Chapter 8

Flood Hazard Regulations

11-08-01: General Provisions


1. Chapter Purpose:

A. The flood hazard areas of Boise City, Idaho, are subject to periodic inundation, which may result in loss of life and property, health and safety hazards, disruption of commerce and government services, extraordinary public expenditures for flood protection and relief, and impairment of the tax base, all of which adversely affect the public health, safety and general welfare.

B. Flood losses are caused by natural forces and construction practices which increase flood heights and velocities, and by structures which are inadequately anchored and which may damage property in other areas. Uses that are inadequately flood-proofed, elevated or otherwise unprotected from flood damage also contribute to flood losses.

C. It is the purpose of this chapter to promote public health, safety, and general welfare, and to minimize public and private losses due to flood conditions in specific areas by provisions designed:

(1) To protect human life and health;

(2) To minimize expenditures of public money and costly flood control projects;

(3) To minimize the need for rescue and relief efforts associated with flooding which are generally undertaken at the expense of the general public;

(4) To minimize prolonged business interruptions;

(5) To minimize damage to public facilities and utilities such as water and gas mains; electric, telephone and sewer lines; and streets and bridges located in Areas of Special Flood Hazard;

(6) To help maintain a stable tax base by providing for the sound use and development of areas of special flood hazard so as to minimize future flood blight areas;

(7) To ensure that potential buyers are notified when property is in an Area of Special Flood Hazards; and

(8) To ensure that those who occupy the Areas of Special Flood hazard assume responsibility for their actions.


2. Methods Of Reducing Flood Losses: This chapter describes guidelines and provisions for:

A. Restricting or prohibiting uses which are dangerous to health, safety, and property due to water or erosion hazards, or which resulting damaging increases in erosion or in flood heights or velocities;

B. Requiring that uses vulnerable to floods, including facilities which serve such uses, be protected against flood damage at the time of initial construction;

C. Controlling the alteration of natural floodplains, stream channels, and natural protective barriers, which help accommodate or channel flood waters;

D. Controlling filling, grading, dredging, and other development which may increase flood damage; and

E. Preventing or regulating the construction of flood barriers which will unnaturally divert flood water or may increase flood hazards in other areas.


3. Applicability: The provisions of this chapter shall apply to all areas of special flood hazard, within the jurisdiction of Boise City, and as such lands are identified, within the Floodway, Floodway Fringe, or the Area of Shallow Flooding. The areas of special flood hazard are identified by the Federal Emergency Management Agency in a scientific and engineering report entitled "Flood Insurance Study" for Ada County, Idaho, and incorporated areas dated February 19, 2003, which includes Flood Insurance Rate Maps, and flood profiles, along with all subsequent amendments which are hereby adopted by reference and declared to be a part of this chapter. The Flood Insurance Study is on file with the Boise City Planning Director, Boise City Planning and Development Services Director, and the Boise City Engineer, Department of Public Works.


4. Creation Of Zones: The Floodway Zone, the Floodway Fringe (FF) Zone and Area of Shallow Flooding (ASF) Zone: The Floodway zone, the Floodway Fringe Zone and Area of Shallow Flooding Zone are hereby created and shall have the boundaries as defined in this chapter (Section 11-08-08) and shall have the requirements as set forth in this chapter.


5. Exclusions: Upon issuance of a Letter of Map Amendment or Letter of Map Revision, such land shall be deemed to be automatically excluded from the Floodway, Floodway Fringe and Area of Shallow Flooding.


6. Compliance: No new development shall hereafter occur within the Area of Special Flood Hazard (ASFH) unless such new development is undertaken in full compliance with this chapter. Enforcement of violations shall be in accordance with Section 11-01-08-8.


7. Abrogation & Greater Restrictions: The provisions of this chapter shall be in addition to, and shall not be deemed to repeal, abrogate, or impair any other ordinance, regulation, easement, covenant or deed restriction. In the event that the provisions of this and any other ordinance, regulation, easement, covenant or deed restriction conflict or overlap, whichever has the more restrictive requirements shall control.


8. Severability: Each section, clause, and provision of this Code is declared severable as per Section 11-01-06.


9. Interpretation: All of the provisions of this chapter shall be liberally construed in favor of the governing body and shall not be deemed to limit or repeal any other powers granted under state statutes.


