100-yr flood (Base Flood)
The flood having a one-percent chance of being equaled of exceeded in
magnitude in any given year. It is not a flood occurring every 100 years
Base Flood Elevation (BFE)
The height (above sea-level) that flood waters will reach at a given location
in the event of the 100-year flooding event.
Community Rating System
A National Flood Insurance Program that provides incentives for NFIP
communities to complete activities that reduce flood hazard risk. When the
community completes specified activities, the insurance premiums of NFIP
policyholders in these communities are reduced.
A tool used by NFIP to ensure compliance with community floodplain management
ordinances, and to determine the proper insurance premium rate.
A rapid rise in water levels associated with heavy rainfall, or failure of
dam. These fast moving waters can move boulders, tear out trees, and destroy
A general and temporary condition of partial or complete inundation of
normally dry land areas from : (a) the overflow of inland or tidal waters; (b)
the unusual and rapid accumulation of runoff of surface water from any
Flood Insurance Rate Map (FIRM)
The insurance and floodplain management map issued by FEMA that identifies
areas of 100-year flood hazard in a community. In some areas the map also
shows base flood elevations and 500-year floodplain boundaries and
occasionally, regulatory floodway boundaries. These maps are usually located
at the Town/City Hall.
Flood Insurance Study (FIS)
An engineering study performed by FEMA to identify flood hazard areas, flood
insurance risk zones, and other flood data in a community.
A flood is imminent or occurring. Take immediate action to protect
Conditions are in place for a flood event but location and magnitude are still
uncertain. Prepare for flooding.
Any land area susceptible to inundation by floodwaters from any source.
Geographical Information Systems (GIS)
A system of computers, spatial data, and personnel to help store, manipulate,
and analyze and display geographically referenced information. Generally it
is used to map physical features on the earth.
Sustained actions taken to reduce or eliminate long-term risk from hazards and
An intense tropical cyclone, formed in the atmosphere over warm ocean areas,
in which wind speeds reach 47 miles-per-hour or more and blow in a large
spiral around a relatively calm center or “eye”. Hurricanes develop over the
North Atlantic Ocean, northeast Pacific Ocean, or the South Pacific Ocean east
of 160 degrees longitude. Hurricane circulation is counter-clockwise in the
northern hemisphere and clockwise in the southern hemisphere.
Letter of Map Amendment
Report that must be submitted to FEMA to change a FIRM in order to move a
property out of the 100 year floodplain.
The water from rainfall that is not absorbed by the ground that flows in the
local drainage system, and ultimately rivers and streams.
Flooding of or produced by a river.
Special Flood Hazard Area (SFHA)
An area that has a one percent chance of being flooded in any given year.
Also called the 100-year floodplain, this area is shaded on the Flood
Insurance Rate Map into FIRM Zones A, AO, AH, A1-A30, AE, A99, V, V1-30, and
Flooding that has occurred where there has been development within stream
floodplains. Urbanization in floodways increases the magnitude and frequency
of floods by destroying the floodways and natural wetlands that serve as
natural basins for flood waters.
The geographic area that contributes surface water from rain, or melting snow
to a particular stream or river system.
Flood Zones (A, V, X)
- AE, A, or AO Zone - These properties have a 1 percent chance of flooding
in any year, and a 26 percent chance of flooding over the life of a 30-year
- VE or V Zone - These properties have a 1 percent chance of flooding in
any year and also face hazards associated with coastal storm waves.
- Shaded X Zone - These properties are outside the high-risk zones. The
risk is reduced but not removed.
- X Zone - These properties are in an area of overall lower risk.