SLOPE STABILITY ASSESSMENTS IN THE SOUTHERN APPALACHIANS. DATA ACQUISITION AND ANALYSIS AT THE COMMUNITY AND LOCAL SCALE

Community and local scale slope stability assessments are often limited in time and scope of work. These projects require an investigation designed to meet project goals, which can include mapping for municipal planning, laying out development or evaluating landslide risks on a residential parcel.

Slope steepness and aspect, fracture/foliation orientations and distribution of colluvial deposits are used to assign a hazard ranking for community scale, slope stability maps. Fieldwork includes measuring bedrock structures and mapping slope deposits. Steep slopes with daylighting foliations and fractures and/or colluvial deposits are assigned a high-risk ranking. Steep slopes without these features are assigned a medium risk and moderate slopes are assigned a low risk ranking.

Desktop studies using soil survey maps and LiDAR data can effectively map high-risk slopes on a development scale. Soil data including parent material, slippage potential, rock fragments, percent slope and landform position can all be derived from USDA soil survey maps. These data are combined with LiDAR topography to assess slope stability and identify areas where development could initiate slope failure.

The Town of Boone, NC requires landowners to evaluate slope stability prior to building on parcels with steep slopes. The regulations require a geologic study to evaluate the thickness of unconsolidated soils, potential for daylighting fractures and distribution of existing slope movement deposits. These assessments involve field reconnaissance to identify colluvium and evidence of soil creep as well as measuring bedrock foliations and fractures at the outcrop. Field data is used with NC Geologic Survey slope hazard maps and geologic maps to determine if site development has the potential to decrease slope stability.

These three assessment scales use a different data to address specific project goals. These examples show some of the ways that the geologist can design slope stability assessments to help educate and protect landowners and mountain communities.