Watch the “Flood Resiliency for the National Mall” Webinar Hosted by AIA|DC

Note: This presentation was originally scheduled to be a public exhibition and reception at the George Washington University Museum in April 2020 but was reconfigured into a public webinar due to the coronavirus.

June 3, 2020 — The National Mall Coalition’s presentation “Resiliency for the National Mall” turned out to be “Architecture Month’s biggest event,” according to the sponsor American Institute of Architects, drawing 225 registrants and 135 actual attendees.

During the one-hour webinar, Coalition chair Judy Scott Feldman presented an overview of DC’s little-known history of devastating flooding, of unsuccessful attempts by government entities to solve stormwater flooding such as inundated the Federal Triangle and Mall area in 2006, and of the Coalition’s proposed National Mall Underground solution.

Architect Arthur Cotton Moore, vice chair of the Coalition, discussed the evolving design of the Underground facility: the basic box of the flood water reservoir, which also includes a Mall Welcome Center, tour bus and car parking, irrigation water cisterns, and geothermal wells. In the Q&A discussion, members of AIA and the public posed questions about the desirability of parking, structural engineering feasibility, and who can make it happen.

“We were thrilled at this opportunity to reach out to the public, to show both the existential threat of flooding to our Smithsonian museums and national heritage on the Mall and a possible solution with multiple benefits not only to government but to the American people,” said Feldman.

AIA’s Architecture Month theme, “Civic Spirit,” is perfectly apt when we consider who can make it happen, she said.  In 1900, it was local residents working with AIA and Congress who led the effort to create the McMillan Commission’s 1902 plan that is the basis of today’s Mall. Once again, the public, AIA, and Congress need to take action: to solve the flooding problem and create resiliency for the National Mall.

The webinar can be viewed in full below, including the online question and answer session. Additionally, see below answers to the numerous questions that could not be answered in the limited webinar timeframe. Feel free to submit comments or questions to Judy Scott Feldman at

Full presentation

Questions, comments and  answers from the Resiliency for the National Mall Webinar hosted by the American Institute of Architects (AIA) on June 3, 2020.

 1) Can you overcome the security concerns?

 The major security concern is probably blast from an explosive device contained in a bus or car. The Coalition made a point, from early in the concept development, to seek input from federal and DC security agencies – Homeland Security, Secret Service, US Park Police, Capitol Police – and encountered no serious concerns. The National Mall Underground, unlike other Mall-area underground parking (Air & Space, Hirshhorn, American History museums), will not be located under any museum or other structure containing people or precious artifacts. Instead, the facility will be located beneath the grass panels of the Mall, minimizing any danger from blast. To further protect against any danger of blast, buses and cars will be screened as they enter. The vehicle screening process used at the nearby Ronald Reagan International Trade Building (which has parking directly under an occupied public building) is a potential model that has proved successful. To be realistic, the Underground would be an unlikely target, since it would be full of empty buses and robotically parked, unoccupied cars.

2) If they dig up the National Mall for this project, what happens to the beautiful new turf that they put in recently? It’s so nice and green right now since the pandemic.

The beautiful new turf, and the four feet of soil beneath it, will be carefully removed, stored, and reinstalled. Costs of Underground construction will include costs of removing and reinstalling the turf.

4) What can we, as citizens, do to support the plan for the National Mall Underground? Should we write letters and if so, to whom?  Besides donations to the Coalition, is there an existing fund to raise money for this?

The Coalition is an all-volunteer, non-profit organization and we welcome public support, donations, and new members. Ultimately, Congress will have to decide if and how Washington’s existential flood threat is to be solved; the numerous federal and DC stakeholders have neither the jurisdiction nor funding to proceed. There is as yet no fund to raise money for this; the financial plan lays out a model for funding in the future. Congress needs to be informed of both the urgent need and the public’s interest in the National Mall Underground solution. So writing letters to your elected representatives is an important step. The Coalition will provide on our website a basic template letter to Congress and links to Congressional offices:

5) What are the Park Service’s specific objections?

The National Park Service staff who have stated their opposition say that the National Mall Underground is not consistent with the Park Service’s 2010 National Mall Plan, their maintenance plan for the areas of the Mall under their jurisdiction. These areas include the grass panels where the Underground would be located. In particular, the Park Service says they are opposed to any new public parking on the Mall.

6) How many buses might be parked in the bus area?

