I represent parts of Boston and the inner suburbs that were built on the historically marshy flood plains of the Charles and Mystic. With climate change, as sea level rises, storms become more powerful and rainfall increases, we need to be concerned about increased risk of flooding in these areas. Because these areas are now protected by sea walls, we have a little time, but everyone in the region needs to also be concerned about nearer-term risks to the metropolitan infrastructure — key roads, tunnels, transit, water and sewer.
This post collects current information on activities underway to assess and address these risks. Comments identifying additional activities and resources will be much appreciated.
Cambridge has invested substantially in assessing the risks of climate change, especially the risks of increased flooding due to sea level rise, increased storm surge and increased precipitation in the Charles and Mystic basins. The challenge in both of these basins is to assess the combined risks of rainfall and storm tides as mitigated by the seawalls and pumps at the mouths of the basins. Cambridge has done some very sophisticated modeling which it has elegantly presented in a flood risk viewing tool.
The key finding from Cambridge’s vulnerability analysis is that storm tide flooding in the basins, while still not a material risk in 2030, is likely to become a material risk in the second half of this century. According to the vulnerability analysis, “Overland flooding from a storm surge into the Charles River appears to be a generally low probability through 2070. However, the raised river level could cause river water to back up through the storm drainage pipes and discharge onto some streets.”
The underlying technical report shows that annual flood risk in the Charles Basin will mostly remain below 1% through 2070 with the exception of the North Point area. The areas of Back Bay closest to the Charles mostly show annual flood risks around 2070 in the 0.1% to 0.5% range, although a couple of blocks of Beacon Street are at higher risk and will become harder to insure. Even for the 500 year storm — the storm that has an 0.2% chance of occurring in a given year around 2070 — the flood depths forecast in most of Back Bay are not great (a few inches or feet).
The Mystic will become vulnerable sooner, with the Alewife area possibly subject to storm surge flooding with annual probability of 20% by 2070.These risks are very substantial and Cambridge has embarked on a conversation towards improving the resiliency of the Alewife area.
A consideration addressed in the report is the possibility that an unprecedented storm tide might coincide with unprecedented riverine flooding due to increased precipitation. In the case of flooding around or over the river seawalls, “the flood volume associated . . . [is] orders of magnitude larger than from rainfall events.” This reality makes less relevant the complex statistical analysis one might perform to evaluate the risks of coincidence of storm surge and precipitation. It also means that the huge pumps that are sized to protect the basins when rain is heavy will not be able to keep up and make much of a difference during a flanking or over-topping storm tide, although, if they survive, they could accelerate the post-event drainage. The concern when rainfall and storm surge coincide is that the storm drainage system would back up, causing localized flooding at elevations above those affected directly by the storm tide.
The report highlights the infrastructure assets at risk to storm tide flooding in the Alewife Area — the drinking water in Fresh Pond, the Red Line, Route 2 and the huge North Cambridge electrical substation and the natural gas facility that serves all of Cambridge — finer analysis of the infrastructure vulnerability has to be a high priority.
Both seawalls will be flanked before they are overtopped, so there is an emerging conversation about whether we can reduce or defer storm surge risks by raising surrounding land. For the Charles, there are flood pathways around the south of the dam and also through Charlestown. For the Mystic, there is a flood pathway through the Assembly Square Mall and also a large one up and around through Everett.
Boston has also undertaken a very substantial analysis of climate exposures. Boston conducted a process to build consensus on just how much sea-level rise they should be worrying about. They chose to use roughly the same maximum rise scenario as Cambridge for 2070 (approximately 3 feet).
Like the City of Cambridge, Boston has identified areas subject to increased risk flooding. The underlying models are the same and the results are similar — the risk of overland flooding for most of the neighborhoods along the south bank of the Charles Basin remains at or below the 1% (annual percentage) level in 2070. The Public Gardens are a low lying area that is more vulnerable. Also, there will be local storm drainage backups that will be consequential and more frequent.
Back Bay, North Allston and other neighborhoods on the Charles get excellent discussion starting at page 176 of the main report. For neighborhoods along the Charles, one medium-term strategy of interest, also identified in the Cambridge report, is to close “breach points” where storm-tides would invade the basin. The city quantifies cost-savings possible in breach points where exposure to flooding could be reduced by the construction of barriers.
The Boston report also highlights infrastructure impacts in considerable depth:
Since most of these assets are regional, the report calls for an Infrastructure Coordination Committee (ICC). This echoes legislation that I filed several years ago, but which remains unimplemented, although it was passed in part.
Additionally, the report highlights the need for building code improvements to support resiliency.
Boston has created an elegant viewer for storm water flooding risks. Caution: The City’s website still also carries outdated sea-level impact imagery and analysis that overstates the impact of sea level rise and does not reflect the more sophisticated modeling that the City has done to incorporate the protective effects of the Charles River seawall/dam.
MassDOT has completed a preliminary Central Artery/Tunnel vulnerability assessment. The modeling that they did has become the foundation for the modeling done by the other municipalities and agencies in the area. They are currently conducitng a broader and deeper coastal transportation vulnerability assessment. So far, the vulnerability results have not translated into particular targeted projects. It may be that much of the necessary resiliency investments will be made in the course of ordinary periodic maintenance projects.
The MBTA does not have a comprehensive vulnerability assessment in place. According to their March 2017 strategic plan, they hope to have an assessment by the middle of 2018 (see p.36). The T has had to start a little further back with a winter resiliency effort and, as to flooding, with a focus on the Blue Line which is the agency’s most exposed coastal asset.
MassPort is appropriately focused on the issue of resiliency. Logan Airport has studied the water elevations from MassDOT’s flood scenarios and compared those elevations to its critical assets, revealing that many of its assets will become increasingly subject to flooding. MassPort has hired a resiliency program manager and defined a mission for its resiliency program “to prepare for disruptive events, recover within a reasonable timeframe with minimal damage, and sometimes emerge even stronger.” All construction is to follow a flood proofing design guide.
The MWRA has long been conscious of flooding risks as all of their assets are sensitive to flooding. Their critical assets — Deer Island and the water supply — appear to be safe for some time, but there are other some shorter-run vulnerabilities.
In September 2016, Governor Baker issued Executive Order 569 which calls upon the Secretary of Environmental Affairs to
. . . within two years of this Order, publish a Climate Adaptation Plan that includes a statewide adaptation strategy incorporating: (i) observed and projected climate trends based on the best available data, including but not limited to, extreme weather events, drought, coastal and inland flooding, sea level rise and increased storm surge, . . .;
within one year of this Order, establish a framework for each Executive Office to assess its and its agencies’ vulnerability to climate change and extreme weather events, and to identify adaptation options for its and its agencies’ assets;
This is a matter that takes gubernatorial leadership — I was unable to get a similar approach moving legislatively several years ago. In March 2014, in the waning days of the Patrick administration, I did pass legislation to the same effect (see section 39 of this supplemental budget), but there was no follow-through from the executive branch. I certainly welcome Governor Baker’s initiative. Hopefully, it will help get the necessary enormous efforts moving.
As to the risks of flooding, my priority areas for follow up as state senator from the Second Suffolk and Middlesex district include:
As to private assets, I think the role of government right now should be to make sure that the risks are being widely discussed. I’m less interested in legislation to push building code changes that will improve resiliency for structures facing increased risks. As long as the state government is not being asked to insure structures, we probably cannot mandate that private individuals and businesses extend themselves to make resiliency investments in structures that they may not occupy when the risks materialize.
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