SPATIAL PATTERNS OF HURRICANE-INDUCED LANDSLIDES IN EASTERN TENNESSEE AND THEIR RELATION TO RAINFALL RETURN PERIOD

The Tropical Storm that stemmed from Hurricane Helene left a significant mark on the Southern Appalachians, including East Tennessee (ETN). The radar-estimated 7-day rainfall from September 22 - 29 identified the highest rainfall totals of 6 - 9 inches in ETN. The Pigeon, Upper French Broad, Nolichucky, Doe, and Watauga rivers in ETN, with headwaters in Western North Carolina, experienced deadly flash floods as the heavy rain rapidly drained through these rivers. This "once-in-a-generation storm" caused widespread devastation and significant loss of life.

In addition to flooding from the heavy rainfall, the hillslopes in ETN experienced numerous landslides. Still, they received little attention at the state level compared to the urgent recovery effort from the fatal flood. Slope failures were pronounced in the hillslopes of Blue Ridge and the ridges along the Valley and Ridge Physiographic provinces, driven by rainfall triggers that primarily fell at the location. These landslides ranged from a few thousand cubic meters of debris flows to a hundred cubic meters of translational or rotational slides. An abundance of bank erosion was also widespread due to the stream bank undercutting triggered by the flooding. These slope failures corresponded to cumulative rainfall from the headwaters and the region’s rainfall. This ongoing work establishes a post-storm landslide inventory to document all categories of unstable slopes ranging from debris flows and rotational and translational slides to bank undercutting and expand the sparse database of event-triggered landslides in ETN. Additionally, this work studies the storm's rainfall patterns and the antecedent conditions to better predict the rainfall thresholds and return periods for similar 50- to 100-year events in ETN, which will likely contribute to future landslides. The study will significantly provide a broader understanding of storm-induced landslides in the region and its community impacts, particularly in areas with limited historical data. It will also support long-term planning and hazard mitigation and improve regional resilience.