Hurricane Sandy battered NYC 8 years ago. Since then, how has the city shored up against future superstorms? Oyster castles.

An artificial oyster reef in upper Manhattan is part of the ongoing effort to use “green” infrastructure to mitigate rising sea levels and increased flood risks.

NEW YORK CITY — The Sherman Creek shoreline in upper Manhattan, which has seen rapid erosion in recent years, remains an important flood buffer for residents of the Dyckman Houses, a collection of seven 14-story buildings run by the New York City Housing Authority that is home to more than 2,000 people. This low-lying part of the Inwood neighborhood is already prone to flooding, and suffered significant damage when Sherman Creek overflowed at high tide during Hurricane Sandy. 

Residents at the property reported knee-deep flooding in the lobby of the building and even deeper flooding of the surrounding streets. Since the Dyckman Houses were developed on top of the river and Sherman Creek now flows through the building’s sewer pipes, the property’s sewage system is at risk of being destroyed if another storm were to flood the area again.

Many environmentalists argue that green barriers, like oyster reefs, are a better solution because they will grow over time and adapt to the changes in sea levels.

Fortunately for Dyckman House residents, a newly installed oyster reef now spans 500 feet of Inwood’s Sherman Creek wetland. And this is simply the most recent of many coastal restoration projects in the eight years since Hurricane Sandy slammed New York City, adding oysters as a natural barrier to protect waterfront areas from storm surges. Installed by the New York Restoration Project, the reef is the latest effort to keep one of New York’s last stretches of undeveloped shoreline from disappearing, leaving nearby residents vulnerable to extreme flooding. 

Made with oyster castles—interlocking cement blocks that are fitted together like giant Legos—the reef will protect the shoreline from the battery of rough surf by absorbing the shock of the waves and letting smaller amounts of water trickle through to the shore. As the water flows through the castles, sediment is also deposited on the land, which not only protects the shoreline from erosion, but also slowly builds it up over time. 

Two people make

The “oyster castles” are made from interlocking cement blocks which allow small amounts of water to trickle through to the shore.

Ben Hider

“We aren’t only preserving wetlands. We are creating them,” said Jason Smith, NYRP’s Director of Northern Manhattan Parks. “When you rebuild New York’s shoreline to welcome the tides and to deal with storms, you actually can create really beautiful, really healthy, fun, engaging, shorelines.”

Centuries ago, there were an abundance of oyster beds in New York Harbor but the population was decimated through over-harvesting, pollution, and rapid development of the waterfront. Research has shown that increasingly severe storm damage has a direct relationship to the loss of these oyster reefs. A 2016 study by the University of Massachusetts, Amherst, found there has been as much as a 200 percent increase in wave energy in the harbor in recent decades. 

But the tides are turning.

Soon after the Sherman Creek reef installation was finished in July, it was colonized by oysters that seeded themselves naturally. The creek already had a sizable population of oysters that grew from an oyster garden started in 2014 by Friends of Sherman Creek Conservancy, a volunteer group that helps maintain Sherman Creek Park. Middle schoolers from upper Manhattan and the Bronx worked with director Obed Fulcar to care for four oyster cages that were acquired through a Billion Oyster Project research station program. Knowing that most of the Dyckman-207th Street area is classified as a flood zone, Fulcar wanted to teach his student volunteers the importance of installing natural defenses against future superstorms, known as “green” infrastructure, or green barriers. 

A man building a green barrier oyster reef. December 2020

New York City’s shift to green infrastructure began in 2013 with the launch of the Rebuild by Design competition, developed by President Obama’s Hurricane Sandy Taskforce.

Ben Hider

“Building green barriers is very cost-effective and is a great way to use nature to prevent flooding,” said Fulcar. 

More traditional solutions to protect against flooding, like seawalls, can cost millions of dollars to build, and risk becoming obsolete as sea levels continue to rise. Many environmentalists argue that green barriers, like oyster reefs, are a better solution because they will grow over time and adapt to the changes in sea levels. According to a 2015 report by The Nature Conservancy, protections against flooding that combine both green and “gray” infrastructure are more cost-effective and have the added benefits of creating functional green spaces and more biodiverse ecosystems. Using Howard Beach in Queens as a case study, the report estimates that hybrid infrastructures that include features like oyster reefs could save more than $200 million in damages during a storm event like Hurricane Sandy. Green coastal defenses also offer protection against multiple effects of the climate crisis, such as water pollution and dangerous levels of carbon emissions. 

Features like oyster reefs could save more than $200 million in damages during a storm event like Hurricane Sandy.

While the oyster reefs offer a buffer along the shoreline, the oysters themselves are also hard at work filtering nitrogen out of the water. As flooding worsens with climate change, excess nitrogen is deposited in the water through overflow of raw sewage. As climate change causes stronger storms and heavier rain events, more and more sewage flows into the city’s waterways. Adult oysters can filter as much as 50 gallons of water per day, absorbing the excess nitrogen as they grow and feed. Also, as the reef presents the erosion of marshes, these environments are naturally able to sequester more carbon from the atmosphere, which is stored in the soil of growing wetlands. 

Wild oysters growing on a cement block. December 2020

Chester Zarnoch

Wild oysters that seeded at the Sherman Creek reef installation in July.

New York City’s shift to green infrastructure began in 2013 with the launch of the Rebuild by Design competition, developed by President Obama’s Hurricane Sandy Taskforce. One of the winning projects was the Living Breakwaters initiative, which was awarded $60 million to build a green barrier off the southern shore of Staten Island. That project will include an oyster reef, which is expected to be completely installed by 2021. In 2022, the Billion Oyster Project will begin seeding oysters there, according to director of restoration Katie Mosher. 

In New Jersey’s Sandy Hook Bay, an oyster reef barrier was installed by Naval Weapons Station Earle in 2016. By 2017, baby oysters were found to be growing naturally, and in 2019 the naval base added one million more oysters to the reef. At the mouth of the Bronx River, Billion Oyster Project has helped to build the city’s largest oyster reef with 15 million live oysters. 

As New York continues to expand its efforts to use oysters as a natural protection against storm surges, Mosher believes that the most important component of a successful green barrier is the monitoring and care-taking that happens after the oysters are seeded. 

“It’s never one and done,” she said. “You can’t put [oysters] in the water and walk away from them.”

Carmen Russo is a freelance food writer with work in publications including The Interlude, Wine4Food, Slate, and Saveur. She also writes features for a newspaper in her home state of Rhode Island and is a passionate home cook.