Rising groundwater threatens New York researchers are investigating how much

Groundwater lurks under the radar as a threat on the New York City coast, but officials halted 50 years of routine monitoring in 2013. Now environmental agencies are starting to take a deep look again.

Rising sea levels and more intense rainfall, both consequences of climate change, are causing the water stored underground to also increase, leading to an increased risk of flooding – particularly where the water table is already high or the land is particularly low.

There are gaps in knowledge about the groundwater levels in the five districts. The Bronx, Manhattan and Staten Island were not consistently monitored. The city’s Department of Environmental Protection (DEP) and the United States Geological Survey (USGS) monitored Brooklyn and Queens for about half a century, but stopped doing so nearly a decade ago.

Now a new collaboration is emerging to study groundwater across the city.

“After a nearly 10-year hiatus, it looks like we’re about to resume hydrological monitoring in the City of New York,” said Ronald Busciolano, a senior hydrologist at the New York Water Science Center, operated by the USGS will. “This will be important over the long term to see if sea level rise will have a large impact on additional flooding in some areas as groundwater levels rise over time.”

The five-year program to monitor groundwater levels and quality at more than 150 wells in the five counties should begin in the next six months, Busciolano said.

Rising groundwater is challenging the effectiveness of strategies to reduce stormwater flooding, as well as plans to build barriers to prevent coastal flooding. Meanwhile, efforts to stem groundwater flooding could lead to other problems, experts say.

“It’s a relatively new topic that policymakers are considering,” said Daniel Rozell, a scientist and engineer at Stony Brook University. “As sea levels rise, so does coastal groundwater, and if the groundwater isn’t that far from the surface, it can cause all sorts of problems as sea levels rise.”

The flow of history

For about 50 years, DEP has worked with USGS to monitor water tables in Queens and Brooklyn by surveying dozens of wells. Those efforts ended in 2013 when the DEP ruled out using groundwater as a possible source of drinking water during the Delaware Aqueduct shutdown for repairs. Since then, wells in Queens have been regularly monitored, but elsewhere in the city there has been a gap in data collection and water level monitoring.

Low-lying neighborhoods developed on bodies of water (like ponds and swamps) tend to experience chronic flooding from groundwater, which gets worse when it rains.

As previously reported by THE CITY, residents in places like Hollis, Queens have seen water gushing from drains; In The Hole, a wet neighborhood on the Queens-Brooklyn border, residents struggle with standing water on their streets no matter the weather. Last summer, owners of waterfront restaurants in Greenpoint told Gothamist they encountered water after digging just six inches into their filthy basements.

Uncontrolled, rising groundwater can cause flooding, cause sinkholes in streets, and damage underground tunnels, utilities, parking garages, and basements. Near the coast, the salt in seawater can infiltrate freshwater and cause corrosion. Groundwater flowing up from toxic sites could also lead to the spread of contaminants.

“We’re really talking about a permanent type of flooding that will seep up very slowly from the bottom up and will affect underground infrastructure, human health and the foundations of structures before we ever see it on the surface,” said Kristina Hill, a Professor at the University of California, Berkeley and Director of the Institute for Urban and Regional Development there. “It will also affect our ability to dissipate this excess precipitation.”

Installing green infrastructure — like rain gardens and roofs with a layer of vegetation — is one of the city’s signature approaches to preventing flooding. However, experts say these projects could actually result in more flooding – or they might not work as intended depending on the location of the water table.

“We need to understand groundwater in terms of green infrastructure and blue belts,” said DEP Commissioner and Chief Climate Officer Rohit Aggarwala. “The green infrastructure, the downpour [projects] and the bluebelts all work much better where the groundwater is lower, and that way the ground can hold more rainwater.”

Bluebelts are drainage systems that improve natural watersheds to handle stormwater—like the one at Midland Beach on Staten Island.

Unintended Consequences

Although there is little data on how sea level rise has affected or could affect groundwater in New York, the city has kept a close eye on groundwater levels in some parts of southeast Queens over the years.

Between 1996 and 2007, New York City shifted its reliance on groundwater wells as part of its drinking water supply. Before that, pumping of groundwater since 1887 had caused the water table to drop several dozen feet in east Queens, where many residents are now experiencing flooding in their basements.

