WSP10235

• File Number: 8281.910
• Description: Colorado River Studies and Investigations -- Grand Valley Salinity Study
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 12/1/1976
• Author: Soil Cons Serv
• Title: Grand Valley Salinity Study - draft
• Water Supply Pro - Doc Type: Report/Study

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Both natural runoff and irrigation contribute to the problem, either
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by salt concentration or by s~lt loading. Salt concentration is caused

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by the removal of water from the river system through consumptive use by

irrigated crops and phreatophytes. As water is consumed through evapora-
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tion and transpiration, its mlneral constituents remain in the ground

water. Salt loading occurs a~ ground water dissolves subsurface minerals

while flowing back to the COloradO River.
at work in the Grand Valley, s~lt loading

Although both processes are

is the major cause of the

salinity Increase.

Ground water return flows from the irrigated area to the Colorado

River contain as much salt now as they did at the Inception of irri-

gation and it Is assumed this will continue because excess water

dissolves salt from the Mancos Shale formation. Two conditions

substantiate this conclusion: (1) water quality information on the

artesian ground water aquifer collected at several well sites by

the U. S. Department of Agriculture in 1915; Agricultural Research

Service-Soil Conservation Service Project in 1951, and Agricultural

Research Service in 1973, to 1975, indicate no change in water quality

of the aquifer. Hydrostatic pressures toward the Colorado River rule

out the river as a source of water to the aquifer; (2) diversions to

the irrigated area since installation of Government Hlghline Canal In

1917 are essentially unchanged. Situations indicate that salt loading

by subsurface return flows to the Colorado River from irrigated areas

have been relatively constant over this 60-year period.

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