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by Allen Best

The risk of lower and lower water levels in Lake Powell and other reservoirs in the Colorado River Basin keep getting higher and higher.

An analysis by the U.S. Bureau of Reclamation released Sept. 22 finds an elevated risk of 25% to 35% of the water level in Powell falling below the minimum power pool by July 2022.

Minimum power pool is the level below which there is insufficient power to produce electricity.

The drought began in 2000, but as several studies have concluded that drought fails to fully describe what is happening in the river basin. Those studies point to rising temperatures that have produced aridification. Even with the same volume of water falling from the sky, less of it will become river water.

As an Aug. 24 article in Science magazine pointed out, about 17% of baseline precipitation ended up in the Colorado River in the 1930s and ‘40s, with a majority of that water coming from Colorado in the form of snowmelt. Today, it’s about 14%.

Since July, the Bureau of Reclamation began releasing wat from its smaller reservoirs upstream of Powell—Flaming Gorge, Blue Mesa and Navajo—with the hope of augmenting Powell sufficiently. The headwaters states for the Colorado River had an exceptionally dry spring, exactly opposite of what was happening east of the Continental Divide in Colorado. The runoff into Lake Powell was 26% of average, despite near-average snowfall last winter.

Total storage in the Colorado River reservoirs today is 39% of capacity, down from 49% at this time last year.

John Fleck, writing on his website, Inkstain, called the latest announcement “something remarkable.” The government predictions used something pioneered a decade by Eric Kuhn and Dave Kanzer of the Glenwood Springs-based Colorado River District along with John Carron of Boulder-based Hydros Consulting. They thought it not useful to base predicts on the full hydrologic record of the Colorado River going back to 1906. Instead, they said, better would be to use a short-term frame, the last 30 years. They call it the stress test.

“The idea is that the traditional approach—using the entire period of record to model the probabilities of future river flows—is no longer valid because climate change is changing the river,” he explained.

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