FLOOD06898

• County: Statewide
• Basin: Statewide
• Title: Managing Floodplain Development in Approximate Zone A Areas
• Date: 4/1/1995
• Prepared By: FEMA
• Floodplain - Doc Type: Historic FEMA Regulatory Floodplain Information

Appendix 1
Glossary of Floodplain Analysis ~erms

l-P.rc.n~ Annual Chane. Flood: the flood that has a one-percent chance of being
equaled or exceeded on the average in any given year; equivalent to the 100-year
flood.

100-Year Flood: the flood that is equaled or exceeded once in 100 years on the
average; equivalent to the one percent annual chance flood.

Alluvial S~r...: a stream that has formed its channel by the process of
aggradation. The sediment in the stream is similar to the material in the bed
and banks.

Bas. Flood: the flood having a one percent chance of being equalled or excesded
in any given year (the 100-year flood).

Bas. Flood El.va~ion (BVE): the water-surface elevation associated with the base
flood.

Conveyance: a measure of the carrying capacity of the channel section. Flow
(Discharge (Q)) is directly proportional to conveyance (K). The pro~rtional
factor is the square root of the energy slope; expressed as Q = K · S .

Cross S.c~ion: a vertical profile of the ground surface taken perpendicular to
the direction of flood flow. The profile is defined by coordinates of ground
elevation and horizontal distance (station).

Discharge: a measure of flow volume per unit of time. In hydrology, units of
flow are usually cubic feet per second (cfs).

Exceedence Frequency: the frequency that a flood of a certain discharge will be
equaled or exceeded in any given year; equal to the inverse of the recurrence
interval.

Flood: (a) a general and temporary condition of partial or complete inundation
of normally dry land areas from: (1) the overflow of inland or tidal waters; (2)
the unusual and rapid accumulation or runoff of surface waters from any source;
(3) mudslides (L e., mudflows). which are proximately caused by flooding as
defined in (a)(2) above and are akin to a river of liquid and flowing mud on the
surfaces of normally dry land areas, as when earth is carried by a current of
water and deposited along the path of the current. (b) The collapse or
subsidence of land along the shore of a lake or other body of water as a result
of erosion or undermining caused by waves or currents of water exceeding
anticipated cyclical levels or suddenly caused by an unusually high water level
in a natural body of water, accompanied by a severe storm, or by an unanticipated
force of nature, such as flash flood or abnormal tidal surge, or by some
similarly unusual and unforeseeable event, which results in flooding as defined
in (a) (1) above.

Flood Cr.s~: the maximum height of a flood, usually measured as an elevation or
depth.

Flood Hazard: the potential for inundation that involves the risk to life,
health, property, and natural floodplain values.

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