It’s a great rarity in modern times for the Upper Snake River watershed to resemble anything close to its natural condition.
But in less than a week, it’ll be about as close as it gets. The most upstream impoundment in the river system, Jackson Lake, is about the height of a human higher than it would be without the Jackson Lake Dam, which ordinarily adds up to 39 feet. And the Snake River through the heart of Jackson Hole will soon carry close to the same volume of water as would naturally be draining off the landscape. In the fall, that means not much.
First, though, the Bureau of Reclamation must make some major adjustments. It has been a particularly poor water year in the Snake watershed and the American West in general, and the federal agency that manages the dam has kept flows high — emptying Jackson Lake — at the behest of senior water right holders in Idaho’s Magic Valley. Slowly over the next five days, that will change. On Wednesday there was about 3,000 cubic feet of water coming through the dam’s gates every second.
“We have to get down to about 300 cfs by the morning of Oct. 5,” said Brian Stevens, water operations manager for the Bureau of Reclamation.
The 90% reduction in river flows will be gradual. The ramp-down starts at 9 a.m. today. At noon and then again at 3 p.m. the Jackson Lake Dam’s gates will slowly close, the effect being a 6- to 10-inch daily decrease in the Snake River’s water level all down the valley.
The federal agency stretched out the drawdown and is executing it more incrementally throughout the day at the request of the Wyoming Game and Fish Department, which had concerns about fish being stranded in Snake River side channels that will soon be dewatered.
“It was originally going to be four days,” Stevens said. “But now it’ll be six days, so we’re starting a day earlier and wrapping up on Tuesday morning.”
But even the elongated drawdown schedule hasn’t allayed all concerns.
Retired fly-fishing guide and longtime Jackson Hole News&Guide columnist Paul Bruun remembers falls from decades ago when flows out of the dam were slashed too abruptly. Mature cutthroat trout and larger fish of other species generally figured it out and found their way to the main channel in time.
“But the smaller fish — the dace and sculpins and all the aquatic invertebrates — they don’t move out,” Bruun said. “They get stuck, and that’s the tragedy of a fast drawdown.”
Bruun, the Snake River Fund and others will be monitoring the river stages and bug communities as the water volume falls by 90% over the next week. Their intent is to build their case, with the hope that the Bureau of Reclamation would consider an even lengthier drawdown if similar conditions arise in the future.
“There’s a lot of people fired up about this,” Bruun said. “This is an unusual year, but we’re going to be facing a lot of unusual years, because, let’s face it, winters aren’t the same as they used to be.”
The drought-stricken 2021 water year is emblematic of that likely future, the result of humankind’s warming of the planet. At the moment there’s near-record lack of water in the Upper Snake River system.
As of Monday, the combined storage between Jackson Lake and Palisades Reservoir was only 1% away from the all-time record low for Sept. 27. Just 17% of the augmented pool in Jackson Lake remained on Wednesday, while Palisades was sitting at 7% full. The largest impoundment in the Upper Snake watershed, American Falls Reservoir, is holding just 6% of its capacity.
Projections are that the Upper Snake watershed’s nine reservoirs will collectively contain just 15% of the 4.2 million acre-feet of water they’re capable of holding going into the winter, Stevens said. It’ll be about as bad of a year as 2013.
“Storage is really low,” he said. “Soil moistures [are] still really low; actually they’re setting record lows. On the bright side, I’m surprised that inflows or base flows have kept up.”
As of Wednesday, about 200 cubic feet of water was flowing down the Snake River and into Jackson Lake every second, 33% less than the historical average. So even once the dam releases lower to 300 cfs by the middle of next week, the lake will continue to gradually empty.
This winter even a normal snowpack won’t cut it, at least if the goal is to return to hydrological normalcy. It will take approximately a 130%-of-average snowpack to refill the reservoirs in the Upper Snake watershed next year, Stevens said.