The Hidden Threat to Coastal Erosion and Flooding: Ocean Water Pushing Groundwater Upwards

 NEEF Study of US Groundwater over a century plus

                                                                      Surfside, Florida Condominium collapse                                                              

According to the National Environmental Education Foundation (NEEF), with 50% of the US population living on or close to the coast, we are ignoring one huge factor from climate change: Groundwater. “The amount of water that is stored underground varies across the US depending on the geology of the area, recharge (from sources such as precipitation, snowmelt, lakes, and rivers), and withdrawal from wells. If water is discharged at a rate that is greater than recharge, it is possible for groundwater to run out or become unusable in some areas. A changing climate impacts the quantity and quality of groundwater through increased risks of drought, changes in precipitation and temperature, decreases in snowmelt, and rising sea levels.

“Groundwater in coastal regions of the US is particularly at risk due to a combination of changes in precipitation, withdrawal rates, and sea level rise. Along the coast, groundwater and saltwater from the ocean are naturally separated by the seaward movement of groundwater and a transition zone where freshwater and saltwater mix. As changes in precipitation and rises in sea level continue, the occurrence of saltwater infiltrating groundwater resources may increase and reduce the availability of freshwater for coastal communities. For example, the Biscayne Aquifer at the southern tip of Florida is the primary water source for the Florida Keys, Miami, and the lower east coast of Florida. As sea level rises, the amount of saltwater infiltrating the groundwater aquifer will increase, which can make the water too salty for human consumption.”

As we have watched a Florida coastal condominium collapse from the eroding limestone beneath (pictured above), the potential risk becomes obvious. NEEF reminds us: “Since 1880, global sea level has risen about eight inches. Scientists expect global sea level to rise another one to four feet by 2100.” Simply put, it’s happening now and getting worse. This is hardly a Florida phenomenon; it’s happening in coastal regions all over the world, though perhaps in different ways depending on the regional geology.




The recent deluge from a spate of atmospheric “rivers” that has soaked California has caused some geologists to watch groundwater rise in places like San Francisco. It’s not pretty. Rosanna Xia, writing for the January 17th Los Angeles Times explains a recent study: “The new findings are the result of an unprecedented joint effort by May, the San Francisco Estuary Institute (SFEI), UC Berkeley and a wide-ranging team of regulators, building officials and flood-control agencies to identify where the groundwater along the bay shoreline is close to, or already breaking, the surface. A set of searchable maps, available online to the public, zooms in on Alameda, Marin, San Francisco and San Mateo counties — the first of many jurisdictions that researchers hope will undergo this intensive data-refining process…

“Amid dramatic ocean swells and drenching atmospheric rivers, a new report lays bare a hidden aspect of sea level rise that has been exacerbating flooding in the Bay Area… The report, which was released Tuesday [1/17], maps areas that could flood from groundwater hovering just a few feet or even inches below ground. This layer of water gets pushed upward as denser water from the ocean moves inland from rising tides. On its way up, even before the water breaks the surface, it can seep into the cracks of basements, infiltrate plumbing, or, even more insidiously, re-mobilize toxic chemicals buried underground.

“Communities that consider themselves ‘safe’ from sea level rise might need to think otherwise, said Kris May, a lead author of the report and founder of Pathways Climate Institute, a research-based consulting firm in San Francisco that helps cities adapt to climate change...

“When talking about groundwater, there are two types to keep in mind: One, the kind researchers are now worried about, is the unconfined water that gathers in the pore spaces of soil very close to the surface. This is the water that runs off streets and soaks into the ground. The other type, confined in aquifers many hundreds of feet deep, is the water that we tap for drinking.

“When the tide moves inland, the shallow freshwater tends to float on top of the denser saltwater — and gets pushed upward toward the surface as sea levels rise. Because the shallow groundwater is not consumed, few people have studied this layer of water in California.

“[Kristina Hill], who directs the Institute of Urban and Regional Development at UC Berkeley, first realized almost a decade ago that this shallow groundwater layer had been overlooked in sea level rise conversations. Together with May and Ellen Plane, who is now an environmental scientist at SFEI, she analyzed data from 10,000 wells across the Bay Area and concluded more than twice as much land could flood from groundwater as the ocean continued to rise…

“Officials in San Francisco are already taking the data into account as they consider new building projects. Other cities and counties are starting to rethink their flood-protection options — a traditional levee or seawall, after all, would do nothing to stop the groundwater as it moves with the rising sea.

“Ultimately, officials need to figure out what to do with all the contaminated sites along the bay that are still awaiting cleanup — or those that need to be further remediated, said Hill, who has been finalizing another set of maps that will show where, and in which direction, rising groundwater might remobilize harmful chemicals underground. The oft-used approach of ‘capping’ a toxic waste site rather than actually removing the contamination from the soil, for example, may no longer be sufficient…

“Similar research into vulnerable communities in Southern California is now also being conducted by a team led by Cal State Long Beach and Cal State Northridge.” There are so many variables, from landfill subject to its own form of erosion, toxic waste finding new paths to spread as groundwater moves, destabilization of surface buildings by subsurface erosion… and uncontrolled flooding. And so much more!

I’m Peter Dekom, and this roiling and continuous destruction won’t stop until the world wakes up to the need to stop and reverse climate change as opposed to simply reacting to resulting “natural disasters” and only treating the symptoms.