|
<br />......
<br />w
<br />~
<br />~
<br />
<br />1000
<br />
<br />. . . . . . , . . . . , . , , , ,. . . . . , . . . . . , , , , , , , , , , , , , , , , , , , , , , , , , . . . f':\.!
<br />Numeric criterion-879 mgil I
<br />................../................,......,.......p......
<br />
<br />............. ......... ... ..................[.!.........
<br />; Projections
<br />............ . ..., Hi~i~;I~~I..... .....1.'.':~~fs..
<br />,........,.... .... .dats............,...j.................
<br />
<br /> 950
<br /> 900
<br /> 850
<br />..! 800
<br />'"
<br />E
<br />.5 750
<br />en
<br />f2 700
<br /> 650
<br />
<br />
<br />
<br />600
<br />
<br />550
<br />1940 1950 1960 1970 1990 1990 2000 2010
<br />Years
<br />
<br />Figure 3,-Historical data and salinity projections without further controls at Imperial Dam.
<br />
<br />Moderate variations in the salinity levels in
<br />impoundments like Lake Powell and Lake Mead
<br />and at Imperial Darn can be ascribed to several
<br />factors, such as water demands, weather, and
<br />salinity control activities. Howsver, there are
<br />two factors for which the salinity levels at
<br />Hoover Dam and below are very sensitive,
<br />
<br />. Accumulated reservoir inflow and resulting
<br />high reservoir storage - Whenever
<br />reservoir inflow is significantly greater
<br />than normal, dilution is generally occurring
<br />within the large reservoirs of Powell and
<br />Mead.
<br />
<br />. Reservoir discharge&-Whenever river
<br />flows are low, salinity concentrations are
<br />high; and the opposite occurs when river
<br />flows are high,
<br />
<br />Very rapid changes in salinity concentration can
<br />be observed when both these conditions exist at
<br />the same time; i.e, (1) previous reservoir inflows
<br />have been high for several seasons and (2) above
<br />average reservoir discharge will produce very
<br />low salinity concentrations as observed in 1986
<br />Oess than 600 mg/L), Conversely, high
<br />concentrations can be expected when reservoir
<br />
<br />6
<br />
<br />inflow has been low for several seasons and the
<br />reservoir discharge has been at a minimum.
<br />
<br />Because of the vast water storage behind Glen
<br />Canyon and Hoover Dams, Upper Basin salinity
<br />control projects implemented at any given year
<br />do not begin to reduce salinity levels at Imperial
<br />Dam until many years thereafter. This time lag
<br />needs to be recognized when scheduling project
<br />implementation to achieve desired results in
<br />some timely manner.
<br />
<br />The Program
<br />
<br />The plan of implementation is designed to
<br />maintain the average salinity concentration of
<br />the river at or below the numeric criteria at the
<br />three stations on the river without impairing the
<br />development and use of compact-apportioned
<br />water in the Colorado River Basin. The
<br />Basin-wide salinity control plan is designed to
<br />offset salinity increases caused by man's
<br />development of the State's compact-apportioned
<br />waters. The plan makes no attempt to offset
<br />salinity increases which result from natural
<br />hydrologic variations of the river system,
<br />Salinity control is accomplished primarily by
<br />
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