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. o CO N 00 . . DESCRIPTION OF BASIN (Continued) The Green River, its major tributary, rises in western Wyoming and discharges into the Colorado River in southeastern Utah--730 river miles (1175 km) south of its origin and 220 miles (350 km) above Lee Ferry. The Green River drains 70 percent more area than the Colorado River above their junction but produces only about three-fourths as much water, The Gunnison and the San Juan are the other principal tribu- taries of the Upper Colorado River. The flows of the San Juan River are now controlled by the Navajo Dam, the Green River by Fontenelle and Flaming Gorge Dams, and the Gunn- ison River by the Curecanti Unit Dams. Glen Canyon Dam is the only major dam on the main stem of the Colorado above Lee Ferry, but it will permit control of almost all flows leaving the Upper Basin. The flow at various points in streams in the Colorado River Basin for the 1941-76 period is given in Tables 1 through 20. The records of flow depict the characteristic wide fluctuations from month-to-month and the considerable variation from year-to-year. The storage reservoirs now level out some of the fluctuations in the reaches below the dam. The natural drainage area of the lower Colorado River below ~ee Ferry and above Imperial Dam is about 75,100 square miles (195,000 km ). This section storage and Imperial Dam. of the river is now largely controlled by a series of diversion dams starting with Hoover Dam and ending at At the present time there is no significant storage on the main river or on the tributaries between Glen Canyon Dam and Lake Mead, The intervening tributary inflow is erratic but amounts to almost enough to offset the evaporation from Lake Mead. Lake Mead provides most of the storage and regulation in the Lower Colorado River Basin with the water being stored for irrigation and municipal and industrial uses, generation of electrical power, flood control, and other beneficial uses. Lake Mohave, the reservoir formed by Davis Dam, backs water at high stages about 67 miles (108 km) upstream to the tailrace of Hoover Power- plant. Storage in Lake Mohave is used for some reregulation of releases from Hoover Dam, for meeting treaty requirements with Mel<ico, and for developing power head for the production of electrical energy at Davis Powerplant. The river flows through a natural channel for about 10 miles (16 km) below Davis Dam at which point the river enters the broad Mohave Valley 33 miles (53 km) above the upper end of Lake Havasu. 10