Didn’t officials and investigators agree that a major catastrophe was narrowly missed at Lower San Fernando 6-015 Dam? The Lower San Fernando 6-015 Dam is located in Los Angeles County. Its coordinates are N34.28500 degrees and W118.47925 degrees.
Lower San Fernando 6-015 Dam’s story is one of engineering ambition. It also tells of a near-disaster and crucial lessons learned. Constructed between 1912 and 1930, the Lower San Fernando 6-015 Dam was a key part of Los Angeles’ water supply. It held approximately 80 percent of the city’s water. The dam employed hydraulic and rolled fill techniques. This was common practice at the time. Engineers considered it a sound method for building earth dams.
Hydraulic fill was placed up to approximately 1105 feet in elevation. The shells consisted of silty sand, sandy silt, and clay layers. The core was created from puddled clay. Rolled earth fill raised the Lower San Fernando 6-015 Dam in four stages. The final crest elevation reached 1144.6 feet. A rolled earth berm was added to the downstream toe in 1940. The Lower San Fernando 6-015 Dam reached a maximum height of 142 feet. Its length was 2080 feet.
The Lower San Fernando 6-015 Dam operated for many years near its full design capacity. Reviews in 1966 led to a reduction in the maximum operating reservoir level. This was a result of seismic hazard evaluations. The 1971 San Fernando earthquake struck on February 9. It caused significant damage to the Lower San Fernando 6-015 Dam. The earthquake’s epicenter was about 10 km northeast of the Lower San Fernando 6-015 Dam. Ground shaking lasted approximately 15 seconds.
The earthquake caused a major slide on the upstream slope of the Lower San Fernando 6-015 Dam. It resulted in a substantial loss of freeboard. The embankment spread approximately 250 feet. The slide occurred after the strongest shaking had subsided. The reservoir level was at 1109 feet during the earthquake. The slide reduced the freeboard to about 5 feet.
The outlet tower near the center of the Lower San Fernando 6-015 Dam was severed and toppled. Sandbags were rushed to the site to increase freeboard. Approximately 80000 residents were evacuated as a precaution. The reservoir was lowered using pumps. A major catastrophe was narrowly avoided. The Lower San Fernando 6-015 Dam retained 10000 acre-feet of water.
A post-failure investigation was conducted. It concluded that liquefaction caused the slide. The investigation focused on the performance of hydraulic fill during earthquakes. The Lower San Fernando 6-015 Dam incident had far-reaching impacts. It changed how seismic safety was evaluated for earth dams. Hydraulic fill was effectively no longer considered for dams in seismic zones.
The Los Angeles Dam and Reservoir replaced the failed Lower San Fernando 6-015 Dam. The old dam was reconstructed as a holding basin for storm water. It also backs up the new dam. The remnant Lower San Fernando 6-015 Dam suffered heavy damage again in the 1994 Northridge earthquake. The Lower San Fernando 6-015 Dam is a reminder of the importance of dam safety. It highlights the need for continuous evaluation and adaptation.