Van Norman Dams facts for kids
Quick facts for kids Van Norman Dams |
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An oblique aerial view of the Lower Van Norman Dam. It was taken after the February 9, 1971, San Fernando Earthquake.
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| Country | United States |
| Location | Los Angeles County, California |
| Coordinates | 34°17′10″N 118°28′47″W / 34.2862°N 118.4796°W |
| Purpose | W |
| Status | Decommissioned |
| Construction began | upper dam 1919 lower dam 1911 |
| Opening date | upper dam 1921 lower dam November 5, 1913 |
| Demolition date | February 9, 1971 |
| Dam and spillways | |
| Type of dam | Earth fill dam |
| Impounds | Los Angeles Aqueduct Bull Creek |
| Height (foundation) | 60 feet (18 m) |
| Length | 1,200 feet (370 m) |
| Elevation at crest | 1,218 feet (371 m) |
| Width (crest) | 20 feet (6.1 m) |
| Reservoir | |
| Total capacity | 1,800 acre⋅ft (2.2×106 m3) |
| Normal elevation | 1,213.2 feet (369.8 m) |
| Power station | |
| Commission date | October 1922 |
| Type | Conventional |
| Turbines | 2× 2.8 MW |
The Van Norman Dams, also known as the San Fernando Dams, were very important dams in Los Angeles County, California. They were at the end of the Los Angeles Aqueduct. These dams supplied about 80 percent of the water for the city of Los Angeles.
However, the dams were badly damaged during the 1971 San Fernando earthquake. Because of this damage and the risk they posed to nearby towns, they were later taken out of service.
Contents
Building the Dams
The Van Norman Dams were built to help bring water to Los Angeles.
Upper Van Norman Dam
The Upper Van Norman Dam was first built using a method called hydraulic fill. This means dirt and water were mixed and pumped into place. It was about 42 feet (13 m) tall. In 1922, the dam was made taller by adding another 18 feet (5.5 m) of rolled fill. This is a method where soil is compacted in layers.
Lower Van Norman Dam
The Lower Van Norman Dam was built using both hydraulic fill and rolled fill. The hydraulic fill part was about 102.4 feet (31.2 m) high. Over time, more rolled fill was added at least five times. This made the dam taller each time. The last addition was made between 1929 and 1930.
The 1971 San Fernando Earthquake
A big earthquake hit San Fernando in 1971. This earthquake caused serious damage to both Van Norman Dams. Because of the danger, thousands of people living in the San Fernando Valley below the dams had to leave their homes. About 80,000 people were evacuated for three days. It was a very serious situation, and experts believed many lives could have been lost if the dam had completely failed.
Upper Van Norman Dam Damage
When the earthquake happened, the Upper Van Norman reservoir was only about one-third full. The earthquake caused the dam to sink about 3 feet (0.91 m). It also moved the dam sideways by about 5 feet (1.5 m).
Lower Van Norman Dam Damage
The Lower Van Norman reservoir usually held a lot of water. But before the 1971 earthquake, its maximum water level had been lowered for safety reasons. Luckily, when the earthquake hit, the water level was even lower. It was only about half full.
During the earthquake, a large landslide fell into the reservoir. About 30 feet (9.1 m) of the top and front part of the dam also collapsed. This happened mainly because the hydraulic fill material turned into a liquid-like state, which is called liquefaction.
To prevent the dam from completely failing, workers quickly lowered the water level. They removed water at a fast rate for about three and a half days. This was a difficult task because the earthquake had damaged the pipes and towers used to release water.
What Happened Next
After the earthquake, people thought about rebuilding the dams. However, studies showed that the ground where the dams were built was not stable. So, the idea of rebuilding them was stopped.
Instead, a new dam called the Los Angeles Dam was built. It was placed in a safer spot between where the old Lower and Upper Van Norman Dams used to be. Later, during the 1994 Northridge earthquake, the area where the Lower Van Norman reservoir was located was damaged again. But by then, it was only used as a holding basin, so the damage was not as serious.
What We Learned
The near failure of the Lower Van Norman Dam taught engineers and public agencies a lot about safety. It changed how they thought about earthquake safety for dams, especially those made of certain types of soil. It also led to new rules requiring many dams to be checked again for safety.
