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Van Norman Dams

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Coordinates: 34°17′10″N 118°28′47″W / 34.2862°N 118.4796°W / 34.2862; -118.4796
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Van Norman Dams
An oblique aerial view of the Lower Van Norman Dam, taken after the February 9, 1971, San Fernando Earthquake
CountryUnited States
LocationLos Angeles County, California
Coordinates34°17′10″N 118°28′47″W / 34.2862°N 118.4796°W / 34.2862; -118.4796
PurposeWater supply
StatusDecommissioned
Construction began1919; 105 years ago (1919)
(upper dam)
1911; 113 years ago (1911)
(lower dam)[1]
Opening date1921; 103 years ago (1921)
(upper dam)
November 5, 1913;
111 years ago (1913-11-05)
(lower dam)[2]
Demolition dateFebruary 9, 1971;
53 years ago (1971-02-09)
Built byLos Angeles Bureau of Water Works and Supply
Upper dam and spillways
Type of damEarth fill dam
ImpoundsLos Angeles Aqueduct
Bull Creek
Height (foundation)60 feet (18 m)
Length1,200 feet (370 m)[3]
Elevation at crest1,218 feet (371 m)[4]
Width (crest)20 feet (6.1 m)[4]
Upper reservoir
Total capacity1,800 acre⋅ft (2.2×10^6 m3)
Normal elevation1,213.2 feet (369.8 m) [4]
Lower dam and spillways
Type of damEarth fill dam
Height (foundation)142 feet (43 m)[5]
Length2,080 feet (630 m)[5]
Elevation at crest1,144.6 feet (348.9 m)[5]
Lower reservoir
Total capacity20,000 acre⋅ft (25×10^6 m3)
Normal elevation1,134.6 feet (345.8 m)[5]
Commission dateOctober 1922[6]
TypeConventional
Turbines2× 2.8 MW [6]

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,[5] until they were damaged 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

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The Upper Van Norman Dam initially was constructed with 42 feet (13 m) of hydraulic fill.[4] In 1922, the dam was raised 18 feet (5.5 m) with rolled fill.[1][4]

The Lower Van Norman Dam was constructed with hydraulic and rolled fill. Hydraulic fill height was about 102.4 feet (31.2 m), while rolled fill was added at least five times in the dam's history, each time increasing the dam's height, totaling 39.6 feet (12.1 m) rolled fill. The last addition was made in 1929–30.[5][1]

1971 San Fernando earthquake

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For broader coverage of this topic, see 1971 San Fernando earthquake.

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.[7] Later, it was estimated that a dam failure could have killed 123,400.[8]

Upper Van Norman dam

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The Upper Van Norman reservoir was operating at about one-third 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

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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 half capacity:[3] 3.6 billion US gallons (14×10^6 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).[8] This failure was predominantly due to liquefaction of the hydraulic fill.[9][10][11][12][4] To reduce the risk of catastrophic failure, the water level was lowered as rapidly as possible, 13.5 feet (4.1 m) in 3+1⁄2 days, at the rate of 700 cubic feet per second (20 m3/s). This rate was limited by earthquake damage to the outlet lines and drainage towers.[13]

Aftermath

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Reconstruction was proposed, but abandoned after geologic evaluation showed the inherent instability of the dams' foundations.[14][15]

As a replacement, the Los Angeles Dam was constructed between the original Lower and Upper Van Norman Dam structures in a more stable location.[16] 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.[5]

Lessons learned

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The near failure of the Lower Van Norman Dam brought about major changes in the way public agencies and engineers viewed seismic safety, particularly regarding embankments of fine sands and silts and numeric dynamic analysis of dams. Also, it resulted in many mandated dam safety reassessments.[9][17]

See also

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References

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  1. ^ a b c 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).
  2. ^ "75,000 to Witness Official Aqueduct Opening Tomorrow". Section 2. Los Angeles Evening Herald. Vol. XL, no. 2. November 4, 1913. p. 1.
  3. ^ 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. Archived (PDF) from the original on December 8, 2020. Retrieved July 18, 2021. {{cite book}}: Unknown parameter |agency= ignored (help)
  4. ^ a b c d e f "The Upper San Fernando Dam" (PDF). GeoSlope. Retrieved July 22, 2021.
  5. ^ a b c d e f g 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. Archived from the original on June 10, 2021. Retrieved July 18, 2021.
  6. ^ a b "San Fernando Hydro Power Plant CA USA". Global Energy Observatory. Retrieved July 23, 2021.
  7. ^ Borden, Frank (March 31, 2017). "LAFD History – Los Angeles Dam Failures". The Firemen's Grapevine. Los Angeles Firemen's Relief Association. Archived from the original on November 26, 2020. Retrieved July 18, 2021.
  8. ^ a b Sahagún, Louis (February 10, 2021). "California's aging dams face new perils, 50 years after Sylmar quake crisis". Los Angeles Times. Archived from the original on July 18, 2021. Retrieved July 19, 2021.
  9. ^ a b Proceedings : Fifth Benchmark Workshop on Numerical Analysis of Dams. Denver, CO: U.S. Committee on Large Dams. 2000. p. 11. ISBN 1-884575-17-X.
  10. ^ "Lest we forget: learning from international dam incidents". International Water Power & Dam Construction. October 28, 2010. Archived from the original on March 6, 2021. Retrieved July 19, 2021.
  11. ^ "San Fernando: a case in history". International Water Power & Dam Construction. January 17, 2013. Archived from the original on June 9, 2021. Retrieved July 19, 2021.
  12. ^ "The Lower San Fernando Dam" (PDF). GeoSlope. Retrieved July 22, 2021.
  13. ^ California Sec. Earthquake Task Force Committee, Association of Metropolitan Water Agencies (1973). "Contending With Earthquake Disaster: Committee Approved Report". Journal (American Water Works Association). 65 (1): 22–38. doi:10.1002/j.1551-8833.1973.tb01785.x. ISSN 0003-150X. JSTOR 41267174.
  14. ^ 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. Circular (691–A). United States Geological Survey. doi:10.3133/cir691A. Archived (PDF) from the original on April 3, 2021. Retrieved July 18, 2021.
  15. ^ 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. Circular (691–B). United States Geological Survey. doi:10.3133/cir691B. Archived (PDF) from the original on May 6, 2021. Retrieved July 18, 2021.
  16. ^ Page, Robert A.; Boore, David M.; Yerkes, Robert F. "USGS Fact Sheet 096-95: The Los Angeles Dam Story". U.S. Geological Survey. Archived from the original on June 14, 2021. Retrieved July 18, 2021.
  17. ^ "History of California Dam Safety". California Department of Water Resources. Retrieved July 22, 2021.
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