How can we protect Boston from rising sea levels? Various proposals
I. Build a dike around the harbor
Metro Boston Dikelands: A 14 mile dike around the harbor.
A 14-mile dike could protect Greater Boston from sea level rise. The barrier would run from Cohasset to Swampscott
…The metropolitan Boston estuary is uniquely different from many others around the nation. It is protected on its flanks by the shoulder highlands of Swampscott and Cohasset. The Metro Boston DikeLANDS proposal takes advantage of the estuary’s unique geological characteristics.
We propose building a 14-mile dike barrier between the shoulder highlands of Cohasset and Swampscott. The dike would be located some eight miles out from Deer Island, complete with residential and commercial developments, windmills, solar collector farms, and recreational areas.
A simple dike barrier with a 200-foot-wide top and reaching 120 feet from seafloor to storm-surge top would require some 246 million cubic yards of material. Bi-directional locks could provide access for all crafts, protecting Boston’s commercial activity and its waterfront integrity.
The new dike system will prevent storm tides from inundating the entire metropolitan estuary while allowing rivers to discharge their water into a harbor reservoir capable of holding more than 10 billion gallons of river-fed water… By lowering the reservoir level to half the current tidal range, the cherished Boston Harbor Islands and their recreational potential would be protected.
At a cost of $100 per cubic yard, with two bi-directional shipping locks of $500 million each (plus soft and contingency costs), this macro-engineering and macro-economic project would probably cost between $30 billion and $50 billion. The 200-foot wide top of the 14-mile stretch would create 68 acres of new dike lands, which in turn would need to be supported by a complete infrastructure system of water, sewer, electricity, and transportation …
The project could help pay for itself if the newly-created, flat-top area of the dike, amounting to some 68 acres, was sold as waterfront property at between $3 and $7 million per acre. That would raise between $100 billion and $400 billion (after return on invested capital)
Source: 14-mile dike could protect Greater Boston from sea level rise, Commonwealth Magazine, Jan 2018, Peter Papesch, Franziska Amacher and A. Vernon Woodworth, members of the Boston Society of Architects
Plan details Metro-Boston-Dike-Barrier.pdf
II. Climate Ready Boston: Planning three possible harbor dikes
The team, led by Paul Kirshen, a professor of climate adaptation at UMass’ School for the Environment, is weighing three harbor barrier configurations. The barrier study was recommended in the city’s Climate Ready Boston report.
The smallest would connect Logan Airport in East Boston with Castle Island in South Boston, protecting the city’s inner harbor and downtown from tidal flooding.
The medium-sized solution is a barrier from Deer Island, in the harbor, to Quincy, which would wall off all of Boston’s neighborhoods.
The largest of the proposed harbor barriers would protect not just Boston, but also Weymouth, Hingham, Quincy and Hull.
Learn about our climate-ready vision to enhance Boston’s waterfront. We want to protect Boston’s neighborhoods from sea level rise and flooding due to climate change.
Adapted infrastructure: Elevated roadways, strengthened seawalls, and flood barriers.
Protective Waterfront parks: Waterfronts include living shorelines, beaches, elevated parks, and access to water transportation.
Elevated harborwalks: By improving elevation and access, we can use our harborwalk system to protect against floods.
IV. Make parts of Boston a city of canals
From the Urban Land Institute of Boston/New England’s “The Urban Implications of Living with Water”
With the future unclear about exactly when the full impacts of sea level rise will occur, designing now for flexibility and the ability to adapt becomes critical. For example, with major street sections to be rebuilt, the typical 60 or 75 foot cross-section can be planned to be able to change when conditions warrant.
The goal is to provide for current urban linkages across the district without limiting the ability to accommodate future needs. Such needs could take the form of green infrastructure or surface channels to move water safely and quickly back to the ocean.
Build canals through Boston’s Back Bay
A street view of what this could look like
V. As done in the past, raise the level of parts of Boston
Can lessons from Boston’s landfill, 250 years ago, help Boston deal with sea level rise today?
Alex Wilson, in A Bold Idea for Addressing Sea Level Rise, writes
… I was struck by the realization that 250 years ago Boston was an island, connected by just a single land-bridge …there must have been a fairly massive effort to build the current land base of Boston. Might strategic land-building be an option for us as we are forced over the next century to address sea level rise as global warming melts the huge ice masses in Greenland and Antarctica?
…Rising seas are making life increasingly difficult in low-lying portions of dozens of U.S. cities today. The journal Nature Climate Change published a paper projecting the number of people in coastal regions of the U.S. who would be affected by sea level rise of 0.9 meters (3 feet) and 1.8 meters (5 feet). Unlike previous assessments of impact, this study considered not only current populations, but also projected population growth in these regions.
Populations in U.S. states that would be affected by 0.9 and 1.8 meter sea level rise.
Source: Nature Climate Change paper, “Millions Projected To Be At Risk From Sea-Level Rise in the Continental United States,” by Matthew Hauer, et. al., published online March 14, 2016.
By the year 2100, U.S. residents affected by 0.9 m and 1.8 m sea level rise would total 1.46 million and 3.85 million, respectively. Factoring in projected population growth in these regions, however, the number of people affected increases to 4.31 million and 13.1 million, respectively.
Can lessons from Boston’s landfill, 250 years ago, help with sea level rise today?
The comprehensive book, Gaining Ground: A History of Landmaking in Boston, by Nancy S. Seasholes, describes more than three centuries of effort to the Boston area to create new land and raise the elevation of existing land.
