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Researchers study whether mulch can help prevent flash floods after wildfires

Burned land is especially bad at absorbing water, leading to flash floods for years to come.

COLORADO, USA — It’s been two years since fires across Colorado burned more than half a million acres. Now it seems like every time it rains, the burn scars flood.

Sunday, we saw flash flood warnings in the Cameron Peak burn scar as heavy rain poured over the area where flames torched the land. 

That could continue for several more years.

"The increased risk of floods and debris flows typically remains elevated for two to five years after the fire. That’s the amount of time that it might take the vegetation to regrow," said Peter Nelson, an Associate Professor of Civil and Environmental Engineering at Colorado State University. "The soil becomes sealed, and in some cases the soil becomes hydrophobic, meaning water beads up and is repelled off of the surface."

Nelson is researching whether dumping mulch over burn scars is an effective way of trying to prevent that water from running off and causing floods. Helicopters drop wood chips onto the land to try to increase vegetation growth and stop water runoff.

"There are limited resources and it’s expensive to do that kind of a treatment. A lot of planning goes into the development of those mulching operations," Nelson said. 

The Cameron Peak Fire burned more than 208,000 acres in 2020. About 24,000 of those acres were identified as high priority for mulching, meaning the soil was severely burned and there was a high likelihood that the area could flood or water quality could be impacted. 

But mulching is expensive. After spending more than $20 million, groups working on the project have treated only about 10,000 acres.

"A lot of the planning involves identifying, 'what are the highest risk areas?'" Nelson said. "What are the areas that were burned at the highest severity that might have a steep slope that could pose a higher risk? Those areas get prioritized."

This team of researchers started looking into whether mulching was an effective strategy after the High Park Fire in Larimer County in 2012. So far, they’ve found it is useful. They’re testing a larger area of land in the Cameron Peak and East Troublesome burn scars for more research.

RELATED: Aerial mulching aims to restore land burned by Cameron Peak Fire

RELATED: Burn scar traits that lead to high flood threat

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