Transportation leaders said Thursday that Metro-North Railroad's Waterbury Branch could be out of service for more than a month. It comes after historic flash flooding left two large craters under the tracks.

"It's probably about 40 feet deep, 220 feet long cavity now to fill in," said Steve Kilpert, the railroad's Deputy Director of Track Projects.

Metro-North president Catherine Rinaldi and Connecticut Transportation Commissioner Garrett Eucalitto got a first-hand look at flood damage in Seymour. It's one of two washouts along the Waterbury Branch. The other is near Beacon Falls. Both will require weeks of hauling heavy stone in from outside quarries.

"We'll start at the bottom with large rock," said Kilpert. "Building it, layering it up."

Eucalitto said the job is a lot more complicated than just bringing rocks in.

"It's not like the normal stone that we see on the track bed," he said. "It's going to be a larger."

The trains are being replaced with 16 commuter buses a day.

"We have Route 8 right here, so the bussing is not too much of an inconvenience," Eucalitto said.

The commissioner said that most state roads are now at least partially reopened, although Route 34 in Monroe and Route 67 in Seymour could take months to fix.

"We're going to have to go and do a full debris removal," he said. "Inspecting the structures to see whether the structures are salvageable. And then if they are, then we can do just a road replacement. If they're not, we're going to have to do a bridge replacement."

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As flash flooding becomes more common, the longer-term focus is resiliency.

"Assessing vulnerable locations, trying to come up with funding strategies to be able to make those kinds of investments," Rinaldi said.

DOT officials said it's too early to estimate the total repair cost. But the federal government could ultimately cover 75% of the price tag, since the White House issued a federal disaster declaration for western Connecticut.