ETL 1110-2-540
30 Sep 96
(2) The value of a flood forecast is governed by two
the reliability of the forecast and warning system dictate the
important attributes, accuracy and timeliness, which are
types of emergency response actions that take place. More
mutually exclusive. Having the most accurate forecast and
lead time provides more opportunity to take damage-reducing
the most timely forecast is usually not possible. For example,
actions. Higher accuracy, increased specificity, and better
it is possible to provide a very accurate forecast by checking
reliability mean floodplain residents can focus attention on the
the current stream levels and make a forecast 1/2 hr before
exact areas and elevations expected to flood, making response
flooding begins. However, the forecast would have little
actions more efficient.
value since it is not timely enough to allow effective response
actions to occur. On the other hand, it may be possible to
b. Advanced warning can be used in a variety of ways
make a forecast for a small stream indicating that a flood will
to respond to the impending flood (Owen 1980).
occur tomorrow. However timely this forecast is, in all
Emergency response actions can include warning low-lying
likelihood, it will not be very accurate.
areas to evacuate, providing evacuation assistance, curtailing
electric and gas service to prevent fire and explosions,
(3) Automating much of the flood-threat recognition
establishing traffic controls, and dispersing fire and rescue
system reduces the time needed for certain activities, particu-
services. If there is sufficient lead time, more aggressive
larly, data transmission, data processing and analysis, and
activities can be accomplished to reduce property damage
forecast preparation. The extra time can be used to increase
further such as moving public vehicles and equipment from
time to respond or to get more information to provide a better
low areas, relocating or stacking contents of private structures,
forecast. It is often purely a judgment call of the forecaster
or initiating flood-fighting efforts (e.g., sandbagging). Each
which choice to make.
action taken as the result of advanced planning and increased
warning time has direct consequences in terms of derived
benefits. The anticipated benefits from an enhanced flood
2-3. Warning Dissemination
warning - preparedness program can be categorized and
Flood warning dissemination is a key element of any flood
associated with the contributing actions.
warning - preparedness program. Warning dissemination is
the mechanism by which local officials and the effected
2-5. Continued Plan Management
public are informed that a flood threat condition exists.
Methods of initially warning key personnel may include
The flood warning - preparedness program is a closed loop
audio alarms, voice dial-out systems to "call" key officials, or
continuum of activities beginning and ending with plan
beeper systems. Once emergency personnel have been
management. Without a current and effective preparedness
activated, mass dissemination techniques come in to play.
plan, any program is doomed to failure. Emergencies,
These techniques may include the use of public radio and
particularly flash floods, leave little time to wonder how to
television or special portable National Oceanic and
respond. Preparedness planning identifies what needs to be
Atmospheric Administration (NOAA) weather radios. Door-
done and who is to do it. The course of action is predeter-
to-door warning dissemination can be used as well as sirens
mined and documented, reviewed, and practiced in advance.
and public address systems. Procedures for evaluating
Once a flood emergency begins, forecasts are made and
warning dissemination techniques are included in Chapter 4.
floodplain occupants respond. As the emergency subsides,
the recovery process begins. Emergency activities are
reviewed and evaluated for continued plan management. The
2-4. Emergency Response
results of the evaluation may then lead to improvements to the
a. Preparedness planning identifies what must be done
preparedness plan. Closing the loop in this fashion is vitally
and who must do it. Emergency response actions are
important so that reactions and responses can improve based
predetermined, documented, reviewed, and practiced in
on the experience gained during an actual flood event.
advance. The lead time available, accuracy, specificity, and
2-3
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