10. Warning And Disclaimer: The degree of flood protection required by this chapter is considered reasonable for regulatory purposes and is based on scientific and engineering considerations. Larger floods can and will occur on rare occasions. Flood heights may be increased due to artificial or natural causes. This chapter does not imply that lands outside the identified areas of special flood hazard will be free from flooding or flood damages or that uses permitted within the identified areas of special flood hazard will be free from flooding or flood damages. This chapter shall not create liability on the part of Boise City, or any officer or employee thereof, for any flood damages that result from reliance on this chapter or any administrative decision lawfully made hereunder.

11-08-02: Floodway Zone


1. Permitted Uses: All uses permitted by the base zone district within this Code, and as amended are permitted in Floodway Zones to the extent that the uses are consistent with the standards of this Section.


2. Standards:

A. No new development shall be permitted including fill, new construction, substantial improvements or other development, unless

(1) It is public infrastructure, including but not limited to bridges, roadways, sewer and water lines, and

(2) A licensed professional engineer certifies that there is not any increase in flood levels during the occurrence of the Base Flood discharge, either as a result of the development or its cumulative effect.

B. All new development, new construction and substantial improvements shall comply with the applicable standards for uses in the Floodway Fringe.

C. Existing structures in the Floodway Zone which are displaced by floodwater shall not be reconstructed.

D. No alteration or relocation of a water course shall be permitted which would diminish the flood carrying capacity of the water course, or which would result in the flooding of lands which are not subject to flooding prior to such alteration or relocation of the water course, or which will result in adverse effects on other properties including but not limited to, bank erosion resulting from higher velocities, increased heights of floodwaters, extended flood duration, or alterations that may promote channel blockage.

E. Uses on parcels which include any portion of a floodway shall provide for channel stabilization, bank stabilization, or a setback from the edge of the floodway sufficient to protect the use from flood related erosion. Such measures shall be reviewed by a licensed professional engineer for effectiveness for the flood flow and velocity conditions anticipated at the site.

F. Check dams shall be designed and reviewed by a licensed professional engineer, and reviewed and approved by the Boise City Engineer to ensure the safety of persons and property which could be affected by the construction of the check dam.

G. In areas where a regulatory floodway has not been designated, no new construction, substantial improvements, other development (Including fill) shall be permitted within zones A1-30 and AE on the community's FIRM, unless it is demonstrated that the cumulative effect of the proposed development, when combined with all other existing and anticipated development, will not increase the water surface elevation of the base flood more than two feet at any point within the community.


3. Prohibited Uses:

A. New construction or substantial improvements of residential and non-residential structures, including both principal and accessory use structures, except as provided in 11-08-02.2.

B. Manufacture and storage of materials which are buoyant, flammable, toxic or explosive, or which may present a hazard to public health or safety in time of flooding.

C. Standards for Sand and Gravel Extraction - Material stockpiles and permanently installed structures shall not be located within the floodway.


4. Relocating The Floodway (Line):

A. All proposals to redefine the floodway boundary lines require a resolution from the Boise City Council to adopt the amendments to the Floodway Insurance Rate Map, Floodway Boundary Maps, Floodway Maps, and the Flood Profiles. The procedure shall include a review by the U.S. Army Corps of Engineers, the Federal Emergency Management Agency, the Boise City Department of Public Works, and the Boise City Planning and Development Services Department, prior to submittal to the City Council.

B. The Floodway Boundary Line may be relocated due to refinements of the floodway calculations based upon new information concerning the existing conditions.

C. The floodway boundary line may not be relocated through physical alterations to the lands in the floodplain.

11-08-03: Floodway Fringe (ff) Zone And Area Of Shallow Flooding (asf) Zone


1. Permitted Uses: All uses permitted in the base zone district within the this Code and as amended, are permitted in the Floodway Fringe Zone and Area of Shallow Flooding Zone to the extent that such uses are consistent with the standards within this Section.


2. Standards:

A. Uses:

(1) Except for levees, all new development shall utilize methods and practices that minimize development and prevent the increase in flood damage potential to other properties or other adverse impacts including but not limited to, bank erosion resulting from higher velocities, increased heights of floodwaters, extended flood duration, or alterations that may promote channel blockage.

(2) All new development shall utilize materials and utility equipment resistant to flood damage.

(3) All new construction and substantial improvements to structures shall be anchored to prevent flotation, collapse or lateral movement of the structure.

