Baseline and Pre‐Restoration Construction Assessment of a Stream‐Aquifer Connection in the Southeastern <scp>US</scp> Coastal Plain

ABSTRACT Stream–aquifer connections in incised coastal plain floodplains with shallow aquifers are controlled by sediment type, seasonal climate forcing, and channel geometry, but remain poorly quantified. This study characterizes these interactions along Cub Creek, a coastal plain stream, using an integrated approach that combines borehole stratigraphy, natural gamma logs, electrical resistivity (ER) surveys, and 2 years (2022–2023) of hydrologic monitoring. A shallow unconfined aquifer was identified along the studied stream reach within Quaternary alluvium and the Wilcox Formation and is underlain by the Porters Creek Clay confining unit. ER imaging indicated lateral discontinuity of sand bodies within the Wilcox Formation and an incised channel geometry in the downstream alluvium. Grain‐size analysis also showed a downstream coarsening trend (upstream: 67%–71% fines; downstream: 59%–66% fines). These textural differences are reflected in soil‐moisture behavior at the two monitoring locations. During cooler seasons, VWC at 150 cm stabilized near equilibrium values of ~45% upstream and ~38% downstream. Together, these conditions contributed to differences in water‐table fluctuations between the upstream and downstream reaches. Mean annual groundwater recharge was 0.40 m year −1 at the upstream monitoring well and 0.43 m year −1 at the downstream well. Recharge variability was greater downstream due to coarser sediments and a thicker vadose zone. Recharge events occurred more frequently during cooler seasons and less frequently during warmer months. Consistent with these observations, the upstream reach of Cub Creek likely behaved as a losing stream during warmer periods, while the downstream reach acted as a gaining stream. During construction, a channel blockage in October 2023 produced an abrupt upstream water‐table rise, indicating the sensitivity of shallow coastal plain aquifers to channel modification. These results establish a foundational hydrogeological framework for assessing restoration effectiveness in reestablishing floodplain–aquifer connectivity.