Boston — As the City of Boston advances solutions to protect neighborhoods from climate change-induced flooding, a new independent report released by the Sustainable Solutions Lab at UMass Boston advises against pursuing a harbor barrier in coming decades as part of larger resilience efforts. The analysis found a barrier strategy to be technically impractical and less effective, dollar for dollar, than continued investment in shore-based coastal protection solutions such as those described in the city’s Climate Ready Boston plans.

The report, Feasibility of Harbor-wide Barrier Systems: Preliminary Analysis for Boston Harbor, was sponsored by the Boston Green Ribbon Commission, a group of business, institutional, and civic leaders working side-by-side with the City of Boston to develop shared strategies for confronting climate change, and funded by the Barr Foundation.

“Harbor barrier systems have been a helpful tool for certain other coastal cities, but in this case, Boston would be making a bet on a massive infrastructure project with limited benefits compared to the alternative,” said Paul Kirshen, academic director of the Sustainable Solutions Lab, professor of climate adaptation in the School for the Environment, and the report’s lead author. “The more impactful strategy the city can pursue is to stay focused on neighborhood, shore-based resilience, moving quickly and working closely with communities. Local protections can also provide additional public realm advantages that maximize investment and benefit everyone plus provide us the flexibility to adjust to the uncertainties of climate change.”

The researchers tested the feasibility of both inner- (from Logan Airport to the Seaport) and outer- (from Winthrop to Hull) harbor barrier configurations. They studied the technical effectiveness of a barrier over time, the environmental impacts of a barrier, and the cost-benefits of a barrier as compared to shore-based resilience investments. The analysis found that while a barrier likely wouldn’t pose additional environmental risk to an already-evolving harbor ecosystem, either configuration would face major technical challenges and provide only marginal benefit on top of the immediate shore-based solutions that need to be constructed under any scenario.

The report’s cost-benefit analysis assumes that the city continues to pursue some level of shore-based solutions due to the long lead time required for permitting and constructing a barrier. By 2050, the earliest a barrier could be reasonably erected, Boston will potentially have already faced multiple billions of dollars of damage without neighborhood resilience projects like those proposed in Climate Ready Boston.

“This report reaffirms the direction already set by the City of Boston,” said Bud Ris, co-chair of the Green Ribbon Commission’s Climate Preparedness Working Group. “Shore-based solutions will not only protect vulnerable neighborhoods along the waterfront, but also provide substantial co-benefits in the form of new open space buffers and parks.”

“Given Boston’s significant vulnerabilities to sea level rise and other climate-related impacts, all options that will make our city more resilient merit consideration. Boston is fortunate to have the Green Ribbon Commission calling for this study, and the Sustainable Solutions Lab at UMass Boston undertaking such a rigorous analysis of various approaches to prepare for the changes ahead,” said Jim Canales, president and trustee of the Barr Foundation. “Armed with this insight, we must move with urgency to advance solutions that protect people and communities throughout Boston.”

Beyond the cost-benefits, a barrier strategy would also face major technical challenges. The researchers focused efforts on a barrier configuration that features gates that would remain open except during flood conditions caused by storm surge; this configuration is the only design that would provide some protection against storm surge in the early years of operation, minimize interference with Boston’s maritime economy and the thousands of jobs it supports, and protect the environmental gains of the Boston Harbor cleanup.

However, this configuration is challenged by the nature of Boston’s climate vulnerabilities, which eventually will be defined by less catastrophic, but more frequent, flooding events. A barrier opening and closing frequently creates too many environmental impacts and shipping disruptions to be functional, and becomes vulnerable to mechanical failure. A barrier could also not manage tidal or nuisance flooding whereas shore-based solutions can.

The costs of a barrier could range from $6.5 billion to $11.8 billion, depending on whether the inner- or outer-harbor configuration were selected. The outer-harbor configuration would become the largest barrier in the world and its water-span the longest in the world. The report offers options for refining and extending harbor barrier research further should the city determine it’s worthwhile to revisit a harbor barrier in the decades ahead as climate science evolves.

The project team included UMass Boston’s School for the Environment, the Woods Hole Group, Arcadis, and Woods Hole Oceanographic Institution.