Planning for the Hundred Year Storm

By Danny Lewis

Imagine the torrential rains from Hurricane Irene and the storm surge of Sandy happening at once. On top of that, sea levels are expected to rise about 31 inches within the next few decades. This is what engineers call “the hundred year storm,” and it’s the benchmark for designing New York’s defenses against future storms. So how do you plan for a storm worse than Hurricane Sandy?

Eymund Diegle is an advocate for daylighting streams, a process where historic creeks are dug up and reintegrated into the city streets.

By trade, he’s an urban planner, but he’s also a history buff. Diegle knows every inch of the Gowanus, including the location of every stream that ran through this area in the mid-19th century. One of them ran just a block west of the canal, and after more than a hundred years buried deep beneath the concrete, Diegle found it.

These days it’s not so much a stream as it is a trickle of water bubbling out from the side of a sewer grate. But back in the 18th century it was known as Denton’s spring, and it provided a nearby mill with clean water.

“You can see it, that is the original drinking water that was used by the slaves and millers in 1650,” Diegle said. “And if the apocalypse ever comes, just remember that spot because that’s where everyone’s going to be crowding to get their buckets of water.”

Unfortunately for local survivalists, a few months ago what was left of Denton’s spring was blocked off when the city dug up the street for a new drain pipe. But there are other historic streams sneaking into the canal. There’s one by the First Street Basin; another, Vechte’s Brook, travels almost a mile underground from Prospect Park to the Gowanus, where it empties out right next to a Whole Foods.

Just below New York’s streets is an entire network of underground streams. Back in the 1850’s, when the city was a fraction of the size and Brooklyn was still mostly farmland, these streams got in the way of the prime real estate next to the newly-built Gowanus Canal. So, engineers buried them, corralled them into the then state-of-the-art underground sewer to make way for the big warehouses and factories that define not just the Gowanus, but most of New York’s waterfronts.

“When people ask me why do we flood, I say you are on a landfilled wetland,” Diegle said. “And when people ask me why is my basement always soggy, it’s because you built on top of an old farm pond.”

What was once an engineering marvel is now a major weak point in the city’s infrastructure. The sewers were built when the best way to keep storm water from flooding the streets was to dump it into the same pipes as raw sewage. These days, those pipes lead to wastewater treatment plants, but those are limited. Even just an inch of rain makes the pipes dump everything – sewage and stormwater alike – straight into the harbor. And during big storms like Sandy, that water could rise right back up from the harbor and into the streets.

“We know we’re gonna flood, we know the water’s gotta go somewhere,” Diegle said. “The question is where do you want it to go?”

Check out some of Diegle’s maps of the buried streams of the Gowanus below.

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