Common Flood Terminology Defined
Addition means any activity that expands the enclosed footprint or increases the square footage of an existing structure.
Base Flood or 100-year Flood means a flood having a recurrence interval that has a onepercent chance of being equaled or exceeded during any given year (1-percent-annual-chance flood). The terms “one-hundred-year flood” and “one percent chance flood ” are synonymous with the term “100-year flood”. The term does not imply that the flood will necessarily happen once every one hundred years.
Base Flood Elevation means the elevation shown on a FEMA Flood Insurance Rate Map for Zones AE, AH, AR, AR/A, AR/AE, AR/AH, and AR/AO that indicates the water surface elevation resulting from a flood that has a one percent chance of equaling or exceeding that level in any given year.
Basement means any area of a building having its floor subgrade (below ground level) on all sides.
Conditional Letter of Map Revision (CLOMR) means FEMA’s comment on a proposed project that would, after construction, affect the hydrologic or hydraulic characteristics of a stream or other flooding source and thus result in the modification of the existing FEMA regulatory floodplain, flood way, the effective Base Flood Elevations (“BFEs”), and/or the Special Flood Hazard Area (“SFHA”). A CLOMR does not revise an effective Flood Insurance Rate Map (FIRM), it indicates whether the resulting floodplain from the project, if built as proposed, would result in a FIRM change. Building permits cannot be issued based on a CLOMR. Once a project has been completed, the City of Centennial and Arapahoe County will require that a revision (“LOMR”) to the FIRM be submitted to FEMA to reflect the project.
Critical Facilities is a structure or related infrastructure, but not the land on which it is situated, that if flooded may result in significant hazards to public health and safety or interrupt essential services and operations for the community at any time before, during and after a flood.
Development means any manmade change to improved or unimproved real estate, including, but not limited to, buildings or other structures, dredging, filling, grading, paving, excavation, drilling operations, or storage of equipment or materials, channel improvements, channel rehabilitation, channel stability projects, flood control projects and stormwater detention facilities located within the floodplain.
Encroachment means an addition to or change to the physical condition of a specified type of flood hazard area that results in the blockage, diversion or displacement of floodwaters.
FEMA means the Federal Emergency Management Agency, the agency responsible for administering the National Flood Insurance Program (NFIP), or successor agency. FHAD (Flood Hazard Area Delineation)a flood study often prepared on a watershed basis by the Urban Drainage and Flood Control District. FHADs are adopted by the State and affected communities similar to LOMCs.FHADs are eventually submitted to FEMA as PMRs and become part of the updated FEMA FIRM map.
Fill means a deposit of materials of any kind placed by artificial means.
(D)FIRM – (Digital) Flood Insurance Rate Map means a digital version of the FEMA flood insurance rate map that is designed for use with digital mapping and analysis software.
Five-Hundred Year Floodplain means the area of land susceptible to being inundated as a result of the occurrence of a five-hundred-year flood.
Floatable Materials means any material that is not secured in place or completely enclosed in a structure, so that it could float off site during the occurrence of a flood and potentially cause harm to downstream property owners, or that could cause blockage of the channel or drainageway, a culvert, bridge or other drainage facility. This includes, without limitation, lumber, vehicles, boats, equipment, trash dumpsters, tires, drums or other containers, pieces of metal, plastic or any other item or material likely to float.
Flood or Flooding means a general and temporary condition of partial or complete inundation of normally dry lands areas from:
- The overflow of waters from channels, drainageway or reservoir spillways; and/or
- The unusual and rapid accumulation or runoff of surface waters from any source.
Flood Fringe means that portion of the one-hundred-year floodplain between the floodway boundary and the limits of the base floodplain. Sheet flow areas with flood depths of less than one (1) foot are not considered part of the flood fringe. Sheet flow areas with flood depths between one (1) and three (3) feet, inclusive, are part of the flood fringe.
Flood Insurance Rate Map (FIRM) means the official map on which the Federal Emergency Management Agency has delineated the areas of special flood hazard, designated as A Zones, which is applicable to the City of Centennial.
Floodplain or Flood-Prone Area means any land area susceptible to being inundated by water from any source (see definition of flooding) during a 100-year flood as defined by FEMA, FHADs, or channels or drainageways with tributary areas that are 130 acres or greater.
Floodplain Management means the 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 means zoning ordinances, subdivision regulations, building codes, health regulations, special purpose ordinances (such as a 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.
Floodproofing means any combination of structural and non-structural additions, changes, or adjustments to property and structures subject to flooding which reduce or eliminate flood damage to real estate or improved real property, water and sanitary facilities, structures and their contents in a flood-prone area. FEMA only recognizes floodproofing as a means for flood management for nonresidential structures.
Floodway means the channel of a river or other drainageway and the adjacent land areas that must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than one-half (0.5) foot.
Freeboard means the vertical distance, in feet, above the base flood elevation to which development must be elevated.
Historic Structure means any structure that is:
- Listed individually in the National Register of Historic Places (a listing maintained by the Department of the Interior) or preliminarily determined by the Secretary of the Interior as meeting the requirements for individual listing on the National Register;
- Certified or preliminarily determined by the Secretary of the Interior as contributing to the historical significance of a registered historic district or a district preliminarily determined by the Secretary to qualify as a registered historic district;
- Individually listed on a state inventory of historic places in states with historic preservation programs which have been approved by the Secretary of the Interior; or
- Individually listed on a local inventory of historic places in communities which historic preservation programs that have been certified either:
- An approved state program as determined by the Secretary of the Interior; or
- Directly by the Secretary of the Interior in states without approved programs.
Impacts means a change in the extent or elevation of the floodplain by development.
Letter of Map Amendment (LOMA) means a letter from FEMA officially amending the effective National Flood Insurance Rate Map, which establishes that a property is not located in a FEMA SFHA.
