skip to the content of this page Arizona's Official Website Arizona Department of Water Resources
Arizona Department of Water Resources Arizona's Official Web Site
Securing Arizona's Water Future

Lower Colorado River Water Supply - Colorado River

Water supplies in the Lower Colorado River Planning Area include groundwater, surface water, Central Arizona Project (CAP) water and effluent.  As shown on Figure 7.0-13, most water used is surface water.  Colorado River water is the major supply in the Lower Gila, Parker and Yuma basins and CAP water is the largest supply in the Harquahala Basin. Gila River water combined with effluent discharge from the Phoenix AMA is an agricultural supply in the Gila Bend Basin.  Elsewhere, groundwater is the primary water supply.  Colorado River water is also used to meet environmental needs at the Imperial Wildlife Refuge in the Parker and Lower Gila basins. A discussion of Colorado River water entitlements and accounting is presented below.  For purposes of the Atlas, water diverted from a watercourse or spring is considered surface water and if it is pumped from wells it is accounted for as groundwater.  This is reflected in the cultural water demand tables in each basin section.

Figure 7.0-13 Average Annual Water Supply Utilized in the Lower Colorado River Planning Area, 2001-2005 (in acre-feet)

Figure 7.0-13

Colorado River Water

Decree Accounting

The right or authorization to beneficially use Colorado River water is defined as an entitlement.  Entitlements held by Colorado River water users are created by decree of the United States Supreme Court in Arizona v. California et al. (Decree), through a contract with the Secretary of the Interior (Secretary) under Section 5 of the Boulder Canyon Project Act (BCPA) of December 21, 1928, or by Secretarial Reservation.

Table 7.0-6 shows the annual total amount of Colorado River water that was consumptively used for each category of water use within each basin in the planning area based on an accounting system established by Decree.  Article V of the Decree directs the U.S. Bureau of Reclamation (Reclamation) to prepare an annual report of diversions from the mainstream, return flow of water to the mainstream that makes water available for downstream consumptive use in the U.S. or in satisfaction of the Mexican Treaty obligation, and the consumptive use of such water.  The Article V report lists diversions and return flow separately by diverter, point of diversion and state, for each of the lower basin states.

Colorado River

Colorado River in the Parker Basin

According to the Article V report, consumptive use of Colorado River water in the planning area for agricultural, municipal, industrial and environmental purposes averaged 1,144,541 acre-feet annually for the 2001-2005 time period out of a total annual entitlement of 1,676,209 acre-feet. The table shows the quantities of water diverted by surface water diversions, in-river pumps, or pumped from wells assumed to be located within the hydraulically connected aquifer of the Colorado River.  When determining consumptive water use, the Article V accounting system considers measured return flow and estimates of unmeasured return flows to the mainstream. 

Reclamation has made a preliminary delineation of the lateral and vertical extent of the Colorado River aquifer to provide a basis for accounting of withdrawals against river water allocations.  On July 16, 2008, Reclamation proposed to develop a rule for Regulating Non-Contract Use of Colorado River Water in the Lower Basin (73 Federal Register 40916 et seq.) to prevent non-contract Colorado River water use from depleting the river and taking water from holders of Colorado River water entitlements.  Reclamation’s most current assessment indicates that most existing non-contract water use results from water withdrawn from wells located within the hydraulically connected aquifer of the Colorado River or from river pumps. The proposed rule would establish a methodology that Reclamation would use to determine if a well pumps Colorado River water and a process for a water user to appeal a subsequent finding (USBOR, 2008). As of October 2009, Reclamation had not adopted a rule.

Because of the complexity of the accounting system and its unique methodology that includes return flow and other considerations, the surface water and groundwater discussions in this overview section and the cultural water demand tables in sections 7.4, 7.5 and 7.11 (those basins that utilize this supply), reflect the amount of water pumped from wells and diverted from streams. This approach is comparable to that used for other planning areas. The tables do not attempt to distinguish whether the water is used pursuant to the entitlement system. 

