WSP09925

• File Number: 822.600.10
• Description: Colorado River Annual Operating Plan - Annual Reports
• Basin: Colorado Mainstem
• Date: 1/1/1999
• Author: USDOI/BOR
• Title: Annual Operating Plan
• Water Supply Pro - Doc Type: Annual Report

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Lake Mead

For calendar year 1998 the surplus condition was the criterion governing the operation of Lake
Mead in accordance with Article III(3)(b) of the Operating Criteria and Article II(B)(2) of the
decree in Arizona v. California. On February 28, 1998, Reclamation informed the International
Boundary and Water Commission (IBWC) that there existed for calendar year 1998 surplus
waters of the Colorado River within the provisions of Article 10(b) of the 1944 Mexican Water
Treaty. On March 27, 1998, the IBWC sent Reclamation a revised delivery schedule for Mexico
with total deliveries of 2,096 MCM (1.7 MAF).

Lake Mead began water year 1998 at elevation 368 meters (1205.81 feet), with 29,319 MCM
(23.769 MAF) in storage, 94% of the conservation capacity of31,919 MCM (25.877 MAF).
During the year, Lake Mead reached its maximum elevation of'70 m"ters (1214.64 feet) at the
end of December, with 30,967 MCM (25.105 MAF) in storage, 97% of capacity. Lake Mead
reached its.J)linimum elevation of369 meters (1209.98 feet) at the end of Tune.

Flood control releases were required for January, February, and March of 1998. With the
reservoirs being near full, the potential threat of EI Nino, and showing required flood control
releases in 1999, releases were made from Hoover Dam starting on December 26,1997, and
ending the second week of April 1998. Releases averaged about 20,000 cfs. In total, 2,122
MCM (1.72 MAF) was released above downstream requirements during these months. The total
release from Lake Mead through Hoover Dam during water year 1998 was 14,760 MCM (11.966
MAF) with an additional 283 MCM (0.229 MAF) being diverted from Lake Mead by the Robert
Griffith Water Project. .1.''\

Under the most probable inflow conditions during water year 1999, Lake Mead is expected to
rise to elevation 371 meters (1216.6 feet) by the end of December, 1998, with 31,341 MCM
(25.408 MAF) in storage, 98% of conservation capacity. Lake Mead will drop to 367 meJers
(1204.43 feet) by the end of June, 1999, with 29,066 MCM (23.564 MAF) in storage, 91% of
conservation capacity.

Flood control releases are projected under the most probable scenario in January, February, and
March 1999 at the 19,000 cfs level. Hoover Dam is expected to release 14,186 MCM (11.501
MAF) during water year 1999. Downstream demands are expected to be about 12,504 MCM
(10.137 MAF) for water year 1999.

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No flood control releases are anticipated in 1999 under the minimum probable scenario. Under
the maximum probable, flood control releases are required January through June, 1999, all above
the 19,000 cfs level. Space building is required from August through December, 1999 under the
maximum probable scenario.

Drawdown during the peak largemouth bass spawning period in April and May is planned to be
near the limits of decline recommended in the July 1982 final report of a five-year study by the
Arizona Game and Fish Department and the Nevada Department of Wildlife.

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