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Demolition of Union Dam

A step forward in the plan to restore more than 65 miles of fish and eel spawning habitat on the Patapsco River.
  • The 100-year-old Union Dam before demolition – Gannett Fleming

    The Union Dam had to be removed due to safety concerns and to revitalize the aquatic habitat.

  • A view of the Patapsco River following the Union Dam demolition – Gannett Fleming

    The Patapsco River restoration was part of the new national practice of removing obsolete dams.

  • Aerial view of the new river channel under construction with flow diverted to the bypass channel.

    The new river channel under construction with flow diverted to the bypass channel.

Maryland Department of Natural Resources and Maryland Department of General Services

Howard County, Maryland

Our Role
Engineering, Design, Permitting, Hydrologic and Hydraulic Study, Construction Phase Services.

1 year
  • Improved flow and preservation of the Patapsco River’s function and ecology
  • Protected an existing 42-inch sanitary sewer situated along the river bank
  • Safe removal of the Union Dam, which constituted a public safety hazard.

Situated along the Patapsco River on the border of Howard and Baltimore Counties in Maryland, the Union Dam incurred significant damage during Hurricane Agnes in 1972. Three decades later, the damaged bridge had become a threat to the stability of an adjacent sanitary sewer that served nearly 11,000 people. 

The Maryland Department of Natural Resources decided that the best course of action for both the nearby communities and the Patapsco River would be to remove the nearly 100-year-old Union Dam. The agency turned to Gannett Fleming to engineer the demolition.

What We Did

In providing engineering design services for the demolition of the dam, Gannett Fleming utilized an innovative and flexible approach to construction sequencing. The firm prepared a plan to divert the river, dewater the area around the dam, and demolish it “in the dry,” safe from the river flows. The diversion employed natural stones and concrete blocks as a bulkhead, with a vinyl-lined diversion channel to convey the Patapsco River around the dam.

Following removal of the dam, a new channel bottom was established and several stabilizing structures were installed. The 42-inch sanitary line was protected, as were several remaining structures, including the original 1808 stone abutment and the control gates from the 1912 concrete dam.

Key Features

  • Avoiding impacts to the surrounding Patapsco Valley State Park
  • Commitment to sustainability
  • Coordination of civil, hydraulics and hydrology, structural, and historic preservation professionals
  • Flexible construction sequencing approach
  • “In the dry” demolition
  • Navigation of joint waterway construction permit requirements.

Sustainability Features & Outcomes

  • Improved conditions for local aquatic communities
  • Increased dissolved oxygen
  • Provided fish passage to the upper reaches of the river
  • Recycled concrete used to construct an access road from Route 40
  • Reduced thermal impacts
  • Sections of the demolished dam reused as in-fill for deeper river sections.

Similar Projects: Water/Wastewater: Dams & Levees, Information Technology, Dams & Levees: Special Services, Water/Wastewater