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Why New York City Keeps Flooding

A 2021 report from the city called “The New Normal” estimated that “recalibrating our sewers for storms like Ida” would take decades and cost $100 billion. Upgrading the system in Southeast Queens alone cost $2 billion, it noted.

In the meantime, the city has been working with federal officials to create some places for the excess water to go, other than straight into the sewer system, and potentially into the waterways, said Ben Furnas, a former director of the Mayor’s Office of Climate and Sustainability who is now executive director of the 2030 Project at Cornell University.

“There are lots of strategies to make a place for the water to go and be stored so it doesn’t end up tipping off into the creeks or canals,” Mr. Furnas said. He said significant investments had been made in “gray infrastructure” like large holding tanks and “green infrastructure” like gardens set in sidewalks that can absorb some of the rainwater.

“It’s a really challenging problem to solve because we have this legacy infrastructure system and its capacity is being exceeded,” said Franco Montalto, a flooding expert and engineer. “You can either manage excess water underground or you manage it on the surface.”

Dr. Montalto cited an initiative in Copenhagen, where officials redesigned streets to hold water temporarily. Certain intersections, he explained, are depressed or sunken, to draw water away from neighborhoods and allow it to pool at a depth that is safe for cars to pass through. Eventually, the water runs off into parks and other green spaces.

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