22-13 Spatial Assessment of Sea-Level Rise and Flooding Risks to Onsite Wastewater Treatment Systems in Charlestown, Rhode Island

Session: Advances in characterizing groundwater, surface water, and their interactions (Posters)

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Coastal communities that rely on onsite wastewater treatment systems (OWTS) are increasingly exposed to the impacts of sea-level rise (SLR) and associated coastal flooding. This GIS-based analysis assesses the present and future exposure of OWTS to coastal flooding in Charlestown, Rhode Island, a low-lying town on the Atlantic Coast, where all residences rely on decentralized wastewater systems. High-resolution (1-m) LiDAR-derived elevation data were integrated with STORMTOOLS Design Elevation (SDE) flood rasters representing 100-year storm events under three SLR scenarios (0.5, 1.0, and 1.5 m above current mean sea level). Flood depths were extracted at each OWTS location and categorized into hazard classes using established coastal flooding thresholds. Under a moderate SLR scenario of 1.0 m, more than 40% of systems shift from minor or moderate exposure into major or extreme hazard categories, with impacts intensifying under higher scenarios and affecting over 75% of systems at 1.5 m. Overall, the study highlights the utility of GIS-based flood hazard mapping as a screening-level approach for identifying at-risk wastewater infrastructure. These findings provide a spatial framework for future integrated assessments of groundwater and nutrient dynamics. As a transferable framework, the approach is broadly applicable to low-lying coastal communities reliant on decentralized wastewater, particularly in settings with shallow groundwater and complex geomorphology.

Geological Society of America Abstracts with Programs. Vol. 58, No. 2, 2026

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