WSP08301

• File Number: 8273.100.50
• Description: Colorado River Basin Salinity Control - Federal Agency Reports - BOR
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 2/1/1988
• Title: Estimating Economic Impacts of Salinity of the Colorado River - Final Report - February 1988
• Water Supply Pro - Doc Type: Report/Study

20 Estimating Economic Impacts of Salinity...

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Salinity concentrations at Imperial Dam
decreased steadily from 1970-79, reflecting a
buffering of annual fluctuations in salinity caused
by nearly 50 million acre-feet (mal) of reservoir
storage. Salinity dropped notably in 1980 as
Hoover Dam discharges increased to 11.1 maf,
diluting the salinity at Imperial Dam temporarily.
With more normal flows in the river in 1981 and
1982, the salinity levels rebounded slightly.
Higher releases from Hoover and Glen Canyon
Dams in 1983 and 1984, caused by record
breaking reservoir inflows, caused salinity at Im-
perial Dam to drop again. With nearly 50 maf
of high quality water in storage, salinity at
Imperial remained relatively low in 1985 and
1986.6

The salinity projections between 1987 and
2010, shown in Figures 3-5, result from projec-
tions of depletions and salt pickups caused by
Colorado River Basin development. These
projections are based on the historic water sup-
ply and on estimates of future depletions of
water from the Upper and Lower Basins reflect-
ing irrigation, transbasin diversions, municipal
and industrial uses, evaporation, and uses in
mineral development?

The steady increases in salinity levels fore-
casted in Figures 3-5 are based on the level of
development anticipated to occur by 2010. At
that time, the salinity at Imperial Dam is ex-
pected to reach about 963 mgiL of total dis-
solved solids (TDS). The computer programs
used in the CRSS are based on certain assump.
tions: complete mixing, steady-state transport of
both water and TDS, and no losses of salinity
due to chemical precipitation or salt stratifica-
tion within the river/reservoir system.S

Salinity of Metropolitan Water
Supplies In the Lower Basin

Determination of the TDS level of delivered
municipal and industrial water supplies in the

lower Colorado River Basin is difficult at best.
Much of the water used is a blend of Colorado
River water and other water supplies-
groundwater, surface water from northern
California or from the Salt and VerdeRivers,etc.
In addition, salinity is not regularly monitored
under local water quality regulations and is there-
fore measured only infrequently. Records of
TDS levels usually are not found charted with
consistency. Further, the number of water pur-
veying agencies in the Lower Basin is several
hundred, each with different sources of supply,
blending activities, and reporting standards.
Typically, TDS levels vary geographically within
a water supply agency's service area, and also
vary over time due to fluctuations in distributing
supplies from different sources with different
TDS levels. The best any researcher can do
without months of detailed record searches is to
sample and estimate the average systemwide
TDS for some major metropolitan areas and for
a few subareas within them.

This is the approach selected for this study,
primarily because of constraints on project
resources. In Arizona and Nevada it is possible
to estimate what the future blend of water might
be since Colorado River water will be added to
existing and well-identified local water supplies.
In southern California, estimates of future
blended water are not possible because of the
uncertain status of State Water Project supplies
that will be imported from the north, and be-
cause of the more complex possibilities involved
in blending and distributing water from the
Colorado River and a variety of local surface
and groundwater sources. More or less use of
State water will affect the ultimate TDS level, as
will the future quality of such State water.

Table 4 provides the best available data on
current and (where possible) estimated TDS
levels for the bulk of the municipal and indus-
trial water supply in the lower Colorado River
Basin. It should be noted that 1984-85 was a
period of unprecedented high flows in the river,

6 A more complete discussion of historical and current salinity conditions in the Colorado River can be found in Part V of
Department of the Interior, Ollali(y or WSlt~r C'.olomdn River Ha1llin Pmur:&.li: R~nn'l't No 12 Washington, D.C.: January
]985, pp. 23-29.

7Details of future development assumptions on which the salinity projections are based can be found in ibid., pp. 30-60.

BOetails of the CRSS and the assumptions on which salinity projections are based can be found in ibid., pp. 100-105.