Why Groundwater is Another Sea Level Rise Concern

Sea level rise brings to mind the threat of coastal flooding from menacing storm surges, with growing risks to shore-based infrastructure — but a new study indicates there’s another sea level rise-related threat that has so far slipped under the radar.

According to the study, as sea level rises, so will groundwater levels, and since underground infrastructure —  including sewer pipes and utility equipment  — was built with historical groundwater levels in mind, this could lead to expensive headaches for coastal communities.

A projection for what New Haven would look like after three feet of sea level rise. Blue areas are at or below three feet in elevation. Click on the image for a larger version, or explore the interactive maps from Climate Central's Surging Seas project.

The study, by the U.S. Geological Survey (USGS) and Yale University, looks at the threat to New Haven, CT, Yale’s home city. Sea level rise may indeed raise groundwater levels significantly underneath the city, according to the study, leading to problems not just with pipes and pumps and buried cables but also with the arch-nemesis of many New England homeowners — basement flooding.

“Scenarios for the resulting higher groundwater levels have the potential to inundate underground infrastructure in lowlying coastal cities,” the study states.

Since the 1960s, sea level has risen by about 0.38 feet, at a rate of about .008 feet per year, at Bridgeport, CT, about 20 miles southwest of New Haven. Because the land in this area is slowly sinking at the same time the sea is rising, the amount of local sea level rise is expected to be greater here than in some other parts of the country. According to the study, some climate change scenarios show that sea level may rise by nearly three feet above current levels by 2080.

According to the study, under a scenario involving a three foot rise in sea level, the simulated rise in New Haven groundwater levels ranged from three feet at the shore to less than 0.5 feet in northern parts of the city.

A different scenario, involving a three foot sea level rise and an increase in the rate at which groundwater is replenished (known as “groundwater recharge”), presumably due to heavier precipitation, the researchers found that simulated groundwater levels would rise by a considerably greater amount. In recent decades, precipitation has been increasing in the Northeast, a trend that is expected to continue as the world warms.

Acting together, these trends may cause groundwater levels in New Haven to rise even more, the study states.

Recent research by Climate Central scientists found that even small amounts of sea level rise can greatly increase the risk of rare floods by adding to tides and storm surge. Climate Central’s work, which was published in the journal Environmental Research Letters, shows a projected sea level rise in Bridgeport of about a foot by 2050. The amount of sea level rise projected to take place in the New Haven area is not as significant as projections for many other locations in the U.S., which suggests that other cities may face much greater groundwater challenges.