NPS to rebuild Tidal Basin sea walls amid rising sea levels

By Andres Picon | 06/02/2023 04:20 PM EDT

The Washington reservoir faces chronic flooding as water levels have risen and the protective barriers have sunk into the ground.

Rising water covers up stairs along the Tidal Basin in Washington.

Rising water covers up stairs along the Tidal Basin in Washington on Oct. 29, 2021, after heavy rains caused tidal flooding in the mid-Atlantic region. Drew Angerer/Getty Images

The National Park Service cleared a major regulatory hurdle this week in its effort to protect Washington’s Tidal Basin from the impacts of climate change.

The agency completed its environmental assessment for a $120 million rehabilitation project that will involve raising the reservoir’s sea walls by about 5 feet to stave off floodwaters as sea levels rise.

A major tourist attraction known for the ornamental cherry trees and monuments that line its perimeter, the Tidal Basin is already beset with chronic flood issues. Portions of the walkways that sit on top of the sea walls flood twice a day during high tide, making certain sections impassable for pedestrians and threatening the iconic trees.


“The sea wall systems in the National Mall are failing,” said Mike Litterst, a spokesperson for NPS.

The protective barriers have sunk into the ground by about 3 feet since the basin was built more than 100 years ago, and water levels have risen by about a foot, creating a “net loss of about 4 feet of protection,” he said.

The rising waters are “attributable to climate change to some extent,” but also to increased development in the nation’s capital, which has caused more runoff to flow into the reservoir, Litterst said. The sea walls have settled deeper into the ground over time because they were not built directly on top of the bedrock.

With climate change hastening the rate of sea-level rise, NPS is looking at the rehabilitation project as a long-term fix.

“We’re looking for a sustainable solution here,” Litterst said. “We don’t just want to repair the damage; we want to repair it and rebuild it in a way that it’s not going to continue to be a problem.”

The new sea walls will be 4.75 feet higher along the Tidal Basin and 5.5 feet higher along the stretch that runs adjacent to West Potomac Park. They will be built to the bedrock to prevent further sinking.

“That’s going to account for the wind and wave conditions of the future,” Litterst said.

The environmental review completed this week found that the project will not have any significant impact on the area’s “natural, cultural or human environment.” NPS hopes to award a design and construction contract by the end of the summer.

The project is funded by the Great American Outdoors Act. The 2020 law provides up to $1.9 billion to address a backlog of maintenance and repair needs on public lands.