WSP00672

• File Number: 822.600.10
• Description: Colorado River Annual Operating Plan - Annual Reports
• Basin: Colorado Mainstem
• Date: 1/1/1993
• Author: USDOI/BOR
• Title: Annual Operating Plan
• Water Supply Pro - Doc Type: Annual Report

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Inflow into Lake Powell was only 4.16 MAF or 51 percent of average during April
through July 1992. This resulted in the continued drawdown of the Colorado River
system reservoirs. It is estimated that an additional 1.1 MAF will be lost from storage
during 1992. The October I, 1992, system vacant space is expected to be about
18.1 MAF. This large vacant space is a result of the lowest 6 consecutive years of
inflow on record (1987 through 1992) into Lake Powell. During this drawdown period,
all deliveries of water to meet obligations pursuant to "The Law of the River" have been
maintained. Table 1 lists the expected October 1, 1992, reservoir vacant space, reservoir
storage, percent of capacity, change in storage, and change in elevation during water year
1992.

1993 WATER SUPPLY ASSUMPTIONS

For 1993 operations, three reservoir inflow scenarios were developed and analyzed and
have been labeled as probable maximum, most probable, and probable minimum. The
attached graphs provide the reservoir projected inflows, releases, and contents for each
scenario. The National Weather Service Extended Streamflow Prediction (ESP) computer
model uses current basin conditions, as well as historical data, to predict a range of
possible future streamflows. The ESP model was employed to develop each inflow
scenario, based on current soil moisture conditions within the basin. Although confidence

Table 2
Projected Unregulated Inflow Into Lake Powell
for 1993
(Units: 1,000 acre-feet)
Time Probable Most Probable
Period Maximum Probable Minimum
10/92- 12/92 1,364 1,125 782
1/93 - 3/93 1,420 1,223 804
4/93 - 7/93 11,517 7,200 3,955
8/93 - 9/93 1,536 987 796
10/93 - 12/93 1,297 1,297 1,297
WY 1993 15,837 10,535 6,337
CY 1993 15,770 10,707 6,852