2-2 Hybrid Geospatial-Analytical Frameworks to Assess Regional Saltwater Intrusion and Water Table Rise Vulnerabilities

Session: Coastal Hydrogeology in an Age of Rising Seas

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Abstract:

Homeowners in rural, coastal communities often rely on private wells and septic systems, which are vulnerable to oceanic and atmospheric climate change. For example, sea-level rise (SLR) can simultaneously drive saltwater intrusion (SWI) and water table rise in coastal aquifers. When water tables rise and cross critical thresholds, the vadose zone underlying septic systems becomes too thin for effective treatment. Patterns of potential SWI or water table rise and their impacts on private wells and septic systems can be simulated using physics-based (analytical or numerical) models or empirical, parametric approaches applied in geospatial frameworks (e.g., GALDIT method). Numerical models are robust, but their regional applications are often challenged by a lack of appropriate parameterization data and computational resources. Analytical solutions are parsimonious, scalable approaches, but these are rarely applied within the geospatial frameworks used for decision making.  Empirical, parametric approaches integrate well in geospatial frameworks at any spatial scale, but the methods rely on arbitrary weighting and lack predictive capacity given the lack of any physical basis.

Here, we advocate for a hybrid approach that leverages the strength of both analytical models (mathematical simplicity, reproducibility) and geospatial frameworks (integrable in existing risk frameworks and with existing georeferenced datasets). Our study site is the Atlantic Canadian province of Nova Scotia, where almost half of the population relies on private wells and septic systems. We apply modifications of the well-known Strack solution (Werner et al., 2012; Morgan, 2024) to map SWI (in confined aquifers) and water table rise (unconfined aquifers) vulnerabilities due to SLR. Unlike previous analytical studies predominantly conducted for local study sites, we map these vulnerabilities along the entire 13,300 km coastline of Nova Scotia. We use newly developed ArcGIS toolboxes to extract/calculate hydrogeological parameters from public datasets and run the analytical vulnerability indices along the gridded coastline. Results reveal spatial variability in mapped vulnerabilities due to heterogeneity in forcing and parameters. For example, the southern coast of Nova Scotia was identified as the ‘hot spot’ for SWI vulnerability, while Annapolis County (Bay of Fundy coast) had the most septic systems and roadways impacted by shallow groundwater. These results are useful for first-order mapping of relative vulnerabilities. Outputs can be used to prioritize areas for detailed hydrogeological assessments and to communicate risks to communities.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7086

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