July fire stabilization helicopter

A helicopter with a sling load applies WoodStraw mulch material over land burned by the July fire as part of an emergency stabilization project. 

Courtesy BLM Malta Field Office

Earlier this month, a helicopter took flight again over the site of the July fire in the Little Rocky Mountains, this time dropping mulch instead of water.

In all, the Bureau of Land Management covered 61 acres of burned soil on a northeastern slope of Sugar Loaf Butte with nearly 80,000 pounds of the mulch in order to mitigate the dangers flooding and erosion could pose to the town of Landusky below, where around 40 people live.

The burn area emergency stabilization project, which also included the installation of lines made up of 75 straw wattles along the slope in August, cost $800,000, according to Tom Darrington, field manager for the BLM’s Malta Field Office.

The July fire was first reported northwest of Zortman late in the afternoon on July 3 and grew to 11,699 acres. Officials think it was caused by humans. A Type 2 Incident Management team was tasked with incident command on the fire and at one point evacuation orders were issued for Landusky. Hundreds were dispatched to the fire, which destroyed four outbuildings and a cabin. 

Tests and modeling on the soil covering the slopes in the wake of the fire showed fire-induced hydrophobicity. That means ash left behind by a fire can absorb some moisture, but the soil won’t absorb any.

“It’s basically like running off a sheet of glass,” Darrington said.

In a worst-case scenario, which Darrington called unlikely, one big rainstorm could lead to a landslide. More likely, though, “flashy precipitation events" could cause flooding, he said.

By late June precipitation totals recorded about five miles away in nearby Zortman showed 6.42 inches in 2017, or 63 percent of the precipitation the area sees on average, according to National Weather Service Glasgow Fire Weather Program Leader Victor Proton. NWS has a limited number of weather-monitoring stations in the area, so Proton said data for Zortman could be a reasonable substitute for Landusky.

Drought conditions persisted through September, with the area still sitting at 62 percent of its yearly average precipitation by month’s end, making it the driest that time period has been in the 52 years NWS has data for Zortman.

Just a year before, Zortman saw above-average precipitation in September when 4.54 inches of rain was recorded, compared to its recorded average of 1.29 inches. Darrington said he’d heard that parts of the mountains that year near Landusky may have seen as much as 10 inches of rain in five days.

“We looked at the hydrophobic soils and we said ‘If we get 10 inches of rain on this thing, it’s not going to be pretty,'” Darrington said.

After a fire is contained, the clock starts ticking quickly to secure BLM funding for stabilization projects and other post-fire land treatments. An initial report of the fire identifying anticipated treatments is due at various BLM offices within a week. In all, Darrington said there is a 21-day window to submit a full emergency stabilization plan.

"We felt lucky to get that money," Darrington said. "It's not easy to ask for that type of money and have it awarded to you."

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WoodStraw mulch on Sugar Loaf Butte

WoodStraw mulch rests on the snow of Sugar Loaf Butte near the town of Landusky. The mulch was applied to the land by the Bureau of Land Management in order to prevent erosion and flash flooding from the July fire. 

The project isn't common for the area, Darrington said. He couldn't recall the last time an emergency stabilization and rehabilitation project was conducted in the district.

The solution for hydrophobic soil may sound counter intuitive. At a basic level, the soil needs is more water, said Pete Robichaud, an Idaho-based research engineer with the U.S. Forest Service's Rocky Mountain Research Station. Though he was not involved in July fire project, Robichaud said he's specialized in post-fire environment research for decades. Hydrophobicity occurs when chemical compounds produced by burned fuels, like trees, are carried by smoke and pushed in every direction by what’s known as the fire’s “heat pulse.”

The water-repellent compound responsible for hydrophobicity is a hydrocarbon, Robichaud said. The soil acts as an insulator for the hydrocarbon, allowing it to condense on soil particles when it cools. Fuels for the July fire included ponderosa pine, which Robichaud said is among the species of vegetation with “more waxy-type materials,” that “tend to have higher hydrocarbon loading than other species.”

Hydrophobic soil is less common in grass fires, Robichaud said.

"It might be kind of hot, but it burns so quick," he said.

Lots of fire fuel on the forest floor and sustained burning from objects like logs can prolong the heat pulse's ability to push hydrocarbons into the soil. Hydrophobia is usually seen at soil depth between an inch or two, but Robichaud has seen it as far down as six inches, he said. 

Exposure to water over time dissolves hydrocarbons and restores the soil's ability to absorb water. With the July fire stabilization project, the mulch can help the forest floor covering to act like a sponge, holding moisture in place over the soil so that the hydrocarbons can break down.

The 1,400 bales of mulch used for the July fire project were made by a company named WoodStraw. Packaged in 550-pound bales, the mulch is specifically designed to stop erosion.

Hydrophobia and the burning of forest floor covering can increase flood risks and "can generate some serious runoff," especially in steep areas where moving water can pick up the energy to generate more erosive force and detach soil particles, Robichaud said.

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WoodStraw mulch closeup

A close up look at 550-pound bales of WoodStraw mulch that was applied over the July fire earlier this month to prevent soil erosion. 

Though it prevented a helicopter from flying on the first day of planned mulch drops, the estimated 18 inches of snow that fell in the area of the July fire on Oct. 2 will help with the process. Repeated freezing and thawing of snow and soil helps break up the water-repellent layer of hydrocarbons, Robichaud said. 

The one-time mulch distribution was also supplemented by some reseeding in the area using a natural seed mix made up in large part by native grass seeds, Darrington said. That work finished on Oct. 7. The soil's natural properties usually return within a few years, Robichaud said. 

"Burnt landscapes do recover," he said. "They always have and they always will." 

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Night Reporter

General assignment reporter for The Billings Gazette.