Castaic Dam is an embankment dam in northwestern

Los Angeles County Los Angeles County, officially the County of Los Angeles, and sometimes abbreviated as L.A. County, is the most populous county in the United States and in the U.S. state of California, with 9,861,224 residents estimated as of 2022. It is the ...

California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...

, in the unincorporated area of

Castaic Castaic () (Chumash: ''Kaštiq''; Spanish: ''Castéc'') is an unincorporated community in the northwestern part of Los Angeles County, California. As of the 2010 census it had a population of 19,015. For statistical purposes the Census Bureau ...

. Although located on

Castaic Creek Castaic Creek (Chumash: ''Kaštiq'') is a , accessed March 16, 2011 stream in the Sierra Pelona Mountains, in northeastern Los Angeles County, California. It is a tributary of the Santa Clara River. Castaic Lake Castaic Dam on the creek form ...

, a major tributary of the Santa Clara River, Castaic Creek provides little of its water. The lake is the terminus of the West Branch of the

California Aqueduct The Governor Edmund G. Brown California Aqueduct is a system of canals, tunnels, and pipelines that conveys water collected from the Sierra Nevada Mountains and valleys of Northern and Central California to Southern California. Named after Cali ...

, part of the State Water Project. The dam was built by the

California Department of Water Resources The California Department of Water Resources (DWR) is part of the California Natural Resources Agency and is responsible for the management and regulation of the State of California's water usage. The department was created in 1956 by Governor ...

and construction was completed in 1973. The lake has a capacity of and stores

drinking water Drinking water is water that is used in drink or food preparation; potable water is water that is safe to be used as drinking water. The amount of drinking water required to maintain good health varies, and depends on physical activity level, a ...

for the western portion of the

Greater Los Angeles Area Greater Los Angeles is the second-largest metropolitan region in the United States with a population of 18.5 million in 2021, encompassing five counties in Southern California extending from Ventura County in the west to San Bernardino Coun ...

Dimensions

Castaic is an earth-fill dam with its surfaces covered with

boulder In geology, a boulder (or rarely bowlder) is a rock fragment with size greater than in diameter. Smaller pieces are called cobbles and pebbles. While a boulder may be small enough to move or roll manually, others are extremely massive. In c ...

s and

cobble Cobble may refer to: * Cobble (geology), a designation of particle size for sediment or clastic rock * Cobblestone, partially rounded rocks used for road paving * Hammerstone, a prehistoric stone tool * Tyringham Cobble, a nature reserve in Tyr ...

-sized rocks to prevent

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

. The dam is high above the streambed, above the foundations, and long, containing of material. The maximum thickness of the base is . Flood waters are released through an ungated, concrete overflow spillway on the west side of the dam, emptying into a stilling basin called Castaic Lagoon (colloquially referred to as the "Lower Lake", while the larger Castaic Lake is called "Upper Lake"). The total storage capacity of Castaic Lake is , of which is considered active capacity and are considered inactive. The inactive capacity is only used during periods of extended drought or interrupted water delivery, most recently in 2014. At maximum water elevation of AMSL, the lake covers , with of shoreline. The much smaller Castaic Lagoon can hold and covers .http://www.water.ca.gov/pubs/swp/castaic_lake__west_branch_/castaic_lake.pdf

Operations

Water supply

Castaic Lake is the lower and larger of two main storage reservoirs for the West Branch of the

. Water drawn from the

Sacramento–San Joaquin River Delta The Sacramento–San Joaquin River Delta, or California Delta, is an expansive inland river delta and estuary in Northern California. The Delta is formed at the western edge of the Central Valley by the confluence of the Sacramento and San ...

is transported down the

San Joaquin Valley The San Joaquin Valley ( ; es, Valle de San Joaquín) is the area of the Central Valley of the U.S. state of California that lies south of the Sacramento–San Joaquin River Delta and is drained by the San Joaquin River. It comprises seven c ...

via the California Aqueduct and pumped over the

Tehachapi Mountains The Tehachapi Mountains (; Kawaiisu: ''Tihachipia'', meaning "hard climb") are a mountain range in the Transverse Ranges system of California in the Western United States. The range extends for approximately in southern Kern County and northwest ...

, where it splits into the East Branch – providing water for

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and

San Bernardino San Bernardino (; Spanish language, Spanish for Bernardino of Siena, "Saint Bernardino") is a city and county seat of San Bernardino County, California, United States. Located in the Inland Empire region of Southern California, the city had a ...

and eastern Los Angeles Counties – and the West Branch, which supplies western Los Angeles and parts of

Ventura County Ventura County () is a county in the southern part of the U.S. state of California. As of the 2020 census, the population was 843,843. The largest city is Oxnard, and the county seat is the city of Ventura. Ventura County comprises the Oxnar ...

