GEORGE WASHINGTON MEMORIAL PARKWAY Patowmack Canal and Locks (Great Falls Section) Historic Structures Report — Architectural Data Section

The stabilization of the canal is not a new approach or philosophy, as it can be traced back to the historic operating period in the form of routine maintenance. The major features of the system, i.e., the locks, are documented as having undergone several major overhauls involving reconstructions of several masonry wall sections, as well as replacement of lock gates and hardware. Considering the abandonment of the canal was ca. 1830, today's remaining features are a tribute to the early builders and backers of this project.

At first glance, the most obvious intrusion on the resource has been nature, with trees and vegetation having a major impact on the numerous canal features. A more subtle and disconcerting intrusion has taken place during the twentieth century with the attempt of man to stabilize the various features along the canal. Although well intentioned at the time, these preservation efforts were done in a piecemeal fashion, with no overall plan, and in some instances may have done more harm than good.

The development of a preferred alternative (Memorandum of Decision) was an attempt at defining a more generalized approach to the preservation of the resources at the canal. It is important that this alternative be expanded upon, in more detail, so that management has a more comprehensive plan for the future preservation of this valuable resource.

In keeping with the system of prioritization of features that was alluded to in the Memorandum of Decision, the preservation program for the Patowmack Canal can be expanded as follows:

Priority 1

The features in this category represent the best of what the canal has to offer after a century and one-half in abandonment. These features maintain the most historical integrity and also provide the highest degree of visual impact to the visiting public. They are listed in the order of highest priority first for preventing further deterioration.

A.) Head Gate

• Remove microbiological growth on stone to prevent further deterioration.

• Stabilize rubble stone back-up wall at east elevation of gate structure.

• Excavate at southwest end of structure to define path of canal at west side.

B.) Lock 1

• Create a drainage system at base of lock to carry both surface water and spring water away from the stone at the base of the walls. The drain should be located at the center portion of the lock.

• Remove microbiological growth on stone to prevent further deterioration. See note relative to growth at Lock 2. The mason's mark located at the berm side, north end has been traced to a mason who also had done work on the White House. Special care should be taken to preserve these marks.

• Stabilize the wing walls at the north end of the lock.

• Remove inappropriate and harmful infilling (i.e., brick and mortar) and replace with a more appropriate material that is compatible with the existing stone.

• Investigate other methods for stabilizing walls so that steel and timber bracing system can be removed.

• Create a circulation system to allow access into the lock by the public.

• Stabilize bulge near head of lock at west wall.

• Replace and stabilize deteriorated stone at base of walls.

• Reestablish cap stones where possible.

C.) Lock 2

• Stabilize river wall at south end adjacent to gate pocket. This wall needs to be keyed back into the gate pocket wall and stabilized at the southern end. The work will entail removal of the rubble back up wall and resetting of the seneca sandstone veneer. As the gate pocket was reconstructed improperly during the 1978-1979 work, several stones may need to be modified in order for this wall to be tied back into the adjacent wall. It is also recommended that the south end of this wall be stepped down similarly to the walls located at the south end of Lock 1, and reintegrated with the prism wall if future evidence deems this historical appropriate.

• Remove microbiological growth on stone to prevent further deterioration. Special care needs to be taken in developing a specific solution for removal of this material. A large number of stone mason's marks are located within this lock and need to be preserved along with the stone.

• Investigate bulge at the north end of the berm wall. At the present time, the existing steel support system is stabilizing a portion of this wall. It is recommended that several test holes be drilled at the slumped section behind this wall to try to determine a solution.

• Investigate other methods of stabilizing the north end of the lock walls so that the existing steel structure can be removed. The filling in of this structure should only be considered as a last resort effort in the stabilization of this feature.

• Create positive drainage at base of lock.

D.) Lock 3

• Stabilize bulge at north end of berm wall.

• Stabilize end of berm wall at south end where trail crosses over canal. Create alternative method for public to cross over wall without climbing onto structure.

• Fill in void adjacent to berm wall created by the flooding in 1985. Use existing sand/silt deposits on site to fill void.

