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<br />High Colorado Ril'er Flows
<br />
<br />forecam indicated that the April
<br />through July Upper Basin runoff
<br />would be substantially abovt:> normal,
<br />and the Water and Power Resources
<br />Service made studiE.><; that showt"d
<br />high probabililiE.><; of poltmlially
<br />damaging releasE.><; being required from
<br />Hoover Dam in the next few years.
<br />After consultations with the states and
<br />concerned agencies as to the best
<br />course of action, the Service
<br />announced its decision to make
<br />anticipatory flood releases of 700,000
<br />acre-feet from Lake Mead between
<br />May 1 and September 30, 1979.
<br />Actual excess releases amounted to
<br />689,000 acre-feet. The 1979 schedule
<br />of deliveries to Mexico was increased
<br />by 100,000 acre-fE'f't to a total of
<br />1,700,000 acre-ff'el, as allo.....ed by the
<br />1944 Treatv wih Mexico.
<br />
<br />In addition 10 the high Colorado
<br />River flow at Lee Ferrv during the
<br />1978-79 water year noted in the
<br />previous section, heavy precipitation
<br />in the Lower Colorado Ri\'er Basin
<br />caused unusually high streamflows on
<br />tribularies below Hoover Dam and
<br />excess deliveries to ~exico.
<br />During the early part of 1979,
<br />releases from Hoover Dam were at a
<br />minimum rate because the flood
<br />control releases from Alamo Dam on
<br />the Bill Williams River and Painted
<br />Rock Dam on the Gila River provided
<br />more than enough water to supply
<br />Mexico with its scheduled deliveries.
<br />However, this release pattern resulted
<br />in substantial deficiencies in
<br />hydroelectric power generation at
<br />Hoo\'er, Davis, and Parler
<br />powerplants. late season runoff
<br />
<br />7
<br />
<br />,
<br />
<br />These excess flows caused some
<br />flooding problems for Mexico in the
<br />Colorado River Delta, particularly in
<br />the area where the Rio Hardy joins
<br />the Colorado. The problems arose
<br />because (1) Mexican farmers had
<br />been farming on the river side of the
<br />levees; (2) recreational housing had
<br />been located in the floodplain; (J I for
<br />a long period there had been little or
<br />no maintenance of the river channel;
<br />and (4) a sediment barrier had been
<br />created at the mouth of the normally
<br />dry Colorado River which impeded
<br />the outflow of Colorado River water
<br />10 the Gulf of California. Mexico
<br />attt:>mpted to make maximum
<br />beneficial use of the excess flows,
<br />diverting over 1,000,000 acre-feet into
<br />its irrigation system that serves lands
<br />throughout the Colorado River Delta
<br />on both sides of the river and
<br />correspondingly decreased pumping
<br />from the ground-water basin.
<br />Preliminary sludies have shown the
<br />possibility of flooding problems along
<br />the river in the United States, in the
<br />Imperial Valley and Salton Sea areas,
<br />and in Mexico, associated with
<br />forecasted high Colorado River flows
<br />over the next several years.
<br />Concerned over these potential
<br />problems, the Chief Engineer wrote
<br />letters to the Corps of Engineers,
<br />Water and Power Resources Service,
<br />and lnlernational Boundary and Water
<br />Commission and made an inspection
<br />trip of the Colorado River Delta area.
<br />The Chief Engineer recommended that
<br />the Service move fOM'ard with a
<br />management plan for the Parker II
<br />Division of the river, that Ihe Corps
<br />sludy mt:>asures 10 reduce potential
<br />damages from flood control releases
<br />in the entire lower Colorado River
<br />area, and that the Corps. in
<br />cooperation with the Service and the
<br />Commission, expand ils current study
<br />of the Hoover Dam Flood Control
<br />Regulations to include determination
<br />of measures necesSolry to provide Solfe
<br />discharge of flood (ontrol releases to
<br />the Gulf of California without causing
<br />flood damages in ~exico and in the
<br />Imperial Valley. Investigations along
<br />the lines suggested are under way.
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