(4) All manufactured homes must likewise be anchored to prevent flotation, collapse, or lateral movement, and shall be installed using methods and practices that minimize flood damage. Anchoring methods may include, but are not limited to; use of over-the-top or frame ties to ground anchors (Reference FEMA's "Manufactured Home Installation in Flood Hazard Areas" guidebook for additional techniques).

(5) Drainage practices shall be utilized which minimize exposure to flood hazards.

(6) Manufacture and/or storage of material which is buoyant, flammable, toxic or explosive is prohibited.

(7) River crossings shall be designed to withstand the flows and velocities of the base flood discharge and shall not impede the flows.

(8) All development and structures shall meet or exceed the requirements of Section 11-05-06 Boise River System Overlay District if applicable.

(9) Water velocities within the floodway fringe are not significantly increased so as to cause adverse effects on the site or to surrounding properties.

(10) Require adequate drainage paths around structures on slopes to guide floodwaters around and away from proposed structures.

B. Utilities:

(1) All new and replacement water supply systems shall be designed to prevent infiltration of flood waters into the systems.

(2) New and replacement wastewater disposal systems shall be designed to minimize or eliminate infiltration of flood waters into the systems and discharge from the systems into flood waters.

(3) On-site waste disposal systems are prohibited in the Floodway Fringe Zone and Area of Shallow Flooding Zone.

(4) Electrical, heating, ventilation, plumbing, and air-conditioning equipment and other service facilities shall be designed and/or otherwise elevated or located so as to prevent water from entering or accumulating within the components during conditions of flooding.

C. Subdivisions:

(1) All subdivision proposals shall be consistent with the need to minimize flood damage.

(2) All subdivision proposals shall have public utilities and facilities such as sewer, gas, electrical, and water systems located and constructed to minimize flood damage.

(3) All subdivision proposals shall have adequate drainage to reduce exposure to flood damage.

(4) Base flood elevation data shall be provided and shown on the preliminary plat for all subdivision proposals. Such elevation data shall be certified by a licensed professional engineer or registered land surveyor.Where base flood elevation data has not been provided or is not available from another authorized source, it shall be generated for subdivision proposals and other proposed developments which contain at least 50 lots or 5 acres (whichever is less).

D. Residential Structures:

(1) New construction and substantial improvement of any residential structure (including but not limited to mobile or manufactured homes) located in the Floodway Fringe shall have the lowest floor including basement, elevated one foot above the base flood elevation.

(2) New construction and substantial improvement of any residential structure located in the Area of Shallow Flooding (AO Flood Zone) shall have the lowest floor, including basement, elevated to the base flood elevation. The height of the adjacent grade and the lowest floor including basement and/or the first floor shall be certified by a licensed professional engineer or registered land surveyor.

(3) Fully enclosed areas below the lowest floor that are subject to flooding shall be designed to automatically equalize hydrostatic flood forces on exterior walls by allowing for the entry and exit of floodwaters. Designs for meeting this requirement must either be certified by a registered professional engineer and must meet or exceed the following minimum criteria:

(a) A minimum of two openings having a total net area of not less than one square inch for every square foot of enclosed area subject to flooding shall be provided.

(b) The bottom of all openings shall be no higher than one foot above grade.

(c) Openings may be equipped with screens, louvers, or other coverings or devices provided that they permit the automatic entry and exit of floodwaters.

E. Manufactured Homes:

(1) All manufactured homes shall be placed or substantially improved on sites:

(a) Outside of a manufactured home park or subdivision;

(b) In a new manufactured home park or subdivision;

(c) In an expansion to an existing manufactured home park or subdivision; or

(d) In an existing manufactured home park or subdivision on which a manufactured home has incurred substantial damage as the result of a flood.

(2) All manufactured homes shall be elevated on a permanent foundation such that the lowest floor of the manufactured home is elevated to or above the base flood elevation and be securely anchored to an adequately anchored foundation system to resist flotation, collapse and lateral movement.

(3) Manufactured homes to be placed or substantially improved on sites in an existing manufactured home park or subdivision that are not subject to the provisions of "A" above, be elevated so that either:

(a) The lowest floor of the manufactured home is at or above the base flood elevation, or

(b) The manufactured home chassis is supported by reinforced piers or other foundation elements of at least equivalent strength that are no less than 36 inches in height above grade and be securely anchored to an adequately anchored foundation system to resist flotation, collapse, and lateral movement.

