Drivers encountered a startling scene in the Ted Williams Tunnel Wednesday night after a deluge of heavy rain battered the region: a roadway submerged by several feet of water because of a clogged drain.
The wheel-deep waters lapped like ocean waves against motorists’ vehicles as they carefully attempted to navigate their way through the flooding. Dramatic video footage of the partially submerged tunnel and cars moving at a slow crawl quickly circulated online.
“I have never seen [a] flood in the tunnel, it was my first time,” said Maria Barajas, 32, of Boston, who was traveling in an Uber with her fiancé and a friend from the Seaport to the Liberty Hotel.
When they reached the swamped tunnel, their driver slowed the car to make sure it wouldn’t stall out. They were part of a line of vehicles moving in single file on the left side of the roadway.
While the severe flooding was deemed a “pretty rare occurrence” by MassDOT highway administrator Jonathan Gulliver on Thursday, he was also clear that the event highlighted the reality of climate change. There is a critical need to boost the resilience of infrastructure across the state as intense weather events are becoming increasingly common, he said.
“You only have to look at the last few winters to see that things have changed. We’re getting a lot more rain events . . . and we have to treat our infrastructure differently,” Gulliver said.
About 400 feet of roadway in the tunnel, which travels under Boston Harbor, was submerged during the powerful storm, which dropped about 4 inches of rain in parts of the Boston area, Gulliver said. It took crews about four hours to clear the clogged drain.
At its height, the flooding reached about 3 feet and engulfed two travel lanes. It dumped the equivalent of roughly 130,000 gallons of standing water on the concrete, said Gulliver.
Although localized flooding was reported statewide, Gulliver said the flooding in the tunnel was the most serious and widely reported issue.
Rainfall rates reached between 1 and 2 inches per hour Wednesday evening, with wind gusts of 40 to 60 miles per hour blowing debris, clogging rain drains, and leading to exacerbated flooding in urban areas, said Globe meteorologist Ken Mahan.
Officials initially thought that one of the roughly 40 pump stations throughout the tunnel had failed. They later determined that a clog in the inlet line, which was about 15 to 20 feet from the main catch basin feeding the pump station, was the culprit.
Unclogging the drain required an extensive response, including a 10,000-gallon pump truck, Gulliver said. The ramp was ultimately reopened to traffic around 11:30 p.m. after several hours.
“This is an issue that we hope not to have to deal with again, but they do happen, especially when you’re dealing with storms that are this extensive,” Gulliver said. “We don’t see these kinds of things happen very often but our crews will be looking at drain structures over the next few days into this weekend to just make sure that there’s nothing that we may have missed.”
Maintenance crews look at the drainage systems and clear them on a regular basis, Gulliver said, noting that was last done about three weeks ago.
“I want to assure people the tunnel systems are safe,” he said.
Persistent heavy rain fueled by an atmospheric river slammed New England and dumped between 1 to 4 inches of rain across nearly all of the region. The most intense rain fell across Rhode Island and Southeastern Massachusetts, with some local amounts nearing 4½ inches, Mahan said.
The heavy rains led the Boston Public Health Commission to issue a public health alert Thursday warning the public to avoid contact with some bodies of water for at least 48 hours due to increased health risks. Large storms can overwhelm combined sewer systems causing a mix of rain and wastewater to discharge into local waters, according to the commission.
Officials could not recall a similar flooding event like the one that occurred in the tunnel to the same extent in recent years. Still, Gulliver said the next time the agency does major rehabilitation on the Ted Williams Tunnel, officials will look at the pump systems and make sure they are upsized.
“As we go through upgrades, that’s what we’re addressing systematically. Any project we do now, we consider climate change and resiliency as part of that design and make sure that we’re well prepared for whatever the future brings,” he added.
In 2015, a MassDOT-FHWA report assessed climate change, extreme weather vulnerabilities, and infrastructure adaptation options across the Central Artery and tunnel system. The report noted that much of the infrastructure will become more at risk as sea levels rise.
Boston Mayor Michelle Wu echoed that concern Thursday, saying that as the rain grows more severe, “we really are starting to see some impacts.”
“It’s terrifying . . . on any given day here in Boston, we’re seeing it,” Wu said. “There are a couple ways that we have to keep going on this.”
The city is addressing climate change in several ways, including by improving infrastructure and talking with property owners who live in areas highly susceptible to flooding to ensure that they have protections in place, she said.
“These types of flash floods can happen really anywhere in the country, but particularly here,” she said. “We have to be not only trying to do our best to tackle the long-term problem . . . but in the very, very short term, how do we keep people safe?”
Shannon Larson can be reached at shannon.larson@globe.com. Follow her @shannonlarson98. Travis Andersen can be reached at travis.andersen@globe.com.