Flooding Projections Due To Groundwater Emergence Caused by Sea Level Variability

Abstract

Rising groundwater tables due to sea level rise (SLR) pose a critical but understudied threat to low-lying coastal regions. This study uses field observations and dynamic modeling to investigate drivers of groundwater variability and to project flooding risks from emergent groundwater in Imperial Beach, California. Hourly groundwater table data from four monitoring wells (2021–2024) reveal distinct aquifer behaviors across soil types. In transmissive coastal sandy soils, groundwater levels are dominated by ocean tides, with secondary contributions from non-tidal sea level variability and seasonal recharge. In this setting, we calibrated an empirical groundwater model to observations, and forced the model with regional SLR scenarios. We project that groundwater emergence along the low-lying coastal road will begin by the 2060s under intermediate SLR trajectories, and escalate to near-daily flooding by 2100. Over 20% of San Diego County's coastline shares similar transmissive sandy geology and thus similar flooding risk. Results underscore the urgency of integrating groundwater hazards into coastal resilience planning, as current adaptation strategies in Imperial Beach—focused on surface flooding—are insufficient to address infrastructure vulnerabilities from below. This study provides a transferable framework for assessing groundwater-driven flooding in transmissive coastal aquifers, where SLR-induced groundwater rise threatens critical infrastructure decades before permanent inundation.