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General Description| Plan| Development| Benefits


General Description

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.

In addition to its water supply benefits, the project also provides substantial benefits from power generation, flood control, outdoor recreation, fish and wildlife conservation, and sediment control. For administration and construction purposes, the project was divided into the Granite Reef, Orme, Salt-Gila, Gila River, Tucson, and Indian Distribution divisions. During project construction, the Orme Division was re-formulated and renamed the Regulatory Storage Division. Upon completion, the Granite Reef Division was re-named the Hayden-Rhodes Aqueduct, and the Salt-Gila Division was renamed the Fannin-McFarland Aqueduct.

The CAP was authorized by the Colorado River Basin Project Act of 1968. This Act provided for the Secretary of the Interior to enter into an agreement with non-Federal interests, whereby the Federal Government acquired the right to 24.3 percent of the power produced at the non-Federal Navajo Generating Station, Navajo Project. The agreement also includes the delivery of power and energy over the transmission facilities to delivery points within the Central Arizona Project service area.

Construction of the project began in 1973 with the award of a contract for the Havasu Intake Channel Dike and excavation for the Havasu Pumping Plant (now Mark Wilmer Pumping Plant) on the shores of Lake Havasu. Construction of the other project features followed. The backbone aqueduct system, which runs about 336 miles from Lake Havasu to a terminus southwest of Tucson, was declared substantially complete in 1993. The new and modified dams constructed as part of the project were declared substantially complete in 1994. All of the non-Indian agricultural water distribution systems were completed in the late 1980s, as were most of the municipal water delivery systems. Several Indian distribution systems remain to be built; it is estimated that full development of these systems could require another 20 years or longer, depending on the availability of funds and scheduling of future construction starts.

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The CAP consists of a system of pumping plants and aqueducts that convey Colorado River water from Lake Havasu to the project service area. When authorized, the plan included the construction of two dams and reservoirs (Hooker Dam and Buttes Dam) on the Gila River to provide conservation storage, flood and sediment control, and recreation opportunities, and Orme Dam at the junction of the Salt and Verde Rivers to provide flood protection and water conservation. None of these facilities have been built. Following concerns about the social and environmental impacts of Orme Dam, a new plan -- Plan 6 -- was developed to fulfill the authorized functions of this facility.  The proposed Gila River structures, although still authorized, were not constructed because of cost considerations, a lack of demand for the water, lack of repayment capability by the users, and environmental constraints. Reclamation continues to work with the State of New Mexico and other interests to collect and evaluate technical, environmental, socio-economic and cultural resource information to assist the state in determining whether to pursue a construction project or other water supply alternative in the Upper Gila Basin.

Facility Descriptions

New Waddell Dam

New Waddell Dam is located on the Agua Fria River about 35 miles northwest of Phoenix, Arizona.  The primary purpose of this facility is to store Colorado River water for CAP use.  The dam also stores Agua Fria River runoff and provides flood protection by controlling the river flows.  New Waddell Dam is located one-half mile downstream of the original Waddell Dam, which is now covered in the enlarged Lake Pleasant.  The original Waddell Dam was built by the Maricopa Water District (MWD) to provide water for MWD lands on the west side of Phoenix. MWD continues to receive its water supply from Lake Pleasant.. The dam has a crest elevation of 1,728 feet and a crest length of 4,900 feet.

Camp Dyer Diversion

Camp Dyer Diversion Dam is a concrete and masonry dam located on the Agua Fria River about 1.25 miles downstream from New Waddell Dam. The dam was originally constructed in 1926 to divert water from the river to farmlands.  It was modified in 1992 using a roller-compacted concrete method to raise the dam four feet to ensure delivery of a constant volume of water from New Waddell Dam to MWD water users. The dam has a structural height of 79 feet and a crest length of 872 feet.

Havasu Intake Channel Dike and Hayden-Rhodes Aqueduct

This dike creates an intake channel on Lake Havasu on the south side of the Bill Williams River arm of the lake, through which Colorado River water is delivered to the high-lift Mark Wilmer Pumping Plant.  A key purpose of the dike is to help prevent sediment from entering the intake channel.  The Mark Wilmer Pumping Plant lifts the water approximately 824 feet from the lake to the inlet portal of the Buckskin Mountains Tunnel. The water flows through the approximately 7-mile-long tunnel and discharged into the Hayden-Rhodes Aqueduct, which conveys it to the Phoenix metropolitan area. The Hayden-Rhodes Aqueduct consists of about 173.9 miles of open, concrete-lined canal, seven major inverted siphons with a total length of about 7.4 miles, three tunnels totaling 8.2 miles, and 0.6 mile through three pumping plants. The aqueduct has a maximum capacity of 3,000 cubic feet per second (cfs). Relift pumping stations are located at Bouse Hills, Little Harquahala Mountains, and near the Hassayampa River. The total pump lift from the Colorado River to the Phoenix service area is about 1,200 feet.

