Planners have settled on two possible designs for a new levee crossing 17th Street on the National Mall, a crucial deluge-protection system that must be in place in less than a year.
David Rubin, a partner with the Philadelphia-based design firm Olin, told the National Capital Planning Commission on Thursday that the goal of a strengthened West Potomac Park Levee is to shield the National Mall and the federal triangle from a historic flood, and simultaneously “incorporate this into the landscape in as little egregious a way as possible.”
Both levee alternatives comprise concrete walls of varying heights on either side of 17th Street between Constitution Avenue and the World War II Memorial. In the case of a flood, steel posts and plates would be inserted into holes built across the roadway to stop rushing waters. The plates would be stored in an underground bunker constructed nearby, and the concrete walls would be clad in stone, money permitting.
“We could be looking at concrete walls for a long time,” said Jose Galvez, a presidential appointee to the commission.
The 70-year-old Potomac Park levee, part retaining wall and part earthen barrier, stretches from the Potomac River past the Lincoln Memorial to the Washington Monument grounds. It has two gaps, at 23rd and 17th streets, both of which are closed with sandbags and Jersey barriers in the event of flooding rains.
But sandbags are no longer acceptable post-Hurricane Katrina, the Federal Emergency Management Agency has said.
The U.S. Army Corps of Engineers plans to permanently shutter 23rd Street, near the Lincoln Memorial. D.C., meanwhile, committed $2.5 million to close the 17th Street levee gap after FEMA threatened a broad expansion of the downtown 100-year flood plain insurance map.
The revised map, which FEMA withdrew on the condition that the levee is strengthened by November 2009, would have forced developers to meet stringent design standards and cost thousands to buy high-priced flood insurance. The main difference between the two alternatives offered by Olin: One is closer to Constitution Avenue and the other is further south, nearer the World War II Memorial. The National Park Service has final say, but Rubin said he favored the northern alternative because it would have the least impact on the historic line of sight across the Mall.
“You don’t want to muddy that dialogue by moving it further south,” Rubin said.
