Series: Colorado Water Law Basics #14.1 - Apportionment of Colorado River Water, by State

In the LWS blog about the importance of Lee Ferry (Nov 17, 2020) we discussed the 1922 Colorado River Compact that allocated 7.5 million acre-feet per year (MAF) each to the Upper Basin States and the Lower Basin States. However, the 1922 Compact did not apportion water within the Upper or Lower Basin States. So how do the states within the Colorado River Basin know how much of the full 7.5 MAF allocation they can put to beneficial use? There are four Upper Basin States (Colorado, Wyoming, Utah, and New Mexico) and three Lower Basin States (Nevada, Arizona, and California).

The answer is two-fold, the 1928 Boulder Canyon Project Act established the apportionment of the rights to Colorado River water for the Lower Basin States, while the 1948 Upper Colorado River Compact (1948 Compact) established similar state apportionments for the Upper Basin States. The further apportionment of these waters to each state was established as follows:

Upper Basin ²⁾

• Colorado
• Utah
• Wyoming
• New Mexico

Lower Basin ³⁾

• California
• Arizona
• Nevada

Apportionment of the Total Allocation¹⁾

• 51.75%
• 23.0%
• 14.0%
• 1.25%

•  

• 58.7%  (4.4 MAF)
• 37.3%  (2.8 MAF)
• 4.0%  (300 KAF (thousand acre-feet))

1. The apportionments in the Upper Basin States was based on percentages because of the uncertainty related to interpretation of Article III of the 1922 Compact.
2. An additional 50,000 ac-ft/yr was apportioned to Arizona in the Upper Basin.
3. Apportionments to the Lower Basin States was by quantity, percentages were just developed based on the total 7.5 MAF.

An additional commitment as part of the Colorado River Compact, based on a treaty signed in 1944, is to provide 1.5 million ac-ft/yr to Mexico (see “Treaty Between the United States of America and Mexico, Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande, February 1944”). Water delivered to Mexico is measured at the Morelos Dam near Yuma, Arizona.

Why are these apportionments and the terms of Article III of the 1922 Compact so important today? Even though 15 million ac-ft/yr was allocated under the 1922 Compact, recent flow data indicate that the average annual flow of the river is 13.5 million ac-ft/yr. there is also ongoing controversy about the meaning of Article III of the 1922 Compact, do the Upper Basin States have a duty to not deplete more than 7.5 MAF or do they have an obligation to deliver 7.5 MAF to the Lower Basin? Interim guidelines related to how to deal with shortages in Colorado River supplies below the full allocation were initially put in place in December 2007, i.e., Colorado River Interim Guidelines. These interim guidelines defined how varying levels of shortages would be addressed.

There were three levels of shortages identified in the Interim Guidelines. A summary of these interim guidelines is shown below.

Delivery Obligation to Lower Basin (MAF)

• Total: 7.167 MAF
• CA: 4.4
• AZ: 2.48
• NV: 287 KAF

• Total: 7.083 MAF
• CA: 4.4
• AZ: 2.4
• NV: 283 KAF

• Total: 7.0 MAF
• CA: 4.0
• AZ: 2.32
• NV: 280 KAF

Elevation in Lake Mead (ft MSL)

Less than 1,075, greater than 1,050

<1,075 and >1,050

Less than 1,050, greater than 1,025

<1,050 and >1,025

Less than 1,025

<1,025 ft MSL

Currently, Lake Mead’s water level elevation is approximately 1,079 ft MSL. As a reference point, the elevation of Lake Mead at full normal pool is 1,229 ft MSL. In other words, the lake is currently approximately 150 feet below a full reservoir pool.

Gates near Morelos Dam, Yuma, Arizona.

Lake Mead, 2020.

Subsequent to the 2007 Interim Guidelines, the Colorado River Basin Drought Contingency Plan (DCP) was developed in May 2019 to help maintain water levels in Lake Mead and Lake Powell, as well as protect power production. The DCP has shortage tiers that are implemented based on water levels in Lake Mead as well as Lake Powell. Based on future forecasting by the Bureau of Reclamation, implementation of the provisions of the DCP through a shortage declaration is likely in 2022. Look for an upcoming blog that dives into some of the details of the DCP and what it means for states’ water use under the varying water shortage tiers.

If you have any water resources issues, LWS can help! For more information on this subject or any Western water rights issue, please contact us for help at 303-350-4090 or by email.

Bruce Lytle, P.E. bruce@lytlewater.com

Chris Fehn, P.E., P.G. chris@lytlewater.com

Anna Elgqvist, EI anna@lytlewater.com

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