When you build your capital in a swamp*, you’d better have a plan for when the water rises—especially if you plan on building important memorials, museums and federal buildings close to the river. For Washington D.C., the Potomac Park Levee System, originally completed in 1939 is supposed to protect the National Mall and surrounding area from storm surges and river flooding.
Part of a much-needed upgrade to that system just completed its first test on October 31, reports the U.S. Army Corps of Engineers. The Corps placed a removable barrier, featuring aluminum panels supported by steel post, across 17th Street—you can see photos on the Army Corps Flickr page. The barrier can put into place by the National Park Service given advance notice of a potential flood.
The original levee system includes 12-foot-high earthen levees running around the Lincoln reflecting pool and a plan to close gaps left for streets with sandbags and Jersey barriers (those concrete barriers that separate traffic). The system was constructed after a 1936 flood "damaged much of downtown Washington and transformed the Jefferson Memorial into an island," according to a 2013 ClimateWire article by Elizabeth Harball. She writes:
D.C.'s levee system is meant to hold back 457,000 cubic feet of water per second during what the Federal Emergency Management Agency has designated as a 100-year flood, protecting an area that extends from the Federal Triangle to the Capitol and curves down to just north of Fort McNair in southwest Washington.
But Hurricane Katrina forced officials to re-evaluate the system, and they determined that the sandbags wouldn’t be enough. So they came up with a new plan to protect the area in the case of a 100-year flood. Construction began in 2011, and the cost was estimated at $9.4 million.
For the next phase of the upgrade, which hasn’t been funded yet, the Army Corps writes that plans include:
…providing a small floodwall at 2nd and P streets near Ft. McNair and raising the existing grade along 23rd Street to eliminate sandbag closures at these locations. Additionally, Phase II would raise the Potomac Park Levee system up to a uniform elevation to provide flood risk reduction up to the Congressionally-authorized 700,000 cubic feet per second flow-rate event, or approximately 19 feet above sea level.
But given the changing climate, is a 100-year flood plan enough? More extreme events are happening more frequently. "Everyone now is focused on meeting the challenge of the 100-year flood," University of Maryland professor Gerald Galloway told ClimateWire. "That's probably far too low a level of protection for the iconic nation's capital." A 500-year event, perhaps caused by a powerful hurricane could send water over the existing levees. Sea-level rise could contribute to an even higher surge.
*A "Washington DC history discussion list" has alerted us to its members' discussion of the truth of D.C. swampiness. D.C. interns, please note: there are some very good reasons not to think of the whole district as a swamp (despite the mugginess)—some discussion list members call it a tidal marsh, while others point to Tiber Creek's poor drainage as problem. Apparently local historians have been trying to quash the "swamp" terminology for about a decade; as one historian notes, though, this language goes back as far as the early 1800s when an early attorney general called the district "a meagre village, a place with a few bad houses and extensive swamps."