The Sea-Level Rise No One Thinks About: Rising Coastal Water Tables Filling With Seawater In American Southeast

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As climate change pushes seas to rise ever higher, shallow groundwater could become a more costly hazard across the Atlantic coast, particularly in South Florida where the water table sits just feet below the surface, according to a new study from the U.S. Geological Survey. Up to 70% of residents between North Carolina and Florida, and a trillion dollars in property, could be impacted by the end of the century with just over three feet of sea rise. South Florida represents the vast majority of that risk, with about 7 million people and $750 billion in property expected to face increasing risks as groundwaters rise, the study found.

“We often get fixated on overland flooding. It’s more dramatic. It happens during hurricanes,” said Patrick Barnard, a research geologist at USGS and lead author on the study. “But that water table is going to rise through time and it’s going to amplify those overland flooding impacts.”That means that in addition to fixating on elevations in low-lying South Florida, we also need to pay attention to the hidden water table.

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That last risk proved to be the greatest in South Florida, where impacts from groundwater are already being experienced, from failing septic tanks to more severe inland flooding. Until now, most studies and forecasts have focused on coastal flooding worsened by high tide and hurricane storm surges. That has helped steer resilience work to shorelines, where homes are being elevated, aging coastal pumps are being replaced and seawalls elevated. Yet rising groundwater remains a mostly uncalculated risk even as it compounds flooding from storm surges and heavy rainfall.

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The study also found that hardening shorelines to protect residents from flooding could have a downside – major beach loss. Historic rates of beach renourishment will likely do little to stop shores from migrating landward. Yet efforts to protect coasts with seawalls or other hard infrastructure will likely lead to an 80% loss of beaches with about three feet of sea rise. “This presents a challenge to coastal managers,” the study said: defend shorelines to protect residents and communities at the expense of beaches or allow shores to move and wrestle with the economic and social consequences of losing coastal communities.

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https://www.miamiherald.com/news/local/environment/climate-change/article297502608.html#storylink=cpy