San Francisco’s Water Supply.
The water system supplying the city of San Francisco is owned by the Spring Valley Water-works, a large and wealthy concern. The supply is derived partly from San Francisco peninsula and partly from Alameda county. The sources of supply on the peninsula consist of three artificial reservoirs, constructed by building large dams across three respective valleys. These reservoirs are: The Pilarcitos reservoir, formed by a substantial earth dam 95 feet high, built in 1865-6. The dam is provided with a large waste weir, constructed of brick and iron, across Pilarcitos valley. The elevation is 696 feet above tide, and the capacity of the reservoir is 1,050,000,000 gallons.
The San Andreas resetvoir, formed by a substantial earth dam across the San Andreas valley 95 feet in height, has an elevation of 455 feet above tide and a capacity of 6,200,000,000 gallons. It was constructed in 1867-8, and is also provided with a substantial large waste weir of similar construction as that Pilarcitos dam.
The Crystal Springs reservoir is formed by a dam constructed across the mouth of the Crystal Springs canyon, about four miles above the town of San Mateo. The massive dam is of concrete, 167 feet thick at the base, 25 feet at the top and 170 feet in height (when finished). At present its height is 145 feet and its capacity 19,000,000,000 gallons, while its final capacity, when finished up to 170 feet, will be 29,000,000,000 gallons.
Lake Merced, a natural lake in San Francisco county. It had an original capacity of 1,800,000,000 gallons and will soon be increased to 2,700,000 000 gallons.
A new pumping station, erected in 189T, of a daily capacity 7.500,000 gallons, lifts the water 430 feet high, where (at Ocean View) it joins the water coming from Pilarcitos reservoir.
Besides these sources now in active operation the Spring Valley Water-works owns water rights and a new reservoir site on the San Francisquito creek, near Menlo park, where a fine concrete dam 80 feet in height was constructed in 1891, which is now full of water, holding over 300,000,000 gallons of water. but which is not yet connected by a pipeline with the Alameda creek pipe at Belmont station. This dam will eventually be raised to a height of 120 feet, giving a storage capacity of over 3,000,000,000 gallons.
In addition to this the Spring Valley Water-works owns a magnificent reservoir site at Calaveras valley, in Alameda and Santa Clara counties, with a proposed capacity of over 30,000,000,000 gallons storage, and also valuable lands and water rights on the coast streams in the southern portion of San Mateo county.
The pipe lines that connect the above reservoirs with the San Francisco city reservoir and distributing pipe systems are of the following dimensions : Main pipe from Crystal Springs reservoir to San F’rancisco, 44 inches diameter and 22 miles in length ; two separate pipe lines from San Andreas and Pilarcitos reservoirs respectively to San Francisco, each 30 inches diameter and 16 and 13 miles in length respectively. Pipe line from Alameda creek, via Belmont, to 44 inch pipe near Millbrae, 36 inches diameter, the 36-inch pipe being 29 miles in length and the two submarine pipes miles long each. Pipe from Lake Merced, new pumps to Ocean View junction, 23 inches diameter, 1⅝ miles in length. From this it will be seen that the present storage capacity of the reservoirs of the Spring Valley Water-works is nearly 29 000,000 000 gallons, while with the Crystal Springs and Searsville dams completed to their proposed heights the storage capacity will rise to 42,000,000,000 gallons. When to this the Calaveras reservoir is added eventually, the storage capacity ot the company’s reservoirs combined will be 72,000,000,000 gallons.
One of the difficulties the Spring Valley Water-works labors under is the very hilly character of the site of San Francisco, requiring the division of the city pipe system into five separate districts for the different levels, so that all such portions as lie between o and 50 feet above tide, between 50 and 100 feet, too to 200 feet, 200 to 275 feet and 275 feet to 375 each have their separate pipe and reservoir system with a good pressure. These enormous reservoirs can comfortably weather a dry spell even if it extended over three years.
STOPPING A LEAK IN A WATER Main.—An ingenious method of stopping a leak in a water main is reported to have been made use of at Port Huron by the superintendent of the water-works of that city. The pipe, which runs under the river at that point, and was sixteen inches in diameter, had been split for about three feet by a government dredge. A half circle of wood conforming to the outside diameter of the pipe was made of one and one-half by two-inch strips and in the form of a stave, fastened together on each end by a flexible band. On the inside of this wooden circle « as tacked a sheet of one quarter inch rubber packing, and a sheet of light steel boiler plate was placed on the outside in a similar manner. The patch was then placed over the break by the driver and securely fastened to the pipe with four by one-inch wroughtiron bands, made to the circle of the pipe and drawn together by one-inch-bolts, the space between the bands being seven inches. By this means the pipe was made perfectly tight, and has repeatedly withstood fire pressure.