Threat from below: Sea rise is pushing up groundwater — and flood risks for South Florida
Unlike the climate changedriven threats from tides, rain and storm surge, groundwater has been an often-ignored and littleunderstood enemy.
You don’t have to dig deep to hit water in South Florida. In some places in Miami-Dade, a mere foot or two is all that stands between the dry ground and the water running through the porous rock below.
As global warming swells sea levels, groundwater rises too. But unlike the climate change-driven threats from tides, rain and storm surge, groundwater has been an often ignored and little understood enemy.
That’s quickly changing. Scientists say there is now enough data to show that rising groundwater levels will add to flood risks for South Florida — particularly in low-lying areas or coastal areas that already see repeated problems during heavy rains, like Little River and North Miami.
And new studies, like one charting sharp increases in sea rise at the site of Champlain Towers South, point to potential concerns beyond flooding. The Florida International University analysis found the number of times per year sea level rose higher than the underground garage floor of the doomed Surfside condo has nearly tripled over the last 30 years.
This emerging research raises questions about the impact of rising seas and groundwater on coastal construction, especially for aging high-rises whose stability depends on ramming giant cylinders of concrete and steel hundreds of feet below the surface.
For now, there are no clear answers, but Randall Parkinson, the FIU professor behind the Champlain
Towers study, said he believes South Florida has been ignoring a problem right below its feet.
“The lack of anecdotal information isn’t because there’s no evidence, it’s because no one has been looking for this,” Parkinson said. “I suspect the more we do that the more we’ll find.”
The Surfside tragedy was a bellwether moment in many ways, elevating climate change concerns and questions with policymakers, the public and researchers.
Although sea level rise has not been identified as a potential factor in the domino effect that led to the shocking collapse of a 12-story condo, basic engineering and science dictate that water (especially saltwater) interacting with the concrete and steel that sustain a building isn’t a good thing.
In the wake of the collapse, a team of researchers, including ones from FIU and the University of Miami, applied for a National Science Foundation grant to study the impacts of rising shallow groundwater on old coastal buildings. There are no researchers, agencies or governments exploring the issue, and if funded, this collaboration would be the first.
Mike Sukop, a hydrogeologist at FIU, is one of the groundwater experts on the research proposal. His previous research in North Miami found that groundwater is rising at nearly the same rate as sea level in low-lying spots in the county — a potential looming threat down the road for many areas of the county.
“It seems really important to me,” he said. “The risks from it seem pretty substantial.”
GROUNDWATER LEVELS ARE RISING
Throughout most of Miami-Dade, there’s an average of five feet between the ground and water underneath during the wettest time of the year — October. But in coastal, riverfront and far western pockets of the county, that number drops below three feet.
The best way to see how high groundwater levels are is to look at the canals crisscrossing the county. It’s a safe bet to assume the water there is the same height as underground.
“When you look at any canals and they have water, that’s the groundwater table. You know the groundwater is higher than sea level, but not that much higher,” said Parkinson, a research associate professor with FIU’s Institute of Environment. “On rainy days when it ponds inland, it’s ponding above sea level.”
The effect of high groundwater on flooding is obvious just about every rainy season in South Florida. After repeated heavy rains saturate an area, much of what doesn’t run off into drainage canals filters down into the porous lime rock underlying much of South Florida. It recharges the drinking water supply in the shallow Biscayne Aquifer, but every inch of dirt turned soggy by higher groundwater and sea levels leaves less room to absorb torrential summer downpours.
It’s why Miami-Dade and Broward saw tremendous flooding after Tropical Storm Eta in 2020; the ground was already soaked with days of rain and couldn’t hold much more. Rising groundwater can have the same effect.
Current predictions show Miami-Dade could see around two feet of sea level rise by 2060. And research done by FIU scientists in North Miami, one of the areas where groundwater levels are already high, shows that groundwater is rising at the same rate as the sea. The study projects that sections of North Miami could go from experiencing about three months of rain-driven flooding a year now to six months a year by 2060. And that was considered a conservative estimate.
A University of Florida hydrology researcher, Young Gu Her, is working on a long-term project that models how sea rise and climate change are affecting groundwater in South Florida. His early results show a “quite obvious” rise in groundwater levels along the coast, where sea levels have risen about five inches over the last 30 years.
He said that although other factors like development, pumping drinking water and rainfall changes due to climate change may complicate the picture inland, “sea level rise is the most influential factor that may increase groundwater level in
South Florida.”
In South Florida, which relies on gravity and canals to drain water toward