§ 55.2 Terminology. ( a ) With the exception of those terms defined in paragraph (b) of this section, the terms used in this part shall follow the definitions contained in section 6 of Executive Order 11988, section 7 of Executive Order 11990, and the “Guidelines for Implementing Executive Order 11988, Floodplain Management, and Executive Order 13690, Establishing a Federal Flood Risk Management Standard and a Process for Further Soliciting and Considering Stakeholder Input”; the terms “special flood hazard area,” “criteria,” and “Regular Program” shall follow the definitions contained in FEMA regulations at 44 CFR 59.1; and the terms “Letter of Map Revision” and “Letter of Map Amendment” shall refer to letters issued by FEMA, as provided in 44 CFR part 65 and 44 CFR part 70, respectively.
( b ) For purposes of this part, the following definitions apply: ( 1 ) *Coastal high hazard area* means the area subject to high velocity waters, including but not limited to hurricane wave wash or tsunamis. The area is designated on a Flood Insurance Rate Map (FIRM) or Flood Insurance Study (FIS) under FEMA regulations, or according to best available information. (See § 55.8(b) for appropriate data sources.)
( 2 ) *Compensatory mitigation* means the restoration (reestablishment or rehabilitation), establishment (creation), enhancement, and/or, in certain circumstances, preservation of aquatic resources for the purposes of offsetting unavoidable adverse impacts that remain after all appropriate and practicable avoidance and minimization have been achieved. Examples include, but are not limited to: ( i ) *Permittee-responsible mitigation:* On-site or off-site mitigation undertaken by the holder of a wetlands permit under section 404 of the Clean Water Act (or an authorized agent or contractor), for which the permittee retains full responsibility;
( ii ) *Mitigation banking:* A permittee's purchase of credits from a wetlands mitigation bank, comprising wetlands that have been set aside to compensate for conversions of other wetlands; the mitigation obligation is transferred to the sponsor of the mitigation bank; and
( iii ) *In-lieu fee mitigation:* A permittee's provision of funds to an in-lieu fee sponsor (public agency or nonprofit organization) that builds and maintains a mitigation site, often after the permitted adverse wetland impacts have occurred; the mitigation obligation is transferred to the in-lieu fee sponsor.
( 3 ) ( i ) *Critical action* means any activity for which even a slight chance of flooding would be too great, because such flooding might result in loss of life, injury to persons, or damage to property. Critical actions include activities that create, maintain or extend the useful life of those structures or facilities that: ( A ) Produce, use or store highly volatile, flammable, explosive, toxic or water-reactive materials;
( B ) Provide essential and irreplaceable records or utility or emergency services that may become lost or inoperative during flood and storm events (*e.g.,* community stormwater management infrastructure, water treatment plants, data storage centers, generating plants, principal utility lines, emergency operations centers including fire and police stations, and roadways providing sole egress from flood-prone areas); or
( C ) Are likely to contain occupants who may not be sufficiently mobile to avoid loss of life or injury during flood or storm events, *e.g.,* persons who reside in hospitals, nursing homes, convalescent homes, intermediate care facilities, board and care facilities, and retirement service centers. Housing for independent living for the elderly is not considered a critical action.
( ii ) Critical actions shall not be approved in floodways, LiMWAs, or coastal high hazard areas unless they meet an exception at § 55.8 or § 55.21.
( 4 ) *Federal Flood Risk Management Standard (FFRMS) floodplain* means the floodplain as defined by Executive Order 13690 and the Guidelines for Implementing Executive Order 11988, Floodplain Management, and Executive Order 13690, Establishing a Federal Flood Risk Management Standard and a Process for Further Soliciting and Considering Stakeholder Input and further described as applied to HUD-assisted activities by § 55.7 of this part.
( 5 ) *0.2-percent-annual-chance (500-year) floodplain* means the area, including the base flood elevation, subject to inundation from a flood having a 0.2 percent chance or greater of being equaled or exceeded in any given year. (See § 55.8(b) for appropriate data sources).
( 6 ) *Floodway* means that portion of the floodplain which is effective in carrying flow, where the flood hazard is generally the greatest, and where water depths and velocities are the highest. The term “floodway” as used here is consistent with “regulatory floodways” as identified by FEMA. (See § 55.8(b) for appropriate data sources.)
( 7 ) *Functionally dependent use* means a land use that must necessarily be conducted in close proximity to water (*e.g.,* a dam, marina, port facility, water-front park, and many types of bridges).
( 8 ) *High hazard area* means a floodway or a coastal high hazard area.
( 9 ) *Impervious surface area* means an improved surface that measurably reduces the rate of water infiltration below the rate that would otherwise be provided by the soil present in a location prior to improvement, based on the soil type identified either by the Natural Resource Conservation Service Soil Survey or geotechnical study. Impervious surfaces include, but are not limited to, unperforated concrete or asphalt ground cover, unvegetated roofing materials, and other similar treatments that impede infiltration.
( 10 ) *Limit of Moderate Wave Action (LiMWA)* means the inland limit of the portion of Coastal A Zone where wave heights can be between 1.5 and 3 feet during a base flood event, subjecting properties to damage from waves and storm surge. (See § 55.8(b) for appropriate data sources.)
( 11 ) *1-percent-annual-chance (100-year) floodplain* means the area subject to inundation from a flood having a one percent or greater chance of being equaled or exceeded in any given year. (See § 55.8(b) for appropriate data sources.)
( 12 ) *Substantial improvement* — ( i ) *Substantial improvement* means either: ( A ) Any repair, reconstruction, modernization, or improvement of a structure, including a manufactured housing unit, the cost of which equals or exceeds 50 percent of the market value of the structure either: ( 1 ) Before the improvement or repair is started; or
( 2 ) If the structure has been damaged, and is being restored, before the damage occurred; or
( B ) Any repair, reconstruction, modernization, or improvement of a structure, including a manufactured housing unit, that results in an increase of more than twenty percent in the number of dwelling units in a residential project or in the average peak number of customers and employees likely to be on-site at any one time for a commercial or industrial project.
( ii ) *Substantial improvement* may not be defined to include either: ( A ) Any project for improvement of a structure to comply with existing state or local health, sanitary or safety code specifications that is solely necessary to assure safe living conditions, or
( B ) Any alteration of a structure listed on the National Register of Historical Places or on a State Inventory of Historic Places.
( iii ) Structural repairs, reconstruction, or improvements not meeting this definition are considered “minor improvements”.
( 13 ) *Wetlands* means those areas that are inundated or saturated by surface or ground water with a frequency sufficient to support, and under normal circumstances does or would support, a prevalence of vegetative or aquatic life that requires saturated or seasonally saturated soil conditions for growth and reproduction. Wetlands generally include swamps, marshes, bogs, and similar areas such as sloughs, prairie potholes, wet meadows, river overflows, mud flats, and natural ponds. This definition includes those wetland areas separated from their natural supply of water as a result of activities such as the construction of structural flood protection methods or solid fill roadbeds and activities such as mineral extraction and navigation improvements. This definition includes both wetlands subject to and those not subject to Section 404 of the Clean Water Act as well as constructed wetlands.
[59 FR 19107, Apr. 21, 1994, as amended at 78 FR 68729, Nov. 15, 2013; 89 FR 30904, Apr. 23, 2024]