The risk we weren’t talking about

A lot of attention has been given to the flooding that would result if rising sea levels lead to the over-topping of the dams at the mouths of the Charles and Mystic rivers. Until recently, no one was talking about what high water could do to the dams themselves.

The New Charles River Dam and the Amelia Earhart Dam are both about 50 years old. They serve similar functions for the Charles and the Mystic respectively. They regulate the water level in the lower basins of both rivers to a level that roughly equates to mid-tide in the harbor. Under normal conditions, gates close at high tide to keep the ocean from raising the water level in the basins. At low tide, the river flow in the basins is allowed to drain out.

The dams are both equipped with a set of massive pumps to throw the river flow over the walls into the ocean in case rain-driven flooding coincides with high tide. These pumps have been adequate to handle all the storms we have had over the past 50 years. I have seen the pumps in the Amelia Earhart drain the Mystic basin down to exposed mudflats in the middle of a heavy rainfall event.

The dams were both built to survive the highest harbor water levels that had ever been observed to date (the flood of 1851) plus another foot and a half. Their decks sit at about 8 feet above normal high tide level (“118 MDC Datum”), roughly 2 feet higher than the highest more recently measured storm surge levels (the Blizzard of 78 and the January 2018 storm).

That level seemed awfully safe when the dams were built, but with rising seas it is now recognized that by the latter part of this century there will be a material risk in any given year that the ocean will surge over and around these dams.

The flows associated with ocean storm surge are much too big for the pumps to handle, so a flanking/overtopping event would mean severe flooding in the Charles basin and in the Mystic basin, all the way out to Alewife. Discussions as to how to reduce the risk of flanking and over-topping are underway in both Boston and Cambridge. The risk analysis depend on complex modeling of how long the over-topping event lasts and so how much water actually flows upstream.

A few weeks ago, DCR educated the legislature about a much more proximate risk. Even a brief overtopping event could severely damage, even cripple the pumping systems of the dams. They are not built to handle overtopping. Salt-water could quickly flood into critical electrical and mechanical areas that are just not designed to get wet. The damage could reach $150 million to repair and the entire region would be vulnerable until the repairs were complete.

Fortunately, state engineers who lie awake worrying about these dams surfaced the risks up the chain of command and set in motion a pair of projects to harden the dams to handle over-topping events. The fix design is complete for the Charles and work will likely begin in this construction season on the Charles. The Mystic dam is a few months behind — as part of the project, they have to move the operating staff into portions of the facility that have hazardous building materials in them that need to be removed.

Once these fixes are in place, the conversation will turn in earnest to what it will take to raise these structures and the areas around them so that the point when sea level rise becomes an urgent threat to riverside neighborhoods can be pushed much further out into the future. Fortunately, it appears that even without increased elevation, the overtopping flood risk remains low for the next few decades.

Published by Will Brownsberger

Will Brownsberger is State Senator from the Second Suffolk and Middlesex District.

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22 Comments

  1. Will, I applaud what you have done for prisoners and their rights. Freedom is the most important value. One of my favorite books is How I Found Freedom in an Unfree World by Harry Browne. Prisoners of course have little freedom, and putting them in solitary is horrendous. Humans are social animals and require the company of others to thrive. I hope you will continue your efforts on their behalf as president pro tem of the Senate.

    1. Thanks for your work in many areas. I hadn’t even known or
      thought about storm damage to dams. I appreciate your
      concerns and your communications.

  2. What about the Watertown dam on the Charles? Many of us have hoped that dam could be removed, as fish have a hard time climbing the ladder (it was built on the wrong side of the dam) and it could also prove dangerous if/when the river flooded.

