WSP01269

• File Number: 8170
• Description: Arkansas Basin Water Quality Issues
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 8/1/1997
• Author: Doug Cain
• Title: U.S. Geological Survey Data Collection and Studies in the Arkansas River Basin
• Water Supply Pro - Doc Type: Report/Study

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<COLORADO WATER

was about a I 0 percent decrease in dissolved
solids with 100 percent dryup. There was
about a 30 percent decrease in dissolved solids.
We can see thaI some of these changes thaI are
happening in the basin can have positive effects
on water quality, although there are also the
associated effects that might not be so positive.
AnOlher thing I have nOl shown here but that
will be in the publication is how this change
might have affected water quality in the river
itself.

We have looleed at how specific conductance,
which is a measure of the salts in the water, has
changed at sites downstream from both Pueblo
Reservoir and John Martin Reservoir before
and after Pueblo Reservoir went in (about
1974) and before and after the 1980 operating
plan for John Martin Reservoir. The first site
is above Pueblo,just down.stream from Pueblo
darn. We will show the daily mean slreamflow
for various months, both before and after
Pueblo Reservoir went into place. Loole at the
average salt concentration in water coming out
of Pueblo Reservoir (Figure 6). We see a shift
in the monthly concentrations of salts passing
the site after the reservoir was built, so there is
much less variation on an annual basis in the
salts coming out of the reservoir. Before, we
would see higher salts in the spring and much
lower salts during spring runoff. Now, because
all of that water is mixed together in the
reservoir, we do not see nearly as much change.
This means that people using the water,
irrigators downstream, see more consislent
water quality but the water is not as clean as it
was in the past during the spring.

To show this more dramatically, instantaneous
measurements of salts in the river at the site
from 1966 to 1994 showed that before the
reservoir went in there was a lot of variation.
After the reservoir wem in, the annual variation
is much smaller (Figure 7). We also saw a
slight, average improvement in waler quality at
lhis site.

Downslrearn, at the next site (Avondale is just
east of Pueblo and downSlream from Foumain
Creele, the outfall from CF&I and the outfall
from the Pueblo Wastewater Treatment Plant),

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20~o DRYUP

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100% DRYUP

700
1971

1975

1980

1985

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Fig.5. Simulated Change in Groundwater Salinity Relative to Historil:
Conditions for Scenarios of Agricultural Dryup.

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Fig. 6. Arkansas River Above Pueblo.