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Here’s one idea for what to do with rainwater that floods low-lying areas of Boston during bad storms: store it in the Fort Point Channel.

The Boston Water and Sewer Commission has been studying a proposal to build a floodgate next to the federal courthouse at the mouth of the channel. The gate, when closed, would turn the waterway into a huge manmade bowl that could hold rainwater at high tides and prevent backups that are expected to increasingly flood city streets.

For a few months now, John Sullivan, the commission’s chief engineer, has been talking up the proposal in meetings with neighbors, environmental groups, and other constituencies. While the idea is still in conceptual form, Sullivan is trying to build support.

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A man walks slowly through a flooded sidewalk off Congress Street during a storm, where water was flowing over from Fort Point Channel in the Seaport district in 2018.
A man walks slowly through a flooded sidewalk off Congress Street during a storm, where water was flowing over from Fort Point Channel in the Seaport district in 2018.John Tlumacki

One reason for that is money: Sullivan expects the project could cost about $200 million, far beyond the commission’s current financial resources. But he argues that protecting the land around the Fort Point Channel — which includes South Station, the Ted Williams Tunnel, and a major postal service hub — is of regional interest and should be funded primarily by state and federal sources, not just the city’s residents and businesses.

“You have to plan for the worst,” Sullivan said. “All we’re trying to say is, ‘we’ve got to start thinking about this, kids.’ … What we hope to do is to have a good preliminary cost justification for why this seriously has to be looked at.”

It would be one of the boldest measures yet to protect the city’s waterfront from the ravages of climate change, particularly after billions of public and private funds have been invested in development in the Seaport and other vulnerable neighborhoods over the last two decades.

But it’s not the only such measure.

The Boston Planning & Development Agency, for example, is planning a 6-foot-high berm along much of the east side of the Fort Point Channel, from Procter & Gamble’s Gillette campus nearly to the Summer Street bridge, to fend off floods from high tides and severe coastal storms. A Federal Emergency Management Agency grant would fund $10 million of the estimated $20 million project, to be built along the Harborwalk in the next four years. Related Beal, National Development, and Alexandria Real Estate Equities, which are developing former Gillette properties along the channel, would chip in through their respective projects.

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To Sullivan, the two resiliency projects would complement one another. The berm, he said, would help keep rising seas out of the Seaport, while helping the floodgates temporarily store rainwater in the channel.

Here’s how his concept would work.

When the forecast shows that a high tide and a heavy storm will coincide, the barrier would be closed while the channel is still at low tide, when water levels can be roughly 10 feet lower than during high tides. That would create enormous capacity to hold excess rainwater that drains into it from nearby parts of the city. When the storm passes and low tide returns, the gates could be opened, and the water released out into the ocean.

The idea came to Sullivan one day when he was at the Barking Crab and noticed just how low the water in the Fort Point Channel can get.

“I ... thought, my God, this thing is a huge gigantic pit at low tide,” Sullivan said.

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A formal study is underway; the Water and Sewer Commission has hired engineering firm Hazen and Sawyer to examine the Fort Point Channel and other crucial stormwater collection areas across the city, and consider infrastructure upgrades, such as this channel barrier, to help reduce flooding. Sullivan expects that report will be done in late spring. Permitting, financing and building the barrier could take at least another decade, however.

The concept, Sullivan said, isn’t as radical as it might sound.

He points to a similar barrier about two miles away: the dam that controls the water levels of the Charles River. And he notes other cities have far more expensive systems, such as the massive underground tunnels that store rainwater in Chicago and Milwaukee.

A Fort Point Channel barrier, he said, could have a broad impact, helping to control rain-related floods not just in South Boston but also neighborhoods further inland such as Roxbury and the South End — roughly 10 percent of the city’s land area in all.

Kayakers paddle along the Fort Point Channel as the Boston Sykline forms the backdrop.
Kayakers paddle along the Fort Point Channel as the Boston Sykline forms the backdrop. John Tlumacki/Globe Staff

The idea coincides with the city’s efforts to rebuild the old Northern Avenue Bridge, also at the mouth of the channel. Sullivan suggested to the city’s Public Works Department that the bridge and the barrier go up in tandem but was told that the bridge is too far along in design to incorporate such a radically new feature. Plans for that bridge remain in the permitting stage and have not advanced recently amid the pandemic and the changes in administrations at City Hall.

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It’s not yet clear how the city’s new mayor, Michelle Wu, will respond to the proposal; Sullivan said he hasn’t fully briefed her on it. It’s also not clear who would run it, if it’s built.

Several environmental groups said all options to manage rainwater, and control inevitable floods, should be on the table.

“We know the rain is coming, it does need to go somewhere and when you’re looking at the amount of [buildings and pavement] we have as well as the ocean coming in, it really does create a challenge,” said Julie Wood, deputy director of the Charles River Watershed Association.

Wood said her organization hopes city officials can also explore greener alternatives, such as developing more parks and wetlands in flood-prone areas. Given the density and demand for real estate in Boston, that could be difficult, though the watershed association and other like-minded groups have long eyed the city’s public works yard and Widett Circle, just south of the Fort Point Channel, to potentially include new open space.

“A place like Fort Point Channel, a place like Widett, it’s going to be plagued with flooding issues at both ends from stormwater and sea level rise,” Wood said. “We think it’s worth it for the city to start thinking about where it might make sense to invest instead of building the next neighborhood right on the coast. There are ways to use this land to protect the surrounding areas.”

Sullivan’s proposal has prompted some skepticism in Fort Point. Tom Ready of the Fort Point Neighborhood Association argued the city should focus its efforts on the berm project and worries about what the Fort Point Channel might be like if it becomes a bathtub for stormwater.

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“Is it going to smell? Is there going to be trash in there? How is all that going to be managed?” Ready said. “What does it do to the property value of the neighborhood? There are a lot more questions than answers at this point.”

It’s not the first time gates to close the Fort Point Channel have been considered. City officials, in their “Climate Ready South Boston” report in 2018, suggested two options to guard the area against sea level rise: a flood barrier at the mouth of the channel, and a landscaped berm along the Harborwalk. They ultimately decided the berm was the more cost-effective solution.

But Bud Ris, an adviser to the city’s Green Ribbon Commission who participated in those discussions, said the focus of that report was on ways to ward off sea water, not to deal with surplus rainwater.

“I’m just glad that the Boston Water and Sewer Commission is thinking very carefully about not only keeping the saltwater out but also dealing with the increased precipitation,” Ris said. “We’re asking the private sector and the government sector to spend a lot of money on beefing up the protection along that shoreline. We just have to make sure all of it is in sync, that it will all work together.”


Jon Chesto can be reached at jon.chesto@globe.com. Follow him on Twitter @jonchesto.