| San Gabriel Dam | |
|---|---|
View of the nearly full reservoir from the north, with the dam and spillway in the background |
|
| Country | United States |
| Location | Los Angeles County, California |
| Coordinates | |
| Construction began | 1932 |
| Opening date | 1939 |
| Construction cost | $17 million |
| Owner(s) | Los Angeles Department of Water and Power |
| Dam and spillways | |
| Type of dam | Rockfill |
| Height | 315 ft (96 m) |
| Length | 1,520 ft (460 m) |
| Crest width | 30 ft (9.1 m) |
| Base width | 1,000 ft (300 m) |
| Volume | 148,000,000 cu yd (113,000,000 m3) |
| Impounds | San Gabriel River |
| Type of spillway | Uncontrolled concrete overflow |
| Spillway capacity | 65,000 cu ft/s (1,800 m3/s) |
| Reservoir | |
| Creates | San Gabriel Reservoir |
| Capacity | 53,344 acre·ft (65,799,000 m3) (nominal) 44,183 acre·ft (54,499,000 m3) (current) |
| Catchment area | 205 sq mi (530 km2) |
| Surface area | 525 acres (212 ha) |
| Power station | |
| Owner(s) | City of Azusa |
| Commission date | 1898 |
| Turbines | 1 |
| Installed capacity | 3 MW |
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 (4.0 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 44,183 acre·ft (54,499,000 m3) of water when full,[1] creating one of Southern California's larger reservoirs. Its capacity was 53,344 acre·ft (65,799,000 m3) when the dam was first built, but sedimentation has since reduced its volume by about 17%.[2] 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 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 Called the San Gabriel Forks Dam, this project was later withdrawn in the wake of the March 1928 St. Francis Dam failure and a landslide that destroyed a large portion of the construction site at the San Gabriel forks.[3] 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.[4] 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 1,520 ft (460 m) long and receives water from an area of 205 sq mi (530 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 150,000 cu ft/s (4,200 m3/s) of water poured into San Gabriel Reservoir at flood's peak, but the dam's extra capacity was able to knock about 40,000 cu ft/s (1,100 m3/s) off the peak of the flood. Further downstream, Morris Reservoir was able to absorb roughly 30,000 cu ft/s (850 m3/s), reducing the flood to less than half of what it would have been if not for the dams.[5]