Hurricane Sandy's waves arrived at high tide, destroying 650,000 homes, flooding lower Manhattan, and inundating coastal wetlands. In a few places, however, the storm's fury have wrought positive changes in the landscape.

"That really opened up a lot of the marshes for new growth," Sheehan says. Dirt and sand piled into some ponds that had been widening, he adds, filling them with sediment that served as a seedbed for fresh marsh grass stands.

"Nature moves things around," Sheehan says. "Wetlands are meant to handle those changes. Towns aren't."