A. General Standards: In all special flood hazard areas the following provisions are required:
1. 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.
2. All new construction, substantial improvements, and development shall be constructed with materials and utility equipment resistant to flood damage in accordance with the Technical Bulletin 2, Flood Damage-Resistant Materials Requirements, and available from the Federal Emergency Management Agency.
3. All new construction, substantial improvements, and development shall be constructed by methods and practices that minimize flood damages.
4. 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.
5. All new and replacement water supply systems shall be designed to minimize or eliminate infiltration of floodwaters into the system.
6. 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.
7. On-site waste disposal systems shall be located and constructed to avoid impairment to them or contamination from them during flooding.
8. A fully enclosed area, of new construction and substantially improved structures, which is below the lowest floor shall:
a. Be constructed entirely of flood resistant materials at least to the flood protection elevation; and
b. Include, in Zones A, AE, AH, AO, and A1-30, 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:
(1) A minimum of two (2) flood openings on different sides of each enclosed area subject to flooding;
(2) 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;
(3) If a building has more than one enclosed area, each enclosed area must have flood openings to allow floodwaters to automatically enter and exit;
(4) The bottom of all required flood openings shall be no higher than one foot (1') above the interior or exterior adjacent grade;
(5) 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
(6) Enclosures made of flexible skirting are not considered enclosures for regulatory purposes, and, therefore, do not require flood openings. Masonry or wood underpinning, regardless of structural status, is considered an enclosure and requires flood openings as outlined above.
9. Any alteration, repair, reconstruction, or improvements to a structure, which is in compliance with the provisions of this chapter, shall meet the requirements of "new construction" as contained in this chapter.
10. Nothing in this chapter shall prevent the repair, reconstruction, or replacement of a building or structure existing on the effective date of this chapter and located totally or partially within the floodway, flood fringe area, or stream setback, provided there is no additional encroachment below the flood protection elevation in the floodway, flood fringe area, or stream setback, and provided that such repair, reconstruction, or replacement meets all of the other requirements of this chapter.
11. New solid waste disposal facilities and sites, hazardous waste management facilities, salvage yards, and chemical storage facilities shall not be permitted, except by variance as specified in subsection 7-1-4E9 of this chapter. 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 7-1-4C3 of this chapter.
12. 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.
13. 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.
14. All subdivision proposals and other development proposals shall have adequate drainage provided to reduce exposure to flood hazards.
15. 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.
16. 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.
17. 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.
18. Fill is prohibited in the Washington County AE Zones and Floodways, including construction of buildings on fill without a floodplain development permit and an adverse impact study. The Adverse Impact Study is also commonly called a Hydrology and Hydraulic Analysis which includes a No-Rise Certification.
B. Specific Standards: In all special flood hazard areas where base flood elevation (BFE) data has been provided, as set forth in subsection 7-1-3B of this chapter, or subsection D of this section, the following provisions, in addition to the provisions of subsection A of this section, are required:
1. 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 7-1-2 of this chapter.
2. 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 7-1-2 of this chapter. Structures located in Zones A, AE, AH, AO, and A1-30 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 F2 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 7-1-4C3 of this chapter, along with the operational plan and the inspection and maintenance plan.
3. Manufactured Homes:
a. New and replacement manufactured homes shall be elevated so that the lowest floor of the manufactured home is no lower than the flood protection elevation, as defined in section 7-1-2 of this chapter.
b. 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.
c. All enclosures or skirting below the lowest floor shall meet the requirements of subsection B4 of this section.
d. 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 flood prone areas. This plan shall be filed with and approved by the Floodplain Administrator and the local Emergency Management Coordinator.
4. Additions/Improvements:
a. 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:
(1) 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
(2) A substantial improvement, both the existing structure and the addition and/or improvements must comply with the standards for new construction.
b. Additions to post-FIRM structures that are a substantial improvement with no 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.
c. Additions and/or improvements to post-FIRM structures when the addition and/or improvements in combination with any interior modifications to the existing structure are:
(1) Not a substantial improvement, the addition and/or improvements only must comply with the standards for new construction; or
(2) A substantial improvement, both the existing structure and the addition and/or improvements must comply with the standards for new construction.
d. Any combination of repair, reconstruction, rehabilitation, addition, or improvement of a building or structure taking place during a two (2) year period, the cumulative cost of which equals or exceeds fifty percent (50%) of the market value of the structure before the improvement or repair is started, must comply with the standards for new construction. For each building or structure, the two (2) year period begins on the date of the first improvement or repair of that building or structure subsequent to the effective date of this chapter. If the structure has sustained substantial damage, any repairs are considered substantial improvement regardless of the actual repair work performed. The requirement does not, however, include either:
(1) Any project for improvement of a building required to correct existing Health, Sanitary, or Safety Code violations identified by the building official and that are the minimum necessary to assume safe living conditions; or
(2) Any alteration of a historic structure provided that the alteration will not preclude the structure's continued designation as a historic structure.