F. Nonresidential Structures:

(1) Elevating: New construction and substantial improvement of any nonresidential structures shall meet the following:

When located in the Floodway Fringe, such structures shall have the lowest floor, including basement, elevated to one foot above the base flood elevation. When located in the Area of Shallow Flooding, such structures shall have the lowest floor, including basement, elevated to the level of the base flood elevation.

(a) Elevations of adjacent grade and the first floor shall be certified by a licensed professional engineer or registered land surveyor to the Building Director.

(b) Nonresidential structures that are elevated, but not floodproofed, must meet the same standards for space below the first floor as described in subsection D above.

(2) Flood-proofing: In lieu of elevating nonresidential structures as required in this Section, new construction and substantial improvement of any nonresidential structures shall meet the following:

(a) When located in the Floodway Fringe, such structures together with attendant utility and sanitary facilities shall be flood-proofed to one foot above the base flood level so the structure is watertight with walls substantially impermeable to the passage of water.

(b) When located in the Area of Shallow Flooding, such structures, together with attendant utility and sanitary facilities, shall be flood-proofed to the base flood level so the structure is watertight with walls substantially impermeable to the passage of water.

(c) Such flood-proofing may not be required if a licensed professional engineer certifies that such flood-proofing is not necessary to resist hydrostatic and hydrodynamic loads and the effects of buoyancy because uplift will not occur due to the nature of the flood, provided however, that flood-proofing of attendant utility and sanitary facilities is still required.

(d) Structural components shall be capable of resisting hydrostatic and hydrodynamic loads and the effects of buoyancy.

(e) A licensed professional engineer shall certify that the design and methods of construction are in accordance with accepted standards of practice for meeting provisions of this Section based on their review of the structural design, specifications and plans. Such certifications shall be provided to the Planning Director.

G. Accessory Structures And Uses:

(1) New accessory structures are prohibited in the floodway. Accessory structures shall not exceed the following standards if constructed or placed in the Floodway Fringe:

(a) Accessory structures to nonresidential principal uses shall meet the standards listed for nonresidential structures (subsection F above) if the accessory structure exceeds 1,000 square feet in size.

(b) Accessory structures to residential principal uses shall not exceed 1,000 square feet in size; or 40 percent of the area of the rear yard of the property; or have construction costs of more than 10 percent of the market value of the principal residential structure, whichever is the least.

(2) Accessory structures and uses shall be designed to have a low flood damage potential and shall be placed on the building site and constructed so as to offer the minimum resistance to the flow of floodwaters.

(3) Accessory structures shall meet the requirements of subsection A above, Standards for Uses.

H. Recreational Vehicles: Recreational vehicles placed on sites within areas of special flood hazard (ASFH) or areas of shallow flooding (ASF) as identified on the City's most recently adopted Flood Insurance Rate Map (FIRM) shall either:

(1) Be on the site for fewer than 180 consecutive days, or

(2) Be fully licensed and ready for highway use, or

(3) Meet the permit and elevation requirements for residential structures (subsection D above) and the anchoring requirements for manufactured homes (subsection E above).

11-08-04: Unnumbered "a Zones"


1. Permitted Uses: All uses permitted in the Base Zone District within this Code and as amended, are permitted in the Unnumbered "A Zone" to the extent that such uses are consistent with the standards within this Section.


2. Standards:

A. Uses:

(1) The use shall meet the standards listed in the standards for uses in the Floodway Fringe Zone and Area of Shallow Flooding Zone (Section 11-08-03.2.A).

(2) Where elevation data is not available either through the Flood Insurance Study or from another authoritative source (Section 11-8-01.3), applications for building permits shall be reviewed to assure that proposed construction will be reasonably safe from flooding. The test of reasonableness is a local judgment and includes use of historical data, high water marks, photographs of past flooding, etc., where available. Failure to elevate at least two feet above grade in these zones may result in higher insurance rates.

(3) Require adequate drainage paths around structures on slopes to guide floodwaters around and away from proposed structures.

B. Utilities: The utilities shall meet the standards listed for utilities in the Floodway Fringe Zone and Area of Shallow Flooding Zone (Section 11-08-03.2.B).

C. Subdivisions: The subdivision shall meet the standards listed for subdivisions in the Floodway Fringe Zone and Area of Shallow Flooding Zone (Section 11-08-03.2.C).

