BOARD00259

• Board Meeting Date: 1/12/1998
• Description: WSP Section - Colorado River Issues - San Juan Recovery Program and Section 7 Consultation for the City of Durango
• Board Meetings - Doc Type: Memo

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Lt. Colonel Dorothy F. Klasse

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BASIS FOR BIOLOGICAL OPINION

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ThiS biological opinion addresses an average annual depletion of approximately
1409 acre-feet from the San Juan River. Of this amount. 1051 acr~-feet is
considered to be new and 388 acre-feet is considered to be historic. New
depletions are currently defined as those depletions occurring after
December 31. 1982. Historic depletions are currently defined as those
occurring prior to January 1. 1983. These cutoff dates are consistent with
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dates used to derive the baseline for the Animas-La Plata Project Biological
Opinions in 1991 and 1996. The proposed Animas-La Plata Project is the
largest recent project that may impact the San Juan River Basin and:
therefore. is driving section 7 consultation throughout the San Juan River
Basin.

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 high of 19.790 cfs in May 1941 (mean monthly values) at 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. According to the Bureau of Reclamation, 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 and the San Juan-Chama Project. 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.

The biological opinion issued by Region 6 of the Service on February 26. 1996.
for the Animas-La Plata Project found that the proposed development and
subsequent depletion of 149.220 acre-feet of the San Juan River's flow would
jeopardize the continued existence of the endangered Colorado squawfish and .

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