DC Levee Upgrade Races Against Climate Change

Grey clouds race over the National Mall, seemingly as fast as the airliners that would normally be making their approach to National. The airport is still closed.

It is 2018.

The city is reeling from a surge of floodwater sent up the Potomac by the fierce winds of a slow-moving hurricane, and is preparing for a second punch.

Will the floodwaters gush over Washington DC’s levee? Will they cover Constitution Avenue and threaten the capital’s Maginot Line of bureaucratic fortresses?

A touch of New Orleans

When we think of levees, we think of New Orleans. But DC also has a levee. The problem is that our levee is not very good, says Gerry Galloway, engineering professor at the University of Maryland.  

I recently joined Galloway and members of American Water Resources Association to learn about our capital’s alarmingly porous flood defenses and what’s being done to beef them up.  

Climate change is already fueling more frequent extreme weather events, Galloway said. Meanwhile, we continue to pave the Potomac’s watershed with concrete and asphalt, which increases runoff and intensifies floods.

It all seemed so remote on this autumn afternoon. The warm sun, the lively scene of tourists, bicyclists, and joggers―how many of them knew that the grass-covered berm that parallels the Reflecting Pool is DC’s levee?

As we stood on that levee, Galloway challenged us to imagine floodwaters sweeping in from the Potomac during a category four hurricane.

“It could push as much as 20 feet of water onto Constitution Avenue,” he said. The flood would inundate an enormous crescent-shaped swath of downtown DC, from the Ellipse, through Federal Triangle, all the way to Ft. McNair.

A lot of it has to do with the city’s origins. A large part of DC once belonged to the river, either as marshlands or as open water, he said. As the city grew, the river was forced to retreat to make way for houses, government agencies and our famous monuments.  

The river remains determined to win back what it has lost. In 1936, the Potomac aimed an almost unimaginable 486,000 cubic feet of water per second (cfs) directly at the city. 

Congress ordered the U.S. Army Corps of Engineers to build a levee to protect the city that would stand up to a flow of 700,000 cfs.  

But the plan was never completed. Parts of the levee are still too low. It also has two big holes at 23rd and 17th streets. When flood warnings sound, park employees are summoned to plug up the gaps with sandbags, dirt, and plastic sheeting.

The final straw came in July 2006 when nine inches of rain fell in 24 hours. Constitution Avenue disappeared under three feet of water. IRS headquarters had to close for six months. Justice also shut down, and the new auditorium at the National Archives was damaged.

Now, though, the Corps of Engineers and the National Park Service are filling the long-standing gaps in DC’s flood defenses.  

No more sandbags

At 17th street we peered through a chain-link fence at a pair of monolithic masonry walls nearing completion. In the future, when floodwaters threaten, workers will attach a removable post and panel barrier to the walls. In other vulnerable places, the levee is being raised and new works are being built.

At the end of the tour, we peered into the great hole at 15th Street that will soon be the National Museum of African American History and Culture. It’s a prime site, right next to the Washington Monument.

It is also the lowest spot on whole Mall.