Beginning fairly early in Boston’s history—certainly by the 1700s—there was a massive effort to fill in the tidal flats around Boston. These efforts ultimately created some 5,250 acres of new land in Boston, East Boston, and Charlestown. In other areas, the land was significantly raised with fill. The original peninsula of Boston, known as Shawmut by the Native Americans, was just 487 acres. Today, merged with surrounding land, it is many times that size.
…Boston’s well-known Back Bay region was originally the back bay of the Charles River—an extensive estuary on the western side of the Shawmut Peninsula. The Fenway and Fenway Park (the Boston Red Sox’s home stadium) get their names from the fens or bogs in the area. It was only after extensive filling that building here was possible.
Logan Airport was open water in the 1930s. Today it is part of the extensive new land in East Boston.
I haven’t seen estimates of the amount of fill been used in Greater Boston over the last three centuries. If one assumes an average fill of six feet over the 5,250 acres of made land, that would total roughly 1.4 billion cubic feet or 50 million cubic yards.
I was particularly intrigued to learn in Gaining Ground that not only was new land made on the tidal flats of Boston, but in some places the elevation of existing land was raised. In the Church Street and Suffolk Street Districts (new Bay Village and Castle Square), sewage back-up was a problem in the mid-1800s, because there wasn’t enough pitch to the sewers (which no doubt dumped into the Bay).
The solution was to elevate the land and the buildings that were located there. In the 1860s, the City decided to raise the grade of the entire District. They would fill basements and abandon them, elevate buildings on cribbing and build new foundations beneath them.
On Church Street, starting in July 1868, the City hired contractors to bring in more than 150,000 cubic yards of fill and elevate 296 brick buildings by as much as 14 feet and 56 wooden buildings by as much as 17 feet. Remarkably (by today’s standards), this work was virtually completed by October 1869—ahead of schedule and under budget.
A similar project was carried out in the Suffolk Street District starting in July 1870 and being completed by the end of 1872. Nearly 250,000 yards of fill were brought in, and 600 buildings were elevated—also under budget.
Boston isn’t alone in having seen extensive landmaking over the centuries. In Manhattan, several thousand acres of land were created using fill, and more than 3,000 acres were created in Chicago. But nowhere in the U.S. has the landmaking been as extensive as in Boston.
What this suggests about our long-term response to rising sea levels is that we shouldn’t rule out the idea of raising the grade in our most important cities. I was astounded to learn just how significant the earthmoving was centuries ago; with today’s equipment and engineering prowess, one can imagine raising a low-lying city by tens of feet.
Of course, there would be huge challenges and tremendous costs with such an initiative, not to mention environmental risks. Our buildings are bigger than those in Boston were in the 1860s; they are closer together and more complex. Our infrastructure—streets and highways, bridges, sewers, power grids, pipelines—are tremendously complex. And, we’re much more conscious of ecological damage today than we were 150 years ago.
But consider the alternative. Are we ready to abandon cities like Boston, New York, Philadelphia, and Charlestown? It could well be easier to raise a city than to move it. And we will have to figure this out before the end of this century. I don’t know if raising the elevation of our low-lying cities will make sense, but I think we should begin that discussion.
We can start by looking at past experience, and Gaining Ground provides a good starting point in doing so. In some cases, it may be possible to fill in basements, compacting the fill to equalize the pressure on the outside of those walls, and turn first floors into basements—essentially eliminating an occupied floor of a building.
In other cases, entire buildings may have to be elevated and new foundations built on compacted fill 15 or 20 feet higher. Streets would have to be covered and rebuilt on fill. Very challenging will be the need for such modifications to be coordinated on a neighborhood-by-neighborhood basis. You can’t raise one building 20 feet and not do anything with the building next door.
This would be an extraordinarily complex process in terms of phasing, implementation, and environmental protection. But it’s time to take sea level rise seriously and begin looking at our options. Raising land mass may be one such option.
Source: Alex Wilson, Resilientdesign.org, A bold idea for addressing sea level rise, Mar 28, 2016
Explore the spatial data used in Climate Ready Boston – This app allows you to learn more about the data layers used in the Climate Ready Boston recommendations for protecting our City from a changing climate, and helps you better understand how projections are influencing resiliency solutions. Read the introduction to this interactive tool.
Sasaki : Sea Change Boston. Designing in the Face of Climate Change– Sasaki is a global design firm specializing in architecture, planning, urban design, landscape architecture.
A much-anticipated new report on how best to protect the Seaport District and other Boston neighborhoods from the effects of climate change finds that the cost to build a massive, multibillion-dollar wall in Boston Harbor is not worth the benefits.
Instead, it finds that the city of Boston and other coastal cities and towns should focus on more localized projects to counteract the flooding and higher sea levels wrought by global warming, said the report… “Right now, it doesn’t make sense for the city to consider any kind of harborwide barrier system,” said the report’s lead investigator, Paul Kirshen of UMass Boston’s Sustainable Solutions Lab. “It doesn’t make sense for decades, if not ever.” The report was sponsored by the Boston Green Ribbon Commission, a coalition of business and civic leaders formed more than a decade ago to help the city address climate change
… Either barrier could cut down on coastal flooding without significantly disrupting shipping or the environment, according to the report. But “shore-based” solutions, as the researchers call them, can provide the same level of protection at a cost of just $1 billion to $2 billion, with additional benefits to boot, Kershen told reporters Tuesday. Shore-based systems could include flood walls on a much smaller scale than a harborwide barrier, changes to zoning laws, and the raising of land using berms, among other projects.
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