Entitlement Priority Levels

Rights to Colorado River water include the following several priority levels: 

    a.  1st Priority: Satisfaction of Present Perfected Rights as defined in the Arizona v. California decree;

   b.  2nd Priority: Satisfaction of Secretarial Reservations and Perfected Rights established prior to September 30, 1968;

    c.  3rd Priority: Satisfaction of entitlements pursuant to contracts between the United States and water users in Arizona executed on or before September 30, 1968 (2nd and 3rd priority are coequal);

    d.   4th Priority: i) Contracts, Secretarial Reservations and other arrangements between the U.S. and water users in Arizona entered into after September 30, 1968, for a total quantity not to exceed 164,652 acre-feet of diversions annually and ii) contract No. 14-06-W-245, dated December 15, 1972, as amended, between the United States and the Central Arizona Project (CAP).  Entitlements having a 4th priority as described in (i) and (ii) are coequal;

    e.   5th Priority: Unused entitlement; and

    f.   6th Priority: Surplus water.

In general, the lower priority entitlements will be the first to be impacted when the Secretary declares a shortage on the Colorado River system.  Within the planning area, entitlement holders with a 1st Priority or Present Perfected Rights include the Cocopah Indian Reservation, Colorado River Indian Tribes Reservation, Fort Yuma Indian Reservation, Yuma County Water Users’ Association, North Gila Valley Irrigation District, Unit “B” Irrigation and Drainage District, the City of Yuma and the Town of Parker.  2nd and 3rd priority entitlement holders (which are coequal), include the Ak-Chin Indian Community, Imperial and Cibola National Wildlife Refuges, Yuma Proving Grounds, the Marine Corps Air Station–Yuma, Wellton-Mohawk Irrigation and Drainage District and others.  Information on Colorado River entitlements in the Lower Colorado River Planning Area is provided in Appendix C.  Entitlements may be transferred under certain conditions. Within the planning area, the Cibola Valley Irrigation and Drainage District has assigned a portion of its entitlement to the Mohave County Water Authority (MCWA, 5th and/or 6th), to the Hopi Tribe (Priority 4th, 5th and 6th) and to Cibola Resources for municipal use at Ehrenberg. More information on entitlement transfers is in Appendix D.

Agriculture in the Yuma Basin

Agriculture in the Yuma Basin

Coordinated Operations and Shortage Criteria

In December 2007, Reclamation issued a Record of Decision (ROD) on interim operating criteria (2008-2026) including the coordinated operation of Lake Powell and Lake Mead and criteria for implementing shortage reductions in the Lower Basin.  Historically, the reservoirs were operated independently; annual Lake Powell water releases were determined based on applicable law and relevant factors contained in the Long-Range Operating Criteria.  The ROD adopted four key elements: 1) establishes rules for shortages; 2) allows coordinated operation of Lake Powell and Lake Mead to avoid Lower Basin shortages and avoid curtailment of Upper Basin water use; 3) establishes rules for surpluses; and 4) address ongoing drought by encouraging new initiatives for water conservation. If regional drought conditions continue, shortage operations could begin as early as 2011.  The ROD could have implications for water supply availability in the planning area.

Colorado River Water Supply Distribution System

In the Lower Colorado River Planning Area, dams on the Colorado River were constructed primarily for the purpose of regulating river flow and creating storage to facilitate water diversions to Arizona, California and Mexico via canals pursuant to decrees, international treaties and other legal agreements.  Figure 7.0-14 shows the location of major dams, water delivery and diversion structures, and other features along the Colorado and Gila Rivers in the planning area.  The agricultural and municipal water delivery systems are discussed in the cultural water demand section (7.0.7).  The Colorado River system is described briefly below, from north to south. 

Figure 7.0-14 Operational Diagram of the Colorado River Lower Colorado River Planning Area

Click to view Figure 7.0-14

Parker Dam

Parker Dam, at the northern edge of the planning area in the Parker Basin, is a concrete arch structure 320 feet high and 856 feet long at its crest.  It is the deepest dam in the world with 73 percent of its structural height below the original riverbed. Completed in 1938, it impounds Lake Havasu and provides a desilting basin and forebay for diversion of Colorado River water.  The Metropolitan Water District of Southern California pumps water into its Colorado River Aqueduct from the forebay, conveying it 242 miles west to Lake Mathews near Riverside, California. On the Arizona side, water is pumped from the forebay into the CAP canal for use in central Arizona. (USBOR, 2007c)  The dam includes a powerplant that is integrated with the Davis and Hoover powerplants, providing power to Arizona and southern California.  The powerplant is remotely operated from the Hoover Control Center. (USBOR, 2006)

Headgate Rock Dam

Downstream of Parker Dam, irrigation water for the CRIT near Parker is diverted at Headgate Rock Dam.  This dam was constructed in 1942 to stabilize the river channel and provide reliable irrigation supplies. (USBOR, 2007d)  A levee system protects areas downstream from flooding.

