National Geographic : 1897 Dec
THE WASHINGTON A Q UEDUCT was commenced in November, 1853. In order that the city might receive a supply of water as soon as possible, work was pushed upon the receiving (Dalecarlia) reservoir and the con duit connecting it with the supply mains, and on January 3, 1859, water from the Dalecarlia reservoir was introduced into the pipes leading to the city. This was not Potomac water, how ever, but was supplied by the streams emptying into the Dale carlia reservoir, which streams are now diverted therefrom by the admirable system of protection works completed in 1895 by Colonel George H. Elliot, U. S. Corps of Engineers, retired. This mode of supply continued until the conduit between Great Falls and the Dalecarlia reservoir was completed, in 1863, and on De cember 5, 1863, Potomac water was introduced into the Dalecarlia reservoir for the first time. Conns island separates the Potomac at Great Falls into two parts, known as the Maryland and Virginia channels respect ively. In order to divert water into the mouth of the conduit feeder at Great Falls a temporary dam of stone and crib work was built across the Maryland channel, 1857 to 1864, which was replaced by a masonry dam completed in 1867. In 1883-'86 the masonry dam was extended across the Virginia channel. In times of very low water in the Potomac this dam, the crest of which was at an elevation of 148 feet above mean tide at the Washington navy yard, did not raise the water to a height suffi cient to fill the mouth of the conduit at Great Falls, and in 1895-'96 the whole dam was raised 21 feet, so that at low stages of the Potomac the mouth of the conduit is just filled. The Washington aqueduct system as it exists today is, with but few modifications, that originally planned by General Meigs. The water supply is taken from the Potomac river at Great Falls, about 14 miles above the city. At this point a masonry dam eight feet in width on the top and 2,877 feet in length, completed in 1896, extends across the river from the Maryland to the Vir ginia shore. The water passes from the feeder, under the Ches apeake and Ohio canal, through the gatehouse and into the conduit, which is circular in cross-section, and for the greater part of its entire length is nine feet in diameter and composed either of rubble masonry plastered or of three rings of brick, but where the soil in which it was built was considered partic ularly good the inner ring of brick was omitted and the diameter was nine feet nine inches. Where the conduit passes as an un lined tunnel through rock the excavation was sufficient to contain an inscribed circle 11 feet in diameter.