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David Ballew,
Floodplain Manager

Building Commission
1 NW Martin Luther King Jr Blvd
Civic Center Complex, Room 310
Evansville, IN 47708
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  • Phone:  (812) 436-7872
  • Assistant:  (812) 436-7867
  • Business:  (812) 436-7885
  • Fax:  (812) 436-7869
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  • Hours: Monday-Friday, 8:00am-5:00pm

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Floodplain Terms and Definitions

A zone means portions of the SFHA in which the principal source of flooding is runoff from rainfall, snowmelt, or a combination of both. In A zones, floodwaters may move slowly or rapidly, but waves are usually not a significant threat to buildings. These areas are labeled as Zone A, Zone AE, Zones A1 – A30, Zone AO, Zone AH, Zone AR and Zone A99 on a FIRM or FHBM. The definitions are presented below:

Zone A: Areas subject to inundation by the one percent annual chance flood event. Because detailed hydraulic analyses have not been performed, no base flood elevation or depths are shown. Mandatory flood insurance purchase requirements apply.

Zone AE and A1 – A30: Areas subject to inundation by the one percent annual chance flood event determined by detailed methods. Base flood elevations are shown within these zones. Mandatory flood insurance purchase requirements apply. (Zone AE is on new and revised maps in place of Zones A1 – A30.)

Zone AO: Areas subject to inundation by one percent annual chance shallow flooding (usually sheet flow on sloping terrain) where average depths are between one and three feet. Average flood depths derived from detailed hydraulic analyses are shown within this zone. Mandatory flood insurance purchase requirements apply.

Zone AH: Areas subject to inundation by one percent annual chance shallow flooding (usually areas of ponding) where average depths are between one and three feet. Average flood depths derived from detailed hydraulic analyses are shown within this zone. Mandatory flood insurance purchase requirements apply.

Zone AR: Areas that result from the decertification of a previously accredited flood protection system that is determined to be in the process of being restored to provide base flood protection. Mandatory flood insurance purchase requirements apply.

Zone A99: Areas subject to inundation by the one percent annual chance flood event, but which will ultimately be protected upon completion of an under-construction Federal flood protection system. These are areas of special flood hazard where enough progress has been made on the construction of a protection system, such as dikes, dams, and levees, to consider it complete for insurance rating purposes. Zone A99 may only be used when the flood protection system has reached specified statutory progress toward completion. No base flood elevations or depths are shown. Mandatory flood insurance purchase requirements apply.

Accessory structure (appurtenant structure) means a structure that is located on the same parcel of property as the principal structure and the use of which is incidental to the use of the principal structure. Accessory structures should constitute a minimal initial investment, may not be used for human habitation, and should be designed to have minimal flood damage potential. Examples of accessory structures are detached garages, carports, storage sheds, pole barns, and hay sheds.

Addition (to an existing structure) means any walled and roofed expansion to the perimeter of a structure in which the addition is connected by a common load-bearing wall other than a firewall. Any walled and roofed addition, which is connected by a firewall or is separated by independent perimeter load-bearing walls, is new construction.

Area of shallow flooding means a designated AO or AH Zone on the community’s Flood Insurance Rate Map (FIRM) with base flood depths from one to three feet where a clearly defined channel does not exist, where the path of flooding is unpredictable and indeterminate, and where velocity flow may be evident. Such flooding is characterized by ponding or sheet flow.

Base flood elevation (BFE) means the elevation of the one percent annual chance flood.

Basement means that portion of a structure having its floor sub-grade (below ground level) on all sides. “Community” means a political entity that has the authority to adopt and enforce floodplain ordinances for the area under its jurisdiction.

Community Rating System (CRS) means a program developed by the Federal Insurance Administration to provide incentives for those communities in the regular program that have gone beyond the minimum floodplain management requirements to develop extra measures to provide protection from flooding.

Critical facility means a facility for which even a slight chance of flooding might be too great. Critical facilities include, but are not limited to, schools, nursing homes, hospitals, police, fire, and emergency response installations, and installations which produce, use or store hazardous materials or hazardous waste.

