|Image: Scupper 2/HOLD system #2, Flushing Meadows Corona Park|
Today would be a good day to visit the HOLD site in Flushing Meadows Corona Park in Queens. HOLD or Highway Outfall Landscape Detention was designed by dlandstudio to manage runoff from adjacent elevated highways. Two variations on the concept were installed in the park and I saw the pilot projects on an Archtober tour led by Halina Steiner. The three-year experiment was designed to test improvement in water quality. Two highway scuppers (downspouts) have been retrofitted to direct runoff into the swale systems. Unmodified highway scuppers direct flow into drains that outfall to the Flushing Creek. In heavy rain events, water is likely absorbed by surrounding soil as well as flows directly into the creek. (The park is historically a wetland.)
|Image: Modified scupper 1 and HOLD infrastructure (Flushing Creek in background)|
These HOLD treatments are designed for 1" rain events but can handle larger events. Instead of being held for evapotranspiration, runoff will flow through the system faster and any excess water will be funneled into a pipe that empties into the creek. Both treatments are closed so runoff cannot infiltrate the surrounding soil.
|Image: Details of HOLD treatments|
The two treatments at Flushing Meadows differ in size, form, depth, and framing (see above). The plant palette is a common component.
|Image: Scupper 2 outfall pipe|
The fate of these installations will be decided at the end of the experimental phase. If water quality changes are not observed or neither NYC Parks or DOT claims maintenance responsibility for the swales, they will be removed by a contractor. There is a possibility that a local NGO or community group could form a stewardship team. (The swales would have to be modified, too, to open them up for infiltration into the surrounding soil.)
|Image: Typical Section, Henry Hudson Parkway via Marcha Johnson (source)|
The HOLD concept is not the first system to manage highway runoff. Curious as to what seems like a late emergence of this type of green infrastructure, I asked Halina Steiner about precedents. She mentioned the work of landscape architect Marcha Johnson, a NYC Parks employee. In the early 1990s, Ms. Johnson was tasked with designing a bikeway to connect two waterfront parks, the Fort Washington-Riverside Gap.
|Image: Highway Stormwater Filter by Marcha Johnson (source)|
Recognizing the adjacent highway as a site of non-point source pollution, Marcha designed a runoff treatment system: a buried trench with different layers to treat different types of pollutants. The filters were pea gravel, compost, activated charcoal, sand, gravel, and fabric. The system was installed in 1995. There is another highway runoff treatment system in Riverside work designed by Thomas Balsley. Unlike the HOLD system in Flushing Bay, neither of these older systems have been systematically monitored. Ms. Johnson's system has a precedent, too. She pointed to the greenspaces adjacent to the highways constructed during the Robert Moses era. Moses was in charge of both highways and parks. Runoff from highways was dumped into the green landscapes below the city's highways. Grass and soil were the original highway runoff retention and infiltration systems.
During the Archtober tour, there were discussions about the aesthetics of the HOLD installations. The current vegetation profile is low - herbaceous perennials. If the installations are approved beyond the experimental phase, a more storied vegetation profile with shrubs and trees might be installed. Others asked if the installations could assume curvy forms, less angular and linear. Finally, others raised concerns about the curbing around the installations. Is such an engineered system necessary in a park setting? Could the actual landscape of soil and vegetation be modified to treat runoff without the modular, framed aesthetic?
P.S. An excerpt from Kathy Poole's "Wet Lands: Civic Stormwater + Contigent Spaces" essay for Landscape Journal Special Issue Exhibit Catalog 1998:
The Box. We attempt to containerize Wet Lands, but it never works. They slip and slide, expand and contract, transform themselves, disappear.