At around 7:30 p.m. on October 29, 2012, Hurricane Sandy made landfall near Atlantic City, NJ. Over the next 24 hours, the storm punished the greater New York metropolitan area and New England with massive surges and a wind field that spanned 1,000 miles.
By the time it was over, Sandy had destroyed at least 650,000 homes, caused $50 billion in damages, left 8.5 million people without power, and killed 43 people in New York alone.
Technically, it wasn’t even a hurricane.
Prior to making landfall, Sandy was downgraded from a Category 1 hurricane to a post-tropical cyclone because it lacked the characteristics of a hurricane (thunderstorm activity, no visible “eye”). Yet an unlikely set of conditions made the storm especially catastrophic: Two storm systems diverted Sandy from a hurricane’s typical path along the East Coast and out to sea; its arrival in New Jersey coincided not only with high tide, but with a full moon and an elevated spring tide.
These circumstances, combined with the sheer size of the storm, resulted in unprecedented storm surges in New York Harbor — and a study by the United States Army Corps of Engineers.
Protecting the metropolitan area from storm surge poses a distinct challenge due to the massive amount of infrastructure, commerce, traffic, and residents in New York City — the highest population density of any city in the United States. Following Hurricane Sandy, President Barack Obama authorized the Corps to investigate coastal storm regional management strategies under the North Atlantic Coast Comprehensive Study.
The Corps determined the New York metropolitan area was a high-risk region and required closer evaluation. They were granted permission to carry out a subsequent study of the area, which stretches from Perth Amboy, NJ to Albany, and east to parts of Long Island. It includes 25 counties and 16 million people.
In July 2018, the Corps presented six proposals to address the threat of storm surge (see below). These proposals consist of a combination of storm surge barriers and shoreline-based measures. The Corps defines storm surge barriers as “a fully or partially movable barrier that includes operable elements (usually gates) that can be closed temporarily…” Shoreline-based measures are typically perimeter-based solutions like levees, floodwalls, or seawalls, as well as nonstructural measures like barrier islands and stormwater management.
Two of the proposed solutions — Alternative 2 and Alternative 3A — involve storm surge barriers across the mouth of the Hudson River in New York Harbor. Alternative 2 would span more than 6 miles from Sandy Hook, NJ to Breezy Point in Queens and, at its tallest point, rise about 46 ft. Alternative 3A, at the Verrazano Narrows, would stretch more than a mile from Staten Island to Brooklyn and rise 21.5 ft.
Alternatives 3B and 4, while still concerning to environmentalists, involve smaller, extremely polluted waterways that do not directly affect the Hudson River. They do, however, implement shoreline-based measures in a number of towns in the lower Hudson Valley.
So far, 23 Hudson Valley towns, villages, cities, and counties have signed resolutions expressing concern or opposition to these proposals. They pose an “existential threat” to the Hudson River, according to John Lipscomb, patrol boat captain and vice president of advocacy at Riverkeeper. The consequences of its construction would be so sweeping that the environmental group American Rivers declared the Hudson the second most-endangered river in the country:
“The storm surge barrier designs that the Army Corps is considering are essentially massive sea walls with gates. These walls could act like partial dams, blocking fish and wildlife, including Atlantic and shortnose sturgeon, American shad, American eel, river herring and sea lamprey, from moving up- and downstream, and restricting the natural flow of the river. Furthermore, barriers across New York Harbor would dramatically alter the tidal exchange essential to transport sediment, nutrients and contaminants. Obstructed by barriers, sewage and other contaminants could flush into the ocean more slowly, increasing localized pollution in the Harbor. With inhibited tidal energy, higher nutrient levels could lead to more frequent algae blooms and lower dissolved oxygen that would impact the health of the estuary and upriver tidal marshes.”
These tidal marshes are invaluable to the Hudson’s ecosystem: Not only do they filter out waste products like nitrogen, they also encourage vegetative growth, provide habitats for fish and waterfowl, and serve as a nature-made shield against storm surges.
Aside from environmental issues, the barriers have elicited concerns over transportation and commerce within the harbor, financing (in addition to sharing the cost of construction with the Federal Government, New York and New Jersey would be responsible for operation and maintenance costs, which could be as much as $1 billion per year), and induced flooding of nearby communities.
The Corps maintains that storm surge barriers are uniquely suited as a solution for the vast area at risk. In a response to public comments, the Corps wrote, “…A relatively short distance of surge gate measures with associated shoreline-based measure tie-ins can address long distances of shoreline that otherwise would have exposure to extreme coastal storm events.”
In other words, it’s easier to address a leaky pipe by shutting off the water than by putting buckets around the house. The Sandy Hook-Breezy Point barrier to be constructed under Alternative 2 would address almost 95 percent of the area at risk; the Verrazano Narrows barrier, 74 percent. By contrast, Alternative 5 — the solution comprising shoreline-based measures (floodwalls, levees, etc.) — would address 3.2 percent. In terms of risk reduction, this translates to 92 percent, 89 percent, and 25 percent decreases, respectively.
Despite the gap in those numbers, Riverkeeper’s Lipscomb says the only viable option is Alternative 5 because shoreline-based measures can protect communities against storm surge and rising sea levels.
