Stopping the Next Sandy: Tunnel plugsBy
Over the years, the MTA has struggled to keep its subway system water-free. When the Sandy storm surge inundated the system’s East River tunnels, the problem was laid bare for all to see. As most experts agree that the next storm is simply a matter of when and not if, the MTA will have to do something to address its vulnerable infrastructure, and that something might just be a giant plug.
The immediate history of the MTA’s water problems started a few years ago when a torrential summer storm led to massive flooding. This wasn’t the first time vulnerable areas suffered water damage, and the MTA decided to do something about it. Street-level grates were raised a few inches, and staircases were elevated as well. For normal storms, these measures alleviated the water problems, but for hurricane storm surges, the MTA’s temporary and permanent preventative initiatives were quickly overwhelmed.
We lose sight of what happened to the subways because the MTA was able to respond quickly to the problem. Some service was up and running within days, and nearly everything is back to normal. But the system suffered extensive exposure to salt water, and even outside of the fiscal costs of the clean-up, key equipment — signals, switches, track beds, wiring — will now have a short shelf lives. Protection remains key.
To that end, scientists with the Department of Homeland Security are working on developing a tunnel plug, and The Times went in depth into the project today. The key parts:
The idea is a simple one: rather than retrofitting tunnels with metal floodgates or other expensive structures, the project aims to use a relatively cheap inflatable plug to hold back floodwaters. In theory, it would be like blowing up a balloon inside a tube. But in practice, developing a plug that is strong, durable, quick to install and foolproof to deploy is a difficult engineering task, one made even more challenging because of the pliable, relatively lightweight materials required…
A subway tunnel is hardly a pristine environment; it is full of grease and grime — and, often, rats. “That’s something we’ve talked about,” Dr. Fortune said. “We’ve actually put Vectran samples in tunnels, to see if rats ate it. They didn’t.”
There are also obstructions like tracks, as well an electrified third rail, pipes and safety walkways, all of which could cause gaps between the plug and the tunnel walls. Most of the obstructions can be dealt with by modifying a short section of the tunnel to accommodate the plug, which is 32 feet long when inflated. Sharp corners can be curved, flush tracks of the type used at grade crossings can be installed, the third rail can be discontinued for a stretch, and pipes can be made to swing against the ceiling.
Those modifications will reduce potential gaps but not eliminate them. In the most recent test, when Dr. Barbero and a colleague, Eduardo M. Sosa, inspected the front of the plug, they discovered a two-inch gap in one corner. The procedure called for filling the plug with water to pressurize it further, and then introducing water behind it to simulate a flood. But a plumbing failure, unrelated to the plug, ended the test prematurely. It was repeated successfully several days later, Dr. Fortune said, and the plug held back all but a small amount of water.
Henry Fountain’s article explores the construction of the plug. It consists of three layers of durable yet flexible materials. It also explores placement: The plug is designed to fold into the sides of the tunnel and can be deployed remotely. The key questions though concern cost and effectiveness. One plug costs around $400,000, and the MTA, for instance, would need a considerable number of these plugs to adequately protect the porous tunnels.
Effectiveness though remains the biggest concern. The MTA’s tunnels are vulnerable at key access points, but plugging tunnels would simply displace water flow to other vulnerable areas. What success is accomplished if floodwaters destroy a train station but spare the tunnels? The MTA also, as The Times notes, must deal with water that enters through ventilation grates and various other entry points. The plugs can only do so much.
Short of sealing up the system, though, these plugs may be one of the more promising areas of progress. The clock is ticking, and the MTA doesn’t have time on its side. Can something like this be in place before the next flood arrives? If the money is there, a solution will be too.