The nation's capital is not exactly a beach town. But the cherry-tree-lined Tidal Basin, fed by the Potomac River, laps at the steps of the Jefferson Memorial. And, especially since Superstorm Sandy, officials in Washington have a clear idea of what would happen in a worst-case storm scenario.
"The water would go across the World War II memorial, come up 17th Street," says Tony Vidal of the U.S. Army Corps of Engineers. "And there are actually three spots where the water would come up where we don't have ... a closure structure right now."
Vidal is standing at one of those spots: the corner of 17th Street and Constitution Avenue, not far above sea level. It's just a few blocks from the White House, though Vidal says that's protected by a slight rise in the land. The U.S. Capitol is likewise protected — it is called Capitol Hill, after all.
But new flood maps in 2010 declared that the area between those two places, known as the Federal Triangle, is a flood zone. It includes key government buildings like the Departments of Justice and Commerce, and the Internal Revenue Service.
Officials have long known the area was vulnerable and have been using sandbags for years. But after 2005's Hurricane Katrina, the Army Corps deemed that approach no longer acceptable. So it's been building a $10 million flood barrier at this corner.
'The Bathtub Of The Whole Area'
A curved, concrete wall stands now on either side of 17th Street. In the event of a flood emergency, Vidal says, officials would close down the road, haul in beams to secure into the street and place big panels between them. The 10-foot-tall barrier would hold back millions of gallons of water, he says.
"We believe it could protect against the 500-year event with a few feet of free board," Vidal says. "But no matter what you design it to, there's always going to be an event that can overtop it."
In fact, even if the wall does keep hurricanes, storm surges and sea level rise in check, there is another threat: increasingly heavy rains.
"The Federal Triangle is actually the lowest point in this large drainage basin that's 24 times its size," says Amy Tarce, a federal urban planner with the National Capital Planning Commission. "So if you can just imagine all that water coming down, it's like the bathtub of the whole area."
When asked what the lowest point in that bathtub is, Tarce gestures to the spot on the National Mall near the Washington Monument where the National Museum of African American History and Culture is being constructed, complete with underground galleries.
The Mall is where people mean when they say Washington was built on a swamp — or more precisely, malarial marshland. Constitution Avenue was once a boggy creek. So you can easily imagine water rushing over manicured lawns, pouring into marble lobbies, threatening the national treasures within — just like in one of those D.C. disaster movies that Hollywood loves.
Except it already happened — in 2006, Tarce says, after a week of continuous rain.
"Basically, all of Constitution Avenue was underwater," she says. "Metro rail tunnels flooded, as well as the basements of the Smithsonian museums. In fact, some of these federal buildings were closed down for months."
The National Archives was among the hardest hit.
"Water was coming through about the door handle height there," says the Archives' facilities manager, Tim Edwards, showing off a beautiful basement theater with rows of red velvet seats and a raised, wooden stage.
"The water was up to the seat backs of that first row," he says. "All that woodwork had to be pulled off and underneath had to be dried out." Luckily, the U.S. Constitution and Declaration of Independence were safe in their vault.
Down the street, the cafeteria flooded at the National Museum of American History. Dorothy's ruby slippers, Julia Child's kitchen and the other artifacts were all safe, but still, who wants to risk it?
Engineering A Solution
The National Archives has installed a self-rising flood wall, tucked underground on the loading dock driveway. Rainwater now runs from a catch pipe in the street to a 16-foot-deep well. When that's full, it spills into a cavity under the fiberglass flood wall, which floats up to seal off the driveway.
The new National Museum of African American History and Culture will also have an automatic flood gate. In addition, plans call for manually installed panels, sandbags and special glazing, all designed to protect against a 500-year flood.
"There's a very interesting discussion always about how bad is it going to get in 50 years," says Brendan Shane, chief of the Office of Policy and Sustainability for the District of Columbia's Department of the Environment. "Well, the problem is, it could get really bad already."
And really costly. A University of Maryland study finds that if D.C. got hit with a Superstorm Sandy, property damage alone would top $24 billion. Cities all along the East Coast are grappling with that risk.
Outside his office, Shane demonstrates how Washington is trying to prevent what flooding it can. In the middle of a wide, public sidewalk is what looks like ordinary city landscaping: a tree, bushes, scraggly grass.
"But then underneath, it's actually sort of engineered," Shane says. "There's specific soils and there's piping to help move the water around. This, I think, can store 6,000 or 8,000 gallons of water that hits."
He also shows off a high-rise condo complex with a spacious second-story patio. "It feels sort of like we're in a park, but it's really a roof," Shane says.
There are sprawling gardens, a woman walking her dog. Washington has installed more than 2 million square feet of green roofs like this and is starting to require them for new construction.
"The idea is that if it rains an inch in a day, or two days, that roof will be able to manage that, and it won't flow off into the pipes and into the sewer," Shane explains.
Down on the National Mall, officials are considering several proposals: a huge underground pumping station; a new sewer tunnel 30 feet in diameter; a giant cistern the size of 20 football fields.
None would be cheap. Estimates range from $300 million to $500 million. But Tarce, the federal urban planner, says there's an even bigger challenge: maintaining a sense of urgency.
"People have short-term memories," she says. "They see the cars are running; they can go to work. The office buildings are back. So it's hard to convince people that there's actually a threat."