5. Recreational Vehicles: Recreational vehicles shall be either:
a. Temporary Placement:
(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
b. Permanent Placement:
(1) Recreational vehicles that do not meet the limitations of temporary placement shall meet all the requirements for new construction, as set forth in subsection A of this section.
6. 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:
a. 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;
b. The name, address, and phone number of the individual responsible for the removal of the temporary structure;
c. The time frame prior to the event at which a structure will be removed (i.e., immediately upon flood warning notification);
d. A copy of the contract or other suitable instrument with the entity responsible for physical removal of the structure; and
e. Designation, accompanied by documentation, of a location outside the special flood hazard area, to which the temporary structure will be moved.
7. Accessory Structures: When accessory structures (sheds, detached garages, etc.) are to be placed within a special flood hazard area, elevation or floodproofing certifications are required for all accessory structures in accordance with subsection 7-1-4C3 of this chapter, 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 A1 of this section;
f. All service facilities, such as electrical, shall be installed in accordance with the provisions of subsection A4 of this section; and
g. Flood openings to facilitate automatic equalization of hydrostatic flood forces shall be provided below flood protection elevation in conformance with the provisions of subsections A8b(1) through A8b(6) of this section.
An accessory structure with a footprint less than two hundred (200) square feet and is a minimal investment of seven thousand five hundred dollars ($7,500.00) or less and satisfies the criteria outlined in subsections B7a through B7g of this section is not required to meet the elevation or floodproofing standards of subsection B2 of this section.
8. Tanks: When gas and liquid storage tanks are to be placed within a special flood hazard area, the following criteria shall be met:
a. 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);
b. 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;
c. Not elevated above-ground tanks, that do not meet the elevation requirements of subsection B2 of this section shall 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.
d. Tank inlets, fill openings, outlets and vents shall be:
(1) 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
(2) Anchored to prevent lateral movement resulting from hydrodynamic and hydrostatic loads, including the effects of buoyancy, during conditions of the base flood.
9. Construction Of Below-Grade Crawlspace:
a. The interior grade of a crawlspace must not be below the BFE and must not be more than two feet (2') below the exterior lowest adjacent grade (LAG).
b. 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.
c. 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.
d. The velocity of floodwaters at the site should not exceed five feet (5') per second for any crawlspace.
10. Other Development In Regulated Floodways And Flood Fringe:
a. Fences that have the potential to block the passage of floodwaters, such as stockade fences and wire mesh fences, in regulated floodways and flood fringe shall meet the limitations of subsection E of this section.
b. Retaining walls, bulkheads, sidewalks, and driveways that involve the placement of fill in regulated floodways and flood fringe shall meet the limitations of subsection E of this section.
c. Roads and watercourse crossings, including roads, bridges, culverts, low-water crossings, and similar means for vehicles or pedestrians to travel from one side of a watercourse to the other side, which encroach into regulated floodways and flood fringe, shall meet the limitations of subsection E of this section.
d. Drilling water, oil, and/or gas wells including fuel storage tanks, apparatus, and any equipment at the site that encroach into regulated floodways and flood fringe shall meet the limitations of subsection E of this section.
e. Docks, piers, boat ramps, marinas, moorings, decks, docking facilities, port facilities, shipbuilding, and ship repair facilities that encroach into regulated floodways and flood fringe shall meet the limitations of subsection E of this section.
f. Gravel and sand and their subsequent extraction on lands within the special flood hazard area that encroach into regulated floodways and flood fringe shall meet the limitations of subsection E of this section. A Reclamation Plan bond for LOMR shall be posted by the mine/property owner with Washington County, Idaho to cover the estimated costs of a Reclamation LOMR as determined by the mine/property owner and shall provide supporting documentation for the estimated LOMR cost. A Reclamation LOMR shall be completed within one year of the completion of mining. Upon failure of the property owner to obtain a Reclamation LOMR of the mining site within one year, the Reclamation Plan bond for LOMR will be forfeited.
11. Subdivision Plats: Flood zones:
a. A note must be provided on the final plat documenting the current flood zone in which the property or properties are located. The boundary line must be drawn on the plat in situations where two (2) or more flood zones intersect over the property or properties being surveyed.
FEMA FIRM panel(s): #160xxxxxxC, & 160xxxxxxE, etc.
