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<br />I
<br />
<br />Flood Control
<br />
<br />The reservoirs within the basin again
<br />received -for greater lotol inflow in 1984 1"
<br />than during normal years. In the Upper
<br />Basin, Nevoio and Blue Mesa Reservoirs are
<br />operated for flood control by providing
<br />space to store snowmelt floods. Although
<br />Flaming Gorge and Glen Canyon Reservoirs
<br />have no specifically assigned requirement
<br />for flood contro/. they do reduce flood
<br />flows since they are operated to reduce
<br />spills. The space they provide is counted
<br />as part of the flood control space that is
<br />required by the Army Corps of Engineers
<br />(Corps) flood control regulations at
<br />lake Mead.
<br />
<br />Damages to bridges, roods, and farmland
<br />in the Upper Basin above lake Powell
<br />reached approximately $20 million. The
<br />worst flooding along the Upper Colorado
<br />mainstem in more than 50 years was
<br />e....ident. Record flows were observed
<br />breaking the pre- \ 922 recorded flows da1ing
<br />back to 1897. Areas along the Upper Basin
<br />mainstem remained above flood stage from
<br />37 to 53 days. Mains1em reservoirs helped
<br />alle....iate these peak flows.
<br />
<br />In 1984, the maximum flow of the Gunnison
<br />River at Crystal Dam was reduced from
<br />over 21,000 cfs to about 9,200 cfs due to
<br />storage in Blue Mesa and Taylor Park
<br />Reservoirs. At the time when the North
<br />Fork of the Gunnison was causing flood
<br />damages near Delta, Colorado, the
<br />regulatory effects of the Aspinall Una
<br />decreased-the maximum- flow by almost
<br />12,000 cfs. Na....ajo Reservoir reduced the
<br />maximum flow of the San Juan River at the
<br />dam from over 9,000 cfs 10 2,100 cfs which
<br />reduced damage near Farmington, New
<br />Me ico. Flaming Gorge Reservoir reduced
<br />thE naximum flow of the Green River 01
<br />the dam from 17,300 cfs to 8,100 cfs which
<br />helped alleviate flooding near Jensen,
<br />Utah, os the flow of the Yampa River
<br />peaked.
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<br />Desert flora near Coccnella Canol, California.
<br />
<br />lake Mead is the only reservoir on the
<br />Colorado River in which 0 specific space is
<br />exclusively allocated for mainstem flood
<br />control. Flood control regulations for
<br />Hoo....er Dam hove been updated and
<br />revised based on findings of a joint study
<br />initiated in 1977 by Reclamation and the
<br />Corps, with consultation and advice of State
<br />and local interests.
<br />
<br />A final report dated July 1982 which
<br />summarized the study findings and
<br />recommended 0 new flood control
<br />operation plan for Hoover Dam was
<br />released July 1983. Flood control storage
<br />space will be maintained in lake Mead as
<br />stipulated in the Report's Field" Working
<br />Agreement between Reclamation and the
<br />Corps for flood control operation of Hoover
<br />Dam and lake Mead. These regulations
<br />establish releases in a manner that
<br />maximizes public benefits in the United
<br />States with reasonable consideration for
<br />conditions in Mexico.
<br />
<br />lower releases this year than last year's
<br />40,000 cis to 45,()(X) cis levels ha....e avoided
<br />any additional significant damages along
<br />the river in the lower Basin. Scour in
<br />some reaches of river channel has
<br />continued to occur, and therefore river
<br />levels have been lower in nearly all areas
<br />than they were with the some release
<br />levels last year and early this year.
<br />
<br />The reservoir system has been operated in
<br />full accordance with established operating
<br />criteria and the Corps flood control
<br />regulations. The combined effect of the
<br />Upper Basin reservoirs, including Flaming
<br />Gorge and Lake Powell, and Lower Basin
<br />reservoirs, Lake Mead, lake Mohave, and
<br />Lake Ha....asu, was to reduce the flow of the
<br />lower Colorado River from approximately
<br />148,000 to obout 32,000 ds,
<br />
<br />Total Colorado River reservoir system
<br />storage at the start of water year 1984 was
<br />approximately 5B,962,OCO acre-feet and
<br />about 57,344,000 acre-feet at the end of the
<br />water year, representing a 1,618,000 acre-
<br />foot increase in- totcil remaining available
<br />reservoir space.
<br />
<br />In addition to the mainstem structures,
<br />Alamo Dam on the Bill Williams River, and
<br />Painted Rock Dam on the Gila River (both
<br />in the lower Basin) received flood inflow
<br />during water year 1984. During water year
<br />1985, Pointed Rock and Alamo Reservoirs
<br />are scheduled to be operated in accordance
<br />with established flood control criteria to
<br />maximize the available flood control space
<br />remaining in their respective reservoirs.
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