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<br />. <br /> <br />/ <br />I <br /> <br />. <br /> <br />w <br />OJ <br />lV <br />~ <br /> <br />In addition, the estimated virgin flow of the Colorado is a mat- <br />ter of some dispute, The estimated average virgin flow at Lee Ferry <br />(the point dividing the Upper and Lower Basins) used in negotiating the <br />1922 Colorado River Compact was 16.8 million acre-feet (maf). Based on <br />this estimated flow, the Compact decrees that delj.veries to the Lower <br />Basin not fall below 75 maf for any ten-year period. Unfortunately, no <br />period since the Compact was signed has matched that flow. The 1922- <br />1977 annual average indicates a flow of 13.8 maf. The historic record <br />used in negotiating the Upper Colorado River Basin Compact in 1948 esti- <br />mates a flow of 15.6 maf. The actual historic flow of the River has <br />dropped as low as 5.5 maf (during the 1977 drought), <br /> <br />This variability of flow in the River seriously complicates <br />water use planning in both the Upper and Lower Basins: the Upper Basin <br />has a legal and historic obligation to deliver an average 7.5 maf of <br />water each year to the Lower Basin; and, in order to meet that obliga- <br />tion, even using the large reservoir system on the River as a storage <br />buffer, the Upper Basin cannot count on having a full allotment of water <br />available for consumptive use in any given year. <br />. 11'11 <br />A further matter of/dispute over the water supply and its avail- <br />ability relates to the ~U.S,-Mexican Treaty. That treaty obligates <br />the United States to deliver 1.5 maf of Colorado River water each year <br />to Mexico, Although the Colorado River Compact states that the obliga- <br />tion is, to the Lower Basin unless there is a water shortage, it is <br />still a matter of dispute whether the 1.5 maf ought to be subtracted <br />equally from the Upper and Lower Basins, totally from the Lower Basin, <br />or on a proportionate basis from the waters held in each basin. In any <br />case, the obligations of the Treaty add to the uncertainty of the water <br />supply. <br /> <br />Salinity of the River. Exacerbating the heavy demand upon the <br />water resources of the Colorado River Basin is the salinity of the water <br />which increases steadily as the River flows toward the ocean. Much (65 <br />percent3) of the salt load occurs naturally as the river and its tribu- <br />taries dissolve minerals and salts from river beds, receive runoff which <br />has transversed saline land, and are fed by saline springs. The hot, <br />dry climate increases river and reservoir evaporation, further concen- <br />trating these salts. Even without the developments created by man the <br />Colorado would remain saltier than most other rivers in this country. <br /> <br />Irrigated agriculture and livestock grazing is the major man- <br />created contributor to Colorado River salinity (34 percent), Irrigated <br /> <br />3U,S, Environmental Protection Agency, The Mineral Quality Prob- <br />lem in the Colorado River Basin: Summary Report (Washington, D.C.: <br />Government Printing Office, 1971), p, 18. <br /> <br />2 <br /> <br />) <br />I <br />I <br />! <br /> <br />.. <br />