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<br />PART II <br /> <br />DESCRIPTION OF BASIN <br /> <br />e <br /> <br />The flow at various points in the Colorado River Basin for the <br />1941-83 period is given in Tables 1 through 20 at the end of this <br />report. The records of flow depict characteristic-wide fluctuations <br />month to month and considerable variation year to year. The storage <br />reservoirs now reduce some of the fluctuation in the reaches below <br />the major dams. <br /> <br />C. Reservoir Storage <br /> <br />Wet and dry cycles have played a significant role in bringing about <br />the development of the Colorado River Reservoir complex. In the past, <br />the annual flow of the river has varied from less than 6 million acre- <br />feet to over 20 million acre-feet per year. The reservoir system allows <br />storage of sufficient water to maintain the flows of the river to meet <br />downstream needs during dry periods. <br /> <br />e <br /> <br />The construction and filling of the main stem reservoirs of the <br />Colorado River Basin have brought about signi{icant changes in the flow <br />patterns of the river. In addition to the major reservoirs, numerous <br />smaller reservoirs have been bui It on many of the tributaries. Since <br />major storage began with Lake Mead in 1935 and concluded with the fill- <br />ing of Lake Powell in 1980, the Colorado River Basin reservoirs now have <br />a combined storage capacity equal to approximately four times the total <br />average annual virgin (undepleted) flow of the entire Colorado River. <br /> <br />The flows of the San Juan River are controlled by the Navajo Dam, <br />the Green River by Fontenelle and Flaming Gorge Dams, and the Gunnison <br />River by the Wayne N. Aspinall Unit Dams. Glen Canyon Dam is the only <br />major dam on the main stem of the Colorado above Lee Ferry, but it will <br />permit control of almost all flows leaving the Upper Basin. <br /> <br />Lake Mead, formed by Hoover Dam, provides most of the storage and <br />regulation in the Lower Colorado River Basin, providing for irrigation, <br />municipal and industrial (M&I) uses, power generation, flood control, <br />recreation, and other beneficial uses. <br /> <br />Lake Mohave, the reservoir formed by Davis Dam, backs water at <br />high stages about 67 miles upstream to the tailrace of Hoover Power- <br />plant. Storage in Lake Mohave is used for some reregulation of releases <br />from Hoover Dam, for meeting treaty requirements with Mexico, and for <br />developing power head for the production of electrical energy at Davis <br />Powerplant. The river flows through a natural channel for about 10 <br />miles below Davis Dam at which point the river enters the broad Mohave <br />Valley 33 miles above the upper end of Lake Havasu. <br /> <br />e <br /> <br />Lake Havasu backs up behind Parker Dam for about 45 miles and <br />serves as a forebay from which the Metropolitan Water District of <br />Southern California pumps water into the Colorado River Aqueduct. Lake <br />Havasu also serves as forebay for the Central Arizona Project pumping <br />plants and aqueducts. Lake Havasu and Alamo Dam and Reservoir, on the <br /> <br />9 <br />