As threats from major storms increase, authorities are proposing surge barriers to protect New York Harbor. Some ecologists are concerned these giant barriers could have serious consequences for the Hudson, now hailed for its much-heralded recovery, and for other area waters.

On a sunny afternoon, John Lipscomb steered the 22-foot vessel Ian Fletcher past the rip-rapped, industrialized shoreline of South Brooklyn and into the vastness of New York Harbor, where the Hudson River meets the sea. The towers of Lower Manhattan glittered to the north, and the Statue of Liberty rose off our bow. Lipscomb — vice president for advocacy for Riverkeeper, a non-profit — let off the throttle, and we paused to take in both the incongruities and the splendors of the scene. Then our thoughts turned to the river. Not two months earlier, Lipscomb told me, American Rivers had named the Hudson the second most endangered waterway in the nation. It wasn’t pollution that put the river on the conservation group’s 2019 watchlist, though parts of it are, in fact, polluted. Nor was the river particularly imperiled by diversions or urban sprawl, like others on the list. For the first time in its history, American Rivers had singled out a waterway solely on the possibility that massive in-river storm surge barriers could rise in its lower reaches, representing an existential threat to a river in the midst of much-heralded ecological recovery. Plans to build barriers in New York Harbor were set in motion by Superstorm Sandy, which in 2012 barreled up the East Coast, killing 72 people in the Mid-Atlantic and Northeast and causing $65 billion in damage. To protect the metro area’s people and property from future Sandys, the U.S. Army Corps of Engineers has devised five possible schemes for erecting walls to hold back the sea during future catastrophic storms. But environmental advocates say such storm surge barriers will do nothing to shield against expected sea level rise from climate change and — judging by the impact of barriers elsewhere — may even destroy the ecological integrity of harbors they’re meant to protect.

The most extreme of the proposed alternatives is a five-mile-long barrier that stretches from New Jersey to Long Island.

Bracing against the wake of a passing ferry, Lipscomb unfurled a harbor map and showed me where the Army Corps proposes to build. He started with the most extreme of its proposed alternatives: a five-mile-long concrete and steel barrier that stretches from New Jersey’s Sandy Hook to Long Island’s Rockaway Peninsula. This outer harbor barrier, which could potentially be topped with a multi-lane toll road, would have 300-foot-wide lift gates and two pairs of curved gates that pivot together to form a wall that rises 30 feet above the sea’s surface. “And don’t forget there’s 10 miles of shoreline fortifications attached to each end of the barrier,” Lipscomb said. A second giant barrier would close off the western outlet of Long Island Sound, where it meets the East River estuary. Three other design alternatives call for combinations of shorter barriers, up to eight of them, across Hudson and East River tributaries and bays, in conjunction with shoreline fortifications, including levies, restored wetlands, vegetated berms, and dunes. A fifth alternative employs only such shore-based measures, many of which are already being built in vulnerable neighborhoods. Lipscomb said he believes those smaller-scale measures are the only thing that will protect the city from sea level rise as the climate warms.

The most extensive U.S. Army Corps of Engineers proposal involves building a five-mile-long barrier across New York Harbor and shoreline fortifications. U.S. ACE/Yale Environment 360

