Page:1902 Encyclopædia Britannica - Volume 25 - A-AUS.pdf/561

 511

AQUEDUCT inches in diameter, crossing a stream with a span of 104 feet, and having no support other than that derived from their arched form. One end of the arch is 24J feet above the other end, and, when filled with water, the deflection with eight men on it was only on the 34-inch pipe where it crosses a canal. Mr Schuyler points out {Trans. Am. Soc. C. E. vol. xxxi. p. 148) that the fact that the entire water supply of a city of 150,000 inhabitants is conveyed in wooden mains, is so radical a departure from all precedents, that it is deserving of more than a passing notice. He says that it is manifestly and unreservedly successful, and has achieved an enormous saving in cost. The sum saved by the use of wooden, in preference to cast-iron pipes, is estimated at $1,100,000 dollars. It is perhaps necessary-to state that the pipe is buried in the ground in the same way as metal pipes. The edges of the staves are dressed to the radius with a minute tongue ^ inch high on one edge of each stave, but with no corresponding groove in the next stave ; its object is to ensure a close joint when the bands are tightened up. Leaks seldom or never occur along the longitudinal seams, but the end shrinkage caused troublesome joint leaks. The shrinkage in California redwood, which had seasoned 60 to 90 days before milling, was frequently as much as 3 inches in the 20 staves that formed the 34-inch pipe, and the space so formed had to be filled by a special closing stave. Metallic tongues, 3 inch deep, are inserted at the ends of abutting staves, in a straight saw cut. The bands, which are of mild steel, have a head at one end and a nut and washer at the other ; the ends are brought together on a wrought-iron shoe, against which the nut and washer set. The staves forming the lower half of the pipe are placed on an outside, and the top staves on an inside, mould. While the bands are being adjusted the pipe is rounded out to bring the staves out full, and the staves are carefully driven home on to the abutting staves. The spacing of the bands depends on circumstances, but is about 150 bands per 100 feet. With low heads the limit of spacing was fixed at 17 inches. The outer surface of the pipe, when charged, shows moisture oozing slightly over the entire surface. This condition Mr. Schuyler considers an ideal one for perfect preservation, and the staves were kept as thin as possible to ensure its occurrence. Samples taken from pipes in use from three to nine years are quite sound, and it is concluded that the wood will last as long as cast iron if the pipe is kept constantly charged. The bands are the only perishable portion, and their life is taken at from fifteen to twenty years. Other portions of the second conduit for a length of nearly 3 miles were formed of concrete piping, 38 inches’ diameter, formed on a mould in the trench, the thickness being 2^ to 3 inches. So successful an instance of the use of wooden piping on a large scale, is sure to lead to a large development of this type of aqueduct in districts where timber is plentiful and iron absent. Pioneer Aqueduct, Utah.—The construction of the Pioneer Aqueduct, Utah, was begun in 1896 by the Pioneer Electric Power Company, near the city of Ogden, 35 miles north of ,!°n*er’ dSalt Lake City. The storage reservoir, from which it Uinn. raws its water, will cover an area of 2000 acres, and contain about 15,000 million gallons of water. The aqueduct is a pipe 6 feet in diameter, and of a total length of 6 miles; for a distance of rather more than 5 miles it is formed of wooden staves, the remainder, where the head exceeds 117 feet, being of steel. It is laid in a trench and covered to a depth of 3 feet. . The greatest pressure on the steel pipe is 200 lb per square inch, and the thickness varies from § to jj inch. The pipe was constructed according to the usual practice of marine boiler-work for high pressures, and each section, about 9 feet long, was dipped in asphalt for an hour. These sections were supported on timber blocking, placed from 5 to 9 feet apart, and consisting of three to six pieces of 6 x 6 inch timbers laid one on the top of the other ; they were then riveted together in the ordinary way. The wooden stave-pipe is of the type successfully used in the Western States for many years, but its diameter is believed to be unequalled for any but short lengths. There were thirty-two staves in the circle, 2 inches in thickness, and about 20 feet long,, hooped.with round steel rods § inch in diameter, each hoop being in two pieces. The pipe is supported at intervals of 8 feet by sills 6x8 inches and 8 feet long. The flow through it is 250 cubic feet per second. The Santa Ana Canal was constructed for irrigation purposes in California, and is designed to carry 240 cubic feet of water per second {Trans. Am. Soc. C. E. vol. xxxiij. p. 99). The Santa Ana. cross secti0n of the flumes shows an elliptical bottom and straight sides consisting of wooden staves held together by iron and steel ribs. The width and depth are each 5 feet 6 inches, the intended depth of water being 5 feet. The staves are held by T-iron supports resting on wooden sills spaced 8 feet apart, and are compressed together by a framework. They were caulked with oakum, on the top of which, to a third of the total depth, hot asphalt was run. The use of nails was altogether avoided except in parts of the framework, it being noticed that decay usually starts at nail holes. It was found possible to make the flume
 * of an inch. A somewhat similar arch, 60 feet span, occurs