E.) Locks 4 & 5

• Stabilize cut stone feature on west elevation located approximately mid-way of cut.

• Have geotechnical engineer check stability of fractured bedrock along entire length of gap.

• Clear debris at base of walls.

Priority 2

The six features in this category, while very important to the historic operations of the canal, have either been tampered with in terms of workmanship (Grist Mill, Foundry, Waste Weir) or vegetation and erosion/siltation has obliterated the original form of the historic features (Canal Prism, Holding Basin, Control Gates). As with the other features, these items are listed with the highest priority item first and then go down in priority.

A.) Foundry Site

• Stabilize ruins uncovered during the flooding of 1985.

• Stabilize dry laid rubble wall at south end of this site impacted by flooding of 1985.

• Stabilize dry laid rubble wall just south of Foundry Site now being used as access points to the river. Create alternative method(s) for public to reach the river area without climbing over walls.

B.) Waste Weir

• Create alternative circulation patterns around the structure to avoid letting the public climb over the walls. This can be accomplished by the introduction of vegetation in certain areas that would force the visitor to go in another direction. It is also recommended that several masonry corners of this feature be relaid to prevent further unraveling of the masonry with a side benefit of helping direct visitors to adjacent paths rather than using the structure as a set of steps.

• Clear vegetation from walls.

C.) Control Gates

• Remove trees and vegetation at control gates adjacent to head gate. Stabilize stone feature after removal of trees and vegetation.

• Remove trees and vegetation at control gates at lower holding basin. Stabilize stone feature after removal of trees and vegetation.

• Clear adjacent area within ten feet of both structures to help better define their locations. It is not intended that a massive clear cut of the surrounding area take place; the objective is to create a small pocket that can be discovered by those visitors that are interested in the operation of the canal.

• Repair and/or replace fence at the cenote located adjacent to the lower control gate. Further research needs to be done on this feature. If it is not important to the canal story or related history, serious consideration should be given to filling in this hole.

D.) Grist Mill Site

• Stabilize rubble walls.

E.) Canal Prism

• Redefine outline of the prism from the Grist Mill site to the Holding Basin, and from the Head Gates to Lock 1.

F.) Holding Basin

• Develop a maintenance plan for the controlled clearing of small caliper trees and vegetation throughout the entire holding basin. As this area is quite large, it is recommended that this task be accomplished over a 5-10 year period to mitigate any possible environmental impact at this site.

• Provide archeological investigations of the western perimeter of the basin to determine the extent of the retaining wall in this area.

• Delineate stone retaining walls on the eastern and western perimeters of the basin.

As an open vista (which would have been present during the historic period) is not possible unless the basin is entirely cleared of all trees and vegetation, it is recommended that the northern perimeter of the basin be cleared to a depth of 20-25 feet from the present grass line. This will help to visually delineate the edges of the basin as it is approached from the north.

Priority 3

Interestingly, the items of lowest priority tend to be grouped together at the upper entrance of the canal. Several of the features are very hard to interpret relative to their existence during the historic operating period of the canal. Also, a number of these structures show evidence of twentieth century workmanship that may have destroyed or modified the historic configuration.

A.) Upper Guard Gate and Spillway

• Remove vegetation from Upper Guard Gate (Berm Side). Stabilize upper courses of stone to prevent damage by visitor traffic.

• No work required at spillway at this time.

• The wall between the Upper Guard Gate and Lower Spillway is in good condition. Vegetation should be removed on a yearly schedule and the wall monitored for any movement.

• Remove vegetation and stabilize remains of canal prism walls north of the upper guard gate.

B.) Lower Spillway

• No work required at this structure at this time. If future flooding should destroy more of this feature, it should then be stabilized to prevent a total loss of the location of this feature.

C.) Wing Wall

• No work required on this structure at this time.

NOTE

The priorities were based on the existing conditions recorded over a period of approximately one year (spring 1985-spring 1986). As these conditions can vary from year to year, the items within each priority group may need to be adjusted. These changes should be made in consultation with the Regional Historic Architect.