Cabin John Aqueduct
MacArthur Boulevard over Cabin John Creek & Cabin John Parkway, Cabin John, Montgomery County
Cabin John Aqueduct carries MacArthur Boulevard traffic on a bridge over Cabin John Creek and over the Cabin John Parkway. The aqueduct conduit is located within the bridge structure under the boulevard. Cabin John Aqueduct is comprised of one principal arch segment of 110 degrees which has a span of 220' and a height at the center of 57'-3". Five additional arches and four spandrel spans form the remainder of the structure. The weight of the principal arch rests on its own pilings. The facing stone of the Aqueduct is Seneca sandstone, with the exception of Quincy (Massachusetts) granite in the arch ring and Port Deposit granite in the skewbacks. The backing stone, dug from a nearby quarry, is "blue" or "Potomac" gneiss. The lead and brick lined conduit, with an average fall of nine inches per mile, acts as an arch, providing support for the bridge. A steel door in each abutment provides access to the interior of the bridge. The deck of the Cabin John Aqueduct, originally of sandstone, was turned into an asphalt roadbed in 1873. The roadway is 17'-2" wide over the main arch, and 19'-2" wide over the abutments and approach spans. The flat surface of the aqueduct is relieved by two projecting courses at the parapet.
The 220' span single arch of the Cabin John Aqueduct was, from 1863 to 1903, the unchallenged longest stone masonry arch in the world. Designed by Montgomery C. Meigs (1816-1892) of the U.S. Army Corps of Engineers, it was an innovational feat of 19th century engineering. The ingenious features of the aqueduct include the method of the control of water flow and water distribution as designed by Meigs. The use of the water main itself as a supporting member of the arch is an innovation. The strength and durability of the arch is further attested to by the fact that it remains in continuous use to carry east-west traffic on MacArthur Boulevard over Cabin John Creek. The aqueduct inside the bridge provided the principal source of water to Washington, D.C. throughout the late 19th century. At peak capacity, the conduit transported 40 million gallons of water per day to the District of Columbia. By 1968 the aqueduct supplied the city with 20% of its water.