Risk and Vulnerability Assessment Tool-Glossary

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Data Dictionary

Risk and Vulnerability Assessment Tool (RVAT)

Glossary

This glossary was adapted from the Coastal Construction Control Manual. For additional terms and definitions pertaining to risk and vulnerability, natural hazards, and mitigation, visit the Vulnerability Assessment Techniques and Applications (VATA) Web site Glossary.

A | B | C | D | E | F | H | J | L | M | N | O | R | S | T | V | W | X |

A

A zone — Under the National Flood Insurance Program, area subject to inundation by the 100-year flood where wave action does not occur or where waves are less than 3 feet high, designated Zone A, AE, A1-A30, A0, AH, or AR on a Flood Insurance Rate Map (FIRM).

Anchoring — To secure a structure to its footings or foundation wall in such a way that a continuous load transfer path is created and so that it will not be displaced by flood, wind, or seismic forces.

B

Base flood — Flood that has as 1-percent probability of being equaled or exceeded in any given year. Also known as the 100-year flood.

Base Flood Elevation (BFE) — Elevation of the base flood in relation to a specified datum, such as the National Geodetic Vertical Datum or the North American Vertical Datum. The Base Flood Elevation is the basis of the insurance and floodplain management requirements of the National Flood Insurance Program.

Beach nourishment — Replacement of beach sand removed by ocean waters.

Building code — Regulations adopted by local governments that establish standards for construction, modification, and repair of buildings and other structures.

Bulkhead — Wall or other structure, often of wood, steel, stone, or concrete, designed to retain or prevent sliding or erosion of the land. Occasionally, bulkheads are use to protect against wave action.

C

Coastal A zone — For the purposes of this manual, the portion of the Special Flood Hazard Area landward of a V zone or landward of an open coast without mapped V zones (e.g., shorelines of the Great Lakes), in which the principal sources of flooding are astronomical tides, storm surge, seiches, or tsunamis, not riverine sources. The flood forces in coastal A zones are highly correlated with coastal winds or coastal seismic activity. Coastal A zones may therefore be subject to wave effects, velocity flows, erosion, scour, or combinations of these forces. See A zone and Non-coastal A zone. (Note: the National Flood Insurance Program regulations do not differentiate between coastal A zones and non-coastal A zones.)

Coastal barrier — Depositional geologic feature such as a bay barrier, tombolo, barrier spit, or barrier island that consists of unconsolidated sedimentary materials; is subject to wave, tidal, and wind energies; and protects landward aquatic habitats from direct wave attack.

Coastal Barrier Resources Act of 1982 (CBRA) — Act (Pub. L. 97-348) that established the Coastal Barrier Resources System (CBRS). The act prohibits the provision of new flood insurance coverage on or after October 1, 1983, for any new construction or substantial improvements of structures located on any designated undeveloped coastal barrier within the CBRS. The CBRS was expanded by the Coastal Barrier Improvement Act of 1991. The date on which an area is added to the CBRS is the date of CBRS designation for that area.

Coastal flood hazard area — Area, usually along an open coast, bay, or inlet, that is subject to inundation by storm surge and, in some instances, wave action caused by storms or seismic forces.

Coastal High Hazard Area — Under the National Flood Insurance Program, an area of special flood hazard extending from offshore to the inland limit of a primary frontal dune along an open coast and any other area subject to high-velocity wave action from storms or seismic sources. On a Flood Insurance Rate Map, the Coastal High Hazard Area is designated Zone V, VE, or V1-V30. These zones designate areas subject to inundation by the base flood where wave heights or wave runup depths are greater than or equal to 3.0 feet.

D

Debris — Solid objects or masses carried by or floating on the surface of moving water.

Debris line — Line left on a structure or on the ground by the deposition of debris. A debris line often indicates the height or inland extent reached by flood waters.

Development — Under the National Flood Insurance Program, any man-made change to improved or unimproved real estate, including but not limited to buildings or other structures, mining, dredging, filling, grading, paving, excavation, or drilling operations or storage of equipment or materials.

Dune — See Frontal dune and Primary frontal dune.

Dune toe — Junction of the gentle slope seaward of the dune and the dune face, which is marked by a slope of 1 on 10 or steeper.

E

Encroachment — Any physical object placed in a floodplain that hinders the passage of water or otherwise affects the flood flows.

Episodic erosion — Erosion induced by a single storm event. Episodic erosion considers the vertical component of two factors: general beach profile lowering and localized conical scour around foundation supports. Episodic erosion is relevant to foundation embedment depth and potential undermining. See Erosion.

Erodible soil — Soil subject to wearing away and movement due to the effects of wind, water, or other geological processes during a flood or storm or over a period of years.

Erosion — Under the National Flood Insurance Program, the process of the gradual wearing away of land masses. In general, erosion involves the detachment and movement of soil and rock fragments, during a flood or storm or over a period of years, through the action of wind, water, or other geologic processes.

Erosion analysis — Analysis of the short- and long-term erosion potential of soil or strata, including the effects of flooding or storm surge, moving water, wave action, and the interaction of water and structural components.

