Learning center

Dams are systems, not dots on a map.

Learn the vocabulary, responsibilities, benefits, and risks needed to read a dam record responsibly. This is public education—not engineering or emergency advice.

What a dam does

A dam impounds or diverts water. Reservoir storage may support flood management, irrigation, water supply, navigation, recreation, hydropower, fire protection, or several purposes at once.

Hazard potential

Low, significant, and high hazard classifications describe the consequences if failure occurs. They are not grades and do not predict the chance of failure.

Condition assessment

A condition label reflects available inspection information at a point in time. “Not rated” means the public record does not support a condition conclusion—not that the dam is safe or unsafe.

Who is responsible

Owners operate and maintain dams. State agencies regulate many non-federal dams. Federal agencies own or oversee specific portfolios, while local emergency managers lead public warning and response.

Emergency action plans

An EAP defines detection, notification, responsibilities, inundation information, and response steps for a potential dam emergency. Public evacuation instructions come from local authorities.

Removal and restoration

Obsolete dams may be removed after engineering, permitting, sediment, cultural, ecological, and community review. Removal can reconnect habitat but is never a one-size-fits-all answer.

The key distinction

High hazard does not mean bad condition.

Hazard potential asks: “What could happen downstream if this structure failed?” Condition asks: “What does the latest available assessment say about the structure?” A high-hazard dam can be well maintained; a low-hazard dam can still require repair.

Plain-language glossary

Abutment: The valley side or structure against which the end of a dam rests.
Embankment dam: A dam built mainly from compacted earth, rock, or both.
Emergency Action Plan (EAP): A dam-specific plan for identifying an emergency, notifying authorities, and protecting people.
Inundation area: Land expected to flood under a modeled dam-failure or release scenario.
Probable Maximum Flood (PMF): An extreme design flood derived from the most severe reasonably possible hydrologic conditions.
Spillway: A structure that safely passes water around, through, or over a dam.

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