Study: Areas may be at risk of floods, ash following fire - Albuquerque Journal

Study: Areas may be at risk of floods, ash following fire

BAER team leader and Santa Fe National Forest soil and watershed program manager Micah Kiesow studies soil burn severity in the Tecolote Creek headwaters. Kiesow said the Calf Canyon/Hermits Peak wildfire could cause flooding and debris flow during monsoon season. (Courtesy BAER)

Copyright © 2022 Albuquerque Journal

The fire was bad.

Now officials say the flash floods, landslides and ash could be just as destructive.

The Calf Canyon/Hermits Peak wildfire has burned hundreds of thousands of acres across four northern New Mexico counties.

A U.S. Forest Service Burned Area Emergency Response, or BAER, team has started publishing data from its post-fire assessments.

Micah Kiesow, team leader and a soil and watershed program manager with the Santa Fe National Forest, said that steep mountain slopes had acted like a sponge before the fire.

Those slopes had “organic material that could suck up the water” when it rained.

“Postfire in some of these areas, especially the high soil burn severity areas and the moderate, we’re looking at now a steep slope that’s more like a parking lot,” Kiesow said.

In many places, tree canopies have burned to black matchsticks.

Soils are repelling water.

Rain will likely run off rapidly if and when intense monsoon events hit.

The team so far has studied soil burn severity across more than 115,000 acres of forest, private and state lands.

The first report focuses on portions of the Gallinas and Tecolote Creek watersheds west of Las Vegas, New Mexico.

About 49% of the acres surveyed ranked as moderate or high on the soil burn severity index.

That statistic is “very concerning,” Kiesow said, and could signal an “extreme change in watershed response” during monsoon season.

Satellite imagery provides a starting point for burn assessments. The multi-agency teams confirm the soil conditions in the field.

Fire can completely change soil structure.

Impacts in patchy, low-burn regions are often limited to the surface.

But in areas that suffered the worst burns, deep roots that hold soils together may be gone.

Some of the most severely burned areas surveyed so far include land west of Storrie Lake and near the City of Las Vegas water treatment plant.

Ash

Flooding presents another problem for communities near burn scars: ash flowing into rivers and streams.

“Anything you might do on the ground, the ash is going to get through and go to the lowest point,” Kiesow said.

And many water treatment facilities aren’t equipped for the expensive, time-intensive process of filtering ash.

Communities such as Las Vegas, New Mexico, will see immediate impacts “if we get any type of monsoon season this year,” said Phoebe Suina, a hydrologist whose Bernalillo environmental consulting company studies wildfire-impacted watersheds.

“A large portion of their drinking water is served from surface sources that are directly downstream from these burned areas,” Suina said.

Ash and debris can harm water quality with high levels of nitrates and phosphorus.

Magnitude

BAER teams usually begin field work when a fire is 70% to 80% contained.

But the sheer size and intensity of this wildfire have added urgency to the project.

“I don’t think we’ve had this magnitude of fire,” Suina said. “Yes, there’s been the Las Conchas Fire. But those watersheds are a quarter or half the size of the watersheds being impacted by the Hermits Peak Fire.”

A hazard assessment from the Forest Service and U.S. Geological Survey shows that some burned areas could see heavy debris flows if they receive about .25 inches of rain in 15 minutes.

The areas with the highest debris-flow hazards are:

• Cañon Del Agua and Cañon Alto northwest of Montezuma.

• Small drainages above Gallinas Creek near Trout Springs.

• Above Forest Service Road 263 and Gallinas Creek near Canovas Canyon.

• Sections of Burro, Hollinger, Tecolote and Porvenir canyons.

To prepare for impacts, agencies could implement an emergency alert system with rain gauges connected to radio frequencies or satellites.

Rain events would trigger messages to emergency responders and residents below the burn scars.

“One of the most important things we can do in this kind of situation is give people enough time to get out of the way,” Kiesow said.

Other post-fire projects may include seeding and mulching to help restore the eroded landscape.

Federal and state agencies are sharing assessment data so that private landowners know potential impacts on their properties.

Las Conchas

Rolf Schmidt-Petersen, director of the New Mexico Interstate Stream Commission, said the looming threat of post-fire flooding echoes the Las Conchas Fire of 2011.

“The rainfall impacts with erosion and debris flows can be very significant,” he said.

The Las Conchas Fire burned more than 150,000 acres and sent sediment and debris into the Rio Grande.

University of New Mexico researchers found that the fire affected water supplies from the Jemez Mountains to Elephant Butte Reservoir.

Flooding after Las Conchas damaged trails and buildings in Bandelier National Monument.

Dixon’s Apple Orchard near Cochiti was ruined by back-to-back flash floods and mudslides in the months after the fire.

The federal BAER team will soon start assessing impacts of the Calf Canyon/Hermits Peak Fire in the Sapello and Mora watersheds.

“Even if the fire is over, we need to start preparing,” Kiesow said. “It’s not if the flooding will happen – it’s when.”

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