Palo Verde Diversion Dam

Palo Verde Diversion Dam is located about 44 miles downstream of Headgate Rock Dam.  It maintains a sufficiently high, constant water surface elevation at the Palo Verde Irrigation District canal headwork for delivery of irrigation water to the west side of the Colorado River near Blythe, California.  The dam is a semipervious barrier of sand, gravel and rockfill, 46 feet high and 1,850 feet long. (USBOR, 2007e).

Senator Wash Dam

Senator Wash Dam and Reservoir is an offstream pumping facility located on the California side of the river about two miles upstream from Imperial Dam.  This structure improves water scheduling by downstream users by storing part of the riverflow upstream of Imperial Dam when it is not needed, releasing it to the river for downstream use when needed.  Without the dam it would take three days for water released at Parker Dam to reach Imperial Dam.  The dam is an earth embankment structure 2,342 feet long with a height of about 94 feet.  Other works include three dikes, a spillway and a pumping plant. (USBOR, 2007d)

Imperial Dam

Imperial Dam is a major diversion point for both Arizona and California.  The dam raises the water surface about 25 feet, allowing controlled gravity flow into the All American Canal and the Gila Gravity Main Canal.  The All American Canal system diverts water from the California side of the dam and serves Imperial Irrigation District, Coachella Valley Water District, the Yuma Project in Arizona and California, and the City of Yuma. The Gila Gravity Main Canal system diverts water from the Arizona side of the dam and serves the north and south Gila Valley, Yuma Mesa, and the Wellton-Mohawk Irrigation District area.  Imperial Dam is also used to regulate water deliveries to Mexico required by international treaty. (USBOR, 2007b)

Imperial Dam

Imperial Dam, Lower Gila Basin

Laguna Dam

From Imperial Dam to the Northerly International Boundary between the U.S. and Mexico, the entire channel of the Colorado River is bounded by a system of levees.  Laguna Dam, located five miles downstream of Imperial Dam serves as a regulating structure for Colorado River water. (USBOR, 2007b)  Because of upstream diversions and dams, from Laguna Dam to Morelos Dam the river consists of a small active channel located within a broad, older riverbed entrenched below the historic level of the unregulated river  (USBOR, 2007d). 

Yuma Desalting Plant, Main Outlet Extension and Bypass Extension

Utilizing Colorado River water for domestic and agricultural purposes has steadily increased the salinity of its waters. In the 1960s crops in the Mexicali Valley were damaged by the high salinity of the Colorado River water used for irrigation.  An amendment to the 1944 treaty with Mexico (Minute 242) guaranteed that the treaty water delivery would be no more than 115 ppm (+/- 30 ppm) more saline than the water diverted at Imperial Dam.

Nine miles downstream from Laguna Dam the Gila River enters the Colorado.  Along the Gila River, extensive agricultural irrigation with Colorado River water in the Wellton-Mohawk Irrigation and Drainage District (WMIDD) has made it necessary to install drainage wells to pump excess irrigation water to keep salts from accumulating in the root zone.  About 120,000 acre-feet of brackish groundwater is pumped annually. If this water was directly returned to the river it would increase salinity levels above the international treaty standard and could not be counted towards Mexico’s Colorado River apportionment of 1.5 million AFA.

To desalinate the drainage water so that it could be returned to the mainstem and counted toward the apportionment, Reclamation constructed the Yuma Desalting Plant (YDP).   Completed in 1992, the YDP is designed to treat up to 96,000 AFA.  It operated briefly in 1993 and was then put on standby status until a 90-day demonstration run in 2007. Currently, WMIDD drainage water is discharged to the Main Outlet Drain Extension (MODE) and its bypass extension in Mexico and delivered to the Santa Clara Slough (Cienega de Santa Clara).  (WMIDD, 2004) 

To desalinate the drainage water so that it could be returned to the mainstem and counted toward the apportionment, Reclamation constructed the Yuma Desalination Plant (YDP).   Completed in 1992, the YDP is designed to treat up to 96,000 AFA.  It operated briefly in 1993 and was then put on standby status until a 90-day demonstration run was conducted in 2007. Currently, Wellton-Mohawk Irrigation and Drainage District (WMIDD) drainage water is discharged to the Main Outlet Drain Extension and its bypass extension in Mexico and delivered to the Santa Clara Slough (Cienega de Santa Clara).  (WMIDD, 2004)  In May 2010, a year-long pilot run of the YDP at one-third capacity is scheduled to begin.  The purpose of the pilot run is to assess the suitability of the treatment process and define its long-term design. The pilot run will include a monitoring program that evaluates impacts to the wildlife and habitat associated with the Cienega.

