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<br />Chapter 2 <br /> <br />Lake Havasu backs up behind Parker Dam for about 45 miles and serves as a forebay from which <br />the Metropolitan Water District of Southern California pumps water into the Colorado River <br />Aqueduct. Lake Havasu also serves as a forebay for the Central Arizona Project Havasu Pumping <br />Plant and pumps water into the Hayden Rhodes Aqueduct. Alamo Dam and Reservoir, on the <br />Bill Williams River, is used to control floods originating above and below Alamo Dam. <br /> <br />Headgate Rock pam, Palo Verde Diversion Dam, and Imperial Dam all serve as diversion <br />structures with very little storage. Imperial Dam, located some 150 miles downstream from Parker <br />Dam, is the major diversion structure for irrigation projects in the Imperial Valley and Yuma <br />areas. It diverts water on the west bank to the All American Canal, which delivers water to the <br />Yuma Project in Arizona and California and Imperial and Coachella Valleys in California. It <br />diverts on the east bank to the Gila Gravity Main Canal. <br /> <br />The Senator Wash Dam, an offstream storage facility, also affords regulation in the vicinity of <br />Imperial Dam and assists in the delivery of water to Mexico. This facility is used for pumpback <br />storage and recreation. <br /> <br />The Morelos Dam, located just below the Northerly International Boundary with Mexico, is the <br />last dam on the Colorado River. This small diversion dam diverts water into the Alamo Canal, <br />which delivers water to northern Mexico. <br /> <br />GEOLOGY AND SOilS <br /> <br />The geology of the Colorado River Basin is highly varied. Igneous, metamorphic, and sedi- <br />mentary rock types are present and range in age from over 500 million years old to recent alluvial <br />deposits. Structural features, including anticlines, domes, and faults, contribute to both the <br />topographic relief and the geohydrology of the region. <br /> <br />Several of the sedimentary fonnations in the Basin were deposited in marine or brackish water <br />environments. Occurrences of heckled :lnd disseminated sodium chloride (halite) and calcium <br />sulfate (gypsum) are observed, as are clays with high contents of exchangeable sodium and <br />magnesium. <br /> <br />The soils of the Basin closely resemble the geologic fonnations from which they were derived. <br />Residual soils derived from shale or sandstone are generally shallow. These soils can contain <br />appreciable soluble mineral content due to residual and secondary mineral fonnation from the <br />parent material. Upon weathering or irrigation, salts may accumulate on or near the surface due to <br />evaporation or consumptive use by plants. <br /> <br />8 <br />