Grizzly Creek burn scar just the half of it in causing devastating Glenwood Canyon flooding last summer
Glenwood Springs Post Independent
A hike into ground zero above Glenwood Canyon where last summer’s mud and debris flows hit hardest provided some interesting observations into that historic weather event, a U.S. Forest Service scientist said.
Flood waters carrying large rocks, trees and massive amounts of mud that forced a 16-day closure of Interstate 70, followed by months of extensive highway repairs, was in part a result of unstable soils in the wake of the previous year’s Grizzly Creek Fire, said Ryan Sparhawk, a soil scientist with the White River National Forest, during a Garfield County commissioners meeting on Monday.
But it was the force and volume of the rain itself, in what weather observers called a 500-year event, that was the key ingredient, he said.
“The fire scar definitely had an impact on the debris flows, but there were other physical forces happening to produce all of that debris flow,” he said.
Sparhawk was part of a team that hiked in from the top of the Blue Gulch watershed in late August last year to try to determine where exactly the material that ended up on I-70 and in the Colorado River originated from.
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What they found was that only about 2 inches of soil materials washed off from the burn scar — which by itself would not have been enough to cause the damage that resulted, he said.
The vast majority of the large rocks and other debris that tumbled down into the canyon came from the scouring effect of all that water collecting in the various drainages and ultimately crashing through Blue Gulch, Sparhawk said.
“That volume of material moved by the water is what eventually made its way down to the interstate,” he said.
A similar scenario played out on the south side of the canyon in Cinnamon Creek above the Hanging Lake Tunnel command center and in nearby Deadman’s Creek, he said.
Different soil types in certain areas above the canyon are more prone to future runoff potential, and are where some of the post-fire mitigation efforts are focused to try to prevent flows of that magnitude from happening again, Sparhawk said.
Sparhawk’s comments came as part of a presentation by the Middle Colorado Watershed Council on its post-fire mitigation and preparations for future events related to protecting area domestic water resources.
County commissioners approved the county’s annual contribution of $10,000 to the MCWC for its general efforts to protect water users, and another $5,000 toward a three-year, $15,000 commitment aimed at post-fire restoration. The latter funding is part of a state funding match.
MCWC Executive Director Paula Stepp said the organization is working closely with municipalities along the I-70 corridor that use water from the Colorado River that have seen water quality impacts from recent wildfire events.
“The risk to water quality and quantity is the main concern we are trying to address,” she said.
Many of the rain gauges placed in Glenwood Canyon that were used to measure the record rainfall in late July and early August — including nearly 1.5 inches in 15 minutes in one instance — were, in part, a result of the MCWC’s efforts following the Grizzly Creek Fire, Stepp said.
The organization continues to work closely with municipal water providers in towns including Silt and Rifle on water quality and sedimentation monitoring, and provides alerts whenever there’s a concern, she said.
Similar efforts have been ongoing with agricultural water users near DeBeque, where another major wildfire, the Pine Gulch Fire, burned during the summer of 2020 at the same time as the Grizzly Creek Fire.