340 THE WASHINGTON AQUEDUCT 



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 8, 

 1859, water from the Dalecarlia reservoir was introduced into the 

 pipes leading to the city. Tliis was not Potomac water, how- 

 ever, but was supplied by the streams emptjdng into the Dale- 

 carlia reservoir, which streams are now diverted therefrom b}'' 

 the admirable S3^stem of protection works completed in 1895 by 

 Colonel George H. Elliot, U. S. Corps of Engineers, retired. This 

 raode of supply continued until the conduit between Great F'alls 

 and the Dalecarlia reservoir was completed, in 1863, and on De- 

 cembers, 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 Mar3dand 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 2} 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 originall}^ planned by General Meigs. 

 The water supph'- is taken from the Potomac river at Great Falls, 

 about 14 miles above the city. At this point a masomy 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 inclies. Where the conduit passes as an un- 

 lined tunnel through rock the excavation was sufficient to 

 contain an inscribed circle 11 feet in diameter. 



