Will the Central Arizona Project be an empty ditch?

The recent report that Lake Mead is at one of its lowest levels since Hoover Dam was constructed is causing a lot of worry in California and Arizona.

Global climate change alarmists predict significant reductions on the flow of the Colorado River in the future. They worry that the Colorado River may not be able to continue to supply millions of acre feet of water to farms and cities.

 Will Phoenix and Tucson run out of Colorado River water? Will the Central Arizona Project be an empty ditch?

First one needs to understand the “Law of the River” and how Colorado River water is allocated.

A total of 7.5 million acre feet of river water is allocated to Arizona, California and Nevada and another 1.5 million acre feet to Mexico by treaty.

Nevada has 300,000 acre feet of river water. California has 4.4 million acre feet, Arizona has 2.8 million acre feet.

But the story gets more interesting because each state has internal priorities.

Out of California’s 4.4 million acre feet per year, 3.85 million acre feet are allocated to the  Palo Verde Irrigation District, the Yuma Project, Imperial Irrigation District and the Coachella Valley Water District

Los Angeles, via the Metropolitan Water District of Southern California has an allocation of 500,000 acre feet at 4th priority.

Thus if the river runs short of the 4,4 million acre foot share , Los Angeles gets cut off first.

Arizona’s 2.8 million acre is allocated as follows:

Coloado River Water Allocations…Arizona

First Priority

Colorado River Indian Reservation    662,402

Fort Mojave Indian Reservation         103,535                              

                        Total Indian share                                          765,939

Yuma County Water Users’ Association 254,200

               Total Agricultural share         254200                                                                                                                         

First Priority share of water for Arizona: 1,020, 137

 Third Priority

Wellton-Mohawk Irrigation and Drainage District 278,000

Yuma Mesa Irrigation and Drainage District              141,519                               

 Third Priority share of water for Arizona     419,515

 Fourth Priority

 Central Arizona Water Conservation District 1,500,000 (approximate)         1,500,000

 Total  Arizona allocations 2,939,652

The important thing to note is that in the event Arizona cannot receive its full 2.8 million acre feet per year, the allocation goes by priority….with the CAWCD allocation first off the river.

In the 1968 enabling legislation that authorized the Central Arizona Project, 1.2 million acre feet was subordinated to guarantee California’s 4.4 million acre feet per year.

Thus in the case of both California and Arizona the effect of a prolonged drought hits cities first, and Indians and farms last.

Obviously if the river cannot keep supplying 4.4 million acre feet of water per year to California and 2.8 million acre feet per year to Arizona, something has got to give.

Would it be easier to relocate millions of urban residents dependent on Colorado River water, or buy rights to senior Colorado River allocations from Indians and farmers?

People are worried that the CAP canal will run dry to Phoenix and Tucson.

It probably won’t….but Colorado River water will cost a lot more than it does now.


Because in the event of a prolonged shortage the urban interests will  have to buy out the higher priority agricultural iunterests and lease water from Indian Tribes.

What urban interests need to focus on is how to purchase and retire farm lands in the Imperial and Coachella valleys to sustain Los Angeles, and in the Yuma area to keep the water flowing to Phoenix and Tucson.

If predictions are correct that the Colorado River may only be able to reliably deliver half the water that was allocated, farming in the Imperial and Coachella valleys and in Yuma is doomed.

Residents of Los Angeles, San Diego, Phoenix and Tucson will pay a premium for Colorado River water to buy out priority agricultural water users and mitigate the economic damage that would come to Yuma and Imperial counties of farms were shut down and water rights transferred to cities.

Water-demanding farms looked at as resources vanish

One reason farmers can take so much water is that they staked their claim first, which is what matters in Western water law. Most of the irrigation districts in Yuma hold rights to the Colorado River that predate Hoover Dam, which means if the river starts to run dry, the farmers get their share before anyone else. They can lease water to other users but keep the long-term rights.

Together, the largest water districts in the Yuma area can divert more than 750,000 acre-feet of water from the Colorado each year. Metropolitan Las Vegas, with a population of more than 2 million, can draw just 300,000 acre-feet a year.


California’s Colorado River Allocation

Metropolitan Water District

  Prior to 1922, when six of the seven states that are visited by the Colorado River or its tributaries signed the Colorado River Compact, there has been discussion about how the assets of the Colorado River should fairly be divided. An annual flow estimate of the Colorado River system was the basis of the 1922 compact which split use of the flow of the river between the Upper and Lower Basin states.

For many years, California has depended on surplus water to meet its water needs—and to supplement its basic apportionment of 4.4 million acre-feet per year. Southern California’s rights to Colorado River Water were thought to be solidified in the 1930s when a number of agencies signed water delivery contracts with the Secretary of the Interior. Contracts detailed the priorities, to use and store California’s apportionment of river water.

On January 16, 2001, outgoing Secretary of the Interior Bruce Babbitt signed a document establishing interim guidelines for determining when surplus Colorado River water would be available for California, Nevada and Arizona. The criteria will be in effect for 15 years, giving California a greater certainty of supply and a transition period in which to further develop water conservation, recycling, storage and transfer programs that will provide for separation from an over reliance on the Colorado River.