D. Standards For Residential Structures: The residential structures shall meet the standards for residential structures listed in Floodway Fringe Zone and Area of Shallow Flooding Zone (Section 11-08-03.2.D).

11-08-05: Critical Facilities


Construction of new critical facilities shall be, to the extent possible, located outside the limits of the Special Flood Hazard Area (SFHA) (100-year floodplain). Construction of new critical facilities shall be permissible within the SFHA if no feasible alternative site is available. Critical facilities constructed within the SFHA shall have the lowest floor elevated three feet or to the height of the 500-year flood, whichever is higher. Access to and from the critical facility should also be protected to the height utilized above. Flood-proofing and sealing measures must be taken to ensure that toxic substances will not be displaced by or released into floodwaters. Access routes elevated to or above the level of the base flood elevation shall be provided to all critical facilities to the extent possible.

11-08-06: Administration


1. Duties Of The Floodplain Administrator (Boise Planning Director): The Boise City Planning Director is hereby appointed to administer and implement this chapter and, as the Floodplain Administrator, shall perform the following duties:

A. Review Applications: Review all applications for Base Zone District changes, subdivisions, special use permits, conditional use permits and planned developments to determine:

(1) If the development is within an area of special flood hazard;

(2) To determine that all necessary permits have been obtained from those federal, state, or local governmental agencies from which prior approval is required; and

(3) For compliance with the provisions of this chapter and disclose to the PZC and Council whether the application is, or is not, in compliance with the provisions of this chapter.

B. Interpretations:

(1) Make interpretations of the location of the boundaries of the Floodway and the Floodway Fringe.

(2) When uncertainty exists as to whether a new development is within an Area of Special Flood Hazard, determine whether development is within the Floodway or Floodway Fringe.

C. Zoning Certificates: Issues zoning certificates for those structures which are to be constructed or modified in compliance with the provisions of this chapter and the other applicable provisions of this code.

D. Variances: Variances may be issued by the Director for the reconstruction, rehabilitation or restoration of structures listed on the National Register of Historic Places or the State Inventory of Historic Places, without regard to the procedures set forth in this chapter.

E. Available Data: Obtain, review, and reasonably utilize any base flood elevation and floodway data available from a federal, state or other source when such data has not been provided in the Flood Insurance Study.

F. Record Keeping: Compile and maintain for public inspection all records pertaining to the provisions of this chapter, including records of all appeal actions and variances, records of first floor elevations, flood-proofing certificates, letters of map amendment and all other records required by this chapter and by federal regulations.

G. Notification: Notify adjacent jurisdictions and the Idaho Department of Water Resources prior to any alteration or relocation of a watercourse, and submit evidence of such notification to the Federal Emergency Management Agency; and require that maintenance be provided within the altered or relocated portion of such watercourse so that the flood carrying capacity of the watercourse is not diminished.

H. Annual Reports: Submit annual reports, and other reports to the Federal Emergency Management Agency, as required and as requested.

I. Engineer Certification:

(1) Require that for all new or substantially improved structures in an Area of Special Flood Hazard along the Boise River or in the gulches, a licensed professional engineer or registered land surveyor certify the actual elevation (in relation to mean sea level) of the lowest floor (including basement) of the structure; and record the certified elevation and whether or not the structure contains a basement.

(2) Require that for all new or substantially improved structures in an Area of Shallow Flooding in an Area of Special Flood Hazard, a licensed professional engineer or registered land surveyor shall certify the actual height in feet, as measured from the building edges at the lowest floor height to the highest ground which surrounds the building and record the certified height and whether or not the structure contains a basement.

(3) Require that for all new or substantially improved flood-proofed non-residential structures; a licensed professional engineer or registered land surveyor certify that the actual elevation (in relation to mean sea level) to which the structure is flood-proofed; and the Boise City Planning and Development Services Director shall maintain copies of the flood-proofing certificates as required in this chapter.

J. Permit Issuance: Issue building or grading permits for new construction, new development, and substantial improvement to structures which are in compliance with the provisions of this Ordinance.


2. Duties Of The Boise City Engineer: Upon request from the Director, the Boise City Engineer shall provide technical assistance and information including but not limited to verify field surveys and technical information submitted by any applicant for new development.

