Harbor-wide dikes get thumbs down
Barr-funded study says miles-long barriers not the way to address sea level rise
A NEW ANALYSIS SUGGESTS incremental, shore-based initiatives are more practical and cost-effective in addressing sea level rise in Boston than harbor-wide dikes or barrier systems.
The study addresses a debate that has been simmering below the surface for some time – what to do about the sea’s encroachment on the city, as exemplified by storms this past winter that flooded many parts of Boston. Officials have begun exploring various on-shore approaches, but many scientists and climate change advocates have been saying more drastic action is needed, including building a barrier out in the harbor that would protect Boston from rising sea levels.
The study examined three options: a barrier stretching from Swampscott to Cohasset providing access to the harbor through a series of locks and two other designs that would install shorter barriers with gates that would be closed only in cases of extreme high tides. The two gated barriers included in the study ran from Winthrop to Hull and from Logan International Airport to the Seaport District.
The study dismissed out of hand the Swampscott-to-Cohasset option because it would essentially create a fresh water lake out of Boston Harbor, disrupt shipping, and cost between $35 billion and $80 billion while providing roughly the same level of protection as the Winthrop-to-Hull option.
Paul Kirshen, a professor at UMass Boston and the principal investigator on the study, told reporters on a conference call that the two barriers across the harbor would take about 30 years to build and cost between $6.5 billion and $12 billion. By contrast, the shore-based solutions for Boston are estimated to cost between $1 billion and $2 billion and offer more flexibility.
“We’re fairly confident that these shore-based solutions can get us through 2070,” Kirshen said. “Right now it doesn’t make sense for the city to consider any kind of harbor-wide barrier system. It doesn’t make sense for decades, if ever.”
Kirshen didn’t completely rule out a harbor-wide barrier, however. “Perhaps in a couple decades we might want to go back and revisit a harbor-wide scenario,” he said.
The $360,000 study grew out of efforts by the city of Boston to prepare for climate change. It was conducted by researchers from UMass Boston, the Woods Hole Oceanographic Institute, the Woods Hole Group, and Arcadis. It was paid for by the Barr Foundation, which has made climate change a top priority.
The conclusions of the study were heavily influenced by self-imposed requirements that any approach protect residents where they work and play, minimize interference with shipping and navigation, and preserve the gains achieved by the cleanup of Boston Harbor.
The Swampscott-to-Cohasset option, promoted earlier this year by three architects, didn’t satisfy the latter two conditions because it would effectively change the harbor ecosystem. The other two options satisfied the conditions, but only by installing enormous gates that would remain open most of the time and allow the free flow of water in and out of the harbor. The gates, according to the study, represent 60 percent of the cost of the barriers and would probably not last 50 years because by then they would be over-stressed by the need to open and shut once a week to prevent shoreline damage.
Peter Papesch, a retired architect who has promoted the idea of a Swampscott-to-Cohasset dike, said he welcomed the new study but felt its scope was way too limited. He said he and his colleagues plan to seek funding for an international competition to come up with ways – even outside-the-box ways – to deal with sea level rise. “This is a fairly rigorous study with professionals, but the scope of their study is deficient,” he said.
The study acknowledged estimates of sea level rise in Boston are fluid, ranging from 6 inches to 1.2 feet by 2050 and 1.8 to 7.3 feet by 2100. The wide variability is caused by uncertainty about international efforts to reduce greenhouse gas emissions. For the purposes of the study, the researchers adopted what they called a “moderate” outlook, assuming sea level rise of 1 foot by 2030, 3 feet by 2070, and 5 feet by 2100.
Kirshen said on-shore measures that can be pursued to reduce the impact of sea level rise include expanding the shoreline of the harbor and building it up to heights of 13 to 14 feet to hold back surging tides. One illustration of this approach can be found on page 44 of a city of Boston report examining coastal resilience solutions for East Boston and Charlestown. The approach envisions building out the shoreline with baseball fields and other amenities that would double as shore protection.
Boston Mayor Marty Walsh outlined a similar vision for Fort Point Channel last fall. He raised the possibility of building slightly elevated parks up and down the length of the channel that would serve as sea walls, and man-made islands and salt marshes in the channel that would disrupt any storm surge. “It’s a big expense and it’s a big idea and it will take awhile,” the mayor said at the time.
Kirshen said another option is to flood-proof buildings along the shore and then join them together with portable walls or gates that would prevent water from rushing inland.
Bud Ris, a member of a commission made up of business and civic leaders, said a number of policy changes could also help address sea level rise, including real estate disclosures about a property’s vulnerability and zoning requirements mandating specific construction standards to mitigate damage caused by storm surge.Funding to address the issue will most likely come from the state and municipalities, as well as the private sector through fees and business improvement districts, Ris said. He added that one benefit of the study is that it reorients the debate away from harbor-wide barrier systems and toward the multitude of on-shore solutions.
“There’s no silver bullet for this problem,” he said.