Los Angeles 200-Mile Conduit Water Supply
The longest artificial water conduit ever planned in America is that which is to increase the water supply of the city of Los Angeles in Southern California, and which is now being completed. While the conduit is notable for its engineering features, it will not only supply water for domestic purposes and for irrigation, but the head of water is so great that it will produce electrical horse-power for pumping, manufacturing, transportation, and other purposes, so that the project achieves three different objects.
The extensive arid district in Southern California has limited Los Angeles in the past to obtaining water from only one source. The rapid growth of the city in population and its industrial development necessitated another supply, hut the nearest considered available was from the Owens river. This stream, which rises in the eastern Sierras of the State, is over 200 miles from 1 .os Angeles, and separated by a country which includes not only mountains, but a large area of absolute desert, presenting many dim culties in the way of constructing such a canal. When the necessary surveys were made, it was found that it would be necessary to build a waterway no less than 215 miles in length. Incidentally. it may be said that the total cost of the project represents about $20,000,000, not counting the purchase of property for reservoir sites and other purposes, which, if included, bring the total cost to nearly $22,000,000. This sum has been provided by the sale of municipal bonds, and such has been the public interest manifested, that all of the money has been raised in the city of Los Angeles, its residents taking its securities.
The canal begins at a dam which has been constructed across the Owens river about forty miles from a lake into which it has hitherto discharged its water. The dam is of the diversion type, and from it extends the main canal for a distance of sixty miles to the llaiwee, the first reservoir in the series planned. On this section is some very difficult work. In a distance of twenty two miles the waterway includes no less than eight miles of tunnel. Three and one-half miles of conduit are composed of heavy steel pipe faced on the outside with concrete. Ten miles of the canal in the same section have walls molded entirely in concrete. The Jawbone division, as it is called, is uninhabited, and it was necessary to transport much of the machinery and all of the food supplies as well as the building material from the desert and mountains in wagons, necessitating the construction of an extensive mileage of roadway.
The tunnels which have been required on the route are notable for their extent. The Coast Range of mountains is pierced by a tunnel, nearly eleven feet in diameter, which is nearly 27,000 feet in length—one of the longest in America. In this tunnel and its approaches, covering a distance of eleven miles, there is a fall from 2.022 feet altitude to 1,520 feet. The head of water thus obtained will be utilized in an electric power plant of 93,000 horse power at what is known as Elizabeth lake. This will be by far the largest power plant in connection with the project. Another tunnel is 7,800 feet in length. The conduit does not extend into the city of Los Angeles; but its waiter is distributed to a series of reservoirs in San Fernando Valley. These reservoirs have a capacity of about 35,000 acre feet, a supply sufficient to serve the needs of the city for a period of several months, even in the dry season.
The development of the water power and its use are notable features of the project which is being carried out. As already stated, several stations are being constructed upon the route at suitable sites. Machinery in some of them has been installed for operating the machinery of the cement mill which has been erected for supplying this material to the project; for the operation of several tramroads for carrying material: and also for dredging a lake which is located on the line, the dredge being constructed especially for this purpose, and operated entirely by electric power. The current is also to be utilized in serving a series of large electric pumps, as the supply of water is ample not only for the city, but for irrigation on an extensive scale. It is calculated that at least 20,000 acres of what is at present unproductive land in this section of California will be reclaimed for the planting of fruit, vegetables, and grain. It might be added that the transmission system from the generating stations to the points of distribution will be about 120 miles in length. In fact, the line is one of the longest in the world, and the current of 73.000 volts is the highest ever attempted over such a length of cable. The concrete-ineased pressure main which leads the water to the main powerhouse—a gradually tapering pipe, so as to accelerate the force of the water at the turbines—is the tirst of the kind ever put in use. Furthermore, the conduit which carries the water to this pressure main is the longest tunnel system in use for this purpose.
Construction was commenced on the eastern section, as it was realized that the tunneling and closed conduits would require so much more time than the open canal. The section in the Jawbone district has been by far the most difficult to complete, for the rock work here comprised nearly nine miles and included no less than twenty tunnels. These tunnels are connected by short redwood flumes, but to all intents and purposes they constitute one continuous underground conduit.
A reference to the headworks and the tunnel system makes clear the entire scheme. A dam, thrown across the canyon at the intake, backs the w’ater up for over a mile, forming a large reservoir, from which the water flows into the tunnels in sufficient quantity to fill them to their required depth of 6 feet 6 inches. From this point the river, in the twelve miles to the powerhouse, drops by a succession of falls and steep grades almost a thousand feet; but the tunnel grade has a fall of only 8 feet to the mile, the total fall to the forebay being only 68 feet. Thus, instead of the waters following their natural course far down in the gorge to the floor level of the power-house, they are run through the gravity conduit high above the bed of the river, emerging from the tunnels in the forebay, S7 feet above the power-house, to which they pass through the immense pressure main to the impulse wheels of the generators. Carrying their full load, the tunnels have a capacity of 410 second feet, or 20,500 miner’s inches. The conduits leading from the forebay to the powerhouse are steel tubes, which taper from a maximum interior diameter of 90 inches to a minimum interior diameter of 28 inches. The thickness of the shell of the piping is 3-16 of an inch where it has a solid rock backing; but where it leaves this formation, and has only the steel to depend upon for withstanding the pressure of the water, the interior diameter is decreased to 72 inches, and the thickness of the pipe is increased to 1⅝ inches. Over 1,000,000 pounds of steel were used in its construction.
The pressure main was built in 10-foot sections. which were hoisted over an aerial tramway to the top of the hill, and from there conveved to an inclined shaft, where they were lowered into place. As each length was riveted, the work taking from ten to twelve hours, the iron workers left and their places were taken by the concrete molders, who formed the concrete casing around the pipe.
The head of water of 877 feet gives a pressure at the impulse wheel of 380 pounds to the square inch. The power is generated in four units, each unit operated by two overhanging impulse wheels carrying eighteen brass buckets. Each impulse wheel is set in a separate masonry compartment which opens directly into the tailrace. where the water is measured before it is returned to its natural channel.
An idea of the immense quantity of material needed for the project is given, when it is stated that the cement alone required amounted to 1,300,000 barrels. Fortunately, large deposits of sand and limestone were found in the Owens river district, and the builders were enabled to manufacture concrete along the route, the largest cement mill having a capacity of 3,000 barrels daily. The volume of water carried by this route will average a flow of over 400 cubic’feet a second. The source of the supply, however the Owens river, is one of the principal water courses in eastern California, and measurements by instrument, which were taken for a considerable period before the work on the conduit commenced, proved that the volume of water it carries is sufficient for the purpose even in the dry season of each year.
The chief engineers of this notable project, and the man to whom the bold scheme for directing the Owens river across the State is due, is Mr. William Mulholland, of Los Angeles, who spent several years in looking over the proposition and preparing plans. He is assisted in the construction by Mr. J. B. Lippincott, formerly in the United States Irrigation service. The Scientific American.