The city of Winnipeg, Canada, has built a gravity aqueduct for a new water supply. It receives water from Indian Bay on Shoal Lake and is approximately 100 miles long. It in volved comparatively simple construction, 85 miles being of covered concrete conduit, 10 miles of five feet steel pipe, less than one-fifth of a mile of tunnel, and slightly over two miles of 48-inch cast-iron pipe. It is designed to de liver over 100,000,000 gallons per day.
The city of Denver, Colo., has been supplied with water by an aqueduct about 20 miles long, consisting of two lines of wood-stave pipe, one of 30 inches and one of 24 inches diameter— the two delivering about 30,000,000 gallons per day.
Many other American cities have aqueducts of greater or less extent and importance con nected with their water supply, and a large number of water power developments and ir rigation projects utilize like structures.
Modern High, massive stone masonry aqueducts are now seldom con structed, and where such elevated structures are unavoidable, they are usually built of hy draulic concrete. The modern engineer finds it generally better and more economical to carry his conduits under, rather than over, streams and depressions.
The introduction of cast-iron and steel pipes of large size, and their comparative cheapness, as well as the wonderful develop ment in the science and art of tunneling, have practically revolutionized aqueduct building since the days of the Romans.
Cast-iron pipes of sufficient strength to with stand the pressures ordinarily required are now available up to a diameter of at least 48 inches and riveted steel pipes of double that diameter and capable of carrying even greater pressures are not uncommon, particularly when encased in concrete.
The general substitution of tunnels for aerial structures is largely due to the very great advancement in the speed and economy of driving tunnels. The perfecting of power rock drills, the introduction of modern high explosives, and improved appliances and methods for handling the excavated material, have greatly simplified and expedited rock tun neling. The invention of the method, the application of compressed air to resist the ingress of water and mud, supplemented by powerful pumps, together with the use of cast iron or concrete tunnel linings, has made tun neling in soft or sub-aqueous material com paratively safe and rapid.
The ability, skill and practical ingenuity of the modern civil engineer and the perfection of instruments of precision for determining and maintaining underground alignments and gra dients have also been an important factor ii overcoming the difficulties and reducing th, cost of modern tunneling.
The construction of pipes and flumes of wood has marked another important advance in aqueduct building in this country. Com paratively large pipes built of wooden staves, accurately jointed with each other and bound by steel hoops at suitable distances apart, arc in common use in the western States; and wooden flumes or canals supported upon wooden trestles, often of considerable height, may take the place of stone, concrete or steel viaducts. The durability of such wooden aque ducts has not yet been satisfactorily determined, but as they are constantly filled with water and often buried in the earth, their useful life ex tends over considerable periods, as experience has already demonstrated, while their low first cost compared with more permanent construc tions makes them very attractive where avail able capital is an important and often control ling consideration. Many miles of such wood stave pipes are now in successful use.
Bibliography.— For ancient aqueducts con sult Merckel, Curt, Ingenieurtechnik im Alterthum' (Berlin 1899). For ancient and mediaeval aqueducts in Asia Minor consult Weber, G., (Wasserleitungen in Kleinasia tischen Stadten) (in >Jahrbuch des Deutsch Archxolog.' Inst. XIX, 1904). For Greek aqueducts consult Curtis, E., (1.1ber Stad tische Wasserbauten der Hellenen' (Arclueo logische Zeilung, 1847). For Roman aqueducts consult Frontinus, Julius, two books on 'The Water Supply of the City of Rome' (translated by Clemens Herschel, 1899). For modern aque ducts consult Bateman, John Frederic, engineer in-chief, (Mechanical Arrangements of the Manchester Water Works' of the Institution of Mechanical Engineers, 1866) ; Wegmann, Edward, (The Water Supply of the City of New York) (1896) ; report of the aqueduct commissioners of New York, "The New Croton (1895) ; annual re ports of the board of water supply of New York; board of public service of the city of Los Angeles; The Final Report of the Construction of the Los Angeles Ague d!ict (101(,)