Coastal cities need to rethink how they deal with rising waters San Francisco bay (Thinkstock)
Coastal cities need to rethink how they deal with rising waters
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Paul Olsen is an environmental engineer by trade. He has spent the last few decades helping people understand rising seas. They threaten many places we live.
 
"I still use Tangier as my closer," Olsen says. He is referring to one of Virginia's most notable sinking islands. It is in the Chesapeake Bay. That is home to a historic community of oystermen. Tangier helps illustrate his point. Rising waters aren't just a fear for the future. "It scares the heck out of people."
 
If that doesn't do the trick, Olsen invokes the memory of Holland Island. It was home to a thriving fishing community for a century. That was until its last house succumbed to the bay. That happened in 2010.
 
"They failed to adapt, retreat or defend," says Olsen. He has spent almost 30 years with the U.S. Army Corps of Engineers. Now he is helping Virginia navigate rising seas. He is a program director at Old Dominion University.
 
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.
 
Hill believes "we're going to withdraw from a lot of places where there are small towns and vacation homes. They won't have the capital to do big projects." Hill is an associate professor. She teaches at the University of California-Berkeley. The towns that need saving on Chesapeake Bay islands are smaller villages. They have 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. They want "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. It acknowledges inevitably higher waters or periodically devastating storms. And it builds with them in mind. In some American cities dealing with rising seas, "transitional architecture" is one way to inhabit the treasured coastlines. 
 
The approach is already being implemented in parts of Europe. Rotterdam is a port city. It is in the Netherlands. Architects in Rotterdam have begun building ultramodern homes. They have been built on pilings in ponds. The new homes are accessible by earthen berms. They create a honeycomb-like pattern of water-absorbing ponds.
 
HafenCity is in Hamburg, Germany. The town is recruiting residents to modern apartment buildings. Instead of shielding the buildings from storm surges, architects designed them with parking garages on the first floors. Elsewhere in the city, they placed metro stops on higher levels. Parks feature few trees. Playgrounds are 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, (and) one that's protected and only in a huge emergency would be flooded. And then a layer that would never be flooded."
 
The concept of structures built to withstand intermittent flooding isn't new. David Waggonner is president of New Orleans-based Waggonner & Ball Architects. He says that's how residents of the Bayou used to build their homes, too.
 
"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. "You can learn a lot from the past, the way people built."
 
In response to the devastation of Hurricane Katrina in 2005, New Orleans and the federal government built an even bigger floodwall. The goal is to defend the city. Waggonner says residents still would be wise to have a backup solution for the water.
 
"You need to know where you're building, what the landscape is and has been," says Waggonner. Otherwise, "you're working against it."
 
Hill isn't a supporter of the New Orleans floodwall. She prefers other solutions. She likes those that encourage cities to work within their natural settings. Like those being used in HafenCity and Rotterdam.
 
Hill says many American cities will require a mix of defensive and adaptive structures. They will be required to endure higher waters. One natural line of defense is 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. They believe it would return 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 admits 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.
 
It's especially difficult to pull up stakes when they involve national assets. Those assets could be shipping ports. And even the world's largest naval base. Such is the case in Norfolk. The Hampton Roads region where Olsen and these landmarks are based has seen water levels rise 14 inches. It has happened since 1930.
 
Olsen is preparing for the future. Some of the naval base's piers will be abandoned. They may be rebuilt elsewhere. 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. Some homes will need to be built on pilings. Or built with flood vents.  Those minimize damage to their foundations.
 
If those waters continue to rise at a rate of six millimeters per year, the base and surrounding area will need to prepare for another foot of water in the next century.

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