11-08-07: Variances And Appeals


1. General Provisions:

A. Consideration Of Size And Location: Generally, the only circumstances under which a variance may be issued are for new construction and substantial improvements to be erected on a lot of 1/2 acre or less in size, contiguous to and surrounded by, lots with existing structures constructed below the Base Flood Elevation.

B. Consideration Of Standards: Variances may only be approved after the standards provided in (see Section C below) have been fully considered. As the lot size increased beyond 1/2 acres, the technical justification for issuing the variance increases.

C. Consideration Of Technical Information: In the review of requests for variances, the Planning and Zoning Commission shall consider all technical evaluations, all relevant factors, and standards specified in this chapter:

(1) The danger that materials may be swept onto other lands to the injury of others;

(2) The danger to life and property due to flooding or erosion damage;

(3) The susceptibility of the proposed facility and its contents to flood damage and the effect of such damage on the individual owner;

(4) The importance of the services provided by the proposed facility to the community; the necessity to the facility of a waterfront location where applicable;

(5) The availability of alternative locations for the proposed use which are not subject to flooding or erosion damage;

(6) The compatibility of the proposed use with existing and anticipated development;

(7) The relationship of the proposed use to the Boise City Comprehensive Plan and floodplain management program for that area;

(8) The safety of access to the property in times of flood for ordinary and emergency vehicles;

(9) The expected heights, velocity, duration, rate of rise, and sediment transport of the flood waters, if applicable, expected at the site; and

(10) The costs of providing governmental services during and after flood conditions, including maintenance and repair of public utilities and facilities including but not limited to sewer, gas, electrical, water systems, and streets and bridges.


2. Conditions For Variances: For new developments and substantial improvements to existing structures, the conditions for a variance shall comply with Section 11-08-07.1 as well as the following:

A. Prohibitions: Variances shall not be issued within any designated floodway if any increase in flood levels during the Base Flood discharge would result.

B. Necessary Minimum: A variance shall only be issued upon determination that the variance is the minimum necessary, considering the flood hazard, to afford relief.

C. Approval Criteria: A variance shall only be issued upon a showing of good and sufficient cause; a determination that failure to grant the variance would result in exceptional hardship to the applicant; and a determination that the granting of a variance will not result in increased flood heights, additional threats to public safety, extraordinary public expense, the creation of nuisances, degradation of or victimization of the public, or conflict with existing local laws or ordinances.

D. Rarely Allowed: Variances as interpreted in the National Flood Insurance Program are based on the general zoning law principle that they pertain to a physical piece of property; they are not personal in nature and do not pertain to the structure, its inhabitants, economic or financial circumstances. They primarily address small lots in densely populated residential neighborhoods. As such, variances from the flood elevations should be quite rare.

E. Variances For Nonresidential Structures: Variances may be issued for nonresidential buildings in very limited circumstances to allow a lesser degree of flood-proofing than watertight or dry-flood-proofing, where it can be determined that such action will have low damage potential, and otherwise complies with of the Standards for Uses and Standard for Utilities.

F. Conditions For Approval: Upon consideration of the factors and the purposes of this chapter, the PZC may attach such conditions to the granting of variances as it deems necessary to further the purposes of this chapter.

G. Flood Insurance Notice Required: Any applicant to whom a variance is issued shall be given written notice that the cost of flood insurance may be commensurate with any increased flood risk.


3. Appeals:

A. Process For An Appeal:

(1) The applicant or any aggrieved party may appeal the Director's decision or determination to the PZC in accordance with this Code (Section 11-03-03.9).

(2) The applicant or any aggrieved party may appeal the PZC decision or determination to the Council in accordance with this Code (Section 11-03-03.9).

(3) Within 10 calendar days after receipt of the appeal, the Council shall establish a date for hearing such appeal and shall notify the appealing party and all persons notified for the previous hearing.

(4) The Council, in reviewing the decision of the PZC, may sustain or deny the PZC, or the Council may amend or modify the decision or determination of the PZC by imposing additional or different conditions or limitations.

B. Basis For An Appeal: An appeal which alleges that there is an error in any requirement, decision, or determination made by any administrative officer of Boise City, or by the PZC in the enforcement or administration of this chapter, shall be supported by technical and scientific evidence, which may include, but is not limited to:

(1) An actual copy of the recorded plat map showing the property;

(2) A topographic map showing ground elevation contours and the curvilinear line representing the area subject to inundation by the Base Flood; and

(3) Certification by a licensed professional engineer or licensed land surveyor of the elevation of the lowest floor (including basement), the elevation of any fill and the date on which the fill was placed, the elevation to which any structure has been flood-proofed, and written statement setting forth the error alleged and the basis for appeal.

