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Living with Dams: Extreme Rainfall Events | 2015

| 19

4. Extreme Incident Planning

including Emergency Action


Dams do fail! Often these failures

will cause extensive property

damage, personal injuries and

in some situations, loss of life. To

minimize the consequences of a

dam failure, it is imperative that a

dam owner prepare an Emergency

Action Plan (EAP) for their dam.

An EAP is a formal document that

identifies emergency conditions

at a dam and the areas that would

be inundated if the dam were to

fail. It specifies preplanned actions

to be followed to moderate or

alleviate problems at the dam and

to provide adequate downstream

warning of failure. In the case of

a dam failure, the EAP may help

to minimize the consequences of

the failure. EAPs are required by

most State Dam Safety Regulatory

Programs for high hazard dams.

Key components of an EAP

would include:

Inundation Maps indicating

areas that will be impacted by

the dam failure flood wave

Notification Flowcharts for

warning of inhabitants in

inundation areas by Emergency

Management Authorities

Monitoring - Emergency

Detection, Evaluation and

Responsibility Protocol

Preventative Action – Effective

response actions to prevent


5. A Dam Owners Obligation -

Meeting Current Standards

Spillway Design Criteria

The spillway capacity of any dam

should, at a minimum, comply

with the current state guidelines

for the dam’s spillway design

capacity. Most all of these state

guidelines relate directly to extreme

rainfall events and to hazard

potential classification of the dam.

Historically, standards for dam

spillway design floods have varied

from state to state, but typically

have been specified as a flood

resulting from some significant

percentage of an extreme rainfall

event known as the Probable

Maximum Precipitation (PMP).

Recently published national

guidelines for selecting and

accommodating inflow design

floods (IDF) for dam structures

(FEMA P-94/August 2013)

recommends more rigorous

analyses such as an incremental

dam breach consequence analysis,

Owner and community

vigilance is critical.