SPATIAL AND STRATIGRAPHIC DISTRIBUTION OF SINKHOLES IN BLOUNT COUNTY, ALABAMA: A STUDY USING LIDAR FOR MAPPING SINKHOLE HAZARDS AND RISK ZONES

Maps of geologic hazards, such as sinkholes, are needed by planners, developers, geologists, and emergency managers for use in urban and environmental planning, land use, and disaster response. This project addresses some of those needs by using high-resolution LiDAR elevation data to identify and evaluate sinkhole density and distribution patterns to produce sinkhole hazard and risk assessment maps. The study area is located in Blount County, Alabama, in the Cumberland Plateau physiographic region and focuses on a 13-mile long swath of the southern portion of the Sequatchie anticline. The LiDAR data were processed and geospatially analyzed using ESRI’s ArcGIS software, and sinkholes were digitized using LiDAR-derived digital elevation models, contour lines, and hillshade. A total of 1,096 sinkholes were identified on the LiDAR-derived data; this represents a 2,183% increase from the number of sinkholes (n=48) identified in the same area on corresponding 1:24,000-scale topographic maps. Over 99.4% of the sinkholes identified in the study area are in four geologic units, with the Mississippian-age Bangor Limestone containing 83.2% of the total sinkhole inventory. An Average Nearest Neighbor calculation indicates that the sinkholes are distributed in clusters in the study area, with less than a 1% likelihood of random distribution. Areas of agricultural and urban development were found to have few to no sinkholes; these may have been infilled in previous years for development purposes. Cross analyzing sinkhole cluster locations with elevation ranges and geologic data indicates that sinkholes are stratigraphically distributed within specific lithologic units with similar distribution on both the eastern and western flanks of the anticline. These results suggest that relatively high levels of both elevation and stratigraphic detail can be attained using LiDAR data for geologic mapping and sinkhole analyses. This stratigraphic specificity can be used to generate new hazard and risk maps for planners and developers, showing ranges of elevation and/or stratigraphic zones most susceptible to sinkhole formation. Future work will include budgeting a greater amount of time for field verification, using higher scale geologic maps, and incorporating water well data where available.