ETL 1110-2-540
30 Sep 96
Event
Appendix B
Glossary of Terms
a.
A meteorological or hydrological occurrence such as
a "storm event" or a "flood event."
Actual Warning Time
Time between receipt of flood warning and the time of flood
b. Incremental change recorded by a meteorological or
occurrence. Actual flood warning time is less than the potential
hydrological instrument. ALERT and IFLOWS
flood warning time. Actual flood warning time is sometimes
systems use the term event to describe an incremental
also referred to as response time.
change in accumulated rainfall or stage.
An
ALERT/IFLOWS "event" is the occurrence of an
ALERT System
additional millimeter of rainfall or the incremental
ALERT is an acronym for Automated Local Evaluation in
increase (or decrease) of stage.
Each
Real-Time. It is the name of a particular type of advanced
ALERT/IFLOWS increment or event triggers a data
automated flood-threat recognition system developed by the
reporting and recording sequence.
National Weather Service (NWS).
Exceedence Frequency
Automated Local Flood Warning System
The percent chance of a flood of a specified magnitude being
A local flood-threat recognition system with capabilities to
exceeded equaled or exceeded during any given year. The
automatically collect precipitation and other hydrometeoro-
exceedance frequency is equal to the reciprocal of the recur-
logical data, evaluate possible alarm conditions (high rainfall
rence interval at a specified location.
rates, high river elevations, etc.), and automatically alert an
Flood Stage
operator.
The water surface elevation where damage begins.
Bankfull Stage
Flood Index
Highest stream elevation that occurs without spilling on to
adjacent floodplain.
Typically, the amount of rainfall required to produce flood stage
at a specified location along a stream. The amount of rainfall
Base Station
required to initiate flooding is generally specified to occur within
Generally, the central location for receiving data from an
a specific period of time (e.g., 3, 6, 12, or 24 hr).
automated local flood-threat recognition system.
Flood
A general and temporary condition of:
Adjustment of parameters in a hydrologic model to achieve
agreement between the simulated hydrographs produced by the
a.
Partial or complete inundation of normally dry land
hydrologic model and observed hydrographs from the
areas from the overflow of inland and/or tidal waters
watershed being modeled.
and/or
Conveyance
b.
The unusual accumulation of waters from any source.
A measure of the carrying capacity of a channel at a specified
Flood Hazard
location.
The potential for inundation which involves the risk to life,
Crest
health, property, and natural floodplain values.
The maximum elevation reached by a flood hydrograph.
Flood Hazard Rating (See Table 3-2, main text)
Discharge
Floodplain
The volumetric flow rate at a specified location.
The lowland and relatively flat areas adjoining inland and
Emergency Preparedness Plan
coastal waters and those other areas subject to flooding.
A detailed written plan documenting the duties and responsi-
bilities of personnel responding to a flood emergency. It is a list
of actions required to minimize the loss of life and property due
to an emergency such as flooding.
B-1
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