The height of the runoff season has either arrived in Jackson Hole or is about to, though rivers are destined to be less flush than in the last couple of years.
Partially, that’s because the preceding runoff seasons came in banner years for river flows. In 2017, flows crested at 30,500 cubic feet per second in the Snake River Canyon — almost double the historical average. Likewise, 2018 beat the norm by more than 50%.
A reason for this year’s more mild-mannered torrents comes from snowfields still held intact by cool weather, said Brian Stevens, water operations manager for the Bureau of Reclamation’s Upper Snake Field Office.
“We had a really good snowpack, and we still have a good snowpack,” Stevens said, “but it doesn’t look like the runoff is going to be too great here.”
Peak Snake flows usually come the first week of June at 14,700 cfs, and it’s possible that the river levels hit their highest level of 2019 several weeks ago when the gauge just above Alpine measured 17,200 cfs. Stevens’ forecast models have called for a return to river levels in that same territory this week, though whether gauges will climb that high will depend on temperature and precipitation.
Bridger-Teton National Forest River Manager David Cernicek said the colder weather that’s moved through the region has caused large swings in river levels.
“We’ve had the Snake fluctuate between 6,000 and 14,000 within a couple of days, up and down,” Cernicek said. “A lot of it is just those tributaries getting frozen back up.”
While tragedy has already struck higher up the Snake in Grand Teton National Park, Cernicek hadn’t heard of any emergencies on the Bridger-Teton as of Friday. Activity on the river has remained relatively quiet, he said.
“The tourists have hit, and we’re seeing them in town, but they’re just starting to go to the river,” he said. “When we have cold, dreary mornings people aren’t inclined to be booking river trips.”
Mad River Boat Trips floor manager Emily Moyer confirmed that it’s been slow going so far. The Snake is just getting high enough, she said, where the company is starting to impose special age restrictions for the canyon’s whitewater stretch. Rafters had to be at least 13 years old on Friday, she said, though the minimum age fluctuates day to day. Private and commercial boaters alike should have safety in mind, Cernicek said. That means, he said, only embarking on floats led by experienced river rafters, leaving behind itineraries with friends and families, and dressing appropriately.
“The thing about this time of year is that the water is a lot colder,” he said. “It may be a 70- or 80-degree day, but the water is straight snowmelt, so dress like you’re going to be swimming in it.”
One upside of the slow-and-steady melt is that it tends to mean more water in the system later in the summer. The high “base flows” that result can be a boon for fishing. They’ll be bolstered by steady releases from Jackson Lake Dam, which Stevens forecast at somewhere in the 2,000 to 2,400 cfs range.
One factor unlikely to upset that schedule this year is drought and the irrigation needs of Idaho’s Snake River Plain, where farmers hold senior water rights. Due to cold and precipitation, irrigation demands dipped into all-time record low territory this spring, though Stevens said he anticipates they will be back to average in a week or two.