“Resiliency for the National Mall” presented by the National Mall Coalition as part of DC American Institute of Architects’ “Architecture Month”
“Resiliency for the National Mall,” a presentation by the nonprofit National Mall Coalition, proposes a solution to the existential threat of flooding on the Mall. First presented on June 3, 2020 in a public webinar co-sponsored by the Washington Chapter of the American Institute of Architects and the Washington Architectural Foundation, the full video can be viewed at nationalmallcoalition.org. The following has been edited for a general audience.
The National Mall, one of our most iconic landscapes, site of museums, monuments, protests and celebrations of national significance, is threatened by devastating flooding. As this reconstruction shows, floodwaters in 2006 inundated Constitution Avenue, the National Archives, Smithsonian museums, and more. This was hardly the first time the Mall area had been flooded; floods did extensive damage in 1889, 1936, 1985, and – as recently as July 2019, when a month’s worth of rain fell in less than an hour, overwhelming storm sewers, flooding the National Archives new visitors center and the White House basement. Flooded walkways around the Tidal Basin are a regular occurrence. Fourteen years after the 2006 flood, with a host of studies confirming the threat – from agencies like DC Water, the National Park Service, and FEMA – there is still no agreement on what to do.
Recent efforts by an inter-governmental flood response team, the DC Silver Jackets, have been unable to bring the relevant federal and DC entities to agreement on a solution. The biggest impediment – and pretty much everyone agrees on this – is the plethora of entities involved in Mall governance. These include the Park Service, Smithsonian, National Gallery of Art, plus DC and federal review agencies. No one entity has the jurisdiction or responsibility – or, importantly, the funding – to tackle flooding. The Covid-19 crisis reminds us of the dire consequences of no big-picture leadership.
We want to show you what we think is an important contribution to solving the stormwater flooding crisis: the National Mall Coalition’s National Mall Underground. The Coalition has been developing this idea since 2013 and refining it in dozens of meetings with DC and federal agencies and civic groups. Both the Army Corps of Engineers and the Silver Jackets have reviewed it.
What is it? The Underground is a multi-purpose stormwater reservoir, Mall visitors center, tour bus parking, geothermal energy facility. The basic box, a large stormwater reservoir, can be constructed beneath the Mall’s grassy panels between the Smithsonian Castle and the Natural History Museum. The Underground can collect 28 to 30 million gallons of floodwater – the volume of a flood like the one in 2006. When not needed to collect stormwater, the lower, floodable level will be a parking garage for tour buses . The upper level – not to be flooded – will contain car and bus parking, plus rest facilities for bus drivers, and a Mall welcome center with restrooms and food service. At one end, a small cistern can collect rainwater, at the other end another cistern can hold groundwater pumped from beneath Mall-area buildings. This water can be used for irrigation of grass, trees, and gardens. Geothermal wells beneath the structure – added to the concept in 2014 at the suggestion of then-GSA Administrator Dan Tangherlini – will provide clean energy to Smithsonian museums and other public buildings. Vehicles may access the Underground via the existing ramp from Independence Avenue to the 12th Street tunnel; via a ramp between the Arts & Industries Building and the Hirshhorn; or through the 9th Street tunnel. Cost estimates for the Underground range between $260 and 320 million. That’s a lot of money, BUT, we have a plan. We’ll get to that.
A beneath-the-Mall stormwater reservoir is not the Coalition’s idea. It was one of four solutions found “viable” in the 2011 “Federal Triangle Stormwater Drainage Study.” That report, commissioned after the 2006 flooding, was a collaboration among 14 federal and District agencies, headed by DC Water and the National Capital Planning Commission. But the cost of the reservoir – 400 million — was deemed prohibitive. The Coalition’s idea was to take the “empty box” beneath the Mall that would sit unused most of the time, and turn it into an active, visitor-friendly facility that will generate revenue year-round.
