WSP00585

• File Number: 8282.600.10
• Description: Colorado River Operating Annual Reports
• Basin: Colorado Mainstem
• Date: 1/1/1986
• Author: USDOI/BOR
• Title: Operation of the Colorado River Basin 1986 Projected Operations 1987
• 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 higher flood control 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 of the hydroelectric power customers. Minimum
daily flow objectives are provided in the river to maintain
fishery habitat. The combination of high runoff conditions and
river rcgulation below Hoover Oam resulted in a total water
year 1986 delivery to Mexico of approximately 9.3 MAF in
excess of the scheduled treaty quantity (1,700,000 acre-feet
per calendar ycar). Of that amount, 105,500 acre.feet of
drainage waters were bypassed to the Gulf of California via
the Bypass Drain during water year 1986. 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 updated flood
control regulations which are specified in the Field Working
Agreement betweel) Reclamation and the Corps of
Engineers, signed in 1982. The regulations stipulate minimum
release levels from Lake Mead to route the reasonable
maximum iollow. 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 hydro meteorological 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.

There were no significant damages along the river in the
Lower Basin during water year 1986. There was, however,
some minor bank erosion in the Lower Basin below Yuma on
the Quechan Indian Reservation, and a contractor was hired
to riprap at that location. In the North Gila area near the
confluence of the Gila River and the Colorado River, some
bank erosion also was experienced. This was repaired by
government forces.

Scour in some reaches of river channel has continued to Occur
and therefore river levels have been lower in some areas th"';
they were with the same release levels during the last 3 years.
In a few areas, however, reaches have refilled due to heavy
sediment loads. One example is the reach below Cibola Valley
in the Lower Basin.

Total Colorado River reservoir system storage at the start of
water year 1986 was approximately 55,514,000 acre-feet and
about 55,~1l,OOO acre-feet at the end of the water year,
representlDg a 97,000 acre-foot decrease in total remaining
available reservoir space.

In addition to the mainstem structures, Alamo Oam on the
Bill Williams River and Painted Rock Oam on the Gila River
(both in the Lower Basin) received flood inflow during water
year 1986. During water year 1987, Painted Rock and Alamo
Reservoirs are scheduled to be operated in accordance with
established flood control criteria to maximize the available
flood control space remaining in their respective reservoirs.

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