ETL 1110-2-540
30 Sep 96
Chapter 4
Closing levee openings
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Hydrologic Analysis of Enhancements to
Moving public and private vehicles and equipment
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Existing Programs
from areas subject to flooding
Relocating or stacking contents of private structures
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4-1. General
Initiating flood-fighting efforts (e.g., sandbagging,
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a. Flood warning - preparedness program enhancements
etc.)
are developed with the members of the interdisciplinary planning
Establishing security to prevent looting
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team. Plan enhancements should be analyzed and evaluated based
on general improvements over the existing condition, the cost of
It is likely that some actions described above will not be
each component, and the potential contributions to reducing flood
appropriate for a specific community. List those beneficial
damages and preventing the loss of life. A strict economic analysis
actions that can be accomplished with the given resources of the
to explicitly quantified flood damage reduction benefits is not
community. Describe priorities, potential benefits, responsible
required. Reasonable estimates of flood damage reduction benefits
parties, available resources, and approximate time required to
based on specific actions that can be accomplished in the time
accomplish the described actions.
afforded are required.
b. Flood-threat recognition systems and warning dissemi-
b. Data monitoring. The objective of the measurement
and detection task is to monitor developing hydrometeoro-
nation procedures should be evaluated based on how to enhance
logical conditions. This includes current and near-term water-
the desired response actions. For some systems, more formal
shed conditions. Atmospheric parameters, measured rainfall,
arrangements for institutional and public response far outweigh the
and current stream conditions can be observed. A knowledge
benefits of enhancements to flood-threat recognition systems.
of developing atmospheric conditions can yield information
Simply implementing more hardware and software and
about the likelihood of future rainfall. Raingages provide an
incorporating a sophisticated monitoring and forecasting system
indication of the volume of water already on the ground.
does not necessarily provide a better overall program. For other
Stream gages provide the current state of the hydrologic con-
areas they do provide needed additional warning time and relia-
veyance systems that result in flooding. Stream gages provide
bility estimates.
the most important and reliable flood estimates. For moderate
4-2. Analysis of Flood-Threat Recognition Systems
and larger streams the principal monitoring and forecasting
from stream flow data are the primary basis of the estimates.
a. Preliminary evaluation of emergency response plans.
Systems with raingages and stream gages provide additional
Some preliminary evaluation of the response plan is necessary
warning time since the hydrologic system is being measured
to determine the type and scope of the flood recognition system.
further upstream. By measuring rainfall and computing its
Develop a preliminary list of possible emergency response
possible impact on future stream flows, additional time is
actions. Example response actions are listed below.
gained for an informed response. This is important for smaller
streams. It is possible to begin response activities before
Providing search, rescue, and evacuation services
significant amounts of runoff have reached the channel and
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detected by the stream gages. Adding meteorological moni-
Scheduling closure of schools and transportation of
toring enables determination if additional rainfall is moving into
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students
the area, is stalled, or is quickly on its way out of the area. Use
of rainfall monitoring can enhance warning times. Incor-
Curtailing electric and gas service to prevent fire and
porating a range of monitoring techniques provides more
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explosions
information to formulate forecasts and heighten the warning
Establishing traffic controls to facilitate evacuation and
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prevent inadvertent travel into hazardous areas
(1) Raingages. Raingage measurements are point esti-
mates of rainfall used to approximate the volume of water fall-
Dispersing fire and rescue services for continued
ing over an area. A raingage measurement is used as an
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protection
estimator of the average of rainfall over a much larger area than
the gage itself. The accuracy of the rainfall measured at
Establishing emergency medical services and shelters
such a point is less important than how consistently the point
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4-1
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