(1) General Standards: In all special flood hazard areas the following provisions are required:
A. All new construction, substantial improvements, and development shall be designed (or modified) and adequately anchored to prevent flotation, collapse, and lateral movement of the structure resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy.
B. All new construction, substantial improvements, and development shall be constructed with materials and utility equipment resistant to flood damage.
C. All new construction, substantial improvements, and development shall be constructed by methods and practices that minimize flood damages.
D. All new and replacement electrical, heating, ventilation, plumbing, air conditioning equipment, and other service facilities shall be designed and/or located so as to prevent water from entering or accumulating within the components during conditions of flooding to the flood protection elevation. These include, but are not limited to, HVAC equipment, water softener units, bath/kitchen fixtures, ductwork, electric/gas meter panels/boxes, utility/cable boxes, hot water heaters, and electric outlets/switches.
E. All new and replacement water supply systems shall be designed to minimize or eliminate infiltration of floodwaters into the system.
F. All new and replacement sanitary sewage systems shall be designed to minimize or eliminate infiltration of floodwaters into the systems and discharges from the systems into floodwaters.
G. On-site waste disposal systems shall be located and constructed to avoid impairment to them or contamination from them during flooding.
H. A fully enclosed area, of new construction and substantially improved structures, which is below the lowest floor used solely for parking, access, and storage shall:
1. Be constructed entirely of flood resistant materials at least to the flood protection elevation; and
2. Include, in Zones A, AE, AH, and AO, flood openings to automatically equalize hydrostatic flood forces on walls by allowing for the entry and exit of floodwaters. To meet this requirement, the openings must either be certified by a professional engineer or architect or meet or exceed the following minimum design criteria:
(A) A minimum of two (2) flood openings on different sides of each enclosed area subject to flooding;
(B) The total net area of all flood openings must be at least one square inch for each square foot of enclosed area subject to flooding;
(C) If a building has more than one enclosed area, each enclosed area must have flood openings to allow floodwaters to automatically enter and exit;
(D) The bottom of all required flood openings shall be no higher than one foot (1') above the grade;
(E) Flood openings may be equipped with screens, louvers, or other coverings or devices, provided they permit the automatic flow of floodwaters in both directions; and
(F) Enclosures made of flexible skirting are not considered enclosures for regulatory purposes, and, therefore, do not require flood openings. Masonry or flood resistant wood underpinning, regardless of structural status, is considered an enclosure and requires flood openings as outlined above.
I. Any alteration, repair, reconstruction, or improvements to a structure, which is in compliance with the provisions of this article, shall meet the requirements of "new construction" as contained in this article.
J. New solid waste disposal facilities and sites, hazardous waste management facilities, salvage yards, and chemical storage facilities shall not be permitted. A structure or tank for chemical or fuel storage incidental to an allowed use or to the operation of a water treatment plant or wastewater treatment facility may be located in a special flood hazard area only if the structure or tank is either elevated or floodproofed to at least the flood protection elevation and certified in accordance with the provisions of subsection 07-10A-09(3) of this article.
K. All subdivision proposals and other development proposals shall be consistent with the need to minimize flood damage and determined to be reasonably safe from flooding.
L. All subdivision proposals and other development proposals shall have public utilities and facilities such as sewer, gas, electrical, and water systems located and constructed to minimize flood damage.
M. All subdivision proposals and other development proposals shall have adequate drainage provided to reduce exposure to flood hazards.
N. All subdivision proposals and other development proposals shall have received all necessary permits from those governmental agencies for which approval is required by Federal or State law, including section 404 of the Federal Water Pollution Control Act amendments of 1972, 33 USC 1334.
O. All subdivision proposals and other development proposals greater than fifty (50) lots or five (5) acres, whichever is the lesser, shall include within such proposals base flood elevation data.
P. When a structure is partially located in a special flood hazard area, the entire structure shall meet the requirements for new construction and substantial improvements.
Q. When a structure is located in multiple flood hazard zones or in a flood hazard risk zone with multiple base flood elevations, the provisions for the more restrictive flood hazard risk zone and the highest base flood elevation (BFE) shall apply.
(2) Specific Standards: In all special flood hazard areas where base flood elevation (BFE) data has been provided, as set forth in subsection 07-10A-05(2) of this article, the following provisions, in addition to the provisions of subsection (1) of this section, are required:
A. Residential Construction: New construction, substantial improvements, and development of any residential structure (including manufactured homes) shall have the lowest floor, including basement, elevated no lower than the flood protection elevation, as defined in section 07-10A-03 of this article.
