Two of our recent parks in New York City--Brooklyn Bridge Park (BBP) and Segment Five of Hudson River Park--were both significantly inundated with several feet of salt water during Hurricane Sandy.
At mid-tide, with thousands of fellow Brooklynites, I stood on the Brooklyn Heights Promenade above BBP and watched as the violently rushing floodwaters of the East River, which had already subsumed the piers and the shoreline edge, continued to bring what would eventually amount to several feet of salt water over major sections of the park. At that point, when I could see that the flooding would indeed be massive, I went back to my apartment, closed the blinds (went to sleep), and returned to the same view the next day.
The immediately visible manifestations of storm damage were few--just the debris-littered flood line and the loss of electricity─ but the injury to the park lay in salt damage to certain plants that were less saline tolerant, which really did not become evident until the summer of 2013. All in all, the damages were exceptionally minor and BBP is now held up--as is our segment of Hudson River Park--as an example of how to build landscapes that are resilient to these kinds of flood events.
The experience left me with several micro-lessons about actual building: to raise the elevations of electrical transformers; to better understand the diverse ability of different plant species to accept saltwater inundation of the root systems; to place more trees on higher ground; and to think about strategies for reducing salt levels in soils after flooding. But beyond these technical responses, Hurricane Sandy really brought home the need for a more overt outlook on general preparedness. This applies to large-scale thinking as urban landscape planners and to the smaller scale of the individual site and project--at both of which we landscape architects work.
Some public infrastructures (the subway, for instance) really need to be protected in a way that affords resistance to external forces such as flooding. However, there are other pieces of the city--parks, of course, but also highways and linear boulevard plantings--where it may be more effective to build for resilience: the incorporation of strategies that will allow the urban landscape to adapt and regenerate after flooding.
Returning to Brooklyn Bridge Park for an example (in my office we are both planners and the park designers), we inherited a site with a mid-20th-century shoreline made with a traditionally engineered edge that, as part of our park design, needed to be reconstructed. We replaced the existing vertical concrete walls and relieving platforms with riprap, which is basically just very large loose rocks, like you might see all along the New England coastline. These new edges offer a wider range of responses to being slammed by massive waves or washed over with Sandy’s kind of flowing tides: these edges are more porous, they let the seawater pass right through, and they move slightly to absorb impacts, rather than cracking and falling apart, even with unusually high volumes of water. The Brooklyn Bridge Park sea edge of riprap was unharmed by the floodwaters during the hurricane. Although this is a simple construction, the lower level of resistance exponentially increases the longevity of the riprap shoreline as compared to vertical sea wall that must withstand the force of waves slamming into it every day.
We should aim to incorporate more flexibility and potential for dynamic change into how we build--especially working collaboratively with our clients and those who will maintain the built projects. Through long-term collaboration we are all able to make adjustments as we learn more.
While we sustained limited tree and shrub losses at both Hudson River Park and Brooklyn Bridge Park, the vast majority of the trees survived. And perhaps more importantly, we learned that a wide variety of plants never missed a beat after the floodwaters of Hurricane Sandy subsided. Much of that can be attributed to prior research both in plant studies we conducted and in visits to sites we knew had experienced flooding. In elevated areas we used species that are proven tolerant of salt on their stems and leaves, but, interestingly, saline tolerance on those parts of plants is different than the impacts of salt water soaking the root zone. For example, the London Plane tree does well near the sea in places like Martha’s Vineyard, yet in the areas of BBP that experienced salt water inundation to root zones, the same trees were truly ravaged. Whole areas along the east side of Manhattan have hundreds or more nearly-dead London Plane trees in the wake of the saltwater flooding. We still need to do more homework--such as studying the comparative resilience of different plant species over time, as well as responses to efforts at flushing salt out of planting areas--and these conversations are in fact occurring in New York City.
Perhaps the best and most productive form of preparation, however, would be to scale our thinking to the epic proportions and paradigm-changing scale of the problem we are confronting. In other words, in addition to looking at how we prepare ourselves on a park-by-park basis, we need to be thinking of both human-made and natural places as parts of an interdependent contemporary coastal system. Ecologies are systems--and we need to think about cities as systems. This big-picture perspective should inform our design work at the scale of the city as we seek some kind of balance between the desire for coastal inhabitation and the real risk of future disruption.
To truly influence preparedness, this kind of systems-based approach would also have to be embraced on the agency level, where many issues related to storm preparedness are currently addressed in isolation of each other. We have learned that the jurisdictional boundaries of federal, state, and city agencies do not correspond to the infrastructures that are impacted by major natural disruptions such as Hurricane Sandy. These organizations--including divisions within cities, such as parks departments and building departments, as well as the different entities that manage and maintain highways--may need to be fundamentally rethought so their duties to operate a city can be more supple while absorbing future Sandy-like events.
[Image: Alexia Hoyer]