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<br />Table 2. Mean concentrations of selected major ions ~n,~ s,liJlity for six sites on the
<br />Colorado River, July 1994--September 1995 ~ "i ~ ,,)
<br />
<br />[Concentrations in milligrams per liter (parts per million)]
<br />Site Magne- Potas-
<br />number Calcium Sodium Chloride Sulfate Alkalinity Salinity
<br />(fig. 1) sium sium
<br />I 62.4 14.6 3.2 99.3 i34 i is i3.4 517
<br />3 61.3 15.1 3.2 97.0 127 114 140 511
<br />5 72.8 19.5 3.3 101 130 158 144 580
<br />6 81.3 24.1 3.1 72.9 66.9 224 140 567
<br />7 83.6 25.3 3.2 74.3 66.8 238 142 587
<br />8 87.8 26.4 3.1 78.3 71.2 252 142 617
<br />
<br />Major-Ion Concentrations
<br />
<br />The monthly samples collected at the
<br />eight sites were analyzed for concentrations of
<br />major ions (table 2). The most notable feature
<br />of the major-ion data listed in table 2 is the dif-
<br />ferences in ion concentrations in the Colorado
<br />River upstream and downstream from the con-
<br />fluence with the Gunnison River (immediately
<br />downstream from site 5, fig. I). The chloride
<br />and sodium concentrations upstream from the
<br />Gunnison River (sites 1,3, and 5) are consid-
<br />erably higher than downstream from the
<br />Gunnison River inflow (sites 6, 7, and 8), and
<br />sulfate concentrations are considerably higher
<br />downstream from the Gunnison River. The
<br />reason for those differences is that chloride
<br />and sodium concentrations are lower and sul-
<br />fate concentrations are higher in the Gunnison
<br />River than in the Colorado River upstream
<br />from site 5. Therefore, chloride and sodium
<br />concentrations are decreased and sulfate con-
<br />centrations are increased in the Colorado
<br />River by inflow from the Gunnison River.
<br />Also of note is the increase in some ion con-
<br />centrations between sites 3 and 5, which
<br />reflects the effects of irrigation return flows
<br />from the eastern Grand Valley, and between
<br />sites 6, 7, and 8, which reflects the effects of
<br />irrigation return flows into the Colorado River
<br />from the western part of the Grand Valley.
<br />
<br />
<br />October 1996
<br />
<br />CONCLUSIONS
<br />
<br />Salinity in the Colorado River in
<br />1994-95 was dependent to varying degrees on
<br />streamflow. The less than average runoff in
<br />1994 probably caused unusually high salinity
<br />in the Colorado River in July 1994. However,
<br />salinity in the Colorado River for August
<br />through November 1994 was not unusual
<br />when compared to historical data that have
<br />been collected at the Cameo and State line
<br />gaging stations. Reservoir releases in the
<br />Colorado River Basin upstream from the
<br />Grand Valley augmented river flows with
<br />dilute water and partially offset the effects of
<br />low natural streamflows on salinity. The high
<br />and prolonged runoff in 1995 seemed to have
<br />affected salinity in the Colorado River more
<br />noticeably than the low-flow period of 1994.
<br />Salinity in July and August 1995 was much
<br />lower than in July and August 1994 at six sam-
<br />pling sites on the Colorado River from Cameo
<br />to the Colorado-Utah State line.
<br />
<br />Salinity during July-October 1994 near
<br />the diversion points on the Colorado River for
<br />the Government Highline Canal and Grand
<br />Valley Canal did not exceed a threshold level
<br />at which crop productivity may be adversely
<br />affected. Salinity increased in the Colorado
<br />River from Palisade (site 2) to the Gunnison
<br />River (site 5) and from the Redlands Parkway
<br />(site 6, downstream from the Gunnison River
<br />
<br />For more information about this
<br />study, write to:
<br />
<br />Subdistrict Chief
<br />U.S. Geological Survey
<br />Water Resources Division
<br />Aspinall Federal Building
<br />402 Rood Avenue, Room 230
<br />Grand Junction, CO 81501
<br />email: pbvongue@cronos.cr.usgs.gov
<br />
<br />inflow) to the Colorado-Utah State line (site 8)
<br />because of salt loading from surface and
<br />subsurface irrigation return flows. During
<br />1994-95, the highest salinity in the Colorado
<br />River between the Redlands Parkway and the
<br />State line occurred during August-November
<br />of 1994, which probably coincides with the
<br />
<br />fl1axiiiiUm salt loading to the river from irriga-
<br />
<br />tion drainwater and return flows.
<br />
<br />REFERENCES CITED
<br />
<br />Crowfoot, R.M., Ugland, R.e., Maura, W.S.,
<br />Jenkins, R.A., and O'Neill, G.B., 1996,
<br />Water resources data, Colorado, water
<br />yeaT 1995-v. 2, Colorado River Basin:
<br />U.S. Geological Survey Water-Data
<br />Report CO-95-2, 471 p.
<br />
<br />Ugland, R.e., Maura, W.S., Wilson, E.A., and
<br />O'Neill, G.B., 1995, Water resources
<br />data, Colorado, water year 1994--v. 2,
<br />Colorado River Basin: U.S. Geological
<br />Survey Water-Data Report CO-94-2,
<br />412 p.
<br />
<br />U.S. Department of the Interior, 1994, Salinity
<br />update: Denver, Bureau of Reclamation,
<br />Colorado River Salinity Program Coor-
<br />dinator, 17 p.
<br />
<br />-1995, Quality of water-Colorado
<br />River Basin: Salt Lake City, Utah,
<br />Bureau of Reclamation, Upper Colorado
<br />Region Progress Report 17, 96 p. plus
<br />appendix.
<br />
<br />-David L. Butler and Paul von Guerard,
<br />Water Resources Division, Grand Junction,
<br />Colorado.
<br />
<br />-The authors acknowledge the data-
<br />collection efforts for this study by
<br />Troy R. Taylor and Darrin A. Miller
<br />of the USGS.
<br />
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<br />
<br />Fact Sheet FS-215-96
<br />
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