WSP04095

• File Number: 8270.100
• Description: Colorado River Basin Water Quality/Salinity -- Misc Water Quality
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1987
• Author: USDOI
• Title: Quality of Water - Colorado River Basin - Progress Report No. 13 - January 1987
• Water Supply Pro - Doc Type: Report/Study

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C. Salinity projections

Since CRSS predicts future salinity based on a series of years (a trace)
from the past, several traces were needed to show what the minimum, maximun,
and average salinity might be. In all, 15 individual runs of the model were
made to estimate these values. Table VIII-2 on the following page shows a
sununary of the CRSS for the Basin. Figure VIII-3 shows the aggregate results
of the 15 individual runs at Impedal Dam. The range shown in the figure is
by no means the minimum and maximum possible; however, the figure does
demonstrate how salinity can vary due to the combined effects of development
and the virgin flow of the river.

~ 1200 .
~ 1100 . . .
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S 1000 . . . . I I I I I
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900 I . I . I . . . . .
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.
11 800 . . I . . . . . . . . . .
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. . . . . .
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700 I . . . . I . . .
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rn . .
. . . . . . . .
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600
1980 1990 2000 2010

Year

Figure VIII-3. Range of mean annual salinity at Imperial Dam (1986-2010).

The general trend in Figure VlII-3 of increasing salinity with time is
due to 2 components. The most obvious one is due me increase in development.
The increased use of water reduces the dilution of salinity in the river. The
less obvious component is the rebounding of the salinity from the abnormally
low levels of salinity observed in 1985-86 which were used as the starting
point for these projections. At the present level of development, more normal
levels of salinity at Imperial Dam would have been in the range of 820 mg/L
instead of 607 mg/L. This demonstrates an important aspect of the projections
shown in Figure VIII-3, that natural variations in the hydrologic and climatic
conditions can have a dramatic impact on the year to year variation in
salinity. The figure shows this variation as the scatter in the possible
salinity for anyone year in the future. The possible salinity for that year
could vary 100 to 200 mg/L on either side of the mean depending on how wet or
dry it is.

VIII-4