Intrigued, the DC Council in 2017 passed a unanimous resolution asking the US Army Corps of Engineers to study its feasibility. In September 2018, the Corps report found that “Flood risk from a storm of the intensity that flooded the Federal Triangle area in 2006 could be reduced significantly during a flood event by implementation of the Underground.” Also, “revenue potential from parking fees and water credits may offer self-financing opportunities that attracts a public-private partnership.” Also in September 2018, the Coalition was invited to present the Underground concept to DC and federal agencies and local universities. There is interest in the concept among Mall stakeholders. However, the Park Service opposes it because it does not conform to its own 2010 National Mall Plan. This 2019 Silver Jackets report confirms that stormwater flooding is an urgent threat, but reports that the agencies cannot agree on a solution and will continue to explore options – kicking the can down the road.
Now I’d like to anticipate some questions you may have.
FIRST: AREN’T THERE ALTERNATIVES THAT DON’T REQUIRE DIGGING UP THE MALL?
Let’s start with some basic flood history. It’s important to understand that DC has 3 different types of flooding. These slides are from a 2018 presentation by the National Capital Planning Commission:
- RIVERINE flooding happens during and after heavy rains as the Potomac overflows its banks. It happened in 1889, and in 1936, and is common at Washington Harbour in Georgetown.
- COASTAL FLOODING or TIDAL FLOODING happens when tides and storm surges push the Potomac northward. The submerged walkways around the Jefferson Memorial result from Tidal Flooding.
- INTERIOR FLOODING has nothing to do with the rivers. It happens when heavy rains overwhelm the storm drains, inundating streets and buildings. This is what happened in 2006, destroying the National Archives’ newly opened visitors center, closing museums and government buildings, and causing tens of millions of dollars in damage. Since then, stopgap measures like sandbags have been used to protect underground Metro stations.
While some corrective actions are being taken to address riverine and tidal flooding, as we’ll see, none of these will protect the Mall from interior flooding.
The 2019 Silver Jackets report concluded that of all the potential solutions to Mall-area flooding examined, only two are “viable.” One is to build a new pumping station to pump floodwaters into the Tidal Basin. But what if DC gets heavy rains that cause both interior flooding and riverine flooding? Where would the water be pumped? The only other “viable solution,” according to the report, is stormwater storage under the Mall. Construction will cause inconvenience. It will close off a three-block area between 9th and 12th Street for about 2 years. But the Park Service’s turf grass renewal project also closed off large swaths of the Mall for two years, from 2014 to 2016, and visitors seemed to adapt in anticipation of the beautiful carpet of green. We believe visitors also will forgive the Underground’s short-term effects once they can experience its benefits, including better parking, fewer buses on the streets, and the new Mall Welcome Center.
SECOND: WON’T THE UNDERGROUND INCREASE TRAFFIC AND CONGESTION?
We think not. Tourist destinations around the world, for example at Amsterdam’s Museumplein park, and close to home, Washington’s National Cathedral, use underground parking to get cars and buses off the streets while supporting tourism and its economic benefits. The Underground will not open until 10 a.m.; it will be only for Mall visitors – not commuters who are the source of DC’s traffic gridlock.
The truth is, DC and federal agencies have for years been searching for ways to get buses off city streets. It’s not just traffic congestion; it’s also public health. The American Lung Association’s 2019 “State of the Air” report gives DC an “F” for ozone, associated with high rates of childhood asthma. Buses parked in the Underground will be off the streets with their engines off. The Metropolitan Washington Council of Governments did a study of bus parking in 2015. They concluded that “The proposed National Mall Underground would be the most dramatic improvement in bus parking capacity if constructed .”
THIRD: CAN IT EVER HAPPEN IF THE PARK SERVICE OPPOSES IT?
The Mall belongs to the American people. Government agencies are stewards of the public trust. Congress has final say. When a new Smithsonian museum is approved, Congress transfers land from the Park Service to the Smithsonian. Such a transfer may be necessary for the Mall Underground.
