WSP05265

• File Number: 8170
• Description: Arkansas Basin Water Quality Issues
• State: CO
• Basin: Arkansas
• Water Division: 2
• Date: 2/1/1998
• Author: Goff Lewis Person Ko
• Title: Simulated Effects of Irrigation on Salinity in the Arkansas River Valley in Colorado
• Water Supply Pro - Doc Type: Report/Study

8a.

1!~:;

FO""j'tl/lC."~

Measured --February 1 972

8b.

Measured -February 1982

F011lroncanll
'...

Simulated -.February 1972

FOIll"""C.,,11
~~2.llOO.-r-
'...

L~1IIII1o

SImulated --February 1982

. Measured -February 1995

t:.XPl.ANA TJrJN

Fll<f__~

. Simulated --February 1995

----il.OllO- ~unllr, III mllDgrams per I"""

MOMI[OIlngwfiill.

Figure 8. .I\leasured and simulated salinity in the allmial aquifer, February 1972, 1982, and 1995.

The model was not calibrated to streamflow at the down-
stream end of the study area because streamflow was not measured
at this location except during the 1971-72 period. Model simulations
of streamflow gains ~nd losses (Figure 10) are consistent with the
current understanding of interactions between the river and the
alluvial aquifer. A substantial percentage of the river is diverted at
the upstream end of me study site by ule Fort Lyon C~nal. At the
downstream end of the study area, streamflow recovery is supplied
primmi1y by irrigation return flow from the aquifer. According to
the current understanding and conceptual model of the stream-

10

8

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! 4
2

o

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____~, I, I, _____
I , , , , ^
v

Range of Error in Salinity (mg/L)

Figure 9. Frequency distribution of errors in model-simulated salin-
ity (simulated minus measured) for individual wells sampled in
February 1972,1982, and 1995.

aquifer system, the gain-loss relation between the river and aquifer
varies seasonally and is a function of streamflow, canal diver-
sions, and hydraulic gradient. Although the river typically experi-
ences a net gain in flow in the study area, streamflow losses to the
aquifer can be substantial during the seasonally high streamflow in
May and lune. The losses during seasonal high flows can vary sub-
stantially depending on whether the year has been wet or dry.
During dry years, less streamflow is available for diversion into the
canal. and the hydraulic gradient between the aquifer and stream
decreases because aquifer recharge from surface water applications
and canal leakage decreases. Therefore, losses from the river to the

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0.6
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-0.4

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Year

Figure 10. Simulated average monthly streamflow gains or losses in
the Arkansas River at tbe downstream end of the study area.

81