Letter of Map Revision Based on Fill (LOMR-F) means a letter from FEMA stating that a structure or parcel of land that has been elevated by fill outside the existing regulatory floodway, would not be inundated by the base flood.
Letter of Map Change (LOMC) means all letters of SFHA changes from FEMA including LOMR, LOMR-F, LOMAs and Physical Map Revisions (PMR).
Letter of Map Revision (LOMR) means a letter from FEMA officially revising the effective Flood Insurance Rate Map to show changes in zones, delineation and water surface elevation of floodplains and floodways.
Manufactured 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 connected to the required utilities.
Manufactured Home Park or Subdivision means a parcel (or continuous parcels) of land that is/are divided into two (2) or more lots for long-term lease or sale, with infrastructure designed for the installation of manufactured homes.
New Construction means development for which the start of construction commenced on or after November 10, 2013.
No-Rise means a calculated rise in flood depth of 0.00 feet as rounded to the nearest hundredth of a foot.
Nonstructural Development means any use of property that does not involve a structure. Nonstructural development may include, but is not limited to, the construction or installation of or use of a property for parking lots, utilities, detention ponds, fences, trails, pathways, outdoor storage, cultivation of vegetation or placement of fill.
Non-Substantial Improvements means any repair, reconstruction, rehabilitation, addition, or other improvement of a structure, the cost of which is less than fifty (50) percent of the market value of the structure before the start of construction of the improvement. The phrase does not, however, include:
- Any project for improvement of a structure to comply with existing state or local health, sanitary, or safety code specifications which are solely necessary to assure safe living conditions.
Obstruction means any physical barrier, structure, material or impediment in, along, across or projecting into a watercourse that may alter, impede, retard or change the direction or velocity of the flow of water, or that may, due to its location, have a propensity to snare or collect debris carried by the flow of water or to be carried downstream. Obstruction shall include, but not be limited to, any dam, wall, wharf, embankment, levee, dike, pile, abutment, protection, excavation, channelization, bridge, conduit, culvert, building, wire, fence, rock, gravel, refuse, fill, structure, and vegetation in, along, across or projecting into a watercourse.
One-Hundred Year Flood See Base Flood
One-Hundred Year Floodplain See Floodplain.
Shallow Flooding Areas (AO or AH Zones) means a designated Zone AO or Zone AH on the Flood Insurance Rate Map (FIRM) with a one percent chance or greater annual chance of flooding to an average depth of one to three feet where a clearly defined channel does not exist, where the path of flooding is unpredictable and where velocity flow may be evident. Such flooding is characterized by ponding or sheet flow.
Special Flood Hazard Area (SFHA) means the land subject to one (1) percent or greater chance of flooding in any given year, i.e. the 100 year floodplain. It is the land area covered by the floodwaters of the base flood on the Flood Insurance Rate Maps. The SFHA is the area where the National Flood Insurance Program’s floodplain management regulations must be enforced and the area where the mandatory purchase of flood insurance applies. The SFHA includes Zones A, AO, AH, AE, A99, AR, AR/AE, AR/AO, AR/AH, and AR/A.
Start of Construction includes Substantial Improvement, and means the date the building permit or GESC permit was issued. The actual start means the first placement of permanent construction of a structure on site, such as the pouring of slab or footings, the installation of piles, the construction of columns, or any work beyond the stage of excavation; or the 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 basement, footings, piers or foundation or the erection of temporary forms; nor does it include the installation on the property of accessory buildings, such as garages or sheds not occupied as dwelling units or not part of the main structure. For substantial improvement, the actual start of construction means the first alteration of any wall, ceiling, floor or other structural part of the building, whether or not that alteration affects the external dimension of the building.
- In general, anything constructed or erected, the use of which requires its permanent location on the ground (or its attachment to something having a permanent location on the ground), including but not limited to: garden walls, fences, signs, kiosks, or similar uses. The term “structure” does not include the word “building” unless the context clearly indicates otherwise,
- A walled and roofed building including a gas or liquid storage tank, or manufactured home that is principally above ground.
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 fifty (50) percent of the market value of the structure just prior to when the damage occurred improvement or cumulative improvements due to damage over ten (10) years.
Substantial Improvement means any repair, reconstruction, rehabilitation, addition, or other improvement of a structure, the cost of which equals or exceeds fifty (50) percent of the market value of the structure before the Start of Construction of the improvement or cumulative substantial improvements over ten (10) years. This phrase includes structures which have incurred Substantial Damage, regardless of the actual repair work performed. For the purposes of this definition, substantial improvement is considered to occur when the first alteration of any wall, ceiling, floor, or other structural part of the building commences, whether or not that alteration affects the external dimensions of the structure. The phrase does not, however, include either:
- Any project for improvement of a structure to comply with existing state or local health, sanitary, or safety code specifications which are solely necessary to assure safe living conditions; or
- Any alteration of a structure listed on the National Register of Historic Places or a State Inventory of Historic Places; provided that the alteration will not preclude the structure’s continued designation as a “historic structure.”
Unduly means improperly or unjustly. In the context of floodplain management, “unduly” is used to mean that a floodplain use shall not improperly or unjustly restrict the capacity of any channels or floodways.
Most Popular Pages
For Park, Metro Dist. & HOA Maint.
Information For Businesses
- GESC Considerations for Pipe Relining Operations
- GESC Considerations for Minor Right of Way/Streetscape Construction
- GESC Considerations for Minor Commercial Construction
- Annual Bore Utility Permits
- Land Development Review Process Explained
- Am I in the Floodplain?
- Working in the Floodplain
- Maintaining your pond or other stormwater feature
- Grant Program
- Pollution Prevention