In January, we reported that major cities on the U.S. atlantic coast are sinking—some more than 5 mm per year, affecting 2 million people and 800,000 properties. Now, in a recent study, earth scientists at the University of Hawai‘i (UH) at Mānoa have compiled additional research from experts worldwide.

Problems decades beforehand

The study shows that in cities where there are complex networks of buried and partially buried infrastructure, interaction with this shallower and saltier groundwater exacerbates corrosion and failure of critical systems such as sewer lines, roadways, and building foundations. 

“Chronic flooding … can start causing problems decades beforehand as groundwater interacts with buried infrastructure,” said Shellie Habel, lead author and coastal geologist in the School of Ocean and Earth Science and Technology (SOEST) at UH Mānoa. “This knowledge gap often results in coastal groundwater changes being fully overlooked in infrastructure planning.”

Sea level rise: unstoppable, irreversible reality for centuries to millennia

Habel and co-authors identified 1,546 low-lying coastal cities and towns globally, where around 1.42 billion people live, that are likely experiencing these impacts.

Well before the visible effects of surface flooding, sea-level rise pushes up the water table and shifts salty water landward. With this, the subsurface environment becomes more corrosive to critical underground infrastructure networks—buried drainage and sewage lines can become compromised and mobilize urban contamination, and building foundations can weaken.

Extensive research has substantiated that critical infrastructure around the world, including drainage and basements, is likely currently experiencing flooding from rising groundwater levels. 

Informed adaptation strategies

“The damage caused by sea level rise-influenced coastal groundwater is often concealed and not immediately perceptible,” said Habel. “As a result, it tends to be overlooked in infrastructure management and planning efforts.”

The study authors emphasize the importance of research efforts that can contribute to informed adaptation strategies. “Being aware of these hidden impacts of sea level rise is of significant importance for the State of Hawai‘i due to the concentration of communities situated along low-lying coastal zones where groundwater is generally very shallow,” said Habel.

Citation: Shellie Habel et al. 17-Jan-2024. Hidden Threat: The Influence of Sea-Level Rise on Coastal Groundwater and the Convergence of Impacts on Municipal Infrastructure. Annual Review of Marine Science. 10.1146/annurev-marine-020923-120737 (open access)

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