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Colorado River Basin Project
Central Arizona Project - Colorado River Basin Project
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General Description| Plan| Development| Benefits


General Description

The Colorado River Basin Project provides a program for further comprehensive development of the water resources of the Colorado River Basin and the provision of additional and adequate water supplies for use in the upper and lower Colorado River Basins. The project was authorized for regulating flows of the Colorado River; controlling floods; improving navigation; providing for storage and delivery of the waters of the Colorado River for reclamation of lands, including supplemental water supplies, and municipal, industrial, and other beneficial purposes; improving water quality; providing for outdoor recreation facilities; improving fish and wildlife conditions; and generation and sale of electric power. It also was intended to provide a program for development of a regional water plan; for the satisfaction of the requirements of the Mexican Water Treaty; and long-range augmentation studies of the Colorado River. A 10-year moratorium was declared, from the date of the act (September 30, 1968), against making any studies or plans for the importation of water into the Colorado River Basin from any river drainage basin lying outside the natural drainage basin of the Colorado River. This moratorium has since been extended.

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Facility Descriptions
Central Arizona Project, Arizona

The Central Arizona Project (CAP) is a multipurpose water resource development and management project that provides irrigation, municipal and industrial water, power, flood control, outdoor recreation, environmental enhancement and sediment control.  In addition, the project will eventually provide delivery of Tribal homeland water, partial settlement of Indian water rights claims, and economic benefits accruing from the leasing of Indian agricultural water rights to municipal entities.  Water is provided to lands in Maricopa, Pinal and Pima counties, and to several communities, including the metropolitan areas of Phoenix and Tucson. Authorization also was included for development of facilities to deliver water to Catron, Hidalgo, and Grant Counties in New Mexico, but these facilities have not been constructed because of cost considerations, a lack of demand for the water, lack of repayment capability by the users, and environmental constraints.

For more information, see the Central Arizona Project.

Dixie Project, Utah

The Dixie Project, proposed for Washington County, Utah, was reauthorized under the Colorado River Basin Project, which provided for its financial integration and participation in the Lower Colorado River Basin development fund.

The project's authorized purpose was to utilize waters from the Virgin and Santa Clara Rivers to provide supplemental irrigation water to about 8,900 acres of developed land and a full supply to about 4,600 acres of new land, as well as municipal and industrial water to the city of St. George, Utah. However, the project was dropped from further consideration when an agreement could not be reached with the Washington County Water Conservancy District for repayment of construction costs.

Upper Basin Projects

The Colorado River Basin Project provides for reimbursement of the Upper Colorado River Basin fund for expenditures made from that fund to meet deficiencies in the generation at Hoover Dam during the filling of Lake Powell.

The construction of five projects in the Upper Colorado River Basin also was provided for in the Colorado River Basin Act. These projects were to be constructed concurrently with the Central Arizona Project and are listed under 'Authorization.'


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There is archaeological evidence that some 2,000 years ago irrigation canals were built and maintained by the ancient Hohokam Tribe (Hohokam is a Pima Indian word which, loosely translated, means `the people who have gone away`) in the Salt River Valley of the Colorado River Basin near present-day Phoenix, Arizona. The Hohokams probably began settlement of the valley as early as 300 B.C. and abandoned it about 1400 A.D., possibly because irrigation raised the water table, which induced water-logging and alkali problems. This would have rendered much of the land unfit for cultivation. Other Indians practiced irrigation in the vicinity before and during the period of exploration of this region of the Southwest by European explorers and settlers.

The next irrigators of the Colorado River Basin were Jesuits who established themselves at the old missions of Cuevavi and San Xavier in Arizona in 1732. In the period of 1768-1822, considerable irrigation was practiced along the Santa Cruz River near the missions and the Spanish presidios of Tubac and Tucson.

After the Gadsden Purchase in 1854, a number of settlers began to develop irrigation in Arizona. The Federal Government first attempted to reclaim arid land on the Colorado River Indian Reservation in Arizona and California in 1867. And in 1883, the Grand Valley Canal, a private development, was started to irrigate large areas in Grand Valley on the western slope of the Rocky Mountains in Colorado.