Development means any manmade change to improved or unimproved real estate for which local permits or approvals are required, including but not limited to:

(1) Construction, reconstruction, or placement of a building or any addition to a building;

(2) Installing a manufactured/mobile home on a site, preparing a site for a manufactured/mobile home or installing a recreational vehicle on a site for more than 180 days;

(3) Installing utilities, erection of walls and fences, construction of roads, or similar projects;

(4) Construction of flood control structures such as levees, dikes, dams, channel improvements, etc.;

(5) Mining, dredging, filling, grading, excavation, or drilling operations;

(6) Construction and/or reconstruction of bridges or culverts;

(7) Storage of materials;

(8) Creation of subdivisions for residential, commercial, or industrial use; or

(9) Any other activity that might change the direction, height, or velocity of flood or surface waters.

Development does not include activities such as the maintenance of existing buildings and facilities such as painting, re-roofing, resurfacing roads, or gardening, plowing, and similar agricultural practices that do not involve filling, grading, excavation, or the construction of permanent buildings.

Elevated structure means a non-basement structure built to have the lowest floor elevated above the ground level by means of fill, solid foundation perimeter walls, filled stem wall foundations (also called chain walls), pilings, or columns (posts and piers).

Elevation certificate is a certified statement that verifies a structure’s elevation information.

Emergency program means the first phase under which a community participates in the NFIP. It is intended to provide a first layer amount of insurance at subsidized rates on all insurable structures in that community before the effective date of the initial FIRM.

Encroachment means the advance or infringement of uses, fill, excavation, buildings, permanent structures or development into a floodplain, which may impede or alter the flow capacity of a floodplain.

Existing construction means any structure for which the “start of construction” commenced before the effective date of the community’s first floodplain ordinance.

Existing manufactured/mobile home park or subdivision means a manufactured/mobile home park or subdivision for which the construction of facilities for servicing the lots on which the manufactured/mobile homes are to be affixed (including, at a minimum, the installation of utilities, the construction of streets, and either final site grading or the pouring of concrete pads) is completed before the effective date of the floodplain management regulations adopted by the City and County.

Expansion to an existing manufactured/mobile home park or subdivision means the preparation of additional sites by construction of facilities for servicing the lots on which the manufactured/mobile homes are to be affixed (including the installation of utilities, the construction of streets, and either first site grading or the pouring of concrete pads).

FEMA means Federal Emergency Management Agency.

Five-hundred-year flood (500-year flood) means the flood that has a 0.2 percent chance of being equaled or exceeded in any year.

Flood means a general and temporary condition of partial or complete inundation of normally dry land areas from the overflow, the unusual and rapid accumulation, or the runoff of the surface waters from any source.

Flood Advisory Committee” means a committee which consists of the following members (or their designated representatives): Executive Director of the Area Plan Commission, Building Commissioner, City Engineer, County Engineer, County Surveyor, Soil Conservation Officer, and a designated representative of the Levee Authority. This committee may call, when necessary, upon other official agencies, including but not limited to the Health Department.

Flood boundary and floodway map (FBFM) means an official map on which the Federal Emergency Management Agency (FEMA) or Federal Insurance Administration (FIA) has delineated the areas of flood hazards and regulatory floodway.

Flood hazard boundary map (FHBM) means an official map of a community, issued by FEMA, where the boundaries of the areas of special flood hazard have been identified as Zone A.

Flood Insurance rate map (FIRM) means an official map of a community, on which FEMA has delineated both the areas of special flood hazard and the risk premium zones applicable to the community.

Flood Insurance study (FIS) is the official hydraulic and hydrologic report provided by FEMA. The report contains flood profiles, as well as the FIRM, FBFM (where applicable), and the water surface elevation of the base flood.

Flood-prone area means any land area acknowledged by a community as being susceptible to inundation by water from any source. See “flood.”

Flood protection grade (FPG) is the elevation of the regulatory flood plus two feet at any given location in the SFHA. See “freeboard.”

Floodplain means the channel proper and the areas adjoining any wetland, lake, or watercourse which have been or hereafter may be covered by the regulatory flood. The floodplain includes both the floodway and the fringe districts.

Floodplain Management means the operation of an overall program of corrective and preventive measures for reducing flood damage and preserving and enhancing, where possible, natural resources in the floodplain, including but not limited to emergency preparedness plans, flood control works, floodplain management regulations, and open space plans.

Floodplain Management regulations means this chapter and other zoning ordinances, subdivision regulations, building codes, health regulations, special purpose ordinances, and other applications of police power which control development in flood-prone areas. This term describes Federal, State, or local regulations in any combination thereof, which provide standards for preventing and reducing flood loss and damage. Floodplain management regulations are also referred to as floodplain regulations, floodplain ordinance, flood damage prevention ordinance, and floodplain management requirements.

