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Dam Failure Inundation

A Broken Dam
Source: waterarchives.org

Dams and reservoirs can hold large volumes of water and represent a potential downstream flooding hazard due to failure or overtopping of the dam caused by extreme runoff events, landsliding, earthquake shaking and other events. In California, dam owners are generally required to map the downstream area that must be evacuated in the event of a dam failure. This potential inundation zone is a “worst-case scenario” that assumes instantaneous dam failure with the reservoir filled to capacity. However, dams rarely fail instantaneously, and reservoirs are not filled to capacity at all times. Dam failure inundation zones are not FEMA regulatory flood zones and a property’s location in a dam failure inundation zone does not itself trigger the FEMA flood insurance requirement.

California law requires disclosure to a prospective buyer of the fact that any portion of a sale property is within a mapped dam failure inundation zone (even during a drought when the reservoir is empty). The statutory Natural Hazard Disclosure Statement includes a space for making this disclosure.