B. Non-Residential Construction: New construction, substantial improvements, and development of any commercial, industrial, or other non-residential structure shall have the lowest floor, including basement, elevated no lower than the flood protection elevation as defined in section 07-10A-03 of this article. Structures located in Zones A, AE, AH, and AO may be floodproofed to the flood protection elevation in lieu of elevation provided that all areas of the structure, together with attendant utility and sanitary facilities, below the flood protection elevation are watertight with walls substantially impermeable to the passage of water, using structural components having the capability of resisting hydrostatic and hydrodynamic loads and the effect of buoyancy. For AH and AO Zones, the floodproofing elevation shall be in accordance with subsection (5)B of this section. A registered professional engineer or architect shall certify that the floodproofing standards of this subsection are satisfied. Such certification shall be provided to the Floodplain Administrator as set forth in subsection 07-10A-09(3) of this article, along with the operational plan and the inspection and maintenance plan.
C. Additions/Improvements:
1. Additions and/or improvements to pre-FIRM structures when the addition and/or improvements in combination with any interior modifications to the existing structure are:
(A) Not a substantial improvement, the addition and/or improvements must be designed to minimize flood damages and must not be any more non-conforming than the existing structure; or
(B) A substantial improvement, both the existing structure and the addition and/or improvements must comply with the standards for new construction.
2. Additions to non-compliant post-FIRM structures that are a substantial improvement with modifications to the existing structure other than a standard door in the common wall shall require only the addition to comply with the standards for new construction.
3. Additions and/or improvements to non-compliant post-FIRM structures when the addition and/or improvements in combination with any interior modifications to the existing structure are:
(A) Not substantial improvement, the addition and/or improvements only must comply with the standards for new construction; or
(B) A substantial improvement, both the existing structure and the addition and/or improvements must comply with the standards for new construction.
D. Manufactured Home Standards:
1. New and replacement manufactured homes shall be elevated so that the lowest floor of the manufactured home is not lower than the flood protection elevation, as defined in section 07-10A-03 of this article.
2. Manufactured homes shall be securely anchored to an adequately anchored foundation to resist flotation, collapse, and lateral movement, either by certified engineered foundation system, or in accordance with the most current edition of the Idaho Division of Building Safety's "Idaho Manufactured Home Installation Standard" in accordance with Idaho Code section 44-2201(2). Additionally, when the elevation would be met by an elevation of the chassis thirty six inches (36") or less above the grade at the site, the chassis shall be supported by reinforced piers or engineered foundation. When the elevation of the chassis is above thirty six inches (36") in height, an engineering certification is required.
3. All enclosures or skirting below the lowest floor shall meet the requirements of subsections (1)H1 and (1)H2 of this section.
4. An evacuation plan must be developed for evacuation of all residents of all new, substantially improved, or substantially damaged manufactured home parks or subdivisions located within a flood prone area. This plan shall be filed with and approved by the Floodplain Administrator and the local Emergency Management Coordinator.
E. Recreational Vehicles: Temporary placement of recreational vehicles shall:
1. Be on site for fewer than one hundred eighty (180) consecutive days and be fully licensed and ready for highway use (a recreational vehicle is ready for highway use if it is on its wheels or jacking system, is attached to the site only by quick disconnect type utilities and has no permanently attached additions); or
F. Temporary Non-Residential Structures: Prior to the issuance of a floodplain development permit for a temporary structure, the applicant must submit to the Floodplain Administrator a plan for the removal of such structure(s) in the event of a flash flood or other type of flood warning notification. The following information shall be submitted in writing to the Floodplain Administrator for review and written approval:
1. A specified time period for which the temporary use will be permitted. Time specified may not exceed six (6) months, renewable up to one year;
2. The name, address, and phone number of the individual responsible for the removal of the temporary structure;
3. The time frame prior to the event at which a structure will be removed (i.e., immediately upon flood warning notification);
4. A copy of the contract or other suitable instrument with the entity responsible for physical removal of the structure; and
5. Designation, accompanied by documentation, of a location outside the special flood hazard area, to which the temporary structure will be moved.
