Lock 20 Bypass Flume Stabilization
During the course of preservation repairs to Lock 20 (PEPC # 16962), Great Falls, MD, park staff discovered that significant voids were present behind the north lock wall, within the bypass flume area of Lock 20. These voids had been caused by water leaks within the bypass flume, which is not operational. These voids affect the structural strength and integrity of Lock 20.
Locks on the C&O Canal had bypass flumes to divert water during lock operations. These structures were parallel to the lock. Most of these bypass flumes were open, but the one at Lock 20 is believed to have been historically covered due to its proximity to the Great Falls Tavern.
The existing flume at Lock 20 is not functioning as a bypass flume. Water is controlled via a waste weir located nearby. The exact date of the existing terra cotta bypass pipe is uncertain but it is believed to be a 20th century repair. Today, the bypass flume area is covered with earth, topped with a brick walkway and grass.
Lock 20 is a functional lock that is used on a regular basis April-October for an interpretive program using a replica canal boat, which transports park visitors through the lock and along the canal. Park personnel and visitors are able to access the area above the bypass flume.
This project will repair the heavily scoured and eroded concrete bypass flume wing walls, stabilize the inlet and outlets of the flume pipe with selective grout injection, and prevent water infiltration into the back of the Lock 20 masonry walls by installing a concrete and masonry bulkhead at the flume inlet. The bulkhead would be reversible. The concrete bulkhead will be totally underwater during normal operations of the canal and therefore not visible to park visitors. The concrete flume head and wing wall repairs would not be reversible as they will become structural strength to replace eroded portions of the existing walls. The existing mechanisms that were installed to raise and lower a inlet cover plate will be restored to give the appearance of an operational feature. There is no evidence remaining of the inlet plate.
The park's Interdisciplinary Team reviewed the project for impacts to natural and cultural resources. The project does not pose any serious or long-term effects to the environmental, historical, cultural, archeological, or visual resources. It meets categorical exclusion #C.4 – Routine maintenance and repairs to cultural resources sites, structures, utilities, and grounds if the action falls under an approved Historic Structures Preservation Guide or Cyclic Maintenance Guide, or if the action would not adversely affect the cultural resource.
The project also meets the National Historic Preservation Act/Section 106 Programmatic Agreement, Exclusion #IV.B 9 – Rehabilitation work limited to actions for retaining and preserving, protecting and maintaining, and repairing and replacing in kind materials and features, consistent with the Secretary of Interior's Standards for Rehabilitation and the accompanying guidelines.
For further information about this project, please contact Exhibit Specialist, C&O Canal NHP, 1850 Dual Highway, Suite 100, Hagerstown, MD 21740.