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Civil Engineering Magazine THE MAGAZINE OF THE AMERICAN SOCIETY OF CIVIL ENGINEERS

Coney Island Creek Redesigned for Resiliency and Recreation

By Kevin Wilcox

A new plan would harden shorelines, create a tidal barrier, and establish parks connected to walking trails.

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The plan proposes hardened elevated walkways to provide flood protection, the edges softened by such green features as a vegetated shoreline or wetlands. © Arcadis/Mathews Nielsen Landscape Architects

October 18, 2016—When Hurricane Sandy struck the New York coastline on October 29, 2012, Coney Island Creek became a "backdoor" for storm surge, pushing floodwaters into low-lying portions of two boroughs—with devastating consequences.

In the aftermath, New York City's mayor at the time, Michael Bloomberg, and the city government created the Special Initiative for Rebuilding and Resiliency to examine the storm's effects throughout the city and institute effective mid- and long-term resiliency measures. One of the initiatives that came from those efforts was a significant reworking of Coney Island Creek.

"The creek was actually the primary source of flooding and inundation for Gravesend, which is the neighborhood to the north, and Coney Island, which is the neighborhood to the south," explains Roni Deitz, the climate risk and coastal resiliency project leader at the global design and consultancy firm Arcadis. "You have low edges along the shoreline and low-lying topography that contributed to the backdoor flooding."

The New York City Economic Development Corporation, in partnership with the Mayor's Office of Recovery and Resiliency, commissioned Arcadis to prepare a comprehensive study of Coney Island Creek and the surrounding areas and develop a suite of feasible alternatives that would address the dangers posed by hurricanes and climate change. Deitz, the project manager for that effort, says that one of the primary challenges of the project was embracing the vast size of the area involved. "The reason for that is the region is extremely low lying as a whole," she says. "You're not going to find elevations high enough to tie into to achieve a 100-year flood risk reduction."

Because a large portion of the area is located at an average elevation of just 6 to 8 ft above sea level, the team found it was necessary to extend hardened berms and elevated trails north into Brooklyn and east into southern Queens to obtain sufficient elevations for protecting the area, Deitz explains.

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One concept for the creek and its surroundings involves elevated walkways (A), tidal salt marshes (B), an outdoor classroom (C), and fishing piers (E). Work on enhancing the habitat of the shoreline of Calvert Vaux Park (D) is continuing, and similar plans for the opposite shore (F) have been proposed. An operable barrier, probably comprising tainter or vertical lift gates (G), would be closed before a major storm and reopened as soon as possible afterward. © Arcadis/Mathews Nielsen Landscape Architects

The team began by reaching out to the community to understand its priorities, develop key questions that could guide its research, and draw on local expertise. From there, the technical analyses began with a shoreline inspection via boats. Experts charted outfalls, sediment conditions, soil conditions, water quality, drainage patterns, and ecological diversity. Desktop modeling also was employed to examine how storm surge currently affects the area and the water quality of the stream.

"From there, we had what we like to refer to as our kit of parts—a tool kit [with which] we could start to [create] a flood protection strategy for Coney Island," Deitz says. The plan included such hardened infrastructure as floodwalls, as well as such "green" infrastructure as a living shoreline or wetlands, he says. "And we tried to think—almost in a puzzlelike fashion—of how these different opportunities and measures could form a system."

One of the concept plans includes an in-water tidal barrier, hardened elevated trails, and walking berms along the creek banks, as well as elements designed to enhance natural habitats in the creek that complement recent efforts by the city to improve water quality.

A central element of the plan is a tidal barrier near Calvert Vaux Park. By moving the barrier up from the mouth of the creek somewhat, the team was able to reduce its size and suggest a site that would be less ecologically vulnerable than an earlier concept that resulted from efforts in the Special Initiative for Rebuilding and Resiliency. The barrier, which would probably comprise tainter or vertical lift gates, would be closed approximately 24 hours before a major storm and reopened as soon as possible afterward.

"It doesn't need to be closed for a long time. Once that huge push of surge comes, that's really when you want the gate to close," Deitz says. "And then as soon as the surge begins to recede, you want to reopen again so that any rainwater subsequently entering the creek has a place to drain. During nonstorm events, the tidal barrier would be open to allow for tidal circulation, navigation, and minimal disturbance to the aquatic habitat."

The team performed significant technical analyses, consulting guidelines from the Federal Emergency Management Agency to understand how waves would interact with the barrier, how much wave overtopping would be acceptable, and what sea level projections indicate about future conditions.

The plan Arcadis developed goes far beyond traditional resiliency, however. The people in the neighborhoods affected by the creek care deeply about their communities and the region's future. Through extensive community outreach and by working with city leaders, the team developed a list of guiding principles to develop a solution that the communities approved.

"We understood that we are looking at a 100-year flood, plus sea level rise, [as] a level of protection," Deitz says. "We want to improve open spaces and community connections through our design. We want to maintain or improve water quality of the creek through whatever investment is put in. [And] we want to preserve the views of the waterfront.

"We were very fortunate that right along the Creek are parks—Kaiser Park on the south side, Six Diamonds Park and Calvert Vaux Park on the north side—that present great opportunities for investment and the integration of resilient infrastructure," Deitz adds. "We thought, 'How do you integrate flood protection into this park space? Could a tidal barrier also serve as a community gateway to bring residents from the south side to these underutilized parks on the north side?'"

So the design embraces dual-purpose flood control infrastructure and includes walking trails that connect the parks. The infrastructure will also include sloped shoreline areas to encourage plant life and habitat creation.

Arcadis began work on the study in the fall of 2014 and completed it in approximately 18 months. The city has committed more than $30 million to realizing the initial phases of the long-term plan for a more resilient southern Brooklyn; however, such long-term investments as the tidal barrier were not included in the initial funding. But the U.S. Army Corps of Engineers, which has been working diligently in the flood recovery effort and resiliency planning, has decided to include that work in a project that it is planning for boosting the resiliency of Jamaica Bay, located to the west of Coney Island Creek. "Through meetings in coordination with the U.S. Army Corps of Engineers, . . . [we] basically give it a home in a way that it would continue to advance," Deitz says.


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