It's a race to protect Flagstaff against monsoon flooding after devastating wildfires
In 2022, a fire tore through 40 square miles of the eastern slopes of the San Francisco Peaks in Flagstaff, burning away the trees and grasses that bolster the hills’ resilience against rainwater runoff and threatening several thousand homes. Since then, county officials have raced against more rain to control that runoff.
Up on the slopes of the Upper Copeland fan restoration project, a massive Caterpillar D9 earth mover works to recreate in months what took nature centuries. The fire’s origins are just on the other side of these hills. When it burned, it snaked over and then down them, charring away pine, brush and grass. And once that happened, there was nothing left on the slopes to keep the summer’s rains from surging down.
"You can see all the erosion taking place," said Lucinda Andreani, Coconino County’s flood control district administrator. She’s driving us onto the slopes of what’s become the county’s biggest project: harnessing flooding and guiding turbulent waters into controlled channels.
"So, as the water comes off the mountain, it’s very channelized, you can see the eroded channels. And then it hits this flatter area, and you can start to see that it’s fanning out," she said.
She maneuvers the SUV onto this fan-shaped deposit, or alluvial fan, where the earth mover is blading away the rubble brought down by last year’s 50 rainfall events, some of which saw several inches falling in less than an hour. New channels have opened up on the mountains like veins, giving the water the momentum of a freight train to fall onto Flagstaff. That wasn't the case in the past.
"If there were big rainfall events, water never ever reached the neighborhoods. Well now, because it’s been eroded and channelized, it is reaching the neighborhoods," Andreani said.
The goal here is to slow the water down, and that’s happening not only on the surface.
"Underneath these big wide areas that they’ve grade out, flattened out, we’ve placed rock underground. So, that if it does start to erode, it will hit that rock, spread out, slow it down and reduce the volume of erosion," she said.
An excavator steadily plucks enormous boulders out of a pile that was brought here from near the Grand Canyon and drops them into an entrenchment.
"See how he’s tamping down the rock. He’s picking out specific rock that needs to go in there. He needs to know how much spacing between the rocks, put the smaller rocks between that," Andreani said.
We step out into a windy day and onto the soils of the restoration project.
"This whole area was very heavily eroded and it was sourcing sediment so it was adding sediment, sediment that was ending up in the neighborhoods and in the infrastructure. This will probably be one of the largest fans that we’ve ever constructed out here," she said.
Andreani describes the whole project as a laboratory starting on high where steep mountains make it impossible to do this kind of work, drifting down into the fans we’re now standing on and then into managed downstream systems.
"The idea is once the water is all spread out, it flows into this terminal trench where they can collect it and then direct into this storm drain inlet there," said flood control community relations manager Sean Golightly.
The cost of these eight watershed restorations on the eastern slopes of the Peaks is running millions of dollars apiece. So far, the county has spent $18 million to restore more than 110 acres of watershed. In total, $90 million is slated toward these projects.
Nick Tordero lives near State Highway 89 amid the restorations.
He remembers watching the Pipeline Fire when it first exploded nearby.
"We were watching the fire coming over the Peaks, and the flames were blowing all over so the sheriff came out and we had to evacuate," he said.
Then the flooding began, and those powerful waters up on the slopes just beyond his house sent giant rocks crashing onto the highway.
"The boulders come down after the flood and they go on the freeway there, right on 89."
The goal for the flood control district is to get these measures built in three of the new flood corridors before monsoons arrive in 2024.