For the past five years, I've had the opportunity to work on an exciting infrastructure initiative that will help improve and sustain the National Mall in Washington, D.C. The project, the National Mall Underground (NMU), is a subterranean visitor center that also functions as a stormwater management system to mediate many challenges that have plagued the area.
Despite its popularity, areas within the National Mall have been plagued with problems, extensive flooding in particular. In 2006, a major three-day storm overwhelmed the capacity of nearby storm sewers and damaged several museums and federal buildings.
What Lies Beneath
The NMU is the innovation of longtime real estate developer and philanthropist Albert H. Small, D.C.-based architect Arthur Cotton Moore, FAIA, and the nonprofit National Coalition to Save Our Mall. Working closely with these visionaries, Dewberry's civil engineering team helped identify the optimum site for the project: underneath a patch of green space that exists between the Smithsonian Institution's Castle building and the National Museum of Natural History.
The NMU will be built entirely underground. A visitor center, housed just below a green roof and turf grass, will address the need for more visitor amenities, while two levels of parking stacked further underground will serve approximately 1,000 cars and buses. Such a garage will provide a destination for the frequent tour buses that idle on nearby roads, contributing to pollution and blocking some scenic views.
The parking areas and visitor center will be flanked by two cisterns. The rainwater collected by the cisterns will in turn be used to irrigate the Mall's grass, thereby reducing reliance on drinking water. During severe storm events, the parking levels will be closed and cleared so it can serve as a 34-million-gallon reservoir for floodwaters.
A National Precedent
Our team has studied dual-purpose traffic and flood control projects in Rotterdam, Kuala Lumpur, and Copenhagen, but the NMU is a breakthrough project for the U.S.: no such multipurpose structure exists in this nation. The proposed project sets up an infrastructure that benefits the National Mall experience on a daily basis while further protecting the historic site from damage caused by severe storm events.
The NMU sets a precedent for the collaborative use of engineering tools. We're using the new Business Case Evaluator (BCE) tool for Stormwater Management, a companion tool for the Institute for Sustainable Infrastructure (ISI) Envision™ rating system, alongside civil BIM applications. The first allows us to evaluate the economic, social, and environmental factors of several sustainable categories, while the second lets us study terrain, hydraulic and hydrologic models for rainwater harvesting, and stormwater detention.
The NMU is a big, bold idea. If completed, this project will reflect the best of integrated design skills, technology, and visionary thinking.
