Tetra Tech is providing engineering services in two phases to assist the District of Columbia, the National Park Service, and the U.S. Army Corps of Engineers to upgrade the flood protection system for the United States’ capital. Two major areas are affected by flooding from the Potomac River—the National Mall area and South East DC. This flood protection system safeguards the downtown DC area from future flooding.

This project consisted of the design and construction of a post and panel closure structure across 17th Street in Washington, DC. The post and panel closure structure can be put in place when flooding is predicted to occur and will not interfere with access to the National Mall or impact traffic circulation on 17th Street at other times. Gauges upstream of the Potomac River provide the Park Service with 24 hours’ notice to put the system in place to prevent flooding.

Tetra Tech developed conceptual design plans for a series of alternatives. Our team held a design workshop and a series of working group meetings to vet the alternatives through the National Park Service, the National Capitol Planning Commission, the U.S. Commission of Fine Arts, the U.S. Army Corps of Engineers, and other interested local agencies. 

Tetra Tech conducted engineering and structural analyses to prepare the construction plans, technical specifications, and engineer’s estimate for the gate closure. Engineering during construction services included providing responses to requests for information RFIs and reviewing submittals.  

Tetra Tech successfully addressed multiple challenges during this project. Tetra Tech provided a robust design to attain the required stability to compensate for poor soil conditions. Our team had to maintain access to the area and limit our work during certain time periods because the project site is a heavily used public area and is 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.

With the gate built and in place, the project is ready to provide protection against a 100-year flood.

As a follow-on to this project, the U.S. Army Corps of Engineers, 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.

View a short video about Tetra Tech’s work on this project here