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IMPERIAL IRRIGATION DISTRICT FAcr Imperial Dam. Located about 20 miles northeast of Yuma, Arizona/Imperial Dam is the diversion point for water flowing from the Colorado River to the All-American Canal, which serves Imperial and Coachella valleys. Imperial Dam was a first for the world of irrigation, where river water would be held and then ~ed into a giant. desilting plant before release into the All-American Canal. Background Construction of Imperial Dam and its desilting works began in 1935 and was completed rnJ938 tinder theauthorization of the Boulder Canyon,)?rojectAct of 1928. Imperial Dam's main function 'is diversion of Colorado River water to the All-American Canal, the Coachella Canal and the Yuma Project; The need for Imperial Dam as a diversion point dates back to the mid-1850s when settlers began searching for the means and the location to divert Colorado River water to the Imperial Valley. Colorado Riverwater was first delivered to the Imperial Valley through the Imperial (Alamo) Canal inJune 1901. George Chaffey, president of the California Development Company, constructed headworks and a canal to take water from the Colorado River at a point in California immedi- ately above the international boundary. The river headgate, known as the Chaffey Gate, was con- structed as a temporary wooden gate on the intake canal about 500 feet north of the international boundary to control inflow of water into the canal. A mote permanent headgate, known as Hanlon Heading, was constructed in 1906 to replace Chaffey Gate. The following year, Southern Pacific Company assumed ownership of the bank- rupt California Development Company. The Imperial Irrigation District was formed in 1911, and by 1916, it had acquired all California Devel- opment assets. There was a growing realization that an AlI- American Canal, located entirely within the United States, was needed. The first field surveyEor the canal was conducted in 1913. However, the Bureau of Reclamation reported that such acanal would be impractical without a dam to control flooding. In the meantime, the District found it increasingly difficult to control the amount of bedload silt brought into the canal system from the Alamo River. So, in 1918 the Rockwood Heading was built one and one-fourth miles upstream from Hanlon Heading to serve as a diversion point and adesilting works. As part of a 1918 contract with the federal government, the llD received the right to use' Laguna Dam (completed in 1909 under the federal Reclamation Act) as a diversion for the All-Ameri- can Canal. But that right was never exercised. In 1919, the Bureau issued its recommendation for an All-American Canal and government construction of a storage reservoir on the Colorado River. The final result of the negotiations with the Bureau of Reclamation was the Boulder Canyon Project Act in 1928 which authorized construction of Boulder (Hoover) Dam, Imperial Dam andthe All-American Canal. Today, the storage capacity of the reservoir above Imperial Dam is minor. Due to its shallow depth, the original storage space was soon filled with silt and sand. The reservoir area now consists of a shallow lake with well-defined channels to the All-American Canal and Gila Headworks. Structures The All-American Canal trashrack and headgates are located adjacent to the California abutment of the dam. Three desilting basins (de- sign capacity 4,000 c.f.s. each) remove the sand from the river water before it passes to the All- American Canal. The sand and sediment removed Continued on back External Affairs Department · P. O. Box 937 · 333 E. Barioni Blvd. . Imperial, CA 92251