WSP04851

• File Number: 8282.600.10
• Description: Colorado River Operating Annual Reports
• Basin: Colorado Mainstem
• Date: 1/1/1988
• Author: USDOI/BOR
• Title: Operation of the Colorado River Basin 1988 Projected Operations 1989
• Water Supply Pro - Doc Type: Publication

River Regulation

Daily releases are made from the storage reservoirs in the
Lower Basin to meet the incoming orders of the water user
agencies or for the regulation of flood control space and
releases of excess water. When possible, all water passes
through the powerplant units.', The daily releases are
regulated on an hourly basis to meet, as nearly as possible the
peaking power needs ofthe hydroelectric power customers.
Minimum daily flow objectives are 'provided in the river to
maintain fIshery habitat.

The combination of high reservoir conditions and river
regulation below Hoover Dam resulted in, a total water year
1988 delivery to Mexico of approximaiely 1.0 MAF in excess
of the scheduled treaty deliveries (1,700,000 acre-feet per
calendar year)., Of that amount, 97,000 acre-feet of drainage
waters were bypassed to the Gulf of California via the Bypass
Drain during water year 1988. This bypass channel was
constructed pursuant to provisions of Minute No. 242 of the
International Boundary and Water Commission.

Flood Control

Lake Mead is operated in accordance with flood control
regulations specified in the Field Working Agreement
between Reclamation and the Corps of Engineers, signed in
1982. The regulations stipulate minimum release levels from
Lake Mead to route the reasonable maximum inflow. The
reasonable maximum inflow is the estimated inflow volume
that, on the average, will not be exceeded 19 out of 20 times.
This volume is derived by adding an "uncertaintY' term to the
most probable runoff forecast. In 1983, unusual
hydrometeorological events resulted in unprecedented large
forecasting errors. Subsequent reassessment of the estimate
of the "uncertainty" term led to adoption of larger values for
use in determining the probable maximum inflow in 1984 and
thereafter.

Routine maintenance and repair of bankIine damage was
carried out during water year 1988. As in the previous year,
some bankline erosion was experienced in the Lower Basin of
the Colorado River. In some river reaches, especially the
Mohave Valley, greater than normal bankline erosion was
caused in part by increased wave action from boating and
other recreational river traffic.

Degradation in some reaches of the river channel has
continued, resulting in a lowering of the river water surface
elevation for any given discharge. In a few areas, bowever, ihe
river channel has aggraded due to heavy sediment loads.

Total Colorado River reservoir system storage at the start of
water yearl988 was approximately 54,921,000 acre-feet and
about 52,404,000 acre-feet at the end of the water year,
representing a 2,517,000 acre-foot increase in total remaining
available reservoir space.

In addition to the mainstem structures, Alamo Dam on the
Bill Williams River (in the Lower Basin) recei~ed minor flood
inflow during water year 1988. During water year 1989,
Painted Rock and Alamo Reservoirs are scheduled to be
operated in accordance with established flood control criteria
to maximize the available flood control space in their
respective reservoirs.

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