Mitigating monsoon damage to Arizona’s burn scars

PHOENIX (3TV/CBS 5) — 2022 was a very “wet” monsoon. In fact, it tied for the 7th wettest summer storm season on record. Over two inches fell in Phoenix from July through September. While it was a wet one here in the Valley, northern Arizona got in on the rain action as well. Over ten and a half inches fell in Flagstaff. Although it helped the dry forests, the heavy rains brought massive flooding along several burn scars left behind from recent wildfires. We decided to revisit one of the hardest-hit areas on the eastern slopes of the San Francisco Peaks.

Hydrologist and Watershed Program manager Kate Day unlocks a once pristine part of the Coconino National Forest that remains off-limits to the general public. As Day gazes back at the smooth hillsides, she described the Pipeline Fire burn scar as well as the old Schultz Creek fire that burned in 2010. Day said, “These areas are really high-hazard areas. We are wearing hard hats now. There are a lot of dead trees that can easily fall over. Roads can get washed out.”

The sheer power of flash flooding after monsoon storms last summer is clear and evident everywhere you look in this part of the forest. Deep gashes in the once fertile forest floor, huge rocks, and dead trees tossed aside from water racing down the blackened hillsides. “A channel like this, during the monsoon, can go from looking like this to literally being full of debris and water in a few minutes,” Day said.

We were sitting in the part of the Coconino National Forest that burned during the Schultz Fire back in 2010. Now 13 years later, the hillsides look different with lots of downed trees and shrubbery. That’s a good thing because those plants and shrubs help hold the soil in place. But the hillside that burned back in the Schultz Fire and re-burned last year during the Pipeline is completely smooth. When monsoon storms hit, the elevation and the smoothness dramatically increase the danger of flooding downhill.

Sandbags, still in place from last year, mark the cluster of homes that sit below the burn scars as construction crews race to finish a variety of measures to control these floodwaters. Day said, “We have these channels coming down off these hillsides. When they come into these flat areas, we are digging them out and putting in large rock control structures to spread out that flow and sediment to slow down that water before it enters the communities.”

Officials with Coconino County and the county’s flood control district describe this type of effort as “plug and spread.” It effectively reduces stream sediment and slows erosion by spreading and slowing the floodwaters. The design is minimally evasive because it takes advantage of existing forest creek beds. They believe these efforts will allow the City of Flagstaff’s new flood detention facility at Schultz Pass Road and Mt. Elden Lookout Road to function more effectively. The restoration of the specific Shultz Creek watershed is estimated to cost over five million dollars using federal funds. The county’s flood control district has invested over thirty-one million dollars between 2011-201 for this area alone.

In one neighborhood just northeast of Flagstaff, you can see the mitigation efforts in full swing. Construction crews will line these canals with concrete to channel water and debris away from neighborhoods. With human intervention happening down below, back up on the lunar-like landscape Mother Nature has provided the ingredients for the forest to heal.

Day said, “That record-breaking winter really helped us out. We also had a very slow snowmelt. We didn’t get a rain-on-snow event that would have resulted in more flooding. So that’s what’s really helped us with the green-up.” So how important is it for people to keep an eye on the weather? Day says it’s incredibly important. “I don’t think people realize how flashy these systems can be,” she said. “Like I said, they can go from nothing to massive flows in a matter of minutes.”

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