Dam Failure Case Study: Lower San Fernando Dam (California, 1971)

The Lower San Fernando Dam near Los Angeles, CA, nearly failed during the February 9, 1971 San Fernando earthquake (Mw=6.6). The peak ground acceleration in the rock beneath the dam was approximately 0.60 g. The upstream slope and crest slid into the reservoir as a consequence of hydraulic fill in the embankment liquefying during strong ground shaking. The slide resulted in a freeboard to the top of the slide scarp of 5 feet. Fortunately, the maximum operating reservoir level had been lowered by 9.6 feet in 1966 as a precaution following a seismic evaluation of this and other DWR dams in California. Otherwise, this slide may have led to a breach and failure of the dam, threatening 80,000 or more residents downstream.