4.1.1 Lower San Fernando Dam

Lower San Fernando Dam is a hydraulic fill earth dam in San Fernando, California. It was constructed 1912-1917, followed by several raises to max height of 140 ft by 1930.
This case history was a milestone to renew all seismic design and evaluation process. Had the reservoir level been a little higher, or the earthquake lasted a few seconds longer, a major disaster would have occurred.

Embankment construction was:
• Founded on recent alluvium consisting of stiff clay with sand and gravel lenses.
• Hydraulic fill between upstream and downstream starter dikes.
• Rolled earth fill on top of hydraulic fill and in downstream berm.

What happened by earthquake is:
• 1971 M=6.6 San Fernando earthquake (Feb 9th, 6:00 a.m.) produced about 0.55 g peak acceleration at the dam crest.
• Dam had 35 ft of freeboard before the earthquake, and only 3 to 5 ft afterward.
• During the earthquake a major slide occurred on the upstream face, taking with it the crest and the upper 9.2m of soil on the downstream slop.
• About 80,000 persons living in the downstream valley had to be hastily evacuated.

Before and after earthquake, Lower San Fernando dam, DSOD

Lower San Fernando Dam after 1971 earthquake, DSOD

Sources:

- Seed, Lee, Idriss, & Makdisi (1975). "The slides in the San Fernando Dams during the Earthquake of February 9, 1971." J.Geotech. Engrg. Div., ASCE, 101(GT7), 651-688.
- Seed, Seed, Harder, Jong (1989). Re-Evaluation of the Lower San Fernando Dam. Contract report GL-89-1 for the US Army Corp of Engineers, Washington, DC.
- Bharat Singh and R.S. Varshney, Engineering for Embankment Dams, 1995, A.A.Balkema