St. Francis Dam

A reprint from American Scientist the magazine of Sigma Xi, The Scientific Research Society This reprint is provided for personal and noncommercial use. For any other use, please send a request to Permissions, American Scientist, P.O. Box 13975, Research Triangle Park, NC, 27709, U.S.A., or by electronic mail to [email protected]. ©Sigma Xi, The Scientific Research Society and other rightsholders ENGINEERING ST. FRANCIS DAM Henry Petroski os Angeles could not have grown into the Mulholland later recalled that he became in- Lmetropolis that it is today without the ex- terested in things technical when serving as pansion of its water supply. In 1900 the city’s a helper on a drill rig digging water wells population was about 100,000 and growing that pierced a buried tree trunk at a depth of rapidly, to reach 175,000 within five years. Since 600 feet. He went to the library to investi- the Los Angeles River watershed was capable of gate the manner by which a tree could be- supporting only about 200,000 people, the city come buried at such great depth, and read had the choice of limiting growth or finding new University of California Professor John sources of water. A drought in 1904 raised the is- LeConte’s Introduction to Physical Geology. sue to crisis proportions. Mulholland liked the subject matter so Los Angeles’s need to import water had been much that he later recalled, “Right there I foreseen a decade earlier by Fred Eaton, who as decided to become an engineer”.… city engineer had identified the Owens Valley, north of the city, as a likely candidate. In the Mulholland eventually became general manager meantime, the U.S. Reclamation Service had be- and chief engineer of the Los Angeles Water Com- gun looking into the feasibility of an irrigation pany. He proved himself to be so knowledgeable of scheme for the farmers of the Owens Valley, and the poorly documented infrastructure and work- Los Angeles had to act fast if it was to obtain the ings of the water distribution system that, when water rights. Eaton took William Mulholland, the company was acquired by the city in 1902, the manager of the newly formed Los Angeles Bu- self-taught engineer was retained as its manager. It reau of Water Works and Supply, to the valley to was in this capacity that he accompanied Fred investigate the possibility of constructing a grav- Eaton to the Owens Valley and secured $1.5 million ity-flow aqueduct from there to the city nearly from the Los Angeles Board of Water Commission- 250 miles south. The distance was unprecedent- ers for engineering studies of the situation. ed. The longest Roman aqueducts were less than The scale of the project and Mulholland’s “lack 60 miles long, and New York’s Croton Aqueduct of substantive experience in constructing such fa- was even shorter. However, Owens Lake was cilities” were used by “other engineers, newspa- more than 3,000 feet higher than the city, provid- per editors and electric power interests” to dis- ing a much greater average gradient than existed credit the scheme. In response to the criticism, the in the successful Croton Aqueduct. Thus the en- City Commissioners appointed an Aqueduct Ad- gineering problems, which would involve in- visory Board, comprising three distinguished con- verted siphons and pressure tunnels to get the sulting engineers, to “make an independent eval- water over and through the mountains in the uation of the proposed aqueduct design.” One of way, seemed solvable. the consultants was John R. Freeman, who had been among the principal designers of the New Mulholland Drive Croton Aqueduct and who had served on the ad- William Mulholland was an engineer of the old visory board to review the design of the Panama school, which essentially means that he had learned Canal. When the external board found Mulhol- by doing. He was born in Ireland in 1855, went to land’s aqueduct design “admirable in conception sea at 15, landed in New York City four years later, and outline,” criticism was quelled. The $23 mil- worked at a variety of jobs in the East and Mid- lion bond issue passed overwhelmingly in 1907. west, and sailed via the Isthmus of Panama to San The construction of the 233-mile aqueduct and Francisco. He settled in the Los Angeles area at the its initial filling were not without incident. Upon age of 22, working as a “water ditch tender” with first carrying water, one of the major siphons in the Los Angeles City Water Company, a small pri- the aqueduct began leaking and was lifted up by vate provider. According to one account: the resulting hydraulic forces. The seepage from the riveted steel conduit also triggered a land- Henry Petroski is A. S. Vesic Professor of Civil Engineering and a slide in which the pipe became