Can space-suit science keep New York’s subways dry?
By Mike Hall
July 22, 2016
In October 2012, I moved to the US from Newcastle, England, to lead Arup’s New York civil engineering team. Two weeks later, Hurricane Sandy hit. My building flooded, and I was evacuated into a shelter — an all-too-personal reminder of the importance of resilient urban infrastructure.
Over the past few years, I’ve been fortunate to be involved in a project that’s a major step in the right direction to help to protect large cities from future flooding.
Sandy devastated New York’s transportation system, shutting down subway and bus service for days and causing billions of dollars in damage.
Soon after the storm subsided, New York City Transit (NYCT) set up meetings with infrastructure consultants to determine how to prevent similar problems during future storms.
Arup was tasked with various pieces of this work. One involved preventing floodwater from entering subway stations through common portals like passenger entrances and ventilation grates.
Stairs, logs, and doors
After studying a given problem, engineers look for existing resources or tools that they can apply or adapt to solve it. In this case, our team quickly realized that off-the-shelf tools simply wouldn’t work.
This was particularly true for subway entrances, which typically consist of surface-level stairways — big holes in the ground, effectively.
A traditional flood management approach would be to place flood logs or marine doors at the bottom of the stairwell entrances. However, these solutions create additional problems before, during, and after floods. For instance, flood-log systems consist of many components, and lost or misplaced pieces can complicate storm preparation.
Another common challenge: during flood surges, the weight of water building up in the stairwell exerts a significant amount of pressure on the station’s structure. These pressures create forces greater than the structure was originally designed for and can necessitate costly reinforcement.
Water and debris also remain in the stairwell after the storm subsides, requiring extensive pumping and cleanup.
From outer space to Canal Street
When Sandy hit, NYCT was aware that ILC Dover, an innovative Delaware-based company that makes NASA space suits, was working on an inflatable tunnel plug. NYCT introduced Arup to ILC’s material scientists to see whether a similar technology could be used to floodproof subway entrances.
Just six months later, I stood at Manhattan’s Canal Street Station as NYCT officials pumped water over a prototype of a product called Flex-Gate. The test: could it withstand a level of flooding associated with a Category 2 hurricane plus an additional 3 feet of water?
A simple, straightforward system comprising just three parts — a box that stores a spool of thin material, a pair of guide rails to stretch the fabric across the opening, and a clamping mechanism securing the assembly to the top of the stairwell — Flex-Gate is designed to be permanently installed at the top of the entrance.
The system has none of the drawbacks associated with marine doors and flood logs. It does not necessitate any structural reinforcement. Water and debris never enter the staircase, eliminating the need for post-storm cleanup. Deployment can be completed in less than 10 minutes. There are no removable parts to misplace.
A subway success story
Having exceeded expectations during the Canal Street test and others, Flex-Gate is now being installed at vulnerable stairwells throughout New York’s subway system.
ILC has further developed the product for use in a vertical plane, turning it into a Flex-Wall.
Together, the two systems offer an excellent example of how technology can help protect society from the elements.
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