  3. Good morning
    Mr. Brownsberger you made very important points.
    Floods, ,the two dams and the rising sea.
    I was involved on the design of these dams
    The origin of all is the global warming.
    Regards,
    Giovanni Aurilio

  4. Sad to say most of the dams in Massachusetts are in poor condition. Where is the dam on the Mystic the lowest one I know of is at the Mystic Lake. Like someone else said the Watertown dam is old but also is the Waltham and I would be in favor of some hydro power extraction from each site. Funds from power sales I would like to see go into a trust for maintenance and replacement of these dams in the future

    1. The Mystic dam (Amelia Earhart Dam) is near the mouth of the Mystic, between Somerville and Everett. At least, Google Maps shows a large, unlabeled dam with locks at that location. It runs from quite near the Assembly T station to the mall in South West Everett with a Costco, Target and Home Depot.
      I think there is another dam on the Mystic near Medford Square, but I can’t find it on Google Maps. It might be hidden under one of the bridges.

      1. P.S. Thank you Will and the (MWRA? MDC? DCR?) engineers for being proactive on this. As a Y2K survivor (I spent about a year and a half preventing Y2K problems), I hope people remember this the first time a flood level exceeds the current top of the dams and nothing happens because this was taken care of.

  5. When searching for a suitable home for our sizeable family of 4 children 41 years ago, we discovered Riverside Street; it is situated on a ridgeline that angles upward toward Perkins, and drops off on both sides, one toward North Beacon Street the other side toward the Chargles River, satisfying my concerns of adaquate run off during severe rain storms, leaving the basement secure and dry. A few years ago I inquired of my homeowners insurance company the thought of obtaing flood insurance, motivated by flooding that has been occurring throughout the country; I opted out, thinking historically, this area has been protected by the dam and pump at the Boston Harbor basin. I will admit that from time to time I have thought about a inland surge, and the height and distance Riverside Street is from the banks of the Charles, yet, have felt relatively safe. Hmmm, but now, not so much? I want to convey our sincere thanks and appreciation of your concern and pro active thinking, along with all of the involved officials, engineers and personnel that are focusing on this potential danger. Thank you one thousand times!!! Will Clifford

  6. Yes and Cities near the Harbor, Boston, Quincy for instance, may need help financially to put in place plans dealing with storm surge that has already seen floods in Boston along the waterfront.

  7. Will, congratulations to the DCR engineers and to you and rest of the legislature for identifying this problem and tackling it. This is how things are supposed to work! I’m sure that it will be much cheaper to address this problem now, before a catastrophic event, than to have to clean up afterwards.

  8. Thank you for thinking about this problem, which has been my major concern. I am greatly relieved to hear that the pump system on the Charles River Dam is to be hardened, but in a few years the dam will be outflanked by major storms.

  9. Thank you, Will. Very interesting piece and I’m glad it was taken care of in advance by the State. I appreciate your updates on a huge variety of topics.

  10. Missing is storm runoff part of equation, that is water coming from rain and snow. Seas warm creating more evaporation clouds get hydrated, when over land they release it. Also Deer Island sanitary and storm capacity may be overburdened by population increase in Boston metro area soon if not already. Advise reference website of American Society of Civil Engineers and their quadrenial audit of USA infrastructure with individual state assessment. I read recent report Mass.needs 4 to7 billion dollars in water infrastructure new investment over ten year period. ASCE states
    thier membership is over 100000 including foreign members.

  11. Thanks for the info, Will!! I would like to add the Moody Street Dam in Waltham, MA to your list; even though it is not in your district (could you forward this info to whomever checks that dam?).
    During a quick spring melt and a heavy rain, water went around the Moody St. Dam (MSD) in Waltham. Someone place several sand bags to prevent the overflow from expanding; however, the amount of water coming over the dam was sufficient enough that a hook and ladder truck and several people with chain saws and ropes were on right right. These people had to move one large log. Sadly, these people did not seem to care what happened to the flotsam as it headed towards an old railroad bright a few hundred yards down the Charles.

  12. Thanks, again, Will, for your careful analysis and sharing this information. There are so many things that average citizens know nothing about and have to count on “government” to take care of. Every time someone bad mouths the “government,” I tell them about the wonderfully committed people in government that I know!

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