- 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.
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.
- 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.
- 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.