- New study finds seawater-linked groundwater could flood Imperial Beach roads by 2060s.
- Over 20% of San Diego County coastline has similar flood-prone geology.
- Existing coastal plans overlook flooding from below ground, researchers warn.
- Groundwater-driven floods may become near-daily events by 2100.
Thursday, July 16, 2025 — A recent study published July 12, 2025, in Earth’s Future
sheds new light on a lesser-known but critical coastal flooding threat: rising groundwater levels caused by sea level rise. The research, led by scientists from UC San Diego and San Diego State University, uses real-world data and modeling to show that coastal communities such as Imperial Beach could see road-level flooding from beneath the ground well before being submerged by ocean waters.
Imperial Beach as a Warning Sign.
The researchers studied groundwater data collected between 2021 and 2024 from four monitoring wells in Imperial Beach, a low-lying city along the southern California coast. The findings revealed that in areas with sandy soils—especially near the shoreline—groundwater levels are strongly influenced by ocean tides and non-tidal sea level changes. In these zones, the groundwater table already rises and falls with each tide, occasionally coming within centimeters of street level.
Using these observations, the team developed a dynamic groundwater model. When tested against current sea level rise projections, the model showed that groundwater will likely begin flooding portions of Seacoast Drive, a low-lying coastal road in Imperial Beach, by the 2060s. By the end of the century, the frequency and intensity of these groundwater emergence events are expected to increase dramatically.
Groundwater: The Overlooked Hazard.
Imperial Beach already faces challenges from high tides and storm-driven flooding. However, existing resilience plans have largely focused on surface water hazards like waves and runoff. According to the study, these plans may fall short if they fail to address what is happening beneath the surface.
“Flooding from groundwater rise may occur decades before permanent surface inundation,” the authors note. This means buried infrastructure like roads, sewer lines, and foundations could be damaged by underground flooding even while the land above appears dry.
Shared Risk Along the Coastline.
The implications stretch well beyond Imperial Beach. More than 20 percent of San Diego County’s coastline shares similar soil conditions—coarse, sandy deposits that easily transmit tidal fluctuations inland. Areas such as Naval Base Coronado, Del Mar, and parts of Camp Pendleton may face the same threat if rising groundwater is not factored into flood risk management.
Planning for the Future.
The research team recommends integrating groundwater data into all coastal flood modeling and resilience efforts. They highlight the importance of direct measurements and localized models that account for both soil characteristics and sea level variability. Tools like the one used in this study, which combines tidal data, precipitation, and climate projections, can offer timely insights for adaptation.
While this new threat remains largely under the radar, the study makes clear that planning now could help coastal communities avoid costly surprises in the coming decades.
Citation:
Barnes, A. T., Merrifield, M. A., Bagheri, K., Levy, M. C., & Davani, H. (2025). Flooding projections due to groundwater emergence caused by sea level variability. Earth’s Future, 13, e2025EF006270. https://doi.org/10.1029/2025EF006270
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