With projections showing a 71-foot rebound coming, Lake Powell resumes Grand Canyon’s experimental floods

Record snowpack expected to put 14.5 million acre-feet of water into upper Colorado, lift drought-depleted reservoir from its record low.

(Rick Egan | The Salt Lake Tribune) The Glen Canyon Dam, which impounds the Colorado River in Lake Powell, on Tuesday, Aug. 3, 2021. The level of the reservoir is expected to rise about 50 feet over its historic lows registered this year as runoff from massive snowpacks reach the river.

For the first time in five years, high volumes of water are gushing from the drought-depleted Lake Powell, replicating the spring floods that would naturally occur were the Colorado River not dammed at Glen Canyon.

The U.S. Bureau of Reclamation on Monday opened the gates at Glen Canyon Dam allowing up to 39,500 cubic feet per second, or cfs, to pour into the river channel at Lees Ferry, sending a flood-stage surge of water through Grand Canyon. That’s like the contents of 27 Olympic swimming pools a minute spouting through the bottom of the dam.

“These experiments are really designed to recreate habitat and the physical attributes that would have existed downstream from the dam, but for the existence of the dam,” said Amy Haas, executive director of the Colorado River Authority of Utah (CRAU), at last’s week board meeting. “In this case, what I’m talking about is building up sandbars using sediment that has accumulated.”

The 72-hour experiment comes as Lake Powell begins to rebound from record low levels as the runoff from record-setting snowpack begins to flow into the upper Colorado River.

Under a plan approved in 2012, the bureau had been conducting high-flow experiments almost annually until 2018. Since then, a string of dry years and excessive water use have depressed levels of Lake Powell, which today is only 23% full, sitting at 3,525 feet above sea level.

That is about to change drastically in the coming weeks as the upper Colorado basin’s snowpacks, which are 157% of normal, melt and flow into Powell and upstream reservoirs. The lake level is projected to climb by more than 50 feet this year, according to Bart Leeflang, the CRAU’s hydrologist.

“If there is a time to gloat about hydrology, now is the time to do it,” he said at last week’s board meeting. “It is amazing what has happened between March and April.”

What happened in those months was a big snowpack getting bigger, holding twice as much water in some places as normal for this time of year, coming after back-to-back years of skimpy snow accumulations. According to Bureau projections, the lake level is expected to peak in July at 3,591 feet, 71 feet above its historic low recorded April 13.

“A couple years ago, we were bemoaning the fact that we had lost 2 million acre-feet from April to May [from Lake Powell],” Leeflang said. “And now you see that we picked up 2 million acre-feet in two weeks in March.”

At 3,576 feet, Powell would still remain 124 feet below full pool, holding just 39% of its capacity. This year’s bounty doesn’t put an end to the crisis on the Colorado River, which supplies 40 million Westerners and irrigates 5 million acres, but it buys Utah and the six other basin states time to find a lasting solution to the river’s chronic deficits. It may even rescue boating this summer at Lake Powell, among Utah’s top recreation draws, where most of the ramps are high and dry and marinas are unusable.

Average flows on the river have declined in recent decades as global climate change turns the West warmer and drier, while the region’s water needs continue growing.

This year, the Bureau plans to increase releases from Glen Canyon Dam to 9.5 acre-feet to bring up the level of Powell’s downstream big sister, Lake Mead. That’s the maximum amount released under the dam’s operating guidelines and 2 million more than what is typically released in a year.

The big spike in Lake Powell’s projected “regulated” inflows, expected to total 13.2 million acre-feet, has enabled federal river managers to resume the high-flow experiments.

“The 2023 water year was an exceptional hydrological period for the Colorado River basin. High snowpack in the western United States was a welcomed change following multiple years of severe drought conditions,” wrote Wayne Pullan, the Bureau’s Upper Colorado Basin regional director, in an April 14 memo. “The low annual release volumes for the last year have also enabled the holdover of large amounts of sand in Marble Canyon, which in higher volume release years is quickly washed downstream.”

These sediments should replenish sandbars and beaches in the Grand Canyon, but Glen Canyon Dam, completed in 1963, disrupted the natural processes that push them downstream, resulting in a loss of habitat for plants, animals and fish.

Much of the water released during the experiments bypasses the dam’s eight hydroelectric turbines, but that won’t result in an increase in the amount of water released by the dam.

Under normal operations this April, dam releases would fluctuate between 8,033 and 14,631, depending on the time of day, according to the Bureau. This week’s high-flow experiment is the sixth since the agency started them in 2012.

Over these past five years since the last experimental release, huge volumes of sediments have piled up in Marble Canyon and where the Paria and other tributaries meet the Colorado below the dam.

“Releases like this one are experimental in nature and are designed to achieve a better understanding of how and when to incorporate them into future dam operations in a manner that maintains or improves beaches, sandbars, and associated habitats,” the Bureau said in a news release.

The Grand Canyon Monitoring and Research Center and the National Park Service will monitor the effects of the high flows on the canyon’s beaches, fisheries, aquatic insects, and archaeological sites.

Meanwhile, the Bureau is studying ways to adjust Glen Canyon releases to prevent smallmouth bass, a nonnative predatory sport fish, from escaping into the lower Colorado River and proliferating in Grand Canyon. Powell’s low water has allowed the species to pass through the Glen Canyon Dam turbines and establish reproducing populations in the river below where it could prey on endangered native fish.