WSP01715

• File Number: 8282.600.10
• Description: Colorado River Operating Annual Reports
• Basin: Colorado Mainstem
• Date: 1/1/1992
• Author: USDOI/BOR
• Title: Operation of the Colorado River Basin 1992 Projected Operations 1993
• Water Supply Pro - Doc Type: Publication

Projected Plan

In addition to compliance with the Operating Criteria, several
specific operating issues were addressed during the
preparation of the annual operating plan for water year 1993.
The operating issues addressed which are listed in no
particular order of priority are: (1) meeting the reasonable
beneficial Colorado River mainstream consumptive water
uses in the Lower Di,ision States as provided by the Operating
Criteria, (2) tbe delivery of firm power in accordance with
energy contracts, (3) minimum and specific rele-ases for fish
and wildlife and recreational purposes, (4) refiUing of vacant
system reservoir storage space, (5) compliance with the 1944
Mexican Water Treaty and Minute No. 242 of the IBWC, (6)
complying fully with compact, decree, statutory, and water
delivery obligations, and (7) other short - and long-term effects
of 1993 water use decisions.

For 1993 operations, three reservoir inflow scenarios were
developed and analyzed. The projected monthly inllows
were based upon current hydrological conditions and the
following assumptions: (1) probable- maximum, based upon
the annual volume of inllow which would be exceeded about
10 percent of the time, (2) most probable-, based upon annual
volume of inflow which would be exceeded about 50 percent
of the time; and, (3) probable minimum, based upon the
annual volume of inllow whicb would be exceeded about 90
percent of the time. Each scenario was adjusted for current
basin conditions; therefore, the magnitude of the three
scenarios does not necessarily match the historical upper
decile, mean, and lower decile inflows, respectively. The
National Weather Service's computer model, known as the
Extended Streamflow Prediction model (ESP), uses current
basin conditions as well as historical data to predict a range
of possible future stream flows. Although there is a wide
confidence band associated with stream flow forecasts made
a year in advance, the data are valuable in analyzing the
possible impacts on project uses and purposes. The inllow
volumes resulting from these assumptions were used as input
data in Reclamation's monthly reservoir operation planning
computer model. which is used to plan reservoir operations
for the upcoming 12-month period.

At several locations in the Colorado River Basin, minimum
instream llow levels have been established which preserve the

present aquatic resources downstream of certain Colorado
River Basin dams. The construction and operation of dams in
the basin have had both positive and negative effects on
aquatic resources. Controlled cool water releases from dams
in the Colorado River Basin have provided for increased
productivity of some aquatic resources and the development
of significant sport fisheries. However, the same releases
could be detrimental to endangered and other native species
of fishes.

Section 7 consultations were continued in 1992 on the
operation of the Aspinall Unit on the Gunnison River and the
Animas La-Plata Project on the San Juan River (which affects
the operation of Navajo Reservoir). These, along with the
ongoing Section 7 consultMion on Flaming Gorge and the
interim flow restriction on releases from Lake Powell, will
continue in water year 1993. Studies associated with these
consultations will be used to better understand the flow
related needs of the endangered and other native species of
fish.

Modifications to planned operations may be made based
upon changes in forecasted conditions. However, because of
the Recovery Implementation Program for Endangered Fish
Species in the. Upper Colorado River Basin, Section 7
consultations, and other downstream. concerns, modification
to the monthly operation plans are no longer primarily
forecast based. Decisions on spring peak releases and
downstream habitat target llows must be made midway
through the runoff season. Reclamation and the Fish and
Wildlife Service will initiate meetings with interested parties, .
including representation of the basin states, to facilitate the
decisions necessary to finalize site specific operations plans.
All operations will be undertaken subject to the primary water
storage and delivery requirements established by the Law of
the River.

There is a reasonable expectation that mainstem consumptive
use in the Lower Division States will not exceed 7.5 million
acre-feet in 1993. It is therefore expected that all reasonable
beneficial consumptive use needs of the Lower Colorado
mainstem users will be met in 1993.

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