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<br />002565 <br /> <br />CHAPTER III <br /> <br />PRESENT WATER SUPPLIES AND USES <br /> <br />Lower Colorado River Mainstream Water <br /> <br />Water Supply--The Colorado River Compact of 1922 divided the <br />Colorado River into the Upper and Lower Basins at Lee Ferry, about <br />1.3 miles below the mouth of the Paria River. The annual historic <br />and virgin flows at Lee Ferry since 1896 are graphically illus- <br />trated on figure 5. The undepleted, or virgin, flow at Lee Ferry <br />since 1896 averaged about 14.9 million acre-feet annually. Histori- <br />cally, during the same period about 13.4 million acre-feet annually <br />passed this point. Historic net gains, Lee Ferry to Hoover Dam, <br />averaged 937,000,acre-feet annually during the 54-year period, <br />1909-62. The estimated inflow to Lake Mead that would have occurred <br />during the wet and dry periods of historic Colorado River record is <br />shown below: <br /> <br />Inflow to Lake Mead <br /> <br /> Estimated <br /> Average Annual Flow <br />(in millions of acre-feet) <br />1896-1908 1909-29 1930-62 1909-62 <br />14.26 16.13 10.90 12.93 <br /> 1.14 .81 .94 <br /> 17.3 11.7 13.9 <br /> <br />Colorado River <br />at Lee Ferry <br /> <br />Net gains <br />Lee Ferry to Hoover Dam <br /> <br />Below Hoover Dam, the chief tributaries to the mainstream are <br />the Bill Williams and Gila Rivers. The~timated average flow of <br />the Bill Williams River at Planet, 1930-61, is about 77,000 acre- <br />feet annually. The Gila River, completely developed, no longer <br />materially contributes to the Colorado River except during major <br />floods. Since 1941, the annual flow near Dome averaged about <br />2,400 acre-feet, the greater portion of which is drainage water from <br />the Wellton-Mohawk Division of the Gila Project. The 12,000 square <br />miles of other drainage area below Hoover Dam is estimated to con- <br />tribute an average of 50,000 acre-feet annually. Total tributary <br />inflow to the mainstream below Hoover Dam, for the period 1930-61, <br />is therefore estimated to average about 130,000 acre-feet annually. <br />Between dry and wet years inflow has varied from 25,000 to over <br />500,000 acre-feet. Ground-water contributions to the mainstream <br />supply below Hoover Dam are unknown but are considered to be nominal. <br /> <br />111-1 <br />