WSP06951

• File Number: 8273.300
• Description: Colorado River Basin Salinity Control - Federal Agencies - USGS
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/1985
• Author: USGS
• Title: Ground-Water Contribution to the Salinity of the Upper Colorado River Basin
• Water Supply Pro - Doc Type: Report/Study

~
~ Valley, which consists mainly of Mancos Shale. These creeks drain the Wasatch
~ Formation and Mesaverde Group in the middle reaches and the Green River
~' Formation in the headwaters region.

An estimated 50 ft'ls of water was diverted from the Colorado River below
Cameo by the Government Highline Canal. Some of this water probably filtered
down the water table and returned to the Colorado River by seepage. The
remaining water from the canal discharged into Big Salt Wash. This would
account for the relatively high discharge of 115 ft'/s and relatively low
dissolved-solids concentration of 1,070 mg/L in Big Salt Wash (site 16) when
compared with other tributary streams draining the Grand Valley.

Adjustments for effects of reservoirs in the upper Colorado River and
Gunnison River subregions were applied to sites on the lower Colorado River.
The adjusted dissolved-solids concentration for the Colorado River near Cameo
(site 11) was 976 mg/L, for the Colorado River near the new Fruita, Colo.,
bridge (site 15) 1,139 mg/L, and for the Colorado River near the Colorado-Utah
State line (site 19) 1,212 mg/L.

The plot of salt load, dissolved-solids concentration, and discharge of
the main stem of the Colorado River as it flows through, this subregion is
shown in figure 19. A downstream progressive increase in salinity is
apparent. Note that diversion of water from the Colorado River by the
Goverrunent Highline Canal resulted in a drop in salt load and discharge but
did not affect the salinity. The addition of the Gunnison River near Grand
Junction caused a drop of about 100 mg/L in the dissolved-solids concentration
of the Colorado River below their confluence.

Between the sites on the Colorado River near Cameo (site 11) and at the
Colorado-Utah State line (site 19), the adjusted base-flow salt load increased
by 1,479,000 ton/yr. The Gunnison River contributed 724,000 ton/yr, Plateau
Creek contributed an estimated 24,500 ton/yr, and measured tributaries in the
Grand Valley contributed 230,100 ton/yr of base-flow salt load. The
remainder, an estimated 501,400 ton/yr, was probably produced by direct
erosion of the Mancos Shale by the Colorado River in the Grand Valley and by
the residual effects of extensive irrigation in the Grand Valley.

Measured base-flow discharges and dissolved-solids concentrations were
compared with historical data from water-quality stations for the months of
December, January, and February, water years 1975-77, for sites on the
Colorado River near Cameo and at the Colorado-Utah State line. The measured
discharge at the Cameo site was 1,320 ft'/s or about 74 percent of the average
of 1,773 ft'/s, and the calculated dissolved-solids concentration of 980 mg/L
was about 34 percent greater than the average of 732 mg/L. The measured
discharge of 2,200 ft'/s near the Colorado-Utah State line was only about
59 percent of the average of 3,742 ft'/s, and the calculated dissolved-solids
concentration of 1,270 mg/L was about 80 percent greater than the average of
705 mg/L.

At the Colorado-Utah State line, the Colorado River has an estimated
adjusted base-flow salt load of 2,734,000 ton/yr (fig. 18). Approximately
1,037,000 ton/yr of this was produced within the Colorado lower headwaters

51