Army Corps Says National Mall Coalition Project Can Solve Mall Flooding

By Judy Scott Feldman, PhD, Chair

Read the USACE Technical Review

The US Army Corps of Engineers has completed its Technical Review of the National Mall Coalition’s proposed National Mall Underground flood reservoir. The Corps concludes that this project could fill a significant gap in Washington’s stormwater flood protection system.

The National Mall Coalition developed the National Mall Underground in response to the urgent need for flood protection for museums and public buildings in the Federal Triangle and Mall area. In June 2006, torrential rains overflowed the DC storm sewers and inundated Constitution Avenue — where Tiber Creek used to flow until it was covered over in the late 19th century. Flooding in nearby buildings including the National Archives and National Museum of Natural History caused millions in damage.

An interagency, intergovernmental task force concluded in 2011 that such devastating flood events were likely to increase in frequency and intensity  in coming years. One proposed solution was to construct a stormwater reservoir under the grass of the National Mall.

The Coalition saw the reservoir solution as an opportunity to solve multiple problems and needs with one multi-purpose facility that also provides benefits to tourists and other Mall visitors.

National Mall Underground flood area
Buses would be removed from the lower level of the National Mall Underground to allow floodwaters to flow from Constitution Avenue into this floodwater reservoir.

Thus, the National Mall Underground, which offers stormwater flooding protection, and much more:

  • A 30 million gallon emergency floodwater reservoir (the targeted 200-year flood requires a 24 million gallon capacity) constructed under the grass, between the 9th and 12th Street tunnels.
  • Parking for tour buses and cars, removing 150 buses and 1072 cars from city streets; during storm events, the lower, bus level would be evacuated and floodwaters would be allowed to fill that lower level.
  • On the upper level, which would not be flooded, car parking and a Mall visitors center with restrooms and food service.
  • Cisterns at each end to collect rainwater and groundwater for Mall irrigation.
  • A field of geothermal wells to provide clean heating and cooling to nearby museums and government buildings.
  • Revenue from parking, water credits, irrigation, and geothermal offers self-financing opportunities that could attract a public-private partnership.

On September 5th, 2018, concept architect Arthur Cotton Moore FAIA and Judy Scott Feldman, PhD, Chair of the National Mall Coalition Board, presented the National Mall Underground project to an interagency, intergovernmental flood group, the DC Silver Jackets, which is seeking solutions to the Federal Triangle/Mall stormwater flooding problem. Those in attendance included representatives of DC Water, the National Park Service, the Smithsonian, GSA, DC’s Department of Energy and Environment, and the Army Corps.

Official US Army Photos by John Sokolowski

Learn more about the National Mall Underground. Read the Army Corps report hereRead the National Mall Coalition statement about that report here. And visit the website of the DC Silver Jackets for more information into government efforts to find solutions to the urgent stormwater threat.


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