A dam inundation map is a scenario, not a condition report

Start with the exact address and dam name. Open the approved inundation map. Then find the county or city emergency plan and sign up for local alerts. Before an incident, write down a route out of the low area. During an emergency, follow the current local warning or evacuation order. Do not rely on the map alone.

An inundation map shows possible flooding from a modeled dam failure. It can also model failure of a critical structure tied to the dam. The event is hypothetical. The map does not show how likely a failure is or the dam’s current condition. It also cannot give the arrival time for every real event or the exact live evacuation area.

A downstream hazard class describes what could happen if the dam failed. It is separate from the dam’s condition assessment.

California requires these maps and emergency action plans for dams under state jurisdiction, except low-hazard dams. The Division of Safety of Dams approves the maps. Cal OES approves the dam owner’s emergency action plan. Approved maps generally need an update at least every 10 years. They also need an update after specified significant changes, so check the map date. Federal dams, dams outside state jurisdiction, and low-hazard dams may use other map paths.

Only local emergency agencies plan and carry out an evacuation. Call 911 for danger now. Leave when ordered, even if the mapped line or route looks different from what is happening.