The great Catskill Aqueduct, the completion of which was celebrated with appropriate cere monies on 12-15 Oct. 1917, augments the water supply of Greater New York by from 500 to 600 million gallons per day. Its purpose is to carry to the city the water from a new source of supply in the Catskill Mountains. The water entering it from the colossal Asholcan Reser voir, about 12 miles west of Kingston, N. Y., flows by gravity through the new Hill View Reservoir just north of the city line, into the distribution system of the city. Its length to the northern boundary of the city is 92 miles, of which 55 miles is cut and cover work, 31 miles is in tunnel and 6 miles is steel pressure pipe. Seventeen miles of the tunneling is be low the hydraulic grade and, therefore, sub jected to greater than normal pressure and is called °Pressure Tunnel?' These pressure tun nels, of circular section, generally feet in side diameter, are used to carry the aqueduct under streams or depressed areas along the route. As the route crosses the drainage sys tem of the region, several of these pressure tunnels are required, though steel pipes are used for the purpose where the conditions made them necessary or more economical. The pressure tunnels are placed at a sufficient depth below the surface of the rock formation, usu ally about 150 feet, to insure sound rock and to resist the internal water pressure. The great pressure tunnel under the Hudson River at Storm King, about four miles above . West Point, is by far the boldest and most remark able undertaking of the kind in the world. In order to secure sound rock and to withstand pressure and leakage, it was found necessary to drop the aqueduct tunnel to a position 1,100 feet below the surface of the river and about 1,500 feet below the hydraulic grade. Vertical shafts from the approach tunnels were sunk on each side of the river, 3,022 feet apart, to the necessary depth, and the horizontal river tun nel driven between them.
All the tunnels are lined with concrete; those upon the hydraulic grade, of horseshoe sec tion, have a completed width of 14 feet 3 inches and a total height, from invert to the soffit of the arch, of 17 feet. The pressure tunnels are of circular section, varying in diameter from 16 The aqueduct proper strictly may be con sidered as extending from the Ashokan Reser voir to the Hill View Reservoir, though in fact it extends into and under the city. The dis tribution of such an enormous volume of water to the different boroughs of the greater city presented a troublesome problem. It was solved by continuing the great tunnel southward through the borough of Manhattan and under the East River into Brooklyn. From the ter mini of this tunnel the water is carried east ward into the borough of Queens and south feet 7 inches to 14 feet—the latter being at the Hudson River crossing'. Where steel pres sure pipes are used they are lined inside and sheathed outside with concrete. The cut and cover work consists of a strongly designed concrete conduit with arched invert, sides and crown, constructed in place and surrounded and covered to a depth of not less than 14 feet with earth.
The difference in elevation between the flow line of the water as it emerges from the Asho kan Reservoir and the water surface of the Hill View Reservoir is 216 feet, giving an average hydraulic gradient of about feet per mile.
ward to the borough of Richmond (Staten Island) through pipes, the last named branch involving the crossing of New York Bay at °The by a pipe laid in a trench dredged into the bottom of the bay. The length of the city tunnel is 18 miles. Its diameter, 15 feet at the northern end, decreases to 11 feet at its ends in Brooklyn as the quantity of water to be delivered diminishes. Its depth below the surface varies from 200 to 750 feet. Frequent shafts facilitated construction and provide for connection with the distributing pipe system under the streets. The cost of the aqueduct proper from the Ashokan Reservoir to the city line has been $61,000,000, and the tunnel from the city line to Brooklyn has cost $22,500,000. The total cost of the project was $140,000,000.
Another of the greatest aqueduct projects in the world is that recently completed to sup ply the city of Los Angeles, Cal., with water. The source of the supply is the Owens River in the heart of the Sierra Madre Mountains. The total length of this aqueduct, including the diverting canal and reservoirs, is about 233 miles. It is designed to deliver 260,000,000 gal lons per day. As this quantity isgreater than will probably be needed for the domestic use of the city for many years, it is intended to utilize the surplus for irrigation purposes, and the great fall in the course of the aqueduct is intended to be utilized for water power pur poses. The water is taken from the Owens River at an elevation of 3,815 feet above the sea, and carried thence by an open canal a distance of about 60 miles to the Haiwee Reservoir, where the aqueduct proper begins, the water surface in this reservoir being 3,760 feet above sea-level. The length of the aque duct from this reservoir to its end in the San Fernando Valley is about 171 miles. The lead ing types of construction and the aggregate length of each type in miles is: Unlined canal, 24; lined canal, 37; covered conduit, 98; tunnel, 43, and steel syphon, 12.
The covered concrete canals are approxi mately of rectangular section, covered by flat slabs of reinforced concrete, with an interior cross-sectional area of 94 square feet. The tunnels, lined with concrete, have curved in verts, straight (inclined) sides and arched roof. Steel pipes are chiefly used to carry the aqueduct under streams and gorges and down the steep declivities below the hydraulic gra dient. Such declivities or steep descents occur at three principal localities, creating great pres sure, which is to be utilized for generating water powers. This will result in no loss of water, since it will be returned to the aqueduct at a lower level. The cost of the aqueduct and its accessories has been $24,600,000.