Time-dependent Effects of Wildfire Ash and Root Decay on Hydrologic Behavior and Shallow Landslide Susceptibility of Wildfire-Burnt Slopes

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An increased incidence of wildfires combined with high-intensity storms due to climate change has increased the wetting-induced shallow landslide susceptibility of hillslopes. Post-wildfire landslides and debris flows in recent years in the Western US have caused dozens of fatalities and tremendous economic loss. This project will deliver a framework specific to wildfire-burnt slopes for analyzing shallow landslide susceptibility of hillslopes with time. The new framework could be used to identify critical slopes and prevent catastrophic events that threatens human life, infrastructure, or natural resources. The goal of this project is to understand why and how the shallow landslide susceptibility of wildfire-burnt slopes changes with time and saturation due to root decay and transport of wildfire ash. A hillslope will be instrumented with suction and water content sensors immediately after a wildfire to determine the evolution of water retention behavior over time. Field samples will be collected monthly and scanned using X-ray computed tomography (XCT) to quantify macropore volume over time. The decay rate of fine roots will be quantified using laboratory-controlled burn experiments and XCT scans. The migration of wildfire ash into soil will be identified through saturated hydraulic conductivity tests. A suction-based slope stability analysis will be used to evaluate the change in the shallow landslide susceptibility of a wildfire-burnt slope with time and saturation. The understanding generated in the proposed research will be the first step toward forming a novel and complete framework specific to post-wildfire slope stability analysis as a function of time and saturation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.