Storage and connectivity across river corridor and watershed scales in three headwater streams of the southeastern USA

Abstract. Watershed characteristics create a mosaic of potential storage zones, and linkages between these result in hydrologic connectivity between groundwaters and surface waters. Watershed storage and connectivity are fundamental controls on stream network dynamics, yet predicting the patterns of hydrologic responses like streamflow remains difficult due to landscape heterogeneity across multiple, interacting spatial scales. Here, we characterize storage and connectivity dynamics at the watershed scale and the hydrogeomorphic feature (HGF) scale using a network of steam and riparian groundwater monitoring wells in three watersheds spanning the Coastal Plain, Piedmont, and Appalachian Plateaus physiographic regions of the southeastern USA. At the watershed scale, we operationalized watershed storage as the slope of streamflow recession at the watershed outlet, and hydrologic connectivity as the relationship between outlet discharge and network length. At the HGF scale, we operationalized storage as the slope of water level recession at seven in-stream monitoring locations, and connectivity as the lateral hydraulic gradient and water level hysteresis relationships between the stream channel and adjacent riparian zone at three locations per watershed. At the watershed scale, we found patterns in storage and connectivity varied across physiographic regions. We also found distinct storage and connectivity dynamics across HGFs, many of which challenged existing conceptualizations for similar geomorphic settings. Notably, channel incision emerged as a key structural control, homogenizing storage and connectivity patterns across otherwise disparate watersheds and producing a common threshold response in watershed storage. Together, these results demonstrate that watershed-scale patterns do not reflect the heterogeneity observed at the HGF scale. Moreover, river corridor structure, particularly channel incision, is a key driver of storage and connectivity dynamics across physiographic settings.