Potomac Dam Number 5 - Left Abutment Stabilization
Left Abutment of Potomac Dam No. 5, upstream of dam, as Viewed from the Potomac River
NPS | Professional Services Division – C&O Canal National Historical Park
The towpath between miles 106 and 106.8 is open.
The Dam No. 5 parking lot (mile 106.8) is open with limited impacts.
The park plans to rehabilitate the Left Abutment of the historic Potomac Dam No. 5 near mile marker 106.8 of the Chesapeake & Ohio Canal National Historical Park in Clear Spring, Maryland.
Generally, the projects consist of stabilizing a historic stone dam abutment and associated components. Specifically, National Park Service (NPS) will be physically buttressing the lower portion of the left abutment wall with dumped stone (riprap); excavating out the existing fill behind the wall, installing secant piles to cut off seepage through the abutment, performing masonry repairs, mechanically tying the wall back, providing a seepage collection system, installing overtopping protection in the form of articulated concrete blocks, performing large scale masonry repairs on multiple structures; stabilizing the guard lock via replacement of structural fill and seepage collection system; and stabilizing a retaining wall (referred to as Mule Bridge Abutment in maps below) supporting the towpath.
Built between 1857 – 1870, the Potomac Dam No. 5 Dam and abutments replaced an earlier rock-filled wooden crib dam founded on bedrock. Potomac Dam No. 5 was constructed by the Canal Company to impound the water in the Potomac River and divert it into the canal so it could be used for navigation. Using the guard lock and associated bypass flume, water diverted from the Potomac River was used to feed the approximately 22-miles of canal downstream to Potomac Dam No. 4 (located in Sharpsburg, MD). The Left Abutment of Potomac Dam No. 5 is comprised of mortared limestone blocks and not only ties the run-of-the-river spillway to bedrock on the Maryland shore, but also provided a guard lock system that facilitated the ingress and egress of boats from the “slackwater” impounded by the dam to canal during the canal’s operating era.
What is the P.L.A.N. ?
Purpose? [Why are we undertaking this project?]
To repair and stabilize the Potomac Dam No. 5 Left Abutment.
Length? [When are we closing, and how long?]
The project is expected to begin work on-site for the construction phase in April 2024 and is anticipated to continue through Fall 2025, weather dependent.
Alternative Activities? [What can I do instead?]
During construction, the Left Abutment of Potomac Dam No. 5 and adjacent parking lot will be closed. The nearest upstream parking lot for towpath access is at Four Locks (mile 108.8) and nearest major downstream parking lot for towpath access is at Williamsport (mile 99.7). While the stretch of towpath between Mile 106-106.8 is closed during construction, you can still bike, walk, run, and fish along the towpath in all areas outside of the work zone. You can still access the towpath via local detours. There are many sections of the towpath to be explored!
Next Step? [What are the future benefits?]
The completion of the repair and stabilization work at the Left Abutment of Potomac Dam No. 5 will improve safety and reduce the impacts of high-water events to the towpath, historic features of the park, and park visitors. The work will make the park more resilient to flooding and climate associated hazards.
Potomac Dam No. 5 Left Abutment Project Area Detour Map
NPS | Professional Services Division – C&O Canal National Historical Park
Potomac Dam No. 5 Left Abutment Project Area – Detail View
NPS | Professional Services Division – C&O Canal National Historical Park
CURRENT DETOURS AND CLOSURES
The towpath between miles 106 and 106.8 is open.
The Dam No. 5 parking lot (mile 106.8) is open with limited impacts.
Beginning at mile 106, this detour diverts traffic from the towpath, across the canal to Dam No. 5 Road, along the shoulder of Dam No. 5 Road, onto a temporary mulch trail, and then to a temporary wooden stairway before rejoining the towpath on the upstream side of the project. Visitors are asked to follow the signage and dismount bicycles while crossing the canal, traversing the mulch portion of the trail, and using the wooden stairway.
Left Abutment of Potomac Dam No. 5, downstream of dam, as viewed from the Potomac River.
NPS | Professional Services Division – C&O Canal National Historical Park
FREQUENTLY ASKED QUESTIONS (FAQs)
What is the need for the project?
Multiple deficiencies have been identified by NPS that require repair and stabilization of the historic Potomac Dam No. 5 Left Abutment. These include recurrent sinkholes in the left abutment, ailing mortar joints, damaged stone masonry units, leaning of the main left abutment wall towards the river, and past erosive events that occurred when the left abutment was overtopped during large magnitude floods by the Potomac River.
What does the project include?
Generally, the projects consist of stabilizing a historic stone dam abutment and associated components. Specifically, National Park Service (NPS) will be physically buttressing the lower portion of the left abutment wall with dumped stone (riprap); excavating out the existing fill behind the wall, installing secant piles to cut off seepage through the abutment, performing masonry repairs, mechanically tying the wall back, providing a seepage collection system, installing overtopping protection in the form of articulated concrete blocks, performing large scale masonry repairs on multiple structures; stabilizing the guard lock via replacement of structural fill and seepage collection system; and stabilizing a retaining wall supporting the towpath.
The National Park Service (NPS) anticipates the contractor will mobilize many various types of heavy equipment and specialty workers (including divers).
Where will the project take place?
This project will take place on approximately 0.8 miles of the C&O Canal towpath from Mile 106 – 106.8, approximately 7 river miles upstream of Williamsport, MD, and directly adjacent to Potomac Dam No. 5.
When will the project begin and end?
Site work for the construction phase began in April 2024 and is anticipated to continue through Fall 2025, weather dependent.
Potomac Dam No. 5 Left Abutment, looking towards Potomac River from Dam No. 5 Road
NPS | Professional Services Division – C&O Canal National Historical Park
How will this project impact park visitors?
To facilitate the work, the Potomac Dam No. 5 Parking Lot (mile 106.8, located off of Dam No. 5 Road, Clear Spring, Maryland) will be CLOSED.
There is no public parking available adjacent to the work area along Dam No. 5 Road. Alternate parking can be found upstream at Four Locks (mile 108.8) and downstream at Williamsport (mile 99.7).
How will this project benefit park visitors?
Once the project is complete, this portion of the significant historic structure will be stabilized and repaired. Many existing impairments will be addressed, resulting in a safer and better visitor experience.
How will this project impact natural and cultural resources?
Every project the NPS executes undergoes review by a multidisciplinary team to ensure compliance with Section 106 of the National Historic Preservation Act (NHPA), National Environmental Policy Act (NEPA), and other federal, state, and local laws.
What is the park doing to protect those resources during the project?
NPS resource protection experts, engineers, and the contractor’s team will be monitoring the Potomac Dam No. 5 Left Abutment construction work along this stretch of the towpath, along with contractor’s operations and visitor safety during the project with the goal of safely protecting the environment surrounding the project. Every project undertaken by the NPS is conducted in compliance with the National Environmental Protection Act (NEPA), the National Historic Preservation Act (NHPA), and other regulations. During the design phase relocation of some in-stream resources were identified and relocated outside of the work area.
How much does the project cost?
The construction contract for the Potomac Dam No. 5 Left Abutment Stabilization project was awarded for $6.7 million and was funded from the National Park Service’s Great American Outdoor Act Legacy Restoration Fund. NPS has established an interagency agreement with U.S. Bureau of Reclamation who executed the design and is administering the construction contract.
Who can I contact if I have further questions regarding the project?
Additional questions are to be directed to the park headquarters at 301-739-4200.
Potomac Dam No. 5, looking upstream from the Potomac River
NPS | Professional Services Division – C&O Canal National Historical Park
