Hillslope-riparian-stream connectivity and flow directions at the Panola Mountain Research Watershed

To obtain a better understanding of water’s journey from the hillslope to the stream, water level time series from 26 groundwater wells in a hillslope–riparian study area in the Panola Mountain Research Watershed, Georgia, USA, were examined with respect to the occurrence of perched groundwater and groundwater flow directions. A connected groundwater table was taken as an indication of a hydrologic connection between the hillslope and the stream. Flow directions were determined based on observed water levels at different combinations of three neighbouring wells. The analyses indicated that the hillslope was disconnected from the stream most of the time but that almost the entire hillslope became connected to the stream during large rainfall events. This coincided with more sustained streamflow during these events. There were clear differences in the timing of the groundwater response between the upper hillslope, lower hillslope and riparian zone, with water levels near the stream and on the upper hillslope rising earlier than on the midslope. The flow directions were generally downslope and were most variable around a bedrock depression on the midslope. On the hillslope, the direction of the water table followed the local bedrock topography when the water level was low at the start and end of an event and the overall surface topography when water levels were high. In the riparian zone, flow directions either did not change significantly during events or turned from a more downstream (i.e. downvalley) direction to a more downslope (i.e. towards the stream) direction. These results highlight the competing influence of surface and bedrock topography on hillslope flow directions and improve our understanding of hillslope–riparian-stream connectivity