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September 1, 2023

Maine's largest construction firm wins $113M contract to fix seawalls in US capital

basin with water on gray day Courtesy / National Park Service Daily flooding along the Tidal Basin has led to hazardous conditions.

Cianbro Corp. of Pittsfield has won a $112.76 million National Park Service contract to rebuild a portion of the National Mall Tidal Basin in Washington, D.C.

The construction firm will rehabilitate 6,800 feet of failing seawalls around the basin, along the Potomac River through West Potomac Park. The Great American Outdoors Act National Parks and Public Land Legacy Restoration Fund is providing the money, according to a news release this week.

“Repairing the seawalls has been a top priority of the National Park Service for years,” National Mall and Memorial Parks Superintendent Jeff Reinbold said. “The Great American Outdoors Act funding not only allows us to protect our nation’s treasures from the immediate threats of failing infrastructure and rising sea levels, but also will ensure these special places are protected for generations to come.”

Cianbro is Maine's largest construction firm, with $1.3 billion in revenue in 2021 and 3,000 employees, including 900 in Maine, according to the Mainebiz 2023 Book of Lists. 

Tidal Basin origin

According to the National Trust for Historic Preservation, the need for the Tidal Basin arose out of a disastrous flood in 1881, which devastated the district so severely that much of the southern part of city was accessible only by boat. Flooded areas included parts of the National Mall such as the unfinished Washington Monument, White House Ellipse and the Capitol.

After the 1881 flood, the Army Corps of Engineers dredged the Potomac River and used sediment from the shipping channel to fill in the tidal wetlands that are now West and East Potomac Park. In 1887, engineers installed gates at the entrance and exit of a newly formed pond — now the Tidal Basin.

At high tide, the gates open and fill the pond with water. At low tide, the water exits into the Washington Channel, and the rush of water is designed to sweep the leftover sediment away. The Tidal Basin also uses a pumping system to keep the reflecting pool at the Lincoln Memorial full of water.

Around the basin itself are icons such as the Jefferson Memorial, the Martin Luther King Jr. Memorial and the cherry trees that encircle it.


But age, rising sea levels, and poor drainage have taken a toll on the Tidal Basin and West Potomac Park seawalls. Portions of the seawalls have settled as much as 5 feet since their initial construction from the late 1800s to the early 1900s. 

As a result of this settlement and sea level rise, water flows over portions of the seawalls twice a day during normal tidal conditions. Despite various repairs over the decades, the seawalls are no longer structurally sound and threaten visitor safety and the historic setting, including the iconic cherry trees around the Tidal Basin.

Construction on the project is expected to begin in mid-2024. 

The repairs will include: 

  • Removing and reconstructing the existing stone masonry seawalls to include a pile-supported platform foundations that will prevent the seawalls from settling, and support height extensions of the walls if needed due to future rising sea levels or increasing storm surge;  
  • Salvaging and reusing stones from the historic wall in the rehabilitated seawalls, when possible;
  • Repairing, or replacing, and widening walkways around the Tidal Basin to provide smoother, more accessible connections to other pathways; and
  • Regrading landscaping adjacent to the seawalls as necessary to provide proper drainage.
  • Repairs are part of nearly $500 million in planned infrastructure improvements on the National Mall prior to the 250th anniversary of American independence in 2026. 

The National Parks and Public Lands Legacy Restoration Fund is part of an effort to address an extensive maintenance backlog in national parks. Supported by revenue from energy development, the fund provides up to $1.3 billion per year for five years to the National Park Service to make significant enhancements in national parks to ensure their preservation and provide opportunities for recreation, education, and enjoyment for current and future visitors.  

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