Areas within Silver Creek Fire perimeter at increased risk of flooding
Although the Silver Creek Fire hasn’t burned in months, the impacts of the fire remain in the visual and physical landscape. In particular there is an increased risk of flooding in the area due to the impact the blaze had on surrounding watersheds.
After the fire was contained in October, a Burned Area Emergency Response (BAER) team conducted an assessment of the affected portions of the Routt and Arapaho National Forests. The team’s report found that floods and debris flows will likely occur more frequently and at a larger magnitude in areas that were already at risk.
“When (the land is) not retaining that water upstream where it’s needed, where there’s vegetation and a landscape and an ecosystem that needs that water upstream, (…) you get not enough water in one spot and too much water, oftentimes, downstream” Aaron Voos, communications director for the Medicine Bow Routt National Forest.
An estimated 38 percent of the area within the Silver Creek Fire perimeter had a high or moderate soil burn severity, where it will be harder for the land to absorb water.
The BAER report indicated that the area most at risk for increased flood flows during thunderstorms is the Elk Creek sub-watershed, which is located north of Latigo Ranch. Models suggest the Elk Creek sub-watershed will see up to a 4,000 percent increase in runoff.
According to the BAER team, the runoff increase is compared to runoff in the area prior to the fire based on .85 to .93 inches of rain.
“It is important to note that these are relative increases for summer thunderstorms as that is when the most damaging post-fire effects are likely to occur,” the report states. “While the rapid runoff reflects a high rate of runoff, the volume would be small.”
Other areas that are likely to be affected by increased runoff are the Muddy Creek watershed on the north portion of the burned area and the Red Dirt watershed, particularly the area above and around the Red Dirt Reservoir.
Both the Muddy Creek and Red Dirt watershed drain into the Wolford Reservoir, which is a key reservoir for the Colorado River District and Denver Water, according to the BAER team.
“Many communities in this nation depend on water that comes off a national forest,” Voos said.
Ultimately, the report finds that areas that flood will see more frequent flooding and at a larger magnitude and areas that did not flood are now at risk for flooding. It also means there will be an increase in erosion in those areas.
According to the report, the potential increase in erosion and flooding mostly puts roads and trails within the burn perimeter at risk of failure, but also increases the threats to life and safety in the areas below high and moderately burned spots, such as near Red Dirt Reservoir and north of Latigo Ranch.
“First and foremost flash flooding is a concern just because depending on the severity of the burn it can impact the absorption of water into soil or woody debris or other types of vegetation,” Voos said. “When it doesn’t soak in then it runs off, so flash flooding is the first concern, especially when there are values at risk downstream.”
The report findings can help agencies and landowners mitigate potential safety concerns and damages, as well as help prepare for post-fire threats, according to the BAER team.
Voos said some long-term and short-term measures that can be taken to encourage healthier watersheds include replanting trees and vegetation or positioning physical barriers that help direct and filter runoff.
Luckily, the BAER report found that the fire did not permanently impair the long-term soil productivity and some areas within the fire perimeter are already starting to regrow vegetation.
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