The possibility of exporting water from the Colorado River to Imperial Valley in California was considered before the Civil War. After passage of the Reclamation Act by Congress in 1902, the Reclamation Service (Bureau of Reclamation since 1923) began investigations to determine the feasibility of constructing large irrigation works in the Colorado River Basin.

In the early 1900s, the growth potential of the Pacific Southwest was realized, and the underlying importance of the waters of the Colorado River Basin to its growth was understood. To ensure that this great resource potential did not become dedicated to the benefit of any one area or State, a series of actions which led to interstate compacts and international treaties, State and congressional legislation, and Supreme Court decisions was instituted. Today, these constitute, in the aggregate, the 'Law of the River.'

The first action comprising the 'Law of the River' began in 1922 with approval of the Colorado River Compact by representatives of the Colorado River Basin States. The compact appropriated the waters of the Colorado River system between the upper and lower basins, but did not divide the water among the States. The Compact was ratified as a six-state compact by the Boulder Canyon Project Act of 1928, which also authorized the construction of Hoover Dam and the All-American Canal system.

This act and the Boulder Canyon Project Adjustment Act of 1940 gave certain key responsibilities to the Secretary of the Interior relative to the comprehensive and coordinated development of the Colorado River. The Mexican Treaty of 1944 obligated the United States to deliver 1,500,000 acre-feet of Colorado River water annually to Mexico. The Upper Colorado River Basin Compact of 1948 divided the Upper Basin Colorado River  apportionments for beneficial consumptive use among the Upper Basin States. This, in turn, led to the Colorado River Storage Project Act of 1956 which established an Upper Basin Development Fund and authorized the initial phase of the comprehensive Upper Basin plan of development.

In January 1963, the Secretary of the Interior began studies to develop a regional Colorado River plan. The Secretary`s report on the Pacific Southwest Water Plan was submitted January 21, 1964, and on March 9, 1964, the Senate Subcommittee on Irrigation and Reclamation began hearings on the plan, including the Central Arizona Project. On September 30, 1968, the Congress passed Public Law 90-537 authorizing the Colorado River Basin Project and established the Lower Colorado River Basin Development Fund.


Comprehensive investigations of development of the water and land resources of the Colorado River Basin were authorized by the Boulder Canyon Project Act and the Boulder Canyon Project Adjustment Acts. The Secretary of the Interior submitted his report and the individual project supplemental informational reports of the Western United States Water Plan in January 1964. Presented in the report was a regional water plan to relieve the acute water problem of the Pacific Southwest. The supplemental reports presented additional information on proposed projects.

The Lower Colorado Region State-Federal Interagency Group for the Pacific-Southwest Interagency Committee of the Water Resources Council prepared a report and appendixes of the Lower Colorado River Comprehensive Framework Studies. The report was issued in June 1971 and presented a framework program for the development and management of the waters and related land resources of the Lower Colorado Region. The Colorado River Basin Project Act of 1968 directed the Secretary of the Interior to conduct reconnaissance investigations for the purpose of developing a general plan to meet the future water needs of the 17 Western States lying wholly or in part west of the Continental Divide. The Westside Study Report of the Critical Water Problems Facing the Eleven Western States was issued in April 1975.


The Colorado River Basin Project was authorized by the act of September 30, 1968 (Public Law 90-537, 82 Stat.885). Authorized developments were:


Central Arizona Project, Arizona, and New Mexico; Dixie Project, Utah.


Animas-La Plata, San Juan River, Colorado and New Mexico; Dolores Project on the Dolores River in Colorado; Dallas Creek Project on the Uncompahgre River and its tributaries in west-central Colorado; West Divide on a series of Colorado River tributaries in Colorado; San Miguel on the San Miguel River in southwestern Colorado.

Guidelines were established in the authorizing legislation for the investigations of augmentation of the Colorado River, protection for areas of potential export, the Mexican Water Treaty obligations, the Lower Basin shortage formula, and the criteria for the coordinated operation of Lake Powell and Lake Mead.


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See Benefits of each facility under individual project/facility descriptions.


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Last updated: Oct 05, 2009