Colorado River Compact
The Compact requires the Upper Basin states not to deplete the flow of the river below 75,000,000 acre-feet (93 km3) during any period of ten consecutive years.
[3] Based on rainfall patterns observed in the years before the treaty's signing in 1922, the amount specified in the Compact was assumed to allow a roughly equal division of water between the two regions.
[9] The Compact did not address a number of issues, including Indian or Mexican water rights, or how evaporation would be shared among the basins.
During the Compact negotiations, Governor-elect Hunt laid out his determination to protect Arizona's rights to irrigate her lands and obtain a portion of the electrical power revenue that would be generated by future dams.
There was also fear that the surplus water would be usurped by Mexico, as treaty rights had not yet been defined and agricultural development of the Mexican delta was underway.
The 1928 Boulder Canyon Project Act provided a way for the nation to move ahead with construction of dams and diversions without the approval of Arizona.
In 1934, Arizona, unhappy with California's decision to dam and divert the river, called out the National Guard and even commissioned a two-boat "navy.
The 1908 Supreme Court decision Winters v. United States recognized a federal obligation to ensure water for tribal homelands.
[15] In negotiations, Arizona has established other conditions that tribes find reprehensible, a factor which has also delayed use or delivery of water to reservations.
The Navajo sued in 2003 for their water rights; the Supreme Court decided in 2023 that the federal government cannot be forced to act in a timely way to quantify or settle their claims to the river.
By volunteering to leave part of their nearly 720,000-acre-foot allocation in Lake Mead, they forestalled deeper cutbacks for others along the Colorado River system under the 2019 Drought Contingency Plan.
[20] The Lower Basin has received a total of 10 million acre-feet of water above and beyond the Compact requirements since January 2000, but the levels of Lake Mead have been dropping.
[22] According to Thomas McCann, former Deputy Manager for the Central Arizona Project, the deficit is caused by 1) avoiding any allocation of evaporation costs to the Lower Basin states, and 2) meeting Mexican Treaty obligations by taking water out of Lake Mead storage rather than out of Arizona and California's allocations.
[36] The book Science be Dammed finds that politicians and boosters repeatedly ignored engineering estimates of the 1920s that provided lower values of flow.
[37] Since 2000, dwindling Colorado River flows and consumption rates in excess of natural replenishment have provoked a need to plan for shortages.
[40] In December 2007, a set of interim guidelines on how to allocate Colorado River water in the event of shortages was signed by the Secretary of the Interior.
[5][41] The guidelines extend through 2026, and, "acknowledging the potential for impacts due to climate change and increased hydrologic variability," interim guidelines provide "the opportunity to gain valuable operating experience for the management of Lake Powell and Lake Mead, particularly for low reservoir conditions...whether during the interim period or thereafter.
[44] In June 2023, U. S. Bureau of Reclamation began preparing an Environmental Impact Statement for further modifications of dam operations at Hoover and Glen Canyon to respond to deepening drought conditions.
On January 1, 2027, the Interim Guidelines and Drought Contingency Plan, which have jointly managed the Colorado River since 2007, will no longer be in effect.
[46] On November 20, 2012, the International Boundary and Water Commission of the United States and Mexico signed an agreement termed "Minute 319," which updated the Law of the River to address how the 1,500,000 acre-feet (1.9 km3) of Colorado River water that Mexico receives every year would be affected by surplus or drought conditions.
[47] Under surplus conditions (when the surface elevation of Lake Mead is above 1,145 feet (349 m) relative to mean sea level) the annual flow to Mexico will increase by 40,000 acre-feet (0.049 km3).
In cases where the surface elevation of Lake Mead is higher than that, the extra deliveries to Mexico progressively increase, reaching a maximum of an additional 200,000 acre-feet (0.25 km3) per year.