G. Accessory Structures:
1. Accessory Structures (Footprint Greater Than 1,500 Square Feet): When accessory structures (sheds, detached garages, etc.) used solely for parking, and storage are to be placed within a special flood hazard area, elevation or floodproofing certifications are required for all accessory structures in accordance with subsection 07-10A-09(3) of this article, and the following criteria shall be met:
(A) Accessory structures shall not be used for human habitation (including working, sleeping, living, cooking, or restroom areas);
(B) Accessory structures shall not be temperature-controlled;
(C) Accessory structures shall be designed to have low flood damage potential;
(D) Accessory structures shall be constructed and placed on the building site so as to offer the minimum resistance to the flow of floodwaters;
(E) Accessory structures shall be firmly anchored in accordance with the provisions of subsection (1)A of this section. All utility equipment and machinery, such as electrical, shall be installed in accordance with the provisions of subsection (1)D of this section; and
(F) Flood openings to facilitate automatic equalization of hydrostatic flood forces shall be provided below flood protection elevation in conformance with the provisions of subsection (1)H of this section.
2. Accessory Structures (1,500 Square Feet Or Less): An accessory structure with a footprint less than one thousand five hundred (1,500) square feet that satisfies the criteria outlined in subsections (2)G1(A) through (2)G1(F) of this section is not required to provide the elevation certificate per subsection (2)B of this section.
3. Accessory Structures Not Used Solely For Parking Access And Storage: Accessory structures not used solely for parking access, and storage must be elevated per subsections (2)A and (2)B of this section.
H. Tanks: When gas and liquid storage tanks are to be placed within a special flood hazard area, the following criteria shall be met:
1. Underground tanks in flood hazard areas shall be anchored to prevent flotation, collapse, or lateral movement resulting from hydrodynamic and hydrostatic loads during conditions of the base flood, including the effects of buoyancy (assuming the tank is empty);
2. Elevated above-ground tanks, in flood hazard areas shall be attached to and elevated to or above the design flood elevation on a supporting structure that is designed to prevent flotation, collapse, or lateral movement during conditions of the base flood. Tank-supporting structures shall meet the foundation requirements of the applicable flood hazard area;
3. Not elevated above-ground tanks may be permitted in flood hazard areas provided the tanks are anchored or otherwise designed and constructed to prevent flotation, collapse or lateral movement resulting from hydrodynamic and hydrostatic loads during conditions of the design flood, including the effects of buoyancy assuming the tank is empty and the effects of flood-borne debris;
4. Tank inlets, fill opening, outlets and vents shall be:
(A) At or above the flood protection elevation or fitted with covers designed to prevent the inflow of floodwater or outflow of the contents of the tanks during conditions of the base flood; and
(B) Anchored to prevent lateral movement resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy, during conditions of the base flood.
I. Construction Of Below-Grade Crawlspace:
1. The height of the below-grade crawlspace, measured from the interior grade of the crawlspace to the top of the crawlspace foundation wall, must not exceed four feet (4') at any point.
2. There must be an adequate drainage system that removes floodwaters from the interior area of the crawlspace. The enclosed area should be drained within a reasonable time after a flood event.
3. The velocity of floodwaters at the site should not exceed five feet (5') per second for any crawlspace.
J. Other Development In Floodways:
1. Fences that have the potential to block the passage of floodwaters, such as stockade fences and wire mesh fences, in regulated floodways shall meet the limitations of subsection (4) of this section.
2. Retaining walls, bulkheads, sidewalks, and driveways that involve the placement of fill in regulated floodways shall meet the limitations of subsection (4) of this section.
3. Roads and watercourse crossings, including roads, bridges, culverts, low-water crossings, and similar means for vehicles or pedestrians to travel from one side of the watercourse to the other side, which encroach into regulated floodways, shall meet the limitations of subsection (4) of this section.
4. Drilling water, oil, and/or gas wells including fuel storage tanks, apparatus, and any equipment at the site that encroach into regulated floodways shall meet the limitations of subsection (4) of this section.
5. Docks, piers, boat ramps, marinas, moorings, decks, docking facilities, port facilities, ship building, and ship repair facilities that encroach into regulated floodways shall meet the limitations of subsection (4) of this section.
6. Gravel and sand extraction: See sections 07-14-17 and 07-14-19 of this chapter.
K. Subdivision Plats In Flood Zone:
1. Development Plan: For any proposed subdivision that is located within a map floodplain, the developer/applicant shall provide a development plan of adequate scale and supporting documentation that demonstrates consistency with subsection (1) of this section and includes the following:
(A) Location of all planned improvements;
(B) The location of floodways and the floodway fringe in accordance with sound engineering practices;
(C) The location of the present water channel;
(D) Any planned rerouting of waterways;
(E) All major drainageways;
(F) Areas of frequent flooding;
(G) Means of floodproofing buildings; and
(H) Means of insuring loans for improvements within the floodplain.
