City of Irvine
2020 Local Hazard Mitigation Plan
location of Irvine, current inundation mapping does not indicate that the City would be impacted by such an event.
Table 3-6 identifies the DSOD Downstream Hazard Potential Classification used to determine the anticipated impacts associated with a dam inundation event. Dams located in and around Irvine are all classified in the “Extremely High” category, meaning they could cause considerable loss of human life and major impacts on critical infrastructure or property that could lead to economic, environmental, and lifeline losses. Table 3-6: Criteria for DSOD’s Downstream Hazard Potential Classification 30 Downstream Hazard Potential Classification Potential Downstream Impacts to Life and Property Low No probable loss of human life and low economic and environmental losses. Losses are expected to be principally limited to the owner’s property. Significant No probable loss of human life but can cause economic loss, environmental damage, impacts to critical facilities, or other significant impacts. High Expected to cause loss of at least one human life. Extremely High Expected to cause loss of at least one human life and one of the following: result in an inundation area with a population of 1,000 or more; or, result in the inundation of facilities or infrastructure, the inundation of which poses a significant threat to public safety as determined by the department on a case-by-case basis. Figure 3-1 below identifies the potential inundation areas that could impact the City of Irvine. This figure shows the areas downstream that would be inundated by an unintentional breach from a dam’s reservoir. The areas that could flood in the case of a dam breach are not necessarily the same areas that could be inundated by a 100-year or 500-year flood (see Flood Hazard Profile below).
Past Events
While California’s dam infrastructure is recent in the state’s history, there have already been major catastrophic dam failure events. One of the earliest in Southern California was the failure of the San Francisquito Canyon Dam. The dam experienced a structural failure as a result of insufficient geotechnical engineering by the then-Los Angeles Bureau of Water Works and Supply. At midnight on March 13, 1928, the 205-foot-tall structure gave way, unleashing a 120-foot-high wave of water traveling 18 miles per hour down the canyon. By 5:30 AM, the wave had traveled 54 miles from the dam site to the Pacific Ocean, killing at least 438 people, razing towns, and destroying infrastructure. It was reported that the bodies of victims were recovered from the ocean as far south as the Mexican border. The disaster is considered one of the worst engineering failures in US history. 31 Another, more recent, dam failure in the region occurred at the Baldwin Hills Dam. On December 14, 1963, a structural failure in the dam caused a breach that unleashed 250 million gallons of reservoir water. Diligent work by maintenance crews detected the developing failure in the dam four hours before it breached, and they, with the cooperation of local law enforcement, were able to successfully evacuate and save nearly 1,500 people downstream from the reservoir. Five lives were lost in the ensuing wave of water, 65 homes were destroyed, and nearly $11 million worth of property damage was incurred. 32 The Baldwin Hills Dam was not rebuilt and is now a grassy basin in Kenneth Hahn Park. 33
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