Big questions loom after inspection of Grizzly Creek Fire burn scar
Flash floods and debris flows are big threats to Interstate 70 in Glenwood Canyon going into spring and summer
The Aspen Times
ASPEN — The Grizzly Creek Fire covered 32,631 acres before it was officially deemed contained Dec. 18. It shut down Interstate 70 for two weeks after it ignited Aug. 10. It threatened Glenwood Springs’ water supply and forced the closure of popular hiking trails and rafting put-ins.
The disruption likely isn’t finished.
“We’re going to learn a lot this summer,” said Steve Hunter, a former engineer with the White River National Forest and member of the Burn Area Emergency Response team. That group of scientists and specialists started assessing the Grizzly Creek burn area for soil burn severity and potential problem areas for flooding and debris flows even before the fire was out.
Hunter discussed the role of the response team and the major issues facing the Grizzly Creek Fire burn scar during a videoconference Thursday night hosted by Roaring Fork Conservancy, a Basalt nonprofit that explores all issues related to water in the Roaring Fork Valley.
The response team’s work helped determine that 12% of the terrain within the perimeter of the fire suffered a high level of burn severity. That means all or nearly all of the ground cover and surface organic matter was consumed by the fire. The soil became hardened and will shed water instead of absorb it.
Another 43% of the terrain suffered moderate burn severity, 33% of terrain sustained low severity and 12% was unburned.
Firefighters did a remarkable job protecting two of the major drainages from the fire. No Name Creek, which drains into a residential area, was only 8% burned. Grizzly Creek was 14% burned. Terrain in other catchments was up to 40% burned.
The areas that suffered the most fire damage could be the most susceptible to flooding, debris flows and rock falls. The Glenwood Canyon walls are steep, Hunter said.
Many of the roots and vegetation that anchored rocks and dirt have disappeared. So a canyon that was susceptible to rockfall events even before the fire is even riper now.
“This canyon is very susceptible to rockfall,” Hunter said.
Several steps already have been taken to try to gauge the risks and provide tools to warn about threats to Interstate 70, utilities in the Colorado River corridor and homes in populated parts of the canyon.
Numerous rain gauges were installed high up the canyon walls to help foresee flash-flooding potential. The U.S. Geological Survey has run hydrologic modeling and runoff for major drainages within the burn area. The U.S. Forest Service assessed areas where culverts need to be cleared, repaired and even enlarged to handle expected debris flows.
“Post-fire (Burn Area Emergency Response) implementation started late last fall and will continue this summer,” said Elizabeth Roberts, ecologist and response team coordinator for the White River National Forest. “We are doing emergency repairs on all recreation trails and roads within the canyon.”
At this point, the Forest Service does not plan to reseed significant acreage within the burn area. One hurdle is the terrain itself. Sending hand crews up the steep slopes is not practical or safe, and it would be difficult to seed by airplane.
“We have to have access, and access in that canyon is challenging,” Roberts said.
Where access isn’t as big of a challenge, the Forest Service will monitor conditions to determine if terrain can be managed for natural recovery. In other areas, such as the interstate right of way and at trailheads, the Forest Service is working on reseeding with the Colorado Department of Transportation.
Specific areas will be targeted for recovery.
“Fire suppression lines need help,” Roberts said.
Places where firebreaks were cut by bulldozers or hand crews, for example, need soil amendments at the least to help natural vegetation grow back. Some of those areas might also need to be seeded.
The Forest Service also has secured funding for trail and road stabilization. Some of the work started last fall and will continue when the snow melts out.
White River National Forest spokesman David Boyd said the agency’s tentative plan is to open trails in the canyon, including the popular Hanging Lake, on May 1. Details will be released in March.
The Grizzly Creek and Shoshone rest areas remain closed. The Forest Service wants to coordinate the opening of the trails with those amenities.
A group called the Glenwood Canyon Restoration Alliance has been created to help with the ongoing restoration effort.
Hunter told an audience of about 50 people on the Roaring Fork Conservancy videoconference that a lot of what unfolds in the Grizzly Creek burn area will depend on weather this summer and over the next three to five years.
Christina Medved, director of community outreach for Roaring Fork Conservancy, noted the paradox facing the Grizzly Creek burn area.
“We really need rain because we’re in a drought, but what’s going to happen (if it rains)?” she asked.
This story is from AspenTimes.com.
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