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<br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />,.... <br />I\;! <br />w <br />r-, <br /> <br />CAUSES OF SALINITI <br /> <br />natural source, abandoned saline flo~ing wells are shown with the natural <br />springs. The largest contributors in the Upper Basin are the Dotsero <br />and Glenwood Springs which supply the major part of the salts from point <br />sources. <br /> <br />Lower Basin.--The inflow for the reach the Colorado River at Lees <br />Ferry to the Colorado River near Grand Canyon has varied from a low of <br />18.000 acre-feet in 1949 to a high of 939,000 acre-feet in 1941 with an <br />average annual inflow for the 1941-74 period of 313,000 acre-feet. The <br />total tons of inflow in this reach varied from a low of 498,000 tons in <br />1962 to a high of 2,022,000 tons in 1941 with an average inflow of <br />1,088.000 tons per year. Springs in the lower portion of the Little <br />Colorado River contribute about half of the measured increase in dissolved- <br />solids discharge in the Colorado River between Lees Ferry and Grand <br />Canyon. <br /> <br />The annual inflow in acre-feet and tons with the average concen- <br />tration for each year is shown in Table B for this reach. <br /> <br />Large amounts of dissolved solids are also added to the Colorado <br />River between Grand Canyon and Hoover Dam. Some of this results from <br />the solution of material in the bed of Lake Mead, but like the reach <br />above Grand Canyon, most is contributed by springs and tributary inflows. <br /> <br />For the whole reach from Glen Canyon Dam to Hoover Dam recent <br />studies have been made by the Geological Survey and the Bureau of Recla- <br />mation to provide information about the contribution of springs to the <br />Colorado River. <br /> <br />Major springs and spring-fed tributaries which could be measured <br />were found to contribute about 760,000 tons of dissolved solids annually <br />to the Colorado River between Glen Canyon Dam and Lake Mead. Storm <br />runoff in small tributaries in this reach of the Colorado River con- <br />tributes an unknown, but probably much smaller, load to the river. The <br />contribution of dissolved solids by these sources of inflow between Glen <br />Canyon and Lake Mead equals about 10 percent of the average dissolved- <br />solids load of the Colorado River at Lees Ferry. <br /> <br />The annual dissolved-solids contributions of the measured major <br />springs, streams, and spring-fed tributaries to the Colorado River <br />between Glen Canyon Dam and Lake Head and to the Virgin River are <br />summarized in Table C. <br /> <br />29 <br />