2. Review: To give additional guidance in approving any proposed subdivision within a floodplain, the commission shall review proposed developments considering the new construction and substantial improvements of residential structures within the floodplain shall have the lowest floor (including basement) elevated to or above the level of the 100-year flood; and for new construction or substantial improvements of nonresidential structures, the lowest floor (including basement) shall be elevated to or above the level of the 100-year flood, or together with attendant utility and sanitary facilities, shall be floodproofed up to the level of the 100-year flood.
3. Justification For Development: Upon determination that buildings are planned within the floodplain or that alterations of any kind are anticipated within the floodplain area that will alter the flow of water, the developer/applicant shall demonstrate conclusively that such development will not present a hazard to life or limb, hazard to property, adverse effects on the safety, use or stability of a public way or drainage channel and not have an adverse impact on the natural environment. Justification shall be submitted in letter form with the preliminary plat.
4. Appropriateness Of Subdivision: In determining the appropriateness of subdivision for land located within the floodplain, the presiding party and board shall consider the objectives of this chapter and at least the following upon consideration of the preliminary plat:
(A) The danger to life and property due to the increased flood heights or velocities caused by subdivision fill, roads and intended uses;
(B) The danger that intended uses may be swept on the other lands or downstream to the injury of others;
(C) The adequacy of proposed water supply and sanitation systems and the ability of these systems to prevent disease, contamination and unsanitary conditions under flood conditions;
(D) The susceptibility of the proposed facility and its contents to flood damage and the effect of such damage on the individual owner;
(E) The importance of the services provided by the proposed facility to the community;
(F) The requirements of the subdivision for a waterfront location;
(G) The availability of alternative locations not subject to flooding for the proposed subdivision and land uses;
(H) The compatibility of the proposed uses with existing development and development anticipated in the foreseeable future;
(I) The relationship of the proposed subdivision to the comprehensive plan and any floodplain management programs for the area;
(J) The safety of access to the property for emergency vehicles in times of flood;
(K) The expected heights, velocity, duration, rate of rise and sediment transport of the floodwaters expected at the site; and
(L) The cost of providing governmental services during the after flood conditions including maintenance and repair of public utilities such as sewer, gas, electrical and water systems, and streets and bridges.
(M) No subdivision or part thereof shall be approved if levees, fills, structures or other features within the proposed subdivision will individually or collectively significantly increase flood flows, heights or danger. If only part of the proposed subdivision can be safely developed, development shall be limited to that part and the County shall require development to proceed consistent with that determination.
5. Floodproofing Plans: Floodproofing plans must be individually approved by the Board upon recommendation from the commission before such uses are constructed. Floodproofing may include, but not be limited to, the following:
(A) Anchorage to resist flotation and lateral movement;
(B) Installation of watertight doors, bulkheads and shutters or similar methods of closure;
(C) Reinforcement of walls to resist water pressure;
(D) Use of paints, membranes or mortars to reduce seepage of water through walls;
(E) Addition of mass or weight to structures to resist flotation;
(F) Installation of pumps or comparable facilities for subsurface drainage systems to relieve external foundation walls and basement flood pressures;
(G) Construction of water supply and waste treatment systems so as to prevent the entrance of floodwaters;
(H) Installation of pumps or comparable facilities for subsurface drainage systems to relieve external foundation wall and basement flood pressures;
(I) Building design and construction to resist rupture or collapse caused by water pressure or floating debris;
(J) Installation of valves or controls on sanitary and storm drains which permit the drains to be closed to prevent backup of sewage and stormwaters into buildings or structures;
(K) Location and installation of all electrical equipment, circuits and electrical appliances so that they are protected from inundation by the regulatory flood; and
(L) Location of storage facilities for chemicals, explosives, buoyant materials, flammable liquids or other toxic material which could be hazardous to public health, safety and welfare at elevations above the height associated with the regulatory protection elevation or design of such facilities to prevent flotation of storage containers, or damage to storage containers which could result in the escape of toxic materials into floodwaters.
L. Critical Facilities: Applications for the construction of a critical facility shall include a statement from a licensed engineer specifying the design flood event and base flood elevations.
