Assessing coastal groundwater flooding due to groundwater emergence caused by Sea Level Rise in Cork City, Ireland

Cork City, Ireland, a tidally influenced urban environment at the head of Cork Harbour. Groundwater flooding risk in coastal cities is projected to intensify under sea-level rise (SLR). This study quantifies current and future groundwater flooding hazards in Cork City by analysing continuous water level data from three river gauges and six groundwater wells using Fast Fourier Transform to characterise tidal signal propagation. A groundwater model (FEFLOW) was developed, calibrated, and validated to simulate groundwater responses to tidal forcing and SLR scenarios. Model outputs were integrated into a geospatial framework to map maximum hydraulic heads and identify spatial vulnerability zones by comparing simulated heads with ground elevations. Tidal fluctuations have a significant impact on groundwater levels near the river, with their amplitude diminishing and reducing with increasing distance inland. Groundwater retains 70–100 % of the river level fluctuations. Under current conditions, ∼10 % of the city experiences groundwater levels above ground, rising to ∼25 % during extreme river events. SLR projections show strong non-linear vulnerability growth: + 0.5 m SLR affects ∼65 % of the city; + 1.0 m SLR affects ∼90 %. Aquitard discontinuities, shallow water tables, buried channels, and leakage from ageing water mains amplify risk. Historical SLR rates in Cork Harbour (2.2 mm/year) exceed assumed values, suggesting critical thresholds may occur sooner. These findings may help decision–makers to develop sustainable groundwater management strategies in the area. • Spectrum analysis (FFT) was used to quantify tidal signal propagation and attenuation. • Groundwater levels retained ∼70–100 % of river tidal fluctuations. • A groundwater model simulated tidal–groundwater dynamics under SLR scenarios. • Groundwater flooding vulnerability risk map utilising spectral, geospatial data analysis and numerical modelling. • Vulnerable areas increase from ∼10 % (2.5 m OD) to 90 % (4.0 m OD) due to SLR.