Flood Protection Overlay

The purpose of the Flood Protection Overlay is to;

i. The flood hazard areas of Boise City 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.
ii. Flood losses are caused by natural forces and construction practices that increase flood heights and velocities, and by structures that are inadequately anchored and that may damage property in other areas. Uses that are inadequately flood-proofed, elevated, or otherwise unprotected from flood damage also contribute to flood losses.
iii. The purpose of this Section is 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 to:

A. Protect human life and health;
B. Minimize expenditures of public money and costly flood control projects;
C. Minimize the need for rescue and relief efforts associated with flooding that are generally undertaken at the expense of the general public;
D. Minimize prolonged business interruptions;
E. 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;
F. 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;
G. Ensure that potential buyers are notified when property is in an Area of Special Flood Hazards; and
H. Ensure that those who occupy the Areas of Special Flood Hazard assume responsibility for their actions.

See More on Sensitive Lands Overlay Districts

Map and Boundaries

Boundary Descriptions

Floodway (F) District Boundary

The Floodway District shall have the boundaries as follows: The Channel of a river or other watercourse and the adjacent land areas that shall 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.

Flood Fringe (FF) District Boundary

The Floodway Fringe District shall have boundaries as follows: The area between the floodway boundary and the boundary of the 100 Year Flood.

Area of Shallow Flooding (ASF) District Boundary

The Area of Shallow Flooding District shall have boundaries as 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.

Critical Facilities

Construction of new critical facilities shall be, to the maximum extent practicable, located outside the limits of the Special Flood Hazard Area (SFHA). 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 used above. Flood-proofing and sealing measures shall 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.

General Irrigation Floodplain Development Permit

A General Irrigation Floodplain Development Permit (GIFD) applies to qualifying activities within the regulatory floodway or SFHA. These permits may be issued to an irrigation entity for a period not to exceed five years. Examples of activities eligible under this provision include:

(a) Dredging and grading of irrigation and drainage channels when the fill from dredging or grading is not deposited on the banks of channels or anywhere within the regulatory floodway or SFHA for longer than 10 days.
(b) Seasonal grading within natural stream channels to check or direct water into irrigation facilities (i.e., earthen “push-up dams” and “wing dams”).
(c) Deposition of fill within the SFHA for less than 10 days. After 10 days, deposited fill shall be removed from the SFHA, or graded and compacted to existing grade within ± 0.2 feet. Deposition of fill includes deposition of material resulting from grading or excavating irrigation or drainage channels. Deposition of fill within the mapped floodway requires an individual permit.
(d) Construction of new underground utilities that do not permanently alter the existing grade elevations by ± 0.5 feet. Excess soil from new pipes larger than two feet in diameter shall be disposed of outside the regulatory floodway and SFHA.
(e) In-kind replacement of irrigation and drainage works or components including but not limited to control gates or head gates, measuring devices and their housing structures/stilling wells, culverts, pumps, pipes, flumes, siphons, and similar works. GIFD permits cannot authorize the In-kind replacement of dams or bridge structures.
(f) New driveways, trails, sidewalks, roads, and streets constructed completely at-or-below existing grade.
(g) Armoring, stabilizing, securing, or in-kind replacement of existing infrastructure within the channel banks (such as bridge piers, sewer/utility supports and storm water/sewer drainage outfalls/headwalls) when the dimensions (bank slopes, channel location, channel elevation) of the channel are not altered. This should not involve replacement with larger or additional above ground infrastructure.

Other Applicable Code Considerations

Floodway Zone

  • Allowed Uses
  • Standards
  • Prohibited Uses
  • Relocating the Floodway (Line)

Floodway Fringe (FF) Zone and Area of Shallow Flooding (ASF) Zone

  • Allowed Uses
  • Standards
  • Uses
  • Utilities
  • Development Including Subdivisions and Manufactured Home Parks
  • Residential Structures
  • Manufactured Homes
  • Nonresidential Structures (Includes Accessory Structures Such as Sheds or Detached Garages)
  • Recreational Vehicles

Unnumbered "A Zones"

  • Allowed Uses
  • Standards
  • Uses
  • Utilities
  • Development Including Subdivisions and Manufactured Home Communities
  • Residential Structures

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