The number of spaces available for bus parking has been evolving. Earlier designs included space for 170 or so buses. The latest design iteration, which includes bus parking on both the floodable lower level and the upper, Welcome Center level, can hold as many as 580 tightly packed buses.

7) Why keep okay-ing so many private cars? Public transportation pleeaaaase.

 While public transportation remains the preferred mode to get around in urban environments, tourist destinations around the world (e.g., Rome, Amsterdam) and this country (Chicago, Boston, Philadelphia) understand that they must accommodate the needs of out-of-town visitors, especially families and people of limited mobility, while also supporting the economic benefits of tourism. This facility is aimed at those visitors and will not be open to commuters, who are the source of DC’s traffic gridlock. While many people might favor a reduction of private cars as the primary means of transport, cars are more likely than not to be with us for many years to come. We need to factor that in regarding Mall visitors.

8) Motorcoaches often drop customers for a short museum visit, say 1 hour, before taking them elsewhere. Will this garage handle frequent entries and exits?

There will be a section of the upper level bus parking garage designated for short-term and in-and-out bus parking.

9) Has the corona virus and possible future needs to social distance affected the visitor center plans?

It’s too early to really understand the long-term implications of social distancing on how our museums accommodate crowds. We believe, however, that once we are past the immediate difficulties, visitation to the Mall will pick up again and continue to grow – as will the need for bus and car parking, and for the Welcome Center public amenities.

10) So a bus drops guests and parks. Then the guests must walk all day between Monuments, White House, Capitol, and Museums? Guests usually complain about that much walking.

Yes, walking long distances is difficult for people. We believe the key to helping people better navigate the huge distances of the Mall will be to coordinate the Underground parking facility with a shuttle service – including DC Circulator and future electric vehicles – to facilitate movement around the Mall while the buses stay put underground and off city streets.

11) What does the geothermal system serve if most buildings are using GSA steam?

As said in the presentation, it was then-GSA Administrator Dan Tangherlini who in 2014 first suggested we add the geothermal field to the project. His reason was that GSA is required to convert the existing steam system used in its many buildings around the Mall to renewable, clean energy. Geothermal is one such clean source. But geothermal also requires a large open area, and the Mall, Tangherlini pointed out, is one of the few spaces in DC not already built up, and so a perfect place for geothermal. The mechanical systems in many of these buildings are reaching the end of their lifespan and will need to be converted to a sustainable system. Geothermal provides that sustainable alternative.

12) How many entities have given buy-in so far?  What is the timetable?

Many Mall stakeholder entities have expressed interest in the Underground concept during our briefings with them and at our presentation to the Silver Jackets inter-governmental workshop in September 2018. But because of the multiple jurisdictions involved in Mall governance, with no one entity having authority for the Mall as a whole, no agency has spoken publicly or taken the initiative to lead further action on the project. The National Mall Coalition, an all-volunteer nonprofit, believes it will take leadership from Congress to assign authority for next steps. The timetable is likely three years after approval by Congress.

13) How would you fetch your car?

When you arrive at the garage, you are asked to go to one of several drop-off stations. There, you leave the car, whereupon the robotic system stacks the car in the garage. When you return to the Welcome Center to retrieve your car, you pay and the robotic system delivers the car to the pick-up location.

14) The facility will experience flooding periodically, so how will you control the inevitable corrosion of the structure from water infiltration?

Since water will contact the outside of the facility as well as the inside of the facility, there is the threat that the rebar used in a reinforced concrete structure would rust, deteriorate, and eventually fail. Therefore, we and our consulting engineers are looking at options and will consider using a plain, unreinforced concrete structure. A complete concrete structure can withstand all kinds of forces – one example being the Pantheon in Rome.

STRUCTUAL ENGINEER comment added post webinar: To protect the structural elements against prolonged exposure to groundwater, the below grade structure would have a waterproofing system surrounding its outer surface. Interior surfaces would be exposed to floodwaters on an emergency basis only, and would be of such a limited duration and frequency so as not to be a concerns regarding concrete deterioration. Elements that were planned for extended exposure to water would be designed with additional protective measures such as special concrete mixes, epoxy coated reinforcing or, potentially, the use of unreinforced concrete, where appropriate.

15) Screening loaded busses filled with suitcases takes a long time. How many buses can you inspect per hour?

