The stakes are even higher because of what’s in those Federal Triangle buildings. Flood damage to the National Archives, EPA, IRS and Department of Justice could be devastating.

The original Potomac Park Levee was a temporary structure built by the Civilian Conservation Corps during a flood in 1936 to keep rising waters from reaching downtown. That weather event spurred Congress to authorize the construction of a larger earthen barrier and make the levee permanent. The Army Corps of Engineers completed the project in 1939. Most people walking along the sloping footpaths around the tidal basin don't realize that they're standing on manmade berms that were carefully laid out to prevent a watery disaster.

17th Street was the only gap in the levee - a deliberate but foolish engineering decision. Building in a gap offered two advantages. First it provided a pleasant even grade for automobile drivers traveling North-South. In the event of flood conditions, the plan called for a hastily built sandbag wall to plug the gap.