Floodproofing (dry floodproofing) is a method of protecting a structure that ensures that the structure, together with attendant utilities and sanitary facilities, is watertight to the floodproofed design elevation with walls that are substantially impermeable to the passage of water. All structural components of these walls are capable of resisting hydrostatic and hydrodynamic flood forces, including the effects of buoyancy, and anticipated debris impact forces.

Floodproofing certificate is a form used to certify compliance for nonresidential structures as an alternative to elevating structures to or above the FPG. This certification must be by a registered professional engineer or architect.

Floodway means the channel of a river, stream, creek or ditch and those portions of the floodplains adjoining the channel which are reasonably required to efficiently carry and discharge the peak flood flow of the regulatory flood of any river or stream.

Freeboard means a factor of safety, usually expressed in feet above the BFE, which is applied for the purposes of floodplain management. It is used to compensate for the many unknown factors that could contribute to flood heights greater than those calculated for the base flood.

Fringe is those portions of the floodplain lying outside the floodway.

Functionally dependent facility means a facility which cannot be used for its intended purpose unless it is located or carried out in close proximity to water, such as a docking or port facility necessary for the loading and unloading of cargo or passengers, shipbuilding, ship repair, or seafood processing facilities. The term does not include long-term storage, manufacture, sales, or service facilities.

Hardship (as related to variances of this chapter) means the exceptional hardship that would result from a failure to grant the requested variance. The Flood Advisory Committee requires that the variance is exceptional, unusual, and peculiar to the property involved. Mere economic or financial hardship alone is not exceptional. Inconvenience, aesthetic considerations, physical handicaps, personal preferences, or the disapproval of one’s neighbors likewise cannot, as a rule, qualify as an exceptional hardship. All of these problems can be resolved through other means without granting a variance, even if the alternative is more expensive or requires the property owner to build elsewhere or put the parcel to a different use than originally intended.

Highest adjacent grade means the highest natural elevation of the ground surface, prior to the start of construction, next to the proposed walls of a structure.

Historic structure means any structure individually listed on the National Register of Historic Places or the Indiana State Register of Historic Sites and Structures.

IDNR means the Indiana Department of Natural Resources.

Increased cost of compliance (ICC) means the cost to repair a substantially damaged structure that exceeds the minimal repair cost and that is required to bring a substantially damaged structure into compliance with the local flood damage prevention ordinance. Acceptable mitigation measures are elevation, relocation, demolition, or any combination thereof. All renewal and new business flood insurance policies with effective dates on or after June 1, 1997, will include ICC coverage.

Letter of map amendment (LOMA) means an amendment to the currently effective FEMA map that establishes that a property is not located in a special flood hazard area (SFHA). A LOMA is only issued by FEMA.

Letter of map revision (LOMR) means an official revision to the currently effective FEMA map. It is issued by FEMA and changes flood zones, delineations, and elevations.

Letter of map revision based on fill (LOMR-F) means an official revision by letter to an effective NFIP map. A LOMR-F provides FEMA’s determination concerning whether a structure or parcel has been elevated on fill above the BFE and excluded from the SFHA.

Lowest adjacent grade means the lowest elevation, after completion of construction, of the ground, sidewalk, patio, deck support, or basement entryway immediately next to the structure.

Lowest floor means the lowest of the following:

(1) The top of the lowest floor of a building;

(2) The top of the basement floor;

(3) The top of the garage floor, if the garage is the lowest level of the building;

(4) The top of the first floor of buildings elevated on pilings or pillars;

(5) The top of the floor level of any enclosure, other than a basement, below an elevated building where the walls of the enclosure provide any resistance to the flow of floodwaters, unless:

(a) The walls are designed to automatically equalize the hydrostatic flood forces on the walls by allowing for the entry and exit of floodwaters, through providing a minimum of two openings (in addition to doorways and windows) in a minimum of two exterior walls having a total net area of one square inch for every one square foot of enclosed floor area subject to flooding. The bottom of all such openings shall be no higher than one foot above the exterior grade or the interior grade immediately beneath each opening, whichever is higher.

(b) Such enclosed space shall not be designed or finished for occupancy and contain any equipment which could be damaged by flooding. The use of the enclosed space shall be usable for the parking of vehicles and building access shall be allowed.

Manufactured/mobile home means 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/mobile home” does not include a “recreational vehicle.”

Manufactured/mobile home park or subdivision means a parcel (or contiguous parcels) of land divided into two or more manufactured home lots for rent or sale.

