WSP05097

• File Number: 822.600.10
• Description: Colorado River Annual Operating Plan - Annual Reports
• Basin: Colorado Mainstem
• Date: 1/1/1991
• Author: USDOI/BOR
• Title: Annual Operating Plan
• Water Supply Pro - Doc Type: Annual Report

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made a year in advance, the data are valuable in analyzing the possible impacts on
project uses and purposes.

The following assumptions were used in the three different assumed hydrologic
scenarios:

UNREGULATED INFLOW ABOVE LAKE POWELL
(Units: 1,000 acre-feet)

Probable Most Probable
Maximum Probable Minimum
10/90 - 2/91 1,894 1,050 1,010
3/91 525 350 290
4/91 - 7/91 10,753 6,075 3,581
8/91 - 12/91 3,136 2,236 1,510
WY 1991 14,702 8,731 5,391
CY 1991 15,055 9,061 5,741
WY 1992 II ,900 II ,900 11,900
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The inflow 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. With assumed water year
1991 inflow and reservoir storage conditions, projected monthly releases were adjusted
until release and storage levels accomplished project purposes and priorities.

Additional Analysis

Special long-range studies using Reclamation's Colorado River Simulation System
(CRSS) were conducted to test the impact on the risk of future shortages if California,
during calendar year 1991, were allowed to use water apportioned to, but unused by,
Arizona and Nevada. The studies were conducted using the entire hydrologic record
(1906 through 1985), utilizing 80 hydrologic sequences indexed by one year. These
studies simulated 50 years into the future to test the risks of shortages to all users of
Colorado River water for beneficial purposes and evaluated several specific parameters.
These studies indicate that for the next 20 years there are: (I) no increase in the risk of
shortages; (2) reduced risk of flood control releases; and (3) reduced excess deliveries
to Mexico.

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