File:The future water supply of San Francisco; a report to the Honorable the secretary of the interior and the Advisory board of engineers of the United States army (1912) (14772836072).jpg

Identifier: cu31924004975805 (find matches)
Title: The future water supply of San Francisco; a report to the Honorable the secretary of the interior and the Advisory board of engineers of the United States army
Year: 1912 (1910s)
Authors: Spring Valley water company, San Francisco
Subjects: Water-supply
Publisher: (San Francisco, Printed by the Rincon publishing company
Contributing Library: Cornell University Library
Digitizing Sponsor: MSN

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8 per cent., con-tinued approximately through the entire 19-year period, we would have an average annualrainfall in the Arroyo Valle watershed properof between 21 and 22 inches per annum. The average daily gross run-off from theArroyo Valle watershed having been closely de-termined above to be about 30 million gallonsper day, it appears that with an average sea-sonal rainfall of say 21 inches of rain on the140 square miles, or round 3,900 million squarefeet of Arroyo Valle direct watershed, the av-erage seasonal gross precipitation on the samewould be round 6,800 million cubic feet, or51,000 million gallons. The average run-offfrom the Arroyo Valle 140 square miles ofwatershed has been shown to be about 30 mil-lion gallons per day, or 10,950 million gallonsper annum, indicating that on this watershedthe percentage that the run-off bears tothe gross precipitation would be about 10,950 = 21.47%. 51,000 The average annual rainfall on the Alamedawatershed (B) of about 35 square miles will
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116 PRECIPITATION IN ALAMEDA DIVISION. 117 I)robably lie somewhere midway between that ofCaUweras and Arroyo Voile. Where the Cala-veras rainfall for the 19 seasons averaged about27.8 inches, and that at Arroyo Valle (obtainedas above by interpolation) about 21 inches, theaverage between these two rainfalls in round fig-ures, about 24 inches, represents the average an-nual rainfall on the Alameda watershed. Thetopograhical as well as the geological featuresof the Alameda watershed (B) represent a me-dium between that of the Arroyo Valle shed (C)and the Calaveras (A). Located as it is, be-tween C and A, its rainfall as well as its run-offwill lie somewhere between those of C and A. While the run-off percentage at Calaveras,from the average rainfall of 27.8 inches (duringthe 19 year period), owing to favorable con-ditions, shows an average percentage of 43.8%,the less favored Arroyo Voile region, with itsrainfall of about 21 inches, shows a percentageof only about 21.5%. Where, as above

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