2003

• UCREFRP Catalog Number: 2003
• Author: U.S. Department of the Interior.
• Title: Quality of Water, Colorado River Basin.
• USFW Year: 1985.
• USFW - Doc Type: Progress Report No. 12,
• Copyright Material: NO

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PART V. HISTORICAL AND PRESENT SALINITY CONDITIONS

The Bureau of Reclamation is continuing to develop methods to evalu-
ate long-term salinity and specific ion trends. The analysis of trends
contained in water quality records is possible with the extensive use of
computers. Accordingly, the past several years have been devoted to
developing computer programs to reanalyze the entire record. This com-
puterization, which is still .in progress, is essential to understanding
the long-term salinity trends throughout the recorded water quality
history of the basin. This section of the report provides a 2-year
update of observed conditions in the basin.

A. Quality of Water Records

The evaluations of the historical salinity in the Colorado River
Basin are based on streamflow records at selected stations. The average
concentrations and loads were determined on a flow-weighted basis using
daily data whenever possible. Salt loads and concentrations were gener-
ally calculated from daily conductivity and flow records using correla-
tions.

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Historical streamflow, salinity concentrations, and salt load data
for the 20 key stations for the 1941-83 period of record are presented
in Tables 1 through 20 at the end of this report.

B. Historical Salinity

Salinity concentrations at Imperial Dam (Figure 1) decreased
steadily from 1970-79, dropped notably in 1980, increased sharply in
1981-82, and dropped again in 1983 and 1984. The 1970-80 salinity con-
centrations show the buffering of annual fluctuations in salinities due
to the effect of nearly 50 million acre-feet of reservoir storage. With
the reservoir storage in the Colorado at near capacity, discharges from
Hoover Dam increased from 7.7 million acre-feet in 1979 to 11.1 million
acre-feet in 1980, diluting the salinity at Imperial Dam temporarily.
With more normal flows in 1981 and 1982, the salinity rebounded. Higher
releases from Hoover and Glen Canyon Dams in 1983 and 1984, combined
with lower salinities in storage, caused salinity at Imperial Dam to
drop again. With the nearly 50 million acre-feet of high quality water
in storage, salinities at Imperial Dam should remain low through 1985.

C. Factors in Salinity Trends

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The downward fluctuation of salinity at Imperial Dam during the
1970.s is within the expected range and was in fact simulated using a
computer model of the Colorado River Basin (see Part VIII for a descrip-
tion of the model, Colorado River Simulation System (CRSS)). Several
factors complicate the analysis of the decline and leveling off of

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