Underwater Repairs for Potomac River Dam #5

Potomac River Dam No.5 is a 20-feet high stone masonry dam in the Chesapeake and Ohio (C&O) Canal National Historic Park in Maryland. The dam is a historic structure built in 1836 to divert flows into the C&O Canal. The dam is a run-of-the-river structure with the Potomac River continuously flowing over the dam crest. In 1991, an underwater inspection by the Bureau of Reclamation discovered large cavernous voids undermined the dam that could precipitate a sudden collapse of the structure. The voids were likely formed by the erosive force of the Potomac River cascading over the dam and impacting along the downstream dam toe. The National Park Service entered into an interagency agreement with the Bureau of Reclamation and the U.S. Navy Underwater Construction Team to engineer and implement repairs. The repairs consisted of filling the voids with concrete pumped from the dam abutment. The mass backfill concrete was anchored into the bedrock and also grouted at the dam base interface. All associated work, including determining many of the engineering requirements, was performed underwater to avoid the expense and time required to cofferdam and dewater. The repairs were completed within a six week period during the fall of 1993.