Fannin-McFarland Aqueduct

The Fannin-McFarland Aqueduct begins at the terminus of the Hayden-Rhodes Aqueduct just east of Phoenix and south of the Salt River. This aqueduct consists of the Salt-Gila Pumping Plant and about 57.5 miles of open, concrete-lined canal and one major inverted siphon with a length of 0.6 miles. The aqueduct's initial capacity is 2,750 cfs; at the end of this aqueduct, the capacity has dropped to 2,250 cfs because of water deliveries along the way. The Salt-Gila Pumping Plant lifts the water 86 feet from the Hayden-Rhodes Aqueduct to the Fannin-McFarland Aqueduct.

Tucson Aqueduct

The Tucson Aqueduct begins at the terminus of the Fannin-McFarland Aqueduct, and ends 87 miles later southwest of Tucson. This aqueduct - which includes nine pumping plants, one major inverted siphon and two major pipeline sections - has an initial capacity of 2,250 cfs, which is reduced to 200 cfs at its terminus.

Indian Distribution System Division

In 1976, project water was allocated for irrigation use by Indian Tribes in Arizona.  In 1980, the Secretary of the Interior announced a modified allocation to 309,828 acre-feet, and raised the Tribes' priority for receiving water.  The allocation of project water to non-Indian irrigation users, municipal and industrial water users,  and Indian users was approved on February 10, 1983.

In 1990, passage of the Fort McDowell Indian Community Water Rights Settlement Act authorized the Secretary to convert an agricultural district's agricultural priority water allocation to an Indian priority water allocation, increasing the Indian priority water to 343,079 acre-feet.  In 2004, the Secretary reallocated water in accordance with the Arizona Water Settlements Act (P.L. 108-451), providing up to 667,724 acre-feet under contract with Arizona Indian Tribes or available to the Secretary for future assignment to these Tribes.  Similarly, up to 764,276 acre-feet is under contract or available to non-Indian municipal and industrial entities, the Arizona Department of Water Resources, and non-Indian agricultural entities.

Currently, the only tribes with completed distribution systems are the Ak-Chin and Salt River Pima-Maricopa Indian Communities. Construction of the Gila River Indian Tribe distribution system was begun in 1998; completion is anticipated after 2012.

Buttes Dam and Reservoir -- Gila River Division

Buttes Dam was investigated for construction on the Gila River about 4 miles upstream of the existing Ashurst-Hayden Diversion Dam, northeast of Coolidge, AZ. The objective of this investigation was to develop additional CAP water through conservation of Gila River flows, to provide flood and sediment control, and to provide outdoor recreation and fish and wildlife benefits. Although Buttes Dam is an authorized part of the project, it has not been constructed and remains in deferred status.

Hooker Dam and Reservoir -- Gila River Division

Hooker Dam and other alternatives were the focus of the Upper Gila Water Supply Study. The objective of the study was to look at alternatives for developing an annual water supply of 18,000 acre-feet for a portion of western New Mexico, and for providing flood protection along the Gila River in eastern Arizona. Although Hooker Dam is an authorized part of the project, it has not been constructed and remains in deferred status.

Charleston Dam

Charleston Dam was authorized for construction on the San Pedro River southeast of Tucson to provide water conservation and flood control. A Presidential review of the project in 1977 recommended elimination of this feature from the project, and no further work or investigation was performed.

Power Sources

The Colorado River Basin Project Act allowed the federal government to participate in the non-federal Navajo Generating Station (NGS), near Page, Arizona, to provide power for pumping water along the CAP aqueduct. NGS provides electricity to customers in Arizona, Nevada and California.  Reclamation's share of NGS' annual output is 24.3 percent, or 546,750 kilowatts per year for the CAP. 

