Laserfiche WebLink
<br />. <br /> <br />. <br /> <br />2 <br /> <br />~ <br />o <br />o <br />u..J <br /> <br />downstream of Glen Canyon Dam. In recent years, 1975 through 1979, <br />the salinity at Lee Ferry averaged 576 mg/l, and the annual salinity <br />at Imperial Dam, the last diversion point in the United States, <br />averaged 818 mg/l. <br /> <br />SOURCES OF SALINITY <br /> <br />Salinity increases result from natural conditions and man's <br />activities through two basic processes: (1) salt loading due to the <br />pick-up of mineral salts from natural and man-made sources, and <br />(2) salt concentrating due to the loss of water from the systerr. <br />through evaporation, plant transpiration, and out-of-basin exports <br />of low s~linity water. <br />Natural salinity increases result from salt accretions from <br /> <br />natural sources such as saline springs, ground water and surface <br />runoff, as well as from water lost to the river system from con- <br />sumption by phreatophytes and other riparian vegetation and by <br />evaporation from the river's water surface and backwater areas. <br />Man's impact on the river's salinity began when pioneering <br />farmers moved into the Coloraio River Basin. Even today, irrigation <br /> <br />remains the main use of river water. Irrigation consumes a portion <br />of the water through evapo-transpiration, resulting in an increase <br />in concentration of the dissolved salts. In addition, salt is picked <br />up frDm the soil as applied water percolates through the soil and <br /> <br />returns to the river as irrigation return flow. Irrigated areas in <br /> <br />the Upper Basin have pickup rates ranging from as little as 0.1 ton <br />per acre farmed per year to in excess of 8.0 tons per acre. Many <br />areas have been farmed for over 80 years and still have pickup rates <br />in the 8 ton per acre range due to saline formations lli1derlying the <br />