It’s Mid-May, I’m at the Boise airport, hopping in a Cessna with pilot Don Reiman and Kevin Lewis, the director of Idaho Rivers United. We’re going to “fly the flood,” to see what the swollen rivers and reservoirs look like from the air, especially along the Boise and Big Wood rivers.
There has been months of flooding on Idaho rivers, with a reservoir system that’s been straining at capacity, as the deep winter snowpack has slowly melted off. Now, in the second half of June, the floodwaters are receding.
Don sketches out the flight path.
“We’ll take off. We’re going to go north. We’ll fly up to the Sawtooth Mountains,” he explains. “And we’ll be able to show you the split between the Payette River drainage and the Boise River drainage and you’ll be able to see how much snow’s up there. And we’ll fly back down. Anderson Ranch, and then Arrowrock, Lucky Peak and then we’ll fly down the river and come back.
First stop: Lucky Peak reservoir, where a thin band of sand meets the water’s edge.
“See the sandy beach?” Don asks. “When it’s clear full, the water is at the top of that sand that you see around the shoreline.”
“That’s the reservoir with the most amount of available storage right now,” Kevin adds. He worries about reservoir capacity and the potential dangers downstream.
Together, Don and Kevin explain how Lucky Peak Reservoir backs up to the face of Arrowrock Dam, which was dedicated in 1915. It would hold the honor as the world’s tallest concrete arch dam for the next nine years.
As we fly over Arrowrock, Don points out that it’s at capacity. Kevin explains how once the dam is full, it goes over into an emergency spillway.
“Are they pumping water out the tubes?” Don says.
“Yeah, it’s coming out the tubes of the dam and of course the powerhouse, Kevin says. “But the powerhouse takes only a couple thousand cfs. So there’s about 20,000 cfs coming out of that dam. You can see the logs and the debris in the reservoir down there.”
We fly north/northeast and climbing above 10,000 feet, looking down on a snow line that is as low as 8,000 feet. Kevin points out fresh snow.
“I think the telling number is we still have over a million acre feet of water in the basin in snowpack. You can see down in the middle fork the flows are really high. All your gravel bars are covered up, it’s running through the bushes.”
Don guides the plane up to 14,000 feet as we approach the crest of the Sawtooth Mountains. He points out where four drainages—the Boise River drainage, the Payette River drainage, the Salmon River drainage and Wood River drainage—all come together.
Kevin notices there’s flooding here, but it’s not where people live.
“There’s other watersheds in the state that are causing problems, but both the Big Wood and the Boise because of how we encroached so much on the flood plains,” Kevin says. “We kind of built ourselves into a place where we don’t have a lot of options in the Boise.”
We pass the upper headwaters of the Salmon River and head over the Galena Range to the Wood River Valley. The Big Wood is right below us. Don points out all the snow that’s headed for the Boise River.
“Oh, Kevin,” he says, “look over here. This river is out of its banks. Boy, it’s really muddy. You don’t see it that high very often down there.”
The airport in Hailey comes into view.
“That’s the drainage dividing line right there,” Don says. “So if you follow that ridge, and that one over the cloud on up, everything on the other side is Boise River.”
“And all that snow in the background all the ridge of the Sawtooths, that’s Boise River you’re looking at,” Kevin adds.
“We’re looking at the future, I guess,” I say.
Then it’s past the Trinity Mountains and on to Anderson Reservoir.
“The backwaters of Anderson ranch reservoir – as you can see it’s essentially full,” Don says.
Then down through the city of Boise, along the river out to Eagle. A squall is brewing in the western sky and we don’t want to be out too much longer. As we approach Eagle Island, we see barricades along the river to keep it out of the surrounding gravel pit. This, says Kevin, is a concern.
“That’s one of the biggest fears,” he says. “Because the waste water treatment plant is below us here at one o’clock. So if you get the river over here and it starts carving a new channel, it could put the waste water treatment plant at risk. Because the south channel of the Boise River is right there in those trees. “
We fly back to Boise to land. It seems dire, and in mid-May it is. But in the month since that flight, those three reservoirs are even more full.
The flows in the Boise River at Glenwood Bridge would hit another peak on June 4th and then recede. Same with the Big Wood River. Another spike in the first week of June before dropping.
Looking back, it was due to some cool weather days and some careful water management that allowed the system to recover.
Support for environmental reporting on Boise State Public Radio comes in part from the Larry & Pam Cardinale Preservation Fund.
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