Glenwood Canyon closes again as forest ecologists scramble to seed burn zone and prevent mudslides — The #Colorado Sun

From The Colorado Sun (Jason Blevins):

“It has not taken a whole lot of rain to move what has moved so far so I anticipate there will be more movement in some of those same drainages but it’s hard to measure and know exactly so much,” said Elizabeth Roberts, an ecologist with the White River National Forest who has spent most of the past year planting grasses in the burn scar to stabilize soil and restore damaged terrain.

New plating at the Glenwood Springs water intake on Grizzly Creek was installed by the city to protect the system’s valve controls and screen before next spring’s snowmelt scours the Grizzly Creek burn zone and potentially clogs the creek with debris. (Provided by the City of Glenwood Springs)

The seeds Roberts and her team sow will eventually become the rooted plants that keep soil from moving in the dozens of debris fields that funnel into Glenwood Canyon’s Colorado River. But since the Grizzly Fire burned into winter last year, she’s racing to get seeds into every path of scorched earth. Many of the Grizzly Creek Fire’s 32,631 acres are in steep, rocky chutes where seeds would not take anyway.Everyone knew the runoff and rains of 2021 would pose a threat to Glenwood Canyon. The City of Glenwood Springs spent more than $10 million on emergency watershed protection projects that included replacing and upgrading water intakes and filtering systems in the No Name and Grizzly Creek drainages where the city collects its water.

Swift protection for the highway from rain-loosened debris was much more difficult, if not impossible…

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

The U.S. Geological Survey created a landslide hazard map following the Grizzly Creek Fire that identified dozens of drainages where the likelihood of debris flows was increased if the area saw only 15 minutes of rain that fell at a rate of roughly an inch an hour. That map was spot on. Debris flows that shoved tons of mud onto the highway have come from three separate areas where the USGS estimated the chance of debris flows was between 40% and 100%.

Forest and transportation officials were working with models, so the actual amount of mud coming down and where it might end up was impossible to predict…

Roberts has been doing most of her seeding work on the rim above the canyon. She’s been surprised to see lots of natural vegetation coming back in the first year. The growth of herbaceous shrubbery — known as forbs, which are neither grassy nor woody, like snowberry, chokecherry and fireweed — has been “quite significant,” Roberts said.

That’s been helpful because forest botanists are generally speeding native grasses, which can take a couple years to firmly establish, depending on the health of the soil…

Mitigation in the narrow canyon is complicated. The stretch of interstate built between 1980 and 1992 is an engineering marvel, heralded not only for its ingenious efficiency but how its minimal footprint protected as much of the canyon as possible. When a fire hit perhaps the worst place on Interstate 70 for a burn scar, there just isn’t much room for barriers and other strategies for protecting roads from rain-riding debris. That isn’t stopping CDOT from trying to find ways to divert flows of mud and rock.

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