Photo credit: NOAA.

It’s Not Just Flooding

The lesser-known threat from sea-level rise? Saltwater intrusion into Florida’s freshwater wells.

By Vickie Machado

When it comes to sea-level rise, Miami is usually deemed ground zero. Time-lapse maps depict the creeping rise of blue, ultimately inundating South Florida and other coastal regions. You don’t have to go to climate-apocalypse movies like the Day After Tomorrow to see flooding of a major American city. It’s a reality as South Florida residents become familiar with wading down the street through high waters or kayaking around their neighborhoods.

But as coastal Floridians fret about the water rising above-ground, the general public hasn’t paid as much heed to sea-level rise’s twin threat from below: saltwater intrusion. Jayantha Obeysekera, chief modeler at the South Florida Water Management District, points out people should be concerned about not only obvious “nuisance flooding” of coastal areas, but unseen saltwater intrusion – the creep of saltwater from the sea into freshwater aquifers.

Saltwater intrusion is not a new concept. In fact, it has a long history in Florida, appearing in a variety of forms since modern settlement in the early 1900s. Intrusion can stem from natural causes including drought or seepage from past geological time. But scientists say a recent rapid succession of saltwater has been caused by human activities and can be attributed to climate change.

At this year’s Public Interest Environmental Conference at the University of Florida’s law school, Florida Sea Grant Director Karl Havens said saltwater intrusion is already aggravating infrastructure challenges and environmental restoration efforts in Florida. As saltwater encroaches, Floridians can lose access to their freshwater wells. Biological hotspots, like estuaries, become further extensions of the ocean rather than protective barriers to the mainland.

Scott Prinos, a hydrologist at the U.S. Geological Survey’s Caribbean-Florida Water Science Center in Davie, has been collecting Florida groundwater data on a number of fronts for two decades. His science shows that both sea-level rise and aquifer pumping can aggravate saltwater intrusion – putting Florida’s coastal freshwater aquifers at risk.

“Any of the pathways of saltwater intrusion could potentially lead to detrimental impacts to a water supply depending on the situation,” Prinos said.

In the early half of the 20th century, Miami-Dade County witnessed the closure of three public water supply well fields due to saltwater intrusion – two of them shut down permanently. “The USGS found that the saltwater came from a combination of leakage of saltwater from canals and gradual encroachment of saltwater inland along the base of the aquifer resulting from declines in aquifer water levels.”

Prinos, who works to model and map the movement of saltwater, noted that sea-level rise “will increase the driving pressure for seawater to move inland through aquifers in contact with the ocean – or to move inland through canals exiting to the ocean, particularly during high tide or storm surge events.”

Obeysekera explained solutions to reduce saltwater intrusion often appear complicated and extremely pricey, such as moving well fields away from the ocean, building reverse-osmosis or desalinization plants, or holding water in surface reservoirs to recharge well fields. But of all possible alleviations, he says, perhaps the No. 1 “ ‘no regret’ strategy is to pump less water.”

About Project Blue Ether

WUFT News is publishing this multi-week series on water by University of Florida students, led by award-winning environmental journalist and author Cynthia Barnett, who is a visiting professor at the University of Florida College of Journalism and Communications.