Hoover Dam Approaches a Hydropower Cliff

Some day in the next 12 months—maybe in late August, maybe not until next spring— Lake Mead will drop below the critical threshold of 1,035 feet above sea level.

That is the water-level elevation at which hydropower generating capacity at Hoover Dam, the largest in the Colorado River basin, will be cut by 70 percent. The drastic and immediate reduction in a cheap source of power that is responsive to hourly changes in electricity demand will have consequences for the region’s power customers and the broader electric grid alike.

Water managers have known for at least a year and a half that elevation 1,035 feet will be a problem for Hoover’s hydropower. Twelve of the dam’s 17 turbines are not designed to operate in low-water conditions that would be present when Mead is below that level. After record-low winter runoff into already-depleted reservoirs, water managers now know that the day of reckoning is coming soon.

“We’re going to go to 1,035,” Tom Buschatzke, director of the Arizona Department of Water Resources, said at a meeting in mid-May. “There’s no question that’s going to happen.”

The Colorado River’s big reservoirs, Lakes Mead and Powell, are filled with trip wires—water-level elevations that, once breached, trigger a negative outcome. Both reservoirs are low enough that those trip wires for hydropower generation are in sight. With so little water in the system, water managers are in a triage situation, trying to minimize damage but acknowledging there will be unfortunate tradeoffs.

Some help is on the way. The Bureau of Reclamation, the federal agency that manages the dams, announced on May 21 that it will spend $52 million on three new wide-head turbines that will be able to generate power down to elevation 950 feet.

“Unlocking these funds allows us to move forward with critical upgrades at one of the nation’s most important hydropower facilities,” said Scott Cameron, acting Reclamation commissioner, in a press release.

Once those turbines are installed and join the existing five wide-head units, the cut to generating capacity when Mead drops below 1,035 feet will be 58 percent—less, but still significant. Reclamation’s press office did not respond to questions about the installation timeline before publication.

Hoover Dam’s hydropower is in jeopardy because of problems upstream at Glen Canyon Dam, which forms Lake Powell. In April, the Bureau of Reclamation decided to reduce water releases out of Powell this year by 20 percent. That stopgap decision was made to protect Glen Canyon’s fragile water-delivery infrastructure and to enable hydropower generation to continue. Without holding back water—and at the same time releasing more water from upstream reservoirs—Powell would have dropped below its hydropower trip wire by the end of the summer.

Hoover Dam annual electricity generation. (Geoff McGhee/The Water Desk)

Less water flowing out of Powell comes with an unfortunate side effect: the acceleration of Mead’s decline. Earlier this month, Mead was dropping roughly one foot every five days. It is now at 1,050 feet. At this rate, the 1,035 mark will be breached later this summer.

There is much uncertainty to that timeline, though. The lower basin states of Arizona, California and Nevada have proposed a conservation plan that might keep Mead above 1,035 until next spring. Mead’s rate of decline in the last week was a foot every five to seven days. The timing of the cliff depends on conservation, summer heat and whatever moisture the summer monsoon brings.

That means a lot of watching and recalibrating, said Dane Bradfield, general manager of Lincoln County Power District, in eastern Nevada.

“It’s not a kick-back summer by any means,” he said.

Rising Costs

Because his district has a contract for Hoover power, Bradfield is among those deep in the trenches. Hoover’s power customers are feeling the repercussions of declining hydropower generation.

Lincoln County Power District has more skin in the game than most. The district, which serves about 5,000 people in a county north of Las Vegas, gets about 70 percent of its electricity from Hoover.

The district forecasts power generation and demand. It then attempts to hedge against any shortfall with market contracts. Even with Hoover’s struggles, Bradfield said he is confident the district has secured enough power through 2026. He’s now looking ahead to 2027. Fortunately, market conditions are favorable right now.

“Our prices are somewhat low from what we’ve seen maybe a year or two ago, but it all changes so fast,” Bradfield said. “And that’s the volatility of the market and also the risk. But our plan right now is to make those purchases a year in advance and just be ready for when the bottom falls out of it.”

Lincoln County has also been acquiring solar power resources, which helped to cushion the hydropower shortfall that already occurred . Hoover’s output today is between 40 percent and 50 percent lower than it was in 2000, when Mead w…