Every year, Colorado River water users anxiously wait for the results of the Bureau of Reclamation’s (“BOR”) August 24-Month Study Report. While the report is updated and published monthly, the August report is particularly significant because it sets the operational tier level for coordinated operation of Lakes Mead and Powell for the next calendar year.
Snowpack in the Upper Colorado River Basin was 21.273 inches (snow water equivalent) on April 14 of this year, well above the average annual high of 16.073 inches. The high snowpack predictably produced high runoff, reaching a preliminary observed estimate of 145% of normal between April and July at 10.410 Million Acre/Feet (MAF).
BOR Commissioner Brenda Burman advised the public to not get too excited about the numbers.
“While we appreciate this year’s above average snowpack,” she said, “one good year doesn’t mean the drought is over.”
Commissioner Burman’s warning was accompanied by sobering news that despite the snowpack and runoff, the August 24-Month Study Report, released August 15, 2019, projects that Lake Mead’s water level will fall below 1,090 feet into Tier Zero in December 2019, triggering mandatory cuts in 2020.
The operational tiers are a product of BLM’s December 2007 Record of Decision on Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations of Lake Powell and Lake Mead (“Interim Guidelines”), which prescribes cuts of water deliveries to some of the states in the Colorado River Basin when the water at Glen Canyon Dam (Lake Powell) and Hoover Dam (Lake Mead) reach certain levels, or tiers. When the Lower Basin States (Arizona, California, Nevada) voluntarily adopted the recent Lower Basin Drought Contingency Plan (“DCP”), an additional tier, Tier Zero, was added to the Interim Guideline tiers to provide even greater protection in shortage conditions. The DCP also made deeper cuts to water deliveries if the other tiers are reached, and even California agreed to take cuts to their deliveries in some tiers (California was not required to take cuts under the Interim Guidelines).
The Colorado River is managed under a legal system of decisions, agreements, compacts, and policy collectively known as the “Law of the River”. The Law of the River includes, among other guidance, these three foundational documents – two agreements and one law – upon which all Colorado River management decisions are based (including the DCP):
- 1922 Colorado River Compact – Divides the Colorado River into the Upper Basin (Utah, New Mexico, Wyoming, and Colorado), and the Lower Basin (Arizona, Nevada, and California). Under the Compact, each basin is entitled to 7.5 MAF annually.
- 1928 Boulder Canyon Project Act – Apportions the Lower Basin’s 7.5 MAF in the amounts of 2.8 MAF to Arizona, 0.3 MAF to Nevada, and 4.4 MAF to California.
- 1948 Upper Basin Compact – Apportions the Upper Basin’s 7.5 MAF on a percentage basis, in the amounts of 51.75% to Colorado, 11.25% to New Mexico, 23% to Utah, and 14% to Wyoming.
In 1968, Arizona politicians agreed to allow California to have a superior right to Colorado River water in exchange for California politicians withdrawing opposition to funding and construction of the Central Arizona Project (CAP) canal. Without the Interim Guidelines or the DCP, Arizona’s CAP customers would be forced to protect California’s apportionment when there is a shortage on the river by absorbing the full impact of cuts before California feels any impact.
Figure 2, published in Exhibit 1 to the Lower Basin Drought Contingency Plan, illustrates the tiers and their respective cuts under the DCP compared to the Interim Guidelines.
The new Tier Zero requirements become effective when the water level at Lake Mead is between 1,090 and 1,075 feet. For Arizona, that means it will take a cut of 192,000 acre/feet (AF) to its 2020 deliveries of Colorado River water and Nevada’s deliveries will be reduced by 8,000 AF. The water will be left in Lake Mead for the benefit of the system rather than be delivered down river. California’s first reduction in deliveries won’t occur until Lake Mead goes below 1,045 feet, but the significance of California agreeing to share in the reductions cannot be overstated.
The good news is that, at least for one year, winter precipitation cooperated in 2019 and produced significant runoff that fed into the system. More good news, according to Chuck Colom at the Central Arizona Project, is that Arizona is prepared to handle the mandatory Tier Zero cut.
“The Tier Zero reduction to CAP, while significant, is largely equivalent to the amount of Colorado River water CAP has been leaving voluntarily in Lake Mead since 2015 as part of our Lake Mead Conservation Program,” Colom writes. “In essence, CAP and its water users have been planning and preparing for Tier Zero reductions for the past five years. The difference is that those previous contributions were voluntary – now, under DCP, these contributions are mandatory.”
Figure 1. http://snowpack.water-data.com/uppercolorado/index.php
Figure 2. https://www.usbr.gov/dcp/docs/final/Attachment-B-Exhibit-1-LB-Drought-Operations.pdf