What’s Beneath New York City (Bloomberg)

Subterranean cartographers are bringing to light the dark, tangled truths buried under the streets.

Before a single raindrop fell, Alan Leidner knew the waters could rise and throw the city into darkness. On this point, the maps were as clear as a crystal ball. All you had to do was look.

It was 2010, and Leidner was consulting for the government services company Booz Allen Hamilton Inc., contracted by the U.S. Department of Homeland Security to identify potential threats and vulnerabilities in the nation’s critical infrastructure. Leidner was examining a region that included New York and New Jersey. One day he was thinking about the area’s electrical power grid. He consulted some flood projection maps the Federal Emergency Management Agency had prepared. Then he stared at a map of the grid maintained by Consolidated Edison Inc., the region’s power supplier. And it just jumped out at him: The substation at East 13th Street, on the banks of the East River, was smack in the middle of a flood zone.

Leidner voiced his concerns with utilities, hospitals, and other major facilities. “The reaction was mostly, ‘Eh,’ ” he recalls, as we sit in the Tribeca offices of the Fund for the City of New York, where he directs the nonprofit organization’s Center for Geospatial Innovation.

When Hurricane Sandy arrived in 2012, barreling up the Eastern Seaboard and heading straight for New York, the National Oceanic and Atmospheric Administration projected a massive surge in New York Harbor. “I realized it would hit the flood maps that FEMA produced,” Leidner says, “which meant East 13th Street was about to be flooded.” He churned out memos, with maps attached, urging the response community to prepare. Con Ed (as the utility is known) workers hastily constructed barriers around the transformers that connected to buried wire ferrying current for blocks. But when the water breached the river wall and spilled across FDR Drive toward the substation, the barriers weren’t enough.

Leidner called up some images on his laptop: a white-hot nova as the transformers exploded; and in the aftermath, an overhead shot of Manhattan, dark below 34th Street (save for a sliver of light in Battery Park City), a blackout that lasted three days. The damage included the shutdown of NYU Langone Medical Center and Bellevue Hospital—their backup generators failing, Leidner notes, because critical components were located in basements, subject to the same East River flooding that swamped the substation.

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