As Boston plans for resilient waterfronts, there’s still a case for a barrier in the outer harbor.

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Along Boston Harbor, the big worries from climate change are sea-level rise and storms—but not in that order, William Golden remarked in a Environmental Business Council (EBC) of New England session on December 10.

Currently in Boston, sea-level rise is “a nuisance issue that can be addressed for another 30 or 40 years with a couple of feet of seawall,” said Golden, an attorney and environmental activist best known for filing the lawsuit that led to the cleanup of Boston Harbor. “The real issue is storm surge.”

That is, when the sea climbs to scary heights—say, the 14-foot-above-high-tide wall of water that swamped lower Manhattan in Superstorm Sandy in 2012.

Much of the Boston waterfront was originally tidal flats and its edges remain highly vulnerable to ocean storms, which are growing more numerous and often more terrifying. In this record-breaking year, 12 named Atlantic storms hit the U.S., one clobbering Louisiana with winds over 150 mph and a storm surge of 17 feet.

Now leading the Boston Harbor Regional Storm Surge Working Group, Golden renewed his call for a harbor barrier stretching from Hull to Deer Island in outer Boston Harbor, guarding against storms for 15 cities and towns with 175 miles of coastline. (Such a barrier wouldn’t do anything about sea-level rise, which instead would be addressed by relatively modest structures onshore.)

Boston turned down this concept in 2018 after a preliminary feasibility study argued that the sea-gate system would be less cost-effective than onshore measures, take decades to build and pose uncertain technical risks. Golden and his allies, however, remained unconvinced.

Sanjay Seth, Boston’s climate resilience program manager, didn’t comment on the harbor barrier proposal at the EDC meeting but did outline the city’s active program to defend itself onshore.

“There are several areas of Boston that can serve as entry points for significantly damaging floods,” Seth noted. “We do have a real but very narrow window to achieve a unified network of protection in the city. .. Climate change really isn’t waiting.”

The downtown Boston waterfront, with its almost completely private ownership and messy underpinnings, may be the hardest neighborhood to handle. “There’s no silver bullet here,” Seth said. Instead, the plan calls for a mix of four options: raising the main roads closest to the waterfront, reconfiguring parks and other open spaces, beefing up the Harborwalk, and placing structures directly in the sea.

The preferred strategy for the downtown is a line of defense along the outside edge of the waterfront. “It’s not going to be easy, but it’s going to be doable,” said Seth. He acknowledged that success will require “entirely new levels of public/private coordination, as well as new, more robust coordination among private property owners themselves.”

Golden applauded Boston’s resilience planning but pointed out the limitations of any land-based measures. “Flood walls, particularly when they’re meant to address storm surge and sea level rise, can separate the public from the water,” he noted. The walls also can leave marine uses such as cargo shipping and ferry traffic unprotected. Moreover, the structures can act as bathtubs that need pumps to clear themselves after heavy rainstorms.

Harbor barriers can minimize those problems. Truly massive barriers are quietly guarding London, Rotterdam, Saint Petersburg and other cities. Smaller ones have worked well in New Bedford and other New England cities, Golden pointed out.

The leading U.S. contender for a giant gate system is the one proposed for Galveston Bay and Houston, part of a grand scheme for the Texas coast that seems headed to Congress this spring.

William Merrell of Texas A&M in Galveston came up with the concept back in 2008 while he was trapped in an apartment building by high water of Hurricane Ike. Once known as the Ike Dike, now as the Texas coastal spine, the idea is “extremely simple,” Merrell said during the EDC meeting. “Stop the water at the coast.”

The central barrier would cross Bolivar Roads, the main entrance to Galveston Bay and the Houston Ship Channel. It would combine a set of 300-foot-wide vertical-lift gates with massive horizontal swinging gates on the navigation channel, like those in Rotterdam. Left open in normal conditions, these entry points would allow almost-normal tidal flow. In addition to the gates, the project would bundle in defensive local measures for the city of Galveston and other sites inside the Bay, along with 43 miles of beach and dune restoration on barrier islands plus a wealth of ecosystem restoration efforts.

A far more colossal harbor barrier has been proposed for metropolitan New York, where Sandy killed more than 100 people. This humongo structure could close the Ambrose shipping channel with a five-mile barrier stretching from the Rockaways to Sandy Hook. Additionally, a one-mile barrier could close the East River.

This regional system would work together with lower onshore barriers designed to deal with sea level rise and most storms, said Robert Yaro, professor of practice at the University of Pennsylvania School of Design, at the EBC session.

However, New York City chose instead to pursue a number of very large onshore projects, with very little to show to date. “Nothing’s operational after eight years, and none of them are fully funded,” Yaro said.

“Every one of these onshore barriers is a lot more complicated, a lot more expensive and a lot more time-consuming than anybody anticipated at the outset,” he added. Many protective measures depend on deployable flood barriers, an operational nightmare. And it’s still not at all clear that there’s even a working concept to protect Wall Street, whose waterfront is particularly constrained.

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“When you add up the cost of the various onshore barrier systems that have been proposed for the New York metropolitan area, they exceed the cost of an offshore barrier system,” Yaro said. He also declared that even projects on this enormous scale can be constructed in a few years if the will is there—for instance, the Army Corps of Engineers rebuilt the New Orleans barrier system in less than five years after Hurricane Katrina.

“We believe that the surge barriers that we’re proposing will give us a hundred years or more to adapt our region to climate change,” Yaro said. “We need to have some time to plan to reinvent our cities and our civilization around the even more destructive changes that may be coming.”

“We’ve got to be more resilient, but we’ve got to be smarter about how we do it,” he summed up.

For Golden, that means a deeper study of the potential for a Boston harbor barrier, leading toward a shovel-ready coastal defense plan that could tap into the federal funding that he sees on the horizon. When and if such big bucks arrive, “we need to know what we’re going to do with that money,” he said.