Map amendment means a change to an effective NFIP map that results in the exclusion from the SFHA of an individual structure or a legally described parcel of land that has been inadvertently included in the SFHA (i.e., no alterations of topography have occurred since the date of the first NFIP map that showed the structure or parcel to be within the SFHA).

Map panel number is the four-digit number followed by a letter suffix assigned by FEMA on a flood map. The first four digits represent the map panel, and the letter suffix represents the number of times the map panel has been revised. (The letter “A” is not used by FEMA, the letter “B” is the first revision.) “Market value” means the building value, excluding the land (as agreed to between a willing buyer and seller), as established by what the local real estate market will bear. Market value can be established by independent certified appraisal, replacement cost depreciated by age of building (actual cash value), or adjusted assessed values.

Mitigation means sustained actions taken to reduce or eliminate long-term risk to people and property from hazards and their effects. The purpose of mitigation is twofold: to protect people and structures, and to minimize the cost of disaster response and recovery.

National Flood Insurance Program (NFIP) is the Federal program that makes flood insurance available to owners of property in participating communities nationwide through the cooperative efforts of the Federal government and the private insurance industry.

National Geodetic Vertical Datum (NGVD) of 1929 as corrected in 1929 is a vertical control used as a reference for establishing varying elevations within the floodplain.

New construction means any structure for which the “start of construction” commenced after the effective date of the community’s first floodplain ordinance.

New manufactured/mobile home park” or “new manufactured/mobile home subdivision means a manufactured/mobile home park or manufactured/mobile home subdivision for which the construction of facilities for servicing the lots on which the manufactured/mobile homes are to be affixed (including, at a minimum, the installation of utilities, the construction of streets, and either final site grading or the pouring of concrete pads) is completed on or after the effective date of the floodplain management regulations adopted by the City and County.

North American Vertical Datum of 1988 (NAVD 88) as adopted in 1993 is a vertical control datum used as a reference for establishing varying elevations within the floodplain.

Obstruction includes, but is not limited to, any dam, wall, wharf, embankment, levee, dike, pile, abutment, protection, excavation, canalization, bridge, conduit, culvert, building, wire, fence, rock, gravel, refuse, fill, structure, vegetation, or other material in, along, across or projecting into any watercourse which may alter, impede, retard or change the direction and/or velocity of the flow of water; or due to its location, its propensity to snare or collect debris carried by the flow of water, or its likelihood of being carried downstream.

One-hundred-year flood (100-year flood) is the flood that has a one percent chance of being equaled or exceeded in any given year. Any flood zone that begins with the letter A is subject to the one percent annual chance flood. See “regulatory flood.”

One percent annual chance flood is the flood that has a one percent chance of being equaled or exceeded in any given year. Any flood zone that begins with the letter A is subject to the one percent annual chance flood. See “regulatory flood.”

Participating community is any community that voluntarily elects to participate in the NFIP by adopting and enforcing floodplain management regulations that are consistent with the standards of the NFIP.

Physical map revision (PMR) is an official republication of a community’s FEMA map to effect changes to base (one percent annual chance) flood elevations, floodplain boundary delineations, regulatory floodways, and planimetric features. These changes typically occur as a result of structural works or improvements, annexations resulting in additional flood hazard areas, or correction to base flood elevations or SFHAs.

Post-FIRM construction means construction or substantial improvement that started on or after the effective date of the initial FIRM of the community or after December 31, 1974, whichever is later.

Pre-FIRM construction means construction or substantial improvement which started on or before December 31, 1974, or before the effective date of the initial FIRM of the community, whichever is later.

Public safety and nuisance means anything which is injurious to the safety or health of an entire community, neighborhood or any considerable number of persons, or unlawfully obstructs the free passage or use, in the customary manner, of any navigable lake, river, bay, stream, canal, or basin.

Recreational vehicle means a vehicle which is (1) built on a single chassis; (2) 400 square feet or less when measured at the largest horizontal projections; (3) designed to be self-propelled or permanently towable by a light-duty truck; and (4) designed primarily not for use as a permanent dwelling, but as temporary living quarters for recreational camping, travel, or seasonal use.

Regular program means the phase of the community’s participation in the NFIP where more comprehensive floodplain management requirements are imposed and higher amounts of insurance are available based upon risk zones and elevations determined in a FIS.

Regulatory flood means the flood having a one percent probability of being equaled or exceeded in any given year, as calculated by a method and procedure which are acceptable to and approved by the IDNR and the Federal Emergency Management Agency. The regulatory flood elevation at any location is as defined in EMC 16.10.050.

