Technical Manual: Conduits through Embankment Dams (FEMA 484)

Chapter 11—Appropriate Emergency ActionsThe emergency classification that a failure is imminent or has occurred shouldconvey the impression that the embankment dam is failing, and appropriateevacuation procedures should be employed. This is a situation where a failure hasoccurred, is occurring, or obviously is just about to occur. Therefore, once anembankment dam owner determines that there is no longer any time available toattempt corrective measures to prevent failure, the “failure is imminent or hasoccurred” warning should be issued. Emergency management agencies, forevacuation purposes, should conservatively interpret the phrase “failure is imminent”to mean that the embankment dam is failing, and all appropriate parties should benotified to commence emergency operations and evacuation.The emergency classification that a potential embankment dam failure situation isdeveloping should convey the impression that some time still remains for furtheranalyses/decisions and remedial actions to be made before an embankment damfailure is considered to be imminent. This is a situation where the condition of theembankment dam is deteriorating rapidly and failure may eventually occur; however,preplanned actions taken during certain events could mitigate or alleviate failure ofthe embankment dam. Even if failure is inevitable, more time is generally availablethan the “failure is imminent” condition to issue warnings and/or take preparednessactions. All appropriate parties should be on standby-alert status and should benotified to commence their emergency operations and evacuation, if required.The “nonemergency or unusual condition” classification applies where an unusualproblem or condition has occurred, but a failure of the embankment dam is notconsidered imminent. This is a situation or circumstance that may affect theintegrity of the embankment dam but is considered controllable. This conditioncould lead to a failure of the embankment dam, if appropriate actions or repairs arenot employed. All appropriate parties should be notified periodically with regard tothe status of the condition of the dam and should be on standby-alert status foremergency actions, should conditions deteriorate.Table 11.1 provides a guide for determining the level of urgency and the emergencyclassification associated with emergency conditions attributed to the internal erosionor backward erosion piping of earthfill materials (Colorado Division of WaterResources, 1997, p. 11; FEMA, 1998).Prompt and effective response to an emergency at a particular damsite could result inthe mitigation or avoidance of a embankment dam failure incident, or help reducethe effects of a dam failure or operational spillway release, and facilitate response tothe emergency. The preventive actions that an embankment dam owner may takeinclude providing emergency flooding operating instructions, and arranging forequipment, labor, and the stockpiling of materials for use in an emergency situation.An effective EAP should describe preventive actions to be taken during thedevelopment of emergency conditions.265