Boston North Shore Study Area

SUMMARY

The Boston North Shore study area includes the cities of Revere, Lynn, Malden and Everett, and the towns of Saugus and Nahant, Massachusetts which would have been protected by the Regional Project, previously widely supported by the communities.  The Regional Saugus River Floodgate Project is the primary option for regional coastal flood protection for these communities which was selected:  after detailed investigations of alternatives (1985-1990); overwhelming support by communities; sponsored by the Commonwealth; authorized for construction by the US Congress; but then placed on hold in 1993.  The Boston north shore study area now needs an updated Feasibility study by the US Army Corps of Engineers to re-evaluate the alternatives including the Regional Project as requested by the communities. The study is being called the "Saugus River Coastal Storm Risk Management Feasibility Study" and would be cost shared 50/50 between the Federal Government and Commonwealth of Massachusetts when funded. The Regional Project is a coastal flood protection project which would provide a very high level of protection against accelerated sea level rise to these communities. The region, five (5) miles north of Boston, is the most vulnerable area along the Massachusetts coast to storm surge flooding and sea level rise.

INITIAL INVESTIGATIONS 

The Corps of Engineers New England Division investigated solutions to the flooding problems in the study area caused by the Blizzard of 1978 when 3100 buildings were flooded and subsequent storms. The study was conducted with 5 Steering Committees over 4 years ('85-'90, $2.6 million) by the Saugus River and Tributaries Flood Damage Reduction Study which recommended the Regional Project (see "Documents"), This option #3 includes a Floodgate structure at the mouth of the Saugus River with a 100-foot-wide Navigation Gate and eight (8) 50-foot wide Flushing Gates, designed to provide safe passage for navigation and the natural tide levels and flushing in the 1,650-acre tidal Estuary landward of the gates. The Estuary would be purchased and managed to protect its flood water storage and environmental resources (see "Photos" for Rumney Marsh video).  The gates would be tied to 3.1 miles of shorefront improvements along Lynn Harbor, Point of Pines and the Revere Beach Reservation. The 1.5-mile Nahant Causeway would be protected and maintained since it significantly reduces wave action in Lynn Harbor, mouth of the Saugus River and at Point of Pines.   The project would protect 5,000 buildings, 8,000 housing units, 10,000 residents, 20,000 employees and 400,000 commuters in the region against the worst coastal storm likely to occur, the Standard Project Northeaster (SPN), and against the historical 1-foot rise in sea level, estimated damages at $ 1.3 billion.           

The Secretary of Environmental Affairs after the NEPA/MEPA review provided a positive Certificate (see "Documents"), the Commonwealth then supported it, and the US Congress authorized the Project for construction, which proceeded into final design at $6 million over 3 years (see "Documents").  Then in the fall of 1993 a new Secretary of Environmental Affairs, an environmental activist from Rhode Island, was opposed to construction along the Massachusetts coast and the project was stopped, and since it has been de-authorized.   

ACCELERATED SEA LEVEL RISE & NEW STUDY

Renewed interest in the Project by the communities due to frequent coastal flooding and accelerated sea level rise resulted in the Boston North Shore Feasibility Study which was authorized by the President on 23 Dec 2022 to investigate the flooding and ecosystem needs for the Study area. The study name has been changed to the "Saugus River Coastal Storm Risk Management Feasibility Study" in order to avoid confusion with other Boston studies.  The initial planning of the Regional Project and other options were based only on the historical rate of sea level rise of one (1) foot, and only subjectively addressed the potential impact of higher rates of sea level rise.  By 2020 accelerated sea level rise was universally accepted and the Corps of Engineers adopted a rate of rise of 5-feet by 2100 for planning projects and Coastal Zone Management (CZM) a high of 7.8-feet by then.  The impacts of accelerated sea level rise have a significant impact on the region and project and were therefore re-evaluated by the Corps' original Project Manager following 2020. He used completed investigations and the forecasted and adopted rates of sea level rise by the Corps of Engineers and by CZM for the year 2100.  The potential damages to the estimated 6,000 to 7,000+ buildings in the higher SPN floodplain would be in the billions of dollars impacting 100,000 residents and employees and half a million commuters, or nearly a million folks affected. 

