SURFACE-WATER/GROUNDWATER INTERACTION BENEATH A GEORGIA PIEDMONT FLOODPLAIN

At a study site in the Georgia Piedmont river stage and hydraulic head in adjacent alluvium, saprolite, and bedrock respond quickly to rainfall. Rapid groundwater hydraulic head changes appear to be controlled primarily by stream stage fluctuations; complex floodplain stratigraphy and topography can result in a locally complex groundwater response in floodplain alluvium. Amplitude and timing of hydraulic head fluctuations and groundwater flow modeling results suggest an elastic groundwater response to stream stage changes rather than more commonly assumed piston-flow infiltration of surface-water. Geochemical data support this conclusion and reveal negligible surface-water infiltration during flood events even in highly permeable, sand-dominated alluvium immediately adjacent to the river. Modeling results suggest that local stratigraphy, stream channel geometry and basin morphology are also important controls of groundwater response. Results further suggest that inferences regarding groundwater flow based on rapidly changing hydraulic head must be made with great care. The study was conducted on the campus of the State University of West Georgia on a riparian wetland adjacent to the Little Tallapoosa River. Piezometers were installed during Hydrogeology class exercises using simple hand-auger techniques, water-levels were monitored using pressure transducers and dataloggers, and major-ion geochemical analysis was performed via ion-chromatography