So far, the ash and debris draining from the mountains into Tucson-area washes from the remaining damage of the 2020 Bighorn Fire is tame compared to last summer’s black goo. Above, the Cañada del Oro Wash flows onto The Loop bike trail at Magee Road.

 Rick Wiley, Arizona Daily Star

The recent monsoon storms have caused burn-scar debris and ash from last summer’s massive Bighorn Fire to run off in various Tucson washes, darkening the water.

Water flowing this week in the Pima and Cañada del Oro washes contained some ash from the 2020 fire on Mount Lemmon and in the Catalina Mountains, said Brian Jones, division manager at the Pima County Flood District.

A flash flood hit the Cañada del Oro Wash near Edwin Road in July 2020, during the burning of the massive Bighorn Fire in the Catalina Mountains north of Tucson. The flash flood carried burned debris and runoff from the fire. 

“There hasn’t been a rain event, yet, that’s really caused any severe issues on the washes that are coming out of the mountain, but they have been enough to get things wet,” Jones said Thursday.

“The last couple of days, the rain has been more focused over the low end and not so much on the mountain. If we get one big storm or a number of ... storms over the mountain, then everything is going to be fairly wet, so the likelihood of significant runoff coming off of the Bighorn burn scar is higher at this point.”

Last summer, videos popped up on social media of of black sludge with bunches of tree limbs moving down the Cañada del Oro wash as a result of the fire damage. While we haven’t seen that this year, Jones said the rains have similar intensity as last year’s and there is still more debris in the mountains.

Wildfires such as the Bighorn Fire north of Tucson leave the ground charred and unable to absorb water, which can increase flood risks. “Even a light rain can produce devastating flash floods and mudflows, often with little warning,” Pima County officials warned. In this July 2020 video, a debris flow oozes down the Cañada del Oro Wash.

“Assuming that we get more intense rainfalls and larger rainfall up on the mountain,” flooding might have the capability of “moving some of the larger dead burned trees and bushes,” Jones said.

Usually, the soil and vegetation can soak up the water and slow the water down. However, the severe fire wiped out vegetation, which increases flow velocities, erosion and volume of water coming down from the mountains, causing heavier flooding.

Jones says drivers should turn around or wait out floods when there’s water across roads. The post-fire flows can be even more hazardous because of the debris, including sticks and logs.

One year after the Bighorn Fire, the scars are still easy to see at Catalina State Park, but so are the signs of recovery. Video by Henry Brean/Arizona Daily Star

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