Van Norman Dams

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Van Norman Dams (San Fernando Dams)

The Van Norman Dams, also known as the San Fernando Dams, were two earth-filled dams in Los Angeles County built to store water for the Los Angeles Aqueduct. They supplied about 80 percent of Los Angeles’ water until they were badly damaged in the 1971 San Fernando earthquake and eventually decommissioned because the site was unstable and located above populated areas.

What they were
- Upper Van Norman Dam: built to hold back water and support the aqueduct system.
- Lower Van Norman Dam: a larger dam below the upper one, also part of the water system.
- Both were earth-fill dams and formed two reservoirs that helped supply Los Angeles.

Construction and sizes (brief)
- Lower dam: completed in the early 1910s.
- Upper dam: built starting in 1919 and opened in 1921.
- Upper dam height: about 60 feet; length ~1,200 feet.
- Lower dam height: about 142 feet; length ~2,080 feet.
- Reservoirs: the upper reservoir held about 1,800 acre-feet of water; the lower reservoir held about 20,000 acre-feet.
- The sites were later found to have instability issues, especially under seismic stress.

1971 San Fernando earthquake
- Both dams were damaged, triggering fears of a potential dam failure that could have endangered thousands of people below.
- Thousands were evacuated from the valley, with about 80,000 people evacuated for three days.
- The earthquake caused the upper dam to settle and shift, and the lower dam suffered severe damage from a landslide and liquefaction of its fill.
- To reduce risk, water was rapidly released from the lower reservoir, and engineers determined the site was too unstable to rebuild these dams.

Replacement and later events
- A new dam, the Los Angeles Dam, was built between the original lower and upper structures in a more stable location.
- In the 1994 Northridge earthquake, the lower reservoir area was damaged again, but the impact was minor because it was no longer used for active storage.

Impact on safety and engineering
- The Van Norman events led to major changes in how engineers assess dam safety, especially for embankments made of fine sands and silts, and in how dynamic seismic analyses are used for dam design and evaluation.