Reconstruct/Stabilize Historic Stone Wall & Towpath McMahons Mill to Lock 42

A portion of the towpath and retaining wall that were rehabilitated as part of this project.

NPS | Joe Reed, Park Engineer

The towpath between miles 88 and 89 is open. The McMahons Mill parking lot (mile 88) is open.

The park rehabilitated a historic stone retaining wall and stabilized the towpath along a 0.9-mile stretch between McMahons Mill (mile 88) and Lock 42 (mile 89) in Williamsport, Maryland. This section of the park was intermittently covered with water during river flooding, causing resource damage and requiring bicycle and pedestrian detours.

The project aimed to lessen high-water event impacts to the towpath, historic features of the park, and park visitors by stabilizing this entire section and raising the elevation of the lowest segments of towpath and retaining wall. Potomac River high waters, driven by floods, caused sections of the towpath in this area to be impassable many times each year, requiring a 3-mile detour for hikers and bikers on narrow, winding county roads.

 

What is the P.L.A.N. ?

Purpose? [Why are we undertaking this project?]

To repair and stabilize the towpath stone retaining wall and to reconstruct the towpath in a manner that lowers its chances of undergoing flood damage, while also allowing for safe visitor use and safe, limited emergency/maintenance vehicle passage.

Length? [When are we closing, and how long?]

The project began in August 2021 and is anticipated to continue through winter 2022/23, weather dependent.

Alternative Activities? [What can I do instead?]

During construction, some portions of the river may be closed while barges perform work in the area directly adjacent to the towpath/walls. While the stretch of towpath between Mile Marker 88-89.1 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 towpath and retaining wall work will improve safety and reduce the impacts of high-water events (including closures) 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.

 

CURRENT DETOURS AND CLOSURES

The towpath between miles 88 and 89 is OPEN. No detours are in place.

FREQUENTLY ASKED QUESTIONS (FAQs)

What is the need for the project?

The historic stone wall was weakened by water impacts from the Potomac River, particularly during storm events, and vegetation growing through the structure. Portions of the historic stone wall were washed out or missing. Periodic flood events weakened the stone wall and created sinkholes, washouts, and slope failures in the towpath.

What does the project include?

The project consisted of work removing vegetation growing within the stone wall and next to the towpath, reconstructing missing or washed out portions of the historic stone wall, stabilizing and building up other portions of the stone wall, and moving some portions of the towpath more inland. It also included re-establishing the towpath with a width to allow for safe, limited passage of emergency/maintenance vehicles, as well as raising the towpath to an elevation that would reduce closures caused by minor flood waters. Even though the towpath was raised at its lowest spots, this section will still go under water during moderate and major river flooding events.

Similar to the 2010 – 2012 work completed on the portion of the towpath between McMahons Mill to Dam #4, the contractor to relied heavily on barges and boats to perform the work from the river. Contrary to the work in 2010 – 2012, no concrete bridges were used for the stabilization work.

 

The Big Slackwater area at McMahon's Mill that was part of this project.

NPS | Joe Reed, Park Engineer

Where will the project take place?

This project took place on approximately 0.9 miles of the C&O Canal towpath from McMahons Mill (mile 88) to Lock 42 (mile 89), approximately 10 river miles downstream of Williamsport, MD, and four miles upstream from Dam #4.

When will the project begin and end?

The project began in August 2021 and was completed in March 2023.

How will this project impact park visitors?

No closures are currently in place.

How will this project benefit park visitors?

The towpath is less likely to experience as many high-water event closures, allowing for more frequent and safe passage for visitors. The existing towpath was stabilized, increasing the resiliency of this fragile length of the towpath and preserving the continuity of the 184.5-mile-long trail. Many existing impairments - such as sinkholes, washouts, deposited river sediment, and encroaching trees/roots - were 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.

An environmental assessment (EA) was prepared by the park, which can be found on Planning, Environment and Public Comment (PEPC) website (https://parkplanning.nps.gov/projectHome.cfm?projectId=92111).

What is the park doing to protect those resources during the project?

NPS resource protection experts, engineers, and the contractor’s team monitored the stone and towpath 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. Please see the Environmental Assessment (EA) prepared by the park for further details.

How much does the project cost?

The design build contract for the rehabilitation of 0.9 miles of towpath and supporting masonry walls between McMahons Mill to Lock 42 near Williamsport, MD, cost around $21 million and was funded from the National Park Service’s Line Item Construction Program.

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.

 

An example of a low-lying portion of the towpath that was rehabilitated during this project.

NPS | Joe Reed, Park Engineer