INVESTIGATING GROUNDWATER/STREAM INTERACTION BETWEEN THE UPPER FLORIDAN AQUIFER AND STREAMS IN THE LOWER FLINT AND CHATTAHOOCHEE RIVER BASINS, GA, USA, USING STREAM CHEMISTRY, REMOTE SENSING AND BEDROCK FRACTURE ORIENTATION

Development of groundwater resources for agricultural irrigation in the Coastal Plain of southwestern Georgia has significantly altered flow parameters and reduced low-flows in streams which are hydraulically connected to the Upper Floridan Aquifer. Further investigations are critical to increasing our understanding of aquifer/stream interaction in this karst system in order to allocate and protect finite water resources critical to the economic and environmental health of this region. We have described systematic bedrock fracturing in mid to upper Eocene Ocala Limestone outcrops in tributaries of the Flint and Chattahoochee Rivers, including Ichawaynochaway Creek in Baker County (Flint River Basin) and Coheelee Creek in Early County (Chattahoochee River Basin), Georgia. Using remote sensing data sets we compared large and small scale changes in stream chemistry (specific conductivity, Sr⁺, Ca⁺, δ¹⁸O, and δD) to fracture as well as stream reach orientation in Ichawaynochaway Creek to determine which characteristics of stream reaches correlate with preferential stream-aquifer exchange. Fracture azimuths (n=110) measured in limestone outcrops found within Ichawaynochaway Creek show a range of orientations dominated by a set of N-S fractures, with lesser sets at approximately N40W and N10E. Our evaluation of 53 km of this tributary, using remote sensing tools, revealed that azimuth orientation of stream reaches (n=2400) also follow a dominant N-S fracturing trend, with lesser sets of N40W, N24W and E-W. Preliminary results appear to indicate that significant changes in stream chemistry, suggesting enhanced groundwater input, occur in some Ichawaynochaway Creek reaches which follow an azimuth orientation of N40W. Although the data set is much smaller in Coheelee Creek (n=47), the dominant fracture orientation of this tributary appears to be around N40W. These data will be useful for updating regional hydrologic models in this region and methodologies should be transferable to basins of similar geologic and hydrologic characteristics.