St. Francis Dam - Pushing the Limits: New Adventures in Engineering - page 133

triggered the dam failure, with the rush of water scouring the dam's foundation and causing the
dam to lean. This in turn opened up preexisting cracks all along the arched structure. According
to Rogers's recent studies, the landslide dumped as much as one million cubic yards of weathered
mica schist—as much as five times the weight of the dam itself—which “created an outpouring
flood wave supercharged with sediment.” If the density of such sediment was sufficiently greater
than that of water, Rogers believes that it could effectively have made large sections of the dam
buoyant enough to be pushed and tumbled down the canyon, where they were found in the wake
of the ensuing flood. This failure hypothesis, like all the others, remains ultimately unprovable in
any incontrovertible sense, of course, but it highlights the complexity of anticipating the forces on
a concrete dam structure.
One vocal opponent of the view of Rogers and others about the causes of and blame for the
failure of the St. Francis Dam is Donald C. Jackson, a historian who has studied contemporary dam
construction. Jackson believes that the official panels that reported so quickly after the disaster were
not thorough or candid enough in their assessments of the causes of the failure. Rather than attrib-
uting the disaster to weak foundations leading to the undermining of the dam, Jackson lays blame
directly on the design of the dam structure itself—and hence on Mulholland. According to Jackson,
the danger of uplift due to pressure from water seeping under an insufficiently designed dam was
recognized by engineers in the late nineteenth century. This upward pressure, combined with the
accompanying effect of a lessened resistance of a dam to being pushed downstream by the water be-
hind it, was believed to have been the cause of the 1911 failure of a dam in Pennsylvania. To avoid
such incidents, engineers such as John R. Freeman, the East Coast engineer who had consulted for
Mulholland on the Los Angeles aqueduct, promoted grout curtains and drainage systems for dams
potentially subject to seepage. Jackson has documented the extensiveness of discussions of uplift in
the contemporary engineering literature and has provided evidence of dams designed to obviate the
phenomenon. The St. Francis Dam did have some uplift-relief wells located under its main chan-
nel section, but there were no similar precautions taken against uplift for the abutments of the dam,
which were located on steep slopes.
Regardless of the exact mechanism by which the St. Francis Dam cracked and gave way, William
Mulholland took full responsibility for the disaster. On the witness stand, he admitted that he could
not explain the failure and that something must have been overlooked. Overlooking something is,
of course, always a danger in the design of large engineering systems, and it is precisely why the
opinion of independent experts is sought during the design stage. In addition to the technical error
of siting the St. Francis Dam on poor foundations, its collapse was blamed on the “human factor,”
which manifested itself in the fact that “engineering work in the Bureau of Water Works and Supply
always had been dominated by one man, the chief engineer, who took upon himself, in this case at
least, entire responsibility, sought no independent opinions and adopted technical policies based on
his unconfirmed judgment alone.” Since “higher officials had absolute confidence in Mr. Mulhol-
land,” outside opinion was not sought, and “there was no intervention from above.” The plans for
the dam were not challenged because “Mr. Mulholland was personally overseeing the work.”
No engineer should have such hubris as to think that his past successes are sufficient to guarantee
the success of his next project. Each new undertaking rests on a new foundation, the hidden faults of
which may or may not be within prior experience. When all dams and the foundations upon which