F

Federal Emergency Management Agency (FEMA) — Independent agency created in 1979 to provide a single point of accountability for all federal activities related to disaster mitigation and emergency preparedness, response and recovery. FEMA administers the National Flood Insurance Program.

Federal Insurance Administration (FIA) — The component of the Federal Emergency Management Agency directly responsible for administering the flood insurance aspects of the National Flood Insurance Program.

Fetch — Distance over which wind acts on the water surface to generate waves.

500-year flood — Flood that has as 0.2-percent probability of being equaled or exceeded in any given year.

Flood — Under the National Flood Insurance Program, either a general and temporary condition or partial or complete inundation of normally dry land areas from:

the overflow of inland or tidal waters,
the unusual and rapid accumulation or runoff of surface waters from any source, or
mudslides (i.e., mudflows) which are proximately caused by flooding as defined in (2) and are akin to a river of liquid and flowing mud on the surfaces of normally dry land areas, as when the earth is carried by a current of water and deposited along the path of the current, or (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 (1), above.

Flood-damage-resistant material — Any construction material capable of withstanding direct and prolonged contact (i.e., at least 72 hours) with flood waters without suffering significant damage (i.e., damage that requires more than cleanup or low-cost cosmetic repair, such as painting).

Flood elevation — Height of the water surface above an established elevation datum such as the National Geodetic Vertical Datum, North American Vertical Datum, or mean sea level.

Flood hazard area — The greater of the following: (1) the area of special flood hazard, as defined under the National Flood Insurance Program, or (2) the area designated as a flood hazard area on a community's legally adopted flood hazard map, or otherwise legally designated.

Flood insurance — Insurance coverage provided under the National Flood Insurance Program.

Flood Insurance Rate Map (FIRM) — Under the National Flood Insurance Program, an official map of a community, on which the Federal Emergency Management Agency has delineated both the special hazard areas and the risk premium zones applicable to the community. (Note: The latest FIRM issued for a community is referred to as the effective FIRM for that community.)

Flood Insurance Study (FIS) — Under the National Flood Insurance Program, an examination, evaluation, and determination of flood hazards and, if appropriate, corresponding water surface elevations, or an examination, evaluation, and determination of mudslide (i.e., mudflow) and/or flood-related erosion hazards in a community or communities. (Note: The National Flood Insurance Program regulations refer to Flood Insurance Studies as "flood elevation studies.")

Flood-related erosion area or flood-related erosion-prone area — A land area adjoining the shore of a lake or other body of water, which due to the composition of the shoreline or bank and high water levels or wind-driven currents, is likely to suffer flood-related erosion damage.

Flooding — See Flood.

Floodplain — Under the National Flood Insurance Program, any land area susceptible to being inundated by water from any source. See Flood.

Floodplain management — Operation of an overall program of corrective and preventive measures for reducing flood damage, including but not limited to emergency preparedness plans, flood control works, and floodplain management regulations.

Floodplain management regulations — Under the National Flood Insurance Program, zoning ordinances, subdivision regulations, building codes, health regulations, special purpose ordinances (such as floodplain ordinance, grading ordinance, and erosion-control ordinance), and other applications of police power. The term describes such state or local regulations, in any combination thereof, which provide standards for the purpose of flood damage prevention and reduction.

Freeboard — Under the National Flood Insurance Program, a factor of safety, usually expressed in feet above a flood level, for the purposes of floodplain management. Freeboard tends to compensate for the many unknown factors that could contribute to flood heights greater than the heights calculated for a selected size flood and floodway conditions, such as the hydrological effect of urbanization of the watershed.

Frontal dune — Ridge or mound of unconsolidated sandy soil, extending continuously alongshore landward of the sand beach and defined by relatively steep slopes abutting markedly flatter and lower regions on each side.

H

High-velocity wave action — Condition in which wave heights or wave runup depths are greater than or equal to 3.0 feet.

Hurricane — Tropical cyclone, formed in the atmosphere over warm ocean areas, in which wind speeds reach 74 miles per hour or more and blow in a large spiral around a relatively calm center or "eye." Hurricane circulation is counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere.

Hurricane clip or strap — Structural connector, usually metal, used to tie roof, wall, floor, and foundation members together so that they can resist wind forces.

J

Jetty — Wall built out into the water to restrain currents or protect a structure.

L

Lacustrine flood hazard area — Area subject to inundation by flooding from lakes.

Littoral — Of or pertaining to the shore, especially of the sea; coastal.

Littoral drift — Movement of sand by littoral (longshore) currents in a direction parallel to the beach along the shore.

M

Manufactured home — Under the National Flood Insurance Program, a structure, transportable in one or more sections, which is built on a permanent chassis and is designed for use with or without a permanent foundation when attached to the required utilities. The term "manufactured home" does not include a "recreational vehicle."

Marsh — Wetland dominated by herbaceous or nonwoody plants often developing in shallow ponds or depressions, river margins, tidal areas, and estuaries.

Mean sea level (MSL) — Average height of the sea for all stages of the tide, usually determined from hourly height observations over a 19-year period on an open coast or in adjacent waters having free access to the sea. See National Geodetic Vertical Datum.

Mitigation — Any action taken to reduce or permanently eliminate the long-term risk to life and property from natural hazards.

