LANDSLIDE SUSCEPTIBILITY MAPPING IN CENTRAL VIRGINIA: RESULTS FROM 2024 MAPPING AND PARALLELS TO HURRICANE HELENE IN WESTERN NORTH CAROLINA

In 2018 and 2020, the Virginia Department of Energy was awarded Federal Emergency Management Agency Pre-Disaster Mitigation grant funds to complete a landslide inventory and susceptibility mapping in Albemarle and Nelson Counties. The resulting maps are intended to help individuals and communities identify areas prone to landslides and take appropriate action to protect lives and property. The maps show potential susceptibility and inundation areas for shallow landslides such as debris flows, during a high-rainfall event. The eastern Blue Ridge of the study area was affected by Hurricane Camille in 1969 and a strong series of storms in 1995, which generated > 7900 landslides. Our analysis suggests that 93% of these landslides were initiated by extreme rainfall (27+ inches in 8-hours) during Hurricane Camille. The susceptibility map was produced using a series of ESRI ArcPro geoprocessing tools to calculate a weighted overlay raster. Parameter values for the raster were derived from 1-meter resolution topographic lidar data (curvature, slope, elevation), soil and bedrock geology data, and by analyzing spatial statistics derived using the landslide inventory. The final output raster was then assigned a susceptibility value (high, moderate, low) based on calculated parameter value ranges and known landslide occurrences. Parameter ranges were adjusted to maximize the number of landslide locations per unit area captured in high-hazard zones. Overall, the susceptibility modeling performed well; 95% of the inventoried landslides were captured in high (62%) or moderate (33%) hazard zones. These zones made up 8% of the study area, while 92% of the area was identified as low hazard. High and moderate hazard zones, average debris flow width and length, and lidar topographic data were then used to produce a map of predicted debris flow pathways using hydrologic flow path tools in ESRI ArcPro. The potential pathways overlap with 12% of the study area. Additional feature classes indicate where public infrastructure (roads, railroads, etc.) intersect these pathways and may be at risk during a future rainfall event. These results provide important constraints for the evaluation of future landslide affects considering the recent devastation from Hurricane Helene in southern Virginia and western North Carolina.