Two major areas are affected by flooding from the Potomac River—the National Mall and Southeast DC. The flood protection system safeguards downtown DC against a 100-year flood.
This project consisted of designing and constructing a post and panel closure structure across 17th Street. The post and panel closure structure can be put in place within 24 hours of flood prediction and does not impact traffic circulation on 17th Street at other times.
One of the design challenges is the poor soil quality for building. Tetra Tech overcame this by designing caisson concrete cylinders, which are embedded in the bedrock to hold the weight of the floodwall.
Patti Sexton, Levee Practice Leader
Our team maintained access to the area and limited our work during certain time periods because the project site is a heavily used public area and near the White House. Our underground work also needed to avoid utilities that could impact the surrounding area. While the entire design was required to meet Federal Emergency Management Agency (FEMA) requirements, Tetra Tech designed the underground infrastructure portion to the higher congressionally mandated level that provides protection against a river discharge of 700,000 cubic feet per second.
As a follow-on to this project, the USACE, Baltimore District, contracted Tetra Tech to prepare the levee safety evaluation report. This report was submitted to FEMA and will be used to update the FEMA floodplain maps and change the insurance requirements in the protected areas.