Washington Aqueduct Tunnels

By Elliot Carter | July 23, 2018

The need for a reliable citywide water supply was painfully illuminated on Christmas Eve in 1851, when a preventable stove fire ravaged the Library of Congress, toasting more than 4,000 volumes purchased from Thomas Jefferson's personal collection, and other  irreplaceable government records. Newspapers pointed out that one or two buckets of water could have extinguished the sparks, if they had been available to Capitol Policemen who first sounded the alarm. “The Congress Library utterly destroyed,” headlines read in the Baltimore Sun the next day, “the cause of the conflagration - the want of water.”

[Click on the Image Above to Launch the Washington Aqueduct Story Map]

Washington relied on wells and springs for its water at the time of the library fire. Indoor plumbing was a rare novelty, largely comprised of hollowed out wooden logs, and limited to government office buildings. Congress tapped a nearby spring using a janky array of piping to fill a small reservoir in the low-ceilinged sub basement of the Capitol Building.

The ad hoc system leaked as you would imagine, and the police had a hard time preventing residents from drilling into the federal government's primitive wooden lines for their own purposes. Public pressure to solve “the water problem” peaked after the Library of Congress fire, leading then-Mayor John Tower to warn the City Council that “there is no subject in which our citizens feel more deeply interested.”

The century-long watery saga that followed showcases the best and the worst sides of Washington; a high-minded, competent civil service arrayed against the opposing forces of incompetence and fraud. The backbreaking effort to build the city's aqueduct flows out off the history book pages every time a shower is run, or a glass of water is filled.

"Let our aqueduct be worthy of the Nation"

Congress directed their elite builders, the U.S. Army's Corps of Engineers, to survey the region and identify an “unfailing and abundant supply of good wholesome water.” The name "Washington Aqueduct" was already in use from this early stage, recalling the water systems of ancient Rome, and optimistically suggesting that the U.S. was equally an empire on the rise.

The Army’s preeminent engineer Montgomery Meigs was ideally suited for the Aqueduct job. Meigs was highly competent, a self-promoter, and well versed in both the high-level and nuts and bolts engineering at hand. (It’s worth noting that Meigs oversaw construction of the Washington Aqueduct simultaneous with extensions of the House and Senate, and construction of the Capitol's new iron dome. The man's administrative capacity was sui genaris.)

"Thus quietly and unostentatiously was commenced the great work. Which is destined I trust for the next thousand years to pour healthful water into the Capital of our union. May I live to complete it & thus connect my name imperishably with a work greater in its beneficial results than all the military glory of the Mexican War." - Montgomery Meigs, November 30, 1852

Meigs considered a number of locations as the source for Washington’s water supply. Rock Creek was close at hand, but its eight million gallon daily supply wouldn’t quench the thirst of the growing city. Washington also had miles of available riverfront, but the tide's flow render it too salty for consumption. Instead, Meigs cast his gaze a distant ten miles above the city on Great Falls, where the Potomac's pure waters remained free of salty adulterants.

It’s difficult to convey how remote Great Falls would have appeared to Washingtonians in the 1850’s. Urban development barely extended a few blocks beyond Georgetown, the White House, Patent Office, and Capitol. Much of the District beyond Florida Avenue (then known as Boundary Road) was blanketed in sprawling farmland. There weren't even roads leading to the Falls, and Army Engineers had to hack their own right of way through the hilly woodlands to make way for construction crews and their wagons. Weary reporters visiting the site concluded that "a more unpromising region for the construction of an aqueduct could not be found."

Meigs didn't send his laborers sweating up the Potomac just for the sake of water purity. The Army's concern was volume, and Meigs was after the estimated 67 million gallons of water available daily at the Great Falls site. Flush with tax revenue from the Gold Rush, the government was building for the future, and no amount was too much when it came to the water supply. Anything they didn’t drink could be flushed through the stagnant sewer system or used to lubricate the city’s proliferating fountains. (Fountains were a particular fixation for Meigs, who believed they "cool the air and protect and preserve the health." The Aqueduct builder wanted a special fountain next to Capitol with jets of water "one hundred and twenty feet in height.")

Meigs' plan centered on a long underground conduit, a circular nine-foot diameter tube excavated alongside their new service roadway. Familiar to modern readers as MacArthur Boulevard, the route was known for a century as Conduit Road, and still has six-ton weight limits to protect the precious old water tunnels. A gang of seven hundred laborers, drillers and blasters worked their way up the Potomac palisades before dusting off their surveying tools and carefully bricking up the conduits at on a precise nine-inch per mile decline. Part of the design's brilliance was that it worked entirely by gravity, just like the Roman aqueducts. If the tunnels were properly maintained, Meigs thought that they wouldn’t need replacement for a thousand years.

Montgomery Meigs thoroughly subscribed to the underground gospel, noting later in life that "there is nothing so lasting in human engineering as a tunnel," and that from a maintenance perspective, "it costs nothing to take care of." Still, select portions of the Washington Aqueduct clearly belonged aboveground. Several of the low lying ravines between Great Falls and Washington required aqueduct bridges in true Roman style. The most significant natural obstacle: a plunging 100-foot-deep valley around Maryland's Cabin John Creek. Meigs spanned the gap with a tremendous single-arch bridge that still carries city tap water a century and a half later. When the structure was completed in 1864 it enjoyed bragging rights as the longest of its type in the world.

The Army Corps of Engineers faced a diverse set of challenges to make their water tunnels functional. Up at Great Falls, a dam was built across the Potomac to divert the river flow through sluice gates into thirsty conduits. Further down the line, crews dug the Dalecarlia Reservoir to “receive” the raw flow and hopefully give unpleasant sedimentation a chance to settle out by gravity. Two miles down, another artificial lake made the water fit for distribution. 

Meigs built his aqueduct tunnels with Spartan-like durability, but recognized the aboveground bits as opportunities for architectural flair. Beautiful little structures dot the reservoir shores like classical temples, concealing the valves and veins of Washington’s circulatory plumbing. Inside, barrel-vaulted brick and steampunk ironwork give the impression of miniature stations on the London Tube.

Go Deeper

"The Congress Library Utterly Destroyed - The Cause of Conflagration - The Want of Water," Baltimore Sun, December 25, 1851

"The Potomac Aqueduct," Baltimore Sun, March 23, 1855

"Maps of the Washington Aqueduct, Md. and Washington D.C.," U.S. Senate, February 22, 1864

"The Washington Aqueduct: Water Supply District of Columbia," Army Corps of Engineers, June, 1939

"Washington Aqueduct: The Supply Division of the District of Columbia Water System," Army Corps of Engineers, April, 1970

"Capital engineers: The U.S. Army Corps of Engineers in the development of Washington, D.C. 1790-2004," USACE Office of History, 2005