2 Coastal Hydrogeology in an Age of Rising Seas

As sea levels rise, understanding hydrogeology is crucial in coastal areas. Seawater intrusion can lead to loss of potable or agricultural water supplies, and water table rise due to increasing sea level can lead to increased flooding and affect infrastructure.

Sunday, 19 October 2025
8:00 AM - 12:00 PM
HBGCC, 210AB

Shallow Groundwater Salinization Patterns Following Hurricane Helene on the Florida Gulf Coast

Paper number: 2-4
Program: Technical Sessions
Time: 8:55 AM – 9:10 AM

Authors

Abstract

Hurricane Helene made landfall as a Category 4 storm on September 26, 2024, bringing 12–16 inches of rainfall and a 9-foot storm surge to Apalachee Bay, Florida, a low-lying karstic coastline vulnerable to both sea-level rise and storm-related inundation. To assess the impact of this extreme event on coastal groundwater systems, sampling was conducted in October 2024, November 2024, January 2025, and May 2025. Samples were collected from shallow groundwater in beach and estuarine settings to evaluate hydrochemical changes and the extent of storm-induced salinization. Our preliminary data shows that shallow groundwater systems exhibited variable and prolonged responses shaped by lithologic differences. The sandy beach aquifer experienced short-term oxygenation and elevated nitrate concentrations following the storm, which later decreased as reducing conditions re-emerged. In contrast, the clay-rich estuarine aquifer retained elevated salinity for over nine months, indicating limited flushing and sustained storm surge influence. Salinity was significantly correlated with ammonium, phosphate, and dissolved organic carbon concentration, suggesting that storm surge infiltration and elevated ionic strength altered redox conditions and sediment sorption processes, leading to solute mobilization. These findings highlight the heterogeneous response of coastal aquifers to extreme events that are governed by local hydrogeologic properties. As sea level rises and the frequency of intense storms increases, understanding site-specific aquifer behavior is essential for predicting groundwater vulnerability and guiding adaptive water management in coastal regions.

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

doi: 10.1130/abs/2025AM-412065

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