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 strengthen ...

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 ...

, spanning Big Tujunga Canyon northeast of Sunland, in the foothills of the

San Gabriel Mountains The San Gabriel Mountains ( es, Sierra de San Gabriel) are a mountain range located in northern Los Angeles County, California, Los Angeles County and western San Bernardino County, California, United States. The mountain range is part of the Tr ...

. Completed in 1931, it provides

flood control Flood control methods are used to reduce or prevent the detrimental effects of flood waters."Flood Control", MSN Encarta, 2008 (see below: Further reading). Flood relief methods are used to reduce the effects of flood waters or high water level ...

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, 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 ...

. Its

reservoir A reservoir (; from French ''réservoir'' ) is an enlarged lake behind a dam. Such a dam may be either artificial, built to store fresh water or it may be a natural formation. Reservoirs can be created in a number of ways, including contro ...

is called Big Tujunga Reservoir, and collects runoff from a

watershed Watershed is a hydrological term, which has been adopted in other fields in a more or less figurative sense. It may refer to: Hydrology * Drainage divide, the line that separates neighbouring drainage basins * Drainage basin, called a "watershe ...

of . Although it is located inside the

Angeles National Forest The Angeles National Forest (ANF) of the United States Forest Service, U.S. Forest Service is located in the San Gabriel Mountains and Sierra Pelona Mountains, primarily within Los Angeles County, California, Los Angeles County in southern Calif ...

, 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 people of California from the Los Angeles Basin and the Southern Channel Islands, an area covering approximately . Some descendants of the people prefer Kizh as an endonym that, they argue, is more historically ...

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 flood control dam in the northeastern San Fernando Valley, in the Lake View Terrace neighborhood of Los Angeles, California, Los Angeles, California.Pitarre, Alyson. "Where country living sidles up to the city." ''Los Angeles Ti ...

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 which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

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 da ...

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 or Gabrieleño) is an extinct Uto-Aztecan language formerly spoken by the Tongva, a Native American people who live in and around Los Angeles, California. It has not been a language of everyday conve ...

), 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 or Gabrieleño) is an extinct Uto-Aztecan language formerly spoken by the Tongva, a Native American people who live in and around Los Angeles, California. It has not been a language of everyday conve ...

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

Los Angeles Department of Water and Power The Los Angeles Department of Water and Power (LADWP) is the largest municipal utility in the United States with 8,100 megawatts of electric generating capacity (2021-2022) and delivering an average of 435 million gallons of water per day to more ...

, 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 Los Angeles flood of 1938 was one of the largest floods in the history of Los Angeles, Orange, and Riverside Counties in southern California. The flood was caused by two Pacific storms that swept across the Los Angeles Basin in February-Marc ...

, 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 rush down mountainsides, funnel into stream channels, entrain objects in their paths, and form thick, muddy deposits on valley floors. They generally ...

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 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 ...

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 term ...

. 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