entangled. Such professor of history at Duke University. Address: Box 90287, setbacks were forgotten by most of the 30,000 Durham, NC 27708-0287. people who gathered on November 5, 1913, to © 2004 Sigma Xi, The Scientific Research Society. Reproduction 114 American Scientist, Volume 91 with permission only. Contact [email protected]. Figure 1. St. Francis dam impounded 38,000 acre-feet of water prior to its failure on March 12, 1928. (Photograph by the Los Ange- les Department of Water and Power.) watch the opening of the world’s longest aque- pensive for Mulholland’s tastes. In fact, he had duct, which was capable of transporting 258 mil- imagined a dam in San Francisquito Canyon dur- lion gallons per day to Los Angeles. ing the construction of the aqueduct. Mulholland While the aqueduct was being planned, specula- saw then that a relatively small dam built where tors bought up large parcels of land in the San Fer- the canyon narrowed would hold back an enor- nando Valley, located north of Los Angeles. Water mous amount of water. He also recognized early from the aqueduct would make the semi-arid re- on that the geology of the location called for spe- gion arable, they anticipated, but when it became cial caution, but these conditions did not keep clear that no such water would ever be made avail- him from designing a dam for the site. He as- able outside of Los Angeles, the San Fernando sumed that the buttressing effect of the dam landowners argued for annexation. By 1924, their would mitigate any slippage at the canyon walls. successful campaign had quadrupled the area of Until 1923, all the dams whose designs Mulhol- the city. This growth, combined with a three-year land had overseen were earthworks—large em- drought, severely taxed the water supply. Under bankments whose fine-grained silt and clay cores the worst conditions, ranchers in the San Fernando were more or less impermeable to water. The first Valley were intercepting virtually all of the aque- concrete dam built for Los Angeles was the 200- duct’s base flow. The city of Los Angeles sought to foot-high Weid Canyon Dam, which was de- acquire more water rights in the Owens Valley, but signed to impound the Hollywood Reservoir. It angry residents, still bitter from the original conflict has been speculated that Mulholland decided to over the claims of the rural valley versus a growing adopt a concrete-dam design over the clay-core city, balked, and some turned to violence reminis- type with which he was so familiar because of the cent of the Old West. Among the retaliatory acts limited supply of clayey materials in the sides of was the dynamiting of the aqueduct, which subse- Weid Canyon. A year before the unique concrete quently had to be protected by armed guards. dam was completed, in 1925, it was christened Mulholland Dam, a testament to the stature to Storage to Stretch Supply which the chief engineer had risen in Los Angeles. In the meantime, in recognition of the fact that the St. Francis Dam was similarly designed to be aqueduct could not supply enough water for both made of concrete, because there was no suitable urban Los Angeles and the rural San Fernando clay or silt available at the San Francisquito Valley without enormous storage capacity, addi- Canyon site. The new dam would also be a tional reservoirs had been planned and designed stepped concrete gravity arch structure: Its down- and were under construction. In fact, between 1920 stream face was constructed like a wide set of and 1926, a total of eight new reservoirs were built steps, its material was mass (unreinforced) con- by the Los Angeles Bureau of Waterworks and crete, and the structural principle by which it held Supply, during which time Mulholland made it back the water was through its sheer weight press- known that it was his goal to have enough reser- ing down on the ground, aided by an arched plan voir capacity to hold in reserve an entire year’s that took advantage of the water pressure behind worth of water for the city. Among the additional it to compress or wedge the dam between the reservoirs Mulholland planned was one that sides of the canyon, which served as abutments. would account for about half the total water re- The original design of the St. Francis called for a quired. This dam, to be located in San Francisquito dam reaching 175 feet above the San Francisquito Canyon, was to be called the St. Francis. Creek bed, which would have given it a capacity The St. Francis Dam site was chosen after in- of 30,000 acre feet of water—that is, enough water flated land values made another location too ex- to flood 30,000 acres to a depth of one foot, enough © 2004 Sigma Xi, The Scientific Research Society.

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