Van Norman Dams
| Van Norman Dams | |
|---|---|
 An oblique aerial view of the Lower Van Norman Dam. It was taken after the February 9, 1971, San Fernando Earthquake. | |
| Country | United States |
| Location | Los Angeles County, California |
| Coordinates | 34°17′10″N 118°28′47″W / 34.2862°N 118.4796°W |
| Purpose | Water supply |
| Status | Decommissioned |
| Construction began | 1912 |
| Opening date | November 5, 1913[1] |
| Demolition date | February 9, 1971 |
| Dam and spillways | |
| Type of dam | Earth fill dam |
| Impounds | Los Angeles Aqueduct Bull Creek |
| Height | upper dam 60 feet (18 m) lower dam 142 feet (43 m)[2] |
| Height (foundation) | upper dam lower dam 1,002 feet (305 m) |
| Length | upper dam 1,200 feet (370 m)[3] lower dam 2,080 feet (630 m)[2] |
| Reservoir | |
| Total capacity | upper dam 1,800 acre⋅ft (2.2×106 m3) lower dam 20,000 acre⋅ft (25×106 m3) |
The Van Norman Dams, also known as the San Fernando Dams, were the terminus of the Los Angeles Aqueduct, supplying about 80 percent of Los Angeles' water,[2] until their damage in the 1971 San Fernando earthquake and were subsequently decommissioned due to the inherent instability of the site and their location directly above heavily populated areas.
Construction
The Upper Van Norman Dam initially was constructed with hydraulic fill. In 1922, the dam was raised with rolled fill.[4]
The Lower Van Norman Dam was constructed with hydraulic and rolled fill. Hydraulic fill extended to 1,105 feet (337 m), while rolled fill was added at least five times in the dam's history, each time increasing the dam's height. The last addition was in 1929–30.[2][4]
Earthquake damage
The 1971 San Fernando earthquake significantly damaged the dams, resulting in evacuation of thousands of people from the San Fernando Valley immediately below. 80,000 were evacuated for three days.[5] Later, it was estimated that a dam failure could have killed 123,400.[6]
Upper Van Norman dam
The Upper Van Norman reservoir was operating at about 1⁄3 capacity at the time of the earthquake. The quake lowered dam height 3 feet (0.91 m) and displaced the dam laterally 5 feet (1.5 m).[3]
Lower Van Norman dam
Originally, the Lower Van Norman reservoir was operated near full capacity of 1,134.6 feet (345.8 m). However, the maximum operating height was reduced to 1,125 feet (343 m) in 1966 following seismic hazard review. Fortuitously, at the time of the 1971 San Fernando earthquake the water height was 1,109 feet (338 m) (about 1⁄2 capacity[3]: 3,600,000,000 US gallons (14×106 m3) of water) as a large landslide fell into the reservoir along with 30 feet (9.1 m) of the crest and upstream face reducing the freeboard to about 5 feet (1.5 m).[6]
Aftermath
Reconstruction was proposed, but abandoned after geologic evaluation showed the inherent instability of the dams' foundations.[7][8]
As a replacement, the Los Angeles Dam was constructed between the original Lower and Upper Van Norman Dam structures in a more stable location.[9] During the 1994 Northridge earthquake, the Lower Van Norman reservoir area was again severely damaged, but as then it was in use only as a holding basin, the consequences were minor.[2]
Lessons learned
- Dams located in seismic areas should be evaluated for liquefaction, cracking, potential fault offsets, deformations, and settlement due to seismic loading.
- Earth and rockfill embankment dams must be stable under the full range of anticipated loading conditions.
- Emergency Action Plans can save lives and must be updated, understood, and practiced regularly to be effective.
See also
- List of national monuments of the United States
- List of dams and reservoirs in California
- Dam failure
- Baldwin Hills Reservoir
- St. Francis Dam
References
- ^ "75,000 to Witness Official Aqueduct Opening Tomorrow". Section 2. Los Angeles Evening Herald. Vol. XL, no. 2. November 4, 1913. p. 1.
- ^ a b c d e Sykora, Davis W. "Lower San Fernando Dam (California, 1971) | Case Study | ASDSO Lessons Learned". Lessons Learned from Dam Incidents and Failures. Association of State Dam Safety Officials. Retrieved July 18, 2021.
- ^ a b c Lews, H. S.; Leyendecker, E. V.; Dikkers, R. D. (December 1971). Engineering aspects of 1971 San Fernando earthquake (PDF). Building Research Division, Institute for Applied Technology, National Bureau of Standards. U.S. Government Printing Office. p. 367. LCCN 70-186531.
{{cite book}}: Unknown parameter|agency=ignored (help) - ^ a b Bardet, J. P.; Davis, C. A. (July 1996). "Performance of San Fernando Dams during 1994 Northridge Earthquake". Journal of Geotechnical Engineering. 122 (7): 554–564. doi:10.1061/(ASCE)0733-9410(1996)122:7(554).
- ^ Borden, Frank (March 31, 2017). "LAFD History – Los Angeles Dam Failures". The Firemen's Grapevine. Los Angeles Firemen's Relief Association. Retrieved July 18, 2021.
- ^ a b Sahagún, Louis (February 10, 2021). "California's aging dams face new perils, 50 years after Sylmar quake crisis". Los Angeles Times. Retrieved July 19, 2021.
- ^ Yerkes, R. F.; Bonilla, M. G.; Youd, T. L.; Sims, J. D. (1974). "Geologic environment of the Van Norman Reservoirs area" (PDF). Geological Survey Circular (691-A). United States Geological Survey. doi:10.3133/cir691A.
- ^ Wesson, R. L.; Page, R. A.; Boore, D. M.; Yerkes, R.F. (1974). "Expectable Earthquakes and their ground motions in the Van Norman Reservoirs Area" (PDF). Geological Survey Circular (691-B). United States Geological Survey. doi:10.3133/cir691B. Retrieved July 18, 2021.
- ^ Page, Robert A.; Boore, David M.; Yerkes, Robert F. "USGS Fact Sheet 096-95: The Los Angeles Dam Story". U.S. Geological Survey. Retrieved July 18, 2021.
External links
- Goldbaum, Elizabeth (February 4, 2021). "The Disaster that Helped the Nation Prepare for Future Earthquakes: Remembering San Fernando". U.S. Geological Survey. Retrieved July 19, 2021.
- Lloyd, Jonathon (February 9, 2021). "February 1971: The Magnitude-6.5 San Fernando Earthquake Shakes Southern California". NBC Los Angeles. Retrieved July 19, 2021.
Dams in Los Angeles County, California | ||
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| CA Department of Water Resources |  | |
| LA Department of Public Works | ||
| LA Department of Water and Power |
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| US Army Corps of Engineers | ||
| Other |
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Category:Dam failures in the United States Category:Dams in Los Angeles County, California Category:History of Los Angeles Category:History of Los Angeles County, California Category:Los Angeles Aqueduct Category:Reservoirs in California Category:Earthquake and seismic risk mitigation Category:Dams completed in 1921 Category:San Fernando Valley Category:1971 in Los Angeles Category:1971 in California Category:1971 earthquakes Category:History of the San Fernando Valley Category:Geology of Los Angeles County, California
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Van Norman Dams
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