The restabilization project, mentioned below and seemn in the thumbnail, was completed in May 2005.
The Monocacy Aqueduct is the largest of the eleven aqueducts erected along the C&O Canal, and is often described by many historians as one of the finest canal features in the United States. Ten of the eleven aqueducts remain as key features of the Chesapeake and Ohio Canal National Historical Park, which was designated as a National historical park in 1971. The Catoctin Aqueduct collapsed after its piers were gradually undercut and a flash flood took it down in 1972.
Construction of the Monocacy Aqueduct began in 1829 and was completed four years later. Three separate contractors labored on the immense stone structure, which was constructed for $127,900. The plan for the Monocacy Aqueduct, often referred to as C&O Canal Aqueduct No. 2, was for a stone masonry structure with a waterway of 19 feet at the bottom and 20 feet at the top. The towpath parapet wall is 8 feet wide and the upstream wall is 6 feet wide. Benjamin Wright drew the plans with 6 piers, 2 abutments and 7 arches, each with a span of 54 feet. The piers are 10 feet thick with pilaster at each end. The aqueduct is 438 feet in length. Much of the building material was large granite stone blocks quarried at the base of nearby Sugarloaf Mountain.
Following the 1972 Hurricane Agnes flood, the National Park Service and the Federal Highway Administration designed a steel banding system to stabilize the structure and installed a steel rod reinforcing system. The National Park Service and park supporters have long been concerned about the structural stability of the aqueduct and a major engineering evaluation is underway to determine stabilization needs and associated cost. The C&O Canal National Historical Park and its partners plan to undertake a major stabilization project for the aqueduct to ensure long-term sustainability for the structure. The project would provide for the removal of the steel banding support system and allow the visiting public to view the structure as originally constructed.