ETL 1110-2-540
30 Jun 96
identify and evaluate needed enhancements. Typically,
many locations for flood-threat recognition systems, especially
recent events are investigated to evaluate flood-threat recog-
in the western United States. The system typically consists of
nition, warning dissemination, and response actions that
an automated reporting precipitation and stream gage network
occurred within existing institutional arrangements and their
and a VHF radio line-of-sight communication system for
overall effectiveness.
transmission of data to one or more base stations. The base
station consists of radio receiving equipment and a PC
a. Flood-threat recognition system. The flood-threat
microprocessor. Software running on the base station PC can
recognition systems currently in place, used for monitoring,
collect, screen, and display precipitation and stream flow data
and in some cases, forecasting, should be the described and
received from the self-reporting gages to monitor the system.
include the following.
Additional software (hydrologic model) is available to forecast
events by simulating stream flow from precipitation data.
(1) Observers. Are observers employed to watch
streams and/or staff gages at key locations during flood
(b) IFLOWS - The Integrated Flood Observing and
events? If so, identify to whom the observations are reported,
Warning System (IFLOWS) consists of a network of
and where, when, and how they are used.
automated self-reporting precipitation gages. The line-of-
sight radio networks are typically county-wide and usually
include several receiving sights so data can be shared among
(2) Simplified charts or tables. Simple charts and table
county, state, and NWS officials. Software employed at the
look-up information may be used to identify a flood threat. If
this is the case, determine how the information is obtained and
receiving sight allows for storing and displaying the
used.
precipitation data.
(3) Precipitation and/or water level gages. Existing rain
If these types of automated data collection and reporting
and stream gages in or near the watershed should have been
systems exist, it is important to determine the type of
identified during the hydrologic analysis to determine
hardware and software installed and how the system is used
discharge-frequency, stage-discharge, and flood warning
during a flood event. The consideration of whether the
times, as previously described. Determine which gages, if
system is used and maintained on a regular bases is impor-
any, are used to help assess the flood threat under current
tant. If the base station includes forecasting capabilities,
arrangements.
model software maintenance is vital. Software maintenance
includes periodically calibrating/updating parameters and
(4) Automated self-reporting gage network and data
analysis of model results for reliability and accuracy. Main-
retrieval systems. If an automated reporting gage network is
tenance must be carried out by a technical person skilled in
currently used, determine the number, type, and location of
the hydrologic aspects of the model and the watershed.
the gages. Identify reporting methods, data storage, manage-
ment, analysis, and displays. Identify key people "in charge"
b. Warning dissemination. Existing warning dissem-
of the network and discuss use, reliability, effectiveness, and
ination arrangements must be defined to evaluate enhance-
maintenance of the system.
ments to the system. The role of participating agencies should
be described in detail. A detailed description of the flood
If an automated reporting gage network exists, a central
warning dissemination process describing formal and informal
location is generally used for data retrieval, storage, and
lines of communication, responsible agencies, points of
management. This central site is usually referred to as a base
contact, and method of communication should be developed.
station. Hardware usually consists of a data receiver such as a
It is generally good practice to describe the process in both
radio antenna or satellite dish and a personal computer (PC) to
text and schematic form.
display and/or process the data. Base station software may
include data collection, storage, display, and management
c. Response actions. Existing emergency response
software provided and installed by the vender. In addition, a
actions that are normally carried out during a flood event
rainfall-runoff forecast model may be part of the system. A
should be described. Consideration should be given to the
description of two popular types of flood recognition data
following when describing the existing situation.
retrieval and processing systems, which are available from the
NWS or private vendors, are given below.
(1) Search, rescue, and evacuation programs.
(a) ALERT - Automated Local Evaluation in Real Time
(2) Law enforcement activities, including traffic control
(ALERT) system was developed by the NWS River Forecast
property surveillance and crime prevention.
Center in Sacramento, CA. Available from the NWS or
private vendors, the ALERT system has been adopted at
3-5
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