N

National Flood Insurance Program (NFIP) — Federal program created by Congress in 1968 that makes flood insurance available in communities that enact and enforce satisfactory floodplain management regulations.

Non-coastal A zone — For the purposes of this manual, the portion of the Special Flood Hazard Area in which the principal source of flooding is runoff from rainfall, snowmelt, or a combination of both. In non-coastal A zones, flood waters may move slowly or rapidly, but waves are usually not a significant threat to buildings. See A zone and coastal A zone. (Note: the National Flood Insurance Program regulations do not differentiate between non-coastal A zones and coastal A zones.)

O

100-year flood — See Base flood.

R

Retrofit — Any change made to an existing structure to reduce or eliminate damage to that structure from flooding, erosion, high winds, earthquakes, or other hazards.

Riprap — Broken stone, cut stone blocks, or rubble that is placed on slopes to protect them from erosion or scour caused by flood waters or wave action.

S

Sand dunes — Under the National Flood Insurance Program, natural or artificial ridges or mounds of sand landward of the beach.

Scour — Removal of soil or fill material by the flow of floodwaters. The term is frequently used to describe storm-induced, localized conical erosion around pilings and other foundation supports where the obstruction of flow increases turbulence. See Erosion.

Seawall — Solid barricade built at the water's edge to protect the shore and to prevent inland flooding.

Shoreline retreat — Progressive movement of the shoreline in a landward direction caused by the composite effect of all storms considered over decades and centuries (expressed as an annual average erosion rate). Shoreline retreat considers the horizontal component of erosion and is relevant to long-term land use decisions and the siting of buildings.

60-year setback — A state or local requirement that prohibits new construction and certain improvements and repairs to existing coastal buildings located in an area expected to be lost to shoreline retreat over a 60-year period. The inland extent of the area is equal to 60 times the average annual long-term recession rate at a site, measured from a reference feature.

Special Flood Hazard Area (SFHA) — Under the National Flood Insurance Program, an area having special flood, mudslide (i.e., mudflow) and/or flood-related erosion hazards, and shown on a Flood Hazard Boundary Map or Flood Insurance Rate Map as Zone A, AO, A1-A30, AE, A99, AH, V, V1-V30, VE, M or E.

Stillwater elevation — Projected elevation that flood waters would assume, referenced to the National Geodetic Vertical Datum, North American Vertical Datum, or other datum, in the absence of waves resulting from wind or seismic effects.

Storm surge — Rise in the water surface above normal water level on the open coast due to the action of wind stress and atmospheric pressure on the water surface.

Storm tide — Combined effect of storm surge, existing astronomical tide conditions, and breaking wave setup.

Structure — For floodplain management purposes under the National Flood Insurance Program, a walled and roofed building, including a gas or liquid storage tank, that is principally above ground, as well as a manufactured home. For insurance coverage purposes under the NFIP, structure means a walled and roofed building, other than a gas or liquid storage tank, that is principally above ground and affixed to a permanent site, as well as a manufactured home on a permanent foundation. For the latter purpose, the term includes a building while in the course of construction, alteration, or repair, but does not include building materials or supplies intended for use in such construction, alteration, or repair, unless such materials or supplies are within an enclosed building on the premises.

Substantial damage — Under the National Flood Insurance Program, damage of any origin sustained by a structure whereby the cost of restoring the structure to its before-damaged condition would equal or exceed 50 percent of the market value of the structure before the damage occurred.

Surge — See Storm surge.

T

30-year erosion setback — A state or local requirement that prohibits new construction and certain improvements and repairs to existing coastal buildings located in an area expected to be lost to shoreline retreat over a 30-year period. The inland extent of the area is equal to 30 times the average annual long-term recession rate at a site, measured from a reference feature.

Tropical depression — Tropical cyclone with some rotary circulation at the water surface. With maximum sustained wind speeds of up to 39 miles per hour, it is the second phase in the development of a hurricane.

Tropical disturbance — Tropical cyclone that maintains its identity for at least 24 hours and is marked by moving thunderstorms and with slight or no rotary circulation at the water surface. Winds are not strong. It is a common phenomenon in the tropics and is the first discernable stage in the development of a hurricane.

V

V zone — See Coastal High Hazard Area.

W

Water surface elevation — Under the National Flood Insurance Program, the height, in relation to the National Geodetic Vertical Datum of 1929 (or other datum, where specified), of floods of various magnitudes and frequencies in the floodplains of coastal or riverine areas.

Wave — Ridge, deformation, or undulation of the water surface.

Wave height — Vertical distance between the wave crest and wave trough.

Wave runup — Rush of wave water up a slope or structure.

Wave setup — Increase in the stillwater surface near the shoreline, due to the presence of breaking waves.

X

X zone — Under the National Flood Insurance Program, areas where the flood hazard is less than that in the Special Flood Hazard Area. Shaded X zones shown on recent Flood Insurance Rate Maps (B zones on older maps) designate areas subject to inundation by the 500-year flood. Unshaded X zones (C zones on older Flood Insurance Rate Maps) designate areas where the annual probability of flooding is less than 0.2 percent.