ASDSO Dam Safety Toolbox

Emergency Spillways

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“An emergency spillway is designed to provide additional protection against overtopping of a dam and/or dike and is intended for use under unusual or extreme conditions such as misoperation or malfunction of the service spillway or outlet works during very large, remote floods (such as the PMF), or other emergency conditions. As with auxiliary spillways, some degree of structural damage and/or erosion may be expected due to releases up to and including the maximum design discharge”.[1]

In the past, auxiliary spillways were commonly referred to as emergency spillways. This practice should be discontinued. Media references to flow through “emergency spillways” often leads to a misconception by the public that an emergency condition exists at a dam when the dam is safely functioning as designed. [2]

Best Practices Resources

Design Standards No. 14: Appurtenant Structures for Dams (Ch. 3: General Spillway Design Considerations), USBR


Revision ID: 7135
Revision Date: 07/11/2023