Public response to the Army Corps’ proposals has been heated. In public meetings and comments, constituents ask if the tall barriers will cause flooding in adjacent but unprotected areas. Will they impede navigation? Some believe the more than $118 billion price tag for the outer harbor barrier (for which the federal government would kick in 65 percent) makes it a nonstarter. But respondents’ number-one concern is, by far, the barriers’ environmental impacts. “Think about all the creatures that spawn here or use the estuary as a nursery,” Lipscomb said from his captain’s chair, referring to crabs, lobsters, starfish, bluefish, shad, eel, herring, and striped bass, the Hudson River’s most-celebrated fish. “What’s gonna happen to them?” he asked, shaking his head. “We don’t even know what these barriers are going to look like. They’ve offered no structural diagrams or plans.” The designs in the Corps’ most recent report are merely suggestive. A short conceptual video of the five-mile barrier is willfully vague: gleaming white gates swivel into place from man-made islands, classical music swells as lightning flashes, ocean water piles against the barrier, and the harbor is saved. Researchers at the Stevens Institute of Technology, in New Jersey, are currently modeling physical processes, like how barriers might affect the downriver flow of nutrients and silt and the upriver flow of sand from the Atlantic. They’re also modeling how river salinity, levels of dissolved oxygen, and temperature might change. “A large barrier would have significant impacts on sediment transport, hydraulics, flow patterns, and biological processes,” said Marit Larson, chief of natural resources in New York City’s Department of Parks and Recreation. “We just don’t know how extensive or how disruptive.” Using existing data and information, the Corps is currently studying the environmental impacts of all its conceptual alternatives, comparing them with a “No Action scenario,” according to Bryce Wisemiller, project manager for the Army Corps. But because the agency has neither an established nor an approved method for evaluating or quantifying ecosystem services, like nutrient cycling or water purification, they aren’t being considered.

“My concern is that in 50 years, with sea level rise, the river will be permanently blocked,” says one researcher.

That’s worrisome, said Pete Malinowski, executive director of the Billion Oyster Project, which cultivates oyster reefs in New York Harbor to both filter water and break up wave energy. “Any cost-benefit analysis that does not take into consideration the ecosystem services provided by oyster reefs and other natural systems is inadequate,” he said. The Natural Resources Defense Council has stated that barriers would “strangle” the river, the harbor, and Long Island Sound. George Jackman, an aquatic ecologist and Riverkeeper’s habitat restoration manager, said in-river barriers “would be catastrophic for the Hudson. They’d disconnect harbor species from the rest of the river, and they’d sever river species from the harbor.” Take the American eel, for example. “They have tiny larvae,” Jackman said. “They’ve been programmed over the eons to go upstream. Will they turn around when they hit that barrier? Will they back up? No one knows.” (Fisheries biologists have found that eels confronted by large, permanent dams are easily picked off by predators.) Or consider shad, Jackman continued. “Their eggs are semi-buoyant, and they need flowing water, or they’ll sink and suffocate. When the gates are shut, will we lose an entire spawning season?” Bigger creatures, like dolphins, seals and whales — which since 2011 have been regularly sighted feeding on menhaden in lower New York Bay — will also be affected. But wouldn’t the gates be closed only for a very short time, I asked. Wouldn’t a whale just wait? “They’re not gonna close those barriers just once a year!” Jackman said. “As sea level rises, they’ll be closed more frequently because smaller storms, and spring tides [which occur twice a month] will lead to major flooding.” According to mid-range projections of the New York City Panel on Climate Change, sea level in New York Harbor will rise 1 to nearly 2 feet by the 2050s, and up to 4 feet by the end of the century. If the Antarctic ice sheet melts, that upper number jumps to more than 9 feet in 2100. “We may not get another Sandy,” Lipscomb told me, “but sea level rise will happen.” And those living close to the shore will feel the tidal results twice a day.

John Lipscomb, of the Riverkeeper conservation group, aboard the Ian Fletcher. Riverkeeper

