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<br />w <br />(Jl <br />0') <br />~ <br /> <br />CHAPTER II. SALINITY OF THE RIVER <br /> <br /> <br />The Colorado River system drains 244,000 square miles <br />of the western United States and a small portion of <br />northern Mexico. Its waters serve some 2.5 million people <br />within the United States portion of the Basin and through <br />export provides full or supplemental water supply to <br />another 16.0 million people outside the Basin. The <br />regional economy is based on irrigated agriculture, <br />livestock grazing, mining, forestry, manufacturing, oil and <br />gas production, and tourism. About 2.5 million acres are <br />irrigated within the Basin and hundreds of thousands of <br />acres are irrigated by waters exported from the Basin. The <br />Colorado River also serves about 1.5 million people and <br />5:00,000 irrigated acres in Mexico. <br />,Salinity!/ has long been recognized as one of the <br />major problem"; of the river. The Colorado, like most <br />western rive~s, increases in saJinlty from its headwaters <br />to its mouth, carrying a salt load of about 9 million tons <br />annually past Hoover Dam. In addition to total salt load <br />(tons), this report also examines salinity in terms of <br />concentration (mg/l). The river's salt load is the result <br />of both natural and human causes. Natural causes include <br />salt contribution of saline springs, non-point ground water <br />flow into the river system, erosion and dissolution of <br />sediments, and the concentrl;lting effects of evaporation and <br />transpiration. Human-caused increases in salinity <br />concentration result from the diversion (including <br />out-of-basin exports), consumptive water use, and salt <br />loading. Studies of the hydrosalinity of the river <br />indi~ate that about half of the salinity of the river can <br />be attributed to natural sources and the other half are the <br />result of human activities,as shown in Figure 1. <br /> <br /> <br />47% Nltu,a/ Sources <br />37% I,rlption <br />'2% Reservoi, EWlPO,etion <br />3% exports <br /> <br />,,, M&I <br /> <br />Figure I . - Salinity sources. <br /> <br />II Salinity is a measure of the total dissolved solids of <br />a water sample including all inorganic material in <br />solution, whether ionized or not. The principal <br />constituents found in Colorado River water are: <br />calcium, magnesium, sodium, sulfate, chloride and <br />bicarbonate. The terms salinity and total dissolved <br />solids are considered equivalent. <br />-6- <br />