Big questions loom after inspection of #GrizzlyCreekFire burn scar — The #Aspen Times

From The Aspen Times (Scott Condon):

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 on 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, or BAER. That group of scientists and specialists started assessing the Grizzly Creek burn area for soil burn severity and potential problems areas for flooding and debris flows even before the fire was out.

Hunter discussed the role of the BAER 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 BAER team’s work helped determined 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 pre-fire ground cover and surface organic matter was consumed. The soil became hardened and will shed water instead of absorb it.

Burned Area Emergency Response (BAER) specialists recently completed their data gathering and verification field work of the Grizzly Creek Fire burn area. The Soil Burn Severity map has been finalized. Soil Burn Severity levels are Unburned, Low, Moderate, and High. The map shows that in the Grizzly Creek Fire area, approximately 45% of the 32,370 acres analyzed by the BAER team is either unburned (12%) or low (33%) soil burn severity, while 43% sustained a moderate soil burn severity, and 12% burned at high soil burn severity. Map credit: Inciweb

Firefighters did a remarkable job protecting two of the major drainages from the fire. No Name Creek, which drains down 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 may be 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 rock falls events even before the fire is even riper now…

The Grizzly Creek Fire jumped Grizzly Creek north of Glenwood Canyon. (Provided by the City of Glenwood Springs)

Several steps have already 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 website wasn’t operating properly Friday.) The U.S. Service assessed areas where culverts need to be cleared, repaired and even enlarged to handle expected debris flows…

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…

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…

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 may also need to be seeded.

The Forest Service has also secured funding for trail and road stabilization. Some of the work started last fall and will continue when the snow melts out.

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