“The community wanted to move away from Jamaica Water Supply [and] Switch to city water,” said Andrea Scarborough, a community activist and longtime resident of Addisleigh Park in southeast Queens. “What they didn’t know was coming is that the water table would start to rise once the wells we got our water from were shut down once they went offline.”

A USGS plot shows how close groundwater was to the surface on Long Island in 2013.

Courtesy US Geological Survey

In this area, the water table was about 40 feet higher in 2013 than it was in the 1970s to mid-1980s, according to USGS data. Levels began to rise as less groundwater was pumped for drinking water — although they remained relatively constant between 2007 and 2013, the data shows. In Queens, the USGS continued to monitor two wells.

“Curning that groundwater use and allowing the water table to recover was really the elephant in the room in terms of increased vulnerability to groundwater flooding,” said Christopher Schubert, a hydrologist at the New York Water Science Center. “Without a return to active drainage or an increase in active drainage for whatever purpose, this groundwater inundation is only going to increase given the changing climate, particularly because of rising sea levels.”

In 2017, the DEP, under former Mayor Bill de Blasio, investigated groundwater flooding in south-east Queens and identified potential projects the city could build — but decided “in the face of buildability challenges,” according to a 2019 letter, “with property owners.” to work together” to improve conditions by then-DEP Commissioner Vincent Sapienza, now the agency’s chief operating officer.

According to DEP spokeswoman Beth DeFalco, the agency is evaluating methods to mitigate groundwater flooding, such as establishing basins to receive and transfer groundwater, installing pipes and creating groundwater flow through streams that existed before the city developed. She noted that the DEP has not currently documented any increased damage to infrastructure from rising groundwater.

Aqueous solutions

Restoring clogged streams to their former state — known as daylight — and installing blue belts could help “drain” the soil, as Schubert put it. Another option is mechanical pumps, which are already being used to protect subway tracks and subway tunnels.

New York City Transit pumps 13 million gallons of water out of the system on a dry day. Track drains collect groundwater, direct it to one of 285 pump rooms, and then discharge it into the sewer system. In certain neighborhoods with high water tables, such as East New York in Brooklyn and Harlem, groundwater is pumped off adjacent to subway tunnels to keep the water table below the height of the tunnels.

However, pumping can cause soil collapse as the water content that holds the soil together disappears.

UC Berkeley’s Hill said New York City can learn from low-lying places like Amsterdam, which has incorporated canals into its cityscape and does “light pumping” to maintain a lower water table without the land sinking.

She pointed out that measures such as levees and gates to protect against storm surges on the coast could lead to groundwater pooling behind infrastructure – since the water table near the coast usually rises in line with sea levels.

“Even if you build a levee, it will rise behind the levee,” Hill said. “This is a fundamental misconception that many people have about how seawalls and earthworks will protect us — actually, no, they are not, unless they find a way to remove all groundwater.”

As part of the Water Resources Development Act of 2022, Congress in December newly directed the U.S. Army Corps of Engineers to study the impact of groundwater outflow — among other climate impacts — when planning storm or flood protection projects.

The city’s coastal flood control projects, such as the East Side Coastal Resiliency and Red Hook Coastal Resiliency projects, include underground seepage barriers to hold back water from the river or harbor, according to the Department of Design and Construction. But they don’t remove groundwater.

According to Walter Rodriguez Meyer, founding director of Local Office Landscape & Urban Design, planting “networked trees” and other rooted greenery can lower water tables as the plants soak it up. His firm landscaped a housing development in the Rockaways that has high water tables with several green infrastructure strategies to keep it dry during heavy rains.

“It’s nature’s living pumps,” Meyer said of the tree networks, adding that the method works best in coastal areas. “That’s important because if you have underground storage capacity, when it rains you can deal with the stormwater without flooding your nearby neighbors.”

This makes it clear that overcoming the problem often requires an individual solution for each location.

“The way groundwater behaves is a bit unpredictable because there’s all these structures underground,” said Stony Brook’s Rozell. “Each little section needs to be treated like its own little place.”