Washington, D.C. and Vicinity Flood Risk Management Project Improvements at National Mall and Memorial Parks

Published April 10, 2020
Expiration date: 5/13/2020

ALL INTERESTED PARTIES: The U.S. Army Corps of Engineers, Baltimore District (USACE) and the National Park Service (NPS), have prepared a draft Environmental Assessment (EA) and a Finding of No Significant Impact (FONSI) for proposed construction of improvements to the Washington, D.C., and Vicinity Flood Risk Management (FRM) Project at the National Mall and Memorial Park (NAMA).  The existing project provides FRM for portions of the monumental core, portions of Pennsylvania and Constitution Avenues, and for other public and private facilities located south of the U.S. Capitol to Fort McNair.  NAMA existing FRM features include a levee between the Lincoln Memorial and Washington Monument adjacent to the reflecting pool; a post and panel closure system at 17th Street; and a temporary closure at 23rd Street (sandbags or inflatable bladders).  The existing project also includes a temporary closure at P and Canal Streets at Fort McNair. 

The project was authorized by the Flood Control Act of 1936, then modified by the Flood Control Act of 1946.  The project provides FRM for downtown Washington D.C., for flood events up to 700,000 cubic feet per second (cfs) from the Potomac River.  The original project was constructed in the late 1930s, but underwent modifications in the 1940s, 1970s, and 2010s.  Proposed improvements to the NAMA FRM project components at the levee and 23rd Street were evaluated in USACE EAs prepared in 1992 and 1996.  However, the improvements were not constructed due to lack of funding.  USACE and NPS have prepared this EA because more detailed project designs have been prepared and environmental regulations have changed.     

With the 23rd Street and Constitution Avenue temporary closure installed, 17th Street post and panel closure erected, and temporary closures installed, the project would provide FRM for a discharge of up to 700,000 cfs, but with less than the authorized 1 foot of freeboard.  Accordingly, the project would require additional temporary closure efforts on the levee crest, likely by sandbag, to provide FRM with adequate freeboard.  The temporary closures at 23rd Street and Constitution Avenue, and on the levee crest, are now considered an inadequate means to provide FRM by USACE and the Federal Emergency Management Agency. 

The proposed improvements would provide long-term FRM to authorized levels with adequate freeboard to increase project reliability under extreme flood events.  USACE is the lead agency for the improvement project; NPS is a cooperating agency.  The project would be constructed by USACE and maintained by NPS. At the levee, up to 4 feet of earthen material would be added along approximately 2,450 feet of the levee crest to raise it to approximately 18.7 feet elevation1.  Sluice gates would be constructed in sewer lines crossing under the levee to prevent floodwater from entering into the sewer system.  An earthen berm would be constructed along the southwest side of the land parcel on the southwest side of the intersection of 23rd Street and Constitution Avenue.  An earthen berm would also be constructed between the east and west bound ramps of the Theodore Roosevelt Bridge at Constitution Avenue on the west side of the intersection.  These berms would crest at 20 feet elevation and have gentle side slopes. Approximately 55 trees would be removed that could threaten how the levee or berm functions.   

In compliance with the National Environmental Policy Act (NEPA), USACE and NPS have prepared this draft EA and evaluated potential effects on the human environment.  All applicable environmental laws have been considered.  USACE and NPS have and will continue to coordinate with the National Capital Planning Commission, District of Columbia Historic Preservation Officer, and other agencies and entities concerned with NAMA.  Project construction would cause temporary minor detrimental impacts to air quality, traffic, and noise.  When completed, slopes of the raised levee and new berm would be gentle and conform to existing landscape character.  The FRM project is designed to manage riverine and tidal flooding only.  It will be incumbent upon Washington, D.C. to address remaining flooding threats to the downtown from heavy precipitation that could cause interior ponding and exceed sanitary sewer system pump capability. 

USACE and NPS request comments regarding the draft EA and FONSI within 30 days of the date of this notice.  For federal and district agencies receiving a copy of this notice, we request that you provide comments concerning your responsibilities.  The draft EA and FONSI are available at the USACE project web page: Comments can be submitted electronically to: ethan.a.bean@usace.army.mil. Written comments can be sent to: U.S. Army Corps of Engineers, Attn: Ethan Bean, Planning Division, 10th Floor, 2 Hopkins Plaza, Baltimore, MD 21201.  If you have any questions, please contact Ethan Bean by telephone at (410) 962-2173 or by email at the address above.