Big Tujunga Dam is a concrete

arch dam An arch dam is a concrete dam that is curved upstream in plan. The arch dam is designed so that the force of the water against it, known as hydrostatic pressure, presses against the arch, causing the arch to straighten slightly and strengtheni ...

Los Angeles County Los Angeles County, officially the County of Los Angeles and sometimes abbreviated as LA County, is the most populous county in the United States, with 9,663,345 residents estimated in 2023. Its population is greater than that of 40 individua ...

California California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...

, spanning

Big Tujunga Canyon Big or BIG may refer to: * Big, of great size or degree Film and television * ''Big'' (film), a 1988 fantasy-comedy film starring Tom Hanks * ''Big'', a 2023 Taiwanese children's film starring Van Fan and Chie Tanaka * ''Big!'', a Discovery ...

northeast of Sunland, in the foothills of the

San Gabriel Mountains The San Gabriel Mountains () are a mountain range located in Los Angeles and San Bernardino counties, California, United States. The mountain range is part of the Transverse Ranges and lies between the Los Angeles Basin and the Mojave Desert ...

. Completed in 1931, it provides

flood control Flood management or flood control are methods used to reduce or prevent the detrimental effects of flood waters. Flooding can be caused by a mix of both natural processes, such as extreme weather upstream, and human changes to waterbodies and ru ...

and

groundwater recharge Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs in ...

for the

San Fernando Valley The San Fernando Valley, known locally as the Valley, is an urbanized valley in Los Angeles County, Los Angeles County, California. Situated to the north of the Los Angeles Basin, it comprises a large portion of Los Angeles, the Municipal corpo ...

. Its

reservoir A reservoir (; ) is an enlarged lake behind a dam, usually built to water storage, store fresh water, often doubling for hydroelectric power generation. Reservoirs are created by controlling a watercourse that drains an existing body of wa ...

is called Big Tujunga Reservoir, and collects runoff from a

watershed Watershed may refer to: Hydrology * Drainage divide, the line that separates neighbouring drainage basins * Drainage basin, an area of land where surface water converges (North American usage) Music * Watershed Music Festival, an annual country ...

of . Although it is located inside the

Angeles National Forest The Angeles National Forest (ANF) of the United States Forest Service is located in the San Gabriel Mountains and Sierra Pelona Mountains, primarily within Los Angeles County in Southern California. The ANF manages a majority of the San Gabri ...

, public access to the lake is forbidden. The water is usually kept at a low level, in order to protect against winter floods. The name of the dam is derived from a

Tongva The Tongva ( ) are an Indigenous peoples of California, Indigenous people of California from the Los Angeles Basin and the Channel Islands of California, Southern Channel Islands, an area covering approximately . In the precolonial era, the peop ...

village name.

Description

The dam is high from the riverbed, high from the foundations, and long. It has a width of at the base, tapering to at the crest. The storage capacity is at the spillway, with a minimum pool of to prevent sediment and debris from entering the dam's outlets. After the completion of

Hansen Dam Hansen Dam is a dam built for flood control in the northeastern San Fernando Valley, in the Lake View Terrace neighborhood of Los Angeles, California.Pitarre, Alyson. "Where country living sidles up to the city." ''Los Angeles Times''. June 12, ...

downstream, the importance of Big Tujunga Dam for flood control has decreased; however, it is still directly responsible for protecting about 4,600 residents living in the

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...

of Big Tujunga Canyon. In addition, the dam conserves about of runoff per year for drinking water and groundwater recharge purposes. This saves the city of Los Angeles about $2,250,000 annually due to the cost difference between local and imported water. Because of the small storage capacity of the reservoir relative to the size of its watershed, frequent

dredging Dredging is the excavation of material from a water environment. Possible reasons for dredging include improving existing water features; reshaping land and water features to alter drainage, navigability, and commercial use; constructing d ...

is required to remove sediment from behind the dam. Most of the sediment is compacted and stored at the Maple Canyon Sediment Placement Site located less than west of the dam. The 2009 Station Fire, which burned some 87% of the Big Tujunga watershed, caused more than 2 million cubic yards (1.5 million m³) of sediment to flow into the reservoir, all of which subsequently had to be removed.

History

Aside from the village of '' Tujunga'' or ''Tuxunga'' (means "old woman's place" in both the languages of the

and

Fernandeño The Tongva language (also known as Gabrielino, Gabrieleño, or Kizh) is an extinct and revitalizing Uto-Aztecan language spoken by the Tongva, a Native American people who have lived in and around modern-day Los Angeles for centuries. It has no ...

), the former Fernandeño (Native American) village in the area of the dam and Big Tujunga Canyon was called ''Muxúnga'', which means "place of shooting" in the Fernandeño dialect of the

Tongva language The Tongva language (also known as Gabrielino, Gabrieleño, or Kizh) is an extinct and revitalizing Uto-Aztecan language spoken by the Tongva, a Native American people who have lived in and around modern-day Los Angeles for centuries. It has n ...

. The name comes from the verb ''muxú,'' which means "shoot him." The dam was completed in 1931 by the

Los Angeles County Flood Control District The Los Angeles County Department of Public Works (LACDPW) is responsible for the construction and operation of Los Angeles County's roads, building safety, sewerage, and flood control. DPW also operates traffic signals and intelligent transportat ...

, at a cost of $1.2 million ($ in dollars). It was originally planned as one of several flood control dams inside Big Tujunga Canyon and was thus referred to as Big Tujunga Dam No. 1 until the larger Hansen Dam was completed in 1940 at the mouth of the canyon, eliminating the need for the other dams. During the Los Angeles flood of 1938, the dam was able to stop a huge

debris flow Debris flows are geological phenomena in which water-laden masses of soil and fragmented Rock (geology), rock flow down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. ...

of boulders and uprooted trees, sparing much of Sunland, Tujunga and Glendale from destruction. In 1976, the dam was recognized as in danger of failure from earthquakes (the

San Andreas Fault The San Andreas Fault is a continental Fault (geology)#Strike-slip faults, right-lateral strike-slip transform fault that extends roughly through the U.S. state of California. It forms part of the tectonics, tectonic boundary between the Paci ...

runs nearby) and the reservoir's level was temporarily restricted to about 25% of capacity. In 2008 the Los Angeles County Flood Control District began a project to rehabilitate the aging structure. Approximately of concrete was added to the dam, transforming it from a thin-arch to a thick-arch design. A new

spillway A spillway is a structure used to provide the controlled release of water downstream from a dam or levee, typically into the riverbed of the dammed river itself. In the United Kingdom, they may be known as overflow channels. Spillways ensure tha ...

was built and the original one was expanded, increasing the floodwater capacity from to more than . In addition, a valve was installed at the dam base to pass low flows for

habitat conservation Habitat conservation is a management practice that seeks to conserve, protect and restore habitats and prevent species extinction, fragmentation or reduction in range. It is a priority of many groups that cannot be easily characterized in ter ...

. The seismic retrofit project was completed in July 2011 at a cost of $100 million.

References

External links

* * * {{LA County dams Los Angeles County Department of Public Works dams Arch dams Los Angeles River San Gabriel Mountains Angeles National Forest Dams completed in 1931 Historic American Engineering Record in California 1931 establishments in California

Description

History

See also

References

External links