THE NORTH CAROLINA GEOLOGICAL SURVEY’S RESPONSE TO LANDSLIDE EVENTS IN 2012 AND 2013 IN THE BLUE RIDGE MOUNTAINS OF WESTERN NORTH CAROLINA: USING A GEODATABASE, LIDAR AND ORTHO-IMAGERY IN A GEOGRAPHIC INFORMATION SYSTEM TO AUGMENT FIELD INVESTIGATIONS AND MAP PRODUCTION

From November 2012 to July 2013 North Carolina Geological Survey (NCGS) geologists responded to 22 requests for technical assistance on landslide events from county, state, and federal agencies, and the public. As part of this response, the NCGS investigated 34 landslides that resulted in 5 destroyed or condemned homes, and damage to 4 homes, 18 private roads, 6 public roads, and a state park trail and footbridge. Twenty of the responses were for landslides that occurred from January and through July 2013, a period of record rainfall in western North Carolina which triggered nearly 300 landslides of various types throughout the region. At least five storms within that period triggered landslides, with the June 27 and July 3-13, 2013 storms being federally declared disasters for “flooding, landslides, and mudslides” in multi-county areas.

Information collected to date indicates that the vast majority of these slope failures involved cut or embankment slopes; and primarily embankment slope failures that mobilized into damaging debris flows. Two landslides that occurred during this period are known to have occurred on slopes not modified by human activity. Evidence of prior landslide activity was identified at, or in the vicinity of all the sites visited. Landslides investigated that were in areas of existing landslide hazard mapping occurred where the maps show an increased likelihood of landslide activity. One notable slope movement is a ~8,600m² reactivated debris slide that occurred on modified slopes within mapped past debris flow deposits.

A basic product the NCGS provides to our customers is a series of custom digital maps, or spatial data files, that depict the extent and relevant features of the landslides being investigated. A landslide geodatabase facilitates the use of existing landslide and landslide hazard mapping to augment new mapping and data collection conducted as part of the response efforts. Using field laptops equipped with LiDAR digital elevation models (sub-meter vertical accuracy, 6m pixel resolution) and their derivative maps, along with various vintages of ortho-imagery, and digital geologic maps simplifies field investigations, data collection and mapping, and helps customers understand the map products during the assessment process.