11-08-08: Definitions


As used in this Chapter each of the terms defined shall have the meaning given in this Section unless a different meaning is clearly required by the context.

Accessory Use or Structure: A use or structure which is subordinate to the principal use structure on the same parcel and which serves a purpose customarily incidental to the principal use or structure. The accessory use or structure shall, in no instance, include a dwelling unit or be used for human habitation.

Appeal: A request to the Planning and Zoning Commission for a review of the floodplain administrator's interpretation of any provision of this chapter.

Area of Shallow Flooding (ASF): An area shown on the flood insurance rate map as an AO zone 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. These areas are also referred to as the alluvial fans, and are characterized as sheet flow.

Area of Special Flood Hazard (ASFH): The lands within Boise City which are subject to flooding from the base flood (or 100 year flood). These areas are also referred to as the floodplain. Designation on maps always include the letters A or V.

Base Flood: The flood having a one percent chance of being equaled or exceeded in any given year, and is synonymous with "one-percent flood" and "100 year flood." Designation on maps always include the letters A or V.

Base Flood Elevation: The elevation in feet in relation to mean sea level as determined by the Federal Emergency Management Agency to which flood water can be expected to rise during a base flood.

Base Flood Height in Areas of Shallow Flooding: The height expressed in feet above adjacent grade to which flood waters can be expected to rise during a base flood. This height is determined by the Federal Emergency Management Agency and is shown on the Flood Insurance Rate Map (FIRM). Adjacent grade is the elevation of the crown of the nearest street or back of the adjacent curb after adjustment is made for slope of the ground.

Base Zone District: The zone district classification which is in effect on any given land for which standards are included in the Development Code of Boise City, Idaho dated June 2002, and as amended.

Basement: Any area of the building with its floor sub-grade (below ground level) on all sides.

Check Dam: A structure erected in a floodway which does not exceed ten feet in height or impound more than fifty acre feet of water. For the purposes of this Chapter, energy dissipating devices shall be considered to be check dams.

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

Development: Any manmade change to improved or unimproved real estate over which the Boise City Council exercises control. In addition to structural construction, the term includes mining, drilling, dredging, grading, paving, excavation and filling.

Elevated Building: For insurance purposes, a non-basement building which has its lowest elevated floor raised above ground level by foundation walls, shear walls, post, piers, pilings or columns.

Existing Manufactured Home Park or Subdivision: A manufactured home park or subdivision for which the construction of facilities for servicing the lots on which the manufactured 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 adopted floodplain management regulations.

Expansions to an Existing Manufactured Home Park or Subdivision: The preparation of additional sites by the construction of facilities for servicing the lots on which the manufactured homes are to be affixed (including the installation of utilities, the construction of streets, and either final site grading or the pouring of concrete pads).

Federal Emergency Management Agency (FEMA): The agency with the overall responsibility of administering the national flood insurance program (NFIP).

Flood or Flooding: A general and temporary condition of partial or complete inundation of normally dry land areas from the overflow of a watercourse and/or the unusual and rapid accumulation of run-off of surface waters from any source, including but not limited to snow melt or heavy rain.

Flood Insurance Rate Map (FIRM): The official report provided by the Federal Emergency Management Agency which has delineated both the areas of special flood hazard and the risk premium zones applicable to the community.

Flood Insurance Study (FIS): The official report provided by the Federal Insurance Administration that includes flood profiles, the Flood-Boundary-Floodway Map, and the water surface elevation of the base flood.

Floodplain: The land that has been or may be covered by floodwaters, or is surrounded by floodwater and inaccessible, during the occurrence of the regulatory flood. The riverine floodplain includes the floodway and the flood fringe.

Flood-proofing: Any combination of structural and non-structural additions, changes, or adjustments to structures which reduce or eliminate potential flood damage to real estate or improved real property, water and sanitary facilities, structures, and their contents.

Flood Protection Elevation (FPE): An elevation that shall correspond to the elevation of the one percent chance flood (one hundred year flood) plus any increased flood elevation due to floodway encroachment, plus any required freeboard.

Floodway (FW): The Channel of a river or other watercourse 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 foot, as shown in the Flood Insurance Study for Boise City, Idaho.

