Flood Control and Resilience with the National Mall Underground

National Mall Underground Exhibit Poster 2014A truly innovative, comprehensive, public-private approach to Mall planning, the National Mall Underground consolidates in one multi-purpose facility the needs of all constituencies – the public, Smithsonian, National Park Service, District of Columbia government, Architect of the Capitol, General Services Administration, and others. The Underground will solve longstanding stormwater flooding problems and create a more welcoming, lively, and resilient Mall in the heart of the nation’s capital.

Copyright Arthur Cotton Moore
CLICK to enlarge this annotated diagram. Copyright Arthur Cotton Moore

The National Mall Underground is a multi-purpose flood protection and parking facility that also provides a much-needed Mall Welcome Center with restrooms and food options. During heavy storms, vehicles will be removed from the lower two stories to allow flood waters to flow into these areas until they can be pumped out later into the sewer system.

This multi-function approach allows the National Mall Underground to use multiple revenue sources — including parking fees and stormwater credits — to finance more than two-thirds of the cost of a stand-alone flood detention facility. The cost is estimated to be $200 million.

The project has been developed since 2011 by the National Mall Coalition in partnership with local philanthropist and businessman Albert H. Small and renowned architect Arthur Cotton Moore FAIA, and in consultation with federal and District of Columbia agencies, as well as engineering, parking, security, and sustainability experts. 

Copyright National Mall Coalition
CLICK to enlarge. The Underground will accommodate cars, tour buses, irrigation cisterns, and a visitors’ center
Copyright National Mall Coalition
CLICK to enlarge. During heavy rains, vehicles will be removed from the lower floors, which will collect stormwater flow

Who benefits and how?

Screen Shot 2015-09-15 at 5.21.50 PM
Watch a 2-minute virtual tour of the National Mall Underground

The project benefits the American public, DC residents, the Smithsonian, and local and federal government:

  • A storm water reservoir able to collect 34 million gallons of floodwater to protect Smithsonian museums and federal and DC government buildings from the kind of flooding that devastated the Federal Triangle and Mall area in 2006*
  • Parking for 150 tour buses to relieve congestion and reduce significant pollution from circling and idling buses on city streets*
  • Parking for 1,100 cars and welcome center with public amenities to improve access, increase the Mall’s vitality into the evening hours, and connect visitors to local cultural life*
  • Irrigation cisterns and geothermal cooling capacity to increase Mall sustainability, reduce the energy footprint, and conserve valuable resources for the National Park Service, Smithsonian, and public buildings*

    Buses line Mall streets
    Parking for tour buses is a federal and District priority
  • Mall Shelter Station to enhance security and public safety during large public events such as the inauguration and provide Mall visitors with shelter during emergencies

*Parking fees and water and clean energy tax credits make this a largely self-funding facility, according to financial analyses conducted in 2014

Why the multi-purpose Underground now?

2011 DC Water/NCPC Federal Triangle Stormwater Drainage Report
CLICK above to read this 2011 Federal Triangle Stormwater Drainage Study study commissioned by DC Water and the National Capital Planning Commission that proposes solutions including construction of a cistern under the National Mall

In June 2006, heavy rains inundated Mall grounds, as well as adjacent museums, roads, businesses, and federal buildings, causing millions of dollars in damage to property and cultural resources. The National Archives remained closed for three weeks.

Extent of 2006 flood - Copyright Arthur Cotton Moore
CLICK to enlarge this reconstruction of the extent of the June 2006 floods that inundated Constitution Avenue, Mall museums, and public buildings, causing millions of dollars in damage.

In response to that flood, 14 Federal and District agencies completed a report that predicted stormwater flooding will increase and intensive in coming years (click at left to read the 2011 report), concluding that one solution was to construct cisterns under the Mall. But the report was put on the shelf because no government entity took responsibility to act on the recommendations.

We saw this data-based study’s findings and recommendations as an exciting opportunity to both solve the flooding problem as well as serve other needs of all Mall constituencies that were not being addressed by government planners. Learn more at this dedicated National Mall Underground website.

Read coverage in the media here. Learn more about Mall flooding history under Resources–Research.

What are the precedents?

Rotterdam’s MuseumPark combines a large parking facility in the museum district with a floodwater cistern 
This dual purpose dike/parking garage in Katwijk, Netherlands helps "Holland deal with an abundance of water on one side of the barrier and an abundance of vehicles on the other."
This dual purpose dike/parking garage in Katwijk, Netherlands helps “Holland deal with an abundance of water on one side of the barrier and an abundance of vehicles on the other.” 

Major cities and tourist destinations across the US and around the world have provided better access for visitors while solving traffic congestion problems by creating underground parking facilities. Chicago’s Grant Park and Millennium Park have over 5,000 underground parking spots; St. Peter’s basilica in Rome has convenient underground tour bus parking. Review these and other examples of underground parking here.

When it comes to innovative, multi-purpose parking/flood solutions, the Dutch have taken the lead, as shown in the examples illustrated above in Rotterdam and Katwijk.

Why a collaborative effort?

The National Mall Underground requires collaboration because there are myriad problems facing the National Mall that, due to fragmented jurisdictions, cannot be addressed by any single current planning entity.

We had over 200 meetings and working sessions that brought together people from a variety of stakeholders — from the White House to District of Columbia government, and the Smithsonian to the American Institute of Architects — to expand the scope of the project so it could solve a host of problems efficiently.

NMU Exhibit photo
The National Mall Underground Exhibition was open to the public from November 2013 to December 2014

We created a year-long National Mall Underground exhibition in Downtown DC, with a speaker series, to further draw input from local residents, members of the business community, and tourists.

Such intense, sustained collaboration has capitalized on innovative thinking while leveraging the limited resources of individual agencies to solve problems that otherwise appear insurmountable.

What’s next? 

Copyright Arthur Cotton Moore
Since fall 2014 architect Arthur Cotton Moore has been creating additional new options such as this one (CLICK to enlarge) that uses automated parking technologies and includes hundreds of geothermal rods beneath the parking facility to provide renewable energy for nearby public buildings. Copyright 2014 Arthur Cotton Moore/Associates

In addition to collaborating with federal and DC stakeholders on developing the design concept, we have consulted a host of federal and DC studies — flooding and flood control, tour bus parking, water resource management, transportation, and visitor needs — and commissioned supplemental studies — engineering, parking demand, geothermal, and cost benefit analyses. We have made all this data available to federal and DC entities.

The Army Corps of engineers is planning to do a “technical review” of these studies to determine what additional studies are needed, if any, to demonstrate the project’s feasibility.

CLICK ON THE PRESENTATION BELOW to review an in-depth review of the Mall needs and the Underground solutions:



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