By Robert L. Reid
When the remnants of Hurricane Ida — at that point downgraded to a tropical storm — slammed into the New York-New Jersey region on Sept. 1, the result was some of the heaviest rainfall the area has ever experienced. In New York City’s Central Park, for example, more than 3 in. of rain fell in just one hour — the highest amount ever recorded in that period of time — and Newark Liberty International Airport “shattered any of the previous records of rainfall for northern New Jersey,” says Sarah Colasurdo, LEED AP, ENV SP, the senior climate resilience specialist at the Port Authority of New York and New Jersey, which operates and maintains airports, rail lines, and other transportation infrastructure in the region.
The storm killed scores of people across the area and threw the regional transportation system into chaos. Flash flooding inundated streets and tunnels, sending as much as 75 million gal. of water into the New York subway system, which is operated by the Metropolitan Transportation Authority, according to a Sept. 16 report from Newsweek. Dozens of underground subway stations flooded, temporarily shutting down a system that normally operates around the clock, because of the “unexpected challenges in the historic volume of water that arrived with Ida — which no forecaster predicted would occur in such a short period of time,” according to information provided to Civil Engineering by the MTA.
MTA commuter rail lines such as Metro-North Railroad and the Long Island Rail Road also shut down temporarily or offered only limited service. Flooded roads forced MTA bus service to be detoured in some locations. Three MTA pump facilities were submerged in water, three boiler rooms sustained flooding, and another 68 MTA locations experienced flooding or high-water conditions, the transportation authority reported. Mudslides, fallen trees, collapsed walls, power outages, and other damage spread across the region.
Post-Sandy and pre-Ida, the Port Authority and the MTA had taken proactive measures to prepare their facilities for flooding.
MTA infrastructure teams, for instance, staged personnel and critical equipment — such as pumps and portable generators — at key locations and covered ventilator openings that are prone to water infiltration during heavy rainfall.
Port Authority staff likewise staged personnel where they were expected to be most needed during the storm, cleaned out storm drains, tested pumps and generators, and made sure those generators and also vehicles were filled with fuel; this included specialized medium- and heavy-duty vehicles that can drive through heavy rainfall and operate during various adverse conditions. In the hours before the storm struck, the Port Authority set up an emergency operations center and began relaying weather updates and warnings to its facilities, which began to implement their own hurricane preparedness checklists, Colasurdo says.
During the storm, Port Authority staff members carefully watched the waters at the Port Authority Trans-Hudson’s Hoboken Station and others rising around them, ready to close the new flood doors that had been installed there after Sandy. “All of our facilities are vital transportation assets for the communities that we serve,” Colasurdo explains. “So we try to continue operations as long as possible.”
Fortunately, “the water never approached any of our entryways at Hoboken Station,” she adds. But if it had, the flood doors could easily and quickly have been deployed by even a single person.
MTA staff used a digital tracking system to follow events at specific sites and set up supplies at locations throughout Brooklyn, Queens, Manhattan, and the Bronx to respond to distress calls. Temporary repairs were needed at three hydraulic pump rooms.
‘Caught on our heels’
Despite the extensive preparations, for the New York and New Jersey transportation systems Ida still represented a “wake-up call,” says Colasurdo. This is because “we were caught on our heels, like the rest of the region,” by the unprecedented amount of rain that fell within such a short period of time, she says.
It wasn’t as if the region’s engineers had ignored the lessons of Sandy: The Port Authority had invested heavily in storm-resiliency measures after Sandy that “most certainly mitigated flooding” during Ida, Colasurdo says.
For example, the PATH rail line’s Harrison, New Jersey, station was heavily damaged during Sandy. So it was rebuilt with an elevated plaza that did not flood during Ida even though the surrounding streets were inundated with water.
Storm surge versus flash flood
Ida “was really a different type of storm” than Sandy, Colasurdo explains, noting that Ida flooded parts of Port Authority facilities that had not flooded during the earlier storm. Examples include portions of the Newark airport’s three terminals and LaGuardia Airport’s Terminal A.
A key reason for the different experiences between Sandy and Ida involves the nature of each storm. The events during Sandy had focused the Port Authority’s flood protection measures on sea level rise and storm surge, Colasurdo says. But Ida struck with extreme precipitation and flash flooding — which “really underscored that we have to prepare for a whole range of storm scenarios,” Colasurdo stresses.
“This was not a situation of flooding overwhelming flood barriers,” Colasurdo says. Instead, “the water rose … quickly in areas where it wasn’t expected,” based on the region’s experiences during Sandy, she explains.
All these locations are slated to be replaced under preexisting redevelopment plans, Colasurdo adds, and the new designs will incorporate flood resilience according to criteria laid out in the Port Authority’s Climate Resilience Design Guidelines. The designs will feature a site-specific design flood elevation for each location that can be adjusted for expected sea level rise.
To prepare the region for future storms, the MTA is working with the New York City Department of Environmental Protection to find ways to bolster the capacity of the city’s sewers to help prevent roadway flooding.
At the Port Authority, a preexisting climate risk assessment is focusing on the identification of residual and emerging flood vulnerabilities — including extreme precipitation — to strategically mitigate the highest-priority risks. Phase 1, a preliminary scan of flood-related risks across all Port Authority facilities, was completed in 2020. Phase 2, a multiyear program that started in 2021, will involve the application of rigorous, engineering-based assessment techniques on a facility-by-facility basis.
Equipped with the knowledge gained through the risk assessment, Colasurdo expects that the Port Authority “will be much better able to assess the impacts of extreme precipitation and implement resilience measures that complement the measures we already have in place.”