Floodway Fringe (FF): The area between the floodway boundary and the outer limits of the 100 Year Flood. These lands within Boise City are subject to flooding from the Base Flood (aka the 100 year Flood), and are also referred to as part of the floodplain or the Area of Special Flood Hazard located outside of the floodway.

Letter of Map Amendment (LOMA): A letter issued by the Federal Emergency Management Agency exempting a specific structure or site from the Flood Insurance requirements. The site is exempted by virtue of its being elevated above the 100 year flood elevation.

Letter of Map Revision (LOMR): A letter issued by the Federal Emergency Management Agency exempting a specific structure or site from Flood Insurance requirements. The site or structure is exempted by virtue of its being elevated above the 100 year flood elevation.

Levee: A levee is a continuous dike or ridge, constructed of earth or other materials that confines flood waters (excluding landfill).

Lowest Floor: The lowest floor of the lowest enclosed area (including basement). An unfinished or flood resistant enclosure, usable solely for parking of vehicles, building access or storage, in an area other than a basement area, is not considered a building's lowest floor, provided that such enclosure is not built so as to render the structure in violation of the applicable non-elevation design requirements of this Chapter. (Section 11-08-03.2.A)

Manufactured Home: 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."

Mobile Home: A transportable, factory-built home designed to be used as a year-round residential dwelling and built prior to enactment of the National Housing include and Safety Standards Act of 1974, which became effective June 15, 1976.

Mobile Home Park or Subdivision: Any area, tract, plot or parcel of land, developed and designed primarily for placement of mobile homes located and maintained for dwelling purposes on a permanent or semi-permanent basis.

New Construction: Structures for which the start of construction commenced on or after the effective date of this Chapter.

New Development: Any development for which final approval entitling the applicant to proceed with the development was issued on or after the effective date of this Chapter.

New Manufactured Home Park or Subdivision: A manufactured home park or subdivision for which the construction of facilities for servicing the lots on which the manufactured 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 adopted floodplain management regulations.

Non-residential Structure: A building other than a residential structure. The term includes but is not limited to: buildings used for places of assembly, education, child care, business, maintenance, storage, manufacturing, government, hospitals, sanitariums and nursing homes.

Ordinary High Water Mark (OHWM): The line which the water impresses on the soil by covering it for sufficient periods to deprive the soil of its vegetation and destroy its value for agricultural purposes.

Recreation Vehicle: A vehicle which is: (a) Built on a single chassis; (b) 400 square feet or less when measured at the largest horizontal projections; (c) Designed to be self-propelled or permanently towable by a light duty truck; and (d) Designed primarily not for use as a permanent dwelling but as temporary living quarters for recreational, camping, travel or seasonal use.

Regulatory Floodway: The channel of a river or other watercourse and adjacent land areas that must be reserved in order to discharge the base flood without cumulatively increasing the water surface elevation more than one foot (1').

Residential Structure: A building used as a dwelling for one or more persons. The term includes, but is not limited to houses, mobile homes, apartment buildings, lodging homes, dormitories, (and the guest or patient rooms of), hotels, and motels. The term also includes accessory use areas used in conjunction with and forming an integral part of a residential structure.

Start of Construction: The date the building permit was issued, provided the actual start of construction, repair, reconstruction, placement or other improvement was within 180 days of the permit date. The actual start means either the first placement of permanent construction of a structure on a site, such as the pouring of slab or footing, the installation of piles, the construction of columns, or any work beyond the stage of excavation; or the placement of a mobile 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, 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.

Structure: Anything constructed or erected, which requires permanent location on the ground or is attached to something having location on the ground.

Substantial Damage: Damage of any origin sustained by a structure whereby the cost of restoring the structure to it's before damaged condition would equal or exceed 50 percent of the market value of the structure before the damage occurred.

Substantial Improvement: Any repair, reconstruction, or improvement of a structure, the cost of which equals or exceeds 50 percent of the market value of the structure either before the improvement or the repair is started, or if the structure has been damaged and is being restored, before the damage occurred. 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 term "Substantial Improvement" 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.

Unnumbered "A Zone": An area shown on the Flood Insurance Rate Map as an "A Zone" in which base flood depths and a clearly defined channel are not shown.

Variance: A grant of relief from the requirements of this Chapter which permits construction in a manner that would otherwise be prohibited by this Chapter.