The Colorado River Basin faces the possibility of two big reservoir crises at once.
By the end of next year, the worst-case forecast has Lake Powell falling to low enough levels to halt electricity production at Glen Canyon Dam. At Lake Mead, a similar forecast has water levels falling low enough by April 2027 to possibly severely curtail power production at Hoover Dam.
If both those events happen, cities, irrigation districts, tribes and other water users throughout the seven-state basin would have to find other power sources, most likely at a sharply higher cost. Among them is the Central Arizona Project, which uses power from Hoover Dam to pump water uphill through its canal system to Phoenix and Tucson for drinking.
The impact of higher rates in Arizona would be particularly acute for Hoover Dam customers. They include the city of Tucson government, about 19 other cities, a number of electrical districts providing power for farms, and a couple of tribes.
For all of them, the curtailment of power production could mean a 30% to 40% increase in the rates they pay to the feds for the power, said Jordy Fuentes, director of the Arizona Power Authority, a state agency that markets Hoover Dam power across Arizona.
Most cities and CAP get only a fraction of their power from Hoover Dam. But farmers and the electrical districts serving them are more dependent on the dam.
Between them, the turbines at the two dams have historically produced enough electricity to serve 13 million people across the seven basin states, although their power production has already been cut somewhat because of existing declines in water levels at the two reservoirs.
In the case of Glen Canyon Dam, the decline in reservoir levels below what’s known as “minimum power pool” at 3,490 feet elevation could also reduce the flow of river water through the dam into the Lower Basin states of Arizona, California and Nevada.
That’s because if Lake Powell falls that low, all of the river’s water would have to then start passing through four steel outlet tubes instead of the dam’s turbines, and U.S. Bureau of Reclamation officials have said those tubes aren’t designed to carry large amounts of water.
The worst-case forecast has Lake Powell falling to low enough levels by the end of next year to halt electricity production at the Glen Canyon Dam.
The specific water level forecasts for the two reservoirs come from the reclamation’s latest monthly 24-month study. It predicts the water levels over the coming two years for 15 reservoirs in the basin, from Fontanelle Dam in Wyoming south to Lake Havasu along the river in western Arizona.
Specifically, the bureau’s “most probable” forecast, which covers 80% of all possible river flow and reservoir levels, doesn’t predict problematic levels for Powell or Mead over the next two years. But the “minimum probable” forecast shows Powell falling below 3,490 starting in December 2025 and staying there through May 2027 — as far out as the forecast goes. For Mead, that same forecast shows it falling below 1,035 feet, the level at which its power production may have to be curtailed, in April and May 2027.
Research led by longtime Colorado River scientist Jack Schmidt at Utah State University has found the bureau’s most probable forecasts have often been too optimistic, and numerous water experts have said it’s important to look at the worst-case scenario in planning for river management.
The possibility of Powell falling below the minimum level for power production is a familiar scenario in the basin. Through much of 2022, the last year of a three-year dry spell, forecasters were regularly predicting the lake would fall below 3,490 by 2024, and possibly fall to “dead pool” at 3,370 feet, a level at which no water could be released through the dam. In 2021, the bureau cut its releases from Powell to Mead to prop the lake up — a cut that a bureau official said may well need to be repeated next year if it looks like Powell will fall below 3,490 feet.
The dire forecasts never came to pass, because extremely heavy snows in 2023 raised the reservoir levels well above the danger zone for a decline. But this year, runoff levels into Powell are again forecast to be very low — about 45% of normal, says the federal Climate Prediction Center. The possibility of Powell dropping to 3,490 comes after only one dry year this time.
“This is one of the five driest years on the river over the past 50 to 60 years,” Dan Bunk, a bureau official, told a state-run Colorado River committee at a meeting Tuesday, although “it’s not quite as bad as 2022.”
At Lake Mead, however, officials thought they had the Hoover power situation under control after they installed five new turbines at the dam a decade ago. Until then, it was believed the dam would stop generating electricity when Lake Mead fell to 1,050 feet elevation — only five feet lower than it was on Friday. But since the turbines were installed, officials had, until very recently, said the dam could keep producing electricity until Mead fell to 950 feet.
But at Tuesday’s meeting of the Arizona Reconsultation Committee, the bureau’s Bunk said a study by a technical services team at the bureau found if Mead falls to 1,035 feet now, the dam’s older 12 turbines may not be able to operate. That’s because at that elevation, the turbines may suffer damage from cavitation, he said.
Cavitation occurs when bubbles get into a liquid, and becomes a problem when it is associated with flowing water. The air bubbles in the moving water implode and create shock waves that travel through the liquid and damage equipment. The result is erosion, outside water experts have told the Star.
If Mead drops that low, “we may have to take 12 of our 17 turbines offline,” said Bunk, area manager for the bureau’s Boulder Canyon operations office. “That would be a drop in our capacity from 1,280 megawatts to 380 megawatts.”
At Hoover, “full capacity is 2,000 megawatts,” the power authority’s Fuentes said. “We’re already operating at 65% capacity. (Taking the older generators offline) takes it down to 30%.”
“We’re probably now up 25% in rates from when the dam was full. If we project to 380 megawatts, we’re probably talking about another 30-40% increase in rates,” Fuentes said.
Bunk told the Arizona committee that the bureau is working with Hoover power customers and the Western Area Power Administration to analyze the possible benefits of installing additional new turbines at the dam to replace the older ones.
“What we’re hearing is it could take potentially three years to install the new turbines,” Fuentes said. “The best case scenario is 2.5 years, probably. Realistically, we’re looking at some sort of phased-in approach.
“Ultimately what that is gong to mean is that if (the lake falls to 1,035) that quickly, and there’s no way other turbines will be in place by then, we will need additional energy conservation,” he said.
Behind the series: The Star's longtime environmental reporter Tony Davis shares what inspired him to write the investigative series "Colorado River reckoning: Not enough water."
