A just-arrived high pressure system that is expected to burn off snowpack and speed runoff has water managers ready to open the spigot at Jackson Lake Dam.
The Bureau of Reclamation since Wednesday boosted water releases from the dam by 50%, and going into the weekend water was coursing into the Snake River at a rate of 3,000 cubic feet per second. Peak outflow from the 30-foot-high dam likely won’t come until early June, but the bureau anticipates upping the volume at a “pretty good rate” over the next week.
“A lot of it depends on what that rain looks like next weekend,” said Brian Stevens, a water operations manager for the bureau’s Upper Snake Field Office. “Tentatively, we’re thinking about going up another 500 cfs.”
River flows lower in the valley are dictated by much more than Jackson Lake releases. Typically, by the time the river reaches the Snake River Canyon, about three-quarters of its volume comes from undammed tributaries like the Gros Ventre, Hoback and Buffalo Fork rivers, and other streams.
Runoff in the Jackson Hole area on average doesn’t peak for a few more weeks. At the urging of the Wyoming Game and Fish Department, the bureau tries to mimic the natural order with releases, Stevens said.
“Game and Fish understands the biology and the response from the fish in the river,” Stevens said, “and they say that that benefits fisheries.”
During the winter of 2017-18 — which had a more substantial snowpack than last winter — the bureau was able to align the releases with the runoff or “inflow” coming into Jackson Lake. Mimicking nature isn’t always possible, though, because the agency has flood control requirements it also must adhere to that include leaving a set amount of capacity available in Jackson Lake and Palisades Reservoir.
“It’s difficult when you’re looking at the fishery and you’re looking at the flood control to shape your outflow,” Stevens said. “You’re looking at so many things.”
The U.S. Army Corps of the Engineers, which manages the river’s erosion-prone levee system, also has to sign off on the water release plan.
As of Friday, Jackson Lake was 77% full and Palisades 51% full, which is as low as they’ll go early this year, Stevens said. Both impoundments are operating under flood control rules, he said, although the watershed isn’t as flush as it was the last two winters.
Stevens will venture to Jackson for the Bureau of Reclamation’s annual water supply and operations meeting, which is set for 5:30 p.m. May 23 at the 49’er Inn conference room.
The following day agency personnel will lead a “windshield snow survey” trip through the headwaters of the Snake River watershed to observe the remaining snow.