By Nancy J. Bauch and Norman E. Spahr, U.S. Geological Survey, Box 25046, MS 415, Denver Federal Center, Lakewood, CO, 80225

Abstract

To assess the effects of salinity-control projects and to determine the status of salinity upstream from control projects in the Colorado and Gunnison River Basins in Colorado, dissolved-solids data from several Federal and State agencies were analyzed for trends in flow-adjusted periodic dissolved-solids concentrations and in monthly and annual dissolved-solids loads for 1970-93, 1980-93, 1986-93. A decrease in dissolved-solids concentrations and loads occurred in the Colorado River near the Colorado-Utah State line, and part of this decrease was probably due to upstream salinity-control projects. In areas of the Colorado River Basin not affected by salinity-control projects, flow-adjusted dissolved-solids concentrations and loads generally were decreasing or had no statistically significant trends for the three analysis periods. For sites in the Gunnison River Basin, just over one-half of all trend results indicated no statistically significant change in flow-adjusted dissolved-solids concentrations and loads, both upstream and downstream of salinity-control projects. More of the statistically significant results were decreasing rather than increasing. Trend results indicating decreasing concentrations and loads of dissolved-solids in areas not affected by salinity-control projects may indicate that other factors, such as variations in streamflow, snowmelt, and runoff; water quality of springs and seeps; and land-use changes, may be affecting salinity in the Colorado and Gunnison River Basins in Colorado.

KEY TERMS: salinity; dissolved solids; trends; Upper Colorado River Basin; Gunnison River Basin; Colorado.

¹Hydrologists, U.S. Geological Survey, Water Resources Division, Colorado District, MS 415, Box 25046, Denver Federal Center, Denver, Colorado, 80225. Phone: 303-236-2101 ext. 231, Fax 303-236-4912, Email: njbauch@usgs.gov, nspahr@usgs.gov.