Who Designed the Ill-Fated St. Francis Dam?

The St. Francis Dam was built by the City of Los Angeles Bureau of Water Works and Supply (BWWS) in 1925-26 as a curved concrete gravity dam, approximately 200 feet high in San Francisquito Canyon, about 35 miles northeast of downtown Los Angeles. The reservoir provided an additional 38,000 acre-feet of storage from the Los Angeles Aqueduct. The dam failed catastrophically on March 13, 1928, killing at least 432 people, making it the most deadly American structural failure of the 20th Century. BWWS Chief Engineer and General Manager William Mulholland accepted complete blame for the failure, but who actually designed the dam has been clouded in mystery for almost 90 years. Recent research suggests that no site-specific rational design methodology was actually performed, only visual comparisons with some published cross sections of then-existing dams. More than a dozen separate investigations of the failure followed, all of which failed to ascertain the dam’s actual maximum cross section or the fact that there were no stability calculations undertaken as part of the design. Recent evaluations have demonstrated that the St. Francis Dam exhibited extremely low safety factors in at least five different failure modes, including internal instability, overturning, arching, keyblock uplift, and reactivation of a megalandslide on the dam’s left abutment.