. The West Branch first enters Pyramid Lake, formed by

Pyramid Dam Pyramid Dam is a dam on Piru Creek located in northern Los Angeles County, north of Castaic and south of Gorman. Its reservoir, Pyramid Lake, stores water from the West Branch California Aqueduct for Ventura County and Los Angeles County. They ...

, before traveling through the Angeles Tunnel to the upper end of Castaic Lake. Together, the two reservoirs can store , or about a year's supply of water. During normal operations, Castaic Lake serves as a regulatory reservoir for water delivered through the California Aqueduct, releasing it at times of peak demand. However, the dam and lake was also built to provide a pool of "emergency storage" that can be drawn down if water deliveries from northern California are interrupted, whether due to construction, equipment malfunction or severe drought. Below the dam, the majority of the water flows to Los Angeles via a system known as the Foothill Feeder, operated by the

Metropolitan Water District of Southern California The Metropolitan Water District of Southern California is a regional wholesaler and the largest supplier of treated water in the United States. The name is usually shortened to "Met," "Metropolitan," or "MWD." It is a cooperative of fourteen cit ...

. The water travels about south via a diameter pipeline to the Jensen Filtration Plant near

San Fernando San Fernando may refer to: People *Ferdinand III of Castile (c. 1200–1252), called ''San Fernando'' (Spanish) or ''Saint Ferdinand'', King of Castile, León, and Galicia Places Argentina *San Fernando de la Buena Vista, city of Greater Buenos ...

, where it connects to the municipal water system. The mostly underground, pre-stressed concrete pipe has walls nearly thick. Water from the Foothill Feeder is stored in the smaller

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in the

San Fernando Valley The San Fernando Valley, known locally as the Valley, is an urbanized valley in Los Angeles County, California. Located to the north of the Los Angeles Basin, it contains a large portion of the City of Los Angeles, as well as unincorporated ar ...

. The water continues south via the Sepulveda Feeder, which provides water to Los Angeles proper and other municipalities in south Los Angeles and

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Counties. The main customer water agencies are the Central Basin Municipal Water District, West Basin Municipal District, and Municipal Water District of Orange County. As many as 12 million people in these areas receive their full or supplemental water supply from Castaic Lake and the feeder system. A smaller portion of the water supply is distributed by the Castaic Lake Water Agency. The service area covers about in Ventura and north Los Angeles counties, providing water to about 287,000 people. The main constituents of the agency include the Los Angeles County Waterworks District No. 36, Newhall County Water District, Santa Clara Water Division, and Valencia Water Company.

Power generation

The 11 MW Foothill Feeder

hydroelectric Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined and ...

power plant is located at the base of the dam and generates electricity when water is needed in

Los Angeles Los Angeles ( ; es, Los Ángeles, link=no , ), often referred to by its initials L.A., is the largest city in the state of California and the second most populous city in the United States after New York City, as well as one of the world' ...

. In 2009, the Foothill Feeder plant generated 49 million

kilowatt hour A kilowatt-hour (unit symbol: kW⋅h or kW h; commonly written as kWh) is a unit of energy: one kilowatt of power for one hour. In terms of SI derived units with special names, it equals 3.6 megajoules (MJ). Kilowatt-hours are a common bil ...

s (KWh). The 1,495 MW (Nominal) Castaic Pumped-Storage Plant is located at the upper end of the west arm of Castaic Lake. The

Elderberry Forebay Dam Elderberry Forebay Dam is a dam located in the Sierra Pelona Mountains of northwestern Los Angeles County, California. The dam partitions Elderberry Forebay from Castaic Lake. It forms the headwater reservoir for Castaic Power Plant, a pumped-sto ...

separates the upper arm from the rest of Castaic Lake, maintaining a small pool for power generation known as the Elderberry Forebay, serving as the lower reservoir of the pumped-storage operation. Pyramid Lake, located to the west, serves as the upper. When demand for electricity is high, usually during the afternoon, water is withdrawn from Pyramid Lake and released into Castaic Lake. At night, when demand is low, water is pumped back into Pyramid Lake. The sale of peak electricity reduces the Department of Water Resources' overall electric costs for operating the California Aqueduct. In 2009, the Castaic pumped-storage plant generated a net 465 million KWh.

Safety

Due to seismic vulnerabilities, and its proximity to the

San Andreas Fault The San Andreas Fault is a continental transform fault that extends roughly through California. It forms the tectonics, tectonic boundary between the Pacific Plate and the North American Plate, and its motion is Fault (geology)#Strike-slip fau ...

, the dam has one of the lowest safety ratings in Los Angeles County.

References

External links

* * {{LA County dams Dams in Los Angeles County, California California Department of Water Resources dams California State Water Project Buildings and structures in Los Angeles County, California Hydroelectric power plants in California Sierra Pelona Ridge Dams completed in 1973 Energy infrastructure completed in 1973 no:Pyramid Lake vannkraftverk