WSP12351 - Laserfiche WebLink

Home Browse Search

Reservoirs have a complex effect on downstream water quality. The primary effect of a large reservoir is a decrease in the seasonal and annual variation ~ in dissolved-solids concentration downstream from the reservoir, because of ~ mixing within the reservoir (Moody and Mueller, 1984), Downstream from Lake ~ Powell, the largest reservoir in the Upper Colorado River Basin, the standard ~ deviation of monthly dissolved-solids concentrations decreased from 299 milligrams per liter before the reservoir began filling (1941-62) to 72 milligrams per liter after initial filling was completed (1965-83), Similarly, the standard deviation of annual dissolved-solids concentrations decreased from 106 to 42 milligrams per liter (Liebermann and Nordlund, 1988). In comparison to irrigation, transbasin diversions and reservoir storage, other types of water-resources development in the Upper Colorado River Basin have had only a minor effect on dissolved-solids concentration and discharge. Previous Investigations Early reports on the Upper Colorado River Basin (LaRue, 1916; Follansbee, 1929; Wooley, 1930) focused on water-supply concerns and made little or no mention of water quality. Stabler (1911) presented chemical analyses of samples collected from several locations in the basin during 1905 and 1906, but he did not include any interpretive material, The first comprehensive study of water quality in the Upper Colorado River Basin was conducted by Iorns and others (1965). They estimated the mean annual dissolved-solids discharge at 30 locations in the basin assuming hydrologic conditions from water years 1914-57 and the 1957 level of water- resources development, The mean annual values of dissolved-solids discharge then were apportioned into the quantities derived from natural sources and from anthropogenic sources. In a similar study, the U.S. Environmental Protection Agency (1971) evaluated the relative contribution of dissolved solids from natural and anthropogenic sources throughout the Upper and Lower Colorado River Basins. This evaluation resulted in the first predictions of increasing dissolved- solids concentrations in the Lower Colorado River Basin, which would be caused by planned water-resources development, In 1982, studies were initiated to provide more accurate, consistent estimates of historical monthly dissolved-solids loads in the basin (Kircher and others, 1984; Moody and Mueller, 1984; Mueller and Moody, 1984; Liebermann and others, 1987), The resultant estimate's were reported by the U,S. Depart- ment of the Interior (1985) and were evaluated by Liebermann and others (1988). Acknowledgments The authors wish to thank John Billings, Jerold Lazenby, and David Trueman of the U.S. Bureau of Reclamation, Salt Lake City, for providing some 6