SPATIOTEMPORAL ANALYSIS OF SINKHOLE DEVELOPMENT IN THE COVERED KARST TERRAIN OF DOUGHERTY COUNTY, GEORGIA

The Upper Floridan Aquifer (UFA) has provided important ecosystem services in Dougherty County for several decades. Alongside increased water demand due to a growing populace in an agricultural area, this area has experienced short and long-term fluctuations in precipitation, surface water discharge, and well levels. Located within karst terrain in southwest Georgia, sinkhole development has placed many areas at risk. Evaluating the causes of sinkhole formation is essential for risk reduction within karst settings.

In this study, we evaluate sinkhole development in Dougherty County utilizing digital elevation models (DEMs) from 1979, 1999, and 2010 processed using ArcGIS and compare them with one another to determine the change in the spatial variation and number of sinkholes through time. Alongside extraction patterns, past sinkhole maps, and geologic maps, USGS well level, river discharge, and precipitation data were used to correlate hydrologic and anthropogenic phenomena with sinkhole formation.

Results indicate a direct relationship between hydrologic factors and sinkhole formation. DEM analysis results show a 97.22% ±5% increase in depression area from 1979 to 1999 and a 26.3% ±5% increase from 1999 to 2010. A 5% error was estimated due to variations in DEM resolution, source, and processing techniques. The increase in depressions is consistent with climatic and hydrogeologic data. The Palmer Hydrological Drought Index shows increases in frequency and magnitude of drought conditions from 1970 – 2014. Historical analyses of precipitation, Flint River discharge, and well level data are consistent with average conditions from 1970 – 1990 (50 inches annually, 6,000 cubic feet per second (cfs), and average well levels, respectively). From 1990 – 2000, conditions were above average (53 inches annually, 7,000 cfs, and increasing well levels). Conditions were below average from 2000 – 2010 (45 inches annually, 5,000 cfs, and declining wells levels). Future research efforts will focus on identifying the temporal evolution of county-wide subsidence using satellite data and radar interferometry. These data will provide higher temporal resolution for more precise correlations between sinkhole formation and hydrologic and anthropogenic patterns.