absolutely watertight, and in case of repair being necessary at any part the framework is easily taken to pieces so that new staves can be inserted. The water in the flume has a velocity of 9'6 feet per second. The Warm Springs, Deep, and Morton, canons on the line are crossed by wooden stave pipes 52 inches in diameter, bound with round steel rods, and laid above the surface of the ground. The work is planned for two rows of pipes, each capable of carrying 123 cubic feet per second ; of these one so far has been laid, lire lengths of the pipes at each of the three canons are 551, 964, and 756 feet respectively, and the maximum head at any place is 160 feet. The pipes are not painted, and it has been suggested that they would suffer in their exposed position in case of a bush fire, a contingency to which, of course, flumes are also liable. Aqueducts of Nero York.—There are three aqueducts in New York—the Old Croton Aqueduct (1837-43), the Bronx River Conduit (1880-85), and the New Croton Aqueduct (1884-93), discharging respectively 95, 28, and 302 million U.S. gallons a New York. day ; their combined delivery is therefore 425 million gallons a day. The Old Croton Aqueduct is about 41 miles in length, and was constructed as a masonry conduit, except at the Harlem and Manhattan valleys, where two lines of 36-inch pipe were used. The inclination of the former is at the rate of about 13 inches, per mile. The area of the cross-section is 53 -34 square feet, the. height is 8^ feet, and the greatest width 7 feet 5 inches ; the roof is semicircular, the floor segmental, and the sides have a batter on the face of | inch per foot. The sides and invert are of concrete, faced with 4 inches of brickwork, the roof being entirely of brickwork. There is a bridge over the Harlem river 1450 feet in length, consisting of fifteen semicircular arches; its soffit is 100 feet above high rvater, and its cost was $963,427. The construction of the New Croton Aqueduct was begun in 1885, and the works were sufficiently advanced by 15th July 1890 to allow the supply to be begun. The lengths of the various parts of the aqueduct are as follows:— Miles. Tunnel . . • • . 29'75 Cut-and-cover . . • . 1T2 Cast-iron pipes, 48 inches diameter, 8 rows. 2'38 Croton Inlet to Central Park

.

. 33)25

The length of tunnel under pressure (circular form) is 7T7 miles, and that not under pressure (horse-shoe form) 23'70 miles. Hie maximum pressure in the former is 55 lb per square inch. The width and height of the horse-shoe form are each 13 feet 7 inches, and the diameter of the circular form (with the exception of two short lengths) is 12 feet 3 inches. The reason for constructing the aqueduct in tunnel for so long a distance was the enhanced value of the low-lying ground near the old aqueduct. The tunnel deviates from a straight line only for the purpose of intersecting a few transverse valleys at which it could be emptied. For 25 miles the gradient is 0'7 foot per mile; the tunnel is then, depressed below the hydraulic gradient, the maximum depth being at the Harlem river, where it is 300 feet below high water. The depth of the tunnel varies from 50 to 500 feet from the surface of the ground. Forty-two shafts were sunk to facilitate driving, and in four cases where the surface of the ground is below the hydraulic gradient these are closed by watertight covers. The whole of the tunnel is lined with brickwork from 1 to 2 feet in thickness, the voids behind the lining being filled with rubble-in-mortar. The entry to the old and new aqueducts is controlled by. a gatehouse of elaborate and massive design, and the pipes which take up the supply at the end of the tunnel are also commanded by a gate-house. The aqueduct, where it passes under the Harlem river, is worthy of special notice. As it approaches the river it has a considerable fall, and eventually ends in a vertical shaft 12 feet 3 inches in diameter (where the water has a fall of 174 feet), from the bottom of which, at a depth of 300 feet below high-water level, the tunnel under the river starts. The latter is circular in form, the diameter being 10 feet 6 inches, and the length is 1300 feet; it terminates at the bottom of another vertical shaft also 12 feet 3 inehes in diameter. The depth of this shaft, measured from the floor of the lower tunnel to that of the upper tunnel leading away from it, is 321 feet; it is continued up to the surface of the ground, though closed by double watertight covers a little above the level of the upper tunnel. Adjoining this shaft is another shaft of equal diameter, by means of which the water can be pumped out, and there is also a communication with the river above high-water level, so that the higher parts can be emptied by gravitation. The cost of the Old Croton Aqueduct was $11,500,000 ; that of the new aqueduct is not far short of $20,000,000. The Nadrai Aqueduct Bridge, opened at the end of 1889, is the largest structure of its kind in existence. It was built to carry •the water of the Lower Ganges canal over the Kali Nadrai. Naddi, in connexion with the irrigation canals of the north-west provinces of India. In the year 1888-89 this canal