FOURTH: WHO WILL PAY FOR IT? From the beginning we’ve believed that revenue generated from the Underground’s various components could provide creative financing opportunities. So, in 2018 we commissioned a financial consultant with strong experience in government projects to develop a financing plan. The consultant concluded that: “For federal and DC stakeholders, the National Mall Underground can achieve a stormwater mitigation solution at significant cost savings in comparison to the other alternatives thus far identified. Of equal value to these stakeholders is that the financing plan is expected to make use of existing federal contracting authorization programs to pay for the project over time, avoiding the need for a substantial upfront appropriation.” The programs to which the consultant referred include stormwater credits, clean energy credits, sale of irrigation water, and parking revenue.
FIFTH: IS THE DANGER REALLY SO GREAT?
Let’s provide some historical context. Recall that the Mall is the product of the visionary 1791 L’Enfant Plan and the 1901 McMillan Commission Plan. Both L’Enfant and the McMillan Commission conceived of the Mall as a designed public space that embodies and promotes the spirit of American democracy. Unfortunately, one of the unforeseen but disastrous legacies of the historic plans is flooding. L’Enfant situated the low-lying Mall along two waterways, the Potomac River and Tiber Creek. By the time the 1901 McMillan Commission came long, Tiber Creek had been paved over to create Constitution Avenue. Also by then, the Army Corps of Engineers had created hundreds of acres of new land with material dredged from the Potomac, thus moving the Potomac shoreline one mile west. The McMillan Plan used that land to expand the Mall, westward to a monument to Lincoln and southward to what became the Jefferson Memorial. In other words, a good half of the Mall is located in what used to be Potomac River bottom, and the complex of government buildings we know as the Federal Triangle sits over old Tiber Creek.
With the best of intentions, L’Enfant and McMillan tried to tame nature. But now nature is roaring back. It’s been roaring back for over a century, and climate change makes its roar louder and more frightening.
FINALLY, WHY HASN’T SOMETHING BEEN DONE? In fact, some important steps are being taken to solve DC’s multiple flooding problems. DC Water’s ongoing $2.6 billion Clean Rivers project is constructing enormous tunnels to collect combined sewer overflow volume from city streets to prevent runoff into the Anacostia and Potomac Rivers. However, this ambitious DC project will not collect stormwater from the Mall area. Another ongoing project is the Park Service’s Potomac Park levee improvements. The levee is intended to address riverine flooding: to prevent the Potomac River overflowing its banks and flowing into downtown. The first stage of this project, completed in 2014, was to replace the sandbag barrier used since the 1930s to close off 17th Street during floods by a removable post and panel closure. The next stage is to raise, by up to four feet, the earthen berm between the Reflecting Pool and Constitution Gardens where the Vietnam Veterans Memorial is located. However, the $14-million-dollar Potomac Park levee, like the Clean Rivers project, is not designed to address interior flooding.
The terrible truth is, even if all these projects are completed, the Mall will be left unprotected from interior flooding and remains vulnerable to another 2006-scale flooding event, or worse. The urgency is real. This 2018 Park Service report projects the effects of sea level rise and storm surge on our national parks. Its projections for a category 3 hurricane in 2050 show almost the entirety of the Mall covered by floodwater, in blue – except for a five-block section that happens to include the site for the National Mall Underground.
There’s a financial cost of inaction, even if we are not visited by a major flood in the next few years. This FEMA Flood Insurance map, updated in 2016, is used to determine flood insurance need and rates. The area dotted in red – which includes all the low-lying land along Constitution Avenue and the Mall – is the “Area remaining [after the Potomac Park levee] closure is constructed because of interior drainage flood risk.” What will be the cost of insuring Mall buildings and facilities – and the priceless national treasures within them?
Consider: what is our role today – the role of American citizens – in shaping the future of the National Mall? One hundred and twenty years ago, it was a group of Washington DC citizens and the American Institute of Architects who helped lead the effort to create the 1901 McMillan Plan and today’s Mall – the stage for American democracy. At that time, the opportunity was to rethink the Mall in celebration of the 100th anniversary of Congress’s move to Washington, DC in 1800.
Today, we have more than an opportunity, we have a civic duty in the face of existential flooding threats – to put our civic spirit into action.
To learn more, please visit nationalmallunderground.org.
Contact: Judy Scott Feldman, PhD, Chair, National Mall Coalition [email protected]