ETL 1110-2-540
30 Sep 96
Chapter 2
and emergency response components for different types of
General Concepts
watersheds.
2-2.
Flood-threat Recognition
2-1.
General
Flood-threat recognition systems consist of activities and
arrangements to enable early identification, location, and
a. This chapter overviews the general concepts and
degree of potential flood situations. The primary elements
components of flood warning - preparedness programs.
of flood recognition systems are indicted below:
Making a distinction between the various components of a
flood warning - preparedness program is important. More
Monitoring
!
detailed descriptions of flood warning - preparedness program
- Measurement and detection
components are included in the discussion of enhancements
- Data transmission
(Chapter 4).
- Data assembly and display
b. The flood warning - preparedness program consists of
Forecasting (additional to monitoring)
!
the following components:
- Data processing and analysis
- Forecast preparation
Flood-Threat Recognition
!
- Validation and updates
Warning Dissemination
!
The purpose of the flood-threat recognition system is to
recognize the potential of a flood threat quickly, to continue
Emergency Response
!
to monitor the situation, and to predict or forecast the nature
of the event. The goal is to determine the impact of the
Postflood Recovery
developing flood in the minimum time possible. The NWS
!
has the overall responsibility for monitoring and forecasting
flood situations for the nation. This information is primarily
Continued Plan Management
!
developed and disseminated for the major river basins of the
country. Many communities have potential loss of life and
Flood warning - preparedness plans vary significantly based on
property due to flooding of smaller and often flashy streams
many factors, including: the hydrometeorological character-
in developed areas. NWS precise forecasts are typically not
istics of the watershed, the population at risk, threatened prop-
available for these streams.
erties, infrastructure, and the institutional capabilities and
arrangements. The period between flood events is also
important. Table 2-1 illustrates typical flood-threat recognition
Table 2-1
Typical Flood Warning - Preparedness Plan Components
Warning
Flood-Threat Recognition Component
Watershed Type
Time
Response Component
Small mountain streams (mountain streams,
<6 hr
NWS precipitation forecasts, regional
Emergency evacuation of flood-plain.
Hawaii coastal streams, small streams
monitoring, observers.
subject to cloud burst rainfall, etc.)
Streams, tributaries, or small rivers (majority
6 to 24 hr
Stream gages and possibly rain gages.
Evacuation assistance, maintenance of
of watersheds with relatively mild slopes and
Monitoring and possible runoff forecasting
vital services, relocation of property and
drainage areas between 51.8 and 777 sq km
model, depending on the capabilities of the
other actions that can be accomplished
(20 and 300 sq mi.))
local agencies. ALERT type systems.
within the warning time.
Large major river basins (Mississippi River,
>24 hr
Raingage and stream gage monitoring,
All of the above in addition to significant
Sacramento River, Colorado River, etc.)
NWS forecasts. Corps water control real-
flood-fighting effort.
time forecasting and regulation,
sophisticated models.
2-1
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