7638 - Laserfiche WebLink

Home Browse Search

. . of the Interior 1987). The Colorado River at its headwaters in the Rocky Mountains has a salinity of 50 mg/l, but contributions from various natural and anthropogenic sources increases salinity up to 890 mg/l at Imperial Dam near the Mexican border (Bureau of Reclamation 1978; Fig. 11). Dissolved-solids concentrations tend to be inversely correlated with discharge (Hem 1970), which varies seasonally in the Colorado River basin. Salinity levels in the Green River drainage stem from erosion, overgrazing, irrigation return, and groundwater discharge sources in the Big Sandy River in Wyoming, and from the White, Price, San Rafael and Dirty Devil drainages in Utah. Delong (1977) estimated that the 113 km reach of the Green River between Fontenelle Reservoir and Green River, Wyoming, including the lower 48 km of the Big Sandy River, sustained an average gain of 103,400 mt of dissolved solids/year. This dissolved solids load was comprised of sodium and sulfate, which comprise 84% of the dissolved solids load from the Big Sandy River. The Douglas Creek member of the Green River Shale is a major source of freshwater for the basin; however, groundwater from the Green River formation produces more than 9,870 mg/l of dissolved solids (Holmes 1980). Significant natural contributions of salts are added by the Meeker Dome in the upper portion of the White River, and by Piceance Creek. The White River contributes 284,000 tons of dissolved salts/year, including elevated concentrations of barium, iron, and manganese (Boyle et al. 1984). Abandoned oil test holes contribute more than 15% of the salinity in that drainage (Masse and Adams 1983). Natural sources of salinity in Colorado are derived from the Paradox Valley in the Dolores River drainage and from Glenwood Springs, and anthropogenic sources from agricultural return-flow include water from the Grand Valley, McElmo Creek, and the lower Gunnison River drainages. The San Juan River in New Mexico contributes 450,000 mt of salts to the Colorado River drainage, and the little Colorado River and Havasu Creek add to the river's salinity in Arizona. The Colorado River carries 8.2 million mt of salt annually past Hoover Dam (U.S. Bureau of Reclamation 1986), of which 47% is derived from natural sources and 53% is man-induced. Anthropogenic contributions are attributed to salt loading and salt concentration. Irrigation is responsible for about 37% of the salt loading as salts are leached from the soil and returned to the river, and reservoir evaporation is responsible for an additional 12% of the salt loading. Water diverted for beneficial uses not returned to the river concentrates the river's salt burden into a smaller volume of water. . I I I . . . . 25 .