California and Pilot Knob Wasteways

Four miles downstream from the mouth of the Gila River, the Yuma Main Canal wasteway returns water to the river to comply with the treaty obligation to Mexico.   In addition, a portion of the water scheduled to be delivered to Mexico is diverted at Imperial Dam, conveyed by the All American Canal, and returned to the river through the Pilot Knob Wasteway west of Yuma. (USBOR, 2007b)

Northerly International Boundary (NIB) to Southerly International Boundary (SIB)/Morelos Dam

The 23.7 mile long reach of the Colorado River between the NIB and the SIB is referred to as the limitrophe section.  Levees have been constructed on both sides of the river. About 1.1 miles downstream of the NIB, Morelos Diversion Dam acts as a diversion control structure for the Alamo Canal, which conveys water to Mexico. Other infrastructure includes wasteways, bypass channel, levees, etc. (USBOR, 2007b)  Below Morelos Dam.  River flow is reduced in this section due to diversions by Mexico into the Alamo Canal and because the channel is overgrown with vegetation.  In addition, sediment buildup around the spillway has caused loss of dam function.  As a result, the flood capacity of the channel has been reduced, posing a threat to the safety of the Valley Division of the Yuma Project. (USBOR, 2007d)

242 Well Field and Lateral

Title I of the Colorado River Basin Salinty Control Act authorized the Protective and Regulatory Pumping Unit, consisting of the 242 well field and lateral. The unit is located east of San Luis in a 5-mile wide protected and regulated zone consisting of 35 wells, the 242 Lateral and other connecting laterals (Figure 7.0-21). The well field intercepts part of the groundwater flow, including irrigation drainage water that moves south into Mexico from the Yuma Mesa. Water pumped from the well field is delivered at the SIB to Mexico through the 242 Lateral and other laterals to meet international treaty obligations for Colorado River water deliveries. (USBOR, 2007a)

Central Arizona Project Water

Colorado River water is withdrawn at Lake Havasu at the Mark Wilmer Pumping Plant into the Central Arizona Project Aqueduct system.  It crosses the Parker, Ranegras Plain and Harquahala basins via the Hayden-Rhodes Aqueduct to the CAP service area in central Arizona (Maricopa, Pima and Pinal counties). 

CAP water is used both directly and stored underground in the planning area pursuant to the Department’s Recharge Program.  Storage facilities in the planning area are listed on Table 7.0-7.  The Vidler Water Company Underground Storage Facility (USF) is located near Centennial in the Harquahala Basin where it is permitted to recharge up to 100,000 acre-feet of CAP water annually.  Harquahala Valley Irrigation District (HVID), located in the southern part of the Harquahala Basin holds a groundwater savings facility permit (GSF).  It receives excess (uncontracted) CAP water which it uses “in-lieu” of groundwater.  The Arizona Water Banking Authority (AWBA) holds water storage permits to store excess CAP water at both facilities.  HVID has been using CAP water since 1986 and it has replaced groundwater as the major water supply in the basin.  As a result of this storage and direct use, groundwater levels have risen in the vicinity of Vidler and HVID.  A long-term storage account was established for the McMullen Valley Water Conservation & Drainage District (Vicksburg Farms) in 2000 in anticipation of the accrual of long term storage credits from storage of CAP water via two injection wells.  However, a water storage permit was never issued and no water has been stored.

Table 7.0-7 Storage facilities in the Harquahala Basin

Table 7.0-7


water drop  Continue to Section 7.0.6 Water Supply - Surface Water


Arizona Water Atlas Home

Lower Colorado River Planning Area Home

Download pdf of Lower Colorado River Planning Area Overview

Colorado River
Lower Colorado River Planning Area

Volume 7

Parker Dam
Agriculture in Yuma Basin