New York City saw it coming. In May, in the kind of clarifying document that invariably gets noticed when it’s too late, the city mapped out the sort of devastation that Hurricane Ida would bring just a few months later.

The message of the New York City Stormwater Resiliency Plan is that, weatherwise, the scale of everything has changed. The city’s current infrastructure — its roads, subway tunnels, sewer systems, storm drains — is not built to withstand the climate-related ravages to come. As a result, the report states, capital investments “provide diminishing returns, as it becomes more and more challenging to treat the large volumes of stormwater released in extreme events.”

Ida put an exclamation point on realities that New York was already grappling with. Like other parts of the world, the report notes, the city is confronting not just calamitous extreme events like the inundations of Ida. It’s the drip, drip of “the chronic worsening of average conditions.”

That beautifully concise yet elastic phrase sounds like the title of a Russian novel. Our current world was constructed to manage one kind of average, with extremes appropriately measured by their distances from that mean. But the chronic worsening of average conditions means that the extremes are growing ever more distant and ever more dangerous.

For example: The city’s sewage system is geared to handle about 1.75 inches of rain per hour. On Sept. 1, between 8:51 and 9:51 p.m., Ida brought down 3.15 inches in Central Park. (New Jersey topped the Big Apple’s record, with Newark registering 3.24 inches of rainfall between 8 and 9 p.m.)

Even on dry days, subterranean New York is a soggy, messy place, with leaking sewer pipes and creaky water mains. Yet even if all had worked perfectly on Sept. 1 — if every storm drain had been clear and every pipe in New York City’s 7,400-mile sewer system had been free of obstruction — the city simply had no way to rid itself of so much water. And since about 60% of the city’s pipes combine stormwater runoff with sewage, it’s not just water that backs up when capacity is surpassed.

“Rainfall rates were really extraordinary and far exceeded the capacity of the system,” Department of Environmental Protection Commissioner Vincent Sapienza said at a briefing after the storm. “Anything over two inches an hour we’re going to have trouble with.”

According to the New York City Panel on Climate Change, by the end of the 21st century, the city could experience as much as 25% more annual rainfall. The number of days marked by extreme rain would also markedly increase.

New York will undoubtedly have to spend billions to deal with water. But it may not be able to buy its way out of trouble without also changing its ways. Since the 1960s, the city has spent about $45 billion on sewer infrastructure. Ida overwhelmed it in minutes. In a post-Ida report, the city noted that “recalibrating our sewers for storms like Ida would require a decades-long, potentially $100-billion investment.” The estimate’s probably realistic: The city is currently upgrading the sewer system in a single neighborhood in Queens at a cost of more than $2 billion.

New Yorkers are utterly surrounded by water, of course, but they rarely needed to give that fact much thought. Until recently.

Sandy, the super storm that hit the city in 2012, resulted in 44 deaths, displaced thousands and brought an estimated $19 billion in damages and economic loss to New York City. Ida was an entirely different animal — its flooding was largely a product of record rainfall, not a storm surge. The city was swamped by fresh water from the sky, not seas slamming the coast.

A lingering question is what would happen to New York if the next extreme event combined the surging seas of Sandy with the torrential downpour of Ida. As sea rise continues, it’s not hard to imagine a worst-case scenario at some point this century. With rain filling the streets and pipes, and surging high tides blocking the outflow of water from the city into rivers and bays, New York could resemble a very dirty Atlantis.

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Eric Sanderson, an ecologist at the Wildlife Conservation Society, studies the flow of water in New York by analyzing how it flowed before there was a New York. His home office on City Island in the Bronx is filled with books on New York City history, geography, topography, geology and hydrology. The three computer screens on his desk offer a seemingly boundless array of coordinated data and visualizations of streams, ponds, brooks, creeks, rivers and marshes that governed the city before the Dutch and English began reworking the grounds.

Sanderson and a team of collaborators have created a database consisting of hundreds of years of city maps and text descriptions. Using historical reference points and geospatial technology, Sanderson overlays the concrete and macadam of New York’s present atop the city’s earthen and aquatic pre-European past.

“We’ve changed the landscape, we’ve changed the topography, we’ve changed the vegetation,” says Sanderson, who is currently working on an atlas and gazetteer of indigenous New York. “We’ve essentially added stone. When I walk down the street or the sidewalk, I just think of it as a thin layer of rock. You know, rock doesn’t absorb water.”

As he wrote in an opinion column in the New York Times last month, the streams and ponds and marshes of old New York didn’t disappear. They were just driven underground, covered by fill and concrete. Understanding where the water used to be tells us where it still wants to go. “Storm drains,” Sanderson told me, “are basically the engineering replacement for the streams.”

