Heatherwick Studio and MNLA bridge structure and botany at Little Island

Natural’s Sorta In It

Heatherwick Studio and MNLA bridge structure and botany at Little Island

New York Harbor, where the mighty Hudson River empties into the Atlantic, is one of the largest natural harbors in the world. It is at the same time a highly engineered environment. Drawing on both these facets—the natural and the man-made—is Little Island, which is transforming a former industrial jetty into idyllic public parkland, at a cost of $250 million.

Situated within Hudson River Park, Little Island rests aloft the remains of Pier 55 on Manhattan’s West Side on hundreds of stepped bulbous concrete piles. When it opens next spring, the hilly landscaped refuge will offer visitors walking trails, a public plaza, and a pair of performance stages, among other recreational spaces. Delineating these uses will be a smorgasbord of native flora, ranging from dozens of tree and shrub species to hundreds of types of grasses and perennials, all nestled atop the giant concrete “tulip pots.”

The London-based design firm Heatherwick Studio was awarded the project in 2013 following a design competition chaired by Barry Diller and Diane von Furstenberg. While the idea of a levitating park was plenty whimsical, the architects showed real concern about disturbing marine life habitats, for which Pier 55 functioned as scaffolding. Working with the New York firm Standard Architects, Heatherwick Studio determined to leave the decayed wooden piles in place, lofting the undulating park over them. The varying heights of the new concrete piles—the tallest reaches 62 feet above the Hudson—should allow sunlight to reach those very habitats.

To fill in the landscaping details of Little Island, Heatherwick Studio tapped local firm MNLA, which had previously designed Piers 25 and 42, as well as the masterplan of Hudson River Park. Still, the topsy-turvy 2.4-acre park presented MNLA with a host of challenges, said founding principal Signe Nielsen. “What consumed the most time and effort—and [was] perhaps the most anxiety-producing—was ensuring that the design conformed to the shifting profile of the piles and the swoop of the concrete pots.”

A diagram of the drainage at little island
MNLA developed an extensive soil and drainage system consisting of a drainage mat, gravel, geofoam, and soil. The load was then analyzed by the structural team at Arup. (Courtesy MNLA)

But any landscape features and the requisite infrastructural supports would place a significant load on the concrete structural system. Anticipating this challenge, Heatherwick Studio and MNLA consulted with collaborator Arup, which used 3D parametric scripts and digital models to calculate whether too much weight was being put on any cluster of columns. For instance, the process helped guide MNLA to select and situate the plantings, which skew toward evergreens to avoid wind loads associated with dense canopies of foliage.

Although they appear to be of one piece, the constituent piles and pots were fabricated by different hands in different places. Engineering firm Mueser Rutledge designed the 267 piles from its New York office, then sent the digital files over to Coastal Precast’s Chesapeake, Virginia, factory for production. Upon fabrication, the piles were delivered by barge to Pier 55 and slowly driven into the bedrock over the better part of a year. (Gaps were left in the installation period to accommodate seasonal fish migration.)

As for the tulip pots (which actually comprise several distinct concrete “petals”), they were fabricated by The Fort Miller Company and two of its subsidiary companies out of Greenwich, New York. Hundreds of unique molds were needed to form the pot modules and scores of steel plates to fasten them together (in groups of four). All the parts were then transported to the Port of Coeymans, just south of Albany, for assembly by marine contractor Weeks Marine and subsequently placed in barges for shipment down the Hudson River.

After the superstructure came together on-site, MNLA moved ahead with plotting the landscaping elements. All that plant life required extensive drainage and soil bedding. MNLA devised a complex system that accounted for the extreme grade changes; rising sequentially from the concrete slab is a ¾-inch drainage mat, followed by an 18-inch layer of gravel, anywhere between 12 inches and 2 feet of geofoam, and, even more dramatically, 18 inches to 6 feet of soil. Downspouts located at the junction of four-pot intervals prevent the park from becoming a pool.

“The evergreens are concentrated on the north and northeast slopes to screen the West Side Highway and nearby Pier 57,” explained Nielsen. “Little Island is angled off the waterfront to both frame views of the Manhattan skyline and the Statue of Liberty and capture greater solar exposure.”

­­­MNLA sourced trees from three separate nurseries for Little Island, which were tagged in the fall and winter of 2019 and planted this past spring and summer. According to Nielsen, each tree was weighed upon delivery to the site and, based on its size—the largest has a 12-foot root diameter and weighs 20,000 pounds—was assigned particular cranes for lifting and insertion. The Hudson is prone to severe winds, especially in winter, and the design and engineering teams countered the risk of uprooted trees by tying the root structures to a mesh of steel cables predrilled into the concrete slab.

“This is by far the best collaborative experience I have had in my career,” said Nielsen. “Every decision derived from continual dialogue, and, designed to account for rising sea levels, I am totally confident it will stay out of harm’s way.”

Architect: Heatherwick Studio
Architect of record: Standard Architects
Landscape architect: MNLA
Construction manager: Hunter Roberts Construction Group
Structural engineer: Arup
Marine contractor: Weeks Marine
Prefabricated concrete fabricators: Mueser Rutledge Consulting Engineers (piles), The Fort Miller Company (tulip pots)