Steady vs dynamic stream-aquifer interactions: Lower Flint River Basin, Southwest Georgia, USA

Study region: The Lower Flint River Basin (LFRB): a karst catchment in southwestern Georgia, USA. Study focus: A year-long field campaign from July 2018 to July 2019 measured steady and dynamic stream-aquifer exchanges on Ichawaynochaway Creek (INC), a fifth-order tributary to the karstic Flint River in Georgia. The net change in discharge along a 24-km Creek segment was determined between two US Geological Survey gaging stations with no surface-water inflows. Stream-aquifer interactions were measured along a 120-m piezometer transect perpendicular to the bank. Hydraulic parameters to aid future modeling efforts were estimated using the method of moments applied to changes in bank flow direction from Hurricane Michael. New hydrological insights for the region: Results display the effects of local water use on streamflow as most channel storage gains occurred in the fall and winter. Negligible net channel gains and some losses occurred during the spring and summer months. Approximately 150 million m3 of net channel gains were observed during the study period. Initial stormflow contributed to aquifer recharge as indicated by reversals in the hydraulic gradient. Diffusivity and transmissivity increased along the transect (9–420 m2/d) and (3–150 m2/d), respectively, and hydraulic conductivity equaled 2.85 m/d. Stream-reach orientation with respect to regional groundwater gradients explains increased stream-aquifer interactions. Surface-groundwater interactions in karst systems are better understood after characterizing variation of hydraulic processes.