When planning for the new World Trade Center site began just a few years after the destruction of the original towers, security was front of mind: Bollards were to be placed around the site, and a dedicated, below-grade routing system for commercial vehicles was among the plans. But when Superstorm Sandy hit in 2012, sending 125 million gallons of water into the WTC Vehicular Security Center, it became a point of vulnerability.

Well into construction, attention turned to adapting the design for climate resilience. Below-grade assets that needed protection from future storm surges included electrical distribution systems, ramps and loading docks.

Any solution would need to work with and protect what was already in place, but also preserve the WTC site’s aesthetic. “We wanted our solutions to really be invisible,” says Carla Bonacci, assistant director for WTC Infrastructure and Project Development at the Port Authority of New York & New Jersey, whose team designed the protection system.

What arose was a “three-ring strategy,” meant to protect against flooding at different levels and locations within the site, deployable when needed, removable when not.

The first ring of protection uses the security bollards that line the site. These turn into supports for a flood wall. Bollard covers are removed, and aluminum flood logs weighing 50 lbs each are placed horizontally to create a wall adjustable from 5 ft to 8 ft, with the addition of mounted steel posts. When fully complete next year, that will amount to 3,800 linear ft of wall that will take about four days to deploy when needed.

For the second ring, Bonacci’s team worked with two manufacturers to produce a Kevlar-weave fabric with a polyester coating that rolls or slides down over all at-grade openings to the vehicle security center. The flexible barriers take about 30 minutes to deploy, fully covering entrances 20 ft or wider, locking in place from the inside. While sometimes referred to by staff as pool covers, they were designed to meet certain hydrostatic, hydrodynamic and impact-load criteria.

Below-grade individual flexible and rigid barriers, up to 30 in. high, serve as the third and final protection for critical infrastructure, as well as a pump system with a 2.2-million-gallon pumping capacity.

Josh DeFlorio, resilience and sustainability chief at PANYNJ, calls the bollard system a “showcase project.” A similar system is under development at the agency’s airports in the two states.

PANYNJ has been considering the impact of climate change on projects since at least 2009. In 2015 it published its Climate Resilience Design Guidelines.

“Hopefully they’re a bridge between a past disaster and future mitigation,” says DeFlorio. An update is planned for late 2020 or early 2021. In addition to sea-level rise and storm surge, the guidelines will likely incorporate concerns such as extreme temperature and precipitation.