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Designing Reef Structures for the Hudson River

June 27, 2018

As we work toward our goal of restoring 1 billion oysters to NY Harbor, designing and redesigning the underwater structures that encourage oyster reef habitat is integral.

This week Billion Oyster Project sent 422 oyster reef structures from our headquarters on Governors Island, where they were designed, welded, and assembled, to a staging area where they await installation into the Hudson River. Once in the Hudson, these oyster reef structures will combine to create the largest reef system in Billion Oyster Project history—covering more than 5 acres of the river.

Let’s take a closer look at the gabion reef structures deployed in the project and how they’ve evolved from conception to today.

The Hudson reefs are part of a joint project managed by the NYS Thruway Authority, to restore wild oyster habitat accidentally displaced in construction of the Governor Mario M. Cuomo (formerly Tappan Zee) Bridge. The reef is also expected to create healthy marine habitat for years to come.

Billion Oyster Project was selected by the NYS Thruway Authority to construct the gabions. AKRF, Inc, is project and engineering lead, and the Hudson River Foundation and the University of New Hampshire are research partners.

DESIGNING FOR DEEP WATERS

Different reef projects require different materials. For the Hudson reefs system, it was important to consider the fact that these waters are deep and fast-moving. Pictured below, the steel gabion structures provide a strong, current-resistant 3D environment that facilities reefing. Since this project is geared toward wild oysters already in the water, note that shells are empty and will provide homes for wild oyster babies (larvae).

PHASE 1

The original gabion deployed in 2015 was designed by Pete Malinowski, New York Harbor School Ocean Engineering instructor Rick Lee, and Harbor School student Marisol, and constructed by Harbor School Marine Systems Technology instructor Clarke Dennis. While the structure effectively prevented oysters from sinking into the mud (a common cause of mortality in murky waters), we found that it could be improved to serve more oysters per foot.

PHASE 2

During the summer of 2017, the Billion Oyster Project initiated a re-design of the reef gabions, with the goal of providing more space on the structure where larvae could set and grow. Ocean Engineering and Marine Systems Technology students from New York Harbor School collaborated with Billion Oyster Project to consider various configurations of materials and submit a proposal to the Thruway Authority.

The main modifications were:

  • A hollow column was added to the middle of the structure, maximizing surface area available to oysters and other animals. This is important for three reasons: (1) Oysters will grow on all available outer surfaces (2) We have seen that baby oysters (larvae) swim only 4–5 inches into shells as they’re seeking a shell to attach to (3) One of the profound benefits of reefs is the 3D habitat that they create. More surface area means more habitat for oysters and for other marine species.
  • A full-unit steel mesh enclosure replaces eight inner cubes, which were held in place with zip ties that sometimes came loose and shifted. Note that the mesh (galvanized steel) holds the shells in, and outer (raw) steel is for stability and ease of lifting and moving the structures.
  • The original design used a PVC-coated wire mesh insert. Within three years time, the oysters had reefed up around this material, growing right through the 1” x 1” openings. In an attempt to reduce the amount of unnatural materials added to NY Harbor, we proposed a switch to uncoated steel mesh, which over several years will break down without adding pollutants to the water. (And in the long run, the oysters will cement together and the mesh will no longer be needed to maintain the structure of the reef.)

The Oyster Restoration Workgroup approved designs in 2017, despite the small increase in cost associated with omitting PVC.

The average weight of each unit is 175 pounds and requires 2,073 cubic feet of shell.

LOOKING FORWARD

Harbor School students took a leadership role in welding the gabion reef structures, with generous guidance and support from Harbor School staff. Hundreds of volunteers assembled wire mesh inserts and filled gabions with shells donated from 70+ NYC restaurants. Governors Island hosted our build, and our neighbors at Earth Matter partnered with us to fill the gabions with shell and move them to the trucks for transport to the pier.

We are so grateful to all who made our participation in this project possible. Explore photos of the process.

Reef structures enter the water in August.

Volunteer to help us restore more reefs and habitat to NY Harbor?