Restoring the coast will be expensive, but inaction would be even costlier, said Mark S. Davis of Tulane University Law School. He said that the nation paid one way or another, and the more than $100 billion in relief is simply replacing what Hurricane Katrina broke — “You didn’t buy a future with that money.”

Yet all that is planned still might not be enough, said Oliver Houck, an environmental law expert at Tulane University Law School. “There is no one that says that $50 billion is going to get us anything but a hold in the status quo,” he said, adding that moving citizens away from the riskiest areas is essential.

Suggestions to retreat go against the grain in Louisiana, where people are tied to their home in a visceral way that can seem peculiar to a more rootless nation. But America benefits from this rich coast, local officials argue, producing energy for its homes and industries, as well as seafood for its tables.

The fact that the newly built land will subside and erode, and that seas will rise and severe storms will do their worst, is no argument against moving forward, said Garret Graves, a Republican member of Congress from Louisiana who formerly led the coastal authority. “You don’t not build a road because you’re going to have to maintain it,” he added.

Standing on the fresh ground in Bayou Dupont, Chuck Perrodin, a spokesman for the coastal authority, took up the question of what will happen when the next hurricane hits. His blunt prediction: “What it’s going to do is mess this up.”

Even so, the ambitious projects, which carry ambitious price tags, are worth it to change the calculus, even a little bit, of what can seem like a Sisyphean task.

“As long as we’re taking two or three steps forward for every step back, we will have a net gain,” he said. “It used to be we’d take one step forward and two steps back. We’re turning that around.”