UPDATED WITH A WHOLE BUNCH OF NEW INFO FROM THE MTA: New York Governor Andrew Cuomo and his MTA chief, Joe Lhota, say the danger of flooding of the East River subway tunnels is quite real.
"Our subway system and salt water do not mix," Lhota said in a briefing with the Governor this morning. "Salt water can corrode switches quite easily." Lhota added that would put the general ability for the system to function "in jeopardy."
Salt water corrosion of switches - some of them 100 years old -- could have long-term, unknowable effects on the subway system.
According to a press release sent late Monday, "MTA New York City Transit has taken strong measures to protect the subway tunnels that cross under the Hudson and Harlem rivers. However, the unprecedented levels of storm surge predicted to accompany Hurricane Sandy present a significant threat to those tunnels and to the speedy restoration of service after the storm." (FULL RELEASE BELOW)
An hour after the Governor's briefing, Mayor Michael Bloomberg downplayed the threat of subway flooding. "If a little water gets in, you pump it out," the Mayor said, arguing that the biggest threat would be inundated trains.
His office offered no immediate explanation for the differing views of the threat of salt water to the subway system.
Five subway tunnels that run under the East River could be in danger, according to an analysis by Columbia University: the A-C, the 2-3, the 4-5, the R, and the F. MTA spokesman Charles Seaton says the MTA has stationed personnel at the mouth of each of the tunnels to monitor flooding. That information is transmitted to a dispatcher. The personnel will remain there "as long as it is safe," Seaton said.
During Tropical Storm Irene, as WNYC reported a year ago, the city came within a foot of seeing the subway tunnels flood. Officials just predicted Sandy will peak at 11.7 feet above flood stage, versus 9.5 feet for Irene.
From my earlier report:
Columbia Univeristy Professor Klaus Jacob has worked with the MTA to model what would happen if you couple sea level rises – the FTA says to expect four feet by the end of this century – with intense storms like Irene. In forty minutes, Jacob says, all the East River Tunnels would be underwater. Jacob says he took those results to the MTA, and asked, if that happened, how long would it take to restore the flooded subway to a degree of functionality?
“And there was a big silence in the room because the system is so old. Many of the items that would be damaged by the intrusion of the saltwater into the system could not recover quickly. You have to take them apart. You have to clean them from salt, dry them, reassemble them, test them and cross your fingers that they work.”
In a best-case scenario, Jacob calculated that it would take 29 days to get the subway working again. But in the meantime, a halted subway would almost halt the city’s economy, which, he says produces $4 billion a day in economic activity.
Here's the full statement from the MTA, released about 4 pm Tuesday:
MTA New York City Transit has taken strong measures to protect the subway tunnels that cross under the Hudson and Harlem rivers. However, the unprecedented levels of storm surge predicted to accompany Hurricane Sandy present a significant threat to those tunnels and to the speedy restoration of service after the storm.
Station entrances and sidewalk vent gratings in low-lying areas such as lower Manhattan have been covered with plywood and reinforced with several feet of sandbags. However, those measures are designed to slow the entrance of water into the system, not to prevent flooding. In addition, the pumps installed throughout the subway system to remove water run on electricity, and will not function if electric power to the system is interrupted.
NYCT personnel and New York City police officers are monitoring conditions in all stations, and patrol trains travel the entire subway system looking for signs of water infiltration. NYCT personnel are also removing stop motors, which interact with automatic brake equipment at track level, so they would not be damaged during any flooding.
If the threat of tunnel flooding appears likely, NYCT is prepared to remove power from the signal system. Because water conducts electricity, and salt water conducts electricity particularly well, signal equipment that is submerged in seawater would be especially vulnerable to damage if power remained on.
When salt water is removed from the system, salt deposits will remain on contact surfaces that will accelerate corrosion, causing potential failures. All those surfaces must be thoroughly cleaned, but they cannot always be cleaned in the field, and some cannot be cleaned at all and must be replaced.
It is difficult to predict the amount of time required to pump water from a flooded tunnel and bring its equipment, as well as adjoining stations, back into service. It depends on the height of the storm surge, how rapidly it penetrates the protective barriers, the length and diameter of tunnel tubes and the extent of flooding into adjacent underground sections and stations.
NYCT has three pump trains available to remove water from under-river tunnels. But the wide range of variables means that merely pumping out water from flooded tunnels – before restoring signals and other equipment – is estimated to take anywhere from 14 hours to more than four days. And as a general rule, the longer a tunnel is flooded, the longer it will take to return to service.
The last time subway tunnels under rivers flooded was December 11, 1992, when all subway lines were suspended for a time and three tunnels filled with water. Some were restored the same day, but the Canarsie Tube carrying the L line under the East River was out of service for several days.