Washington Under Water

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How will the capital city adapt to climate change?

<p><em>Artist’s rendering of the National Mall in the event of the Greenland ice sheet melting. </em></p>

Artist’s rendering of the National Mall in the event of the Greenland ice sheet melting.

John Blackford

Last week, in its coverage of the recent onslaught of record-breaking storms, the Washington Post mentioned that if the 30 trillion gallons of rain Hurricane Harvey dumped on Houston were collected in a single volume over the District of Columbia, the depth would match the height of the Empire State Building.

The comparison is apt, given that both cities were founded on marshes. The Potomac and Anacostia, both tidal rivers, surround the District on two sides, and the Capital Region has a long history of storm surges. Three times over the past 15 years, major floods have swept parts of the city. Already susceptible to deluge, Washington now faces unprecedented risk of extreme flooding due to the exacerbating effects of climate change. According to the US Environmental Protection Agency, the Potomac has been rising about an inch every eight years, and the non-profit Climate Central calculates that elevated sea levels will make record-setting floods six times more likely in coming decades. A flood of eight feet above normal high tide—slightly higher than the worst event on record—is virtually guaranteed by the end of this century, and a 10-foot flood is 85 percent likely.

The dangers to Washington’s public health are clear. Even now, heavy rains tend to spill raw sewage into the riverways, and record flooding surely will contaminate public space. The most vulnerable communities, lying in the lowlands, generally are poorer neighborhoods, such as Anacostia. According to Climate Central, three quarters of the people who live in endangered areas are people of color.

<p><em>The National Mall is at risk of extreme flooding by the end of the century. </em></p>

The National Mall is at risk of extreme flooding by the end of the century.

Climate Central

The cultural risks also are significant. The 2006 flood of Federal Triangle cost millions and swamped the basements of the National Archives and National Museum of American History, threatening the national treasures stored there. Climate Central’s interactive map shows that an eight-foot flood could put the entire National Mall under water, severely damaging some of the country’s most important landmark buildings, including many of the historic memorials and museums. The Old Post Office Pavilion, now the Trump International Hotel, would be engulfed, as would the new National Museum of African American History and Culture. The Wharf project on the Southwest waterfront, which opens next month, cost billions to develop but could become DC’s Atlantis. Will its slogan—“Where DC Meets Its Water”—become literal?

Other parts of the District are being reshaped around water. In the 30s, the Army Corps of Engineers began resculpting the landscape of the National Mall, and the Potomac Park Levee now forms an earth barrier meant to keep flood waters to the south. That hilly terrain in the middle of the Mall isn’t merely picturesque. The one major gap, at 17th Street, allows cars through but also funnels floods across the Mall. The recently-completed granite dam arcing across the land is intended to plug up this hole and hold back water up to 19 feet above sea level.

<p><em>17th Street Dam, Potomac Park Levee. </em></p>

17th Street Dam, Potomac Park Levee.

Elliot Carter

Yet, the fundamental lesson after Hurricane Katrina’s devastation of New Orleans in 2005 was that extreme weather events cannot combated with force alone. Levees break, walls fall. As I first wrote nearly a decade ago, architects and urban planners can rethink the very nature of urban space by reforming the relationships between cities and water. While designers’ visions for adapting to climate change aren’t always thoughtful, as I observed in 2014, the best of them are brilliant. After Katrina, New Orleans planners studied ways to allow floods to seep into the city through a new channel system, redirecting water across a much broader area—Fat City as Venice. In the wake of Superstorm Sandy in 2012, the Rebuild By Design program proposed similar strategies in New York and surrounding regions.

Last year, the District of Columbia released Climate Ready DC, its plan to adapt to a changing climate. The report contains 77 action items to future-proof the capital, including providing incentives to encourage private property owners and developers to implement food resiliency measures. Leading this effort now is Kevin Bush, the city’s newly appointed Chief Resilience Officer, who just started on the job last month. “Thriving in the face of change” is how Bush defines resilience, he told me recently. “What we’re really talking about is the immune system of a city. If you have a strong immune system, it doesn’t matter what the stresses and strains are, you’re going to bounce back.” Bush, who was instrumental in the Rebuild By Design program while at HUD, says he’s most interested in developing ways to solve multiple problems at once. “For example, how can we use the dialogue about climate change to increase the supply of affordable housing?” Through such synergies, Bush hopes to create a new model of development that doesn’t just survive flooding—it prospers in it.

How does he plan to accomplish this? “Check back with me in a year.”