7409 - Laserfiche WebLink

Home Browse Search

6 Chapter 2-Description of Basin offlow depict wide fluctuations from month to month and considerable variations from year to year. The storage reservoirs presently reduce some of the fluctuation in the reaches below the major dams. RESERVOIR STORAGE Wet and dry cycles have played a significant role in bringing about the development of the Colorado River reservoir complex. In the past, the annual flow ofthe river has varied from less than 6 million to more than 20 million acre-feet per year. The reservoir system allows sufficient storage water to maintain the flows of the river to meet downstream needs during dry periods. The construction and filling of the main stem reservoirs of the Colorado River Basin have brought about significant changes in the flow patterns of the river. In addition to the major reservoirs, numerous smaller reservoirs have been built on many of the tributaries. Since major storage began with Lake Mead in 1935 and concluded with the filling of Lake Powell in 1980, the Colorado River Basin reservoirs now have a combined storage capacity equal to approximately four times the total average annual virgin (undepleted) flow of the entire Colorado River. The flow of the San Juan River is controlled by the Navajo Dam, the Green River by Fontenelle and Flaming Gorge Dams, and the Gunnison River by the Wayne N. Aspinall Unit Dams. Glen Canyon Dam is the only major dam on the main stem of the Colorado River above Lee Ferry, but it will permit control of almost all flows leaving the Upper Basin. Lake Mead, formed by Hoover Dam, supplies most of the storage and regulation in the Lower Colorado River Basin. Lake Mead provides water for irrigation, municipal and industrial uses, power generation, flood control, recreation, and many other beneficial uses. Lake Mohave, the reservoir formed by Davis Dam, backs water about 67 miles upstream to the tailrace of Hoover Powerplant. Storage in Lake Mohave is used for some reregulation of releases from Hoover Dam, for meeting treaty requirements with Mexico, 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 below Davis Dam at which point the river enters the broad Mohave Valley 33 miles above the upper end of Lake Havasu. Lake Havasu backs up behind Parker Dam for about 46 miles and serves as a forebay from which The Metropolitan Water District of Southern California pumps water into the Colorado River Aqueduct. Lake Havasu also serves as forebay for the Central Arizona Project, Havasu pumping plant and pumps water into the Hayden Rhodes Aqueduct. Alamo Dam and Reservoir, on the Bill Williams River is used to control floods originating above and ' below Alamo Dam. Headgate Rock Dam, Palo Verde Diversion Dam and Imperial Dam all serve as diversion ' structures with practically no storage. Imperial Dam, located some 150 miles downstream from Parker Dam, is the major diversion structure to irrigation projects in the Imperial Valley and Yuma areas. It diverts water on the right bank to the All American Canal, which delivers water to the Yuma Project in Arizona and California, and Imperial and Coachella Valleys in California. It diverts on the left bank to the Gila Gravity Main Canal. j j The Senator Wash Dam, an offstream storage facility, also affords regulation in the vicinity of Imperial Dam and assists in the delivery of water to Mexico. This facility is used for pumpback storage and recreation. The 1tforelos Dam, located just below the Northern International Boundary with Mexico is the last dam on the Colorado River. This ' small diversion dam diverts water into the Alamo Canal which delivers water to northern Mexico. GEOLOGY AND SOILS The geology of the Colorado River Basin is highly varied. Igneous, metamorphic, and sedimentary rock types are present and range in age from approximately 625 million years old to recent alluvial deposits. Structural features ,