The grade is 0.021 feet per 100 feet, total length 38 miles. It crosses the Manhattan Valley 2 miles in extent, with two 36-inch, one 48, and one 60-inch cast-iron pipes, and over the Harlem River by granite bridge, known as High bridge, 100 feet above high water, composed of seven 50-feet and eight 80-feet spans. The conduit over the bridge consists of two 36-inch cast-iron pipes, and a wrought pipe 7 feet 6½ inches in diameter, resting upon saddles, supported by cast-iron standards placed 12 feet apart between the 36-inch pipes.
The aqueduct over Cabin John Creek, of Washington, D. C., water supply, consists of a single arch of masonry 220 feet span, is the largest masonry arch in the world. The rise is 57 feet 7 inches, thickness of crown 4 feet 2 inches, and at spring 6 feet 2 inches. Water is conveyed in an iron pipe 9 feet in diameter, built in solid masonry.
The bridge over Georgetown Creek, on line of Washington Conduit, is 200 feet span with two cords of iron pipe 4 feet in diameter, 1½ inches thickness, used as water conductors. The pipes were first lined with staves of resinous pine 3 inches thick to prevent freezing, but have been taken out. No allowance is made for expansion or contraction. A similar plan is in use at Philadelphia, over the valley of Wissahikon, consisting of two 20 inch cast-iron flange pipes serving as top members of a series of inverted bow-string trusses. There are four spans, each 169 feet 9 inches. Center span 100 feet above ordinary level of the water.
The Boston aqueduct crosses the Charles River by syphon pipes—two, 30 inches, and the other 36 inches in diameter. Starting from a pipe chamber on the western side of the valley, the pipe descends 52.11 feet below the level of conduit, and rests on a masonry bridge of three arches.
One of the syphons for supplying Madrid, Spain, crosses a valley 4,560 feet in length, consisting of four lines of cast-iron pipes three feet in diameter.
Dublin is supplied through 30,336 yards of 33-inch and 8,272 yards of two lines of 27-inch cast-iron pipes—20,000 yards laid through private property. The average fall is 20 feet per mile. There are three relief-tanks on line of 33-inch pipe. The capacity of this pipe was calculated at sixteen millions per day, while the actual delivery exceeded twenty millions.
Toronto is supplied by a 4-foot wooden pipe, 7,000 feet in length, under pressure.
Manchester, N. H., has a wooden penstock, six feet in diameter, 600 feet in length, that conveys supply to water wheels, under a head of twelve feet at entrance and thirty-eight feet at outlet.
The new conduit for water supply of Baltimore is a continuous tunnel, seven miles long, running from the dam to the receiving reservoir—“Lake Montebello.” In its construction no open cuts were made; all work being done by drifting. Its depth below the surface of ground varies from 65 to 360 feet. The internal diameter is 12 feet; the fall is one foot per mile; capacity 170 millions daily. Fifteen shafts were sunk during the constructive work. Two miles of the tunnel were through material that required to be arched with brick; the remaining distance was through very hard rock that did not require arching. The cost of this structure was about two millions of dollars.
Chicago has two tunnels under Lake Michigan, parallel with each other, 46 feet apart, extending to a crib, located in the lake, two miles from the shore. The first one was started, in 1864, under adverse criticism, and successfully completed in 1867. The cost, with the crib, was $457,800. It is five feet horizontal diameter, and 5′ 2″ vertical diameter, and made of brick. The second one was built in 1872-’74; is five feet in diameter, lined with brick. It extends from the North Side Works, a further distance of 20,000 feet, under the city and Chicago River to West Side Works. The cost of this tunnel, under the river, was $414,000, and under the city $543,000. The nature of the excavation was generally through stiff blue clay with occasionally pockets of quicksand.