Study: Our Water Use Is A Major Cause Of Saltwater Intrusion

May 28, 2014

Both sea-level rise and our pumping of groundwater contribute to saltwater intrusion. Freshwater is less dense than saltwater and will float on top. But with sea-level rise, saltwater pushes in and seeps into the freshwater aquifer. With withdrawals of groundwater, we lower the level of freshwater so there's less of it keep saltwater out.
Credit US Geological Survey

A study finds that South Florida maybe can’t blame the rest of the world for saltwater seeping into the groundwater, also called saltwater intrusion. 

Although South Florida has seen nine inches of sea-level rise in the past several decades, the main contributor to saltwater intrusion in the area targeted by this study was our withdrawals of groundwater. 

The U.S. Geological Survey and Broward County looked at historic data for Pompano Beach from 1900 to 2005. The study considered several factors leading to saltwater intrusion including canal levels and sea-level rise. 

Michael Zygnerski of Broward County, who co-authored the study, said, "We saw that the major contributor that caused the saltwater front to move was well-field withdrawals."

In other words, pumping out a lot of freshwater from our underground aquifer was the biggest factor for saltwater intrusion.

But sea-level rise exacerbated the effects of over-pumping.

Zygnerski explains that it’s not just simple addition: “If you saw that pumping caused a two-foot movement in the saltwater interface and sea-level rise caused a one-foot movement separately, when you have both factors occurring simultaneously the effect doesn’t equal three feet, but can actually double to something like six feet.”

Zygnerski emphasized they do not yet know how applicable these findings are to the rest of South Florida. Pompano Beach sits at a relatively higher elevation than some parts of Broward.

Still, the study highlights the importance of water conservation for prevent saltwater intrusion, says Jane Graham from the Audubon Florida: "While we cannot control how fast the sea encroaches on our wellfields, we can control our demand for freshwater. Increasing water efficiency through measurable and meaningful water conservation will be crucial to help cope with these challenges."