Stabilize Drylaid Stone Wall at Mile Marker 11 (Log Wall)

The downstream portion of the drylaid stone retaining wall that is part of the project (towpath at top of wall).

NPS | C&O Canal NHP Engineering Services Team (Reed)

1. C&O Canal Towapth - Detour in Effect between mile 11 and 11.5

2. Carderock Recreation Area - Parking Lot B (mile 10.75) is CLOSED

The park plans to stabilize an approximately 1,015 linear foot long historic drylaid stone wall, which varies in height up to 35 feet tall. The wall was originally constructed between 1828 and 1831 and is often referred to as the “Log Wall,” as found in an 1890 Engineer’s Report.

This portion of the canal was altered in the 1960s by the installation of the Potomac Interceptor Combined Sewer, which is operated and maintained by DCWATER. In 2015 and 2016 a series of sinkholes formed, necessitating the water in the canal to be lowered throughout a 4-mile stretch, including upstream of Log Wall to Widewater (mile 13.5) and downstream towards Washington, DC.

The project’s main goals include maintaining the “Towpath Continuity” of the 184.5-mile-long primary trail system in the park; restoring the flow of water within the canal prism; reducing risks to adjacent infrastructure; and performing stabilization (reduction of sediment load) of some limited reaches of the tributaries emptying into the canal within the project area.

A 3D view of the wall can be viewed online here: C&O Canal Dry Laid Stone Wall (Mile Marker 11) - 3D Model

CURRENT DETOURS AND CLOSURES

The towpath between miles 11 and 11.5 is CLOSED. The detour is currently in place. Below is a map showing the project area and the detour that will be in place during towpath closures.

We anticipate the detour for the towpath will be activated in the afternoon on Thursday, August 24, 2023. The detour is approximately 0.7 miles in length and provides a pedestrian bypass for the approximately 0.4 mile length of towpath that will be closed to facilitate construction. During this phase of the work, the towpath will be closed downstream of Marden Tract Campground (Mile Marker 11.4) and upstream of the West End of Billy Goat Trail Section C (Mile Marker 11). The detour uses a temporary causeway to cross the canal, temporary mulch trail through the woods, temporary mulch trail along the shoulder of MacArthur Boulevard, existing paved shoulder of MacArthur Boulevard, and the existing Marsden Tract Bridge over the canal.

Visitors are asked to follow the signage and dismount bicycles along this stretch.

At Carderock Recreation Area Parking Lot B (mile 10.75) is CLOSED. Parking lots A, C, and D will remain open through construction.

 

Log Wall Project Area Detour Map

NPS | C&O Canal NHP Engineering Services Team

 

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

Purpose? [Why are we undertaking this project?]

The project includes performing stone masonry repairs; removing accumulated sediments from the canal; replacing the canal liner with a geosynthetic system; restoring sinkholes that have developed; stabilizing limited reaches of the tributaries entering the canal to minimize future erosion; buttressing the drylaid stone wall with dumped stone; and establishing temporary access and best management practices during construction for erosion and sediment control. 

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

The project is anticipated to begin field work in May 2023 and is anticipated to continue through Summer 2024, weather dependent. 

Alternative Activities? [What can I do instead?]

During construction, the towpath will be closed between mile 11 – 11.5. A temporary detour for pedestrians will be established through the woods on the downstream side of the project area to MacArthur Blvd, which will then return to the towpath at the upstream side of the project using the existing Marsden Tract Bridge/access point.  

While the stretch of towpath between mile 11-11.5 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 tributary, canal, and retaining wall work will improve safety, result in a more sustainable system, preserve historic resources, and contribute to the capability of rewatering miles of canal. It will also reduce the impacts of future flooding 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. 

 

An example of existing sinkhole between the towpath and wall.

NPS | C&O Canal NHP Engineering Services Team (Noppenberger)

FREQUENTLY ASKED QUESTIONS (FAQs)

What is the need for the project?

The canal liner needs to be replaced to limit leakage through the towpath and wall, and sinkholes need to be repaired to stop their growth and potential impacts to the adjacent wall or towpath. Sediment from tributaries needs to be removed from the canal to restore water flow within this section, while also reducing the weight that the Log Wall is supporting. Accumulated sediment is over two times as dense as air!

The historic stone wall needs to be stabilized by performing masonry repairs and by physically buttressing it with dumped stone. This will help reduce the effective height of the wall and reduce future potential instability.

What does the project include?

The project includes performing stone masonry repairs; removing accumulated sediments from the canal; replacing the canal liner with a geosynthetic system; restoring sinkholes that have developed; stabilizing limited reaches of the tributaries entering the canal minimize future erosion; buttressing the drylaid stone wall with dumped stone; and establishing temporary access and best management practices during construction for erosion and sediment control.

Where will the project take place?

This project will take place on approximately 0.5 miles of the C&O Canal towpath from Carderock Recreation Area (mile 11) to Marsden Tract (mile 11.5), approximately 3 river miles downstream of Great Falls, MD, and 6.5 miles upstream from the Washington, DC/Maryland Line.

When will the project begin and end?

The project is anticipated to begin field work in May 2023 and is anticipated to continue through Summer 2024, weather dependent.

How will this project impact park visitors?

The Carderock Parking Lot B (mile 10.75) is currently CLOSED in order to facilitate staging for the contractor. There is no public parking available along MacArthur Blvd.

The towpath will be used for access within the work area itself and from the Carderock Recreation Area to the project site.

Alternative parking can be found at the adjacent Carderock Parking areas.

How will this project benefit park visitors?

Once the project is complete, the tributary, canal, and retaining wall work will improve safety. This will result in a more sustainable system, preserve historic resources, contribute to the capability of rewatering miles of canal, and reduce the impacts of future flooding 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. The existing towpath will be stabilized, increasing the resiliency of this fragile length of the towpath and preserving the continuity of the 184.5-mile-long trail.

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. Terrestrial scans of the wall were collected during the design phase to record and provide documentation of the wall prior to it being partially covered by the proposed dumped stone buttress.

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 stone masonry wall, canal, tributary, 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.

How is the project funded?

The construction contract for the stabilization of the drylaid stone wall near mile marker 11 (Log Wall) was awarded in November 2022 for $10.7 million and was funded from the National Park Service’s Great American Outdoor Act – Legacy Restoration Fund 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.

 

Log Wall Major Project Features Map

Log Wall Major Project Features Map

 

Looking downstream into the work area from the towpath – showing the extent of sedimentation and area where towpath overtopping occurs.

NPS | C&O Canal NHP Engineering Services Team (Reed)

 

Looking upstream from inside the work area – showing the extent of previous buttressing down with dumped stone in the foreground and the future area at the tall portion of the wall in the background.

NPS | C&O Canal NHP Engineering Services Team (Reed)