The National Mall Levee
Washington's location at the confluence of the Potomac and Anacostia Rivers creates overbank flooding risks. Following significant river floods, levee systems were constructed in the 1930's to protect downtown Washington.
One levee system is located along the Anacostia River, while the National Mall levee system extends along the National Mall and through Southwest Washington. Both levee systems required improvements to meet tougher flood protection standards established after Hurricane Katrina.
While improvements to the Anacostia levee have been completed, the key improvement needed for the National Mall levee was an improved temporary closure across 17th Street, NW near Constitution Avenue.
Recognizing that the closure design had to be compatible with the Mall's cultural and historic landscape and coordinated among many jurisdictions, NCPC facilitated an intense inter-agency effort to design, review and fund this $9.5 million project.
Construction on the post and panel closure and retaining walls began in 2010 with completion expected in summer 2012.
Stormwater Drainage Flooding
Another type of flooding risk is created by stormwater drainage. Washington's bowl-shaped topography directs stormwater towards the center city, particularly along Constitution Avenue, NW. During heavy rains, the sewers in the downtown area (a combined sanitary and stormwater system) can become overburdened.
In June 2006, intense localized rainfall caused extensive flooding, affecting operations, buildings and infrastructure of key federal agencies, historic landmarks, and tourist destinations within the Federal Triangle. The National Archives, the Internal Revenue Service, the U.S. Department of Commerce, the U.S. Department of Justice, the Environmental Protection Agency, numerous Smithsonian Museums, the National Gallery of Art and Metrorail all suffered damage and interruptions in operations.
In response to this event, NCPC, along with other federal, local and regional agencies, have continued to work together to develop strategies to reduce the risks of stormwater drainage flooding. Recent products have included a technical study to evaluate system-wide solutions and a flood-proofing seminar for facility managers.
Rendering of levee post and panel closure across 17th Street NW
Federal Triangle Stormwater Drainage Study Companion Report - October 2011 [PDF 1.62MB]
Federal Triangle Stormwater Drainage Study - October 2011
Full Study [PDF 6.1MB]
Exec Summary [PDF 852KB]
Watch a video about the study »
Executive Director's Reccommendation for National Mall Levee - February 2011 [PDF 792KB]
National Mall Levee Fact Sheet - November 2010 [PDF 500KB]
Washington, DC - January 2008 [PDF 3.2MB]
Flood Proofing Seminar - October 2011
NCPC Federal Triangle Stormwater Drainage Study Presentation - October 2011 [PDF 2.3MB]
Presentation on Flood Protection to Metropolitan Washington Council of Governments (COG) - March 2011 [PDF 2.6MB]
2007 Flood Forum - June 2007 [PDF 490KB]
Other Related Studies
Flood Risk Maps - District of Columbia Department of the Environment
Executive Order 11988: Floodplain Management
NCPC Implementing Procedures for E.O. 11988 [PDF 625KB]
FEMA Flood Insurance Study for Washington, DC - September 2010 [PDF 1.6MB]
Tetratech Interior Drainage Study for Potomac Park - January 2008 [PDF 2.2MB]