The 17th Street closure structure is situated between the Lincoln Memorial and the Washington Monument, and it reduces risk to human safety and critical infrastructure in downtown District of Columbia from flooding of the Potomac River. It was constructed and is regulated by the Corps of Engineers, and operated and maintained by the National Park Service (NPS).
The 17th Street closure is a removable structure that can be erected in the event of high water to attach to the floodwalls on both sides of 17th Street and consists of aluminum panels between steel posts. Stone cladding application on the 17th Street floodwall was designed to blend in with the historic landscape of the National Mall. The closure is part of the Potomac Park Levee System and the Washington, D.C. and Vicinity Local Flood Protection Project.
The original Potomac Park Levee System was Congressionally authorized to provide flood risk reduction for a flood event up to 700,000 cubic feet per second (cfs) on the Potomac River from river and storm surge flooding. The project was completed in 1939 and relied on sandbags and earthen fill to form a temporary closure across 17th Street.
In January 2007, the Corps determined that the closure structure was unreliable for reducing flood risk from the Potomac River and gave the system an unacceptable rating. This unacceptable rating led FEMA to “de-accredit” the Potomac Park Levee System. In September 2010, FEMA released new Flood Insurance Rate Maps (FIRM) that show the downtown area and the Southwest part of the district without flood protection. With guidance from the Corps, the District of Columbia initiated design of a more reliable removable post and panel closure structure in response to the FIRM revisions. The Corps received American Recovery and Reinvestment Act funds to finalize design and award the construction contract. Construction began January 2011 for a total estimated project cost of approximately $9.4 million.
We work closely with our partners to develop the best strategies we can to reduce flood risk in this critical, densely-populated area. However, we stress that it is imperative for the public to know their flood risk and take appropriate actions to mitigate this risk.
Washington, D.C is susceptible to three types of flooding: Potomac and Anacostia river flooding, coastal storm surge, and interior.
The levee system also includes an existing permanent approximately 12-foot-high earthen levee that runs along the Lincoln Reflecting Pool and temporary sandbag closures at 23rd Street and Constitution Avenue, as well as along P Street SW. The levees and closures function as a system to provide flood-risk management.
NPS completed in fall 2014 a test install of the levee system closure structure at 17th Street to ensure it will be erected properly in the event of high water. The install was also required as part of the Corps’ levee system evaluation.
The Corps provided to FEMA in spring 2016 a positive levee system evaluation report that demonstrates the Potomac Park Levee System will reduce riverine flood risk to communities behind the levee by containing flood waters that equate to the predicted 100-year flood event (a 1 in 100 chance-per-year event); and that shows NPS can install the 17th Street closure structure, and operate and maintain the levee system as required. FEMA "accredited” the levee system after a 90-day public review period and issued in September 2016 a revised FIRM for the District of Columbia. This map includes localized flooding hazards in the Federal Triangle Area, and other vulnerable low-laying areas of the District. The Corps will conduct periodic and annual inspections on the system to ensure authorized risk reduction and to ensure the system is being operated and maintained sufficiently.
According to the District Department of the Environment, completion of the 17th Street closure helps to achieve one of the goals of Sustainable DC—the District Government's long-term sustainability plan—to make the district more resilient by reducing the risk of flooding to district residents, agencies, and businesses.
Upcoming related work as part of Phase II plans for the system includes 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. These plans still need Congressional funding.