USDA funds project to study post-wildfire mudslides and flooding

A new interdisciplinary, multi-institution research project funded by the U.S. Department of Agriculture (USDA) via the National Science Foundation (NSF) will focus on reducing the vulnerability of disadvantaged communities to the impacts of wildfire-related cascading hazards. Professor Timothy D. Stark is Senior Personnel on the project, joining scientists from Mississippi State University (MSU), University of California Irvine, Oregon State University and University of Colorado Boulder. Professor Farshid Vahedifard of MSU is the project’s lead principal investigator.

Areas impacted by wildfire damage are often vulnerable to an additional "cascade" of hazards such as landslides and flooding. A recent example of this type of cascade occurred after the Dolan Wildfire in August 2020. The fire, which burned through approximately 52,000 hectares in Big Sur, Calif., was followed five months later by a significant rainfall event. The amount and velocity of precipitation runoff during the rainfall was higher than usual due to vegetation lost during the fire. The increased runoff in turn led to debris flowing to and blocking Rat Creek.

As the storm continued, this blockage was partially dislodged and became a large debris flow that overtopped the Pacific Coast Highway, retrogressively eroding the embankment supporting the highway. The erosion started near the base of the ocean cliff and retrogressed up the slope until a valley with a volume of about 382,000 cubic meters (500,000 cubic yards) was cut through the highway embankment.

"The embankment failure at Rat Creek is a recent example of how wildfires frequently lead to cascading hazards such as removal of large trees and vegetation that block drainage channels, retention of large volumes of precipitation, and initiation of large debris flows that damage civil infrastructure," Stark said. "A rainfall event without the prior wildfire would not have resulted in as much damage because Rat Creek would have been able to transmit and drain the precipitation."

Researchers on this project will work to improve modeling capabilities for understanding the complex factors leading to cascading hazards. To better understand one of those factors – the impact of wildfires on slope stability – Stark will install instrumentation to monitor soil moisture changes and slope movement on areas affected by a 2018 wildfire that destroyed the town of Paradise, Calif. The data he collects will help Stark identify the relationship between the rate and magnitude of rainfall and the onset of damaging debris flows.

In addition to the technical research, the scientists also seek to identify weaknesses in the preparation for and response to these hazards by emergency managers, planners, and communities and provide tools to better equip them to handle the disasters. For example, Stark’s team at UIUC will help develop a bilingual message service to inform rural Hispanic communities of current and on-going risks of cascading hazards that can continue well after a rainfall or wildfire event.

"Employing a large multi-disciplinary team will allow us to reduce community risks from cascading hazards – which is timely given the increase in wildfires, drought and flooding – by understanding their interaction and being able to communicate the risk to bilingual impacted communities," Stark said.

The three-year, $1.7 million project is sponsored by the USDA’s National Institute of Food and Agriculture through the Cyber-Physical Systems program, which is a joint program with the NSF. UIUC students Abedalqader Idries (Ph.D.) and Lucia Moya (M.S.) will assist with the field instrumentation and bilingual informational communications, respectively.