Each day, rising tides overtop the historic seawalls surrounding the Tidal Basin in Washington, D.C., a challenge more than a century in the making. Originally built in the late 1800s and early 1900s on land formed from dredged Potomac River sediment, these structures have settled by as much as five feet. The resulting tidal overtopping now threatens park infrastructure, visitor safety, and the iconic memorials that define the National Mall.
As part of a joint venture with HDR, Moffatt & Nichol is supporting the National Park Service in a major effort to rehabilitate approximately 6,800 linear feet of seawall along the Tidal Basin and West Potomac Park. The project includes driving roughly 700 piles to bedrock to support a new platform foundation, designed to prevent future settlement and allow for height extensions if needed due to rising sea levels or increasing storm surge elevations. This foundation strengthens the shoreline’s resilience and is expected to extend the seawall’s lifespan by approximately 100 years.
Our team contributed a range of technical studies and conceptual design services, including geotechnical, hydrologic, and climate hazard analyses; water level modeling; historical construction forensics; and long-term sea level rise projections. In addition to ensuring long-term performance, the design preserves the site’s historic character, matching new stonework to the original seawall in form and texture.
As part of the project’s advancement, Moffatt & Nichol presented to key environmental regulatory agencies, as well as to commissions responsible for preserving Washington, D.C.'s historic and cultural legacy. These presentations reflect a collaborative process that integrates environmental resilience with historic preservation to ensure the project meets both regulatory and cultural expectations.
A recent news segment offers a behind-the-scenes look at how the stones are selected and shaped to reflect the site’s legacy.
Watch the video here.
Scheduled for completion in spring 2026, this project is a critical step toward protecting one of the nation’s most visited cultural and recreational landscapes for generations to come.
