As snow melts and recedes into spring, many communities east and west of Glenwood Canyon are keeping a keen watch on whether this awakens the return of disruptive debris flows.

Closures in Glenwood Canyon are especially on everyone’s radar.

For instance, speaking on canyon crashes in February, Glenwood Springs Chamber of Commerce President and Chief Executive Officer Angie Anderson said “approximately $1 million is lost for every hour that (Interstate 70) is closed on the mountain corridor.”

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On Tuesday, Rifle City Manager Tommy Klein echoed this spirit.

“It affects the delivery of food, fuel, the ability of people in our area to travel upvalley for work and to Denver or any location east of us,” he said. “Having to take a detour that adds several hours to anybody’s trip is just very inconvenient.

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“It doesn’t only affect Rifle. It affects interstate commerce, really, and the entirety of Western Colorado.”

Regrowth

One bit of good news heading into the warmer months is that scientists with the United States Forest Service and U.S Geological Survey now say revegetation on the massive burn scar created from 2020’s Grizzly Creek Fire is coming along rather nicely. 

Specifically, vegetation is quantified by what’s called the Normalized Difference Vegetation Index, a formulaic system that essentially determines just how green an area is. According to the burn scar’s NDVI, its vegetation is currently 50% recovered from what it was preceding the Grizzly Creek Fire, an area that encompassed nearly 33,000 acres in Glenwood Canyon.

U.S. Forest Service Ecologist Liz Roberts told the Post Independent on Friday that when a chain being dragged from a vehicle across I-70 likely ignited the Grizzly Creek Fire, the ensuing wildfire burned across variable habitat types, including conifer, aspen and shrub mixes.

Luckily, the majority of these areas sustained low- to moderate-burn severity, GIS maps show. This means seed stock within the soil is better maintained and the likelihood of water being absorbed into the ground is higher.

But it was the high-severity burn areas being hit by a 500-year rain event in the summer of 2021 that led to catastrophic mud and debris slides trapping people in tunnels, prompting millions of dollars in federal aid and, at one point, closing I-70 in Glenwood Canyon for two weeks straight, in addition to ensuing intermittent closures.

“But in the areas that we had more moderate, steady rain we had a vegetation recovery,” Roberts said. “Some of those aspen areas are over six feet now, which is what we typically see when an area is being regenerated in a healthy way.”

This positive vegetation recovery is conducive to stabilization, Roberts said. By stabilizing healthy soils, not only is it promoting plant diversity, it’s deterring the threat of invasive species further damaging an already fragile ecosystem that has continued to close down I-70 and give people like Klein and Anderson unwanted headaches. 

“Long-term benefits are, over time, that seed source is moving into those other moderate to high (burn severity) and providing that seed source for those areas that are taking a little bit longer to recover.”

Soil cycles

White River National Forest Soil Scientist Ryan Sparhawk is tasked with ascending new heights when it comes to rejuvenating the high-burn severity areas still comprising the scar.

Low – to moderate-severity burn areas typically see the top growth burned off, but the organic matter and microbial populations and soil structure retain and remain intact. This is why their revegetation cycles are growing back, Sparhawk said.

High-severity burn areas, however, felt the brunt of Grizzly Creek’s wildfire. The top soil was scorched. All vegetation was lost. All organic matter was gone. The root system was no more.

“Where those high-burn severity locations that occurred were high up in the watersheds, in deeper timber, where higher fuel loads were,” Sparhawk said.

“Just after the monsoons that were causing the debris flows on the interstate, I saw a loss of two to four inches of topsoil in those in those high-burn severity areas.”

This is prompting Sparhawk to spend this coming summer conducting observational activities in the high-burn severity areas near the Flat Tops above Glenwood Canyon. The Forest Service is also planning to use a helicopter to drop a cocktail of fertilizers onto these specific areas with the aim of promoting soil health, while applying wood mulch to decrease soil temperatures.

“In other revegetation projects I’ve done before, depending on the inputs — the fertilizers, soil preparation — I look for a successful revegetation at between three and five years,” Sparhawk said.

If this manipulation goes accordingly, it will allow for water to once again infiltrate the soil as opposed to causing runoff and further debris flows.

“We’re not able to manipulate the soils other than the addition of these amendments and wood chips, because all this is being applied by helicopter,” Sparhawk said. “So there’s no tilling, there’s no breaking up the soil. This is all just adding another addition for nature to do its process on its own. 

“So it’s slow.”

Less flows

Francis Rengers is a USGS research geologist investigating the ensuing debris flows from the Grizzly Creek Fire. By using lidar technology to measure typography — this is done by a plane flying over Glenwood Canyon and pointing a laser at the landscape — he can extrapolate just how much elevation essentially eroded due to the debris flows.

Rengers said on Tuesday that about 300,000 cubic meters of erosion deposited onto I-70, the Colorado River and even the flow channels during the 2021 debris flows. Sediment still stored to this day is in places like Devils Hole and Grizzly Creek itself.

“One of the things that’s great about the revegetation is it just increases the roughness on slopes,” he said. “It makes it so the water doesn’t flow as fast, so it doesn’t have as much energy to scour sediment.”

“The other piece of that is a lot of sediment that was available to get scoured, is now gone.”

As Glenwood Canyon heads into its third year after the Grizzly Creek Fire, there’s still always a chance of another debris flow occurring. But as revegetation continues at a favorable pace, Rengers said the probability of further slides and more closures of Glenwood Canyon “is going down.”

“Probably the best thing I can say about year three is that in the Western United States, there are very few reports of debris flows generated by water runoff three years after a fire. It’s rare,” he said. “I think that bodes well for us.”

Post Independent western Garfield County reporter and Assistant Editor Ray K. Erku can be reached at 612-423-5273 or rerku@postindependent.com