7409

• UCREFRP Catalog Number: 7409
• Author: U.S. Department of the Interior.
• Title: Quality of Water, Colorado River Basin.
• USFW Year: 1991.
• USFW - Doc Type: Progress Report No. 15,
• Copyright Material: NO

22 Chapter 5-HistoricaJ Salinity Concitions

3700 ~ ~
3600
.-
...
: 3500 1985 1988
...
--
; 3400
-
...
41
~
.!l 3300
r&l
3200
3100
200 300 400 500 600 700 800
Salinity (me/L)

3700

3600

.-
...
: 3500
...
--

I::l
.;! 3400
...
41
;.
Gl
-
r&l

3300

3200

1985

1988

3100

200 300 400 500 600 700 800
Salinity (mg/L)

Figure 4.- Salinity at Hite (left) and Wahweap (right) stations in lake Powell.

In addition to salt leaching, the reservoirs may
play an important part in other major factors
that influence salinity. Strong evidence exists
that Flaming Gorge Reservoir and Lake Powell
have stored more saline water and routed the
less saline spring runoff downstream from 1965
through 1980. These more saline waters were
subject to bank storage, chemical precipitation,
ion exchange, oxidation-reduction, and various
biological activities.

Sedimentation in reservoirs may influence both
salinity and the mix of dissolved ions. Sediment
which is subject to mechanical degradation in a
river environment may continue to release salts
and exchange ions (sodium exchanged for
calcium); however, once settled out in the
reservoir, these salts and ion exchange
capabilities may be isolated. Sediment stored in
reservoirs may contain salts that would have
been released with continued mechanical
breakdown in a riverine environment.

Another possible loss of salinity in reservoirs is
due to chemical precipitation. This possible loss
in salinity was investigated by Reclamation for
the two largest storage reservoirs in the basin,
Lakes Powell and Mead. A thermal-
hydrodynamics reservoir model, which
incorporated chemical equilibria, was applied to
each of the two reservoirs.

The estimated potential for calcite precipitation
(the salt that precipitates from solution first)
was found to be 20,000 tons per year for Lake
Powell and 40,000 tons per year for Lake Mead.
These estimates represent the upper limit of
potential precipitation, as it assumes that there
are sufficient nuclei for the calcium carbonate
crystallization and that reaction rate kinetics do
not limit the precipitation. The combined
maximum precipitation is less than 1 percent of
the annual salt load passing through the
reservoirs and is significantly less than previous
estimates which were based on inflow-outflow
budgets using rather incomplete or inadequate
data.

Irrigation and Increased
Depletions

Most of the irrigation projects that deplete W8l;er
and increase salt pickup to the river were in
place before 1965. Moreover, like the newly
inundated soils in reservoirs, newly irrigated
lands are subject to a leach-out period. In cases
where lands with poor drainage stored salt,
these areas were taken out of production. In
addition, irrigation practices changed
significantly during the 1960-80 period, with the
introduction of canal and lateral lining,
sprinkling systems, gated pipe, and trickle

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