When we think of sea level rise flooding, we think of salt water spilling across beaches, wetlands or sea walls and onto the land, but that’s not the whole story.
In many coastal areas, salty seawater sits in porous soil layers beneath the fresh water aquifer. As sea level rises, the salty seawater, which is denser than fresh water is forced inland where it pushes the fresh water table up toward the surface. This type of groundwater flooding is already creating a challenge for many coastal communities battling classic sea level rise flooding.
In Miami, for instance, some neighborhoods far from the coast are flooding because soils saturated from higher groundwater can no longer absorb heavy rains. The saturated soils are also rendering septic systems inoperable as wastewater that’s carried out into leaching fields cannot be absorbed by already saturated soils.
According to an article by Kendra Pierre-Louis published in MIT Technology Review (“How rising groundwater caused by climate change could devastate coastal communities”) rising groundwater presents a “potentially catastrophic” threat to homes and infrastructure. “Roadways will be eroded from below,” she writes, “septic systems won’t drain, seawalls will keep the ocean out but trap the water seeping up, leading to more flooding. Home foundations will crack; sewers will backflow and potentially leak toxic gases into people’s homes.” Pierre-Louis explores the challenges in great detail in her excellent piece.
Experts say Miami (and all of South Florida, for that matter) isn’t alone in confronting this threat. Kristina Hill, an associate professor at the University of California, Berkeley, told the Pierre-Louis that flat coastal areas with a type of geology that allows water to move easily through the ground are at risk. The list also includes Oakland, California, Brooklyn, New York, Mountain View, California and Washington, DC.
Of great concern here is that cities might spend billions of dollars on seawalls, elevating streets and properties, and other efforts to combat classic sea level rise, but if they don’t consider the threat posed by the rising water table that can defeat those measures from below the investment could be a colossal waste of time and money.
Buyers of real estate in coastal communities that are vulnerable to this type of flooding need to understand that flooding from beneath poses as great a threat to their investment as flooding on the surface. They need to make sure that properties of interest — and nearby properties and roads — have not experienced groundwater flooding and are not at risk of experiencing it during the period they intend to own a property. They also need to know if the septic system (if they’re not hooked up to municipal service) is operational, if pipes providing water and sewer service are in good shape, what government officials are doing to address the problem, and how much any efforts to mitigate the problem will contribute to their water and sewer bills and taxes.
Ultimately, with the enormity of the land area at-risk, combatting groundwater rise will likely prove as — if not more — difficult than fighting classic sea level rise. The best choice, therefore, is to prevent the sea level/groundwater rise itself by adopting renewable energy sources that slow and stop the global warming that’s driving it.