While the Corps has accounted for rising sea levels in its design of storm surge barriers, they have not designed their solutions to protect against higher sea levels. Under their current congressional authorization, the Corps’ study is limited to hurricanes and coastal storms; but they insist that strategies for protecting communities against sea-level rise do not differ greatly from those targeting coastal storms. That being said, the Corps acknowledges the need for further analysis under a separate study.
Scenic Hudson gives some insight into what Hudson Valley communities can expect as sea levels, and in turn the Hudson River, continue to rise:
“Over 9,000 acres of riverfront lands lie within the expanding reach of daily high tides, threatening both the most critical river habitats and approximately 3,600 households and 6,900 people. Accompanying shifts of flood-prone areas will put another 6,400 households and 12,200 people at greater risk from damaging storm surges and floodwaters. At the same time, the most critical habitats of the Hudson River ecosystem — the 13,000 acres of tidal wetlands and shallow water vegetation beds — will be increasingly stressed by rising water levels.”
Based on Scenic Hudson’s models for sea level rise, by the 2080s, the following locations will likely be regularly inundated by the Hudson’s high tide: Poughkeepsie Skate Park, parts of the Newburgh waterfront, most of Long Dock Park in Beacon, Constitution Marsh in Garrison, and Grassy Point in Stony Point, among others.
By 2100, not only will the Ruth Reynolds Nature Preserve and the walking path to the Saugerties Lighthouse be flooded, much of Lighthouse Drive in Saugerties will be under water. Waterfront businesses like Frank Guido’s Port of Call in Catskill and Ole Savannah in Kingston will also be flooded.
“The one thing I keep saying to people is there’s no easy choices here,” says Dr. Philip Orton, a research assistant professor of ocean engineering at Stevens Institute of Technology in Hoboken. In October 2018, Orton and a team of researchers published a report on how storm surge barriers would affect the Hudson. While their study did not examine the Corps’ barriers specifically, the team evaluated the effect of a generic barrier on physical properties crucial to ecosystems.
“It’s really a question of expense,” says Orton. “There are scenarios for sure where if they spend enough money and if they have enough gates and a lot of openness to flow to the ocean, then you’d have a small impact on tide range and salt intrusion.”
Thus, there may be an acceptable threshold of disruption if it ensures the safety of residents and infrastructure. Orton and his team are now studying how the duration and frequency of gate closures could impact the Hudson. But without more details on the designs of the barriers or the specific measures to be employed, it is impossible to predict how the barriers will affect the Hudson River. Up until this point, the Corps has emphasized the early stage of its proposals. It describes the alternatives as “preliminary concepts” that have been presented to convey basic information like time and cost. Some features may be removed from consideration as site-specific investigations reveal whether they’re technically feasible, economically justified, or environmentally acceptable. According to the Corps, alternatives may be adapted to account for sea-level rise, but at this point it is too early to speculate further about design.
As a co-sponsor of the study, the states of New York and New Jersey must endorse an alternative in order for it to move forward in the study. So far, Albany has been silent on the subject. But even if New York State were to defeat the Corps’ recommended plan, it’s hard to view that decision as a victory. For one thing, New York City houses the largest urban economy in the world; it is simply too valuable not to save. For another, a veto in the absence of a more effective proposal leaves millions of people at risk.
The Corps’ period of analysis is 50 years from the date of completion, which, depending on the plan that’s selected, concludes between the 2070s and 2090s. Projects typically function longer than their period of analysis, but the question remains: Is it worth investing tens of billions of dollars in a temporary measure that will help shield coastal communities from unpredictable weather events?
Given the improbable conditions that manufactured Hurricane Sandy, it may seem likely that a storm of that magnitude won’t hit the Northeast again, but extreme weather events are expected to increase in coming decades. Indeed, they already have: In 163 years, 12 hurricanes struck New York State; in the last eight years, New York has endured both Hurricane Irene and Hurricane Sandy, not to mention several weather patterns that have resulted in flooding.
Between 1958-2010, the Northeast saw more than a 70 percent increase in precipitation from extremely heavy events — higher than anywhere else in the country. The Department of Environmental Conservation (DEC) predicts that intense downpours are expected to increase, raising the risk of flash floods and erosion. Combined with heat waves and drought, this intense precipitation will make conventional farming even more difficult, and many of the Hudson Valley’s regional economic drivers like winter sports, maple syrup, apple picking, and dairy production will experience “significant adverse effects,” according to the DEC.
As sea levels rise, wastewater infrastructure will flood, leading to more polluted waterways and the spread of pathogen and nitrogen pollution; as saltwater infiltrates the estuary more heavily, communities that rely on the Hudson for drinking water will find their sources increase in salinity.
Heavy precipitation events, exacerbated by higher sea levels, mean coastal flood levels that occur only once per decade will soon occur every one to three years.
By 2050, the number of New York City residents living within the 100-year floodplain will double to 800,000 people. Progressively smaller storms will trigger the proposed storm surge barriers to close more and more frequently — a universally acknowledged fact. And while an open barrier’s impact on the Hudson is debatable, a closed barrier’s is not.
“It’s beyond anything the natural world can adjust to,” says Lipscomb. “It might be the end of the Hudson as we know it.”