Palo Verde Irrigation District, the Yuma Project, Imperial Irrigation District and the Coachella Valley Water District (refer to map below) are the agricultural entities holding the first three priorities to the use of no more than 3.85 million acre-feet under the water delivery contracts.

The Metropolitan Water District (MWD) was allotted 550,000 acre-feet per year under a fourth priority right and 662,000 acre-feet per year under a fifth priority right. (The city of San Diego and San Diego County conveyed their water rights to MWD.) MWD holds a contract to divert additional 180,000 acre-feet of surplus water on an annual basis.

In return for accepting lower priorities, MWD was granted the exclusive right in California to accumulate up to 5 million acre-feet of water in storage at Lake Mead. This storage right has yet to be implemented by the U.S. Bureau of Reclamation.

Water from the Colorado River is delivered into MWD’s service area via the Colorado River Aqueduct (CRA). MWD diverts water from Lake Havasu, above Parker Dam. Between 1986 and 1999, the amount of water unused by agriculture and available to MWD has varied from zero to more than 500,000 acre-feet. This unused amount will continue to vary in the future as it is tied to economics, the type of crops planted, acreage irrigated, and the efficiency with which water is used.

As a result of increased Colorado River diversions by Arizona and Nevada (within their apportionments), MWD’s total diversions could eventually decline to its fourth priority right of 550,000 acre-feet per year plus water available from a conservation program with Imperial Irrigation District and a groundwater storage program with the Central Arizona Water Conservation District. Any water left unused by other California contractors with a higher priority than MWD would also be available.

In addition to the potential supply available to MWD from the unused portion of California’s normal apportionment, the Secretary of the Interior can allow MWD to divert water that is unused by Arizona and Nevada, as well as surplus water. In years in which surplus water is available, MWD would have the highest priority of any California contractor to divert that water by virtue of its fifth priority right.

-At this time, the first three priority rights to use 3.85 million acre-feet per year have not been quantified, making it difficult to develop and implement cooperative water supply programs. When there is no further quantification of the use of water, other than by priority rights, it is difficult to determine how much water has been conserved and is available for transfer to urban areas.

It’s like trying to build a charity food bank where the only guideline given the organizers is a monetary cap. They’ll need to know how best to spend their $10,000 dollars for example—by knowing the history of how much meat is needed, how many vegetables are consumed and how quickly other food staples are used up. There are steps underway to quantify use through a proposed Quantification Settlement Agreement.


Colorado River Compact
 The compact divides the river basin into two areas, the Upper Division (comprising Colorado, New Mexico, Utah and Wyoming) and the Lower Division (Nevada, Arizona and California). The compact requires the Upper Basin states not to deplete the flow of the river below 75,000,000 acre feet (9.3×1010 m3) during any period of ten consecutive years. Based on historical rainfall patterns, the amount specified in the compact was assumed to allow a roughly equal division of water between the two regions. The states within each basin were required to divide their 7,500,000-acre (30,400 km2) foot per year (289 m³/s) share allotment among themselves. The compact enabled the widespread irrigation of the Southwest, as well as the subsequent development of state and federal water works projects under the United States Bureau of Reclamation. Such projects included the Hoover Dam and Lake Powell.

The current specific annual allotments in the Lower Basin were established in 1928 as part of the Boulder Canyon Project. They are:

Upper Basin, 7.5 million acre·ft/year (293 m³/s) total
Colorado 51.75% 3.88 million acre·ft/year (152 m³/s)  
Utah 23.00% 1.73 million acre·ft/year (68 m³/s)  
Wyoming 14.00% 1.05 million acre·ft/year (41 m³/s)  
New Mexico 11.25% 0.84 million acre·ft/year (33 m³/s)  
Arizona 0.70% 0.05 million acre·ft/year (2.0 m³/s)  
Lower Basin, 7.5 million acre·ft/year (293 m³/s) total
California 58.70% 4.40 million acre·ft/year (172 m³/s)  
Arizona 37.30% 2.80 million acre·ft/year (109 m³/s)  
Nevada 4.00% 0.30 million acre·ft/year (12 m³/s)  

In addition to this, 1,500,000-acre-foot (1.85×109 m3)/year of Colorado River water is allocated to Mexico, pursuant to the treaty relating to the use of waters of the Colorado and Tijuana Rivers and of the Rio Grande, signed February 3, 1944, and its supplementary protocol signed November 14, 1944. Also, the lower basin can get an additional 1,100,000-acre-foot (1.36×109 m3)/year.[2]


Novmber 18 Arizona Daily Star article: 

CAP describes costly future water options

See also:

Sharing Colorado River Water: History, Public Policy and the Colorado River Compact
by Joe Gelt
NCSE-NASA Curriculum Module – Colorado River water supply


About Hugh Holub

Attorney and writer.
This entry was posted in environment, water. Bookmark the permalink.

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