Category: Groundwater in the News

Saltwater intrusion is an increasing problem in Florida.  In 2011, Hector Castro, the Hallandale Beach public works and utilities director, told the Sun Sentinel, “It is still progressing westward.  Eventually all coastal communities will deal with this in some way, shape or form.”  Saltwater intrusion has been exacerbated by drought and sea-level rise, and 90% of Florida’s drinking water comes from groundwater sources.

Southern Florida has a unique hydrological system that is extremely vulnerable to salt water intrusion.  In Southern Florida, both the surficial aquifer systems and the underlying Floridan aquifer systems exhibit high conductivity, and karst formations are present.  In the 1960′s the state constructed a canal system that partially drained sections of the Everglades to prevent flooding of urban areas.  The construction of these drains not only lowered the water table in the region, but also removed the natural hydrological barrier that was maintained by the Atlantic Coastal Ridge, protecting the Everglades from saltwater intrusion by the Atlantic Ocean (Dausman & Langevin 2004).

The USGS has identified three vectors for saltwater intrusion in Florida: 1) lateral saltwater intrusion, 2) upconing in the interface formed in response to well pumping, and 3) canal leakage (Dausman & Langevin 2004).

Aerial View of Everglades National Park by Pictureguy (Wikimedia Commons)

Large Scale Maps of Saltwater Intrusion

Tracking saltwater intrusion in Florida on a very large scale is becoming increasingly possible.

In recent years, researchers have begun using electromagnetic geophysical methods to monitor saltwater intrusion.  In 2004, researchers from the USGS presented results at the 18th Salt Water Intrusion Meeting regarding using  airborne electromagnetic surveys to map saltwater intrusion in Southern Florida and the Everglades.  By measuring the water quality in the sparse wells and boreholes, the researchers were able to relate helicopter electromagnetic surveys to salinity in the wells. Using this method, they created a map of conductivity by depth over three counties and the Everglades.  The method contains significant uncertainty, because the conductivity of the pore-water must be separated out from the conductivity of the rock matrix.  Over large scales, where the rock matrix varies widely, this correction becomes more difficult.

But their results clearly show the saltwater/freshwater interface, which is quite abrupt at shallow depths and more gradual at deeper depths.  The survey also shows how man-made features affect the interface.  For example, the affect of constructed canals, which release freshwater in the subsurface through infiltration, can be observed on the conductivity map (Fitterman & Deszcz-Pan 2004).

Learn more about salt water intrusion in Florida:

• Listen to this five part audio series by Barclay Shoemaker which has be posted by the USGS (the Florida Environment, July 16, 2007, copyrighted by Kevin Pierce).
• Check out presentations from SWIM: 20th Salt water Intrusion Meeting (July 23-27, 2008).

Saltwater Intrusion in the US – Part 1: Southeaster NJ

Saltwater Intrusion in the US – Part 2: Groundwater Models of NJ

Dausman, A. & Langevin, C.D. (2004). Movement of Saltwater Interface in the Surficial Aquifer System in Response to Hydrologic Stresses and Water-Management Practices, Broward County, Florida. USGS Scientific Investigations Report 2004-5256. Prepared in cooperation with the South Florida Water Management District. Available at: http://lake.wateratlas.usf.edu/upload/documents/sir20045256.pdf

Fitterman, D.V., & Deszcz-Pan, M. 2004. Characterization of Saltwater Intrusion in South Florida Using Electromagnetic Geophysical Methods.  Proceedings of the 18th Salt Water Intrusion Meeting. Available at: http://sofia.usgs.gov/publications/papers/sw_intrusion_sfl/.