The regulatory flood is also known by the term “base flood.”

Repetitive loss means flood-related damages sustained by a structure on two separate occasions during a 10-year period ending on the date of the event for which the second claim is made, in which the cost of repairing the flood damage, on the average, equaled or exceeded 25 percent of the market value of the structure at the time of each such flood event.

Section 1316 is that section of the National Flood Insurance Act of 1968, as amended, which states that no new flood insurance coverage shall be provided for any property that the Administrator finds has been declared by a duly constituted State or local zoning authority or other authorized public body to be in violation of State or local laws, regulations, or ordinances that intended to discourage or otherwise restrict land development or occupancy in flood-prone areas.

Special flood hazard area (SFHA) means those lands within the jurisdictions of the City subject to inundation by the regulatory flood. The SFHAs of the City of Evansville are generally identified as such on the Vanderburgh County, Indiana and Incorporated Areas Flood Insurance Rate Map prepared by the Federal Emergency Management Agency, dated March 17, 2011. (These areas are shown on a FHBM or FIRM as Zone A, AE, A1 – A30, AH, AR, A99, or AO).

Start of construction includes substantial improvement, and means the date the building permit was issued, provided the actual start of construction, repair, reconstruction, or improvement was within 180 days of the permit date. The “actual start” means the first placement or permanent construction of a structure (including a manufactured home) on a site, such as the pouring of slabs or footing, installation of piles, construction of columns, or any work beyond the stage of excavation for placement of a manufactured home on a foundation. Permanent construction does not include land preparation, such as clearing, grading and filling; nor does it include the installation of streets and/or walkways; nor does it include excavation for a basement, footings, piers, foundations, or the erection of temporary forms. For substantial improvement, the actual start of construction means the first alteration of any wall, ceiling, floor, or other structural part of a building, whether or not that alteration affects the external dimensions of the building.

Structure means a structure that is principally above ground and is enclosed by walls and a roof; including, but not limited to, buildings, walls, signs, pools, gas or liquid storage tanks, and manufactured/mobile homes. The term also includes recreational vehicles to be installed on a site for more than 180 days.

Substantial damage means damage of any origin sustained by a structure whereby the cost of restoring the structure to its before-damaged condition would equal or exceed 40 percent of the market value of the structure before the damage occurred.

Substantial improvement means any reconstruction, rehabilitation, addition, or other improvement of a structure, the cost of which equals or exceeds 40 percent of the market value of the structure before the start of construction of the improvement. This term includes structures which have incurred substantial damage regardless of the actual repair work performed. The term does not include improvements of structures to correct existing violations of State or local health, sanitary, or safety code requirements or any alteration of a historic structure; provided, that the alteration will not preclude the structures continued designation as a historic structure.

Variance is a grant of relief from the requirements of this chapter, which permits construction in a manner otherwise prohibited by this chapter where specific enforcement would result in unnecessary hardship.

Violation means the failure of a structure or other development to be fully compliant with this chapter. A structure or other development without the elevation, other certification, or other evidence of compliance required in this chapter, is presumed to be in violation until such time as that documentation is provided.

Watercourse means a lake, river, creek, stream, wash, channel or other topographic feature on or over which waters flow at least periodically.

Watercourse includes specifically designated areas in which substantial flood damage may occur.

Water surface elevation means the height, in relation to the North American Vertical Datum of 1988 (NAVD 88) or National Geodetic Vertical Datum of 1929 (NGVD) (other datum where specified) of floods of various magnitudes and frequencies in the floodplains of riverine areas.

X zone means the area where the flood hazard is less than that in the SFHA. Shaded X zones shown on recent FIRMs (B zones on older FIRMs) designate areas subject to inundation by the flood with a 0.2 percent chance of being equaled or exceeded (the 500-year flood). Unshaded X zones (C zones on older FIRMs) designate areas where the annual exceedance probability of flooding is less than 0.2 percent.

Zone means a geographical area shown on a FHBM or FIRM that reflects the severity or type of flooding in the area. Zone A. See definition for “A zone.”

Zones B, C, and X means areas identified in the community as areas of moderate or minimal hazard from the principal source of flood in the area. However, buildings in these zones could be flooded by severe, concentrated rainfall coupled with inadequate local drainage systems. Flood insurance is available in participating communities but is not required by regulation in these zones. (Zone X is used on new and revised maps in place of Zones B and C.)