Tour buses will be bringing visitors from local and regional hotels, not from airports. They should not have any baggage or luggage that will require time-consuming screening. To ensure against security threats, screening protocols will be developed to direct bus companies and drivers to arrive with empty luggage compartments, thus minimizing screening times.

16) I’m curious if you are working with the American Bus Association, or/and others who can help you analyze how tour buses and tour groups actually negotiate the Mall, as well as who could help with lobbying efforts?

Yes, we’ve met twice with the American Bus Association, and spoken with them on several occasions as the project has developed. We learned from them that they definitely want parking under the Mall, and they want rest facilities for bus drivers. Bus drivers are unhappy about $100 fines resulting from DC laws that limit drop-offs of passengers to four minutes, and the lack of places to park in-between visitor drop-offs at museums and monuments.

17) Are there estimates of the amount of geothermal energy that could be produced? Could it provide charging for electric buses?

It could produce 3,000 tons of cooling per hour, which could take care of most of the buildings on the Mall. Yes, it can provide charging for electric buses.

18) Who will have ultimate authority over the facility? — Not the NPS which is historically underfunded?

Ultimately, because of the multiple agencies involved, it will probably require Congress to create a public-private entity (similar to the Pennsylvania Avenue Development Corporation) to manage the facility for the public.

19) What’s the future plan about the flood water stored in the proposed storage or cistern area ? Are you proposing to reuse it or let it infiltrate into the ground gradually?

The floodwater in the main reservoir storage area – filthy with dirt, oil, and debris from city streets – will be released in a controlled manner to the DC sewer system and sent to Blue Plains treatment facility. As an alternative, we have been looking at other environmentally sustainable solutions for treating the floodwaters collected in the reservoir. Only water collected in the smaller cisterns – rain and groundwater – will be used for irrigation.

20) Auto parking was once allowed under the Air & Space Museum. What happened?

Yes, many of us used to park in that convenient garage. However, it was closed to the public in the 1980s and now is limited only to staff parking. Here’s how The Washington Post reported the situation in 1992 —

“Smithsonian officials closed the Air and Space garage, and public parking lots at the Natural History and American History museums, in 1986 because of fear that terrorists might drive into the parking areas and detonate bombs.

Although the terrorism fear mostly has disappeared, the 785 parking spaces at the Mall’s three most popular museums have remained off-limits to the public. Meanwhile, senior employees of the Smithsonian have been allowed to park there for free.”

So, while parking was originally intended for the public, today only staff can use these spots. Meanwhile, no one is planning to develop parking for Mall visitors, and the National Park Service rejects additional parking in its 2010 National Mall Plan. Who’s representing the needs of the American public? That’s what the Coalition is trying to do with the National Mall Underground by providing parking under the grass, not under a building.

21) Have you taken into account the future of electrical vehicles and buses? At a minimum stubbing into the additional electrical framework?

Adapting to changing needs is certainly something we intend to do, and electric charging stations seems an obvious addition to the design. So, too, we might add, are potential future uses of the Underground’s huge open space for needs we cannot even know at this time. For example, in future the need for car parking may be reduced by self-driving vehicles and other alternatives. The car parking spaces could be converted to bus parking. One potential use suggested by a nonprofit leader is that the facility could be used, because of its central location in DC, as a shelter-in-place facility in times of weather or security emergency. The beauty of the simple, basic box design is that, once built, the Underground could be adapted to a host of future needs.

22) Is there any support from Congress?

From the beginning, we’ve been briefing members and staff in Congress. There is support for the concept in the Senate and House. Some members are interested in the parking, others in the flood reservoir, still others in the creative multi-purpose function and possibility of private funding; often it depends on the Congressperson’s committee membership and interest. It’s not clear which committee in Congress ultimately will take the lead: Energy? Homeland Security? Infrastructure? An existing entity? Our financial advisors suggest Congress should create a nonprofit entity to complete the design, environmental review, funding, and construction of the project. But yes, there is support, and we hope to mobilize it once the COVID-19 crisis and current unrest are behind us.

23) BS on “only Mall visitors”  NO CARS on The Mall – cut down stop it!!! only buses to drop off and pick up!!

There already is plentiful parking on the Mall – on Madison and Jefferson Drives. Many of these spots are reserved for security, employees, and so on, and also include some public parking. The lines of parked cars on both sides of these inner Mall streets clutter the open space and create barriers for pedestrians navigating between them. Closing the surface streets to cars and putting those cars underground instead will preserve that limited parking capacity while also freeing up the Mall to pedestrians, bicyclists, and pick-up and drop-off alone by cars and buses.

