An environmental engineer by trade, Paul Olsen has spent the last few decades helping people understand how rising seas threaten the places we live — even in a state that hardly thinks of itself as coastal.

“I still use Tangier as my closer,” Olsen says of one of Virginia’s most notable sinking islands in the Chesapeake Bay, which is home to a historic community of oystermen and helps illustrate his point: rising waters aren’t just a fear for the future. “It scares the hell out of people.”

If that doesn’t do the trick, Olsen invokes the memory of Holland Island, home to a thriving fishing community for a century until its last house succumbed to the bay in 2010.

“They failed to adapt, retreat or defend,” says Olsen who, after almost 30 years with the U.S. Army Corps of Engineers, is helping Virginia navigate rising seas as a program director at the state’s Old Dominion University. “Those are the three choices with sea-level rise.”

In San Francisco’s Bay Area, landscape architect Kristina Hill agrees on the options water-threatened communities must consider — but she might disagree on which ones are worth shoring up.

“I actually think what’s going to happen is we’re going to withdraw from a lot of places where there are small towns and vacation homes, because they won’t have the capital to do big projects,” says Hill, an associate professor at the University of California-Berkeley. The towns that need saving on Chesapeake Bay islands are smaller villages with populations of less than 300. According to Hill, moving earth to protect those towns isn’t the best use of public funds.

But for population centers like San Francisco, New York City, New Orleans and Norfolk, Virginia, she adds, architects are looking to adapt their structures, “to keep developing in a way that is ready for sea-level rise.”

Somewhere between retreating and building a giant wall to keep the waters at bay is a middle ground that acknowledges inevitably higher waters or periodically devastating storms — and builds with them in mind. In American cities dealing with rising seas, sinking landscapes and increasingly intense squalls, “transitional architecture” is one way to inhabit the treasured coastlines as long as possible.

The approach is already being implemented in parts of Europe where shutting water out isn’t an option for port cities that rely on shipping traffic.

In the Netherlands’ port city of Rotterdam, architects have begun building ultramodern homes on pilings in ponds. Rather than displacing water with new construction and exacerbating flooding, the new homes are accessible by earthen berms that create a honeycomb-like pattern of water-absorbing ponds.

And in HafenCity, a riverside district in Hamburg, Germany, the city is recruiting residents to modern apartment buildings, even though they are built outside the protection of the city's main dike that prevents flooding. Instead of shielding the buildings from storm surges, architects designed them with parking garages on the first floors. Elsewhere in the city, they placed costly assets like metro stops on higher levels. Parks feature few trees and sturdy playgrounds built to withstand gushes of water during heavy rains.

“They call this ‘tiered development,’ because it’s set up in vertical layers,” Hill explains. “There’s a layer that can be flooded, one that’s protected and only in a huge emergency would be flooded and then a layer that would never be flooded.”

Though such water-minded cities look futuristic, the concept of structures built to withstand intermittent flooding isn’t new. David Waggonner, president of New Orleans-based Waggonner & Ball Architects, says that’s how residents of the Bayou used to build their homes, too. When the Mississippi River swelled beyond its banks, antebellum houses perched on brick pillars remained.

“Maybe it rained hard, but if it was masonry at the bottom and your principal living areas were above that, you could live on,” Waggonner says of the way things were. “You can learn a lot from the past, the way people built.”

Once builders, looking to populate the area quickly with new homes, moved from raised masonry to steel rods and sheetrock, “flooding became a bigger problem.”

In response to the devastation of Hurricane Katrina in 2005, New Orleans and the federal government built an even bigger floodwall to defend the city for the next 100 years. But Waggonner says residents still would be wise to have a backup solution by building in a way that makes room for water or expects to take some into a ground level.

That’s the way homes were built before the advent of flood insurance, he says. Buildings perched on posts expected the waters to rise periodically. Residents used curved roofs and cisterns to store their rainwater locally for use after the storm.

“You need to know where you’re building, what the landscape is and has been,” says Waggonner. Otherwise, “you’re working against it.”

Cities in tidal areas and near flood-prone tributaries need to make room for rising water in ways both new and old if they want to continue living there, says Hill. That’s the essence of transitional architecture.

She sees solutions like New Orleans’ floodwall as “a dumbing down of the human ability to track and respond,” — blocking out water in a way that keeps it out of sight and mind until the next hurricane — and prefers solutions that encourage cities to work within their natural settings like those in HafenCity and Rotterdam.

Hill says many American cities will require a mix of defensive and adaptive structures to endure higher waters. One natural line of defense in a city's arsenal is its wetlands.

In San Francisco’s Bay Area, wetlands are a subject of debate. Some argue that the development and highways that have filled them in over the years should be removed, returning marshes to their natural state.

Wetland restoration projects in northern parts of the Bay Area already have returned thousands of acres of former industrial salt ponds to marsh habitat. But imagine San Francisco’s iconic coastline highway giving way to lush bay grasses and fishing egrets — along with the city zoo and multi-million-dollar Sunset District homes.

Even after a city concedes that it already built where protective wetlands once were, “it’s difficult to pull up stakes and allow a wetland to take over,” says Hill, who advocates for wetlands being reconstructed out into the ocean rather than taking over developed areas.

It’s especially difficult to pull up stakes when those stakes involve national assets like shipping ports and the world’s largest naval base, as in Norfolk, Virginia. The Hampton Roads region where Olsen and these landmarks are based has seen water levels rise 14 inches since 1930.

Olsen is preparing for a future in which some of the naval base’s piers will be abandoned — and rebuilt elsewhere at $35 million apiece — and the Navy will have to double down on protecting the rest. The roads that carry military personnel to their vessels will need to be raised above flood levels, and some homes will need to be built on pilings or with flood vents to minimize damage to their foundations as the waters continue to rise.

If those waters continue to rise at a rate of six millimeters per year (about the thickness of an iPhone), the base and surrounding area will need to prepare for another foot of water in the next century.

“To an engineer, this [sea-level rise] is significant, especially when you put a Nor’easter on top of that,” says Olsen. “But it’s not so significant that we have to run on our heels. We have time to engineer solutions.”