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Dive brief:
- Construction has begun on a $113 million effort replace the sinking seawalls around the tidal basin and along the Potomac River in Washington, D.C., to protect the area from high tides, sea level rise and storm surge, according to an Aug. 15 news release from the National Park Service .
- The project aims to provide a century of protection to the surrounding national monuments and landscapes, including the capital’s famous Japanese cherry blossom trees, the statement said. NPS used Cianbro Construction of Pittsfield, Maine, to do the work.
- The existing century-old levee has sunk more than 5 feet in some areas. That settlement, combined with more than a foot of sea-level rise, causes water to flow over parts of the levees twice a day during normal high tides, according to the release.
Diving knowledge:
Every year, millions of visitors from around the world are drawn to the Tidal Basin, a 107-acre man-made reservoir between the Potomac River and the Washington Canal, to see the national monuments and cherry blossoms. However, despite several repairs over the decades, its levees are no longer structurally sound and pose a threat to the safety of visitors and the landscape, including the historic cherry trees.
According to the statement, a crowd gathered last week to watch the ceremonial driving of the first 80 feet piled into the rock. Contractors will add 700 piles to create a solid foundation for the new expanded stone and concrete wall. They will save and reuse the stones of the historic wall in the rehabilitated seawalls wherever possible.
“This vital levee project will eliminate hazards, improve accessibility and ensure the long-term protection of this world-renowned environment,” National Park Service Director Chuck Sams said in the statement. it is NPS’s most expensive rehabilitation project never, according to WTOP.
The project involves:
- Rehabilitation of approximately 6,800 feet of seawall to extend its service life by 100 years.
- Levee reconstruction with a pile-supported platform foundation to prevent settlement and allow for future height extensions if necessary due to sea level rise or increased storm surge elevations.
- Increased seawall height to 4.75 feet within the tidal basin and 5.50 feet along West Potomac Park to account for wind and waves.
- Repair, replacement and extension of footbridges to improve accessibility around the Conca de la Marea.
- Regrading of landscaping adjacent to levees to provide adequate drainage.
Construction on the Tidal Basin levee is expected to be completed by late spring 2026, and work on the Potomac River is expected to be completed by winter 2026, according to the release. Federal money from the Great American Outdoors Act Legacy Restoration Fund is fully finance the project.
