TRAIL-SCALE SLOPE FAILURE RISK MAPS: A PILOT STUDY IN GREAT SMOKY MOUNTAINS NATIONAL PARK

Public domain slope failure risk maps in the Southern Appalachians are primarily based on slope steepness and aspect, soil cohesion, and in some cases, evidence of slope failures. Slope steepness and aspect strongly correlate with historical slope failure locations, especially debris flows, but this risk assessment approach omits other factors that most likely affect risk at the 1- to 10-m² spatial scales (Wooten et al., 2016).

To simulate a targeted slope risk assessment in a region with bedrock geology, land cover, and terrain common in the S. Appalachians, a 2 month pilot study has been conducted in the Great Smoky Mountains National Park. Bedrock discontinuities, lithology, field soil texture, dominant vegetation, evidence of slope failures, and slope modification features, were mapped along 14 miles of trail corridors. Trail sections were selected based on park visitor usage, range of bedrock exposure, range in slope steepness and slope geomorphic position, and ranking on the existing slope stability risk map. Due to the amount and spacing of bedrock and soil profile exposure, and poor visibility due to the density of >2m high evergreen foliation, mapping these risk factors did not generate higher-confidence and/or higher-resolution datasets than that available from published maps. However, mapping of bedrock discontinuities (foliation, fracture, and intersection orientations) and evidence of past slope failures did generate higher-confidence and -resolution datasets with which to assess slope failure risk. Rock slide, wedge, debris flow, and combination debris flow-rock slide, failure mechanisms were considered in using these data to create single-factor qualitative risk maps with 1- to 10-m² “resolution”. Single factor risk maps were then compiled into a multi-factor risk map. For ~60% of the studied trail corridor length, incorporating these data raised the risk ranking from that on the existing map and increased “resolution” to the ~10-m² spatial scale. This study suggests cost-effective slope failure risk assessments incorporating more factors are possible for selected targets (e.g., road corridors, proposed housing developments) if compiling information from a range of sources (published 1:24,000 and smaller scale maps, remote sensing datasets, and field work).