The US Army Corps of Engineers organized a national team of experts consisting of two hydrologists, one structural engineer, two civil engineers, two planners, one construction specialist, and one mechanical engineer, to conduct a technical review of documents provided by the Coalition, including the 2011 Federal Triangle Stormwater Drainage Study (DC Water, 2011), various parking demand studies, project budgets, concept drawings, and cost benefit analysis. The review included two webinars and one joint meeting with the Coalition during which the Corps shared its questions and concerns. Corps experts assessed the early stage concept, provided comments and recommendations, and flagged important issues that the Coalition plans to address in coming phases as the project develops.

The Corps review finds 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.” The Underground is still an early stage concept so “further study is needed, particularly on the conceptual systems related to phased floodwater intake and evacuation of buses to minimize risk to life safety during a flash flood.” Because of the multiple jurisdictions involved, there will be a need to “(c)ontinue to coordinate with stakeholders.”

Click above to read the Army Corps of Engineers Technical Review of the National Mall Underground (completed September 2018).