Weekend rains bring minor flood

Weekend rains brought a small flood to nearby Greer Canyon, Sunday morning.

Greer Canyon and nearby Heil Valley Ranch, both part of Boulder County Parks and Open Space, or BCOS, suffered significant damage from the Calwood Fire last October.

The areas that burned  at Heil Valley and Greer Canyon have been closed for restoration work since the fire was contained in November 2020. 

The intensity of the rains caused a wash of debris and mud across the burn scar in Greer Canyon, clogging streams and culverts and causing some damage to trails and roads. 

“This is the first rain event that has caused substantial difficulties,” Sharla Benjamin, project manager for BCOS, said. “Previous low-intensity rain events had caused some smaller debris flows.”

Mulching is a key part of soil remediation after severe wildfires like Calwood. According to the Colorado State Forestry Service fact sheet, gases released during a fire condense and form a waxy coating on soil. The soil becomes hydrophobic — repels water — which causes run-off and erosion when it rains. Layering mulch and straw over the burnt soil creates a barrier, which slows the rainfall and helps the soil soak up the water.

According to Benjamin, large-scale mulching operations in the burn scar began early May. Contractors will apply roughly five tons of wood shreds per acre to achieve 70% ground coverage.

“The trees killed by the Calwood fire are processed onsite to create the wood mulch for this effort,” Benjamin said. “This is a win-win, removing hazard trees along trails and roads and reducing the need to import material.”

Work-to-date has had a positive impact on the burn scar, and Benjamin said that preliminary findings have shown that the mulch applications have stayed in place in observed areas after the rainfall.

“In addition, the mulch treatment seems to be doing a great job at mitigating ash and debris flow where it’s been applied,” Benjamin said.

Aerial and ground-based mulching operations will continue across the burn scar through August 2021.