Heavy rains in early late June and early July have triggered flash floods and multiple debris flows in the Grizzly Creek Fire burn scar area, causing extended safety closures along I-70 through Glenwood Canyon, Colorado. These debris flow events on June 26, 27, and July 3 impacted hundreds of feet of road and were reported to be nearly 10 feet deep.
Although debris flows happen suddenly, they are not unexpected in this post-wildfire system.
The Grizzly Creek wildfire ignited on Aug. 10, 2020 in Glenwood Canyon, east of Glenwood Springs, Colo. While burning, the Grizzly Creek Fire was one of the nation’s top priority fires because of the critical infrastructure threatened including I-70, the Shoshone Power Plant on the Colorado River, railroad and numerous recreation opportunities. The fire was not fully contained until nearly four months later in Dec. 2020, after burning 32,631 acres. But the dangers of the Grizzly Creek fire didn’t stop when the fire was extinguished; it left the landscape changed and vulnerable to the exact scenarios Colorado has experienced over the last few weeks.
Utah State University’s Utah Water Research Laboratory and Civil and Environmental Engineering faculty member Belize Lane and doctoral student Haley Canham are part of the team picking up where the firefighters left off. As part of Lane’s National Science Foundation RAPID Grant, she and her students are monitoring the post-wildfire hydrologic response to track changes in streamflow and sediment dynamics in the Grizzly Creek Fire burn scar. Numerous flow gaging stations have been installed on the mainstem Colorado River and burned tributaries within Glenwood Canyon to monitor post-wildfire streamflow in response to precipitation events.
“Soil in a burned area has a decrease in organic matter and increase in ash, which results in a hydrophobic and loose soil that repels water” Lane explained. “As a result, infiltration decreases and runoff increases. When intense rainstorms occur in a burned landscape, such as those seen at Grizzly Creek Fire, the runoff can result in flash floods and debris flows, which are fast-moving landslides that can endanger life and property. This increase in streamflow may also increase the rate and volume of sediment that is transported downstream, where it can cause flooding, reduce reservoir storage and damage aquatic habitat and water resources infrastructure. Understanding how the runoff and sediment response vary for different burn severities (high to low) and landscape conditions (i.e. watershed size, slope, aspect and vegetation) will help natural resource managers manage post-wildfire risk and plan for a future with more fire.”
Lane and her team are collaborating with a broader group of scientists from the Department of Watershed Sciences at USU, Simon Fraser University, Virginia Tech and the United States Geological Survey Landslide Hazards Program to model impacts of wildfire on sedimentation in Utah. Lane and team will continue to monitor and make field visits to the Grizzly Creek Fire area for the remainder of the year to improve understanding of hydrology in burned landscapes and mitigate future risks.
Utah Water Research Lab
Utah Water Research Laboratory, Department of Civil and Environmental Engineering
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