Metropolitan Water District of Southern California
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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.

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Page updated: March 18, 2009