Here’s the release from the Central Arizona Project (DeEtte Person):
A linked lifeline
Colorado River water managers, like CAP, rely upon operating guidelines related to the amount of water stored in the two major Colorado River Basin Reservoirs – Lake Powell and Lake Mead. The operating guidelines determine how much water will be released from those reservoirs to meet water-user needs. The two reservoirs are operated under a system called conjunctive management, meaning the storage conditions in one reservoir affect the releases in the other. Since 2007, the 24-Month Study has been used to implement the operational decisions directed by the guidelines.
How Lake Powell and Lake Mead are designed to rise and fall together
The two largest water supply reservoirs in the United States are part of the Colorado River system—Lake Mead at the Arizona/Nevada border and Lake Powell at the Arizona/Utah border. These two reservoirs are linked by the Colorado River through the Grand Canyon and provide about 90 percent of the system’s storage capacity, supplying seven states and Mexico with water.
The enormous storage capacity in these two reservoirs has provided the resiliency to continue Colorado River water supply deliveries during more than two decades of drought. The two lakes also provide vital, clean, renewable hydroelectricity used across the western United States, as well as environmental and recreational benefits.
In order to operate the Colorado River system efficiently and make optimal use of the available storage in these vital reservoirs, the operations of Lake Powell and Lake Mead are coordinated, known as conjunctive management. In fact, conjunctive management is required by the Colorado River Basin Project Act, which was signed more than 50 years ago to provide a program for the comprehensive development and augmentation of the Colorado River supplies throughout the Upper and Lower Colorado River Basins.
One important goal of coordinated long-term management of these reservoirs is to maintain “as nearly as practicable” equal contents of active storage in Lake Powell and Lake Mead. Lake Mead has about 28 million acre feet (MAF) of storage and Lake Powell can store about 26 MAF. One acre foot can serve three families for a year – so you can see that’s a lot of water!
In 2005, the U.S. Secretary of the Interior directed the Bureau of Reclamation to develop additional strategies for improving the coordinated management of these two reservoirs. The goal was to honor the intent of the Colorado River Basin Project Act, while sharing the water between the Upper (Colorado, New Mexico, Utah and Wyoming) and Lower (Arizona, California and Nevada) Basins during times of lower reservoir levels. The result was the Colorado River Interim Guidelines for Lower Basin Shortages and Coordinated Operations for Lake Powell and Lake Mead, known as the 2007 Guidelines. These guidelines remain in effect through Dec. 31, 2025.
How It Works – 4 Scenarios
The essence of this coordinated approach is that releases and reductions will be coordinated to share risks to water users in each basin. Detailed descriptions and definitions can be found in the 2007 Guidelines, but here is the cheat sheet explaining four basic scenarios:
Normal Supply – If storage and risks are relatively equal in both reservoirs, then Lake Powell will release a “normal” supply to Lake Mead. “Normal Supply” is a release of 8.23 MAF.
Equalization – When runoff is high and inflows into Lake Powell raise the lake’s elevation, increasing the storage level, more water is released to flow down the river to Lake Mead in an attempt to “equalize” Lake Powell’s storage with Lake Mead’s, through what is termed “Equalization.”
Balancing Release – If Lake Powell gains storage while Lake Mead is at risk of shortage triggers, additional water will be released from Lake Powell to “balance” risks between the two reservoirs in what is termed a “Balancing Release.”
Mid-elevation release – If Lake Powell is at risk of approaching critically low elevations while Lake Mead is at a more moderate risk, less water is released from Lake Powell to Lake Mead in what is termed a “Mid-elevation release.”
These operating criteria serve to meet the goals of coordinated operations between Lake Powell and Lake Mead, so the storage in both reservoirs generally rise and fall together. Through the coordinated operations of Lake Powell and Lake Mead, we become one basin – sharing risks and opportunities – linked by two great reservoirs.