In Japan, engineers have devised a $3 billion system called a "Water Discharge Tunnel" that essentially works as a floodwater diversion facility to protect Tokyo's 13 million residents during rain and typhoon season.

Still, making New York's subways watertight would be an "engineering feat equal to the scale and creativity of the original construction (of the system itself)," said Lucius Riccio, New York City's former Transportation Commissioner and lecturer at Columbia University.

"Our engineers are up to it, if given the resources and the free hand."

In the days ahead, New York faces at least two big challenges, according to Ben Orlove, senior climate scientist at Columbia University.

First, the city must cope with its immediate problems -- power outages, stranded residents, suspended subway lines, flooding and fire damage. Then it needs to deal with long-term infrastructure.

"We need to be innovative," said Orlove. "And we should consider things like putting up flood gates at the mouth of the Hudson (River) and other vulnerable points that could help hold back the tide."

An army of municipal workers and private contractors is addressing the more immediate concerns, working around the clock in New York to pump out sea water and wipe down salt-caked machinery like underground transformers, circuit switches and generators.

As workers scrambled to restore equipment, thousands of otherwise stranded commuters defiantly walked to work this week, often abandoning taxi cabs in the city's traffic-clogged streets.

"I left my house at 6:45 a.m. and I'm still walking," said Elizabeth Gorman, a 40-year-old Queens resident who crossed the Queensboro Bridge at around 10 a.m. "I don't know what (else) to do. I have to get to work."

New York's buses, trains and subways are all slowly coming back online. But for many residents across the region where full transit service has yet to be restored, the slog to work continues.