Coastal groundwater model calibration using filtered and amplified hydraulic information retained in the freshwater–saltwater interface

Morphologic, Atmospheric, and Oceanic Drivers Cause Multi‐Temporal Saltwater Intrusion on a Remote, Sand Island

“…This result aligns with model results of Pavlovskii et al. (2022) that show a maximum 0.9 m increase in the water table in response to seasonal recharge, without a corresponding change in the interface depth in the center of the island.…”

“…The fall season on Sable Island is marked by high net aquifer recharge and winds that can temporarily raise both the water table and sea level (e.g., wave set‐up and water table overheight) (Figures S4 and S5 in Supporting Information ; P. Nielsen, 2009). An increase in the water table elevation concurrent with a pronounced decrease in the freshwater lens depth and increase in transition zone thickness does not comport with the Ghyben–Herzberg relation and may be a result of seasonal patterns in beach inundation and wave overweight due to increased wave action in the wave run‐up zone or the impact of extreme events during this monitoring period (Gonneea et al., 2013; P. Nielsen, 2009; Pavlovskii et al., 2022). Higher waves are consistently observed on the south shore of Sable Island, contributing to an increased transition zone thickness in the south and more lens asymmetry (Pavlovskii et al., 2022).…”

“…In general, results show little seasonal variability in the main body of the freshwater lens despite an increase in water table elevation, and indicate that the freshwater lens is not in equilibrium with seasonal forcing. The seasonal stability of the freshwater lens, where island topography is stable, could be attributed to the high hydraulic inertia of the lens compared to the water table and the fact that the freshwater volume required to enter (exit) the lens to maintain the Ghyben–Herzberg equilibrium in response to water table dynamics is more than the natural recharge (discharge) (Pavlovskii et al., 2022). We acknowledge there may be a lag between a water table signal and the interface response, which could be the subject of further field and numerical modeling research.…”

Vertical Saltwater Intrusion in Coastal Aquifers Driven by Episodic Flooding: A Review

“…Geophysical evaluations at different spatial scales may also provide the opportunity to investigate vertical SWI processes across a range of temporal scales (i.e., shallow, recent salinization and older, deeper saline plumes). EM geophysical surveys in pre‐storm conditions can also yield the geometry of the stable freshwater‐saltwater interface (Figure 1a), which can be used to help calibrate and parameterize steady‐state groundwater models that are then applied in transient runs to investigate the impacts of storms and vertical SWI (Pavlovskii et al., 2022). In general, geophysical methods provide the advantage of yielding spatially continuous subsurface salinity data in at least one dimension following flooding events; however, these surveys are often limited to discrete points in time, have uncertainty from the variability of inversion interpretations, and have received limited uptake in prior field investigations of vertical SWI (Table 1) (Cardenas et al., 2015; Huizer et al., 2017; Kiflai et al., 2020).…”

“… An example of a three‐dimensional numerical model domain (adapted from Pavlovskii et al., 2021) of a sandy barrier island including the typical boundary conditions applied for simulating vertical saltwater intrusion (SWI). Modeling challenges specific to vertical SWI are identified in the boxes.…”