dolores
• Water Division: 7
• Date: 2/26/1996
• Title: Final Biological Opinion - 1996
• Water Supply Pro - Doc Type: Biological Opinion

8

BASIS FOR BIOLOGICAL OPINION

This biological oplnlon is based on the full Project development scenario as
requested by Reclamation. Reclamation estimates that the Project would result
in an average annual depletion of 149,220 acre-feet of water from the two
rivers. The Animas and La Plata Rivers are tributaries to the San Juan River,
which is inhabited by Colorado squawfish and razorback sucker.

Water depletions in the San Juan River Basin have been recognized as a major
source of impact to endangered fish species. Continued water withdrawal has
restricted the ability of the San Juan River system to produce flow conditions
required by various life stages of the fishes. In 1963, the Navajo Dam was
closed, and Navajo Reservoir began to fill with water from the San Juan River.
Historically, flows in the San Juan River prior to the Navajo Dam were highly
variable and ranged from a low of 44 cubic feet per second (cfs) in September
1956 to a hlgh of 19,790 cfs in May 1941 (mean monthly values) a~ the U.S.
Geological Survey Station 93680000, Shiprock, New Mexico. Conversely,
post-Navajo Dam flows in the San Juan River have ranged from a low of 185 cfs
in July 1963, while the reservoir was filling, to a high of 9,508 cfs in June
1979. Since 1963, Navajo Dam has significantly altered flow of the San Juan
River by typically storing spring peak flows and releasing water in summer,
fall, and winter months resulting in an average decrease in spring peak flows
of 45 percent, while approximately doubling winter base flows at the Bluff
gauge in Utah. Similar comparisons can be made at the upstream gauges at
Shiprock and Farmington, New Mexico. Significant depletions and
redistribution of flows of the San Juan River also have occurred as a result
of other major water development projects, including Navajo Indian Irrigation
Project (NIIP) and the San Juan-Chama Project. At the current level of
development, average annual flows at Bluff, Utah, already have been depleted
by 30 percent. Further depletions associated with the Project would raise
that figure to 38 percent. By comparison, the Green and Colorado Rivers have
been depleted approximately 20 percent (at Green River) and 32 percent (at
Cisco), respectively. These depletions, along with a number of other factors,
have resulted in such drastic reductions in the populations of Colorado
squawfish and razorback sucker throughout their ranges that the Service has
listed these species as endangered and has implemented programs to prevent
them from becoming extinct.

Critical habitat has been designated for the Colorado squawfish and razorback
sucker within the 100-year floodplain in portions of their historic range
(59 F.R. 13374). Destruction or adverse modification of critical habitat is
defined in 50 CFR 402.02 as a direct or indirect alteration that appreciably
diminishes the value of critical habitat for both the survival and recovery of
listed species. In considering the biological basis for designating critical
habitat, the Service focused on the primary physical and biological elements
that are essential to the conservation of the species without consideration of
land or water ownership or management. The Service has identified water,
physical habitat, and biological environment as the primary constituent
elements. This includes a quantity of water of sufficient quality that is
delivered to a specific location in accordance with a hydrologic regime that
is required for the particular life stage for each species. Water depletions