If Ida transformed the Major Deegan Expressway into water, for example, it’s partly because ancient waterways had been turned into the expressway. “Right along where the Major Deegan goes in that part of the Bronx, there used to be a creek, Tibbetts Brook,” Sanderson said.

Tibbetts Brook drains into Van Cortlandt Lake in the Bronx. Decades ago, the lake was reengineered to drain into city sewers. The city’s post-Ida report acknowledges that channeling natural waterways there is probably a bad idea. The practice, the report states, “has reduced sewer capacity that could otherwise be used for neighborhood drainage during a storm — an issue that was made clear during Ida when parts of the Major Deegan Expressway flooded with multiple feet of water.”

Describing the Major Deegan as under “multiple feet of water” doesn’t quite convey the magnificence of the scene. A major expressway running through the city — or according to the old maps, through the Harlem River Valley —was effectively transformed into a river. With 6,300 miles of roads, New York City has an abundant supply of potential rivers.

In his op-ed, Sanderson pointed out that another spectacular flood site, the water gushing through the subway at West 28th Street and Seventh Avenue in Manhattan, happened to be smack “in the middle of a wetland clearly shown on 18th-century maps.” In his book “Mannahatta,” which relies on history and technology to recreate the Manhattan of the Lenape Indians before Henry Hudson’s 1609 visit, Sanderson writes that Manhattan’s waterways once included 66 miles of streams, more than 300 springs and 21 ponds and salt pools.

Manhattan’s streams have left their mark on the organization of city streets, especially in lower Manhattan. Broad Street, as is often written about, owes its breadth to the Dutch canal that once occupied the space, but before that, in its place was a small stream that wound through low marshy ground, fed by another branch that flowed along the line of Beaver Street (named for the beavers who called it home). Maiden Lane follows the former path of a small spring-fed stream that drained between two hills to the East River. Canal Street reminds us of the canal dug along the line of the outlet stream to drain the Collect Pond and salt meadows that ran to the Hudson River shore. A bridge over the stream at Broadway and Canal Street was the original “Kissing Bridge” of Manhattan. Minetta Street in Greenwich Village was first a winding path alongside a stream called Minetta Water; Minetta Lane was named for the footbridge that crossed the stream. 

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Other coastal cities, such as Norfolk, Virginia, and Charleston, South Carolina, have been resorting to old maps in an effort to understand how to manage the threat of sea rise. They’ve found that their city flood maps hearken back to filled-in creeks and wetlands. “We had the hubris to think that we could engineer our way into a better city and we ended up making it worse for future generations,” George Homewood, Norfolk’s director of city planning, told Smithsonian Magazine.

Norfolk is one of several U.S. cities that has participated in “Dutch Dialogues,” an analysis and planning process inspired by the water management expertise of The Netherlands, where half the population lives on land that’s below sea level. Flood control is a way of life in much of the Netherlands, encompassing vast engineering projects such as the sea gate at the port of Rotterdam and adaptations of everyday space such as the sunken playgrounds that become emergency reservoirs during floods.

New York has taken small steps in the direction of a more comprehensive approach to water. The city lauds the construction in Staten Island of more than 70 “bluebelts,” which it defines as “ecologically rich and cost-effective drainage systems that handle runoff precipitation.” It cites 11,000 “curbside rain gardens” and “infiltration basins,” along with innovative stormwater capture and green infrastructure projects. More trees, porous roadways that allow water to seep into the ground and gardens in lieu of concrete are all landmarks of a future cityscape.

But just as Sandy delivered bad news about the high price of lost marshlands, Ida put the city’s drainage efforts in stark relief.

As part of the New York City Climate Mobilization Act, passed in 2019, the city requires new and renovated rooftops to incorporate sustainable roofing. As of 2019, there were only 736 green roofs covering 60 acres of rooftop. Rotterdam, a city with a tiny fraction of New York’s population, has more than 100 acres of green roofs to absorb rainfall and help manage drainage.

In Eric Sanderson’s neighborhood on City Island, it takes just minutes to walk from the narrow beach on one side of the island to a nascent, postage-stamp-sized marsh on the other. After crossing City Island Avenue, which once marked the front edge of the marsh, we walked on the sidewalk past the public school that Sanderson’s son once attended. “This was marsh,” he said, looking toward the school. “Then it was a shipyard. They made it a big industrial place.”

Behind the school, a grubby patch of smooth cordgrass has gained a perch on the waterfront by the island’s harbor. A local community group has sponsored this mini-marsh’s revival. About the size of a Bronx residential lot, it won’t do much to stop floodwaters, whether they arrive from the sea or the sky. But it’s better than asphalt. It’s a start.

(Corrects name of City Island Avenue in penultimate paragraph.)

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

Francis Wilkinson writes about U.S. politics and domestic policy for Bloomberg Opinion. He was previously executive editor of the Week, a writer for Rolling Stone, a communications consultant and a political media strategist.

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