Maintaining Boston’s Vibrancy and Transportation Systems in the Face of Sea Level Rise
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A city reclaimed from the sea
Settled by European colonists in 1630, Boston was founded on the narrow Shawmut Peninsula behind the protective landforms of what are today Stellwagen Bank, Winthrop, Hull and the 34 Boston Harbor Islands.
Our ancestors sited Boston well. In addition to protecting the city from sea-based attacks, Boston Harbor’s natural topography limits extreme storm surges to a maximum of just over six feet. With a ten-foot tide cycle, Boston is currently only at risk of serious flooding if such a surge occurs close to high tide.
Past Development Decisions Increase Future Flood Risk
Experienced mariners, our ancestors knew exactly how high such storm surges would go. They confidently filled in estuaries and shallow bays to increase Boston’s footprint by over fifty percent. Of course, they never contemplated sea level rise.
Unfortunately, these filled tidelands will begin to flood chronically with only 2-3 feet of sea level rise—predicted to occur sometime between 2070 and 2100. (see Figure 1).
The City recently released Climate Ready Boston, in which top climate experts derived the following findings:
- Boston is most likely to experience between 7.5 and 18 inches of relative sea level rise by 2050, with a maximum plausible increase of 30 inches.
- Depending on carbon emissions, Boston is likely to experience 3.2 to 7.4 feet of relative sea level rise by 2100, with a maximum plausible level of 10.5 feet.
- Such higher seas will increase Boston’s tidal range, wave energy, and tidal flooding, resulting in increased erosion and higher storm surges.
At our country’s founding, Boston’s landmass was approximately 30 percent smaller than it is today. Sometime between now and perhaps a century from now, Boston’s coastline will shrink back to its original configuration once sea levels rise by approximately eight feet.
Additional challenges will vex property managers and transportation officials as coastal flooding becomes chronic in Boston. For example: How do we protect Boston’s transportation tunnels and other below-grade infrastructure from saltwater intrusion? Is it cost-effective to retrofit Boston’s existing buildings and infrastructure? Would district energy plants improve Boston’s energy resilience if specific neighborhoods are cut off from the grid? How can we maintain and even enhance the socioeconomic vibrancy of our city as our coastline moves inland over the coming decades?
Living with Water Design
The concept of Living with Water design focuses on resilience (the ability to bounce back quickly and cheaply from flooding) versus resistance (preventing flooding from occurring in the first place). In 2014, The Boston Harbor Association (now Boston Harbor Now), the City of Boston, Boston Redevelopment Authority (now Boston Planning and Development Agency) and Boston Society of Architects launched an international design competition called Boston Living With Water. The goal was to increase local understanding of flood-resilient design strategies at different scales by engaging with real sites at risk of chronic coastal flooding.
Fifty teams from seven countries worked to redesign a specific building, neighborhood and/or surface highway so that each would continue to thrive once sea levels are five feet higher than today. The three winning entries came from two teams of local designers and a team located unsurprisingly in Venice, Italy. Each team won because it successfully combined feasible flood design strategies with multiple-benefit solutions.
Two critical insights emerged from our collective research, design competition and exchanges with experts from Copenhagen, The Netherlands and Hamburg. First, Boston will require multiple layers of flood protection—flood barriers, floodable transition zones, and flood-prepared buildings and infrastructure. Each will begin to fail as sea levels increase above the surrounding topography, ultimately requiring managed retreat.
Second, individual structures can only be made resilient to storm flooding, not chronic tidal flooding. Once flooding becomes commonplace, regional strategies must be in place to protect the people, buildings, transportation systems and infrastructure of the Greater Boston region as a whole.
When the ocean reclaims its own
There will come a time in perhaps our children’s lifetimes when Boston Harbor will begin to reclaim its filled tidelands. It may come suddenly, with an extreme storm that swamps our defenses. It may happen more gradually, with infrastructure and/or buildings no longer worth the cost of retrofitting or rebuilding.
If we have the will and foresight, I hope that our future involves investing in a graceful waterfront barrier that staves off chronic flooding while maintaining a meaningful connection to the harbor. I hope that we use this borrowed time to prepare the city for the day that the barrier is no longer sufficient and we must make city-wide changes.
Getting from here to there will involve substantial breakthroughs in financing and governance. We will need to develop financial mechanisms for transferring real estate value away from the coastline without devastating either real estate values or Boston’s tax base. We will need new zoning and building codes that predict and adapt to the retreating coast. We will need a central planning agency with a transparent, fair, effective governing structure able to plan, raise funds, secure public support and implement major civil engineering projects across a broad region and hundreds of property ownerships.
Surviving and thriving in a hotter, saltier future involves hope, involves beauty, and involves all of us working together to keep our dear old city from slipping back into the sea. Boston will have to be different. It doesn’t have to be worse. Let’s get started.
On June 20, 2017, one hundred and twenty mobility and climate leaders will convene in Cambridge, Massachusetts to discuss the future of mobility in the face of climate change in the Boston region. While the Boston region continues to remain globally competitive, we are in an altogether unique moment in the history of mobility, transportation, and climate decisions. This summit aims to harness the ingenuity and innovation already underway in the Commonwealth as well as the expertise of invited global thought leaders with best practices directly applicable to Boston’s challenges.
If you are interested in attending this invite-only summit, please fill out this application. Please note that the summit is full and only waitlist spaces are still available.
 The map on the right depicts a portion of the results of a hydrodynamic model developed for the Massachusetts Department of Transportation showing the likelihood of flooding in 2070 under high emission scenarios. The map on the left is from 1775.
 Global averages are just that; some areas of the earth will experience relatively faster sea level rise than others. Unfortunately, coastal New England will experience faster relative sea level rise than global averages due to ocean currents and land subsidence.
 The term of art “Living with Water” came out of a partnership collaboration planners and architects from The Netherlands and their counterparts in post-Hurricane Katrina New Orleans, especially Waggoner & Ball Architects.
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