Encino Reservoir

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Encino Reservoir Encino Reservoir and 6-007 Dam, Encino, California, US.jpg
Encino Reservoir

The Encino Reservoir, is a controlled lake created by the damming of Encino creek. [1] It is located near the Encino neighborhood in the San Fernando Valley, California. With construction completed in 1924, it is owned by the Los Angeles Department of Water and Power (LADWP). [2] The Encino reservoir no longer provides drinking water to the population. However, it is kept open for other uses. [3] The reservoir stores water which can be used to maintain supply through the Los Angeles aqueduct. [4] It also helps to regulate the use of water for irrigation in the summer months. [5] The reservoir was a source of water used for firefighting during the 2025 Palisades Fire.

Contents

History

The reservoir was built in 1921 and 1924 by the civil engineer, William Mulholland to supply drinking water to the population of the San Fernando Valley. It was designed without a control gate. Instead, there would be one pipe from the dam with a valve which would remain open in order to maintain pressure in the water distribution system of the San Fernando Valley. At the time, the reservoir was known as an "equalizer" of water pressure. [6]

A roll-filled dam construction method was used; one where earth is progressively moved into place in layers which are sprinkled with water and then compacted to create an embankment. [6] [7] [8] After the first filling, there was seepage from the dam. [7] Between 1949 and 1950, rectification of this problem was made in the form of a downstream filter and buttress. [7] Between 1960 and 1962 the up-stream part of the original dam and its alluvium, down to bedrock, was removed and a new 51.2 m (168 feet) roll-filled dam was constructed. [7]

Prior to 1971, the Encino reservoir together with the Lower Stone Canyon and Lower Van Norman reservoirs provided 70 percent of the water stored within the jurisdiction of the LADWP. In comparison, 80 percent of water needs of Los Angeles were provided from snowmelt at the eastern slopes of the Sierra Nevada draining into the Owens Valley and from there through the Los Angeles Aqueduct system. [4]

In 2002, the Encino dam and reservoir complex included four 227000 L (60000 gallon) surge tanks buried near an existing pumping station and further elements installed parallel to the reservoir access road including a membrane filtration plant, a chlorination station and a chlorine gas scrubber. [9]

Geography

The reservoir is located in the hills of the north face of the Santa Monica Mountains, south of Encino neighborhood. The reservoir lies at 327 m above sea level. The surface area is 0.69 km2 and the drainage basin is 3.63 km2. [10] The reservoir is found on the United States Geological Survey topographic map Canoga Park area. [11]

The reservoir's geology involves poorly consolidated and consolidated conglomerate sandstone and basalt. [12]

The region of the Encino reservoir has a hot dry summer and a mild wet winter, Köppen climate classification Csa. [13] Based on measurements taken between 1958 and 1978, the average annual rainfall at Encino Reservoir was 48 cm (19 inches). [14] During the same period of study, the rate of evaporation which depends on temperature, wind and humidity, was an average of 120 cm (47.45 inches) per year. [14] Due to this negative value, irrigation of farmland, golf courses and landscaping cannot depend on the Encino reservoir and must use Los Angeles City water instead. [14]

Management and risk

The reservoir is inspected yearly. In 2025, its condition is listed as satisfactory while its hazard potential classification is high. [10] The "high" level means "failure or mis-operation will probably cause loss of human life". [3]

The State of California has, since 1929, placed the management of the safety of dams with the Division of Safety of Dams (DoSD) within the California Department of Water Resources. The DoSD describes the risk of downstream hazard in the case of a dam breach as extremely high. [15]

1971 San Fernando earthquake

In the early hours of February 9, 1971, an earthquake began in the northern part of the San Fernando Valley. The Encino Reservoir was not damaged. Afterward, however, the reservoir's role in the supply of water during emergencies was examined closely. [4] [7] In 1972, three seismoscopes were installed at the reservoir, including at the crest and the west abutment. [16]

1994 Northridge earthquake

At 4.30 a.m. pacific time, January 17, the 1994 Northridge earthquake epicenter formed 7.2 km north of the Encino Reservoir. [7] The ruptured fault plane was 17.7 km (11 miles) from the dam. [7] The peak horizontal ground acceleration was 0.23 g which caused no significant damage to the Encino dam. There was some cracking of the asphalt concrete at the dam top and on a downstream access road. [7]