The Navajo Generating Station was constructed by the Salt River Project Agricultural Improvement and Power District of Arizona, now part of the Salt River Project (SRP). In addition to Reclamation and the SRP, other participants in the Navajo Project are NVEnergy (formerly Nevada Power Co.), Tucson Electric Power Co., and Los Angeles Department of Water and Power.

Construction of the Navajo Generating Station began in April 1970. The third, and last, generating unit was completed and placed in operation on April 30, 1976. Until energy was required for the CAP or other purposes authorized by Public Law 90-537, Reclamation`s share of the interim energy produced was sold to other participants in the station and to the Southern California Edison Co.

Transmission System

An electrical transmission system was also constructed as part of the project to supply power to pumping plants and check structures of the Hayden-Rhodes, Fannin-McFarland and Tucson aqueducts.  Power for the Hayden-Rhodes Aqueduct facilities uses pre-existing federal transmission lines and about 318 miles of new transmission lines constructed specifically for the CAP.  This new line consists of 251 miles of 230-kilovolt (kV) lines and 67 miles of radial 115-kV and 230-kV lines.  Major facilities served by the Hayden-Rhodes Aqueduct radial transmission lines are the Mark Wilmer, Bouse Hills, Little Harquahala, and Hassayampa pumping plants, and New Waddell Dam.  Construction of the Hayden-Rhodes CAP transmission system included building the Harcuvar substation in La Paz County, eight miles north of Wenden, Arizona, and a new tap station, the Hassayampa Tap, in Maricopa County, twelve miles north of Buckeye, Arizona.

Power is supplied to the Fannin-McFarlan Aqueduct via pre-existing federal transmission lines and about 36 miles of new 115-kV and 69-kV transmission lines constructed specifically for the CAP.  The major CAP facilities supplied by these transmission facilities are the Salt-Gila, Brady, Picacho, and Red Rock pumping plants.

Power is also delivered to Tucson Aqueduct facilities on pre-existing federal transmission lines and about 32 miles of new 115-kV lines constructed for the CAP.  The major features of the CAP served by these transmission facilities are the Twin Peaks, Sandario, Brawley, San Xavier, Snyder Hill, and Black Mountain pumping plants. 

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Since prehistoric times, communities have irrigated the lands along the Gila and Salt Rivers by diversion of streamflow into systems of ditches, with temporary brush and rock dams. In the late 1800s, the Pima Indians farmed possibly as much as 35,000 acres along the Gila River within the present Gila River Indian Reservation. In the 1860s, settlers began to redevelop and extend abandoned farmland along the Salt River in the vicinity of Phoenix. These early enterprises were severely handicapped by raging spring floods and low waterflows during the later stages of the growing season.

The Salt River system was almost totally controlled by a series of dams constructed between 1911 and 1946 on the Salt and Verde Rivers. The Bureau of Indian Affairs completed Coolidge Dam on the Gila River in 1928. With the increased control and regulated supply of available water, agriculture expanded and prospered along the desert plains adjoining the streams.

In the Salt River Valley, application of irrigation water led to a rise in the water table and eventually to drainage problems. By 1918, some of the soils were so waterlogged that the productivity of the irrigated area was threatened. A system of shallow wells was established to draw down the water level, and the pumped water was used for new agricultural expansion. Conditions were ideal for ground water development because of the highly permeable alluvial aquifers, a shallow water table, and good quality water. Pumping soon exceeded recharge and eventually led to a decline in water levels below the original levels.

The 1930s through 1950s brought low-cost hydropower, improved well drilling equipment, and high capacity pumps. As a consequence, the pumping rate was further increased, and ground water irrigation spread from the vicinity of the rivers throughout the central Arizona desert basins. The rate of pumping eventually far exceeded the rate of recharge, water levels dropped rapidly, and in some areas, increased pump lifts, poor water quality, and farm crop controls forced farmland out of production.

The mild winters of central and southern Arizona, the development of efficient air conditioning, and the growth of air transportation all contributed to the post-World War II expansion of urban population, particularly in the Phoenix and Tucson metropolitan areas.

As agricultural lands were taken over by urban growth, the surface and ground water supplies shifted to municipal and industrial users at approximately the same delivery requirement per acre. In areas where urban projects expanded onto raw desert areas, municipal and industrial uses contributed to the increasing overdraft of ground water supplies.


Formal investigations for the Central Arizona Project were started in 1944 by the Phoenix Development Office. The Central Arizona Project report was published as House Document No. 136, 81st Congress, 1st session, and was recommended for authorization in 1949.

