In May 2019, state and federal stakeholders in the Colorado River’s water supply reached an agreement designed to reduce risks from ongoing and anticipated droughts in the Upper and Lower Colorado River Basins. The Colorado River drought contingency plans for the Upper and Lower Basins reflect years of collaborative effort by state, federal, tribal, and international stakeholders, and are trumpeted as significant cooperative efforts to fortify the Colorado River’s water supply against the effects of drought in the basins.

Background

The Colorado River provides a water supply for more than 40 million people and irrigates roughly 5.5 million acres of farmland. The Colorado River Basin, which is divided into an Upper and Lower Basin, spans seven states and extends into Mexico. The Colorado River’s water supply is governed by the “Law of the River,” which is comprised of numerous federal laws, regulatory guidelines, judicial decisions, agreements, and compacts developed over the course of nearly a century. An important function of this body of law has been federal-state and interstate cooperation in the dam and reservoir operation of the Colorado River, which has become increasingly important as drought conditions impact the river’s supply.

In particular, in 2007, the U.S. Department of the Interior (Interior) and seven Colorado River Basin states established a set of temporary guidelines (2007 Guidelines) to address the historic drought plaguing the basin. For the Lower Basin, the guidelines provided for coordinated operations of two major reservoirs—Lake Powell and Lake Mead—and for water allocations among the Lower Basin states in the event of water shortages. Specifically, when Lake Powell’s elevation is higher than Lake Mead’s, water must be released from Lake Powell. Additionally, the guidelines provided that a shortage would be declared if Lake Mead’s elevation dropped to 1,075 feet, at which point Arizona’s apportionment of water would decrease from 2.8 million acre-feet to 2.48 million acre-feet. Nevada would also receive less water—287,000 acre-feet compared to 300,000 acre-feet. The guidelines did not establish a scenario in which California would receive less than its 4.4 million acre-feet allotment, but California would not be able to receive deliveries of intentionally created surplus water if a shortage was declared in the Lower Basin.

Also, in 2007, the seven Basin states entered into an Agreement Concerning Colorado River Management and Operations (2007 Agreement). That agreement was designed to improve cooperation and communication among the states, provide additional security and certainty around the Colorado River’s supply, and avoid situations giving rise to disputes under the Law of the River. Both the 2007 Agreement and 2007 Guidelines form an important backdrop to the newly signed drought contingency plans for the Upper and Lower Basins (collectively: Plans), which Congress authorized in April and which are governed by a single “companion” agreement.

Drought and the Colorado River

Generally, drought response actions under the Plans will be triggered by projected reservoir levels according to 24-month studies by the U.S. Bureau of Reclamation incorporated into the Plans. The Plans, which expire December 31, 2025, do not override existing guidelines or agreements. Instead, the Plans allow for the development and testing of “tools” designed to provide security and certainty in the Colorado River’s water supply. The Upper Basin drought contingency plan (Upper Basin DCP) is aimed at minimizing the risk of Lake Powell falling below a target elevation of 3,525 feet (mean sea level). To do this, the Upper Basin DCP provides for adjustments at the Glen Canyon Dam (i.e. Lake Powell), Flaming Gorge Dam, Curecanti, and Navajo Dam in the event of a drought operations response. Volumetric adjustments at Lake Powell will be considered first as part of a drought operation response. At the same time, Glen Canyon Dam operations will be conducted so as to maintain its ability to generate hydropower for other Colorado River system projects and electrical service customers.

For its part, the Lower Basin drought contingency plan (Lower Basin DCP) provides that Lower Basin states will make reductions per the 2007 Guidelines based on projected Lake Mead levels. Additionally, the Lower Basin DCP provides that Lower Basin states will contribute certain water supplies to Lake Mead, again depending on its level. These supplies include intentionally created surpluses, which allow entities in California, Nevada, and Arizona to store water in Lake Mead if they are able to produce an equal amount of water within their state. This results in a water credit, and the credited volume is then delivered from Lake Mead when a surplus is declared. Under the Lower Basin DCP, some of this water may need to be contributed to Lake Mead if levels fall within certain tiered water levels. For instance, if the elevation of Lake Mead drops below 1,045 feet, Arizona, Nevada, and California must contribute 240,000 acre-feet, 10,000 acre-feet, and 200,000 acre-feet, respectively. If projected Lake Mead levels are between 1,045 and 1,090 feet, Arizona would need to contribute 192,000 acre-feet, with Nevada contributing 8,000 acre-feet. California would only need to contribute to Lake Mead levels if they do not exceed 1,045 acre-feet. However, if lake levels fall below 1,030 feet, California would need to contribute 350,000 acre-feet, with Arizona and Nevada contributions set at less than 1,045 foot levels. This arrangement generally appears to reflect the priorities each state has to Colorado River water based on the Law of the River and reflected further in the 2007 Guidelines.

Conclusion and Implications

The drought contingency plan has been widely considered a positive development in the management of the Colorado River water supply. The Plans also reflect a more precise understanding of the hydrological conditions of the Colorado River Basin developed through prior cooperative efforts, such as the 2007 Agreement and 2007 Guidelines. While it is unclear whether the interim drought response tools developed under the Plans will provide long-term solutions to drought conditions along the Colorado River, it is likely that these efforts will advance the parties’ understanding of the river, its basin, and their ability to plan for and respond to anticipated drought conditions in the future. For more information, see: Interior and States Sign Drought Agreements to Protect Colorado River, available at https://www.acwa.com/news/interior-and-states-sign-historic-drought-agreements-to-protect-colorado-river/

(Steve Anderson, Miles Krieger)