San Gabriel Dam
Encyclopedia
San Gabriel Dam is a rockfill dam on the San Gabriel River
in the San Gabriel Mountains
, in Los Angeles County, California
, within the Angeles National Forest
. The dam is situated on the main stem of the San Gabriel about 2.5 mi (4 km) downstream from the confluence of the river's East and West Forks, which drain a fair portion of the San Gabriel Mountains of the Transverse Ranges
.
San Gabriel Reservoir is the name of the lake impounded by the dam. It stretches nearly 3 miles (4.8 km) upstream, extending up a bit of each fork, at full pool. The reservoir stores 44183 acre.ft of water when full, creating one of Southern California's larger reservoirs. Its capacity was 53344 acre feet when the dam was first built, but sedimentation
has since reduced its volume by about 17%. The reservoir is long and narrow, stretching in a southwesterly direction along a steep gorge.
In the 1920s, a proposal was put forth to impound the San Gabriel River just below the confluence of the forks with a 512 ft (156.1 m) concrete arch dam. Called the San Gabriel Forks Dam, this project was later withdrawn in the wake of the March 1928 St. Francis Dam
failure and a landslide that destroyed a large portion of the construction site at the San Gabriel forks. Following these events, the proposed dam for the San Gabriel River was moved about two miles downstream. Construction of the 315 ft (96 m) high San Gabriel Dam at this sitebegun in 1932 and was completed in 1939.
The present dam was built to serve primarily for flood control and water conservation, but it also supports a 3 megawatt hydroelectric plant owned by the city of Azusa
. Releases are coordinated in conjunction with Morris Dam
, which is downstream; Cogswell Dam
, which is located on the West Fork; and Santa Fe
and Whittier Narrows
Dams on the lower San Gabriel River. The dam is 1520 ft (463.3 m) long and receives water from an area of 205 sq mi (530.9 km²).
The San Gabriel Dam played an important role in reducing the flooding on the San Gabriel River in the Los Angeles Flood of 1938
, even though it had not yet been completed at the time. More than 150000 cuft/s of water poured into San Gabriel Reservoir at flood's peak, but the dam's extra capacity was able to knock about 40000 cuft/s off the peak of the flood. Further downstream, Morris Reservoir was able to absorb roughly 30000 cuft/s, reducing the flood to less than half of what it would have been if not for the dams.
San Gabriel River (California)
The San Gabriel River flows through southern Los Angeles County, California in the United States. Its main stem is about long, while its farthest tributaries extend almost altogether...
in the San Gabriel Mountains
San Gabriel Mountains
The San Gabriel Mountains Range is located in northern Los Angeles County and western San Bernardino County, California, United States. The mountain range lies between the Los Angeles Basin and the Mojave Desert, with Interstate 5 to the west and Interstate 15 to the east...
, in Los Angeles County, California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, within the Angeles National Forest
Angeles National Forest
The Angeles National Forest of the U.S. National Forest Service is located in the San Gabriel Mountains of Los Angeles County, southern California. It was established on July 1, 1908, incorporating the first San Bernardino National Forest and parts of the former Santa Barbara and San Gabriel...
. The dam is situated on the main stem of the San Gabriel about 2.5 mi (4 km) downstream from the confluence of the river's East and West Forks, which drain a fair portion of the San Gabriel Mountains of the Transverse Ranges
Transverse Ranges
The Transverse Ranges are a group of mountain ranges of southern California, in the Pacific Coast Ranges physiographic region that runs along the Pacific coast from Alaska to Mexico in North America. The Transverse Ranges begin at the southern end of the California Coast Ranges and lie between...
.
San Gabriel Reservoir is the name of the lake impounded by the dam. It stretches nearly 3 miles (4.8 km) upstream, extending up a bit of each fork, at full pool. The reservoir stores 44183 acre.ft of water when full, creating one of Southern California's larger reservoirs. Its capacity was 53344 acre feet when the dam was first built, but sedimentation
Sedimentation
Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...
has since reduced its volume by about 17%. The reservoir is long and narrow, stretching in a southwesterly direction along a steep gorge.
In the 1920s, a proposal was put forth to impound the San Gabriel River just below the confluence of the forks with a 512 ft (156.1 m) concrete arch dam. Called the San Gabriel Forks Dam, this project was later withdrawn in the wake of the March 1928 St. Francis Dam
St. Francis Dam
The St. Francis Dam was a concrete gravity-arch dam, designed to create a reservoir as a storage point of the Los Angeles Aqueduct. It was located 40 miles northwest of Los Angeles, California, near the present city of Santa Clarita....
failure and a landslide that destroyed a large portion of the construction site at the San Gabriel forks. Following these events, the proposed dam for the San Gabriel River was moved about two miles downstream. Construction of the 315 ft (96 m) high San Gabriel Dam at this sitebegun in 1932 and was completed in 1939.
The present dam was built to serve primarily for flood control and water conservation, but it also supports a 3 megawatt hydroelectric plant owned by the city of Azusa
Azusa, California
Azusa is a city in Los Angeles County, California, United States. The population was 46,361 at the 2010 census, up from 44,712 at the 2000 census. Though sometimes assumed to be a compaction of the phrase "everything from A to Z in the USA" from an old Jack Benny joke, the place name "Azusa"...
. Releases are coordinated in conjunction with Morris Dam
Morris Dam
Morris Dam is a concrete gravity dam across the San Gabriel River in the U.S. state of California. The dam was built in the 1930s as a water supply facility for the city of Pasadena, but is now mostly utilized for flood control and flow regulation for groundwater recharge...
, which is downstream; Cogswell Dam
Cogswell Dam
Cogswell Dam is a rockfill dam on the West Fork of the San Gabriel River in Los Angeles County, California. It forms Cogswell Reservoir, which has a capacity of with an average storage of , and serves mainly for flood control in conjunction with San Gabriel and Morris Dams downstream....
, which is located on the West Fork; and Santa Fe
Santa Fe Dam
Santa Fe Dam is a flood-control dam on the San Gabriel River located a few miles southwest of Azusa in Los Angeles County, California. For most of the year, the -high dam and its reservoir lie empty, but can hold more than of water during major storms...
and Whittier Narrows
Whittier Narrows Dam
Whittier Narrows Dam is a dam on the San Gabriel River in Montebello, California. Built by the U.S. Army Corps of Engineers for flood control, it is a 17 m tall earth dam. Construction of the dam was completed in 1957. Its reservoir has a capacity of .-External links:*...
Dams on the lower San Gabriel River. The dam is 1520 ft (463.3 m) long and receives water from an area of 205 sq mi (530.9 km²).
The San Gabriel Dam played an important role in reducing the flooding on the San Gabriel River in the Los Angeles Flood of 1938
Los Angeles Flood of 1938
The Los Angeles Flood of 1938 or 1938 Los Angeles flood was a major flooding event that was responsible for inundating much of Los Angeles, Orange, and Riverside counties, California, during early 1938...
, even though it had not yet been completed at the time. More than 150000 cuft/s of water poured into San Gabriel Reservoir at flood's peak, but the dam's extra capacity was able to knock about 40000 cuft/s off the peak of the flood. Further downstream, Morris Reservoir was able to absorb roughly 30000 cuft/s, reducing the flood to less than half of what it would have been if not for the dams.