During the 1950s, investigations for the project were halted while the Supreme Court heard the issue of lower Colorado River water rights in the case of Arizona v. California. In 1961, when it appeared a Supreme Court decision favorable to Arizona might be imminent, the Phoenix Development Office reopened investigations, using funds provided by the States of Arizona and New Mexico.

The resulting report, dated January 1962, documented the major changes that had taken place since the initial report. Continuous investigations through authorization provided data for reports on this project in 1964, 1967, and 1968.


The Central Arizona Project was authorized for construction under the Colorado River Basin Project Act, Public Law 90-537 (82 Stat. 885), approved September 30, 1968. In March 1977, a Presidential Review of water projects was initiated. A statement on the water projects was released April 18, 1977, recommending modification of the Central Arizona Project by the elimination of Orme, Hooker, and Charleston Dams and making federal funding contingent upon further study of groundwater supplies and institution of groundwater regulation and management by the State of Arizona.

Since Public Law 90-537 qualified the authorizing language for Orme and Hooker Dams with the phrase 'or suitable alternatives,' other plans were formulated in an effort to determine suitable alternatives for those features. The Central Arizona Water Control Study was initiated in 1978 to study alternatives to Orme Dam, to replace its authorized functions of regulatory storage and flood control on the Salt and Verde Rivers. At the same time, Reclamation was evaluating the existing dams on these rivers under the Safety of Dams Act. Because both studies were looking at modifying the existing dams, they were combined for plan formulation purposes. In November 1981, the Secretary of the Interior identified a proposed action (Plan 6). This plan included New Waddell Dam on the Agua Fria River (which was subsequently constructed) for regulatory storage purposes, Cliff Dam on the Verde River, New or Modified Roosevelt Dam on the Salt River, and Modified Stewart Mountain Dam on the Salt River for flood control and dam safety purposes. Cliff Dam was later deleted from the Plan, but Roosevelt Dam and Stewart Mountain Dam were modified as identified by the Plan.


Initial construction of the Central Arizona Project began in 1973. The backbone aqueduct was declared substantially complete in 1993, and the Plan 6 features were declared substantially complete in 1994. Non-Indian agricultural distribution systems and municipal water delivery systems have also been completed. Only two of the planned Indian distribution systems have been completed.

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The project will ultimately provide Colorado River water to nearly 700,000 acres of non-Indian agricultural lands and up to 136,900 acres of Tribal lands.

Municipal and Industrial

Over 5 million people in several municipalities in the Phoenix metropolitan area receive Colorado River water from the CAP. The delivery system for Tucson is also complete, but CAP water is being used only for groundwater recharge at present.


The Central Arizona Project has created substantial recreational opportunities. Reclamation has helped replace existing facilities and develop new facilities at the enlarged Lake Roosevelt behind Modified Roosevelt Dam, and at the enlarged Lake Pleasant behind New Waddell Dam. Additional recreational facilities have been developed and are being planned for the lands along the CAP aqueduct, including golf courses, picnic areas, hiking trails, polo fields, and equestrian paths, and for other activities like hot-air balloon, auto and boat shows, and horse and dog exhibitions.

Lake Pleasant
Theodore Roosevelt Lake
Recreational Trails
Tournament Players Club-Scottsdale
Reach 11 Sports Recreation Area-Phoenix

Fish and Wildlife

The project has also provided some fish and wildlife benefits for the area, and has greatly enhanced the sport fishery at Lake Pleasant.  In addition, Reclamation continues to construct fish barriers and perform other related work in response to a Biological Opinion issued by the U.S. Fish and Wildlife Service on the transportation of CAP water to the Gila River Basin.  The Opinion concluded that long-term deliveries of CAP water would jeopardize the continued existence of four native threatened or endangered fish species,  but provided several alternatives that could be implemented to avoid jeopardy. 

Flood Control

Although central Arizona usually suffers from water shortages, periodic and destructive floods do occur. Extensive flood control benefits are included in the project through modification of Roosevelt and Stewart Mountain Dams.  The dikes along the CAP aqueduct also provide flood protection.

Reduction of Groundwater Overdraft

By providing an annual average of more than 1.4 million acre-feet of Colorado River water to Arizona through the CAP, the project is helping reduce the State's ground water overdraft and related land subsidence.

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Last updated: Apr 18, 2011