Closures could last seven days, once or twice a year, Jackman said. Meanwhile, river water would pile up behind the barrier, potentially flooding upstream communities. And then there’s all the stuff that streamflow and tides regularly wash out to sea: trash and sewage, treated and — when plants reach capacity — raw. Build the barriers, either across the harbor or on smaller waterways, and all those contaminants would be trapped. That is, until they are released in one great swoosh. Referring to the Gowanus Canal, a Brooklyn waterway that received more than 363 million gallons of untreated sewage last year from combined sewer overflows, Andrea Parker, executive director of the Gowanus Canal Conservancy, said, “The last thing we need is an impediment to flow at the mouth of the canal.” The bigger barriers’ permanent sills also concern environmental advocates. Fixed to the seafloor, these concrete bunkers serve to level the span between tower structures and may be up to 25-feet tall (again, plans are conceptual at this stage). In comments to the Army Corps, Riverkeeper noted that any in-water infrastructure — whether gates, sills, towers, pillars, or stanchions — would slow water and refract wave and tidal energy, reducing the amount of oxygen delivered to the estuary and perhaps contributing to more frequent algal blooms. The barriers could affect globally rare salt marshes 150 miles up the Hudson River. Philip Orton, an oceanographic researcher at the Stevens Institute of Technology, acknowledged that sills will interfere with the movement of sediment and salt, but he said that a small amount of obstruction — say, 20 percent of flow — would have only an insignificant effect on the estuary. That is, if the barriers weren’t raised frequently. “My concern,” Orton added, “is that in 50 years, with sea level rise, the river will be permanently blocked, and that’s a true danger.”

A rendering of a proposed surge barrier near the Verrazano Narrows Bridge, between Staten Island and Brooklyn. U.S. Army Corps of Engineers

To muster their case against barriers, opponents have been considering other in-water storm-surge gates. Relatively small barriers in Stamford, Connecticut, and Providence, Rhode Island, have protected those East Coast cities from big storms for nearly six decades, but they were built in an era of less environmental concern and scientists lack baseline data on their impacts. London’s Thames Barrier, which lies more than 30 miles upriver from the coast and thus makes an imperfect comparison, has both eroded and deposited sediment in salt marshes, intertidal mudflats, and freshwater wetlands. A government monitoring report on the barrier’s impacts predicts that 2,965 acres will be required to replace lost habitat over the life of the barrier.

Venice’s MOSE barrier — a system of yellow-painted, interlocked steel gates that will be hinged to the seafloor until a storm triggers their uplift — won’t be operational until at least 2022 (it has been delayed by cost overruns and environmental concerns). But studies show that the project, by constricting flow through inlets to the city’s three lagoons, will likely change sediment deposition patterns and impact the habitat of bottom-dwelling creatures. A year-long study determined, in 2018, that a proposed Boston Harbor barrier would, as closures became more frequent, degrade water quality, destabilize shorelines, lower dissolved oxygen levels, decrease benthic biodiversity, and turn some sandy beaches into mudflats. The study’s conclusion? Instead, build shore-based defenses — which include restored marshes, deployable floodwalls, elevated waterfront parks, plazas, berms, and wetland terraces. The barrier most frequently tendered as a comparison with a potential New York Harbor barrier is the Eastern Scheldt Dam, the largest of the Netherland’s massive Delta Works, which thwart North Sea surges. Completed 33 years ago, the 5.6-mile-long barrier consists of 65 concrete pillars separated by retractable vertical steel gates. The Eastern Scheldt was at first considered a great success because it retained about 70 percent of its tides (other Delta projects completely block the sea). But scientists have discovered that its structures have profoundly affected the tidal basin. According to a 2004 report commissioned by the Worldwide Fund for Nature, tidal range in the estuary decreased by 13 percent, its salt marshes experienced more erosion and less sedimentation, and estuarian life declined.

New York “should be leading the charge in thinking about how dense urban neighborhoods adapt to have wet feet,” says an activist.