(3) Standards For Floodplains Without Established Base Flood Elevations: Within the special flood hazard areas designated as Zone A (also known as unnumbered A Zones) and established in subsection 07-10A-05(2) of this article, where no base flood elevation (BFE) data has been provided by FEMA, the following provisions, in addition to the provisions of subsection (1) of this section, shall apply:
A. The BFE used in determining the flood protection elevation (FPE) shall be determined based on the following criteria:
1. When base flood elevation (BFE) data is available from other sources, all new construction and substantial improvements within such areas shall also comply with all applicable provisions of this article and shall be elevated or floodproofed in accordance with standards in subsections (1) and (2) of this section.
2. When floodway data is available from a Federal, State or other source, all new construction and substantial improvements with the floodway areas shall also comply with the requirements of subsections (2) and (4) of this section.
3. Require that all new subdivision proposals and other proposed developments (including proposals for subdivisions greater than 50 lots or 5 acres, whichever is the lesser), include within such proposals base flood elevation data. Such base flood elevation (BFE) data shall be adopted by reference in accordance with subsection 07-10A-05(2) of this article and utilized in implementing this article.
4. When base flood elevation (BFE) data is not available from a Federal, State or other source as outlined above, the lowest floor shall be elevated or floodproofed (non-residential) to two feet (2') above the highest adjacent grade (HAG) at the building site or to the flood protection elevation (FPE) whichever is higher, as defined in section 07-10A-03 of this article. All other applicable provisions of subsection (2) of this section shall also apply.
(4) Standards For Floodways: Areas designated as floodways located within the special flood hazard areas established in subsection 07-10A-05(2) of this article. The floodways are extremely hazardous areas due to the velocity of floodwaters that have erosion potential and carry debris and potential projectiles. The following provisions, in addition to standards outlined in subsections (1) and (2) of this section, shall apply to all development within such areas:
A. No encroachments, including fill, new construction, substantial improvements, and other developments shall be permitted unless:
1. It is demonstrated that the proposed encroachment would not result in any increase in the flood levels during the occurrence of the base flood, based on hydrologic and hydraulic analyses performed in accordance with standard engineering practices and presented to the Floodplain Administrator prior to issuance of floodplain development permit; or
2. A Conditional Letter of Map Revision (CLOMR) has been approved by FEMA. A Letter of Map Revision (LOMR) must also be obtained within six (6) months of completion of the proposed encroachment.
B. If subsection (4)A of this section is satisfied, all development shall comply with all applicable flood hazard reduction provisions of this article.
C. Manufactured homes may be permitted provided the following provisions are met:
1. The anchoring and the elevation standards of subsection (2)D of this section; and
2. The encroachment standards of subsection (4)A of this section.
(5) Standards For Areas Of Shallow Flooding (Zone AO And AH): Areas designated as shallow flooding areas have special flood hazards associated with base flood depths of one foot (1') to three feet (3') where a clearly defined channel does not exist and where the path of flooding is unpredictable and indeterminate. In addition to subsections (1) and (2) of this section, all new construction and substantial improvements shall meet the following requirements:
A. The lowest floor shall be elevated at least as high as the depth number specified on the Flood Insurance Rate Map (FIRM), in feet, plus a freeboard of one foot (1'), above the highest adjacent grade; or at least two feet (2') above the highest adjacent grade if no depth number is specified. A minimum of two feet (2') is required and four feet (4') is recommended where a depth is not provided.
B. Non-residential structures may, in lieu of elevation, be floodproofed to the same level as required in subsection (5)A of this section so that the structure, together with attendant utility and sanitary facilities, below that level shall be watertight with walls substantially impermeable to the passage of water and with structural components having the capability of resisting hydrostatic and hydrodynamic loads and effects of buoyancy. Certification is required in accordance with subsection 07-10A-09(3) of this article, and subsection (2)B of this section.
C. Accessory structure (sheds, detached garages, etc.):
1. Used solely for parking, access, and storage:
(A) Shall have the lowest floor elevated to at least as high as the depth number specified on the Flood Insurance Rate Map (FIRM), in feet, plus a freeboard of one foot (1'), above the highest adjacent grade; or at least two feet (2') above the highest adjacent grade if no depth number is specified. A minimum of two feet (2') is required and four feet (4') is recommended where a depth is not provided; or
(B) Shall have flood openings to facilitate automatic equalization of hydrostatic flood forces shall be provided below Flood Protection Elevation in conformance with the provisions of subsection (1)H of this section.
2. Not used solely for parking, access, and storage:
(A) Shall be elevated per subsections (2)A and (2)B of this section.
D. Adequate drainage paths shall be provided around structures on slopes to guide floodwaters around and away from proposed structures. (Ord. 19-038, 8-30-2019)