WSP05409

• File Number: 8220.101.17
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 3/1/1998
• Author: Loftin/et al.
• Title: Replacement Resources Process - Final Methods Report - Executive Summary
• Water Supply Pro - Doc Type: Report/Study

ThelnteriorDeparonenfs
decisiOll on ltie Glen
Canyon Dam 8S called for
restricted water releases
to 1l01Ect do\\l1stream
resources. Operations at
several oltier SlCMP
:facilities also have been
I
modified arllill be
modffiedin ltienearfuture
toaddress en~ronmentll

concerns.

Glen Canyon Dam and Power
Plant

~

Glt:n Canyon Dam and power plant
is located on the ColOTado River in
nonhem Arizona. It is operated by
Reclamation to meet Lower Colorado
River Basin water storage and delivery
requirements. These arc codified in a
variet\' of docuements knO\\TI collectivel\'
. .
as the Law of the River. As the largest
SLeAlIP generating resource, Glen
Canyon Dam represents about two-thirds
of the total SLCAlIP capacity and three
quarters of the energy.

In the past, Glen Canyon Dam was
used primarily to generate peaking power.
While this operational choice made the
power generated at Glen Canyon more
flexible, and therefore more valuable, it
also caused significant hourly and daily
fluctuations in water releases. These
fluctuations caused concern bccause of
their potential effects on the downstream
em-ironment. In December 1982, Recla-
matIOn began Phase I of the Glen Canyon
Environmental Studics (GCES) to respond
to the concerns of environmental and
recreational interests regarding Glen
Canyon Dam operations. In June 19tU~,
Phase II of the GC ES was initiated to
address economic impacts [a power
customers, along with other concerns.

In July 1989, the Secreuryofthe
Interior announced that Reclamation
would prepare an Envlfonmentallmpact
Statement (EIS) on the effects of Glen
Canyon Dam operations on the dO\\TI-
stream ennronment. The EIS record of
decision was signed by the Secretary of
the Interior on October 9,1996,- The
Interior Department's decision on the Glen

. Orwration of Gltn Can)'nn Dam, Final EIS,
U,S. Department of the Inlerior, Bureau of
I Re-=Iarnation. FES95-8, daled March 21, 1995
Record of Decision. dated (ktober 9.1996,

Canvon Dam EIS called for restricted
waler releases to protect downstream
resources. changing the long-term operal-
109 criteria by reducmg hourly and daily
fluctuations in water relt:ases. This
affected the magnitude and timmg of
e1ectnc power available under a range of
possible water condttlons.

The decision also mcluded general
pro\isions which would allow Western to
respond to power system emergencies by
temporarily deviating from nonnally
constramed powerplant operations
FolJo\\ing the record of deCISion. the
Operating Criteria and 1997 Annual Plan
of Operations for Glen Canyon Dam.
approved by Secretary Bruce B.Jbbitt on
February 24. 1997, included similar
provision for emergencies to address
system emergenCIes and load.following
conditions.

The degree to which Western can
use hydroelectric gener.Jtion to respond to
power system emergencies and to satisty
load.follo\\ing obhgations IS an important
consideration In the Replacement Re.
sources Process. With this ability, capac-
ity from Glen Canyon Dam can be used to
serve load under limited emergency
situations. thereby allO\\ing Western to
claim a higher avai!.Jble short-tenn onpeak
capacity at Glen Canyon. Replacement
power can then be obtained at lower cost
on the bulk power market than would be
the case in the absence of these erner.
gency and system regulation procedures.

Other SLCA Integrated Projects
Resources

In addItion to Glen Canyon Dam.
operations at several other SLeMP
facilities also have been modified or will
be modified in the ncar future to address
ennronmental concerns These facilities
mclude the Flanling Gorge Danl and