FIRM effective date(s): mm/dd/year
Flood Zone(s): Zone X, Zone A, Zone AE, Zone AO, Zone, AH, Zone D, etc.
Base Flood Elevation(s): AE .0 ft., etc.
Flood Zones are subject to change by FEMA & all land within a floodway or floodplain is regulated by chapter/section of the City/County Code.
12. Critical Facilities: As a best practice, FEMA recommends protection that exceeds code minimums. For example, FEMA 543, Design Guide for Improving Critical Facility Safety From Flooding and High Winds (2007) recommends protecting critical facilities to withstand at least a 0.2-percent-annual-chance flood event (often called the "500-year flood event"). Flood elevations for the 0.2-percent-annual-chance flood may be greater than the elevation specified by ASCE 24. If Federal funding or other Federal action is involved, the requirements of Executive Order 11988 - Floodplain Management may necessitate protection of critical actions to the 500-year flood elevation (critical actions may include the construction and repair of critical facilities).
In existing facilities that have not been substantially damaged, it may not be possible to floodproof or elevate to provide protection from the 0.2-percent-annual-chance flood event. In those instances, floodproofing or elevating as high as practical is recommended.
C. 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 7-1-3B of this chapter, where no base flood elevation (BFE) data has been provided by FEMA, the following provisions, in addition to the provisions of subsection A of this section, shall apply:
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 chapter and shall be elevated or floodproofed in accordance with standards in subsections A and B of this section.
2. When floodway or flood fringe data is available from a Federal, State, or other source, all new construction and substantial improvements within floodway and flood fringe areas shall also comply with the requirements of subsections B and E of this section.
3. All subdivision, manufactured home park, and other development proposals shall provide base flood elevation (BFE) data if development is greater than five (5) acres or has more than fifty (50) lots/manufactured home sites. Such base flood elevation (BFE) data shall be adopted by reference in accordance with subsection 7-1-3B of this chapter and utilized in implementing this chapter. The applicant/developer shall submit an application for a Conditional Letter of Map Revision (CLOMR) prior to preliminary plat approval and have obtained a Letter of Map Revision (LOMR) prior to any building permits for structures being issued.
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 (2.0') above the highest adjacent grade (HAG) at the building site or to the flood protection elevation (FPE) whichever is higher, as defined in section 7-1-2 of this chapter. All other applicable provisions of subsection B of this section shall also apply.
D. Standards For Riverine Floodplains With Base Flood Elevations But Without Established Floodways Or Flood Fringe Areas: Along rivers and streams where base flood elevation (BFE) data is provided by FEMA or is available from another source but neither floodway nor flood fringe areas are identified for a special flood hazard area on the FIRM or in the FIS report, the following requirements shall apply to all development within such areas:
1. Standards of subsections A and B of this section; and
2. Until a regulatory floodway or flood fringe area is designated, no encroachments, including fill, new construction, substantial improvements, or other development shall be permitted unless certification with supporting technical data by a registered professional engineer is provided demonstrating 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 at any point within the community.
E. Standards For Floodways And AE Zones: Areas designated as floodways or AE Zones are located within the special flood hazard areas established in subsection 7-1-3B of this chapter. The floodways and AE Zones 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 A and B of this section, shall apply to all development within such areas:
1. No encroachments, including fill, new construction, substantial improvements, and other developments shall be permitted unless:
a. 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 practice and presented to the Floodplain Administrator prior to issuance of floodplain development permit; and
b. 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.
2. If subsection E1 of this section is satisfied, all development shall comply with all applicable flood hazard reduction provisions of this chapter.
3. Manufactured homes may be permitted provided the following provisions are met:
a. The anchoring and the elevation standards of subsection B3 of this section; and
b. The encroachment standards of subsection E1 of this section.
F. Standards For Areas Of Shallow Flooding (Zone AO, AH, AR/AO, Or AR/AH): Located within the special flood hazard areas established in subsection 7-1-3B of this chapter, are areas designated as shallow flooding areas. These 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 A and B of this section, all new construction and substantial improvements shall meet the following requirements:
1. 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 two feet (2'), above the highest adjacent grade; or at least four feet (4') above the highest adjacent grade if no depth number is specified.
2. Non-residential structures may, in lieu of elevation, be floodproofed to the same level as required in subsection F1 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 subsections 7-1-4C3 of this chapter, and subsection B2 of this section.
3. Adequate drainage paths shall be provided around structures on slopes to guide floodwaters around and away from proposed structures. (Ord. 82, 11-5-2018; amd. Ord. 92, 1-24-2022)