Shellfish production shifted to another area in the basin, said Arjan Berkhuysen, managing director of the World Fish Migration Foundation, and phytoplankton species changed in composition, abundance, and seasonality. “Lessons learned from the Dutch should be taken into account when planning major changes in river systems like the Hudson,” Berkhuysen wrote to the Army Corps regarding its proposed barriers. “There is no need to make the same mistake.” If barriers aren’t the best way to protect lives and property, what is? The Dutch now promote projects that create minimal impact on nature — levees and dunes, for example, that guard against both storm surge and sea level rise. (In the Netherlands, these dunes can be more than a mile wide, and more than 50 feet high.) New York City has already started down this path. Off the southern tip of Staten Island, a “living breakwater” of submerged rubble will soon rise as far as 1,800 feet from shore. Seeded with oysters and other shellfish, the rough-surfaced mounds will reduce wave energy, which will in turn limit erosion and flood damage. Along the island’s eastern shore, a 5.3-mile-long, $615 million seawall that rises to 20 feet above sea level, with vegetated slopes and a promenade on top, is under construction. And the Parks Department is restoring and replanting miles of wetlands and salt marshes in low-lying areas of Brooklyn and Queens: Research shows that more stems create more friction, the better to scrub energy from surges. Such projects are relatively quick to plan and build and are far cheaper than in-river infrastructure (the Army Corps estimates that doing only shore-based measures would cost $14.8 billion and take nine years to complete); in addition, they can be adapted as sea levels rise or land-use shifts and can start protecting people and property well before every component is in place. Conversely, a cross-harbor barrier can’t stop a storm surge until it’s completed. “That’s twenty-five hurricane seasons after construction starts,” Lipscomb said.

Surveying damage from Hurricane Sandy in October 2012 in the Rockaway section of Queens, New York. Spencer Platt/Getty Images

Malcolm Bowman, a professor of physical oceanography at Stony Brook University who studies and promotes large storm-surge barriers, dismisses the doomsday predictions. “Yes, there are some legitimate concerns about the environment,” he said, “but they can be minimized with good design. We need to find that sweet spot between protecting people and infrastructure and maintaining environmental integrity.” Of near-shore, nature-based measures, he said, “They make sense if you have a 25-year storm. But if you have a 250-year storm, like Sandy, they’ll be overwhelmed.” Proponents of shore-based measures don’t disagree, but they emphasize other types of storm-surge adaptations: flood-proofing where possible, and elevating buildings and critical infrastructure above the water’s creep. “New York City should be leading the charge in thinking about how dense urban neighborhoods adapt to have wet feet,” said the Gowanus Canal Conservancy’s Parker, “because it is impractical and foolhardy to build vertical protection on every settled shoreline across the globe.” After showing me where a barrier would cross the Ambrose Channel, should the Army Corps select its Alternative 3A, Lipscomb motored up the East River and turned the Ian Fletcher into Newtown Creek, an industrialized waterway that separates Brooklyn from Queens, reeks of coal tar and sewage, and is slated for a Superfund cleanup. Parking lots, scrap yards, and warehouses line much of the creek’s 11-mile shoreline, but very few of these businesses depend on the waterway. Lipscomb slowed the boat and uttered a characteristically blunt opinion. “No one is going to build sea walls here,” he said. It’s too expensive, and property values are too low. “What we advocate here is a mix of shore-based measures and managed retreat” — a.k.a., moving out of harm’s way. Either the state would buy out tenants along the creek (as it has in Staten Island and Rockaway neighborhoods demolished by Sandy), or the saltwater itself would drive tenants to higher ground. The creek, in this vision, could return to a more natural state, with trees, marshes, and bi-level esplanades that can flood and drain, taking the place of today’s rotting bulkheads.

No one knows where the Army Corps studies on surge barriers will ultimately land, but doing nothing is extremely unlikely.

We putter past a natural gas plant: That’s not going anywhere, Lipscomb said. “You protect that with a wall.” Wastewater treatment plants on the shoreline? “Protect them like medieval castles. You get an engineer and an economist together and fortify them against surge with 25-foot walls.” Other buildings can float, as a five-story prison barge near Ryker’s Island and a series of gas “peaker” plants, which only run at peak hours of demand, along the East River already do. Early next year, the Army Corps expects to winnow its alternatives to one and publish its draft Tier 1 environmental impact study, which will be followed by a more in-depth analysis after the Corps submits a final report to Congress for funding in 2022. No one knows where the studies will ultimately land, but doing nothing is extremely unlikely. “[B]ased on our damage analyses to date,” Wisemiller said, “we do have considerable concern for what could/will happen should we not take further actions (whatever they may be) to better prepare for the coastal storm risks that are facing the region as exacerbated by further sea level rise and climate change into the future.”