24) Tour groups often visit Memorials before 10AM, especially in the spring. Student groups expect activities to begin before 10am. Capitol opens at 8:30. White House tours start early too.

Good point. We will probably need to have a portion of the bus garage that will open earlier to accommodate early tours. In addition, the future traffic study will need to collect and evaluate this kind of information and make recommendations for opening times – and processes, such as scheduling reservations, to restrict access to the Underground to only tourist vehicles. Thanks for pointing this out.

25) How would the storm water be collected to the proposed reservoir?

Some of it initially will come by gravity, flowing from Constitution Avenue into the lower level of the Underground. As the storm continues, floodwaters will be pumped from low-lying Constitution Avenue and its environs into the Underground.

26) Enjoyed hearing your challenge to rise above today’s piecemeal jurisdiction-based planning. In your opinion what is the profile of the “ideal champion” in government to support such a transformative infrastructure investment?

Our first answer would be someone like Daniel Patrick Moynihan. We need to find a champion. We invite suggestions from all of you. But the AIA had this role in 1900 and helped create the McMillan Commission that gave us the Mall we know today. We believe the flood control function and clean energy geothermal component offer the greatest economic benefit to the federal government, so relevant Congressional committees are a likely source for support and legislative action. For DC residents and government, getting buses off city streets is a major benefit. Also the Mall Welcome Center will add new life to the Mall, which, typically, goes dark and dead at night after museums close; a more lively Mall will help connect thriving Downtown and the growing Southwest Waterfront neighborhood. A strong champion for the continued vitality of our nation’s capital could lead the Underground effort – someone from DC, Congress, or our civic and architectural community.

27) How many cars and buses can currently park along this part of the mall?

There are approximately 1,200 metered parking spaces through the entire National Mall area, which includes parking at the Tidal Basin and other areas of East and West Potomac Park near the Lincoln Memorial. We do not have information on the number of parking spaces on Madison and Jefferson Drives where the National Mall Underground would be located. On a typical day during tourist season, Madison and Jefferson Drives are lined with rows of buses in front of the museums on both sides of the street between 4th Street and 14th Street.

28) Does it connect into the existing stormwater system? How?

Yes, it connects directly to the stormwater system but the engineering has not yet been done on this.

29) Was the area of the Mall that is planned for the parking and flood water storage, actually as flooded as Constitution Ave was in 2006?  If not, what will make the flow of flooding to actually drain effectively to the designated blocks?

The location of the Underground, between the 9th and 12th Street tunnels, is on higher ground – about 20 feet higher – than Constitution Avenue. But the facility will descend 40 feet, close to 50 feet, into the site. That will allow for some gravity feed to the lower level of the Underground. If stormwater flooding continues and grows, floodwater would be pumped into the facility. Engineering details are still being worked out.

30) Properly designed, you can easily modify the parking to accommodate buses or cars in an accordion manner for maximum flexibility.

We are thinking the same, that the facility could adapt to changing parking and other needs as conditions change, and needs for bus parking grow, in coming decades and beyond.

31) Since neither the Smithsonian nor NPS sell tickets for the mall, how would you ensure they are visitors rather than commuters?

Good question. The biggest concern is that commuters, who are the main cause of DC’s traffic gridlock, might try to use the facility. The facility will not open to cars until 10 a.m. or later. This will prevent commuters from gaining access.

32) Cars also will pay for the project or at least reduce the costs. The buses will likely be free or heavily discounted.

Yes, car parking fees will provide an important source of revenue for the facility, the bus parking less so.

33) I’m assuming large parking fee, so how is this different from taking a family of 6 on the Metro?

In our parking study, we estimated hourly and daily costs that are comparable to private parking garages in the Downtown area, currently around $20 per hour. Many Mall visitors economize by staying in hotels in the suburbs; Metro costs from these distant locations can run $15 per person round trip, close to $100 for a family a six. A car can accommodate the entire family plus strollers or walkers plus other needs, such as bag lunches, drinks, etc., that families typically will pack for a day on the Mall. Some families will want that convenience and comfort for what is often a day-long, exhausting – if exhilarating – visit to our national museums and monument. One additional note: Even if visitors are willing to pay high fees to park in DC’s private garages, the fact is that most of them are closed on the weekends, making it difficult to impossible for people arriving by car to find parking. The Underground will fill that weekend need while also bringing in revenue to sustain the facility.

