WSP05106

• File Number: 8276.150
• Description: Grand Valley Unit-Colorado River Basin Salinity Control Project
• State: CO
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 12/1/1977
• Title: Final Report of the Grand Valley Salinity Study - On-Farm Program for Salinity Control
• Water Supply Pro - Doc Type: Report/Study

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federal regulations provide for temporary increases above the 1972
levels if control measures are included in the plan. Should water
development projects be completed Defore control measures are identified
or brought on line, temporary increases above the criteria could result
and these increases will be in conformance with the regulation. With
completion of control projects, those now in the plan or those to be
added subsequently, salinity would return to or below the criteria
level.

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PROBLEMS IN THE GRAND VALLEY

Analysis of water qual ity data by the U. S. Geological Survey (USGS)
indicate that the Grand Valley contributes about 600,000 to 700,000 tons
of salt annually to the Colorado River. Most of these salts are thought
to be leached ,'rom the soil and underlying t1ancos Shale and carried into
the river by deep percolation from irrigation and seepage from water
del ivery and tailwater collection systems.

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Both natural runoff and irrigation contribute to the problem, either by
salt concentration or by salt loading. Salt concentration is caused by
removal of water from the river system through consumptive use by
irrigated crops and phreatophytes. As water is consumed through evapo-
ration and transpiration, its mineral constituents remain in the ground
water. Salt loading occurs as ground water dissolves subsurface minerals
while flowing back to the Colorado River. Although both processes are
at work in the Grand Valley, salt loading is the major cause of the
sal inity increase.

Gr~und water return flows from the irrigated area to the Colorado River
contain as much salt now as they did at the inception of irrigation and
it is assumed this will continue because excess water dissolves salt
from the Mancos Shale formation. Two conditions substantiate this
conclusion: (1) water qual ity 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 instal-
lation of Government High1 ine 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.

Erosion from the upland watershed also contributes sediment and salt to
the Colorado River. Sheet, rill, gully and streambank erosion results
in 2.9 mill ion tons of sediment with about 80,000 tons of salt being
added to river annually.

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