The Regional Project would still include the Floodgate structure and improvements along Lynn Harbor but raised for a 5-foot (or 8-foot) sea level rise by 2100. Building sand dunes and beaches at Point of Pines, along Revere Beach, and along the Nahant Causeway using the abandoned I-95 sand should effectively reduce the SPN overtopping based on detailed studies.  The use of this sand could remove 4,900 feet of the embankment, restore 40 acres of ecosystem habitat buried by the embankment, and restore flushing to the upper 500 acres of the estuary.  Breaching and removing the I-95 embankment to restore the wetlands is a major goal of resource agencies.  The preliminary cost of the Regional Floodgate Project for SPN protection with a 5-foot rise in sea level would be about $300 million initially at 2023 price levels.  As sea levels rise 5- to 8-feet by 2100, it would become necessary to close the floodgates more often reaching about 50 per month at 6 hours each which would interfere with navigation.  To then reduce the number of closures around 2050, walls may be needed along the 25-miles of shoreline to raise the start of damages, increasing the project's cost by an estimated additional $200 million, causing environmental and social impacts, if this option were selected. 

NAVIGATION LOCK REDUCES IMPACTS

A more viable option to consider is a Navigation Lock, shown below, which would modify the single Navigation Gate mentioned above in the Floodgate structure.  The Navigation Lock would allow for boat passage at any tide level.  The Navigation Lock would still be combined with eight (8) flushing gates to maintain tidal flushing in the estuary.   This plan would eliminate the need for any walls around the estuary or along the rivers' shorelines as sea levels rise. As with the original plan, protecting and maintaining the natural flushing and tide levels in the estuary, plus providing for flood water storage (between El. 7-8) from runoff when gates are closed would still be required.  All gates including both gates on the Lock and the eight (8) 50-foot-wide flushing gates would remain open as ocean tides remain below elevation 7 feet NGVD.  At this level, river and estuary water levels would be below the start of damages at El. 8-feet NGVD, and all wetlands would be inundated naturally at and below El. 6 feet NGVD.  As ocean tides rise above 7 ft. NGVD, all gates would close and the lock would be operated.  The cost would be much lower than building 25-miles of walls or dikes, if the additional lock gate and lock chamber walls are added, possibly around 2050.

GATE CLOSURES

The number of times either the Navigation Gate or the Navigation Lock Gates and Flushing Gates would be closed to prevent damages would increase with sea level rise.  For example: by 2030 with 0.7-foot rise, closures would only be about 3 times a month averaging 2.5 hours each; by 2050 with 1.6-foot rise, closing 10 times per month at 4 hours each; in 2070 with 2.7-foot rise, 23 closures at 5 hours each; and, then by 2090 with 4.2-foot rise, 49 closures per month at 6 hours each.  There would be significant impacts on navigation unless locks were available.  A possibility is to construct one Lock Navigation gate and concrete chamber, then after, say 2050 fabricate and install the costly riverside gate.  The information learned from the initial design of floodgates, which included physical and numerical models, could be used to help design a Navigation Lock. 

HOW NAVIGATION LOCK & FLUSHING GATES OPERATE

A Navigation Lock is a concrete chamber with gates on both the ocean end and on the river end of the chamber.  If a recreation or lobster boat wants to leave the riverside to enter the ocean, water level in the chamber is drained to river levels. The riverside gate then opens, and the boat enters the chamber, The river gate then closes and valves open to let ocean water fill the chamber.  Once the chamber water levels and boat reach ocean water levels, the ocean gate opens for the boat to leave. The reverse happens for a boat to leave the ocean and enter the river. 

When ocean tide levels drop to elevation 7-feet NGVD, all navigation lock gates and flushing gates open for the Estuary and rivers to drain as the ocean tides drop to low water levels.  The gates remain open until ocean levels rise back to elevation 7, then all gates close and the lock then operates for boat passage.  While all gates are open, boats can pass freely through the Lock chamber.  By closing gates when ocean levels are above elevation 7, damages to properties, starting at elevation 8, are prevented, and the Estuary wetlands up to elevation 6 are totally submerged.

OPTION #1 & #2 WITHOUT FLOODGATES

Without any Floodgates, the Region would need to be protected against the Standard Project Northeaster in 2100 with 5-feet of sea level rise by Option#1.  The plan would require using walls and dikes up to 12 feet high along roads and yards for the 25-miles of estuary shorefronts.  The cost would likely be at a much higher cost than the Floodgate Project, likely exceeding $500 million ('23 pl,) for walls, dikes and pumping stations.  Option#2, a non-structural plan, to raise all buildings up to 12-feet high would cost considerably more than the Floodgate Project while roads and yards would be continually or frequently under water.  The cost to totally evacuate the floodplain with the removal of all buildings would be in the order of $15 billion or more which would cause extreme hardship to folks in the region.