34) Like the Capitol Visitor Center have you systems for chemical containment from terrorism?

At this time, the still-early concept design for the Underground does not include such a feature. As the design goes through further development in consultation with security experts, anti-terrorism elements will be studied and included as necessary.

35) Looks from the site plan like exits are near the Smithsonian Castle which is very near a Metro stop. what is there to stop workers from parking their cars there and taking metro to their work?

This is, of course, a concern that must be addressed. See our response to Ms. Courtenay at 17:50, above.

36) What happens to the water in the cistern? is it used to water the plants and grass?

Only the water collected in the smaller cisterns at the east and west ends of the facilities will be used for watering Mall plants, trees, and grass. Any stormwater floodwaters collected in the reservoir will be filthy with street oils and debris and cannot be used for watering. Instead, these waters will be pumped out, once flooding ends, in a controlled manner into DC’s sewer system and on to Blue Plains water treatment facility.

37) Have you considered providing an email template for us to forward to our senators and representatives?

This is a good idea. We will prepare such a template and make it available on our website:

38) I believe it was stated this “box” will be constructed of unreinforced concrete.  Why unreinforced with the history of the earthquake in 2011?

STRUCTUAL ENGINEER comment added post webinar: The primary structure will be designed using conventional reinforced concrete technology with appropriate protection for exposure to de-icing salts associated with vehicular traffic. Elements that were planned for extended exposure to water would be designed with additional protective measures such as special concrete mixes, epoxy coated reinforcing or, potentially, the use of unreinforced concrete, where appropriate.

Regarding seismic design, the project will be designed per the latest code requirements for seismic design, however, there will be only nominal impact of seismic- mostly related to good concrete detailing practices, as the proposed structure is entirely below grade and laterally restrained on all sides by the surrounding soil.

39) What is the plan to protect the concrete from the inherent stresses of being underground? (ie freezing and expansion, seismic, etc)

The top of the concrete box will be four feet below the surface and the frost line in DC is two and a half feet below the surface. So, there will be no freezing or expansion of the concrete box. Of course, there will be some expansion and contraction, and it will be accommodated with construction and expansion joints. As for seismic, see our response to Ms. Bazan at 18:04.

40) Thanks! Don’t expect response, and I missed start of session so apologies if my question had been addressed by that list. I’m a licensed DC tour guide – tour groups are not going to walk from 12th St to the memorials, so I do think that question of how quickly buses can move in and out is crucial – they’ll need to drop off at Lincoln and get back there in about an hour to pick up, for example. We have also lost eating places for the eighth grade groups, if you could help with that, would get business! (See the Reagan Building food court on a normal spring day, not 2020) Thanks for what you’re doing here!

There will be a special area on the upper bus level for in-and-out access. See our answer to Ms. Cohen at 17:41, above. As for eating places for schoolchildren, we definitely know of that need from our conversations with DC tour guides and had in it mind when we developed the large area of vending and dining tables in the Welcome Center.

41) Did you include costs of relocating all of the existing utility systems under the Mall in your construction estimates? Have you considered the impacts of such relocation on the existing buildings along the Mall that might depend on them?

Dewberry – the engineering, planning, and design firm – looked at this and picked this particular site because it had no underground utilities.

42) The proposed parking would require extensive exhaust ventilation. Where would the surface air shafts be located, so that they would neither be visual intrusions within the grass panels nor disturb the root systems of the elms along them?

The robotic garage has extensive storage for unoccupied cars that requires no exhaust system and no heating or cooling system. The three or more entrance pavilions, to be situated within the tree panels of the Mall, will have large exhaust shafts for both exhaust and make-up air.

43) Wouldn’t the proposed skylight in the welcome area be a visual intrusion within the center Mall grass panels?

This “skylight” is an artificial skylight using LED lights to simulate natural light and create a welcoming gathering space. This skylight would not penetrate the surface of the Mall.

44) Have you included the cost of restoring the recently rehabilitated Mall grass panels in your cost estimates?

Clark Construction, which constructed the drainage and irrigation system for the Park Service’s turf project, knows what is needed to remove and replace those elements. They have included those costs in their estimate of the Underground costs.