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Broadening the scope of post-wildfire flood risk management

A multi-disciplinary team of operations, engineering and dam safety personnel inspect Detroit Dam Sept. 22 to assess impacts to the project—as well as the project’s functionality and any major safety concerns—after the Beachie Creek and Lionshead fires spread throughout the area upstream and downstream of the dam.

A multi-disciplinary team of operations, engineering and dam safety personnel inspect Detroit Dam Sept. 22 to assess impacts to the project—as well as the project’s functionality and any major safety concerns—after the Beachie Creek and Lionshead fires spread throughout the area upstream and downstream of the dam.

Detroit Dam operators walk through the remnants of Detroit, Ore. after the Beachie Creek Fire moved through the area, Sept. 15, 2020. The fire destroyed lives, homes, businesses and land in the North Santiam Canyon but spared the dam and other major U.S. Army Corps of Engineers infrastructure. Most of the facilities are intact and functioning, which will be important for the upcoming flood season.

Detroit Dam operators walk through the remnants of Detroit, Ore. after the Beachie Creek Fire moved through the area, Sept. 15, 2020. The fire destroyed lives, homes, businesses and land in the North Santiam Canyon but spared the dam and other major U.S. Army Corps of Engineers infrastructure. Most of the facilities are intact and functioning, which will be important for the upcoming flood season.

VICKSBURG, Miss. – As firefighters worked diligently to extinguish a notable number of wildfires this season, researchers with U.S. Army Engineer Research and Development Center’s (ERDC) post-wildfire flood risk management team took a step back to evaluate how they could improve their efforts in assisting with the devastating effects of the fires.

As a result, the team began broadening the scope of their mission to include not only flood risk management, but also emergency management applications and environmental concerns.

“Going forward, we’re going to be looking at wildfires outside of flood risk management,” said Dr. Ian Floyd, a research physical scientist at the ERDC’s Coastal and Hydraulics Laboratory and principal investigator for the post-wildfire flood risk management team. “Our three big objectives will include assessing the post-fire flood risk, assisting in emergency management staging and then the environmental component — how do these ecosystems recover? How can we quantify that recovery, and then how does that translate into saving money and ultimately lives?”

With projects spanning two U.S. Army Corps of Engineers (USACE) division areas of responsibility and at least 16 fires, the team is tying numerical modeling to physically based processes in order to improve outcomes for the best-case scenario, the moderate-case scenario and the worst-case scenario.

“We’re essentially looking at what recovery looks like in Oregon versus recovery in Santa Barbara County versus recovery at Cochiti Lake in New Mexico,” said Floyd. “We are going to be looking at a comprehensive view to fully understand the effects following a fire and how we quantify that.”

The most important aspect of the team’s approach is determining the type of flood event.

“Are these events non-Newtonian, or is there a potential for them to be non-Newtonian?” said Floyd. “There is a dramatic difference in how non-Newtonian materials, like debris flows and post-fire, high-intensity flood events, behave versus clear water. The non-Newtonian flood events act more like molasses or honey.”

The ERDC research team developed the capability to model the non-Newtonian physics, then linked that technology to current USACE numerical models used for predicting compound flooding with hurricanes.

“We are incredibly accurate at mapping those inundation footprints,” said Floyd. “It makes a surprising difference, even with the same inputs — not only in the inundation footprint, but the arrival times are different and the forcings are different. We found that’s the most important thing to consider — is it a debris flow or is it just a sediment-type flow? There is a dramatic difference in the model’s behavior and how that’s reflected in the real world.”

“We’re able do this within a manner of a couple weeks,” he said. “So the districts can start making decisions on operations, potential staging, or in some cases, they are looking at potential remediation.”

With so many stakeholders involved, the team is also working to develop standard operating procedures.

“The idea is that there will eventually be a standardized response across USACE that the districts can either look to or execute, based on their experience,” said Floyd. “We would like to field train the district regional technical specialists and subject-matter experts first, and then conduct more hands-on training with projects over the next couple of years.”

Future plans also include an ERDC center of excellence or expertise, enabling districts to reach back and ask questions or address specific needs.

“That’s the direction we are heading with our district partners,” said Floyd. “A lot of this is driven by the issues being very diverse in disciplines — you have to understand geology, geomorphology, hydrology, hydraulics, sediment and transport. By working with organizations like the U.S. Geological Survey and the U.S. Forest Service, we’re really trying to standardize not only what we’re doing in research, but the whole response.”

As wildfires continue to rage across the western part of the country, Floyd stressed that the devastating effects of them can be felt years later.

“It isn’t over once the fire is contained,” said Floyd. “Post-fire floods are a serious risk compounding an already stressful and uncertain time. As these communities come back home and try to rebuild, people need to be aware that there are elevated flood risks and sedimentation risks. We’re here to try to help alleviate some of that uncertainty and help them better understand quantifying those risks.”


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