Uses

Fire-fighting

During 2025 Palisades Fire, the Encino reservoir was within one of the mandatory evacuation zones. [17] However, it also played an integral part in fire-fighting efforts. [18] Boeing CH-47 Chinooks were used to drop water onto the fire. The helicopters hover above the water of the reservoir. A flight mechanic in the rear of the helicopter lowers a 7m (23 feet) long retractable tube into the water. 11365 L (3000 gallons) of water are drawn into the helicopter tank to be dumped strategically on the fire. [19]

Recreation

The Encino reservoir's recreational assets include walking trails, nature and wildlife areas such as the California scrub oak woodland. [20]

References

  1. ↑ "Encino Dam, California, USA | Info & Map". 2024-07-20. Retrieved 2025-02-10.
  2. ↑ Crosby, Michael (2009). Images of America - Encino. Arcadia Publications. p. 98. ISBN   9780738569918.
  3. 1 2 "Encino Dam, California, USA | Info & Map". 2024-07-20. Retrieved 2025-02-10.
  4. 1 2 3 Federal Disaster Assistance Administration (27 May 1975). Los Angeles Dam and Reservoir Project (Draft ed.). San Francisco: U.S. Department of Housing and Urban Development. pp. I-B-3.
  5. ↑ Journal of the senate during the fifty-second session of the legislature of the State of California 1937. 28 May 1937. p. 266.
  6. 1 2 "Los Angeles adds three new dams to system". Engineering News-Record, a journal of civil engineering and construction. 92 (April). New York: McGraw Hill: 585.
  7. 1 2 3 4 5 6 7 8 Stewart, J.P., ed. (June 1994). "Encino Reservoir". Preliminary report on the principal geotechnical aspects of the January 17, 1994 Northridge earthquake. Earthquake Engineering Research Center, College of Engineering, University of California, Berkley. p. 176.
  8. ↑ Challa, S.N. (2002). Water resource engineering - principles and practice (2nd revised ed.). New Delhi: New Age International Ltd. p. 232. ISBN   9788122413823.
  9. ↑ Santa Monica Mountains final general management plan and environmental impact statement. California: United States Department of the Interior - National Park Service. 2002. p. 587.
  10. 1 2 "Encino in Los Angeles County, CA". The Californian. Retrieved 2025-02-10.
  11. ↑ "Encino Reservoir Topo Map CA, Los Angeles County (Canoga Park Area)". www.topozone.com. Retrieved 2025-02-10.
  12. ↑ Rubey, W.W. (1930). "Geology of eastern part of Santa Monica mountains, California". Lithologic studies of fine-grained upper cretaceous sedimentary rocks of the Black Hills region. U.S. Geological Survey. p. 98.
  13. ↑ "San Fernando climate: Weather San Fernando & temperature by month". en.climate-data.org. Retrieved 2025-02-16.
  14. 1 2 3 Sepulveda Basin master plan and final environmental impact statement - appendix (1981) U.S. Army Corps of Engineers Los Angeles District. p.26
  15. ↑ "Web Map Viewer". fmds.water.ca.gov. Retrieved 2025-02-16.
  16. ↑ Maley, R.P.; Cloud, W.K, (1972). "Preliminary strong-motion results from the San Fernando earthquake of February 9, 1971". Geological Survey Professional Paper. Washington DC: United States Government Printing Office: 163.{{cite journal}}: CS1 maint: extra punctuation (link) CS1 maint: multiple names: authors list (link)
  17. ↑ "Palisades Fire visible from the San Fernando Valley". ABC7 Los Angeles. 2025-01-18. Retrieved 2025-02-16.
  18. ↑ Toohey, Grace (14 January 2025). "Inside the air attack that saved Brentwood and Encino from the surging Palisades fire". Los Angeles Times . Retrieved 16 February 2025.{{cite web}}: CS1 maint: url-status (link)
  19. ↑ Wise, Jeff (2025-01-17). "What It's Like Inside a Helicopter Fighting the California Fires". Intelligencer. Retrieved 2025-02-16.
  20. ↑ "Women's Nature Walk - Board Of Water And Power Commissioners". www.ladwpcommission.com. Retrieved 2025-02-16.
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