Dive Brief:
- Construction has kicked off on a $113 million effort to replace sinking seawalls around the Tidal Basin and along the Potomac River in Washington, D.C., in order to defend the area from high tides, sea level rise and storm surges, according to an Aug. 15 news release from the National Park Service.
- The project aims to provide century-long protection for surrounding national memorials and landscapes, including the capital’s famous Japanese flowering cherry trees, per the release. NPS tapped Cianbro Construction of Pittsfield, Maine, to do the work.
- The existing century-old seawall has sunk by more than 5 feet in some areas. That settling, combined with over a foot of sea level rise, results in water flowing over parts of the seawalls twice daily during normal high tides, per the release.
Dive Insight:
Each 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 Channel — to see the national monuments and cherry blossoms. However, despite various repairs over the decades, its seawalls are no longer structurally sound and pose a threat to visitor safety as well as the landscape, including the historic cherry trees.
A crowd gathered last week to watch the ceremonial driving of the first 80-foot piling deep into bedrock, according to the release. The contractors will add 700 pilings to create a sturdy foundation for the new, expanded stone and concrete seawall. They will salvage and reuse stones from the historic wall in the rehabilitated seawalls where possible.
“This vital seawall project will eliminate hazards, improve accessibility and ensure long-term protection of this world-famous setting,” said National Park Service Director Chuck Sams in the release. It’s NPS’ most expensive rehabilitation project ever, according to WTOP.
The project entails:
- Rehabilitating approximately 6,800 feet of seawall to extend its lifespan by 100 years.
- Rebuilding the seawall with a piling-supported platform foundation to prevent settling and allow for future height extensions if needed due to rising sea levels or increasing storm surge elevations.
- Increasing the seawall height to 4.75 feet within the Tidal Basin and to 5.50 feet along West Potomac Park to account for wind and waves.
- Repairing, replacing and widening walkways to improve accessibility around the Tidal Basin.
- Regrading landscaping adjacent to the seawalls to provide proper drainage.
Construction on the Tidal Basin seawall is expected to finish in late spring of 2026, and the Potomac River work is scheduled to wrap in the winter of 2026, per the release. Federal money from the Great American Outdoors Act Legacy Restoration Fund is fully funding the project.