Proposed Flood Gates May Impact North Shore

Satellite image showing location of proposed sea gate

The Army Corps of Engineers has been tasked with producing a feasibility study on how to best protect the greater New York City area from flooding, a reaction to Hurricane Sandy in 2012 and sea-level rise caused by climate change. The New York-New Jersey Harbor and Tributaries Coastal Storm Risk Management Feasibility Study is expected to be finished by March 2021 and a decision on the best plan to move forward by the Army Corps of Engineers is expected by July 2022.

Sea Gates

An interim report was released by the Army Corps in February that proposes five alternatives, including one that involves putting a sea gate in the East River near the Throgs Neck Bridge that could affect the North Shore of Long Island. The sea gate or storm surge barrier would be in the water, from the sea floor to well above sea-level, and span the whole width of the river. The gate would be left open to allow boating and fish migration and would only be closed when a potential storm was approaching the area.

In the interim report, Alternative 1 involves no action at all by the Army Corps. Alternative 2 involves two sea gates, Sandy Hook-Breezy Point Barrier and the Throgs Neck Barrier, costing an estimated $118 billion and taking approximately 25 years to build. The Army Corps’ net cost-benefit analysis is $57 billion for this project.

Alternative 3A has the Throgs Neck Barrier and the Verrazano Narrows Barrier, Arthur Kill Barrier, Pelham Barrier and the Jamaica Bay Barrier costing an estimated $47.1 billion and taking about 18 years to construct. The net cost-benefit analysss is $124 billion.

Alternative 3B would not include the Throgs Neck Barrier, but have the Jamaica Bay Barrier, Pelham Barrier, Arthur Kill Barrier, Kill Van Kull Barrier, Newtown Creek Barrier, Gowanus Canal Barrier and shoreline-based measures to NJ Upper Bay/Hudson River, NYC West Side and East Harlem costing a total of $43 billion with construction lasting nine years. The net cost-benefit analysis is $117.8 billion.

Alternative 4 contains the Jamaica Bay Barrier, Pelham Barrier, Newtown Creek Barrier, Gowanus Canal Barrier, Hackensack River Barrier and shoreline-based measures to NJ Upper Bay/Hudson River, NYC west side and East Harlem at the cost of $32 billion with a build time of nine years. The net cost-benefit analysis is $116.6 billion.

Alternative 5 has no barriers and only perimeter solutions, including shoreline-based measures to NJ Upper Bay/Hudson River, NYC west side, East Harlem, Newtown Creek and Gowanus Canal and is also the cheapest option at $14.8 billion and built in nine years. The net cost-benefit analysis is $33.8 billion.

“One of the alternatives is to do all on-shore measures and to combine them with some natural systems,” Save The Sound director Tracy Brown said. “That’s Alternative 5 in their proposal and that is the one that shows raising the shoreline and doing shoreline hardening in areas that are hardest hit by storm surges. Also using natural strategies like oyster reefs or artificial reefs offshore to break waves and reduce the wave strength before it reaches the coast. We think that is the smartest way to go.”

Brown and others are worried about the potential deflection and induced flooding into Long Island Sound communities when the Throgs Neck Barrier would be closed for a potential storm.

“The main question is what happens to the parts that are not protected,” said NYU Sociology Doctoral student Malcolm Araos. “What happens to the rest of Long Island that is not within the barriers? I would like to know more about the decision to how they decide to protect one area and not the other. I can imagine that being a very controversial thing that the Army Corps of Engineers would be worried about.”

In 2004, Stony Brook University Marine and Atmospheric Sciences professor Malcolm J. Bowman authored a report titled “Hydrologic Feasibility of Storm Surge Barriers to Protect the Metropolitan New York—New Jersey Region” where he simulated the effects of a storm surge with a barrier near the Throgs Neck Bridge. Using data from Hurricane Floyd, a tropical storm when it hit the area, the report found that a barrier would have increased sea level by one foot on the North Shore. In 2013, the American Society of Engineers published a similar study that involved a Category 4 hurricane and found it would  increase the sea-level by two feet outside the barrier.

In a Long Island Sound Study Science and Technical Advisory Committee meeting on Feb. 15, Bowman stated the need for barriers. Referring to the Sandy Hook-Breezy Point and Throgs Neck barriers, he concluded that they are necessary for storm surge protection and the Throgs Neck barrier may also improve water quality in the Long Island Sound. He also said that the design of the barrier should minimize obstructions to river and tidal flows during calm weather to allow adequate flushing of the East River. Bowman could not be reached for comment.

In the same meeting, Physical Oceanographer and Research Assistant Professor Phillip Orton of Stevens Institute of Technology used modeling to show the effects of the barriers. His simulations found stronger tidal currents and mixing near the barrier gate openings, widespread reductions in tidal range, currents and mixing through the rest of the estuary, increased stratification in the estuary due to the stronger stratification and estuarine circulation and more pronounced changes during spring tides than neap tides. Orton could not be reached for comment.

Araos has been studying the response to catastrophic storms by municipalities. The barriers can be a short-term option, but he is looking at what could be effective in the long-term.

“Whatever you think about these scientific predictions of sea-level rise, if you think it is man-made or not, through geologic times in like 100 years that sea-level rise is going to eventually overcome those barriers,” Araos said. “For a very long-term view, no matter how tall you build those barriers, eventually, you will need to come up with a different solution.”

—Additional reporting by Christina Claus


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